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Biomedical subjects

R J Thoma

Publications and source records attributed to R J Thoma.

5 recordsLinked to original sources

The role of material surface chemistry in implant device calcification: a hypothesis.

We proposed that a similar mechanism for calcification exists for poly(ether)urethanes and glutaraldehyde stabilized tissue. The mechanism is based on the propensity of the polyether component of the materials to complex calcium and provide initiating sites for ultimate formation of calcific deposits. Data evaluating the role ether containing materials have on calcification demonstrate that the rate of mineralization of either tissue valves or polymer valves can be controlled by paying attention to the basic chemical mechanism of complexation occurring at the surface and within the bulk of the implant devices. The molecular models described above, point out that the driving force for complexation with either the polyethers of the polyurethane or the polyether of glutaraldehyde is very strong, therefore, controlling the driving force may lead to medical devices with longer term durability.

Animals

Biomedical applications of polyurethanes: implications of failure mechanisms.

Three mechanisms have been described which explain various observed interactions between polyurethane chemistry and body chemistry. These include calcification, environmental stress cracking, and chain scission. Each may result in implant device failure, and each appears to involve metal ion complexation as a key parameter. Continued expansion of polyurethane into implantable product applications will require further clarification of the effect of each of these interactions on long-term product performance. It is believed that design considerations and polymer modifications will help control the effects of each of the interactions and will result in new and improved polyurethane implant products.

Biocompatible Materials

Studies of poly(ether)urethane pacemaker lead insulation oxidation.

Published reports suggest that silver ions may catalyze the oxidation of poly(ether)urethane soft-segments resulting in the failure of urethane insulations of specific models of pacemaker leads. Attempted oxidation of soft-segment models, poly(tetra-methylene ether)glycols, by silver nitrate has shown that metal-ion catalyzed oxidative-reduction (MICOR) does not adequately explain observed failures unless antioxidants are removed in process. Such cracking can, however, be explained in terms of a metal ion enhanced environmental stress cracking.

Biocompatible Materials

Poly(ether) urethane reactivity with metal-ion in calcification and environmental stress cracking.

Since their introduction to the biomedical community in 1967, polyurethanes have been used in a number of biomedical applications. In chronic applications evidence is now available which suggests that polyurethanes may be subject to various cracking phenomena. Environmental stress cracking and calcification are two phenomena resulting in poly(ether)urethane cracking, which have been shown to be enhanced by ion complexation. Much evidence now exists which defines the ability of poly(ether)urethanes to selectively extract ions, especially calcium ion from solution. Metal ion binding appears to enhance environmental stress cracking and appears to be a first step in the process of calcification.

Biocompatible Materials