Synthetic bone substitutes

A few million patients every year need a bone graft or bone graft substitute to repair a bone defect resulting from an injury or a disease. A large number of bone graft substitutes can be used unprocessed or processed allogenic bone, animal-derived bone substitutes and synthetic bone substitutes, mostly ceramics. ... 

Hydroxyapatite (HAp) [Caj (PO )g(OH2)] is the main inorganic mineral constituent close to human bone chemistry, and is also an outstanding synthetic bone substitute because of its osteoconductive properties. HAp ceramics can be manufactured synthetically from its constituents via a range of production methods. In addition, they have been manufactured by demineralizing bovine or human hard tissues. 

Roeder RK, Converse GL, Kane RJ et al (2008) Hydroxyapatite-reinforced polymer biocomposites for synthetic bone substitutes. Biol Mater Sci 3 38 5... 

Schwartz, C., Liss, R, Jacquemaire, B., Lecestre, R, and Frayssinet, R 1999. Biphasic synthetic bone substitute use in orthopaedic and trauma surgery Clinical, radiological and histological results. Journal of Materials Science Materials in Medicine 10 821-25. 

Natural bone is made of 60% of inorganic calcium phosphate minerals. " To this end, many researchers have developed synthetic bone substitutes based upon ceramics to better mimic the natural composition of bone. Ceramics have been widely used for orthopedic and dental applications, and have been used... 

The lack of effective treatments for the identified clinical needs motivates the current trend in the development of synthetic graft substitutes. Numerous synthetic bone substitutes (SBSs) are commercially available and are presented in block or particulate form, with relatively few nonsetting BGSs being injected to a defect and shaped in situ (Bhandari, 2012). A BGSs should be osteoinductive (promote the differentiation of primitive, undifferentiated, and pluripotent cells to an... 

Although Plaster of Paris was used inl892asabone substitute [Peltier, 1961], the concept of using synthetic resorbable ceramics as bone substitutes was introduced in 1969 [Hentrich et al., 1969 Graves et al., 1972]. Resorbable ceramics, as the name implies, degrade upon implantation in the host. The resorbed material is replaced by endogenous tissues. The rate of degradation varies from material to material. Almost all bioresorbable ceramics except Biocoral and Plaster of Paris (calcium sulfate dihydrate) are variations of calcium phosphate (Table 39.8). Examples of resorbable ceramics are aluminum calcium phosphate, coralline. Plaster of Paris, hydroxyapatite, and tricalcium phosphate (Table 39.8). 

It is important to emphasize that many natural tissues are essentially composed of nanoscale biopolymers or biocomposites with hierarchical architectures. Therefore, by mimicking the structure and property of their natural counterparts, synthetic nanopoiymers and nanocomposites are very likely to enhance/regulate the functions of specific cells or tissues. This principle has been demonstrated by the success of bioinspired polymers and composites in both clinical practice and in laboratory research. In particular, bone is the hierarchical tissue that has inspired a myriad of biomimetic materials, devices, and systems for decades. This chapter focuses on this well-developed area of biomimetic or bioinspired nanopoiymers and nanocomposites for bone substitution and regeneration, especially those with high potentials for clinical applications in the near future. 

Zimmermann, G., Moghaddam, A., 2011. Allograft bone matrix versus synthetic bone graft substitutes. Injury 42 (Suppl. 2), S16-S21. 

Calcium phosphates, particularly apatite, figure prominently in products which cau be categorised in (2), (3) or (4). Bone substitutes for dental or paediatric use can be made from tricalcium phosphate, hydroxyapatite or other P205-containing compounds. In some cases, strengths can be made to exceed that of bone although the synthetic products are usually more brittle thau the latter [17-25]. Both dense and porous products find uses as well as coatings which are plasma-sprayed or sputtered on to metallic implants. 

Bostrom MP, Seigerman DA (2005) The clinieal use of allografts, demineralized bone matrices, synthetic bone graft substitutes and osteoinductive growth factors a survey study. HSS J 1(1) 9-18... 

Based on observed tissue response, synthetic bone-graft substitutes can be classified into inert (e.g., alumina, zirconia), bioactive (e.g., hydroxyapatite, bioactive glass), and resorbable substitutes (e.g., tricalcium phosphate, calcium sulfate). Of these, resorbable bone-graft substitutes are preferred for bone defect filling because they can be replaced by new natural bone after implantation, p-tricalcium phosphate (Ca3(PO )2, p-TCP) is one of the most widely used bone substitute material, due to its faster dissolution characteristics. Preparation of magnesium-substituted tricalcium phosphate ((Ca, Mg)3(PO )2, p-TCMP) has been reported by precipitation or hydrolysis method in solution. These results indicate that the presence of Mg stabilizes the p-TCP structure (LeGeros et al., 2004). The incorporation of Mg also increases the transition temperature from p-TCP to a-TCP and decreases the solubility of p-TCP (Elliott, 1994 Ando, 1958). 

William R. Moore, Stephen E. Graves, and Gregory 1. Bain. Synthetic bone graft substitutes. ANZ J. Surg. 2001 71 354-361. 

Recently, in the work of Landi et al. [40], synthetic HAp doped with Mg was prepared by a wet-chemical synthesis. The best results were obtained for 5.7 mol% Mg-doped HAp - it was biocompatible since it showed no genotoxicity, carcinogenicity or cytotoxicity. Moreover, the authors found that HAp-Mg granulate was comparable to, or even better than, traditional HAp as a bone substitute when tested in vivo in particular, HAp-Mg showed greater osteoconductivity over time and a higher material resorption than stoichiometric HAp (stHAp). 

Yamasaki, N., Hirao, M., Nanno, K., Sugiyasu, K., Tamai, N., Hashimoto, N., Yoshikawa, H., and Myoui, A. 2009. A comparative assessment of synthetic ceramic bone substitutes with different composition and microstructure in rabbit femoral condyle model. Journal of Biomedical Materials Research Part B Applied Biomaterials 91 788-98. 

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