“The ideal bone graft would replace bone defects, such as those from disease or trauma, with a material that allows bone cells to grow into the affected area, thus restoring the bone to its original condition. Currently, autografts are the best material for bone repair because they are biocompatible and there is little risk of disease transfer. However, the downside of autografts is that a separate operation must be performed to remove the person's own bone. Allografts, which consist of bone from another person/cadaver, are also available but carry the risk of immune response and disease transfer that could lead to ultimate failure.
In order to solve the problems associated with bone grafts, many researchers have tried to develop artificial substances for bone grafts. These artificial biomaterials need to possess several qualities in order to be successful. First, the material must be degradable to allow room for new bone to grow into the implant site. Second, it must maintain mechanical strength similar to native bone. Finally, the artificial biomaterial needs to be osteoconductive; that is, it must allow bone cells to attach and propagate on its surface.
Some of the materials that have shown promise as bone grafts include calcium phosphate ceramics such as hydroxyapatite and tricalcium phosphate. These particular ceramics are quite biocompatible because they have characteristics similar to native bone mineral. However, they are hard to shape and do not possess the same mechanical properties as bone. Hydroxyapatite in particular does not degrade quickly either, which inhibits new bone from forming.
Another type of material that has sparked some interest is degradable polymer. It is easy to shape and it degrades at a predictable rate, thereby allowing new bone growth to replace it. Some examples of degradable polymers are poly(glycolic acid), poly(L-lactic acid), and poly(D,L-lactic-co-glycolic acid). Although they are easily formed and have good mechanical strength, degradable polymers alone are not ideal for bone grafts because they are not very osteoconductive. New bone will not attach well or grow well into this material.
It is possible to make a composite using a phosphate ceramic in conjunction with a degradable polymer. Small particles of ceramic can be included within the polymer scaffold material. These particles will be partially exposed on the surface of the biomaterial, thereby making the material more osteoconductive.
Most related methods for making a polymer/ceramic scaffold biomaterial use organic solvents. This can be highly disadvantageous because some residual solvent may remain in the material. Almost all organic solvents are detrimental to cell and tissue growth. Also, it has been noted that these processes may actually leave behind a thin film of polymer that coats the ceramic particles that are supposed to be exposed on the surface. This unintentional thin film disrupts the osteoconductive nature of the ceramic portion of these biomaterials.”
[Kim, US Patent 8,178,013 (5/15/2012)]
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Roger D. Corneliussen
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Copyright 2012 by Roger D. Corneliussen.
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* Date of latest addition; date of first entry is 5/24/2012.