Characterization of the rhEGF-collagen sponges
[1]Determination of the degree of crosslinking
The crosslinking degree could then be obtained from the differences between the absorbance values before and after
the crosslinking. The equation is as follows:
where s is the sample and ncl is non-crosslinked.
[2]Water-binding capacity
The water uptake of the collagen sponges was calculated using the following equation:
where Wd is the weight of the dry sponge and Ws is the weight of the swollen sponge.
[3]Release kinetics
To determine the possible release mechanism, drug release from collagen sponges was fitted to the following power model:
where Mt/M is the fractional drug release percentage at time t, and k is a constant related to the properties of the
drug delivery system and n is the diffusional exponent which characterizes the drug transport mechanism.
Recombinant hEGF released from collagen sponges
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Figure 1 shows the release profiles of rhEGF from collagen sponge at 37 �C in PBS with/without collagenase solution.
Chih-Hui Yang in his study supposed that under the in vitro non-degradation conditions, rhEGF was initially released by diffusion. Generally speaking, since collagen is enzymatically degraded, low final release values are expected in the absence of any enzymes. Therefore, collagenase was employed for the model of the in vitro rhEGF release study. In project, this case is also valuable.
Therefore, the influence of the types and the concentrations of the crosslinking agents and the preparation conditions on the structures and characteristics of collagen sponges, and the rhEGF release from collagen sponges were compared in his study.
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The rhEGF release patterns from collagen sponges
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Three different types of crosslinking agents, GTA, genipin and ECD were used to prepare crosslinked collagen sponges. The rhEGF release patterns from collagen sponges are shown in Figure 2.
The drug release rate from crosslinked collagen sponges treated with EDC was the fastest, followed by collagen sponges treated with genipin and GTA, respectively. The EDC crosslinked collagen showed no release control effect,
which was probably due to the fact that EDC increased the water-solubility and lowered the viscosity of collagen (data
not shown). GTA crosslinked collagen showed the most potent release control effect than the other two (EDC and genipin). However, since we want controlled and orderly release system which will be improved our transgenic bacteria, we used genipin for formation our cellulose Wound Dressing layer in three different types of crosslinking agents, GTA, genipin and ECD.
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