Abstract

Polymer hydrogels are ideal scaffolds for both tissue engineering and drug delivery. A great advantage of poly(amino acid)-based hydrogels is their high similarity to natural proteins. However, their expensive and complicated synthesis often limits their application. The use of poly(aspartic acid) (PASP) seems an appropriate solution for this problem due to the relatively cheap and simple synthesis of PASP. Using amino acids not only as building blocks in the polymer backbone but also as cross-linkers can improve the biocompatibility and the biodegradability of the hydrogel. In this paper, PASP cross-linked with cystamine (CYS) and lysine-methylester (LYS) was introduced as fully amino acid-based polymer hydrogel. Gels were synthesized employing six different ratios of CYS and LYS. The pH dependent swelling degree and the concentration of the elastically active chain were determined. After reduction of the disulfide bonds of CYS, the presence of thiol side groups was also detected. To determine the concentration of the reactive cross-linkers in the hydrogels, a new method based on the examination of the swelling behavior was established. Using metoprolol as a model drug, cell proliferation and drug release kinetics were studied at different LYS contents and in the presence of thiol groups. The optimal ratio of cross-linkers for the proliferation of periodontal ligament cells was found to be 60−80% LYS and 20−40% CYS. The reductive conditions resulted in an increased drug release due to the cleavage of disulfide bridges in the hydrogels. Consequently, these hydrogels provide new possibilities in the fields of both tissue engineering and controlled drug delivery.

Highlights

  • The number of medical applications of polymer hydrogels increased substantially during the last decades due to their similarity to soft tissues [1,2,3]

  • We presented the synthesis of poly(aspartic acid) (PASP) and several preparation methods of PASPbased hydrogels based on cross-linking with diaminobutane (DAB) and CYS in two-step reactions [21,22,25]

  • We showed that MG-63 cells can proliferate on PASP-based hydrogels [25], which led to the idea that similar fully amino acid-based gels may support the growth of untransformed cells

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Summary

Introduction

The number of medical applications of polymer hydrogels increased substantially during the last decades due to their similarity to soft tissues [1,2,3]. Hydrogels can be used as drug delivery systems [4], implants [5,6], coatings [7,8] or scaffolds for tissue engineering [2,3,9,10]. Besides these stimuliresponsive properties, the chemical and physical structure, the mechanical properties [10] as well as biocompatibility and biodegradability are fundamental features of polymers developed for numerous medical applications [11,12]

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