For a number of years, Foster Corporation has been developing its expertise in the compounding of bioabsorbable polymers. These are materials that are finding more and more use in medical device applications.
Currently materials which are classified as bioabsorbables are: PGA (Polyglycolides),PLA (polylactides), PLGA (polylactide-co-glycolides) and PCL (polycaprolactone). The bioabsorbable polymers are synthetic and hydrolytically unstable. This makes them biocompatible and they manifest a wide range of physical properties and degradation characteristics. They are inert to the body but are absorbed into the body and metabolized.
One of the key advantages of these materials is their ability to be processed via thermoplastic melt processing techniques. They are also sterilizable via gamma and ETO. By varying the molecular weight and the copolymers selected you can program different sets of properties into the polymer.
PGA - Polyglycolides are highly crystalline and have a low solubility in water. The body absorbs the polymer quickly ûPGA loses strength within one month and loses mass within 6-12 months. The melt point of the PGA is 225-230 degrees C with a glass transition temperature of 35-40 degrees C. PGA has a high modulus
PLA-Polylactides have a slower rate of absorption requiring two years to be absorbed. This is also a highly crystalline material with a glass transition temperature of 50-80 C and a melting point 173-178 degrees C. PLA has a high modulus and is suitable for load bearing applications. PDLA (What is the chemical name?) has a faster absorption rate than PLA.
PLGA (Polylactic-co-glycolic acid) PLGA is a copolymer depending on the ratio of lactide to glocolide, different forms can be obtained. This is an amorphous polymer with a glass transition temperature of 40-60 degrees C. It has very good solubility. Degradation depends on the ratio ûa 50/50 ratio absorbs in about 2 months.
Polycaprolactone-PCL has a low melting point of 60 degrees C and a glass transition temperature of -60 degrees C. Polycaprolactone is often used as an additive to improve processing characteristics and end-use properties. It has a slow degradation rate of 2+ years.
The factors affecting the biodegradation of polymers are both chemical and physical in nature
Chemical
Chemical structure and composition
Molecular weight and distribution
Morphology-amorphous/crystalline structure
Site of implantation
Mechanism of hydrolysis (enzymes vs. water)
Presence of additives
Physical
Processing conditions
Annealing
Sterilization process
Storage History
Drying
Part shape and design
Presence of additives
The applications where bioabsorbable polymers are typically used are sutures, dental devices, orthopedic fixation (metal replacement), controlled drug delivery, tissue fixation, biodegradable stents, bone and tissue engineering.
Foster has extensive experience processing bioabsorbable polymers like PLA, PGA, PCL, etc. They offer coloring and will do small runs, e.g. 10 pound production and .5 on a HAAKE. They have programmable screw configuration usually with medium shear. They can hold tight tolerances and have the appropriate drying capabilities. Foster plants are environmentally controlled. Most of the bioabsorbable operations are done in the Las Vegas facility because of the low humidity conditions. They also have the appropriate packaging capabilities, e.g. metallized bags, poly bags and vacuum canning.
This is another example of Foster CorporationÆs focus on and commitment to the medical device industry.
For more information, contact Larry Johnson of Foster Corporation.
Foster contact information:
Foster Corporation, 45 Ridge Rd Putnam Ct 06260, USA; Tel 860-928-4102; Fax 860-928-4226 West Coast: 4336 Losee Rd. Suite 8 North Las Vegas, NV 89030-3380, USA; Tel 702-644-4880; Fax 702¼644-5819; www.fostercomp.com; e-mail: foster.corp@fostercomp.com
MedNet contact information:
MedNet GmbH, Borkstrasse 10, 48163 MÆ’enster, Germany; Tel +49 (0) 251 32266-0;
Fax +49 (0) 251 32266-22; www.medneteurope.com; Contact: Matthias Heinz, Sales/Marketing û e-mail:
Matthias.heinz@medneteurope.com