This study has been performed by Pr. Lerouge Lab (The Canada Research Chair in Biomaterials and Endovascular Implants) and published in the JOURNAL OF BIOMEDICAL MATERIALS RESEARCH B: APPLIED BIOMATERIAL.
Sample weighing is the most used method to characterize degradation of gels even if this technique is not directly measuring the actual state of the network that forms a degraded gel. Being able to measure the mechanical properties of a degraded gel would be an interesting way to characterize the resorption of the material.
It has been proposed here to use the ElastoSens Bio to measure during 7 days the viscoelastic changes of chitosan hydrogels when exposed to lysozyme. Tow different compositions of chitosan have been tested: 3 replicates with a high degree of deacetylation and 3 replicates with a low degree of deacetylation. For each type of chitosan, 3 control samples (not exposed to lysozyme) were monitored over the same period of time. The same testing protocol has been conducted in parallel in order to measure the changes on samples weight.
It is important to note that the same samples were mechanically tested on the ElastoSens Bio during the complete duration of the study (7 days). The gel samples were kept into the sample holders of the ElastoSens Bio during 7 days but out of the instrument between the tests. The enzymatic and control (PBS) solutions were also maintained in the sample holders on the top of the gels in order to optimize their diffusion inside the samples. The sample holders were kept into an incubator (at 37℃) between the tests and loaded into the instrument at days 1, 3, 4, 5, 6 and 7 to perform single time measurements.
It has been proposed here to use the ElastoSens Bio to measure during 7 days the viscoelastic changes of chitosan hydrogels when exposed to lysozyme. Tow different compositions of chitosan have been tested: 3 replicates with a high degree of deacetylation and 3 replicates with a low degree of deacetylation. For each type of chitosan, 3 control samples (not exposed to lysozyme) were monitored over the same period of time. The same testing protocol has been conducted in parallel in order to measure the changes on samples weight.
It is important to note that the same samples were mechanically tested on the ElastoSens Bio during the complete duration of the study (7 days). The gel samples were kept into the sample holders of the ElastoSens Bio during 7 days but out of the instrument between the tests. The enzymatic and control (PBS) solutions were also maintained in the sample holders on the top of the gels in order to optimize their diffusion inside the samples. The sample holders were kept into an incubator (at 37℃) between the tests and loaded into the instrument at days 1, 3, 4, 5, 6 and 7 to perform single time measurements.
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The figure above shows the evolution of the shear elastic modulus (G' ) of the two chitosan formulations when they are exposed or not to enzymes. The degradation process appears clearly on the curves. The gels exposed to enzymes exhibit a clear decrease on elastic modulus (between -50% and -70%) over 7 days compared to the control samples that are mechanically stable. An interesting observation is that the two formulations exhibit different degradation rates. The chitosan formulation with a high degree of deacetylation degrades more slowly and starts degrading 3 days after the formulation with a low degree of deacetylation.
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Surprisingly, the left figure above shows that the gels weight did not changed over 7 days even if the gels were exposed to enzymes. The weight of the degraded gels did not changed during the degradation process even if the visual observation of the gels (right figure above) shows clearly that the enzymes were mechanically degrading the gel networks.
The ElastoSens Bio is a suitable tool to measure the degradation of hydrogels over long periods of time. The ElastoSens Bio provides more significant statistical results thanks to its capability to non-destructively measure the mechanical properties of the same sample during a long study. The mechanical characterization of degradation processes appears to be a good way to adapt the chemical formulation of hydrogels in order to tune the degradation rates. This is especially useful for the delivery of drugs by the mean of hydrogels.
The ElastoSens Bio is a suitable tool to measure the degradation of hydrogels over long periods of time. The ElastoSens Bio provides more significant statistical results thanks to its capability to non-destructively measure the mechanical properties of the same sample during a long study. The mechanical characterization of degradation processes appears to be a good way to adapt the chemical formulation of hydrogels in order to tune the degradation rates. This is especially useful for the delivery of drugs by the mean of hydrogels.
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