Role of aluminum monostearate on heat treated-chitosan sponges properties

Abstract

Heat treatment can be employed to modify properties such as biocompatibility and degradation rate of chitosan-based materials. However, heat treatment generally has effect on worsening of physical properties of the biomaterials. Our previous study indicated that fatty additive; aluminum monostearate (Alst), could improve thermal stability of chitosan sponges. Aim of this study is to investigate an effect of amount of Alst on physicochemical properties of chitosan sponges treated by different heat treatment methods. Two methods of heat treatment including moist heat (autoclave at 121°C, 15 psi for 5 minutes) and dry heat (vacuum heat at 110°C for 24 hours) were employed to treat chitosan sponges fabricated by lyophilization technique. Lactic acid solution (2% w/v) was used as solvent of chitosan. Alteration of functional group interaction of the prepared chitosan sponges including untreated, moist heat treated and dry heat treated systems was characterized by using FT-IR spectroscopy. Other physical properties, e.g. water sorption and erosion, morphology and mechanical property of the sponges were evaluated. FT-IR spectra analysis indicated that dry heat treatment created a formation of amide bond between carboxylate groups of side chain molecules; lactate or stearate, and ammonium groups of chitosan. The similar result was observed from moist heat treatment but some peak that indicated hydrolyzed stearic acid was found at 1700 cm-1 in the IR spectra. Increment of Alst had influence on decrement of water sorption and erosion of the prepared sponges both untreated and heat treated systems. Moist heat treated sponges had more rigidity than dry heat treated sponges since moist heat treatment evoked shrinkage of sponge structure whereas dry heat treatment was not clearly affected alteration of sponge structure. Changes of physical appearance of the sponges treated by moist heat treatment was lesser observed in the system containing higher amount of Alst. This result indicated that Alst could improve thermal stability of chitosan sponge during moist heat treatment. Both heat treatment methods led to reduction of aqueous solubility of the prepared sponges. Dry heat treated sponges significantly had higher percent of water sorption and erosion than moist heat treated sponges. In conclusion, Alst could reduce physical changes of chitosan sponges from heat treatment. Moist heat treatment had higher effect than dry heat treatment on changes of the physical properties of the chitosan sponges.