Poly(lactic acid) based hydrogels: formation, characteristics and biomedical applications

Hydrogels are cross-linked polymeric networks that absorb or release water in response to some stimuli and are susceptible to cellular attachment and can be remodeled into complex structures. The properties of hydrogels can be tuned by gentle use of copolymers and cross-linkers. These hydrogels are designed in such a way that they are degraded and subsequently removed from the work area. The hydrogels have ability to carry small amounts of drugs, proteins and other desirable components for medical and other purposes. Poly(lactic acid) (PLA) and its stereoisomers are nonfunctional-hydrophobic polymers that are applicable in biomedical sector. Nevertheless, a high glass transition temperature of PLA limits its application in biomedical field. They, therefore are conjugated or copolymerized with hydrophilic polymers like polyethylene glycol (PEG) and chitosan to form composite hydrogels. The PEG is used to polymerize PLA to form thermo-sensitive hydrogels. Similarly, polyurethanes, polysaccharides, oligomers and peptides are employed for hydrogels formation through physical and chemical routes. The existence of functional moieties in polysaccharides like carboxyl, amine and hydroxyl offers easy cross-linking and conjugation. In addition to this, the use of polysaccharides as hydrophilic part of hydrogels engages the aqueous media which exhibits high swelling capacity of polysaccharides. The PLA based thermo-responsive hydrogels have effectively been used for wound healing, tissue engineering as well as drug control and release. This review gives a thorough focus on recent developments in PLA based hydrogels formation, their properties and possible biomedical applications.