1) The study found that linear microcracks in bone activate remodeling through resorption, while diffuse microdamage alone does not. Remodeling was correlated with the number of linear microcracks but not diffuse damage.
2) Osteocyte viability, as measured by morphology, was unaffected by diffuse damage alone. In contrast, linear microcracks were associated with many abnormal osteocytes.
3) The findings suggest osteocytes activate remodeling in response to linear microcracks through apoptosis, but diffuse damage does not cause a focal injury response or osteocyte death.
This study investigated whether applying low-magnitude vibrations during periods of hindlimb unloading and reambulation in mice could help preserve bone marrow cells and enhance recovery of trabecular bone structure. Mice subjected to hindlimb unloading received either vibrations, sham vibrations, or nothing for 15 minutes daily. After 3 weeks, half of the mice were analyzed and half were allowed to reambulate for 3 more weeks with or without continued vibrations. Vibrations during unloading helped retain osteogenic bone marrow cells and enhanced trabecular bone recovery during reambulation compared to mice receiving only sham vibrations or nothing. Applying vibrations only during unloading was more effective than during reambulation alone at altering tra
This document describes the development of an in vivo rabbit ulnar loading model to study mechanical loading effects on bone. Strain levels during ulnar loading were characterized using strain gauges and finite element models. Rabbits underwent ulnar loading at varying strain levels, and periosteal bone formation was measured using histomorphometry. Loading at 3000-4500 microstrain produced a dose-dependent increase in periosteal bone formation compared to controls, with 4500 microstrain inducing the most robust response. Loading at 5250 microstrain induced woven bone formation. The rabbit ulnar loading model provides a translatable model for studying cortical bone adaptation and responses to pharmaceuticals.
Bioactive Nanoparticle Materials for Bone Tissue RegenerationKathleen Broughton
The document discusses bioactive scaffolds for bone tissue regeneration using emerging nano-materials. It outlines that bone regeneration is a growing medical need and describes criteria for effective bone regeneration scaffolds. The focus is on comparing porous nano-materials in terms of porosity and mechanical strength. Formulas for calculating porosity, compressive strength, and degradation are provided to analyze scaffold materials.
The authors aimed to control the structure of tissue-engineered bone through scaffold design. They seeded human mesenchymal stem cells on silk scaffolds with varying pore sizes using static and dynamic seeding methods. They found that dynamic seeding, where the scaffolds were stirred in a spinner flask, produced bone-like structures that matched the scaffold geometry best. In particular, scaffolds with small pores produced optimal bone growth when seeded dynamically. The experimental design demonstrated the ability to engineer bone-like structures in vitro by controlling scaffold pore size and seeding technique.
The document discusses several studies on the applications and efficacy of hydroxyapatite (HA) scaffolds and composites for bone tissue engineering. Specifically:
1) A long-term study of 276 dual radius HA-coated acetabular cups found an 11% revision rate after 10 years due to aseptic loosening and osteolysis.
2) HA scaffolds containing varying ratios of collagen supported human osteoblast viability, proliferation, and phenotype maintenance in culture.
3) Scaffolds combining HA microparticles and extracellular matrix derived from osteoblasts or fibroblasts in vitro enhanced bone repair in a rat calvarial defect model.
4) A composite of poly-ε-caprolactone and HA supported mouse
Bones regenerate through a process involving hematoma formation, callus formation, callus ossification, and bone remodeling. Various scaffolds, growth factors, and cells are used to promote bone regeneration. A study developed a multifunctional composite containing rhBMP-2, antibiotic-loaded nano-hydroxyapatite, and alginate/gelatin gel for bone regeneration. The composite demonstrated sustained drug release, antimicrobial effects, promotion of bone cell proliferation, and ability to reduce inflammation and promote new bone formation in vivo.
Proposal to National Science Foundation co-authored by Ian Nieves and James Earthman. It describes using FEA simulation and advanced computer-assisted fabrication techniques to develop materials for bone regeneration.
Myanmar Society of Oral Implantology collaborates with Myanmar Dental Association ( Yangon Division) and celebrates Yangon Dental Festival. At this event, as the President of MSOI, I present this topic. References list was collected in separate folder.
This study investigated whether applying low-magnitude vibrations during periods of hindlimb unloading and reambulation in mice could help preserve bone marrow cells and enhance recovery of trabecular bone structure. Mice subjected to hindlimb unloading received either vibrations, sham vibrations, or nothing for 15 minutes daily. After 3 weeks, half of the mice were analyzed and half were allowed to reambulate for 3 more weeks with or without continued vibrations. Vibrations during unloading helped retain osteogenic bone marrow cells and enhanced trabecular bone recovery during reambulation compared to mice receiving only sham vibrations or nothing. Applying vibrations only during unloading was more effective than during reambulation alone at altering tra
This document describes the development of an in vivo rabbit ulnar loading model to study mechanical loading effects on bone. Strain levels during ulnar loading were characterized using strain gauges and finite element models. Rabbits underwent ulnar loading at varying strain levels, and periosteal bone formation was measured using histomorphometry. Loading at 3000-4500 microstrain produced a dose-dependent increase in periosteal bone formation compared to controls, with 4500 microstrain inducing the most robust response. Loading at 5250 microstrain induced woven bone formation. The rabbit ulnar loading model provides a translatable model for studying cortical bone adaptation and responses to pharmaceuticals.
Bioactive Nanoparticle Materials for Bone Tissue RegenerationKathleen Broughton
The document discusses bioactive scaffolds for bone tissue regeneration using emerging nano-materials. It outlines that bone regeneration is a growing medical need and describes criteria for effective bone regeneration scaffolds. The focus is on comparing porous nano-materials in terms of porosity and mechanical strength. Formulas for calculating porosity, compressive strength, and degradation are provided to analyze scaffold materials.
The authors aimed to control the structure of tissue-engineered bone through scaffold design. They seeded human mesenchymal stem cells on silk scaffolds with varying pore sizes using static and dynamic seeding methods. They found that dynamic seeding, where the scaffolds were stirred in a spinner flask, produced bone-like structures that matched the scaffold geometry best. In particular, scaffolds with small pores produced optimal bone growth when seeded dynamically. The experimental design demonstrated the ability to engineer bone-like structures in vitro by controlling scaffold pore size and seeding technique.
The document discusses several studies on the applications and efficacy of hydroxyapatite (HA) scaffolds and composites for bone tissue engineering. Specifically:
1) A long-term study of 276 dual radius HA-coated acetabular cups found an 11% revision rate after 10 years due to aseptic loosening and osteolysis.
2) HA scaffolds containing varying ratios of collagen supported human osteoblast viability, proliferation, and phenotype maintenance in culture.
3) Scaffolds combining HA microparticles and extracellular matrix derived from osteoblasts or fibroblasts in vitro enhanced bone repair in a rat calvarial defect model.
4) A composite of poly-ε-caprolactone and HA supported mouse
Bones regenerate through a process involving hematoma formation, callus formation, callus ossification, and bone remodeling. Various scaffolds, growth factors, and cells are used to promote bone regeneration. A study developed a multifunctional composite containing rhBMP-2, antibiotic-loaded nano-hydroxyapatite, and alginate/gelatin gel for bone regeneration. The composite demonstrated sustained drug release, antimicrobial effects, promotion of bone cell proliferation, and ability to reduce inflammation and promote new bone formation in vivo.
Proposal to National Science Foundation co-authored by Ian Nieves and James Earthman. It describes using FEA simulation and advanced computer-assisted fabrication techniques to develop materials for bone regeneration.
Myanmar Society of Oral Implantology collaborates with Myanmar Dental Association ( Yangon Division) and celebrates Yangon Dental Festival. At this event, as the President of MSOI, I present this topic. References list was collected in separate folder.
Bone marrow mesenchymal stem cells (BM-MSCs) and cartilage fragments were evaluated for their ability to enhance cartilage formation in an ex-vivo osteochondral defect model. BM-MSCs alone, cartilage fragments alone, or a combination of BM-MSCs and cartilage fragments were seeded into osteochondral defects. The combination of BM-MSCs and cartilage fragments showed improved cartilage formation and defect filling compared to BM-MSCs or cartilage fragments alone, as seen on histological and biochemical analysis. The results suggest that a combination of BM-MSCs and cartilage fragments may provide a more effective approach for cartilage repair.
This document discusses bone tissue engineering. It begins by noting the high number of bone fractures that occur each year in the US and the current treatments using metals and ceramics. It then discusses the cells and processes involved in bone formation and repair. The remainder of the document focuses on the strategies and components of bone tissue engineering, including cells sources like stem cells, scaffold materials both natural and synthetic, growth factors, and processing techniques. It emphasizes the properties scaffolds must have to support new bone growth and the need for bioreactors to provide dynamic cell environments.
Rotator cuff repair using a stem cell approachZakary Bondy
This presentation communicates current methods for rotator cuff repair mainly focusing on mesenchymal and tendon-derived stem cells. It looks to expand on future research in this field by communicating a future experiment to expand on current knowledge of tendon-derived stem cells.
This study investigated the effects of heat from an arthroscope on human bone marrow-derived mesenchymal stem cells (hBMMSCs). hBMMSCs were isolated from osteoarthritis patients and exposed to heat from an illuminated arthroscope for various time periods as single cell suspensions or cell pellets. Cell suspensions exposed to heat showed decreased viability over time, while cell pellets maintained or increased viability. Gene expression analysis found increased expression of heat shock and inflammatory genes in cell suspensions compared to pellets after heat exposure. The results suggest that transplanting hBMMSCs as cell pellets may better protect them from heat effects during arthroscopic procedures and thus support cartilage regeneration.
High impact trauma to cartilage can lead to damage and posttraumatic osteoarthritis. This study investigated using genipin crosslinking to strengthen cartilage after impact and reduce wear. Bovine cartilage was impacted and treated with genipin at concentrations of 0, 2, or 10 mM. Impact caused fissures and decreased stiffness. Crosslinking did not increase stiffness but did reduce wear, with 2 mM genipin performing similarly to 10 mM. The results suggest genipin crosslinking may help protect cartilage from accelerated wear after injury.
Effect of Suture Tubularization on Quadruple Stranded Hamstring ACL Grafts wi...CrimsonPublishersOPROJ
Effect of Suture Tubularization on Quadruple Stranded Hamstring ACL Grafts with Femoral Suspensory Fixation: A Biomechanical Study by Matthew Richard Moralle* in Crimson Publishers: Orthopedic Research and Reviews Journal
This document summarizes a study that investigated the effects of total knee arthroplasty (TKA) and neuromuscular electrical stimulation (NMES) on mitochondrial subpopulations in skeletal muscle. The study found that TKA caused significant muscle atrophy and loss of both subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondria. NMES prevented muscle atrophy and maintained IMF mitochondrial content but not SS mitochondrial content. Specifically, TKA reduced IMF mitochondrial area by 19% and SS mitochondria per unit of sarcolemma by 64%, while NMES maintained IMF mitochondrial area above baseline and reduced the SS mitochondrial loss to 55%. The results suggest that decreased neural activation following TKA leads to mitochondrial
The document describes a study that used whole-exome sequencing to identify novel genetic variations associated with osteoarthritis (OA) patients. Several variations were found in genes involved in cartilage development, extracellular matrix organization, and inflammatory/immune responses. Two novel mutations were validated by Sanger sequencing, including a mutation in the SELP gene and another in the COL6A6 gene. The approach identified variations in genes impacting pathways relevant to OA pathogenesis.
The document discusses several topics related to bone physiology, healing, and sterilization. It questions why we wait longer periods of time to load implants in the maxilla versus mandible. It also asks if augmenting a site and placing implants later or doing both at the same time is better. The document discusses the differences between immediate and delayed loading and their effects on bone health. It covers biology, mechanobiology, bone quality determinants like thickness, porosity and connectivity. Principles of bone response, remodeling, microdamage and fragility are discussed. Procedures like drilling, sinus lifts and ridge splits are mentioned. Models of bone injury and repair are presented. Studies on implant survival rates and the mechanostat theory are
Advancement in Scaffolds for Bone Tissue Engineering: A Reviewiosrjce
In last decade, Tissue Engineering has moved a way ahead and has proposed solutions by replacing
the permanently or severely damaged tissues of our body. The field has expanded to tissue regeneration of
cartilage, bone, blood vessels, skin, etc. The domain of tissue engineering is very wide and is the combination of
bioengineering, biology & biochemistry. This review is focus on recent research advancement in bone tissue
engineering. Bone grafting techniques are used to replace the severely damaged due to any accident, trauma or
any disease. These are either allograft, autologous or synthetic bone properties similar to bone. Bone Tissue
Engineering is part of a synthetic technique and overcome the limitations faced in other two mentioned
techniques. Bone Tissue engineering is rapidly developing field and has become important due to its remarkable
therapeutic properties. Mesenchymal stem cells are used as starting cells in tissue regeneration. These cells get
differentiated into bone cells and start multiplying to form bone. One inevitable requirement of these growing
human cells is a strong support which helps in the proper growth. This support is known as scaffold, in tissue
engineering. For proper regeneration of cells scaffold materials plays vital importance in the field of bone tissue engineering. This review attempts is illustrate the biology of natural bone, various desirable properties of scaffold, biomaterials used for fabrication of scaffold and various fabrication techniques with examples of bone regenerate.
Estimating Bone Loss on a Mars MissionAmber Berlin
This document discusses bone density loss experienced by astronauts during prolonged exposure to microgravity conditions like those encountered during long-duration spaceflight and proposes potential mitigation techniques. It estimates that on a hypothetical 972-day mission to Mars, astronauts could lose 26.6-53.2% of their bone density, putting them at serious risk of fractures upon return to Earth's gravity. Current countermeasures like nutrition and exercise have proven ineffective, so alternative approaches like artificial gravity or vibration therapy require further research before long-term space missions.
This document summarizes a study on using cell therapy to assist in regenerating cartilage in cases of avascular bone necrosis. It discusses how mesenchymal stem cells derived from bone marrow were used in 15 patients with avascular bone necrosis of the femoral head. The stem cells were isolated from patients' bone marrow and fat tissue then reintroduced with platelet rich plasma. Follow-ups over a year found improved symptoms and radiological signs of new cartilage formation in the patients. The role of the stem cell microenvironment in differentiation is also discussed. The study suggests cell therapy is a promising alternative to traditional surgery for certain orthopedic conditions.
The document discusses bone grafts, which are used to aid in healing and strengthening bones. There are several types of bone grafts, including autografts which use bone from the patient's own body, and allografts which use donated bone. Alternatives to bone grafts have also been developed, including substitutes made from ceramics, coral, or synthetic materials. The best type of bone graft depends on each patient's individual surgical situation and needs.
Bones have important mechanical, synthetic, and metabolic functions in the body. Tissue engineering aims to induce new functional bone tissue through the use of scaffolds, growth factors, and cells. Strategies for bone tissue engineering generally involve a carrier scaffold and biologically active factors like cells and proteins. Materials used can include metals, ceramics, and natural or synthetic polymers. The goal is for the scaffold to deliver osteoinductive molecules and cells to fill bone defects and facilitate healing through new bone formation.
Topical icing after muscle contusion injury in rats suppressed inflammation and delayed angiogenesis in regenerating muscle. Macrophage numbers and expression of vascular endothelial growth factor and von Willebrand factor were lower after icing at early time points. However, muscle regeneration was not significantly affected by icing, as muscle fibre size and the proportion of regenerating fibres were similar with or without icing. Micro computed tomography showed more blood vessels in injured versus uninjured muscle but could not detect significant differences in vessel number or volume with icing. In conclusion, icing delayed but did not prevent angiogenesis during muscle regeneration.
bone and_cartilage_tissue_engineering by SumitDcrust
This document discusses tissue engineering of bone and cartilage. It defines tissue engineering as applying engineering and life science principles to develop biological substitutes that restore or improve tissue function. The key components of tissue engineering are cells, scaffolds, and bioreactors. Scaffolds provide structure for cell attachment and growth, while bioreactors provide cell signaling and mechanical stimulation. The document outlines current treatments for bone and cartilage defects and their limitations, as well as materials used in scaffolds and bioreactors. It discusses the need for and future of bone and cartilage tissue engineering.
Dr. Raghavendra Raju gave a presentation on tissue engineering. He began by defining key terms like tissue engineering, regenerative medicine, bionics, biomimetic materials, and stem cell therapy. The basic principles of tissue engineering involve using artificial or inert scaffold materials combined with living cells to grow desired tissues. Mesenchymal stem cells from bone marrow are commonly used due to their ability to differentiate into bone and cartilage cells. Applications in orthopedics include treating bone defects, fractures that won't heal, cartilage damage, and tendon/meniscus injuries. Future advances in fields like molecular biology and tissue engineering may help manage anatomical changes from disease.
Rotator cuff tears are a very common cause of shoulder pain. Surgery is very successful in improving pain but biological augmentation is aimed at improving the healing rate. Amniotic membrane allografts, PRP (platelet rich plasma) and stem cells are all currently popular options.
This study is an In vitro analysis of amniotic membrane allograft as a potential agent for biological augmentation of rotator cuff repair performed by Dr Adnan Saithna, Orthopedic Surgeon, AZBSC Orthopedics
Effect of Seeding Density of Mesenchymal Stem Cells on Cell Proliferation and...Jaideep Sahni
High cell seeding densities of mesenchymal stem cells on gelatin scaffolds can improve cell proliferation during osteogenic differentiation. The study found that total RNA content, an indicator of cell proliferation, was significantly higher in osteogenic groups with 0.1M and 0.5M cell seeding densities compared to control groups. The 0.5M seeded osteogenic group also showed significantly higher RNA content than the 0.1M seeded osteogenic group, indicating that higher seeding densities can further improve proliferation. However, preliminary results showed that osteogenic gene expression, a measure of differentiation, did not differ between the 0.1M and 0.5M seeded osteogenic groups, suggesting that cell seeding density alone may not
Tissue engineering aims to augment, improve, treat or replace tissues using cells, biomaterials, and physiochemical factors. It requires appropriate cells, a scaffold for structure, and growth factors. Recent examples include artificial skin, muscle for meat production, implanted bladders, and cartilage for knee repair. Scaffolds must allow cell attachment, migration, and diffusion while providing mechanical support and inducing physiological changes in seeded cells. Bone contains osteoblasts that form bone and osteoclasts that resorb it. Its extracellular matrix includes hydroxyapatite and collagen fibers. Potential artificial bone materials include metals, ceramics, polymers, and coral hydroxyapatite. Osteoconduction provides a scaffold for bone formation, while osteo
This diagram shows the structure of bone tissue, including Haversian canals containing blood vessels that run perpendicular to osteocytes embedded in the bone matrix. The diagram also depicts Volkmann's canals that run parallel to the bone and connect the Haversian canals, allowing for nutrient exchange between blood vessels and osteocytes. Bone marrow is shown within the central cavity of the bone.
Bone is a specialized connective tissue composed of cells and an organic/inorganic matrix. It contains osteogenic stem cells that differentiate into osteoblasts which form bone matrix and osteocytes that reside in the bone tissue. Osteoclasts are large multinucleated cells that resorb bone. The matrix contains collagen fibers, proteoglycans and glycoproteins. Mineral salts such as calcium phosphate crystallize within the matrix. Bones develop through two processes - intramembranous where bone forms within connective tissue and endochondral where cartilage is replaced by bone.
Bone marrow mesenchymal stem cells (BM-MSCs) and cartilage fragments were evaluated for their ability to enhance cartilage formation in an ex-vivo osteochondral defect model. BM-MSCs alone, cartilage fragments alone, or a combination of BM-MSCs and cartilage fragments were seeded into osteochondral defects. The combination of BM-MSCs and cartilage fragments showed improved cartilage formation and defect filling compared to BM-MSCs or cartilage fragments alone, as seen on histological and biochemical analysis. The results suggest that a combination of BM-MSCs and cartilage fragments may provide a more effective approach for cartilage repair.
This document discusses bone tissue engineering. It begins by noting the high number of bone fractures that occur each year in the US and the current treatments using metals and ceramics. It then discusses the cells and processes involved in bone formation and repair. The remainder of the document focuses on the strategies and components of bone tissue engineering, including cells sources like stem cells, scaffold materials both natural and synthetic, growth factors, and processing techniques. It emphasizes the properties scaffolds must have to support new bone growth and the need for bioreactors to provide dynamic cell environments.
Rotator cuff repair using a stem cell approachZakary Bondy
This presentation communicates current methods for rotator cuff repair mainly focusing on mesenchymal and tendon-derived stem cells. It looks to expand on future research in this field by communicating a future experiment to expand on current knowledge of tendon-derived stem cells.
This study investigated the effects of heat from an arthroscope on human bone marrow-derived mesenchymal stem cells (hBMMSCs). hBMMSCs were isolated from osteoarthritis patients and exposed to heat from an illuminated arthroscope for various time periods as single cell suspensions or cell pellets. Cell suspensions exposed to heat showed decreased viability over time, while cell pellets maintained or increased viability. Gene expression analysis found increased expression of heat shock and inflammatory genes in cell suspensions compared to pellets after heat exposure. The results suggest that transplanting hBMMSCs as cell pellets may better protect them from heat effects during arthroscopic procedures and thus support cartilage regeneration.
High impact trauma to cartilage can lead to damage and posttraumatic osteoarthritis. This study investigated using genipin crosslinking to strengthen cartilage after impact and reduce wear. Bovine cartilage was impacted and treated with genipin at concentrations of 0, 2, or 10 mM. Impact caused fissures and decreased stiffness. Crosslinking did not increase stiffness but did reduce wear, with 2 mM genipin performing similarly to 10 mM. The results suggest genipin crosslinking may help protect cartilage from accelerated wear after injury.
Effect of Suture Tubularization on Quadruple Stranded Hamstring ACL Grafts wi...CrimsonPublishersOPROJ
Effect of Suture Tubularization on Quadruple Stranded Hamstring ACL Grafts with Femoral Suspensory Fixation: A Biomechanical Study by Matthew Richard Moralle* in Crimson Publishers: Orthopedic Research and Reviews Journal
This document summarizes a study that investigated the effects of total knee arthroplasty (TKA) and neuromuscular electrical stimulation (NMES) on mitochondrial subpopulations in skeletal muscle. The study found that TKA caused significant muscle atrophy and loss of both subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondria. NMES prevented muscle atrophy and maintained IMF mitochondrial content but not SS mitochondrial content. Specifically, TKA reduced IMF mitochondrial area by 19% and SS mitochondria per unit of sarcolemma by 64%, while NMES maintained IMF mitochondrial area above baseline and reduced the SS mitochondrial loss to 55%. The results suggest that decreased neural activation following TKA leads to mitochondrial
The document describes a study that used whole-exome sequencing to identify novel genetic variations associated with osteoarthritis (OA) patients. Several variations were found in genes involved in cartilage development, extracellular matrix organization, and inflammatory/immune responses. Two novel mutations were validated by Sanger sequencing, including a mutation in the SELP gene and another in the COL6A6 gene. The approach identified variations in genes impacting pathways relevant to OA pathogenesis.
The document discusses several topics related to bone physiology, healing, and sterilization. It questions why we wait longer periods of time to load implants in the maxilla versus mandible. It also asks if augmenting a site and placing implants later or doing both at the same time is better. The document discusses the differences between immediate and delayed loading and their effects on bone health. It covers biology, mechanobiology, bone quality determinants like thickness, porosity and connectivity. Principles of bone response, remodeling, microdamage and fragility are discussed. Procedures like drilling, sinus lifts and ridge splits are mentioned. Models of bone injury and repair are presented. Studies on implant survival rates and the mechanostat theory are
Advancement in Scaffolds for Bone Tissue Engineering: A Reviewiosrjce
In last decade, Tissue Engineering has moved a way ahead and has proposed solutions by replacing
the permanently or severely damaged tissues of our body. The field has expanded to tissue regeneration of
cartilage, bone, blood vessels, skin, etc. The domain of tissue engineering is very wide and is the combination of
bioengineering, biology & biochemistry. This review is focus on recent research advancement in bone tissue
engineering. Bone grafting techniques are used to replace the severely damaged due to any accident, trauma or
any disease. These are either allograft, autologous or synthetic bone properties similar to bone. Bone Tissue
Engineering is part of a synthetic technique and overcome the limitations faced in other two mentioned
techniques. Bone Tissue engineering is rapidly developing field and has become important due to its remarkable
therapeutic properties. Mesenchymal stem cells are used as starting cells in tissue regeneration. These cells get
differentiated into bone cells and start multiplying to form bone. One inevitable requirement of these growing
human cells is a strong support which helps in the proper growth. This support is known as scaffold, in tissue
engineering. For proper regeneration of cells scaffold materials plays vital importance in the field of bone tissue engineering. This review attempts is illustrate the biology of natural bone, various desirable properties of scaffold, biomaterials used for fabrication of scaffold and various fabrication techniques with examples of bone regenerate.
Estimating Bone Loss on a Mars MissionAmber Berlin
This document discusses bone density loss experienced by astronauts during prolonged exposure to microgravity conditions like those encountered during long-duration spaceflight and proposes potential mitigation techniques. It estimates that on a hypothetical 972-day mission to Mars, astronauts could lose 26.6-53.2% of their bone density, putting them at serious risk of fractures upon return to Earth's gravity. Current countermeasures like nutrition and exercise have proven ineffective, so alternative approaches like artificial gravity or vibration therapy require further research before long-term space missions.
This document summarizes a study on using cell therapy to assist in regenerating cartilage in cases of avascular bone necrosis. It discusses how mesenchymal stem cells derived from bone marrow were used in 15 patients with avascular bone necrosis of the femoral head. The stem cells were isolated from patients' bone marrow and fat tissue then reintroduced with platelet rich plasma. Follow-ups over a year found improved symptoms and radiological signs of new cartilage formation in the patients. The role of the stem cell microenvironment in differentiation is also discussed. The study suggests cell therapy is a promising alternative to traditional surgery for certain orthopedic conditions.
The document discusses bone grafts, which are used to aid in healing and strengthening bones. There are several types of bone grafts, including autografts which use bone from the patient's own body, and allografts which use donated bone. Alternatives to bone grafts have also been developed, including substitutes made from ceramics, coral, or synthetic materials. The best type of bone graft depends on each patient's individual surgical situation and needs.
Bones have important mechanical, synthetic, and metabolic functions in the body. Tissue engineering aims to induce new functional bone tissue through the use of scaffolds, growth factors, and cells. Strategies for bone tissue engineering generally involve a carrier scaffold and biologically active factors like cells and proteins. Materials used can include metals, ceramics, and natural or synthetic polymers. The goal is for the scaffold to deliver osteoinductive molecules and cells to fill bone defects and facilitate healing through new bone formation.
Topical icing after muscle contusion injury in rats suppressed inflammation and delayed angiogenesis in regenerating muscle. Macrophage numbers and expression of vascular endothelial growth factor and von Willebrand factor were lower after icing at early time points. However, muscle regeneration was not significantly affected by icing, as muscle fibre size and the proportion of regenerating fibres were similar with or without icing. Micro computed tomography showed more blood vessels in injured versus uninjured muscle but could not detect significant differences in vessel number or volume with icing. In conclusion, icing delayed but did not prevent angiogenesis during muscle regeneration.
bone and_cartilage_tissue_engineering by SumitDcrust
This document discusses tissue engineering of bone and cartilage. It defines tissue engineering as applying engineering and life science principles to develop biological substitutes that restore or improve tissue function. The key components of tissue engineering are cells, scaffolds, and bioreactors. Scaffolds provide structure for cell attachment and growth, while bioreactors provide cell signaling and mechanical stimulation. The document outlines current treatments for bone and cartilage defects and their limitations, as well as materials used in scaffolds and bioreactors. It discusses the need for and future of bone and cartilage tissue engineering.
Dr. Raghavendra Raju gave a presentation on tissue engineering. He began by defining key terms like tissue engineering, regenerative medicine, bionics, biomimetic materials, and stem cell therapy. The basic principles of tissue engineering involve using artificial or inert scaffold materials combined with living cells to grow desired tissues. Mesenchymal stem cells from bone marrow are commonly used due to their ability to differentiate into bone and cartilage cells. Applications in orthopedics include treating bone defects, fractures that won't heal, cartilage damage, and tendon/meniscus injuries. Future advances in fields like molecular biology and tissue engineering may help manage anatomical changes from disease.
Rotator cuff tears are a very common cause of shoulder pain. Surgery is very successful in improving pain but biological augmentation is aimed at improving the healing rate. Amniotic membrane allografts, PRP (platelet rich plasma) and stem cells are all currently popular options.
This study is an In vitro analysis of amniotic membrane allograft as a potential agent for biological augmentation of rotator cuff repair performed by Dr Adnan Saithna, Orthopedic Surgeon, AZBSC Orthopedics
Effect of Seeding Density of Mesenchymal Stem Cells on Cell Proliferation and...Jaideep Sahni
High cell seeding densities of mesenchymal stem cells on gelatin scaffolds can improve cell proliferation during osteogenic differentiation. The study found that total RNA content, an indicator of cell proliferation, was significantly higher in osteogenic groups with 0.1M and 0.5M cell seeding densities compared to control groups. The 0.5M seeded osteogenic group also showed significantly higher RNA content than the 0.1M seeded osteogenic group, indicating that higher seeding densities can further improve proliferation. However, preliminary results showed that osteogenic gene expression, a measure of differentiation, did not differ between the 0.1M and 0.5M seeded osteogenic groups, suggesting that cell seeding density alone may not
Tissue engineering aims to augment, improve, treat or replace tissues using cells, biomaterials, and physiochemical factors. It requires appropriate cells, a scaffold for structure, and growth factors. Recent examples include artificial skin, muscle for meat production, implanted bladders, and cartilage for knee repair. Scaffolds must allow cell attachment, migration, and diffusion while providing mechanical support and inducing physiological changes in seeded cells. Bone contains osteoblasts that form bone and osteoclasts that resorb it. Its extracellular matrix includes hydroxyapatite and collagen fibers. Potential artificial bone materials include metals, ceramics, polymers, and coral hydroxyapatite. Osteoconduction provides a scaffold for bone formation, while osteo
This diagram shows the structure of bone tissue, including Haversian canals containing blood vessels that run perpendicular to osteocytes embedded in the bone matrix. The diagram also depicts Volkmann's canals that run parallel to the bone and connect the Haversian canals, allowing for nutrient exchange between blood vessels and osteocytes. Bone marrow is shown within the central cavity of the bone.
Bone is a specialized connective tissue composed of cells and an organic/inorganic matrix. It contains osteogenic stem cells that differentiate into osteoblasts which form bone matrix and osteocytes that reside in the bone tissue. Osteoclasts are large multinucleated cells that resorb bone. The matrix contains collagen fibers, proteoglycans and glycoproteins. Mineral salts such as calcium phosphate crystallize within the matrix. Bones develop through two processes - intramembranous where bone forms within connective tissue and endochondral where cartilage is replaced by bone.
This document provides an overview of dental histology and embryology. It discusses ground sections and decalcified sections of enamel, dentin, cementum, pulp, and periodontal ligament. Key topics covered include enamel tufts, Hunter-Schreger bands, incremental lines of Retzius in enamel. In dentin, it describes tubules, intertubular dentin, and lines of von Ebner and Owen. Cementum sections show cellular and acellular cementum as well as Sharpey's fibers. Periodontal ligament fiber groups and epithelial rests of Malassez are also summarized.
Histology slides snapshots (first year mbbs)Usama Nasir
This document provides identification points for various tissues and organs that would be seen under a microscope in histology slides for first year medical students. It includes summaries of simple and stratified epithelia, cartilage, bone, muscle, nervous system structures, blood vessels, lymphatic structures, endocrine glands, respiratory system, adipose tissue and more. The purpose is to aid students in identifying and distinguishing between different tissue types commonly seen in histology.
Bone tissue is a specialized form of connective tissue composed of cells and a mineralized extracellular matrix. The matrix is made up of collagen fibers and hydroxyapatite crystals that give bone its rigidity. There are two types of bone tissue: compact bone which forms the dense outer layer, and spongy or cancellous bone which is found at the ends of long bones and has a spongy, mesh-like structure. Bones develop through two processes - intramembranous ossification which forms flat bones, and endochondral ossification where cartilage is replaced by bone to form most other bones including long bones.
Bone is a living tissue capable of changing its structure as the result of the stress to which it is subjected. It consists of cells, fibers and matrix. Calcification of extra cellular matrix makes it hard. The slight degree of elasticity in the bone is due to the presence of the organic fibers. The main function of the bone is protection of some of the vital organs like brain, spinal cord, heart and lungs. It also acts as a lever which helps in locomotion and movement. It is the main storage house of the calcium salts. The cavity of the bone consists of delicate blood forming bone marrow.1 The two forms of bones are compact and cancellous bone. Compact bone exists as a solid mass however the cancellous bone has a branching network of trabeculae. The arrangement of trabeculae is such that it resists the stress and strain to which the bone is exposed. Entheses is an interface where the tendon meets bone. These are the sites of stress concentration at the hard and soft tissue function where mechanical properties differ. They play a pivotal role in the diagnosis of various types of arthritis. However, not much importance has been given by the anatomists and the clinicians towards the study on entheses. This article aims to provide a brief account on entheses to draw the attention towards the known but ignored entity called entheses.
Iaetsd bone quality assessment using mems accelerometerIaetsd Iaetsd
The document describes a study that developed a low-cost device to assess bone mineral density (BMD) using MEMS accelerometers. The device uses an automated hammer to generate stress waves that propagate through the bone in the leg and are measured by the accelerometers. Data was collected from subjects in different age groups and it was found that the acceleration values measured were higher in subjects over 35 compared to those below 35, indicating deterioration of bone quality with age. The technique provides a non-invasive, inexpensive way to evaluate bone quality and has potential for diagnosing osteoporosis.
Fuzzy knee proprioception would be of benefitKHALIFA ELMAJRI
This summary provides the key points from the document in 3 sentences:
The document discusses how osteoarthritis may begin with pathology in the subchondral bone that causes problems transmitting mechanical signals to neurological signals, leading to reduced proprioception and joint control. Improved implant designs that add slots to allow remaining healthy cartilage to function could help preserve mechanical signal qualities. Targeted minimally invasive interventions and implant designs that better simulate cartilage's transmission of mechanical stress may provide new ways to manage arthritic knees by improving subchondral bone's ability to translate mechanical signals to neurological signals.
This research article analyzes the biomechanical behavior of a virtual model of the mandibular bone loaded with monophasic and biphasic dental implants through finite element analysis (FEA). The purpose is to evaluate the biomechanical differences between monophasic and biphasic implants and assess their proper clinical use. The FEA shows that the stress distribution on the bone crest is different for the monophasic and biphasic implant configurations. Specifically, the case with the monophasic implants shows a maximum stress slightly higher than the biphasic implant case. However, the stress distribution on the mandibular ridge appears more uniform for the monophasic implant case.
This paper of finite element analysis of the rib cage model is applied to recognize stress distributions and to determine the rate of bone fractures(especially for pathologically changed bones). Also to determine the load and stress to occurs on the human rib cage at any accident. Also find the maximum load sustain capacity of human rib cage and according to the load sustain capacity of the human rib cage by finite element analysis and search a material as like a bone cement and it take on a rib fracture and see the result . This paper is only of to nullify the rib fracture as present medical treatment give the elastic belt but due to respiration, the human ribs are contract and relax that’s the rib fracture are only minimize not a nullify. The human models are considered in between age 15 to 40 year. The Simulation result shows a good agreement with the cadaver test data.
This document discusses bone mechanics and osteopathic techniques for restoring bone's elastic response. It explores bone architecture, types, crystals and their ability to absorb energy from forces. When bones repeatedly experience forces beyond their elastic limit, microfractures can occur and the bone loses its elasticity. Osteopathic techniques like myofascial release and craniosacral methods may help restore bone's elastic response by increasing biotensegrity and homeostasis in the body. Treating bone like fascia acknowledges their interconnection and bone's ability to regain motion and elasticity through manual therapy.
This document provides a literature review on monitoring bone healing in the pelvis through vibration analysis. It discusses the anatomy of the human pelvis and details on bone structure. It also reviews non-invasive methods currently used to monitor bone healing, such as X-rays, DEXA scans, quantitative CT, ultrasound, and vibration analysis. The document proposes using vibration theory and an FE model of a fixated pelvis to determine healing by measuring changes in resonant frequency as bone stiffness recovers. An experimental plan is outlined to replicate the analysis on a synthetic pelvis using epoxy to simulate healing, which could help determine when a patient's pelvis has regained stability.
The document discusses the hierarchical structure and mechanical properties of bone. At the macrostructural level, bone is divided into cortical and cancellous bone based on their density. Cortical bone forms the hard outer shell, while cancellous bone is found at the interior and has an irregular structure. Cancellous bone remodels more frequently than cortical bone. Mechanical properties vary between cortical and cancellous bone as well as between different bones and regions within the same bone.
This document summarizes a study that performed a 3D finite element analysis of the human femur bone. The analysis used a 3D CAD model of the femur obtained from medical scans. The model was meshed and material properties were assigned to different bone tissues. Nonlinear analyses were conducted to simulate loads on the femur during normal activities. Results were compared to previous studies to validate the model. The study found that cancellous bone tissue reduces stresses in the femur, with its absence causing stresses almost double the amount.
Non linear 3 d finite element analysis of the femur boneeSAT Journals
Abstract In this paper a 3D stress analysis on the human femur is carried out with a view of understanding the stress and strain distributions coming into picture during normal day to day activities of a normal human being. This work was based on the third generation standard femur CAD model being provided by Rizzoli Orthopedic Institute. By locating salient geometric features on the CAD model with the VHP (Visible Human Project) femur model, material properties at four crucial locations were calculated and assigned to the current model and carried out a nonlinear analysis using a general purpose finite element software ABAQUS. Simulation of Marten’s study revealed that the highest stress formed in the absence of the cancellous tissue is almost double the value of stress formed with cancellous tissue. A comparative study was made with the Lotz’s model by taking into consideration two different sections near the head and neck of the femur. An exhaustive number of finite element analyses were carried out on the femur model, to simulate the actual scenario. Index Terms: Fracture, Cortex, Cancellous, femur bone, finite element
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1. Extracorporeal shockwave therapy is an effective treatment for bone non-unions and delayed unions, achieving healing rates of over 70% according to clinical studies.
2. The mechanism of action involves stimulating osteoblastic activity and new blood vessel formation at the treatment site through a stromal cell response.
3. Proper patient selection and stabilization of the treatment area after shockwave therapy is important for success. Younger, hypertrophic non-unions tend to have better outcomes than older, atrophic cases.
Motor Unit Conduction Velocity During Sustained Contraction Of The Vastus Med...Nosrat hedayatpour
in the current study, we analyzed the
Effect of eccentric exercise on the conduction velocity of
individual motor units at two locations of the vastus
medialis muscle during sustained contractions.
Efficiency of Stem Cell After Spinal Cord Injury with Clip-Compression_ Crims...Crimsonpublisherssmoaj
Efficiency of Stem Cell After Spinal Cord Injury with Clip-Compression by Tae Hoon Lee* in Crimson Publishers: Surgery Journal Impact Factor
Our experiment grafted mouse embryonic stem cell (mESC) to influence behavioral deficiency in rodent animal models of clip compressive surgery inducing spinal cord injury (SCI) of central nervous system. Our research proved the effect of grafted stem cells to the injured spinal cord region, focusing the application of mouse embryonic stem cells for regeneration of spinal cord nervous injury. Therefore, our research suggests manifest results that implantation of mouse embryonic stem cell could show behavioral improvement after severe spinal cord damage.
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The document summarizes a study comparing the mechanical performance of the SUTUREFIX Ultra soft suture anchor to two commonly used hard suture anchors (SutureTak and Gryphon) for shoulder labral repair. Key findings include:
- The SUTUREFIX Ultra anchor demonstrated significantly higher fixation strength and lower displacement following cyclic loading compared to the hard anchors, both in poor bone and bone with cortical layers.
- No SUTUREFIX Ultra anchors failed during cyclic loading testing, while some SutureTak and Gryphon anchors failed before completing 500 load cycles.
- The results suggest the SUTUREFIX Ultra soft anchor provides mechanical performance equal or superior to hard anchors, with potential
Histological changes in dentofacial orthopaedics1 /certified fixed orthodont...Indian dental academy
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Deep Learning-based Histological SegmentationDifferentiates Cavitation Patte...Wookjin Choi
Unsupervised segmentation (unlabeled regions of interest, ROIs) and autoencoder (AE)-based classification were used to classify differences in cavitation patterns in knees and digits using the stained images (n=20-30 images/group).
Each image was divided into 256 x 256 pixel patches, and a convolutional neural network (CNN)-based unsupervised segmentation was used to identify ROIs. These patches were subsequently fed into a CNN-based AE whose latent space layer was connected to a classifier for input patch classification.
The AE was trained using the ROIs identified by the unsupervised segmentation, and the image classes were used to train the classifier. Whole image classifications were determined by maximum voting of the patch results and evaluated by accuracy.
This document discusses muscle plasticity, which refers to the ability of skeletal muscle to adapt structurally and functionally in response to environmental changes such as increased or decreased activity levels. It provides definitions and history of the concept. It describes the effects of chronic low frequency electrical stimulation on muscles, including fiber type transformations, increased mitochondria and vascularization, and changes to contractile properties. Over time periods of hours to weeks, stimulated muscles demonstrate metabolic and structural adaptations that increase their fatigue resistance and transform them from fast-twitch to slow-twitch phenotypes. Several studies are summarized that investigate muscle adaptations to long-term stimulation in animals and humans.
2. pharmacologically suppressing remodeling and observing the resulting accumulation of
microcracks in vivo. (3,13,15,38,39,51,52,55,56,65-71,76,77).
Linear microcracks are just one of several matrix damage types in bone that result from fatigue.
Numerous recent studies have described a range of “small-crack”-type damage processes that
occur with fatigue (3,7,19,26,30,45,59,75). These small crack processes produce what has
come to be termed “diffuse” matrix microdamage, owing to the diffuse pooling of histological
stains seen under the light microscope in such damaged regions. Confocal microscopy studies
demonstrate that these diffuse staining regions in fatigued bone are composed of clusters of
very small (sublamellar) sized bone matrix cracks, on the order of 1 μm or smaller (7,26,75).
Typical linear fatigue microcracks lead to degraded bone material properties, with decreases
in stiffness, strength and fracture toughness (12,68,74,75). However, intriguing recent work
by Diab and Vashishth (21-23) shows that diffuse damage production (and its presence) is a
hallmark of bones with improved fracture resistance.
Whether living bone remodeling responds similarly to diffuse damage as it does to linear
microcracks, i.e. by activation of bone targeted remodeling, is not known. In studies of rat
ulnae fatigue in vivo, Bentolila et al (3) found that diffuse damage removal by intracortical
remodeling was significantly less effective than linear microcrack removal, providing
intriguing preliminary evidence that the response to diffuse damage and linear microcracks
may differ. However, their experiments were not designed to specifically differentiate the
biological consequences of diffuse matrix damage and more typical linear microcracks. In the
current study we directly tested whether diffuse matrix damage and more typical linear
microcracks differ in their ability to activate bone remodeling.
MATERIALS AND METHODS
Experimental approach
To test the hypothesis that there is a differential relationship between microdamage type and
activation of resorption, we systematically varied fatigue damage levels in rat ulnae by applying
different numbers of loading cycles (1500, 3000, and 4500 cycles) to 3 cohorts of rats. Fatigue-
induced losses of bone stiffness were allowed to vary freely in these animals. An additional
group of ulnae were loaded to a fixed mechanical degradation level (23% stiffness loss from
baseline) that was used in previous studies in order to provide a reference value.
In Vivo Fatigue Loading
In vivo fatigue loading was performed to induce matrix damage in ulnae of adult female
Sprague-Dawley rats (283 ± 10 grams, 4-5 months old, Charles River). Under isoflurane
anesthesia (1-3%), right ulnae were subjected to fatigue loading in end-load bending via the
olecranon and flexed carpus as previously described (3,15,77,78). Briefly, loading was carried
out under load control using a closed-loop servo-hydraulic materials testing system (Instron
Model 8841, Instron Corp., Canton, MA, USA) at a frequency of 2 Hz, using a mean peak load
magnitude of 16N corresponding to 3800±500 μstrain. This approximates the peak physical
strains reported in racehorses and military recruits under vigorous physical activity (11,25,
50,58). In the first phase of these studies, a group of animals (n=7/group) were fatigue loaded
to a single endpoint based on whole bone stiffness loss (23% decrease in secant structural
stiffness) to provide an identical reference point to previous studies with this model by our
laboratory (3,15,76,77) and others (19,29,39,44). This fatigue level induces bone microcracks,
focal osteocyte apoptosis and subsequent targeted intracortical remodeling in rat ulnae (3,15,
76,77). Three additional groups of rats (n=22) were fatigue loaded in vivo as described above
for fixed numbers of cycles, based on the mean number of cycles needed to reach the fatigue
endpoint for animals in the first phase of this study. This allowed us to produce bones that
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3. sampled a range of damage patterns and levels throughout the typical fatigue history of these
bones in vivo. Accordingly ulnae in the fixed cycle groups were loaded for either 1500, 3000
or 4500 load cycles, respectively. After loading, rats recovered from anesthesia and resumed
normal cage activity for 14 days with access to food and water ad libitum. At this point, which
reflects the peak intracortical resorption phase in the remodeling response of fatigued rat ulnae,
the contralateral ulnae were loaded identically in order to define initial baseline levels of fatigue
microdamage within each animal prior to bone remodeling (3). Rats were immediately
sacrificed without recovery from anesthesia and both the post-loading bones (“survival bones”)
and the contralateral baseline bones (“Non-survival bones”) were harvested. Ulnae from
independent, non-loaded control rats were examined as well.
Following euthanasia, forelimbs were immediately removed and bones dissected free of soft
tissues. Ulnae were fixed in neutral buffered formalin, stained in basic fuchsin for microdamage
assessment (3,10), and embedded undecalcified in polymethylmethacrylate (46). Using a low
speed circular diamond saw, cross-sections (150 μm thick) were cut from the ulnar mid-
diaphyseal region and polished to 70 μm for fluorescence and confocal microscopy studies.
This is the site at which where microdamage concentrates with fatigue loading in these bones
(3,44).
Histomorphometric Analysis
Specimens were analyzed for intracortical remodeling sites (Rs.N, #/mm2) and microdamage.
Linear and diffuse microcracks were identified using fluorescence microscopy based on their
patterns of staining with basic fuchsin, which cannot penetrate mineralized matrix that is devoid
of cavities or microdamage. (7,10,32). Confocal microscopy was used to examine damage at
higher magnification for qualitative studies and illustrative purposes. Microdamage content
was measured from number density of typical linear microcracks (Cr.Dn, #/mm2) and from
area fraction occupied by patches of diffuse basic fuchsin staining within the cortex
(Diff.dx.Ar/B.Ar, mm2/mm2), following methods detailed elsewhere (3,7). Briefly,linear
microcracks, on the size order of 10's to approximately 100 μm, were distinguished by linear
regions of basic fuchsin uptake with sharp boundaries. Diffuse microdamage was visualized
as pooled basic fuchsin that formed a “diffuse staining pattern” in regions of fatigued ulnae
that did not exhibit this staining pattern in control bones. A “diffuse pattern” was defined as
one in which clusters of microcracks were too small to be distinguished from one another (i.e.,
<1-2 μm). Linear microcracks and diffuse damage regions were measured using a 10 mm × 10
mm eyepiece grid reticule at 400x magnification. Measurements were made by a single
observer (BCH) who was blinded to specimen identification, with confirmation by a secondary
observer (MBS) on randomly chosen sections.
Osteocyte Integrity
Osteocyte apoptosis has been shown to be a key control point in fatigue-induced bone
remodeling (15,76,77). However, specific molecular markers of apoptosis could not be studied
directly in the thick, undecalcified sections that were needed in this experiment to image diffuse
matrix damage. Therefore, we adapted the approach of Bentolila et al (3) and Cardoso et al
(15) who used osteocyte morphology as an index of osteocyte integrity. Specifically, Verborgt
et al (76) confirmed that the number of osteocytes with pyknotic nuclei correlated strongly
with the numbers of apoptotic osteocytes in fatigued ulnae as determined by
immunohistochemistry and TUNEL staining. Accordingly, measurements were made as
follows: normal osteocytes (fully occupying lacunae, N.Ot/B.Ar, #/mm2) and atypical
appearing osteocytes (retracted or pyknotic, At.N.Ot/B.Ar, #/mm2) were counted (Figure 1).
For linear microcracks, this area was within ± 80 μm on either side of the linear microcrack.
For diffuse microdamage, the area included the entire region of diffuse microdamage and
extended to ± 80 μm on either side of the damaged region. The tissue was sampled in the same
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4. region of interest (mid-diaphysis) as for the microdamage quantification, and measurements
were made using brightfield microscopy at 400X magnification. The measurements were
repeated three times using the grid reticule as described above.
Statistical analyses
Two-way ANOVA was used to analyze stiffness loss as a function of both duration of loading
and damage type. Multiple comparison tests were performed with the post-hoc Dunn Procedure
(GraphPad Instat For MacIntosh, GraphPad Software, San Diego, CA, USA). Plots of
resorption number (Rs.N/B.Ar) versus linear (Cr.Dn) or diffuse (Diff.Dx.Ar/B.Ar) damage
content were analyzed using regression analysis. χ2 analysis with equations for three-
dimensional contingency analysis (82) was used to determine if activation of resorption
depended on the number of loading cycles and/or the microdamage type. Osteocyte viability
was analyzed using Kruskal-Wallis ANOVA with the post-hoc Dunn Procedure (GraphPad
Instat For MacIntosh, GraphPad Software, San Diego, CA, USA).
RESULTS
In Vivo Fatigue
Fatigued, non-survival ulnae containing only diffuse microdamage exhibited low stiffness loss
even at high loading cycles (Figure 2 and Table 1). In contrast, fatigued, non-survival ulnae
containing both linear microdamage and diffuse microdamage sustained significantly higher
stiffness loss at all loading cycles than the fatigued, non-survival ulnae containing diffuse
microdamage alone (Figure 2, p<0.005). Moreover, in ulnae exhibiting solely diffuse
microdamage, loading duration did not significantly affect stiffness loss (Figure 2, p=0.3).
Linear microdamage content and number of resorption spaces were correlated (Figure 3A, r2
= 0.60, p<0.01). In contrast, there was no activation of resorption in the ulnae that had only
diffuse microdamage (Figure 3B). Bones that exhibited linear microdamage also had diffuse
microdamage. In those bones with both damage types, resorption spaces were absent in diffuse
damage regions that did not also contain adjacent linear microcracks. Some ulnae in the high
cycle load group (4500 cycles) sustained only diffuse damage, while some in the low (1500
cycle) load group showed both linear microcracks and diffuse damage. However, there was no
relationship between activation of resorption and duration of loading; i.e. bones that sustained
large numbers of loading cycles with only diffuse damage did not activate intracortical
remodeling. Contingency analysis of resorption, linear microdamage, and duration of loading
(number of cycles or time) shows that activation of resorption depends on the presence of linear
microdamage but not on duration of loading (Overall: χ2 = 25.9, p<0.001; Activation of
Resorption Vs. Duration of Loading: χ2 = 2.41, p=0.3; Activation of Resorption Vs. Presence
of Linear Microdamage: p<0.001, Fisher's Exact Test).
Osteocyte Integrity
The numbers of normal and pyknotic osteocytes in diffuse microdamage sites were similar to
control bones (Figure 4, p=0.23). This was true for both bones that showed only diffuse damage
regions (i.e., lower damage levels) and discrete diffuse damage regions in bones that also had
linear microcracks (i.e., higher damage levels). In contrast, the number of atypical osteocytes
in association with linear microcrack sites was increased dramatically (by more than 600%)
over that in control bones (Figure 4, p<0.0001).
DISCUSSION
The results of this study indicate that linear microcracks provide a physiologically relevant
stimulus for bone remodeling, as previously established (3,15,55,55,76,77). However, there
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5. was no bone remodeling activity associated with diffuse microdamage foci. Moreover, the
observed remodeling responses were due to the presence of linear microcracks and not to the
cumulative loading history itself; bones that sustained large numbers of loading cycles with
only diffuse damage did not activate intracortical remodeling.
Previous studies testing the effects of microdamage on bone remodeling activation did not
differentiate between linear and diffuse microdamage. Bentolila et al (3), in the first description
of the rat ulnar fatigue model, observed that diffuse damage removal by intracortical resorption
was significantly less effective than linear microcrack removal, hinting that the response to
diffuse damage and linear microcracks was different. However, because of the high fatigue
levels examined in their study, the ulnae possessed both damage types, making it impossible
to separate completely the effects of these two damage types. In the current studies we built
on the recent observations from our laboratory and others showing that small-crack-type (i.e.,
diffuse) damage occurs earlier in bone's fatigue loading history than linear microcracks and
also in different areas from linear microcracks (3,7,21-23,69,70,75). Diffuse damage leads to
changes in local material properties. A recent study using probabilitistic failure analysis
suggests that diffuse damage can be viewed as occurring when debonding at mineral-collagen
interfaces takes place at a large scale (24). If debonding at mineral-collagen interfaces is non-
existent or limited in scope relative to the location of the defect, the formation of a linear
microcrack would be probabilistically favored based on finite element analysis. Diffuse
damage can also be a precursor to linear microdamage (23).
There is inherent variability in fatigue life of rat ulnae resulting from inter-animal differences
in diaphyseal cross-sectional geometry. For example the coefficient of variation for cortical
bone area in rodent long bones is in the range of 10-15% (42,64). As area weighted moments
of inertia, these small differences in bone geometry will lead to different structural stiffnesses
among bones such that stresses applied to the ulnae (and resulting local strains) will differ
among animals for the same applied load magnitude. This mechanical variability is typical of
load controlled structural tests in engineering and biomechanics, where structures are similar
but not identical. By taking advantage of this inherent variation and examining ulnae loaded
to varying numbers of cycles, rather than to a specific level of mechanical degradation as in
previous studies, we were able to generate bones that contained only sublamellar microdamage
and also some bones containing combinations of both diffuse matrix damage and typical linear
microcracks. This approach also produced bones at the higher loading cycles end of the
experiment that developed only diffuse damage, and also some with both damage types.
Similarly, some bones at the low cycle end of the experiment had diffuse damage only and
others had both types.
This uncoupling of damage types from the number of cycles (or duration of loading) allowed
us to directly test in Survival bones the relationships among damage type, bone resorption and
the duration of loading (number of cycles or time). Remodeling was not activated in any bone
that contained solely diffuse matrix damage regardless of the duration of loading. Moreover,
there was no relationship between activation of resorption and duration of loading. Some bones
sustained large numbers of loading cycles and developed only diffuse damage, but did not
activate intracortical remodeling. Conversely, intracortical remodeling was activated in bones
that contained linear microcracks, independent of the number of load cycles.
Typical linear microcracks in bone causes localized osteocyte apoptosis around the crack. This
region of apoptosis co-localizes the region of bone that will subsequently undergo osteoclastic
resportion (3,15,55,56,76,77). Moreover, Cardoso et al recently demonstrated that this
osteoctye apoptosis plays a direct, controlling role in the activation and targeting of the focal
remodeling-repair response to microdamage that follows fatigue in vivo (15). We found that
pharmacological suppression of this osteocyte apoptosis after fatigue completely prevented the
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6. activation of intracortical remodeling. The results of the current study indicate that diffuse
matrix damage does not alter osteocyte viability, nor does it activate focal bone remodeling
activities to remove and replace the damaged region. Thus, it seem reasonable to posit that the
absence of osteocyte apoptosis in zones of diffuse matrix damage may explain why diffuse
damage does not evoke a targeted remodeling response seen with other bone microdamage.
In the current studies, we examined osteocyte apoptosis and intracortical remodeling in the
ulnar cortex at only a single time period (14 days) after fatigue. Whether osteocytes in diffuse
damage zones might die much later than we have examined in this study is certainly possible
and awaits future studies. However, previous studies have shown that at linear microcrack sites,
osteocyte apoptosis occurs very rapidly, within 1-2 days, after loading. Thus the absence of
osteocyte death in diffuse damage zones at 2 weeks after loading strongly argues that the
response of osteocytes to diffuse damage is different from the response to linear microcracks.
The absence of any intracortical resorption in diffuse damage zones at 2 weeks after loading
– the timing for peak resorption at linear microcracks – reinforces the argument that bone's
response of to diffuse damage is fundamentally different from its response to linear microcracks
The long-term fate of this diffuse microdamage in living bone remains unclear. Without the
associated local osteocyte apoptosis, diffusely damaged matrix does not appear to be
specifically targeted for remodeling and removal. One possibility is that it may remain
substantially unresolved or unrepaired over time. However, Bentolila et al (3) reported a small,
non-significant reduction of diffuse damage in fatigue loaded rat ulnae by two weeks after
loading, compared to a multifold increase in resorption of linear microcracks that resulted in
a 50% reduction in microcrack content within the same time frame. Given that linear
microcracks and diffuse damage region were co-localized at the higher fatigue level examined
in the Bentolila study, the diffuse damage could have been removed incidentally, and not
particularly effectively, by the other targeted remodeling sites nearby. An intriguing,
alternative speculation is that diffuse microdamage may be dealt with in an entirely different
and hitherto largely unappreciated manner - perhaps by a direct matrix repair mechanism
effected through the osteocytes (8). Tissue repair by remineralization occurs routinely in
enamel, where mineral damage from wear or acid is reversed by a physico-chemical process
dependent on the pH, protein and ionic composition of saliva (1,14,20,36,61,72). In bone, these
micro-environmental properties would be directly dependent on the behavior of the osteocytes.
Furthermore, osteocytes have been shown to produce a range of matrix proteins and regulators
of bone mineralization that might also participate in direct matrix repair (4-6,27,33,35,37,40,
41,43,54,79,80). Given the extensive infiltration of osteocyte process and canalculi thought the
bone tissue, no area of the bone matrix is located farther than about 1 μm from an osteocyte
process (78), thus, providing a close spatial relationship between cells and matrix that could
enable osteocytes to repair sublamellar size cracks in bone through local biochemical
processes.
The reason why diffuse damage does not cause osteocyte apoptosis is currently unknown.
However, several recent studies provide intriguing insights. Tami et al showed that linear
microcracks impair local canalicular fluid transport between osteocytes (71) and this loss of
canalicular fluid transport due to linear microdamage may lead to osteocyte apoptosis by
causing hypoxic stress on cells (38). In addition, linear microcracks that directly transect
osteocytes likely cause necrosis of those few cells involved. This may drive apoptosis of
adjacent osteocytes, analogous to other focal injury systems, such as focal heart or brain
ischemia and also focal trauma, where the small core of necrotic cells at the center of the injury
induces a much larger zone of apoptosis in neighboring cells (2,17,18,28,34,62). We speculate
that sublamellar (diffuse) damage does not similarly impair the effectiveness of local fluid and
solute transport to and from osteocytes and thus does not cause metabolic stress on the
osteocytes that leads to cell death. Another possibility is that submicron-sized cracks in
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7. sublamellar damage may be too small to directly injure osteocytes and activate a focal injury
response as the size of sublamellar cracks is on the order of <1 μm, compared to the length of
a typical osteocyte cell process (~8-10 μm) and the diameter of an osteocyte (~10-15 μm).
The design of the current study and nature of the animal model itself impose several limitations
that will require future studies to resolve. Stiffness loss in ulnae exhibiting solely diffuse
microdamage was less than in ulnae exhibiting both diffuse and linear microdamage (9.8 ±
5.8% vs. 20.6 ± 4.4%, respectively), as the linear microcracks appear at a later stage of fatigue
than does diffuse damage. It is possible that the relatively greater overall deformations of
osteocytes resulting from this lower stiffness in fatigued bone would contribute to cell injury.
However, osteocyte integrity was normal in discrete diffuse damage sites in bones that also
had linear microcracks in other areas, arguing that the higher tissue deformations resulting
from lowered stiffness in fatigue bone did not contribute significantly to cell injury. The nature
of the local stresses causing each of these damage types may have also influenced the degree
of local osteocyte death and activation of bone remodeling. Typical linear microcracks in this
model occur largely in compressive cortices, while diffuse damage is characteristic of tensile
regions (3,7,23,75). Whether the chronic compression of osteocytes in one bone damage region
differs in its effects from chronic tensile loading in other damage regions is not known and
requires further study. As the intracortical remodeling activated by microdamage stimulus
originates principally from periosteal and endocortical surfaces, it is possible that the
differential response to the microdamage types observed may also be influenced by location
of the damage type. The linear microdamage observed in this study was located mostly in the
compressively-loaded regions of the ulnar diaphysis (44,69,70) nearer to the periosteal
surfaces, while the diffuse damage characteristically occurred in tensile-loaded regions of the
ulnar cortex and was distributed throughout the cortex. However, in previous canine (9,51)
fatigue studies, both linear microdamage and the associated intracortical remodeling activity
were observed away from bone surfaces, indicating that it is unlikely that location of
microdamage plays a major role in governing the remodeling response to the overuse stimulus.
Lastly, intriguing recent studies by Diab and Vashishth (21-23) show that linear microcracks
and diffuse damage have differential biomechanical response/outcomes: diffuse damage is
hallmark of bones with better fracture resistance, i.e. unlike linear microcracks diffuse damage
allows bones to dissipate energy and postpone fracture. Thus, it seems reasonable to speculate
that bone has evolved fundamentally different matrix-level repair responses to deal with
different damage types with different mechanical consequences.
In conclusion, these studies demonstrate that bone responds differently to linear microcracks
and diffuse damage. Typical linear microcracks affect surrounding osteocytes in a profound
manner, such that the surrounding osteocytes undergo apoptosis that in turn provides the tissue
focus for the activation and targeting of subsequent intracortical remodeling. In contrast,
diffuse microdamage does not induce osteocyte apoptosis nor does it elicit an intracortical
remodeling response. Regardless of the mechanisms of cellular injury, or the lack thereof in
the case of diffuse damage, the current studies show that diffuse damage after fatigue does not
result in osteocyte death, and this appears to be key to explaining why remodeling does not
occur in these regions in response to diffuse matrix damage.
Acknowledgments
Research supported through NIH grant AR 41210
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12. Figure 1.
Photomicrograph showing examples of osteocyte integrity at assessed from the thick basic
fuchsin stained sections used in this study. Normal osteocytes (N.Ot) fully occupying lacunae
and atypical-appearing osteocytes (At.Ot) appears retracted or pyknotic (Scale bar = 50 μm).
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13. Figure 2.
Linear microdamage in bone was associated with stiffness loss, as shown by fractional stiffness
loss (stiffness after loading divided by initial stiffness) of rat ulnae loaded for 1,500, 3,000 or
4,500 cycles in vivo (rats immediately euthanized after loading). Post-hoc observation of these
ulnae allowed us to group them into two cohorts: bones showing only diffuse microdamage
and bones showing diffuse and linear microdamage (no specimens were observed with solely
linear microdamage). Note that bones with solely diffuse microdamage sustained little stiffness
loss despite higher numbers of loading cycles. Stiffness loss was markedly higher in ulnae
containing both linear and diffuse microdamage than in ulnae loaded to the same number of
cycles but exhibiting only diffuse microdamage. Stiffness loss did not depend on loading cycles
for ulnae exhibiting solely diffuse microdamage. In contrast, in ulnae containing both diffuse
and linear microdamage, increased numbers of loading cycles tended to increase stiffness loss
(*p<0.05, **p<0.005).
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14. Figure 3.
Panel A that intracortical remodeling activity (Rs.N) at 14 days after fatigue in vivo was linearly
dependent on the amount of linear microdamage in the ulna. Duration of loading did not affect
activation of resorption. The confocal photomicrographs below the plot show examples of
linear microcracks (left, acute fatigue, non survival), a resorption space at a microcrack (14
days post fatigue loading) and nonloaded control bone. Panel B shows the differential response
to diffuse microdamage. Diffuse (sublamellar) microdamage did not evoke an intracortical
remodeling response at any level of damage or number of loading cycles. (Scale bars on
confocal photomicrographs = 32 μm)
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15. Figure 4.
Osteocyte integrity (normal and atypical appearing osteocytes N.Ot/mm2 and At.Ot/mm2,
respectively, see text for definition]) in association with different bone microdamage types.
There was no significant change of osteocyte integrity in diffuse microdamage regions (p=0.23
vs. non-loaded control bone); however, linear microdamage resulted in a significant loss of
normal osteocyte integrity. (* p<0.0001 relative to non-loaded control).
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16. NIH-PAAuthorManuscriptNIH-PAAuthorManuscriptNIH-PAAuthorManuscript
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Table1
Summarydataforlinearmicrocracks(Cr.Dn),diffusemicrodamaae(Diff.Dx.Ar/B.Ar)contentandintracorticalresorptionspacenumber(Rs.N)foracutely
fatigued(Non-survival)andSurvival(Fatigue+14days)ulnaeateachfatiguelevelsexamined.
Fatigueloadinglevels
4500Cycles3000Cycles1500Cycles
Non-survivalSurvivalNon-survivalSurvivalNon-survivalSurvival
Diff.Dx.Ar/B.Ar(mm2/mm2)0.085±0.0390.071±0.0290.054±0.0270.049±0.0290.055±0.0300.051±0.038
Cr.Dn(#/mm2)1.97±0.521.18±0.31*1.51±0.430.95±0.33*1.88±0.76*1.09±0.41*
Rs.N(#/mm2)01.14±0.6101.16±0.6801.23±0.52
*
P<0.025forNon-survivalvs.survivalulnaewithinaloadinggroup
Bone. Author manuscript; available in PMC 2011 October 1.