Thermal stability of films The thermogravimetric analysis of native chitosan powder

Thermal stability of films
The thermogravimetric analysis of native chitosan powder, cel-lulose crystals and Ch/CMC (20)450film is shown in Fig. 3. It can be seen that cellulose powder suffers a drastic weightloss of nearly 76% in the temperature range of 200–380?C whereall cellulose is pyrolyzed. The drastic weight loss is attributable tothe liberation of volatile hydrocarbon from rapid thermal decom-position of cellulose chains. However, beyond 400?C there isgradual weigh loss probably due to the steady decomposition ofthe remaining heavy components mainly from lignin. The thermo-gram of chitosan powder showed a two stage degradation behavior.The range of ambient to 390?C. In the second phase, the weight lossobserved was almost 37% in the temperature range of 400–800?C.Such a two stage degradation of chitosan has also been reportedpreviously 25. The thermogram of Ch/CMC(20)450shows an inter-mediate degradation behavior. The degradation is a little faster thanthat of chitosan but is slow enough as compared to that of cellulosecrystals. More interestingly, the thermogram of Ch/CMC (20)450ismore similar to that of chitosan in nature, probably due to the rel-atively much higher content of chitosan in the film as comparedto cellulose content which is only 20% to that of chitosan. Finally,it is also noteworthy that presence of curcumin did not affect thethermal stability of the film because of very negligible content ofcurcumin as compared to the total mass of polymer (see TGA of curcumin in inset as obtained from the literature) .
.
Fig. 3. TGA of Ch, CMC and Ch/CMC(20)450 with curcumin TGA in inset.

Curcumin release study
Cellulose crystals, present within the chitosan films, serve asdiffusion barrier and they are expected to retard the releaseof curcumin from the films. The release profiles of Cur-loadedfilm samples Ch/CMC (0)450, Ch/CMC(10)450, Ch/CMC(20)450, andCh/CMC(30)450are shown in Fig. 6.It can be seen that the film sample Ch/CMC (0)450exhibits maxi-mum release while minimum release of curcumin was obtained forthe film sample Ch/CMC (30)450. This indicates that amount of Curreleased decreases with the increase in the cellulose content of thefilms. The amounts of Cur released from the samples Ch/CMC (0)450,Ch/CMC(10)450, Ch/CMC(20)450, and Ch/CMC(30)450in 36 h was365, 300, 270 and 140 _g, respectively. Here, it is also noteworthythat the total loading of curcumin in each film was around 450 _g.Such a lower curcumin release from these films is attributable to thefact that Cur has very poor solubility in water. It has been reportedthat Cur has a solubility of around 2.67 _g/ml at pH 7.3 . Many preclinical and clinical studies in mice, rats and humans have also revealed a low bioavailability of curcumin 18.

Fig. 6. Curcumin release profiles for various Cur-loaded film samples in the physiological fluid at 37?C.Antibacterial activity
The antibacterial action of sample curcumin loadedCh/CMC(20)450was investigated qualitatively by using zoneinhibition method. The results of antibacterial tests are shown in Fig. 9. The radius of zone developed was found to be 4 cm . Fig. 9. Antibactarial activity of film samples (a) Ch/CMC(20) and (b) Ch/CMC(20)450against E. coli.

Antifungal activity
The use of representative sample Ch/CMC(20)450as functionalwound dressings was also assessed by observing their antifun-gal against C. albicans and C. parapsilosis. Fig. 10(a) and (b) shows the typical antifungal test results of films by the disc method. Itwas found that the curcumin loaded film sample Ch/CMC(20)450demonstrated inhibition zones of nearly 3 and 3.5 cm for C. albicans,and C. parapsilosis, respectively. It is noteworthy here that the plainsample Ch/CMC(20) did not show any antifungal action, but a densepopulation of colonies was observed(data not shown). Althoughchitosan has fair reputation as an antimicrobial compound 45, butin the presence study we did not observe its antimicrobial action.This may probably be due to the fact that the chitosan used in the study had a higher molar mass.

Fig. 10. Antifungal activity of film samples (a) Ch/CMC(20)450against Candida albicans and (b) Ch/CMC(20)450 against Candida parapslosisConclusion
This study concludes that curcumin loaded Ch/CMC filmsdemonstrate controlled release of Cur, extended over a time periodof 36 h. The amount of curcumin released shows a negative depend-ence on the concentration of cellulose crystals dispersed within thechitosan matrix. The dispersed CMC produce additional physicalcrosslinks and retard the release rate. The films show fair antimi-crobial activities against bacteria and fungi.

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