Degradation and drug delivery properties of poly(1,4-cyclohexanedicarboxylic anhydride)

Polyanhydride Chemistry

Polyanhydrides (PAs) are a class of synthetic biodegradable polymers employed as controlled drug delivery vehicles. They can be synthesized and scaled up from low-cost starting materials. The structure of PAs can be manipulated synthetically to meet desirable characteristics. PAs are biocompatible, biodegradable, and generate nontoxic metabolites upon degradation, which are easily eliminated from the body. The rate of water penetrating into the polyanhydride (PA) matrix is slower than the anhydride bond cleavage. This phenomenon sets PAs as "surface-eroding drug delivery carriers." Consequently, a variety of PA-based drug delivery carriers in the form of solid implants, pasty injectable formulations, microspheres, nanoparticles, etc. have been developed for the sustained release of small molecule drugs, and vaccines, peptide drugs, and nucleic acid-based active agents. The rate of drug delivery is often controlled by the polymer erosion rate, which is influenced by the polymer structure and composition, crystallinity, hydrophobicity, pH of the release medium, device size, configuration, etc. Owing to the above-mentioned interesting physicochemical and mechanical properties of PAs, the present review focuses on the advancements made in the domain of synthetic biodegradable biomedical PAs for therapeutic delivery applications. Various classes of PAs, their structures, their unique characteristics, their physicochemical and mechanical properties, and factors influencing surface erosion are discussed in detail. The review also summarizes various methods involved in the synthesis of PAs and their utility in the biomedical domain as drug, vaccine, and peptide delivery carriers in different formulations are reviewed.

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.