Thermoresponsive, in situ cross-linkable hydrogels based on N-isopropylacrylamide: Fabrication, characterization and mesenchymal stem cell encapsulation

Abstract

Hydrogels that solidify in response to a dual, physical and chemical, mechanism upon temperature increase were fabricated and characterized. The hydrogels were based on N-isopropylacrylamide, which renders them thermoresponsive, and contained covalently crosslinkable moieties in the macromers. The effects of the macromer end group, namely acrylate or methacrylate, and the fabrication conditions were investigated on the degradative and swelling properties of the hydrogels. The hydrogels exhibited higher swelling below their lower critical solution temperature (LCST). When immersed in cell culture media at physiological temperature, which was above their LCST, hydrogels showed constant swelling and no degradation over eight weeks, with methacrylated hydrogels having higher swelling than their acrylated analogs. In addition, hydrogels immersed in cell culture media under the same conditions showed lower swelling as compared to phosphate buffered saline. The interplay between chemical crosslinking and thermally induced phase separation affected the swelling characteristics of hydrogels in different media. Mesenchymal stem cells encapsulated in the hydrogels in vitro were viable over three weeks and markers of osteogenic differentiation were detected when the cells were cultured with osteogenic supplements. Hydrogel mineralization in the absence of cells was observed in cell culture medium with the addition of fetal bovine serum and β-glycerol phosphate. The results suggest that these hydrogels may be suitable as carriers for cell delivery in tissue engineering.

A novel thermo-responsive hydrogel based on salecan and poly(N-isopropylacrylamide): Synthesis and characterization

“…In contrast, pure PNIPAm hydrogel (PN gel) was non-degradable when immersed in PBS at 37 • C [59]. The loss of the pure PNIPAm hydrogel (PN gel) might be mainly resulted by erosion instead of degradation after long term immersed in PBS at 37 • C. Similar result could be found in the literature [60]. For salecan/PNIPAm semi-IPNs, the notable weight loss might be accounted for the disintegration of primary semi-interpenetrating network and the diffusion of salecan chains.…”

Injectable dual-gelling cell-laden composite hydrogels for bone tissue engineering

“…MSCs were harvested from rat femora and tibiae of 6–8 week old Fisher 344 rats (Charles River Laboratories, Wilmington, MA) in accordance to approved protocols by the Rice Institutional Animal Care and Use Committee as previously described [10]. The MSCs were plated in 75 cm 2 tissue culture flasks at 37°C under humidified, 5% CO 2 atmosphere and cultured in osteogenic media without dexamethasone, which was replaced every 2–3 days.…”

“…Hydrogels (n = 2 halves) were processed at each timepoint for hematoxylin & eosin (H&E) and von Kossa histological staining as previously described [10, 13]. Hydrogels were fixed at 37 °C for 24 h in 10% buffe red formalin, dehydrated for 24 h in 70% ethanol, and stored in Histo-prep for another 24 h prior to freezing at −20 °C and cryosectioning into 10 μm slices.…”

Biodegradable, in Situ-Forming Cell-Laden Hydrogel Composites of Hydroxyapatite Nanoparticles for Bone Regeneration

“…11 Experimental levels for hydrogels and hydrogel composites analyzed in swelling ratio and compressive mechanical experiments are listed in Table 1. At the desired timepoints, the gels were removed from the PBS 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 and weighed (swollen weight).…”