Photopolymerized Thermosensitive Hydrogels: Synthesis, Degradation, and Cytocompatibility

Abstract

In situ forming hydrogels based on thermosensitive polymers have attractive properties for tissue engineering. However, the physical interactions in these hydrogels are not strong enough to yield gels with sufficient stability for many of the proposed applications. In this study, additional covalent cross-links were introduced by photopolymerization to improve the mechanical properties and the stability of thermosensitive hydrogels. Methacrylate groups were coupled to the side chains of triblock copolymers (ABA) with thermosensitive poly( N-(2-hydroxypropyl) methacrylamide lactate) A blocks and a hydrophilic poly(ethylene glycol) B block. These polymers exhibit lower critical solution temperature (LCST) behavior in aqueous solution and the cloud point decreased with increasing amounts of methacrylate groups. These methacrylate groups were photopolymerized above the LCST to render covalent cross-links within the hydrophobic domains. The mechanical properties of photopolymerized hydrogels were substantially improved and their stability was prolonged significantly compared to nonphotopolymerized hydrogels. Whereas non-UV-cured gels disintegrated within 2 days at physiological pH and temperature, the photopolymerized gels degraded in 10 to 25 days depending on the degree of cross-linking. To assess biocompatibility, goat mesenchymal stem cells were seeded on the hydrogel surface or encapsulated within the gel and they remained viable as demonstrated by a LIVE/DEAD cell viability/cytotoxicity assay. Expression of alkaline phosphatase and production of collagen I demonstrated the functionality of the mesenchymal stem cells and their ability to differentiate upon encapsulation. Due to the improved mechanical properties, stability, and adequate cytocompatibility, the photopolymerized thermosensitive hydrogels can be regarded as highly potential materials for applications in tissue engineering.

Photopolymerized Thermosensitive Poly(HPMAlactate)-PEG-Based Hydrogels: Effect of Network Design on Mechanical Properties, Degradation, and Release Behavior

“…As reported previously, this decrease in CP is due to an increased polymer hydrophobicity as a result of the introduction of methacrylate groups on the lactate side chains. 30,31 The variation of PEG molecular weight had no influence on the cloud point of the triblock copolymers M 20 P 4 , M 20 P 10 , M 20 P 20 , and M 20 P 40 ( Table 1). The molecular weights of the polymers, calculated according to 1 H NMR and measured by GPC are listed in Table 1.…”

Scaffolds in Skeletal Repair

“…Various carriers such as guanidine-extracted DBM matrix, polymeric or ceramic implants, bone grafts, or human recombinant osteogenic protein-1 containing growth factors were tested and shown to result in induced bone repair in various systems [ 7,[106][107][108] . IGF-1 incorporated into type I collagen gel enhanced nasal defects healing, and TGF-b incorporated into acid gelatin hydrogel enhanced healing of rabbit skull defects [109][110][111] as well as in others [112][113][114]. In order to further increase the osteogenic potential of scaffold-based implants, a cell therapy approach is used to incorporate osteoprogenitor cell derived from bone marrow stem cells (MSCs) in the scaffold to enhance bone repair.…”

Rapid Photocrosslinkable Thermoresponsive Injectable Polyphosphazene Hydrogels

“…However, the use of hydrogels is often limited in biomedical applications because it requires surgical implantation. [13] Communication T. Potta, C. J. Chun, S. Rapidly photocrosslinkable and thermosensitive polyphosphazene polymers have been prepared to overcome the limitations associated with long UV exposure. Short UV exposure on the thermosensitive gels under mild conditions leads to quick photocrosslinking of the acrylate groups in the polymer network, and results in a dual crosslinked network with enhanced mechanical strength.…”

“…[13,14] Through these systems, various bioactive molecules, such as growth factors or cells, can be delivered with minimal invasion. The components to be delivered can be mixed with a liquid macromer solution and be injected subcutaneously, and then the surface of the skin can be exposed to the UV or visible light.…”