Biomaterial resorbable biomaterials

Sittinger, M., Bujia, J., Rotter, N., Reitzel, D., Minuth, W. W., and Burmester, G. R. (1996). Tissue engineering and autologous transplant formation Practical approaches with resorbable biomaterials and new cell culture techniques. Biomaterials 17, 237-242. 

Considerable development has occurred on sintered ceramics as bone substitutes. Sintered ceramics, such as alumina-based ones, are uru eactive materials as compared to CBPCs. CBPCs, because they are chemically synthesized, should perform much better as biomaterials. Sintered ceramics are fabricated by heat treatment, which makes it difficult to manipulate their microstructure, size, and shape as compared to CBPCs. Sintered ceramics may be implanted in place but cannot be used as an adhesive that will set in situ and form a joint, or as a material to fill cavities of complicated shapes. CBPCs, on the other hand, are formed out of a paste by chemical reaction and thus have distinct advantages, such as easy delivery of the CBPC paste that fills cavities. Because CBPCs expand during hardening, albeit slightly, they take the shape of those cavities. Furthermore, some CBPCs may be resorbed by the body, due to their high solubility in the biological environment, which can be useful in some applications. CBPCs are more easily manufactured and have a relatively low cost compared to sintered ceramics such as alumina and zirconia. Of the dental cements reviewed in Chapter 2 and Ref. [1], plaster of paris and zinc phosphate... 

Resulting poly(a-hydroxyacids) are important biomaterials used as resorbable sutures and prostheses [196]. The mechanism of polymerization is not well established. Polymerization may be initiated with Lewis acids (SbF3, ZnCl2, SnCl4) however, other typical cationic initiators (e.g, triethyloxonium or triphenylcarbenium salts) fail to initiate polymerization [197]. Thus, it is not clear whether polymerization proceeds by typical cationic mechanism or rather involves the coordination mechanism. The chain transfer to polymer resulting in transesterification was postulated [198,199] and confirmed later by detailed, 3C NMR studies of lactide copolymers [200]. 

Cook, A.D. Hrkach, J.S. Gao, N.N. Johnson, I.M. Pajvani, U.B. Cannizzaro, S.M. Danger, R. Characterization and development of RGD-peptide-modified poly (lactic acid-co-lysine) as an interactive resorbable biomaterial. J. Biomed. Mater. Res. 1997, 35, 513-523. 

Regrettably, no biomaterial is known to date that is both mechanically stable and sufficiently osseoinductive classic bioceramics such as alumina or stabilised zirconia are strong but bioinert, osseoconductive hydroxyapatite is mechanically weak and essentially non-resorbable, whereas the even weaker osseoconductive tricalcium phosphate is resorbable (Figure 3.9). 

Bohner, M. (2010) Resorbable biomaterials as bone graft substitutes. Mater. Today, 13 (1/2), 24-30. 

The solubility of apatites is becoming more important as emphasis is being placed on biomaterials for regeneration of tissues (Hench 1998b). Where apatites are incorporated with resorbable polymers for tissue engineering applications, it will become necessary to match the solubility rate of the inorganic and organic components within the composite. 

Campoccia D, Doherty P, Radice M, Brun P, Giovanni A, Williams DF. Semisynthetic resorbable materials from hyaluronan esterification. Biomaterials 1998 19 2101-2127. 

Polymers are the most versatile class of biomaterials, being extensively used in biomedical applications such as contact lenses, pharmaceutical vehicles, implantation, artificial organs, tissue engineering, medical devices, prostheses, and dental materials [1-3]. This is all due to the unique properties of polymers that created an entirely new concept when originally proposed as biomaterials. For the first time, a material performing a structural application was designed to be completely resorbed and become weaker over time. This concept was applied for the... 

Depending on the calcium/ phosphorus (Ca/P) molar ratio and solubility of the compound, it is possible to obtain numerous calcium phosphates of different composition. Molar Ca/P ratio and solubility are connected with the pH of the solution. Majority of materials of this class are resorbable and dissolve when inserted in a physical environment. Calcimn phosphates that are most frequently used in the biomaterial field are demonstrated in Table 1 (Dorozhkin, 2009c El Kady, 2009 Shi, 2006). 

The CBBCs including Ca-aluminate based biomaterials can be produced at low temperatures in-situ, in vivo. The chemistry of these systems is similar to that of hard tissue in living organisms. The CBBCs easily form nanostructures with crystal sizes similar to those found in hard tissue. Both stable and resorbable CBBCs can be produced. The stable phases are found within the Ca0-Al203-H2O and Ca0-Si02-H20 systems, while resoibable phases are seen within the Ca0-P205-H20 system and within sulphate systems. 

The CBBCs can be divided into two main groups resoibable and stable biomaterials. Ca-aluminate based biomaterials and to some extent Ca-sihcates are stable materials after hydration, and can favorably be used for load-bearing applications. The Ca-phosphates, Ca-sulphates and Ca-carbonates are known to be resorbable or slowly resorbable when inserted in the body, and their main applications are within bone void filUng with low mechanical stress upon the biomaterial. The resorbable materials are after various time depending on the specific chemical composition replaced by new bone tissue. This can start immediately after injection and the material can be completely dissolved after months and in some cases after a few years. 

Relatively inert ceramics elicit minimal tissue response and lead to a thin layer of fibrous tissue immediately adjacent to the surface. Surface-active ceramics are partially soluble, resulting in ion-exchange and the potential to lead to a direct chemical bond with bone. Bulk bioactive ceramics are fiilly resorbable, have much greater solubility fiian surface-active ceramics, and may ultimately be replaced by an equivalent volume of regenerated tissue. The relative level of bioactivity mediates the thickness of Ae interfacial zone between the biomaterial surface and host tissue (Fig. 13.1). There are, however, no standardized measures of reactivity, but the most common are pH changes, ion solubility, tissue reaction, and any number of assays that assess some parameter of cell function. 

The question whether silk fibroin filaments are resorbable or permanent is open to interpretation. Having a polypeptide chemical structure, silk fibroin, like any other protein, is susceptible to proteolytic degradation, and will become weaker and eventually over a period of 2 years will be totally resorbed in vzvo. However, given the definition for an absorbable suture in the United States Pharmacopeia as a material that loses most of its tensile strength within 60 days post-implantation silk can therefore be classified as a permanent biomaterial. 

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