Tissue-implant interface materials

Adsorption of proteins from solution onto synthetic materials is a key factor in the response of a living body to artificial implanted materials and devices. Adsorbed proteins mediate cell attachment and spreading through specific peptide sequence-integrin receptor interactions and may therefore favorably influence the mechanical stability of the subsequently developed tissue—implant interface. However, the uncontrolled nonspecific adsorption of proteins from the extracellular matrix results in interfaces with many types of proteins in different conformations—a situation that is believed to cause deleterious reactions of the body, such as foreign-body response and fibrous encapsulation. ... 

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). 

The foreign body reaction occurring around soft tissue implants and thrombosis on surfaces in contact with blood are the major reactions encountered with implants. Both reactions involve the interaction of cells with the implant, especially in the later stages, and much previous study has therefore emphasized cellular events in the biocompatibility process. However, cells encounter foreign polymer implants under conditions that ensure the prior adsorption of a layer of protein to the polymer interface. The properties of the adsorbed layer are therefore important in mediating cellular response to the material. 

The aim of this paper is to present the use of a microwave digestor to prepare nanopowders via hydrothermal route. In the field of biomaterials the researchers (due to some problems with the traditional materials) are looking for the design of biomaterials with surface properties similar to physiological bone (grain sizes in the nanometric range [5]). This would aid in the formation of new bone at the tissue/biomaterial interface and therefore improve implant efficacy. With the advent of nanostructured materials (materials with grains sizes less than 100 nm in at least... 

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... 

It is clear that future efforts to improve the host tissue responses to implant materials will focus, in large part, on controfling cell and tissue responses at implant interfaces. This goal will require continued acquisition of fundamental knowledge of cell behavior and cell response to specific materials characteristics. It is likely that a better understanding of the cellular-derived extracellular matrix-implant interface wiU offer a mechanism by which biologic response modifiers such as growth and attachment factors or hormones may be incorporated. Advancements of this type will likely shift the focus of future research from implant surfaces which as osseoconductive (permissive) to those which are osseoinductive (bioactive). 

While much recent work has been described to develop polyacetals for drug delivery applications, and historically they have been used as implant materials, more recently, they have been examined as potential scaffold materials in tissue engineering. Implants of Delrin (polyoxymethylene) to repair heart valves were examined, but there was too much swelling in vivo [127]. However, this polyacetal has been used as an orthopedic implant [128] and as an orthopedic implant-coating material [129,130] to interface with bone tissue as this polyacetal has a similar modulus to bone. Ultrasound is used in the diagnosis of osteoporosis and porous polyacetal blocks were found useful to gain insights into bone porosity and ultrasonic properties [131]. 

Basically, all of the events occurring at the tissue-miaterial interface can be categorized as biological responses toward the implant material (host tissue responses) and, conversely, material responses to the host tissue [62], These two categories can be further viewed from the host tissue and the biomaterial perspectives as illustrated in Figures 1.12 and 1.13, respectively. 

A bioactive material is one that elicits a specific biological response at the interface of the material which results in the formation of a bond between the tissues and the material. A common characteristic of bioactive glasses, bioactive glass-ceramics, and bioactive ceramics is that their surface develops a biologically active hydroxy carbonate apatite (HCA) layer which bonds with collagen fibrils. The HCA phase that forms on bioactive implants is equivalent chemically and structurally to the mineral phase of bone. It is that equivalence which is responsible for interfacial bonding ". ... 

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