An MD&DI April 1997 Feature
MEDICAL PLASTICSA crop of new plastics offer improved features for medical manufacturing.
There is a bewildering array of medical plastics available for manufacturers today, and the choices are still expanding as materials developers find innovative ways to deliver greater strength, flexibility, resistance to sterilization or bodily materials, or just simple aesthetic appeal.
Several materials companies have recently released new medical plastic compounds that promise important advantages for manufacturers.
AlphaGary Corp. (Leominster, MA). New medical-grade compounds that are free of bovine materials are now available from AlphaGary for extrusion and molding. According to the manufacturer, the materials, which are made with vegetable-derived stabilizers and lubricants, exhibit greater clarity and continued high performance in heat stability and melt viscosity as compared with compounds containing animal-fat microingredients. The materials are suitable for a variety of applications including Class VI radiation-resistant tubing, film, or fittings and connectors, drip chambers, and oxygen therapy equipment.
Bayer Corp., Polymers Div. (Pittsburgh). Bayer has recently announced that it is offering the first lipid-resistant polycarbonate. Makrolon DP1-1805 is highly transparent, bonds well with PVC tubing, and is designed to alleviate the problem of cracking in high-stress applications where there is contact with intravenous fluid products, particularly lipid emulsions. Selected tints and colors of the new polycarbonate meet FDA biocompatibility requirements. The material can also withstand radiation, EtO, and steam autoclave sterilization.
A lipid-resistant polycarbonate from Bayer resists cracking.
GLS Corp. (Cary, IL). GLS Corp. has just released a translucent thermoplastic elastomer compound for medical applications, Dynaflex G-2755 grade, made with one of the company's polymers. The 100% recyclable compound typically has a 52 Shore A hardness, a 415-psi tensile modulus at 300% elongation, and a 790-psi tensile strength at break.
GLS Corp.'s thermoplastic elastomer compound is 100% recyclable.
Unichem Products, a div. of Colorite Polymers (Ridgefield, NJ). A recent release, Flexchem is a medical-grade PVC compound that is designed to replace silicone rubber in applications where a high degree of resilience is required. Flexchem compounds rebound readily after compression, making them suitable for tubing that is designed for repeated pinching and releasing, like the tubing for peristaltic pumps. According to the manufacturer, the compound costs only half the price of silicone rubber. The USP Class VI compound contains ingredients that are appropriate for use in medical applications, and can be supplied in colored, white, or translucent formulations.
Dow Plastics, a business group of The Dow Chemical Co. (Midland, MI). Dow Plastics has developed a new resin that exhibits improved mold release. The company says that the Calibre 2071 polycarbonate resin was designed to respond to a substantial need in the medical device industry for a material that will produce parts that can be easily ejected from their molds. Using only minimal force when releasing newly formed parts would allow manufacturers to reduce wear on molds.
Norton Performance Plastics Corp. (Wayne, NJ). Norton has recently announced a new Tygon 2075 tubing material that is plasticizer-free, so no plasticizer can contaminate the fluid that is being delivered. The material is also flexible and can produce tubing with smooth inner surfaces, high resistance to aggressive chemicals, and good clarity. It can be sterilized with radiation, EtO, or steam methods.
The company has developed the material primarily for endoscopy, administration of chemotherapy agents, or other applications that involve circulating blood or bodily fluids. In endoscopic devices, the tubing's smooth, nonwetting surface prevents fluid adsorption or the trapping of fluids in crevices, ensuring complete delivery of irrigation fluid volume. In chemotherapy, aggressive drugs can be handled in the tubing without risk of altering the dosage or preservative content.
Gamma-10 Plastics, Inc. (Minneapolis). A new family of polypropylene medical resins that can withstand repeated high doses of gamma radiation as well as other methods of sterilization has been introduced by Gamma-10. Several of the new resins are gamma and E-beam stable even at very high doses, and all of the materials can be sonic welded, heat sealed, or heat welded.
Some of the resins, which can be supplied with customized melt indices or gamma capabilities, were developed for the manufacture of medical parts that must undergo radiation sterilization, such as syringes. The resins do not degrade or discolor after radiation dosing. Two of the materials, which are film grade, are designed for straight-line tearing for medical pouches, drapes, and tapes.
Raychem Corp. (Menlo Park, CA). Raychem has introduced MicroFit tubing, a very small, medical-grade tubing offered in two materials, MT1000 and MT2000. According to Mark Burns, product manager at Raychem, "The microtubing line features the industry's highest shrink ratio and accommodates the drive toward producing smaller, more compact medical devices." The tubing has a shrink ratio of 3:1 and fits diameters from 0.007 to 0.045 in.
Raychem's MicroFit tubing is suitable for use with compact devices.
MT1000 tubing uses a tough, semirigid fluoropolymer that is suited for applications requiring high-temperature autoclaving and cut-through resistance. The tubing can be sterilized by radiation, ethylene oxide, steam, and dry heat with no significant change in properties.
MT2000 tubing is a tough, modified polyolefin that demonstrates flexibility, lubricity, and good electrical insulation performance. The low shrink temperature enables the tubing to shrink faster than other similar materials, reducing the risk of damage to temperature-sensitive substrates.