Poly(anhydride-ester) fibers: role of copolymer composition on hydrolytic degradation and mechanical properties

Poly(anhydride-esters), based on carboxyphenoxydecanoate (CPD), are biocompatible polymers that hydrolytically degrade. The mechanical properties of the poly(anhydride-esters) can be altered by copolymerization with para-carboxyphenoxyhexane (pCPH). Mechanical properties of three CPD:pCPH compositions (30:70, 40:60, and 50:50) are reported as a function of hydrolytic degradation. The mechanical characteristics evaluated were tensile modulus at 1% strain (E(1%)), tensile strength (sigma(B)), ultimate elongation (epsilon(B)), and toughness (E(r)). The 30:70 CPD:pCPH fibers maintained higher values for tensile modulus at all time points than the two other fiber compositions. In addition, the 30:70 CPD:pCPH fibers maintained lower values for both tensile strength and toughness than the two other fiber compositions. These phenomena resulted from the brittle nature of pCPH, the major component of the 30:70 CPD:pCPH fibers; increasing the pCPH concentration in the polymer lowers both tensile strength and toughness of the polymer by decreasing ductility. With increasing amounts of pCPH, the hydrolytic degradation occurred more slowly, as reflected in the copolymers' improved ability to retain their mechanical properties. Therefore, copolymerization is useful for controlling the mechanical properties of the fibers as well as the polymer degradation rate, which ultimately determines the rate at which physically or chemically encapsulated drugs can be released.