# Bio-Based Polymers with Potential for Biodegradability
## 4 Other Bio-Based Polymers with Potential for Biodegradability
### Medical Applications  
Polymers have been a valuable material in medicine, and over the past half-century, biodegradable, biocompatible polymers have gained increasing popularity in drug delivery. Indeed, bio-based polymers that are capable of dissolving in the body after the drug is delivered to its target are highly desirable [177]. It is possible to design polymers for specific applications by manipulation and control of the polymer composition, thermal behavior, hydrophobicity/hydrophilicity, mechanical properties, ability to retain the encapsulated or entrapped drug, and the interactions of the polymer in a biological environment [178]. Other applications outside the realm of drug delivery include surgical devices, implants, tissue engineering, gene therapy, regenerative medicine, coatings on implant biosensors, components of diagnostic assays, bio-adhesives, ocular devices, and materials for orthopedic applications [178; 179].  
The applications of a specific bio-based polymer are greatly dependent on its composition. Unsaturated oils have become an attractive source for polymers due to their carbon-carbon double bonds within the fatty acid chains. These double bonds serve as ideal reactive sites for polymerization [180]. Hydrophobicity and flexibility of vegetable oil-based polymers can be tuned by monomer composition and by the selection of the specific oil to be used as a monomer. It has been shown that oil-based polymers do not form uniform blends due to the variable fatty acid composition within each oil, which can result in a micro-phase separation of the matrix, compromising the mechanical properties of the final polymeric material [178; 181]. In order to limit this effect, monomeric triglyceride units have been added to a filler or a template backbone polymer, such as polyanhydrides, co-polyesters, or polyamides. In anticancer treatments, fatty acid dimer (FAD) systems were originally created to control the release of water soluble and unstable chemotherapeutics [182]. Drugs impregnated with FAD were shown to allow for prolonged and controlled drug release [182]. FADs have also been shown to have local anesthetic and antibiotic properties. Most fatty acids undergo condensation to form polyanhydrides that can easily be hydrolytically degraded. Though polyanhydrides can degrade by surface erosion, there are many factors that influence the mechanism and rate of degradation [178].  
Tissue engineering is a popular field in medicine and the current market is estimated to be approximately $23 million dollars, with a projected continuous growth in the coming years [183]. Polyesters are one of the most competitive polymers for regenerative implantation surgeries, therapeutic cell culturing, and tissue repair. Of all the current commercial products, polyesters act as biologically passive supporting materials such as sutures, surgical mesh or netting, or drug-releasing vehicles. To address more advanced medical and regenerative applications, polyesters are modified to overcome issues such as low cell adhesion, hydrophobicity, and inflammatory side effects. Some of the most commonly used bio-based polyesters are poly(lactic acid) (PLA), poly(lactic-co-glycolic acid) (PLGA), poly-3-hydroxybutyrate (or poly-hydroxybutyric acid, PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) (Figure 3) [19; 184; 185]. PLA is most commonly used in sutures due to its high tensile strength and elongation at break [186].