Resorbable polymers degradation

The concept of using biodegradable materials for implants which serve a temporary function is a relatively new one. This concept has gained acceptance as it has been realized that an implanted material does not have to be inert, but can be degraded and/or metabolized in vivo once its function has been accompHshed (12). Resorbable polymers have been utilized successfully in the manufacture of sutures, small bone fixation devices (13), and dmg dehvery systems (qv) (14). 

Key words resorbable polymer, biocompatibility, hydrolytic degradation, enzymatic degradation, mechano-active tissue engineering, elastomeric properties, copolymerization, particulate leaching, gel spinning. 

Degradation process of resorbable polymers in the living body. 

Tomihata K, Suzuki M, OkaT and Ikada Y (1998a), A new resorbable monofilament suture, Polymer Degrad Stabil, 59,13-18. 

Arosio, P., Busini, V., Perale, G., Moscatelli, D. Masi, M. 2008. A new model of resorbable device degradation and drug release - Part I zero order model. Polymer International, 57, 912. 

The industrial production of a medical device is a complex activity that requires fine-tuning of the technical parameters to satisfy the requirements of quality, reproducibility, and reliability that are necessary to meet customer needs and regulatory directives. For bioresorbable polymers, this activity is even more complex, due mainly to the following factors (1) aptitude to degradation of resorbable polymers, (2) high costs of production, and (3) scarcity of suppliers. 

As can be seen from the process flow chart (Fig. 3.1), in order to fabricate and assemble a resorbable biotextile device, a resorbable polymer has to withstand exposure to a range of potentially hazardous environments, such as thermal processing, mechanical abrasion, chemical treatment (lubricants, solvents, binders etc.), and atmospheric conditions, which include relative humidity. Each of these factors can drastically affect the rate of resorption and can cause premature degradation of the resorbable implant. 

The extrusion rate of a polymer is dependent on the rotational speed of the extruder which determines the residence time and shear rate of the polymer. The extrusion rate and the shear forces on the polymer have been found to affect its subsequent degradation profile [3, 4, 10]. One study found that a weaker, less drawn, and less crystalline fiber resorbed more quickly in PBS solution [10]. The extrusion speed determines the residence time at an elevated temperature, because it controls the time the material remains in the barrel of the extruder. Longer residence times (from 50 to 300 s) and higher shear rates result in higher rates of polymer degradation even at lower temperatures. 

The in vivo degradation mechanisms according to Hutmacher (2001) are illustrated in Figure 12 for typical resorbable polymers such as PLA. Initially, the hydration... 

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