4.1 Chitosan cross-linked hydrogels formulation
For the chitosan hydrogel, at higher concentrations (above 5%), chitosan dissolves partially in lactic acid. This phenomenon can be accredited to lack of lactic acid concentration (i.e. 2%). Increase to 5% in the concentration of lactic acid, allows for the more chitosan (up to 10%) to be dissolved. But an increase in concentration of lactic acid leads to an increase in toxicity, which reduces the biocompatibility of the hydrogel. Hence, the chitosan concentration used for chitosan hydrogels was kept at 5% for all further analysis.
In the composite hydrogel, the concentration of gelatin was higher than chitosan to obtain more gelatin-like properties, due to better stability and compactness of gelatin hydrogels. Further, gelatin hydrogels rely on sub-zero temperatures, which keeps the structural moiety of hydrogels intact. The genipin cross-linked hydrogels were prepared as shown in Fig. 3.1. Both hydrogels similar in their color appearance but have different mechanical properties due to the addition of gelatin in the composite hydrogel. The biopolymeric genipin cross-linked hydrogels display a dark blue color. The general reason for any material to impart a particular color is based on how a particular color is reflected maximum with respect to the other colors in the visible spectrum. In this case, genipin, the cross-linking substance, imparts the color to the hydrogel. Therefore, it can be said that genipin reflects dark blue maximum in the visible spectrum.
4.2 Swelling Analysis: The swelling index of the cross-linked hydrogels follow the same swelling pattern, but with a huge difference amongst their values. The general swelling pattern can be observed from Fig. 3.2 (a & b) for the hydrogels.
For the hydrogels, initially, the swelling index rapidly increases up to a certain amount of time, and then increases slightly before it becomes constant and stabilizes. To obtain a controlled release of bioactive agents, it is important to have a stabilized swelled hydrogel. Therefore, the genipin cross-linked hydrogels can produce the output required for an efficient drug delivery system.
4.3 Compression (Mechanical) Analysis: The mechanical compression was computed in terms of the compressive modulus of the cross-linked hydrogels. The chitosan-based hydrogels showed a higher compressive strength than the composite hydrogels. The interpretation of having a lower mechanical compression may be due to the excessive load that gelatin and chitosan induce over each other, whereas, in the case of only chitosan, that extra load is reduced by a large amount. Hence, when an external load is applied to the hydrogels, the composite hydrogel releases its stress built up within its structure and reaches its breaking point rapidly but the chitosan hydrogel take longer for the stress to build up within its structure. Table 3.1 shows the compressive modulus values for the hydrogels.
Table 4.1
Compressive modulus values for Genipin cross-linked hydrogels.
Sample Composition
|
Compressive Modulus (Mean ± SD)
|
Chitosan + Genipin
|
0.1539 ± 0.03
|
Chitosan + Gelatin + Genipin
|
0.0347 ± 0.01
|
4.4 SEM Analysis: The SEM microstructures present the morphology of the genipin cross-linked hydrogels. The morphology shows how each of the hydrogels blend into each other to form a complex structure. The SEM results for the genipin cross-linked hydrogels are as given below in Fig. 3.4 (a & b).
Well-defined boundaries can be observed in the chitosan hydrogels, whereas, in the composite hydrogels, there is an overlapping exhibited. As explained in the earlier sub-section, the stress developed in the composite hydrogel is much higher, which allows it to reach failure faster. Therefore, the overlapping displayed in the SEM microstructure compliment the compression values.
4.5 In Vitro Drug Release Profile:
The drug release profile gives an impression of how the drug is released in a controlled manner, and the region at which it gets saturated. The drug release profile postulates an understanding of drug diffusion at a controlled rate with time. The absorbance values obtained from the spectrophotometry imply that the amount of drug diffusion gets saturated within a period of 24 hours. Initially, there is a burst release within the first 2–3 hours and later, it gets saturated as time increases. Hence, chitosan and composite hydrogels are excellent candidates for drug delivery systems. Finally, while analyzing it under the spectrophotometer the concentration of Indomethacin increases with time.
Table 4.2
% Release values of Indomethacin from chitosan hydrogels cross-linked with 1% genipin (Refer to Annex 1)
Time (Hours)
|
% Release (Mean ± SD) with chitosan
|
% Release (Mean ± SD) with composite
|
1
|
15.35 ± 1.44
|
7.91 ± 1.2
|
2
|
18.95 ± 1.44
|
10.12 ± 0.96
|
3
|
22.89 ± 0.96
|
13.31 ± 0.96
|
4
|
27.95 ± 1.2
|
17.25 ± 0.96
|
5
|
32.62 ± 1.51
|
20.55 ± 0.72
|
22
|
39.91 ± 1.68
|
23.09 ± 0.96
|
23
|
41.85 ± 0.96
|
24.63 ± 0.72
|
24
|
43.10 ± 0.72
|
25.41 ± 0.48
|