Interface bone-material

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... 

The presence of a fibrous layer surrounding the PLA coupons is characteristic of a mild foreign body response. That such a fibrous layer was not formed at the bone/material interface for poly(DTE carbonate) and poly(DTH carbonate) is an important characteristic of these polymers. Intimate contact between bone and implant, even at 48 weeks post-implantation, is a strong indicator of the biocompatibility of the tyrosine-derived polycarbonates. 

In order to design better implant materials, it is important to understand the events at the bone-material interface. Figure 16.2 below describes the series of events that take place after the insertion of an implant. As mentioned earlier, one of the... 

As discussed in Section 10.2, bioinert materials do not release any toxic constituents, but neither do they show any positive interaction with living tissue. As a response of the body to these materials, a nonadherent capsule of connective tissue is usually formed around the bioinert material that, in the case of bone remodeling, manifests itself by a shape-mediated contact osteogenesis. Hence, only compressive forces will be transmitted through the bone-material interface ( bony on-growth ). 

We observed that all the devices were separated from neighbouring bone by a fibrous capsule with an average thickness of 292 pm. This is probably due to the material itself, since the fibrous capsule was obvious both in actuators and static devices, with no statistical significant differeiKes in capsule thickness between the two groups (289.59 131.20 pm in actuated films vs 293.93 84.79 pm). It would be mandatory to develop and test a material with improved biocompatibility to evaluate accurately the bone material interface. 

Interface within material within material within bone within material not specified within material... 

Neo, M., Kotani, S., Yamamuro, T., Ohtsuki, C., Kokubo, T. and Bando, Y. (1992) A comparative study of ultrastructures of the interfaces between four kinds of surface-active ceramic and bone. Journal of Biomedical Materials Research, 26, 1419-1432. 

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). 

Garcia, R., and Doremus, R. H., Electron microscopy of the bone-hydroxyapatite interface from a human dental implant. /. Mat. Sci. Materials in Medicine 3,154-156 (1992). 

Based on the clinical reports, 10-45% of patients who received the surgical implant with the bone cement need revision surgery mainly due to the cement fracture [36,37]. It is commonly accepted that the fatigue is the major mechanism for the fracture of bone cement [37,38]. The weak resistance of bone cement to the fatigue loading has been addressed to the low molecular weight of matrix, weak interfaces between filler materials and matrix, agglomeration of X-ray-opaque powder, bubbles, and so forth [38-40]. 

Since the X-ray-opaque filler (e.g., Zr02) is one of the basic components of bone cement, the physical properties of bone cement should be treated as a composite material of polymethyl methacrylate (PMMA) and fillers. The physical properties of composite materials depend on the matrices, fillers, and interfaces between them. The most desirable situation may be the combination of good properties of each component material. For this purpose, the role of interface is very important for an efficient stress transfer from the matrix to the fillers [41,42]. 

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