Biodegradable Materials for Clinical Applications: A Review

Abstract

This review article focuses on mechanical properties and composition of degradable polymer, metal (magnesium), ceramic and composite materials with respect to clinical application involving cortical/cancellous bone, dentin and enamel, and ligament, tendon and fascia. On the basis of mechanical property comparison, each class of densified material may be used to substitute cortical bone, may not be used to substitute cancellous bone, may be used to substitute enamel and dentin, may be used to substitute lower limb ligaments and tendons, and may be used to substitute selected upper limb and trunk ligaments and associated tissues. For relatively longer times of recovery from more severe orthopedic trauma, PLLA (poly L-lactic acid) and TMC (trimethyl carbonate) polymers, selected Mg alloys containing zinc (Zn), calcium (Ca) and/or rare-earth (RE) elements, or hydroxyapatite (HA) and tricalcium phosphate (TCP) as crystalline bioceramics apparently are most suitable. Mg alloys or composites have significant potential for clinical application where the ability to bear appropriate load at least in the initial stages of recovery prior to significant resorption and load transfer to new tissue is critical. However, there is no clear opinion at present regarding the toxicity levels of many alloying elements in Mg alloys, particularly concerning RE elements. There is also the potential issue of nanoparticle cytotoxicity concerning alloy nanocomposite degradation invivo. Compared to crystalline bioceramics, the higher index of bioactivity (IB) of amorphous glasses and glass ceramics reflects their superior ability to form a dense interphase and bond strongly with bone, despite their mechanical inferiority. The combination of bioceramic and biodegradable polymer is synergistic based on direct improvement of mechanical property and degradation resistance of the polymer, indirect reduction of foreign body interactions, and direct increase in toughness of the ceramic. Future directions of this field regarding developments on cellulose as a biodegradable material, bone tissue regeneration and engineering, stronger and more corrosion resistant and biocompatible magnesium alloy systems, applicable nanoparticles and nanotechnology, and soft tissue engineering such as vascular tissue engineering are also addressed.