Polymer replacement implants

If a nearly inert material is implanted into the body it initiates a protective response that leads to encapsulation by a nonadherent fibrous coating about 1 i.m thick. Over time this leads to complete isolation of the implant. A similar response occurs when metals and polymers are implanted. In the case of bioactive ceramics a bond forms across the implant-tissue interface that mimics the bodies natural repair process. Bioactive ceramics such as HA can be used in bulk form or as part of a composite or as a coating. Resorbable bioceramics, such as tricalcium phosphate (TCP), actually dissolve in the body and are replaced by the surrounding tissue. It is an important requirement, of course, that the... 

Abstract Wear processes are discussed for polymers used in a wide variety of implants in the human body, such as in joint replacement implants for the hip and knee. The articulation of metal or ceramic components against a polymer component can lead to the generation of wear debris and the effect this debris may have in the body is examined. 

Wear is defined as the loss of material from a surface as the result of relative motion. In this chapter, the wear processes in polymer implants are discussed. Polymers are used in a wide variety of implants in the human body such as joint replacement implants, pacemakers, catheters and heart valves. Wear of polymer implants is almost exclusive to joint replacement implants, such as those used to replace the hip or knee. These implants involve the articulation of a metal or ceramic against a polymer. Typically these implants operate with a mixed or boundary lubrication regime and, therefore, there is contact between the bearing surfaces that can lead to the generation of wear debris. The chapter is divided into sections that cover implants, wear processes, polymers used in implants, the effect of wear debris on the body and, finally, likely future trends. 

Joint replacement implants have traditionally involved a metal against polymer or ceramic against polymer articulation, but these materials have a much... 

There are a variety of polymers used in joint replacement implants that can be subject to wear. In this section UHMWPE, crosslinked polyethylene, poly(ether ether ketone) (PEEK), silicone and polyurethan are discussed. Some of the mechanical properties for these polymers are shown in Table 7.1. 

Table 7.1 Typical mechanical properties of polymers used for joint replacement implants...

A very effective method of analysing the wear of polymer parts in joint replacement implants is to make measurements on implants retrieved from patients. This typically happens where revision surgery is performed and... 

Biodegradable starch-based polymers have recently been proposed as having great potential for several applications in the biomedical field, such as bone replacement implants, bone cements, drug delivery systems, and tissue engineering scaffolds [273], The development of new processing techniques and the reinforcement with various (nano)fillers has resulted in materials with mechanical properties matching those of bone [274],... 

Biomaterials for Cardiovascular Devices. Perhaps the most advanced field of biomaterials is that for cardiovascular devices. For several decades bodily parts have been replaced or repaired by direct substitution using natural tissue or selected synthetic materials. The development of implantable-grade synthetic polymers, such as siHcones and polyurethanes, has made possible the development of advanced cardiac assist devices (see... 

The first ever injectable crude biomaterial, that is a dental implant, appeared early in ad 6oo (Fig. 12.1). During those times, Mayan people trimmed seashells into artificial teeth to replace missing teeth (Michael, 2006 Ratner et al., 2004). Early biomaterials also led to problems, including sterilization, toxicity, inflammation, and immunological issues. Since the Mayan s initial use of artificial teeth, biomaterials have evolved to be used in modem artificial hearts, hip and knee pros-theses, artificial kidneys, and breast implants. Materials used in these applications include titanium, silicons, polyurethanes, teflon, polybiodegradable polymers, and most recently bio-nanomaterials (Pearce et al., 2007)... 

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... 

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