Effect of Block Length and Stereocomplexation on the Thermally Processable Poly(ε-caprolactone) and Poly(Lactic acid) Block Copolymers for Biomedical Applications

Abstract

The current research concentrates on the synthesis of linear block copolymers with their backbone consisting of hard and soft segments, that is, poly­(L-lactic acid) (PLLA)/ poly­(D-lactic acid) (PDLA) and poly­(ε-caprolactone) (PCL), with the detailed investigation of the effect of block length on the thermal, mechanical, and crystallization behavior followed by their processing and biocompatibility evaluation. In the current work, sequential ring opening polymerization has been employed wherein PCL is used as a macroinitiator for the synthesis of diblock (PCL-PDLA and PCL-PLLA) and stereotriblock copolymers (PCL-PLLA-PDLA) of targeted molecular weight, which is confirmed by 1H NMR spectroscopy. The block length of PCL, in the case of diblock copolymer, is fixed; however, that of PLLA or PDLA is varied, and the enantiomeric blends thereof are made to achieve the merits of stereocomplexation. The length of the individual blocks is the same in the case of stereotriblock copolymer. The presence of two crystalline domains is manifested from differential scanning calorimetry and thermogravimertric analysis. An interesting improvement in the mechanical properties is observed upon increasing the block length of PDLA/PLLA in the block copolymer system which may be ascribed to the confined crystalliztion of PCL in the microdomain structure. Additionally, the synthesized materials are found to support the adhesion of MG-63 (human bone osteoscarcoma) cells as determined from in vitro studies indicating their potential in bone repair and regeneration. Further, the block copolymers possessing superior mechanical properties are thermally processed by injection molding to fabricate representative orthopedic fixation devices such as cancellous and cortical bone screws. Eventually, the thermo-mechanical stability of the cancellous bone screw made from the synthesized block copolymer is presented as compared to that made from the commercial PLA at the sterilization temperature of the biomedical devices.

Recent Developments in the Crystallization of PLLA-Based Blends, Block Copolymers, and Nanocomposites

“…The polymer synthesis method is described in Ref. [12]. The molecular weight information is reported in Table 2.…”

“…The highest elongation at break was found for the specimen 10CL-30D. To understand such an DSC thermograms of (a) neat PCL, neat PDLA, and PCL-PDLA diblock copolymers and (b) enantiomeric diblock copolymer blends and trisb copolymer (adapted from reference [12] with a permission).…”

“…The judgment of morphology was uncertain due to the presence of only a first order peak. For the 10CL-30D specimen, there may be the Representative data for stress vs. (%) Strain of (a) homopolymers and diblock copolymers; (b) diblock blends and trisb copolymer (adapted from reference [12] with a permission).…”

“…In such a situation, the crack propagation of glassy PDLA matrix is terminated at the PCL microdomains when the specimen is drawn which could be attributed to amorphous PCL phase (rubbery domain) at room temperature. Also, the PCL block chains are much easier Lorentz-corrected scattering intensity vs. q of (a) homopolymers and diblock copolymers and (b) enantiomeric diblock copolymer blends and trisb copolymer (adapted from reference [12] with a permission).…”

“…In this chapter, we review the recent developments [7][8][9][10][11][12][13][14][15] of crystallization of PLLAbased blends, block copolymers and nanocomposites. This chapter contains four sections.…”