ABSTRACT
Abbreviations ......................................................................................................... 139 7.1 Introduction .................................................................................................. 140 7.2 General Information on Composites and Biocomposites ............................. 143 7.3 Major Constituents ........................................................................................ 145
7.3.1 Calcium Orthophosphates ................................................................ 145 7.3.2 Polymers ........................................................................................... 146
7.4 Biocomposites and Hybrid Biomaterials Based on Calcium Orthophosphates ...150 7.4.1 Biocomposites with Polymers ........................................................... 150
7.4.1.1 Apatite-Based Formulations .............................................. 154 7.4.1.2 TCP-Based Formulations ................................................... 159 7.4.1.3 Formulations Based on Other Calcium Orthophosphates ... 160
7.4.2 Injectable Bone Substitutes ............................................................... 161 7.5 Bioactivity and Biodegradation of Calcium Orthophosphate-Based
Formulations ................................................................................................. 162 7.6 Conclusion .................................................................................................... 165 References .............................................................................................................. 166
PCL Poly(ε-caprolactone) PDLLA Poly(D,L-lactic acid) PE Polyethylene PEEK Polyetheretherketone PEG Polyethylene glycol PGA Polyglycolic acid PHB Polyhydroxybutyrate PHBHV Poly(hydroxybutyrate-co-hydroxyvalerate) PLA Polylactic acid PLGA Poly(lactic-co-glycolic) acid PLLA Poly(L-lactic acid) PMMA Polymethylmethacrylate PP Polypropylene PPF Poly(propylene-co-fumarate) PS Polysulfone PTFE Polytetrauoroethylene PVA Polyvinyl alcohol SEVA-C Blend of EVOH with starch UHMWPE Ultrahigh molecular weight polyethylene
The fracture of bones due to various traumas or natural aging is a typical type of tissue failure. An operative treatment frequently requires implantation of a temporary or a permanent prosthesis, which still is a challenge for orthopedic surgeons, especially in the cases of large bone defects. Fast aging of the population and serious drawbacks of natural bone grafts make the situation even worse; therefore, there is a high clinical demand for bone substitutes. Unfortunately, a medical application of xenografts (e.g., bovine bone) is generally associated with potential viral infections. In addition, xenografts have a low osteogenicity and an increased immunogenicity, and they usually resorb more rapidly than autogenous bone. Similar limitations are also valid for human allografts (i.e., tissue transplantation between individuals of the same species but of nonidentical genetic composition), where the concerns about potential risks of transmitting tumor cells, a variety of bacterial and viral infections, as well as immunological and blood group incompatibility are even stronger [1,2]. Moreover, harvesting and conserving allografts (exogenous bones) are additional limiting factors. Autografts (endogenous bones) are still the golden standard among any substitution materials because they are osteogenic, osteoinductive, osteoconductive, completely biocompatible, nontoxic, and do not cause any immunological problems (nonallergic). They contain viable osteogenic cells and bone matrix proteins as well as support bone growth. Usually, autografts are well accepted by the body and are rapidly integrated into the surrounding bone tissues. Due to these reasons, they are used routinely for a long period with good clinical results [2-4]; however, it is fair to say on complication cases, those frequently happened in the past [5]. Unfortunately, a limited number of donor sites restrict the quantity of autografts harvested from the iliac crest or other locations of the patient’s own body. In addition,
their medical application is always associated with additional traumas and scars resulting from the extraction of a donor tissue during a superuous surgical operation, which requires further healing at the donation site and can involve long-term postoperative pain. Thus, any types of biologically derived transplants appear to be imperfect solutions, mainly due to a restricted quantity of donor tissues, donor-site morbidity, as well as potential risks of an immunological incompatibility and disease transfer [6-8]. In this light, man-made materials (alloplastic or synthetic bone grafts) stand out as a reasonable option because they are easily available and might be processed and modied to suit the specic needs of a given application. What is more is that there are no concerns about potential infections, immunological incompatibility, sterility, and donor-site morbidity. Therefore, investigations on articial materials for bone tissue repair appear to be one of the key subjects in the eld of biomaterials research for clinical applications [9,10].
