Use in artificial joints

The mechanical properties at the surface of the UHMWPE will also play an important role in determining the tribological behavior. The UHMWPE pins were produced and machined in the same way and y-irradiated with the same dose before use to ensure the same surface properties as UHMWPE used in artificial joints. It can, therefore, be assumed that there is little variation in the mechanical properties. However, small variations in the shear strength at the surface may be sufficient to determine whether lumpy transfer of poljoner occurs or a smooth transfer fOm is formed. If the transfer film was thinner than 10 nm it would not be detected in the fluorescence imaging but may have been formed in those cases where the friction coefficient dropped to a lower value. 

The results of this study support the use of UHMWPE-on-HTOZ for use in artificial joint surfaces. The fiictional behaviour of UHMWPE-on-HTOZ was less than UHMWPE-on-TZP when lubricated with physiological lubricant (diluted bovine serum). The wear of UHMWPE-on-HTOZ was similar to UHMWPE-on-alumina, which is used in current ceramic knee prostheses. The wear of UHMWPE-on-HTOZ was significantly less than the wear of UHMWPE-on-CoCr (P<0.05). 

C. J. Schwartz, S. Bahadur, and S. K. Mallapragada. Effect of crosshnking and Pt-Zr quasicrystal fillers on the mechanical properties and wear resistance of UHMWPE for use in artificial joints. Wear 263,1072-1080 (2007). 

Long-term inertness without loss of strength, flexibility, or other necessary physical property is needed for use in artificial organs, prostheses, skeletal joints, etc. Bioerodability is needed when the polymer is used as a carrier such as in controlled release of drugs, removal of unwanted materials, or where the materials purpose is short-lived, such as in their use as sutures and frames for natural growth. 

Tantalum alloys are used in artificial knees as well as hips and other joints. IMAGE COPYRIGHT 2009, VADIM KOZLOVSKY. USED UNDER LICENSE FROM SHUTTERSTOCK.COM. 

Another application for tantalum alloys is in medical and dental applications. The metal has no effect on body tissues. It is used in artificial hips, knees, and other joints. Pins, screws, staples, and other devices used to holds bones together are also made of tantalum alloys. 

Other uses are found in plastic surgery, artificial skin and blood substitutes. An unique field is found in membranes for dialysis. PE, mostly linear (including UHMW), serves in many implants or in artificial joints. PVC is the most useful polymer in medicine, in plasticized form for flexible tubing, dialysis and infusion systems. PP is offered for disposible injections and, together with ethylene (copolymer), in blood bags. PS serves as a substitute for glass in tubes, bottles and petri dishes, and as the copolymers SAN or ABS in a wide host of uses. Polyester (PET) is used in sewing threads or nets in prostheses. PC is used (as a replacement for cellophane) in membranes for dialysis as well as in blood pumps and other systems. 

Since 1962, UHMWPE also has been used in orthopedics as a bearing material in artificial joints. Each year, about 1.4 million joint replacement procedures are performed aroimd the world. Despite the success of these restorative procedures, UHMWPE implants have only a finite lifetime. Wear and damage of the UHMWPE components is one of the factors limiting implant longevity. 

Biomaterials are synthetic or natural materials that are in contact with biological tissues or fluids and may enhance or replace tissues, bones, organs, or body functions (4). They include metals, alloys, glasses, ceramics, natural or syndetic polymers, biomimetics, and composites. Typical biomaterials may be used in artificial skin, tissues, and bones, dental fillings, wire plates and pins for bone repair, artificial hips and joints, implantable drug delivery systems, and other dental, surgical, and medical devices. New and improved biomaterials continue to be sought... 

Figure 4.20. A representative TEM image of a chemically cross linked UHMWPE, used as an implant material in artificial joints, prepared by staining with chlorosulfonic acid and poststaining in 2% uranyl acetate [261], shows numerous lamellae. (From Kurtz [261] used with permission.)...

Improvement in wear is frequently cited as a motivation for current composite research in UHMWPE for orthopedic implants [43, 44, 47—51]. Thus far, the use of fillers alone has not proven effective in reducing the wear rate of UHMWPE by an order of magnitude, as has been observed with extensive radiation crossfinking. Whereas conventional UHMWPE may have been the state of the art when early research on UHMWPE composites was initiated, today UHMWPE matrix composites need to demonstrate superior properties when compared with unfilled radiation crosshnked materials. Because the tribology of UHMWPE in artificial joints is strongly dependent on the kinematics and lubricant, additional research is needed to fuUy characterize the biotribological behavior of UHMWPE micro- and nanocomposites for specific orthopedic bearing applications. 

L. V. Wilches, J. A. Uribe, A. Toro. Wear of materials used for artificial joints in total hip replacements, Wear 265,143-149 (2008). 

The present work was done with the aim to evaluate the efficiency of the acoustic emission method as a diagnostic tool for analysing a carbon plastic composite and its adhesive joints. The samples of the carbon plastic type UKN-5000 were used in the test. Non-defected samples and samples with artificial defects were tested. 

The materials used in a total joint replacement ate designed to enable the joint to function normally. The artificial components ate generally composed of a metal piece that fits closely into bone tissue. The metals ate varied and include stainless steel or alloys of cobalt, chrome, and titanium. The plastic material used in implants is a polyethylene that is extremely durable and wear-resistant. Also, a bone cement, a methacrylate, is often used to anchor the artificial joint materials into the bone. Cementiess joint replacements have mote tecentiy been developed. In these replacements, the prosthesis and the bone ate made to fit together without the need for bone cement. The implants ate press-fit into the bone. 

Hydroxyapatite (HA) coating on the surface of the hip stem and the acetabular cup is the most recent advancement in artificial hip joint implant technology. This substance is a form of calcium phosphate, which is sprayed onto the hip implant. It is a material found in combination with calcium carbonate in bone tissue, and bones can easily adapt to it. When bone tissue does grow into HA, the tissue then fixes the hip joint implant permanently in position. These HA coatings are only used in press-fit, noncemented implants. 

Hip replacement surgery is now routinely used to relieve pain and restore mobility in patients suffering from osteoarthritis. In this condition the surfaces of bone in contact with each other within the joint become worn and the layer of lubricating cartilage disappears. This makes movement of the joint both difficult and painful. By replacing the hip with an artificial joint patients stop experiencing pain and are once again able to move freely. 

A few elements, among them fluorine and phosphoras, occur naturally with just one isotope, but most elements are isotopic mixtures. For example, element number 22 is titanium (Ti), a light and strong metal used in Jet engines and in artificial human Joints. There are five naturally occurring isotopes of Ti. Each one has 22 protons in its nuclei, but the number of neutrons varies from 24 to 28. In a chemical reaction, all isotopes of an element behave nearly identically. This means that the isotopic composition of an element remains essentially constant. The isotopic composition of Ti (number percentages) is... 

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