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Team:METU-Gene/Collagen Sponge
From 2009.igem.org
Contents |
The release rate of bioactive hEGF from crosslinking collagen sponges
The purpose of this study was to prepare
recombinant human epidermal growth factor (rhEGF)
collagen sponges for topical applications and investigate
the effects of different types of crosslinked collagen
sponges as platforms for the controlled release of rhEGF.
The microstructure and the drug release rates of collagen
sponges were modified through treatment with different
types (glutaraldehyde (GTA), genipin and 1-ethyl-3-
(3-dimethylaminopropyl)carbodiimide (EDC)), different
concentrations of crosslinking agents and various preparation
conditions.
A good correlation was obtained for
in vitro release rates of rhEGF using the power model. The
crosslinked rhEGF collagen sponges showed a successful
delivery of rhEGF in bioactive form to stimulate cell
proliferation.
In addition, EGF can inhibit gastric
acid secretions in the stomach, enhance the proliferation
and keratinization of epithelial tissues and
accelerate wound healing. Due to its wound healing
properties, EGF is an attractive candidate for a therapeutic
drug. Studies have demonstrated that topical applications
of EGF promote wound healing in healthy and impaired
healing animals.
Since Carpenter and co-workers
first reported that for a mitogenic effect of EGF, a continuous
exposure of the target cells to EGF was required for
a minimum of 6–12 h, maintaining an effective topical
concentration at the wound site for a certain period of time
has become vital in the application of EGF. Indeed, we increased this continuous exposures by using Quaroum Sensing Mechanism of E.coli.
Collagen is a major constituent of the connective tissue
and is potentially a highly useful biomaterial. It has characteristics
that are suitable in medical application, such as
biodegradability and weak antigenicity, and it has been
used in resorbable surgical sutures, hemostatic agents, and
wound dressings for many years.
An in vitro controlled release study was conducted
to investigate the mechanism of recombinant human
epidermal growth factor (rhEGF) release from the different
degree of crosslinked collagen sponges.
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 release from collagen sponges
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.
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.
Conclusion
Crosslinked rhEGF-collagen sponges can be useful for
controlling the release of rhEGF. Results have shown that
upon increasing the amount of genipin or GTA or EDC, the microstructure of
collagen sponges becomes more rigid, and the hydrophilicity
is reduced, resulting in a decreased drug release rates
and an increased water uptake. A good correlation was
obtained for in vitro release rates of rhEGF from crosslinking
collagen sponges using the power model.
