Introduction: There is a need for materials to improve outcomes following trauma to soft tissue associated with numerous conditions including combat injury, tumor excision or diabetes. Hydrogels with anti-inflammatory properties are potential candidate materials for such clinical indications, and may aid in the healing process. Methylcellulose (MC) hydrogels have been shown to serve as stable injectable fillers[1]-[3], but do not possess inherent wound healing properties. Curcumin is an active component of the spice turmeric with multiple reported therapeutic attributes, including anti-inflammatory and anti-cancer activity[4]. In this study, curcumin was incorporated into injectable MC hydrogels, and the mechanical and physical properties of the gels were investigated together with the curcumin release profile.
Materials and Methods: A combination of MC (14kDa:41kDa, 1:1) polymer methacrylated at ~9% was prepared as previously described[1]-[3]. Methacrylated MC was dissolved in PBS at concentrations of 1%, 2%, and 3% (wt/vol) and combined with ammonium persulfate (APS) and ascorbic acid (AA) free-radical initiators at 10 mM each, and cast in cylindrical molds using a dual-barrel syringe. Curcumin-loaded gels (MCcurc) were prepared with 50 µg/mL curcumin. Confocal microscopy was used to visualize the curcumin-encapsulated hydrogel network. The equilibrium Young’s modulus (Ey) was measured in unconfined compression and the equilibrium weight swelling ratio and other physical properties (mesh size, crosslinking density) were calculated as previously[1],[2],[5]. Cytocompatibility was assessed by co-culture with human dermal fibroblasts based on DNA measurements and live/dead staining. Curcumin release was measured from gels immersed in PBS at 37℃. The concentration of curcumin was quantified fluorometrically at an excitation wavelength of 450 nm and emission wavelength of 535 nm[6]. The diffusion coefficient was measured based on prior studies[7] and gels were imaged with a stereomicroscope to visualize the temporal change in curcumin intensity.
Results and Discussion: Curcumin incorporated into the MCcurc gels was uniformly distributed throughout the polymer network, as shown via confocal imaging.
Consistent with the theory of rubber elasticity and with previous work, swelling properties displayed an inverse relationship to macromer concentration; MCcurc,1% hydrogels exhibited the highest swelling ratio and mesh size, and lowest crosslinking density, which was significantly different from the MCcurc,2% and MCcurc,3% gels. By varying macromer concentration, the Ey ranged between 2.06±1.60 and 4.32±1.15 kPa, for MCcurc,2% and MCcurc,3% hydrogels, and 4.71±2.15 and 8.93± 3.04 kPa for MC2% and MC3% gels, respectively. These values were on par with human adipose tissue[8] (MC1% gels were too weak for mechanical testing). Live/dead staining showed robust cell viability, which was confirmed by DNA content of the cells in co-culture with MC or MCcurc gels. Cumulative release was monitored for 2 weeks, with the bulk of curcumin released by 48 hours. Release was lowest in the MCcurc,3% gels, which also displayed the significantly lowest diffusion coefficient.
Conclusion: Taken together, curcumin-loaded MC hydrogels polymerized using a redox crosslinking system have potential for various clinical indications requiring soft tissue reconstruction. The therapeutic effect of curcumin delivery from MC hydrogels will be investigated in the future.
Acknowledgement: Dr. Lane Gilchrist and Eric Fried for assistance with confocal microscopy
References:
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