Modification of Polyhydroxyalkanoates (PHAs)

Abstract

The excellent biodegradability, compatibility and versatile structural composition of polyhydroxyalkanotes (PHAs) have secured their significance for industrial applications. More importantly, these polymers can also play a critical role in biomedical applications such as a 3D scaffold for tissue engineering, bio-adhesive, surgical sutures, implants and anticoagulant films. Unfortunately, their hydrophobicity, crystallinity and lack of surface ligand groups potentially limit their applications in this area. Hence, the future of these biodegradable polymers as biomedical device components is strongly dependent on successful modifications to tailor their properties and characteristics. Chemical, physical and enzymatic approaches have been explored for polymer modifications, resulting in a uniquely transformed PHA endowed with functionalized reactive groups and/or enhanced properties such as thermal stability, elasticity, improved hydrophilicity and degradability. While chemical modification processes provide a large degree of freedom in controlling and designing modified PHAs in bulk quantities to suit a particular function, most often they have to contend with the drawback of toxic impurities that require difficult downstream processing. Physical or enzymatic modifications are therefore considered to be alternative methods that involve no toxic compounds. A number of modified PHAs are easily prepared by physical methods and have been successfully applied in diverse applications where neat PHAs may have easily failed. However, the current concern over environmental degradation and deterioration coupled with elevated health hazards discourage the use of high energy radiation and co-initiator chemicals in physical methods, pushing the emerging environmentally friendly enzyme catalyzed process to the center stage of the modification arena. In this chapter, the chemical, physical and enzymatic processes typically employed for polymer modification and functionalization are discussed.