Biodegradable synthetic polymers: Preparation, functionalization and biomedical application

Abstract

Biodegradable polymers have been widely used and have greatly promoted the development of biomedical fields because of their biocompatibility and biodegradability. The development of biotechnology and medical technology has set higher requirements for biomedical materials. Novel biodegradable polymers with specific properties are in great demand. Biodegradable polymers can be classified as natural or synthetic polymers according to the source. Synthetic biodegradable polymers have found more versatile and diverse biomedical applications owing to their tailorable designs or modifications. This review presents a comprehensive introduction to various types of synthetic biodegradable polymers with reactive groups and bioactive groups, and further describes their structure, preparation procedures and properties. The focus is on advances in the past decade in functionalization and responsive strategies of biodegradable polymers and their biomedical applications. The possible future developments of the materials are also discussed.

Introduction

A biomaterial can be defined as a material intended to interface with biological systems to evaluate, treat, augment or replace any tissue, organ or function of the body [1]. Biomaterials play an important role in human health. Biopolymers are the main type of biomaterials. According to their degradation properties, biopolymers can be further classified into biodegradable and non-biodegradable biopolymers. Many implants, such as bone substitution materials, some bone fixing materials, and dental materials, should possess long term stable performance in the body. In recent years, developments in tissue engineering, regenerative medicine, gene therapy, and controlled drug delivery have promoted the need of new properties of biomaterials with biodegradability. Biologically derived and synthetic biodegradable biopolymers have attracted considerable attention [1]. Polysaccharides and protein are typical biologically derived biopolymers, while aliphatic polyesters and polyphosphoester (PPE) are typical synthetic biopolymers.

Biopolymers with diverse specific properties are needed for in vivo applications because of the diversity and complexity of in vivo environments. Nowadays, synthetic biopolymers have become attractive alternatives for biomedical applications for the following reasons: (1) although most biologically derived biodegradable polymers possess good biocompatibility, some may trigger an immune response in the human body, possibly one that could be avoided by the use of an appropriate synthetic biopolymer; (2) chemical modifications to biologically derived biodegradable polymers are difficult; (3) chemical modifications likely cause the alteration of the bulk properties of biologically derived biodegradable polymers. A variety of properties can be obtained and further modifications are possible with properly designed synthetic biopolymers wihout altering the bulk properties.

Specific properties are sometimes required for biomaterials. For example, tissue engineering scaffolds should have both good biocompatibility and cell adhesive properties, in addition to needed biodegradable properties. Drug delivery systems should be endowed with stimuli-responsive properties for intelligent-control release. Functionalization is inevitable to improve the properties of traditional synthetic biopolymers. There are two commonly used functionalization strategies: (1) functional groups are introduced to the monomers of polymers, sometimes in a protected form before polymerization, to be deprotected after polymerization; (2) functional groups are introduced to polymer chains by further chemical modification of the as-prepared polymers.

This review is focused on recent progress of different strategies of functionalization of synthetic biodegradable polymers and the applications of these.