Orthopedic implant applications

Cook SD, Thomas KA, Kay JF, Jarcho M (1988) Hydroxyapatite-coated titanium for orthopedic implant applications. Clin Orthop Relat Res 232 225-243... 

TABLE 15.6 Characteristic Properties of Polymers Used in Orthopedic Implant Applications... 

ZnO and MgO nanoparticles have been shown to increase bone cell functions and decrease infection (Liu et al., 2015 Weng and Webster, 2012). Nano zinc oxide (ZnO) also can induce osteogenic properties from stem cells (Liu et al., 2015). Composites incorporating ZnO nanoparticles with a diameter near 60 nm can form a scaffold for tissue regeneration. The size of laminin, collagen, and fibronectin, which are all major components of the natural ECM, is on the same order of magnitude as a ZnO nanoparticle. Moreover, the piezoelectric and antibacterial properties of ZnO particles make it a good choice for orthopedic implant applications (Sell and Webster, 2(X)8). 

Initial tests in the rat revealed a high degree of tissue compatibility of Dat-Tyr-Hex derived polymers. More detailed tests are now in progress. In addition, tyrosine derived polymers are currently being evaluated in the formulation of an intracranial controlled release device for the release of dopamine, in the design of an intraarterial stent (to prevent the restenosis of coronary arteries after balloon angioplasty), and in the development of orthopedic implants. The use of tyrosine derived polymers in these applications will provide additional data on the biocompatibility of these polymers. 

Nanostructured ceramics provide alternatives not yet fully explored for orthopedic and dental implant applications the improved mechanical properties of these novel ceramic formulations, in addition to their established exceptional biocompatibility, constitute characteristics that promise improved orthopedic and dental efficacy. Requirements applicable for the design of nanophase ceramics for orthopedic and dental applications include the following ... 

Clinical Applications. Lipophilic Tc-exametazime has been shown to label leukocytes without affecting cell viability (Mortelmans et al. 1989 Peters et al. 1986 Roddie et al. 1988). HMPAO-labeled leukocytes have been used to locate site(s) of focal infection (e.g., abdominal abscess, abdominal sepsis) (Kelbaek et al. 1985) it is also indicated in conditions of fever of unknown origin, and in conditions not associated with infection such as inflammatory bowel disease (Arndt et al. 1993 Lantto et al. 1991). Labeled leukocytes have offered superior information when compared with bone scanning for the detection of osteomyelitis in children (Lantto et al. 1992). In a retrospective study in 116 patients with infection suspected to involve orthopedic implants, osteomyelitis, and septic arthritis, HMPAO-labeled leukocytes have been an effective tool in the diagnosis of chronic osteomyelitis and joint infection involving implants (sensitivity > 97%, specificity > 89%) (Devillers et al. 1995). 

Flarm caused by the use of metallic implants is essentially due to the release of ions resulting from the corrosion of these alloys. This concerns principally Ni, Cr and Co for any application. Be, Cd, Pd, Ag and Cu for dental alloys, and Ti for stomatological and orthopedic implants (Flildebrand etal. 1995 Flildebrand and Flornez 1998 Hornez et al. 2002). 

The use of carbon materials has been attempted for orthopedic implants, and they are still used for heart valves and dermatological applications. 

Ti-6A1-4V was developed for applications requiring high strength and low-to-moderate temperatures. The alloy has a high strength-to-weight ratio and good corrosion resistance in many environments. Ti-6A1-4V finds use in aerospace, automotive, and marine applications as well as for orthopedic implants. 

Biodegradability is often an important consideration in the development of biomedical, pharmaceutical, and agricultural products for a number of applications. Biodegradable polymers have been formulated for uses such as controlled release and drug-delivery devices, surgical sutures, scaffolds for tissue regeneration, vascular grafts and stents, artificial skin, and orthopedic implants. 

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]. 

There are opportunities for polyolefins in biomedical applications as many types are nontoxic, non-thermogenic, non-inflammatory, non-carcinogenic, and non-immunogenic. Polyolefins are used in many applications such as artificial skin, orthopedic implants, heart valves, and disposal items used in medical applications such as syringes. 

The American Standards for Testing and Materials (ASTM) has compiled a list of the recommended properties that polyethylene components must meet or exceed if they are to be used in orthopedic devices. This list is summarized in ASTM F648 and D4020-01a. The FDA usually refers to these standards when considering a new UHMWPE for orthopedic implants. A summary of all possible tests, including their ASTM standard numbers, where applicable, is summarized in Table 12.2, and indicates where the individual tests are appropriate for UHMWPE powder, consolidated stock, or irradiated stock. 

There are extensive studies centering on the fabrication of nanostructured metals in order to improve their mechanical properties. Since mechanical performance of orthopedic implant is critical to its applications, liability and lifetime, superior mechanical properties are always wanted. Depending on clinical settings, the wanted properties include, but are not limited to, enhanced mechanical strengths, toughness, ductility, wear resistance, corrosion resistance, and special characteristics such as superplasticity and shape-memory effect. Due to space limitations, only the typical aspects and examples of implant mechanical properties enhanced by nanotechnology are introduced here. 

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