Why COLLAGEN AND HYDROXYAPATITE Collagen is used extensively as a scaffold biomaterial due to its biocompatible and biodegradable properties . Indeed, both collagen type I and Hydroxyapatite were found to enhance osteoblast differentiation but when combined they showed osteogenesis From an orthopedic perspective however, collagen scaffolds are limited by their poor mechanical characteristics and for this reason we aim to combine collagen with Hydroxyapatite to improve their mechanical properties Also, if alone collagen is used , it is degraded by the collagenase of the body. Thus, to decrease the rate of degradation also Coll/HA composites are in demand Eucare pharmaceuticals Ltd. Sybograf-C http://www.eucareindia.com/product.html
The natural bones contain mainlycollagen and Hydroxyapatite. That is thereason because many researchers tryfor (nano)Hydroxyapatite/collagencomposite for hard tissue repairingComposition of Bone Tissue• 25% Water• 25% Protein or organic matrix 95% Collagen Fibers 5% Chondroitin Sulfate• 50% Crystallized Mineral Salts Hydroxyapatite (Calcium Phosphate)
Coll/HA composite (Left) Fiberized hydroxyapatite and collagen compound composite immediately after adjustment (Right) Hydroxyapatite and collagen compound composite made porous
Advantages/Properties of Coll/HAcomposites Biodegradable Resorbed into the body over time Biocompatible and Bioactive Facilitates complete osteogenesis High porosity Facilitates bone cell migration through matrix Increases cellular nutrient and waste exchange High permeability Facilitates conductivity of fluids through matrix Mechanically strong Facilitates handling and ease of use Provides structure within which bone can reform High degree of pore connectivity prevents avascular necrosis , increases cell mobility The interest in temporary substitutes is that they permit a mechanical support until the tissue has regenerated and remodeled itself naturally. Furthermore they can be seeded with specific cells and signaling molecules (growth factors,VEGF, TGR) in order to maximize tissue growth and the rate of degradation and absorption of these implants by the body can be controlled.
Preparation of microspheresWater-in-Oil emulsion system (microspheres of 200- 300 µm) Bovine collagen in phosphate-buffered saline (PBS) was mixed with HA powders in a ratio of 35:65 (w/w, collagen:HA) at 4°C, the mixture was added into olive oil while stirring at 400 rpm at 37°C for 2 h to allow the reconstitution of collagen. Glutaraldehyde was then added to the emulsion at a ﬁnal concentration of 2.5% in the aqueous droplets, and the mixture was incubated for 1 h. After centrifugation, collagen/HA microspheres were collected from the lower portion of the tube and washed repeatedly with 0.1m PBS. Microspheres in suspended form can be delivered to the targeted and hard-to-reach areas with ease,e.g. by syringe injection for applications as cell or tissue carriers, bone grafting and drug delivery and there is no need of surgery in this case , They can be directly injected into the bone defect
Freeze drying process(lyophilization) Firstly a stable nHA suspension was produced and added to a collagen slurry (suspension method), and secondly, porous collagen scaffolds were immersed in nHA suspension after freeze-drying (immersion method). Significantly stronger constructs were produced using both methods compared to collagen only scaffolds, with a high porosity maintained (>98.9%). It was found that Coll-nHA composite scaffolds produced by the suspension method were up to 18 times stiffer than the collagen control . The suspension method was also more reproducible, and the quantity of nHA incorporated could be varied with greater ease than with the immersion technique. In addition, Coll-nHA composites display excellent biological activity, demonstrating their potential as bone graft substitutes in orthopaedic regenerative medicine.
Effect of pore size Pore size is an essential consideration in the development of scaffolds for tissue- engineering If pores are too small cell migration is limited, resulting in the formation of a cellular capsule around the edges of the scaffold. This in turn can limit diffusion of nutrients and removal of waste resulting in necrotic regions within the construct. Conversely if pores are too large there is a decrease in surface area limiting cell adhesion. Also, large pore size may compromise the mechanical properties of the scaffolds by increasing void volume Pores greater than ~300 µm lead to direct osteogenesis while pores smaller than ~300 µm can encourage osteochondral ossification
Effect of scaffold pore size Previous studies in bone tissue-engineering have indicated a range of mean pore sizes (96–150 µm) to facilitate optimal attachment. Other studies have shown a need for large pores (300–800 µm) for successful bone growth in scaffolds. These conflicting results indicate that a balance must be established between obtaining optimal cell attachment and facilitating bone growth. Cell adhesion decreased with increasing pore size and that the highest levels of cell attachment were found on the scaffolds with the smallest pore size (96 µm) Initial studies demonstrated that the minimum pore size for significant bone growth is 75–100 µm with an optimal range of 100– 135 µm.Since this early work it has been reported that pores greater than ∼300 µm are essential for vascularisation of constructs and bone growth, while pores smaller than ∼300 µm can encourage osteochondral ossification.
Col/HA Products in marketProduct/ Company Name HydroxyColl www.enterprise-ireland.com/en/Events/.../Poster-HydroxyColl.pdf Ossfill SEWON CELLONTECH CO., LTD. http://www.gobizkorea.com/blog/ProductView.do?blogId=cellontech&i d=982532 SyboGraf™- C Eucare Pharmaceuticals Private Limited http://www.eucareindia.com/product.html Collapat® II http://www.biomet.fi/ammattilaiset/biomateriaalit/luunkorvikkeet/collap at MCH-Cal™ : <850 micron, < 250 micron and < 150 micron Waitaki biosciences http://www.waitakibio.com/manufacturer/natural-calcium
Other Competitive Three dimensionalporous biomaterials Collagen / Hydroxyapatite/ Tricalcium phosphate Cross.Bone® Matrix is made of hydroxyapatite (HAP), β- tricalcium phosphate (β-TCP) and collagen. The biphasic and synthetic bone substitute has an optimized micro and macro- porosity. http://www.implants.fr/en/pageLibre0001164f.asp Nano-carbonated Hydroxyapatite/Collagen/PLGA (Poly glycolic acid)or poly(lactic)-co-glycolic acid HAC-PLA scaffolds nano-Hydroxyapatite/ Collagen/Calcium alginate Collagen /Calcium alginate Fibracol http://skin-wound- care.medical-supplies-equipment-company.com/product/fibracol- plus-collagen-wound-dressing-with-alginate_5049.html
Other competitive compositesavailable in market
References Karageorgiou V. Kaplan D. Porosity of 3D biomaterial scaffolds and osteogenesis.Biomaterials 2005;26:5474-91. DA Wahl et al. Collagen-Hydroxyapatite Composites for Hard Tissue Repair.European cells and materials Vol. 11. 2006 (43-56) Murphy CM, Haugh MG, OBrien FJ. The effect of mean pore size on cell attachment, proliferation and migration in collagenglycosaminoglycan scaffolds for tissue engineering. Biomaterials. 2010;31(3):461-6. Kuboki Y, Jin QTakita H. Geometry of carriers controlling phenotypic expression in BMP-induced osteogenesis and chondrogenesis. J Bone Joint Surg Am2001;83-A Suppl 1:S105-15. Cunniffe GM, Dickson GR, Partap S, Stanton KT, OBrien, FJ. Development and characterisation a collagen nano-hydroxyapatite composite scaffold for bone tissue engineering. Journal of Materials Science: Materials in Medicine. 2010;21(8):2293-8. Hsu F-Y, Chueh S-C, Wang JY (1999) Microspheresof hydroxyapatite/reconstituted collagen as supports for osteoblast cell growth. Biomaterials 20: 1931-1936 Ciara M Murphy1 and Fergal J OBrien1,2†Understanding the effect of mean pore size on cell activity in collagen-glycosaminoglycan scaffolds. Cell Adh Migr. 2010 Jul-Sep; 4(3): 377–381 Wu et al, Studies on the microspheres comprised of reconstituted collagen and hydroxyapatite. Biomaterials 25 (2004) 651–658 J.-S. SUN ET AL ,Collagen-Hydroxyapatite/Tricalcium Phosphate Microspheres as a Delivery System for Recombinant Human Transforming Growth Factor-b 1,International Society for Artificial Organs, 2003,27(7):605–612
Conclusion Collagen along with Hydroxyapatite is the best choice for artificial bone , or as a filler in bone defects, due to its quick adaptation in the body. For preparation of the scaffold many methods are available , among them the best is the freeze drying process in which the nHA is combined with collagen and then freeze dried. The pore size of this product should be decided on the basis of the exact use of the product for eg:if Osteogenesis is the aim , we should use 300-800 micron pore size. And , if the choice is only cell attachment and osteochondal ossification we should use less than 300micron pore size . Also, from the market study , we found that there are handfull of products containing the combination of Collagen and hydroxyapatite.
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