Implant/bone interface

Composites provide an atPactive alternative to the various metal-, polymer- and ceramic-based biomaterials, which all have some mismatch with natural bone properties. A comparison of modulus and fracture toughness values for natural bone provide a basis for the approximate mechanical compatibility required for arUficial bone in an exact structural replacement, or to stabilize a bone-implant interface. A precise matching requires a comparison of all the elastic stiffness coefficients (see the generalized Hooke s Law in Section 5.4.3.1). From Table 5.15 it can be seen that a possible approach to the development of a mechanically compatible artificial bone material... 

Biomaterial scientists and engineers are currently investigating novel formulations and modifications of existing materials that elicit specific, timely, and desirable responses from surrounding cells and tissues to support the osseointegration of the next generation of orthopedic and dental biomaterials (Ratner, 1992). Enhanced deposition of mineralized matrix at the bone-implant interface provides crucial mechanical stability to implants. Proactive orthopedic and dental biomaterials could consist of novel formulations that selectively enhance osteoblast function (such as adhesion, proliferation and formation of calcium-containing mineral) while, at the same time, minimize other cell (such as fibroblast) functions that may decrease implant efficacy (e.g., fibroblast participation in callus formation and fibrous encapsulation of implants in vivo). 

Dee, K. G, Andersen, T. T., Rueger, D. G, and Bizios, R., Conditions which promote mineralization at the bone/implant interface a model in vitro study. Biomaterials 17, 209-215... 

Promotes bone ingrowth Does not induce soft tissue growth at bone/implant interface... 

Lemons, J.E. (1994) in Bone Implant Interface (ed. H.U. Cameron), Mosby, St. Louis,... 

Osteonecrosis producing in some cases sclerosis of the bone/implant interface, the so-called metallosis, has also been observed. 

Puleo DA, Nanci A (1999) Understanding and controlling the bone-implant interface. Biomaterials 20(23-24) 2311-2321... 

Hench, L.L. 1994. Bioactive glasses, ceramics and composites. In Bone Implant Interface, R. Hurley (Ed.), pp. 181-190, Mosby, St. Louis, MO. 

In vitro experiments designed to study the ultrastructural details of bone-implant interfaces made from cpTi and Ti alloy may provide additional clues as to the histologic and ultrastructural differences which have been observed with these materials. Since cHnical implants made from both materials appear to be successful [Branemark, 1983 De Porter et al., 1986], it is possible that because of the difference in mechanical properties between unalloyed and Ti alloy material, the longer-term tissue interface results from differences in bone remodeling due to the local biomechanical environment surrounding these materials [Brunski, 1992]. This hypothesis requires continued investigation for more definitive... 

Walpole A, Briggs E, Karlsson M, Palsgard E, Wilshaw P. Nano-porous alumina coatings for improved bone implant interfaces. Mater Werkst 2003 34 1064-8. 

Figure 3.2 Computerized histomorphometric approach to evaluation of the bone-implant interface. The bone-to-implant contact percentage is the linear contact area between bone and implant in the inside zone percent bone ingrowth is the ratio of bone inside to that outside in the mirror zone.

Besides having an inert material for fibroblastic cells observed at the bone-cement interface, PMMA is still the current standard for cement-held prostheses. Vallo and his group measured the flexural, compressive, and fracture properties of PMMA bone cements that incorporated various amounts of HAp. They found that addition of up to 15 wt% HAp increases the flexural modulus and fracture toughness [89]. It was also observed that, with increasing HAp incorporation into PMMA, the biological responses of the bone cement increased and thus increased osteoblast adhesion and response [88]. Kwon and coworkers reported that a PMMA/HAp composite with 30 wt% of HAp increased the interfacial shear strength at the bone-implant interface 6 weeks after implantation in rabbits [101]. Several other research studies revealed that, depending on the type of bone cement, the addition of HAp can improve the mechanical properties of bone cements [102]. 

The bone tissue response w as characterized by active bone remodeling at the surface of the degrading implant, the lack of fibrous capsule formation, and an unusually low number of inflammatory cells at the bone-implant interface. Poly (DTH carbonate) exhibited very close bone apposition throughout the 26 week... 

Ballarre, J., Manjubala, I., Schreiner, W., Orellano, J., Fratzl, P., Cere, S., 2010. Improving the osteointegration and bone-implant interface by incorporation of bioactive particles in sol-gel coatings of stainless steel implants. Acta Biomater. 6,1601—1609. http //dx.doi.org/ 10.1016/j.actbio.2009.10.015. 

Urban RM, et al. The bone-implant interface of femoral stems with non-circumferential porous coating — a study of specimens retrieved at autopsy. J Bone Jt Surg Am 1996 78(7) 1068-81. 

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