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.

1. Bone Tissue Engineering
Mehdi Chamani
Pharmacy Student,Tehran university of medical sciences

2. Introduction
 Each year, more than 6.3 million fractures occur in the United
States of which almost 1 million require hospitalization
 Metals such as iron, cobalt, and titanium may be permanently
placed in bone to fill a defect
 Ceramics are also used in the treatment of bone injuries
 Ceramics offer excellent biocompatibility, they are too brittle to
provide structural support to load-bearing bones.
fatigue, corrosion, tissue
infection
poor implant-tissue interface

3. Bone
Bone
Osteoblasts
Osteocytes
Osteoclast
Haversion system or Osteon
 The differentiation of osteoproginitor cells
into osteoblast is acclererated by some
hormones and some bone proteins called
Skeletal growth factors.

5. Ossification

6. Repair of bone after fracture

7. Bone Tissue
Engineering

8.  Tissue Engineering is the in vitro development (growth) of tissues or organs to
replace or support the function of defective or injured body parts.
 Research is presently being conducted on several different types of tissues and
organs, including :
 Skin, Cartilage, Blood Vessels, Bone, Muscle, Nerves, Liver, Kidney
Before a tissue can be developed in vitro, first we must understand how tissues are
organized. The basic tenant here is that:
“all tissues are comprised of
several levels of structural hierarchy”

9.  Tissue engineering strategies fall into
three general categories:
i. cell-based strategies
ii. growth-factor based
strategies
iii. matrix-based strategies
 Researchers hope to reach this goal by
combining knowledge from physics,
chemistry, engineering, materials
science,biology, and medicine in an
integrated manner.

10.  potential bone tissue-engineering device must:
1. Provide temporary mechanical strength to the
affected area.
2. Act as a substrate for osteoid deposition and growth.
3. Contain a porous architecture to allow for
vascularization and bone ingrowth.
4. Encourage bone cell migration into a defect and
enhance cell activity for regeneration and repair.
5. Degrade in a controlled manner to facilitate load
transfer to developing boneand to allow bone growth
into the defect.
6. Degrade into non-toxic products that can safely be
removed by the body.
7. Not cause a significant inflammatory response.
8. Be capable of sterilization without loss of bioactivity.

11. Cells for Bone Tissue Engineering
 In fact, an ideal cell source should be :
i. easily expandable to higher passages
ii. non-immunogeneic
iii. protein expressionpattern similar to the tissue to be regenerated
 Osteoblasts:
The first, and most obvious choice because of their nonimmunogenicityis
the isolation osteoblasts from biopsies taken from the patients.
Few cells are available
expansion rates are relatively low
protein expression profile
An alternative to the referred methodology is the use ofcells obtained
from non-human donors (xenogeneic cells)
the immunogenicity
stem cell biology appears as the most valid and more promising solution

12.  Stem cell:
i. The most primitive derive from the fertilized oocyte (the zygote) Totipotent
ii. Inner Cell Mass (ICM) from which the embryo derives also known as embryonic stem cells
(ES)pluripotent
iii. Multipotent stem cells, also known as adult stem cells (ASC), in the fully differentiated
tissues
iv. Stem cells located in the bone marrow,known as Mesenchymal Stem Cells (MSC)
these cells were able to develop into distinct terminal and differentiated cells including
bone,Cartilage,fat,and tendon
They can be extensively expanded in vitro, immunosuppressive roles in vivo, which would
make them suitable for allogeneic or xenogeneic transplantation

14. Scaffolds – Temporary Matrices for Bone Growth
 Any tissue consists of a matrix and one, or usually, manycell types.
The matrix is, in vivo, a 3D scaffold for cells, and provides them with
a tissue specific environment and architecture.
 Scaffolds Essential Properties :
i. Biocompatibility : Scaffolds should be well integrated in the host’s
tissue without eliciting an immune response.
ii. Porosity : Scaffolds must posses an open pore, fully interconnected
geometry in a highly porous structure with large surface to area
volume ratios that will allow cell in-growth, cell distribution, allow
capillary in-growth
iii. Pore Size : It is well accepted that for bone tissue engineering
purposes, pore size should be within the 200–900 um Range.

15. Scaffolds – Temporary Matrices for Bone Growth
i. Surface Properties : Surface properties, both chemical and
topographical, can control and affect cellular adhesion and
proliferation
ii. Osteoinductivity : Osteoinduction is the process by which stem
and osteoprogenitor cells are recruited to a bone healing site
iii. Mechanical Properties and Biodegradability :
In vitro, the scaffolds should have sufficient mechanical strength to
withstand the hydrostatic pressures and to maintain the spaces required
for cell in-growth and matrix Production.
the scaffolds degradation rate must be tuned appropriately with the
growth rate of the neotissue, in such a way that by the time the injury
site is totally regenerated the scaffold is totally degraded.

17.  Synthetic ceramic scaffolds :
i. Ceramic scaffolds including hydroxyapatite (HA)
ii. Tricalcium phosphate (TCP)
iii. HA-TCP beta-tricalcium phosphate / bioactiveglass (I-TCP/BG)
iv. I-TCP with Mg (I-TCMP)
v. Calcium phosphate cement (CPC)
 Defects were either cranial, calvarial, or subcutaneous. Their sizes were at a
range of 5 mm to 12 cm. The defect closure was observed one to 10 weeks
after the surgery.

18. Natural ceramic scaffolds
i. Scaffolds such as human demineralized cancellous bone
ii. Human autoclaved cancellous bone
iii. demineralized bone matrix (DBX®)
 Defect sizes were between 1.5 to 3 cm and the results were analyzed after one
to four months.

19.  Polymers and non-ceramic scaffolds :
i. Scaffolds including polycaprolactone (PCL)
ii. PCL/collagen (PCL/Col) polyurethane
iii. phosphoester-poly (ethylene glycol) (PhosPEG)
iv. poly (lactic-co-glycolic) acid (PLGA) and open-cell
v. poly-L-lactic acid (OPLA)
 Defects were cranial, calvarial, femoral, or subcutaneous and their sizes were at a range of 4
mm to 1.2 cm.
The defect closure was observed 12 days to 12 weeks after the surgery.

20.  Composite scaffolds (polymer+ceramic)
i. fibrin-alginate-HA
ii. PLGA-CaP
iii. PLGA-bioactive
 Defects were cranial, femoral, or subcutaneous and their sizes were at a range of 2.5 mm to 5
mm. The defect closure was observed 4 days to 6 months after the surgery.
 Metal-based scaffolds
i. Scaffolds such as titanium and titanium alloys (Ti6 AL4 V and Ti6AL4 V with a CaP coating)
ii. titania-silica coated Ti fibers and silver
 Defects were 1.5 to 4 mm and histologic evaluations were performed 1 to 12 weeks after
surgery.

21.  Nano-scaffolds
i. Nono-sintered
ii. Nanocrystalline
iii. phase-pure HA and silica -CaP nanocomposite
 Animals were rabbits and goats with 8 mm to 25 mm defects. Animals were sacrificed 4 to 12
weeks post-surgery.

22. Processing Techniques
Solvent casting/particulateleaching is probably the best known and most widely used method
for the preparation of bone tissue engineering scaffolds.
This method consists in dispersing calibrated mineral (e.g., sodium chloride, sodium tartrate and
sodium citrate) or organic (e.g., saccharose) particles in a polymer solution.This dispersion is then
processed either by casting or by freeze-drying in order to produce porous scaffolds.
Fiber bonding is a scaffold processing technique that consists of individual fibers woven or
knitted into three-dimensional patterns of variable pore size.

26. Growth Factors
 Growth factors are cytokines that are secreted by many cell types and function as signalling
molecules
 promotion and/or prevention of cell adhesion, proliferation, migration and differentiation by
up-regulating or downregulatingthe synthesis of several proteins, growth factorsand receptors.
i. Bone morphogenetic protein (BMP) : Stimulate mesenchymal stem cells to differentiate
towards an osteoblastic phenotype
ii. Platelet Derived Growth Factor (PDGF) : Increasing DNA synthesis and mitosis activity
and collagen synthesis in osteoblasts
iii. Transforming Growth factor-Beta (TGF-ᵦ) : Modulating bone cell metabolism and
includingneovascularization
iv. Vascular endothelialgrowth factor (VEGF) : potent angiogenic factor and is expressed
in a variety of highly vascularized tissues.
v. Insulin-Like Growth Factor (IGF)
Increase matrix apposition rates.In addition
they maintain collagen integrity in the bone

27. Bioreactors
 that simulate the dynamic environment that cells encounter in vivo can improve mass transfer
throughout a scaffold to address these concerns .
 These devices uniformly distribute cells onto three-dimensional scaffolds with appropriate
nutrient concentrations, facilitate mass transfer to growing cells, and impart mechanical
stimuli to these cells .
 The flow system enhances mass transport and introduces shear stress onto developing cells to
induce differentiation, proliferation, and mineral deposition

35. Mehdi Chamani
Department of pharmacy,Tehran University of medical sciences