The medical sector is the fourth largest consumer of plastics after packaging, construction, and automotive sectors. It has a relatively high growth rate (8% per year). The growth is in part due to our long life expectancy but also because of new technological advances in medicine. As is evident from the conducted studies, the majority of problems within the sector are very typical of the plastics industry in general. These include the need to improve reinforcement, durability, fatigue resistance, adhesion, reduce water absorption, etc. In addition to these problems, there are some issues which are only related specifically to medical applications such as toxicity and biocompatibility.
E.G: The area of prosthesis and dental applications seem dominated by polymethylmethacrylate. The use of fillers is mostly limited to hydroxyapatite and glass. Distressingly studies report numerous fatal failures due to the lack of adhesion between the bone substrate and the implant due to unsatisfactory properties of "Plexiglas" related cements.
Some pioneering studies are being conducted. One involves the crystallization of inorganic materials in the presence of simulated or specific body fluids. This process affects the structure of the crystal which develops a surface structure similar to that of bone. In this way it becomes more acceptable (or difficult to recognize as artificial) to living tissues.
Some medical plastics must perform under constant water immersion. It was reported that absorption of 1% water reduces the fatigue life of PMMA by a factor of four, since bone cement can only be replaced by a surgical operation; such a performance is clearly unacceptable.
The use of silane to treat the hydroxyapatite filler in this material reduced water uptake. The water uptake increased with increased concentration of hydroxyapatite. In applications, such as dental fillings, increased water uptake is considered helpful since it compensates for the loss of volume due to shrinkage of the filling during curing.
This article is an excerpt from the Handbook of Fillers, by George Wypych and published by ChemTec Publishing.