Design of Cysteine Functional Polyesters through Michael Addition

The use of amino acid molecules to tailor polymer properties is gaining traction in the field of biomedical applications like tissue engineering. Following this trend, in this work, L-cysteine (Cys) and N-acetyl-L-cysteine (NAC) were used to modify linear polyesters of butenedioic acid, specifically polymaleates and polyfumarates, via thio-Michael addition. The covalent attachment of amino acids via their thiol groups was evidenced by NMR and FT-IR analysis. NMR-based calculations also revealed that polymaleates showed a higher degree of addition (AD) than polyfumarates, with nearly 100% AD achieved using Cys. Further characteristics of the thermal properties and solubility of the obtained adducts revealed that polymaleates are more promising for such applications, as they showed high thermal stability (> 200 ℃), a low glass transition temperature (< 0 ℃), and solubility in many organic solvents. The use of polyfumarate adducts is limited due to their insolubility in the majority of organic solvents. Considering the low molecular weight of the obtained polyesters, it was concluded that the obtained polymaleate adducts could not serve as standalone components of tissue engineering scaffolds. However, it did not exclude them from being used as modifiers for common polylactide or poly(ɛ-caprolactone) scaffolds, as they showed solubility in the same organic solvents.