Physical properties UHMWPE

Thermal and physical properties of plastics (typical values) LDPE HDPE UHMWPE 50% glass-filled HDPE... 

Improving the wear resistance of the UHMWPE socket and, thereby, reducing the rate of production of wear debris would extend the useful life of artificial joints and permit them to be used successfully in younger patients. Consequently, numerous modifications in physical properties of UHMWPE have been proposed to improve its wear resistance. In particular, modifications of UHMWPE include (12) ... 

Typical Average Physical Properties of HDPE, UHMWPE... 

Champion A.R., S. Li, K. Saum, E. Howard, and W. Simmons. 1994. The effect of crystallinity on the physical properties of UHMWPE. Transactions of the 40th Orthopedic Research Society 19 585. 

The physical properties of UHMWPE include its morphology, which encompasses both microscopic and macroscopic analysis of the material, as well as thermal properties and molecular weight. 

Polymers are widely used as implant materials because they have physical properties that are similar to those of natural tissues. Examples are long-term and shortterm implants such as blood vessels, heart valves, membranes, mesh prostheses, corneas, tracheal prostheses, dental materials, parts of the nose and ear, knee and hip joints, and others. The synthetic polymers used include polyethylene (PE), particularly ultrahigh molecular weight PE (UHMWPE), poly(ethylene terephthal-ate) (PET), poly(tetrafluoroethylene) (PTFE), polyurethane (PU), and poly(methyl methacrylate) (PMMA). The necessary sterilization before implantation can be performed by y-irradiation, heat (steam), or chemical treatment (ethylene oxide), which should not cause any structural degradation of the polymers. Current challenges in research include the development of biomimetic materials that match both the mechanical and biological properties of their natural counterparts. 

The selection of process involves size of part. For example, you can t injection mold 50-foot lengths of garden hose, but you can readily extrude them. Ultrahigh molecular weight polyethylene (UHMWPE) has fantastic resistance to abrasion, but if your part must experience temperatures of 100°C or higher, UHMWPE will lose its physical properties rapidly. 

TABLE 1.1 Typical Average Physical Properties of High Density Polyethylene (HDPE), Ultra-high Molecular Weight Polyethylene (UHMWPE), Adapted from [3]... 

In this work we report a detailed XPS study of the influence of SC-CO treatment on UHMWPE surface composition. Characterization of XPS data is based on differential charging, which reflects inhomogeneity of physical properties of the polymer. In this case, the inhomogeneity related to presence of oxygen, crystalhnity, and porous structure. Oxygen may be in molecular state as H O, O, CO and/or in bonded state as CH O groups. 

PE, being a commodity polymer, is used in its different physical forms viz. fibres, sheets, membranes, moulds with different backbone chemical configurations (LPE, LLDPE, LDPE, HDPE, UHMWPE, UHSPE etc). Each of these forms of PE requires surface modification at some stage of application. The surfaces of PE fibres are often modified to make them compatible in the composites, whereas PE sheets/tapes are modified to achieve adhesion. Moulds are frequently surface-modified for probability and membranes for selective permeation. In the same way, different chemical configurations of PE, by the virtue of their properties, are used for different applications after surface modification. 

Table 1.1 summarizes the physical and mechanical properties of HDPE and UHMWPE. As shown in Table 1.1, UHMWPE has a higher ultimate strength and impact strength than HDPE.

Each of tiiese three principal steps produces a subtle alteration of the properties of UHMWPE. In some cases, such as machining, the change in the material may occur only in the topography and appearance of the surface. On the other hand, changes in the polymerization and conversion of the UHMWPE can impact the physical and mechanical properties of the entire implant. 

DCM has been used for more than 20 years to produce tibial and acetabular inserts. Historically, the process may have been adopted because the cutting and milling machinery of the day was not numerically controlled and thus less able to accurately produce complicated curves as required to make knee inserts. The physical and mechanical properties of the finished product can be tailored to some degree by varying die DCM cycle, as detailed by Chen, Truss, and others (Han et al. 1981, Truss et al. 1980, Chen, Ellis, and Crugnola 1981). DCM can also be used to produce UHMWPE with properties indistinguishable from stock material produced by closely monitored conversion of compression-molded sheet and extruded rod. 

Kurtz S.M., C. Cooper, R. Siskey, and N. Hubbard. 2003. Effects of dose rate and thermal treatment on the physical and mechanical properties of highly crosslinked UHMWPE used in total joint replacements. Transactions of the 49th Orthopedic... 

Chapter 12 Physical, Chemical, and Mechanical Properties of UHMWPE... 

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