Hydrolytic degradation of porous scaffolds for tissue engineering from terpolymer of l-lactide, ε-caprolactone and glycolide

Segmental terpolymer of l-lactide, ε-caprolactone and glycolide have been synthesized by ring-opening polymerization with the use of zirconium acetylacetonate as a biocompatible initiator. Porous scaffolds aimed at tissue engineering have been prepared from resulting terpolymer by solvent casting/particulate leaching technique. Sieved sodium citrate particles of 500–700 μm size have been used as porogens. The obtained scaffolds have been submitted to degradation in phosphate buffered saline (PBS) at 37 °C for 26 weeks and characterized as a function of incubation time by: Fourier transform infrared spectroscopy in the attenuated total reflection mode (FTIR-ATR), nuclear magnetic resonance (1H NMR), gel permeation chromatography (GPC) and scanning electron microscopy (SEM). The scaffolds start to degrade immediately after contact with PBS, as demonstrated by decrease in molecular weights (Mn and Mw). In the first stage (6 weeks in PBS) when the scaffolds are still dimensionally stable, the degradation is generally due to cleavage of ester bonds between glycolidyl (GG) and caproyl (Cap) groups present in chain sequences such as –GGCapCap–, –GGGCap–, as shown by 1H NMR. The analysis of FTIR spectra of the initial scaffolds and after 6 week immersion in PBS reveals a shift of the band attributed to C6-point double bond; length half of m-dashO vibrations and considerable changes in the shape of the bands attributed to C–O and C–O–C vibrations. These changes are due to chain-scission of polyester bonds in hydrolysis reaction. Subsequently, when the concentration of sequences containing glycol, glycolidyl and caproyl groups decreases, the influence of cleavage of polyester bonds between longer lactyl microblocks on the degradation increases gradually. As a result, two separate polymer fractions are formed.