Introduction to Chitosan Hydrogels

Synthesis and Evaluation of pH- and Temperature-Responsive Chitosan-p(MAA-co-NIPAM) Hydrogels

• Chitosan-poly(methacrylic acid-co-N-isopropylacrylamide) [chitosan-p(MAA-co-NIPAM)] hydrogels synthesized via emulsion polymerization are biocompatible, biodegradable, and multi-responsive, making them suitable for drug delivery systems.
• Copolymerization of MAA and NIPAM with chitosan forms the hydrogel.
• FTIR spectroscopy confirms stable chitosan-based hydrogel formation, with PNIPAM coating the outer surface.
• Chitosan and PMAA contribute to the hydrogel's zeta potential.
• Chitosan controls hydrogel shrinkage beyond human body temperature.

Introduction to Hydrogels

• Hydrogels absorb water, responding to physical, chemical, or biochemical stimuli.
• They are used as drug carriers for extended periods in the body.
• Chitosan, a natural polymer, is biocompatible and biodegradable.
• Modifying chitosan with cross-linking agents enhances pH and temperature sensitivity, improving its drug release properties.
• Chitosan cross-linked with PNIPAM and PMAA separately show low toxicity and efficient drug release profiles, with PNIPAM's sol-gel transition at body temperature.

Experimental Procedures

• Materials like NIPAM, MBA, chitosan, Span 80, acetic acid, and ammonium persulfate (APS) were used.
• Chitosan-p(MAA-co-NIPAM) hydrogels synthesized via free-radical emulsion polymerization.
• Initial synthesis showed inhomogeneous, aggregating particles; SPAN80 addition was tried.
• Optimized synthesis for homogeneity involves carefully controlled reaction times.
• Samples characterized using FTIR spectroscopy, FESEM, zeta potential, and dynamic light scattering techniques.
• Different reaction times (30, 60, 120, 180 min) studied for structural and functional characterization.

Hydrogel Characterization

• FESEM: Morphology of freeze-dried hydrogels examined (irregular shape at early stages; homogeneity improved later).
• FTIR: Functional group identification in hydrogels and chitosan samples.
• Characterization of PMAA (1655-1598 cm-1) and PNIPAM (1638-1619 cm-1) components; cross-linking evident.
• 13C NMR: Validation of structural components (PMAA, PNIPAM, chitosan). Absence of unlinked alkene groups confirmed successful incorporation.

Response to pH

• Hydrogel swelling/de-swelling behavior studied across different pH environments at 37°C (human body temperature).
• Increasing pH generally led to more swelling.
• Chitosan's protonation/deprotonation behaviour, along with PMAA, influenced the swelling/de-swelling at various pH.

Response to Temperature

• Hydrogel's volume phase transition temperature (VPTT) under different reaction times at pH 7.4.
• Prolonged reaction times result in higher VPTT (~34°C).
• PNIPAM's hydrophobic characteristics drive temperature response; higher crosslinking prevents shrinkage as temperature rise.
• Lower LCST means higher swelling at lower temperatures.

Zeta Potential Studies

• Zeta potential measurements across various pH environments at 37°C to study stability.
• Positive values at low pH indicate potential of -NH3+ on chitosan.
• Negative values at higher pH indicate deprotonation of -COOH groups on PMAA.

Conclusion

• Emulsion polymerization successfully synthesized chitosan-p(MAA-co-NIPAM) hydrogels.
• Hydrogels' properties (swelling behavior, stability) noticeably influenced by reaction time.
• Optimal reaction time for drug delivery application identified.
• Suitable for use in drug delivery due to pH and temperature sensitivity.