Photopolymerization of Hybrid Hydrogels

Photopolymerization of Methacrylated Chitosan/PNIPAAm Hybrid Hydrogels

• A series of hybrid hydrogels were designed using glycidyl methacrylated chitosan (CS-GMA) and N-isopropylacrylamide (NIPAAm) via photopolymerization.
• Hydrogels were characterized using FT-IR, DSC, and optical transmittance.
• Scanning electron microscopy (SEM) examined the hydrogel morphology.
• Swelling experiments showed pH and temperature sensitivity in the hybrid hydrogel.
• Acid orange 8 (AO8) and 5-fluorouracil (5-Fu) were used as model drugs to test release profiles.
• Hydrogel composition and buffer pH significantly affected drug release.

Synthesis of Glycidyl Methacrylated Chitosan (CS-GMA)

• Chitosan (Mw = 200 kDa, degree of deacetylation = 88%) reacted with glycidyl methacrylate (GMA) via epoxy ring opening reaction in acetic acid at 60°C.
• The degree of substitution (DS) was approximately 10.4%.
• This was determined using 1H NMR.

Preparation of CS-GMA/PNIPAAm Hybrid Hydrogels

• CS-GMA and NIPAAm were photopolymerized using a UV-light.
• Various compositions were prepared, each with varying amounts of CS-GMA and NIPAAm.
• The hydrogels were immersed in water to leach residues before further measurements.

FT-IR Analysis

• FT-IR spectra of CS-GMA, PNIPAAm, and a hybrid hydrogel (Sample C2) were analyzed.
• Key peaks indicated the presence of chitosan, indicating GMA incorporation.
• Also showed presence of amide I, amide II, and isopropyl groups (from PNIPAAm).
• The peaks due to isopropyl group displayed lower intensity for the hybrid hydrogel, suggesting crosslinking.

Phase Transition Studies

• DSC thermograms showed a slight increase in the lower critical solution temperature (LCST).
• The LCST was higher in the hybrid hydrogel (34.7°C) than in pure PNIPAAm hydrogel (33.4°C).
• Optical transmittance measurements supported pH/temperature sensitivity observations.
• Lower CS-GMA concentration hydrogels showed more obvious phase transition.

Swelling Kinetics and Equilibrium Swelling Ratio (SReq)

• Swelling kinetics were studied gravimetrically.
• Swelling ratios increased with time but reached equilibrium.
• Hybrid hydrogel swelling rates were faster than PNIPAAm hydrogels.

pH and Temperature Dependence of Swelling

• Swelling ratio was found to depend on both pH and temperature.
• At lower pH (acidic), swelling was greater than at higher pH (basic).
• At higher temperature, swelling was lower due to hydrophobic interactions.
• The hybrid hydrogel's swelling behaviour showed pH-dependence due to ionization of amine groups in chitosan.

Drug Release Analysis

• AO8 and 5-Fu were used as model drugs.
• Drug release was affected by pH.
• Release rates varied based on CS-GMA composition.
• Initial burst release followed slower release for some samples.