Biomedical Applications of Bioplastics
Authors: Vipin Chandra Kalia and Subhasree Ray


Introduction
Plastics, the synthetic polymers are an integral part of our daily life. Incidentally, their excessive use has resulted in their accumulation in the environment and are becoming difficult to manage. The major reason is their non-biodegradable nature. Biodegradable plastics or bioplastics are produce by certain bacteria through a unique metabolic route. Bioplastics especially, polyhydroxyalkanoates (PHAs) are finding their applications in the field of medicine because they are biodegradable, biocompatible, and non-toxic. PHAs can be used as biocontrol agents, carriers of drugs, implants, engineering tissue, enhancing memory and inhibiting cancerous growth.

Antimicrobial agents
PHA metabolism leads to the production of 3Hydoxy acids (3HAs). Pseudomonas fluorescens possess depolymerase to produce monomers from PHAs, which can be used for synthesizing antimicrobial compounds in the pharmaceutical companies. Transformation of 3HAs in to hydroxycarboxylic acids: 2-alkylated 3HB and β-lactones, act as oral drugs and as carbapenem or macrolide antibiotics against infections caused by Staphylococcus aureus. 3HAs - D-peptide combination acts against cancers. P3HB and P4HB have strong role in skin and wound healing.

Biocontrol molecules
Antibiotics at low doses are used as feed supplement for livestock and aquaculture. However, regular usage of antibiotics is likely to disturb the gastrointestinal microflora, which may also develop resistance to them. PHAs being biopolymers of β-hydroxy lower-chain fatty acids, can generated in the intestine by bacteria. These fatty acids have been reported to act as anti-pathogenic for giant tiger prawn.

Carriers for drugs
Drug delivery within the body is an important factor in improving their efficiency. Thus their targeted delivery is a desirable feature. PHAs as biomaterials, are used to producing nano-particles, scaffolds for eluting drugs and tablets. Monomers like 3HB are helpful in synthesizing novel biodegradable polymers like Dendrimers, and have surface-functional moieties and monodispersity. These properties enable them to act as drug carriers - tamsulosin, ketoprofen and clonidine. PHA microspheres loaded with rifampicin act as hemoembolizing agent and as drug carriers. Implantable rods prepared from PHA and its co-polymers are good for delivery of antibiotics.

Tissue engineering
PHAs modified chemically can be used in tissue engineering, using them for therapeutic and medical purposes: (i) nerve tissue, (ii) cardio-vascular valves, and(iii) grafts. Chemically modified PHAs can be used as screws, pins, sutures, films, and employed as scaffolds for engineering liver tissue and cartilage repair.

Medical devices
PHAs as medical devices are biodegradable, biocompatible, and strong. They are resistant to infections, lack immunogenicity and are non-toxic. A few potential devices include orthopedic pins, cartilage repair, rivets and tacks, cardiovascular grafting, meniscus repair, stents, staples, repair patch, mesh, sutured fastener. PHA sheets coated with lysozyme prevent biofilm formation and prove helpful in wound dressing.

Anti-osteoporosis effect
PHAs act as undergo rapid diffusion and prevent brain damage, improve cardiac efficiency by generating energy. The monomers like 3HB can cure diseases such as Parkinson and Alzheimer, by preventing neuronal cell death. 3HB improves calcium deposition, as it has anti-osteoporosis activity.

Memory enhancer
Memory loss is common among dementia - Alzheimer’s disease. To prevent these diseases, modifications of monomers i.e., methyl esters of 3-hydroxybutyrate can act as drug molecules. It protects mitochondrial damage. HA can stimulate Ca2+ channels, to help memory enhancement.

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About Author / Additional Info:
Researchers in Microbial Biotechnology and Genomics at CSIR-IGIB, Delhi.