ABSTRACT
Currently, there is a high demand to develop new materials that can be used to repair or replace damaged tissue owing to injuries, diseases, and/or genetic malformations. The term ‘‘biocomposite’’ means a material that consists of two or more distinct constituents to obtain complex physicochemical, mechanical, and biological properties, which are required by biomedical applications and cannot be satisfied by any individual components. Owing to the widespread use of biocomposites in regenerating bone, orthopedic applications will be emphasized here. In the U.S.A. in 1995, there were 216,000 total knee replacements, 134,000 total hip replacements, and close to 100,000 bone grafting procedures. In all, musculoskeletal conditions cost the U.S.A. $214.9 billion in 1995.[1] Traditionally, autografts, allografts, xenografts, and metal implants have been used to repair bone fractures and other skeletal defects. However, these substitutes are far from ideal as each has its own problems and limitations. For example, autografts are associated with donor shortage and donor site morbidity, whereas allografts and xenografts have the risk of disease transmission and detrimental immune responses. Most common metal implants are made of stainless steel, cobalt-chromium alloys, and titanium-based alloys. Major problems of those metals for implant applications are their mismatched mechanical properties compared to host tissue, which causes necrosis of the surrounding tissue and subsequent implant loosening owing to the well-documented ‘‘stress shielding’’ effect.[2] It has also been well documented that metals do not possess surface properties that allow for sufficient quick new bone growth.[2] Collectively, the above-mentioned problems (as well as others) with orthopedic implants have led to an average 10-15 yr current functional implant lifetime before clinical failure necessitates a replacement. To overcome such limitations of these traditional materials, over the past
25 yr, researchers have been interested in developing biocomposites that provide for a wide diversity of properties necessary for successful orthopedic implants.[1-15] This desire comes from considering that living tissues are composites themselves with a number of levels of hierarchy. In almost all biological systems, a range of tissue properties (such as physicochemical, mechanical, biological, etc.) is present. All properties are of great importance and are key to the success of a tissue. Because of this, often a clinical need can only be fulfilled by a material that exhibits a similar complex combination of properties. The development of biocomposites offers great promise to improve the efficacy of current tissue substitutes that are too frequently single-phase materials that lack such property diversification.
