N-Hydroxysuccinimide Bifunctionalized Triblock Cross-Linker Having Hydrolysis Property for a Biodegradable and Injectable Hydrogel System

Abstract

The design of biocompatible, degradable, and injectable hydrogel has been attractive for achievement of safe and efficient tissue engineering. Herein, we designed a N-hydroxysuccinimide (NHS) ester-terminated ABA triblock copolymer composed of poly­(ethylene glycol) (PEG) as hydrophilic A segments and poly­(dl-lactide) (PLA) as B segment having hydrolysis property (NHS-PEG-b-PLA-b-PEG-NHS) to be a cross-linker of polymer segments having amine groups for facile construction of injectable and degradable hydrogel. The PLA domain, which is widely accepted hydrolyzable segments, is inherently hydrophobic and simple introduction of the NHS group on the ends of PLA would not have high reactivity in aqueous milieu to construct injectable hydrogel. Thus, in this design, hydrophilic PEG was introduced as A segments to increase the reactivity of NHS groups at the ends of linkers by increasing the mobility. To demonstrate the property as a cross-linker for constructing degradable and injectable hydrogel, carboxylmethyl chitosan (CH), which is a polymer segment having amine groups, and NHS-PEG-b-PLA-b-PEG-NHS solutions were mixed to form the hydrogel (CH/PEG–PLA-PEG) under physiological condition. The formation of CH/PEG–PLA-PEG hydrogel proceeded within minute-order period after mixing the solutions, suggesting NHS-PEG-b-PLA-b-PEG-NHS is applicable to the cross-linker for construction of injectable hydrogel system with time-dependent gelation property. Degradation of the obtained CH/PEG-PLA-PEG hydrogel was observed, whereas that of CH/PEG, which was prepared from NHS-PEG-NHS and CH, was not observed, appealing the degradation property of the CH/PEG-PLA-PEG hydrogel based on hydrolysis of the PLA domain. Furthermore, chondrocytes embedded in CH/PEG-PLA-PEG hydrogels promoted collagen synthesis compared to CH/PEG. These demonstrations indicate the designed NHS-PEG-b-PLA-b-PEG-NHS is a promising cross-linker to construct the injectable and degradable hydrogel and eventually promote hydrogel performance as a tissue regeneration scaffold.

Enhanced function of chondrocytes in a chitosan‐based hydrogel to regenerate cartilage tissues by accelerating degradability of the hydrogel via a hydrolysable crosslinker

“…To investigate the degradation behavior of CH/PEG and CH/PEG‐PLA‐PEG as a cell culture scaffold, weight loss of the hydrogels with encapsulating chondrocytes was traced. Note that this hydrogel system showed nontoxicity and good cell dispersion during the gelation process . CH/PEG‐PLA‐PEG showed higher weight loss compared to CH/PEG in all the periods [Figure (a)].…”

“…In our previous report, we confirmed that the mixtures of CH solution with NHS–PEG–NHS and NHS‐PEG‐ b ‐PLA‐ b ‐PEG‐NHS solutions formed hydrogels within minutes through the reaction of the amine group of CH and the succinimide group of the crosslinkers . CH/PEG‐PLA‐PEG showed accelerated degradability in physiological conditions compared to CH/PEG due to the hydrolysis property of the PLA segment.…”

“…Bifunctionalized degradable triblock crosslinker, NHS‐PEG‐ b ‐PLA‐ b ‐PEG‐NHS, was synthesized as described in previous report . Briefly, THP‐PEG‐ b ‐PLA‐OH was synthesized by ring‐opening polymerization of dl ‐lactide using THP‐PEG‐OH as an initiator.…”

“…The final product was determined to have 5380 Da in M n . As for synthesis of NHS–PEG–NHS, OH‐PEG‐OH was reacted with DSC as described in previous report and the obtained NHS–PEG–NHS was determined to have 4580 Da in M n .…”

“…As for the crosslinker, we previously developed an N ‐hydroxysuccinimide (NHS) bifunctionalized ABA triblock copolymer composed of poly(ethylene glycol) (PEG) as the A segment and poly( dl ‐lactide) (PLA) as the B segment (NHS‐PEG‐ b ‐PLA‐ b ‐PEG‐NHS). We demonstrated the triblock property of the crosslinker to form a degradable hydrogel with the polymer segments containing amines, including a CH segment (Scheme ) . We assumed that the comparison between the chondrocyte‐specific functions of the chondrocytes cultured in a CH‐based hydrogel using NHS–PEG–NHS (CH/PEG) and NHS‐PEG‐ b ‐PLA‐ b ‐PEG‐NHS (CH/PEG‐PLA‐PEG) would fairly reflect the effect of the accelerated degradation of the hydrogel on chondrocyte function.…”