(17b) Evaluation of Catechol Use As a Crosslinker and to Functionalize Chitosan to Produce a Bone Adhesive with Aqueous Adhesion
Our previous works have shown that for comminuted fracture treatment, the use of a biocomposite based on chitosan, hydroxyapatite, and glutaraldehyde can be used as an adhesive holding a TBS of 0.2MPa. Nevertheless, while testing this hydrogel under aqueous conditions it was evident that the adhesion property was lost. As a solution we propose the implementation of catechol in order to functionalize and crosslink the gels to allow different chemical interactions with the bone mineral and organic matter.
The adhesion mechanism proposed in previous studies depended heavily on the interaction of aldehydes present in the crosslinker to the amino groups on tissue. Nevertheless, when in contact with water, aldehyde groups hydrolyze and as a result there is no interaction to (with) the tissue. Additionally, since glutaraldehyde forms immine links to chitosan, the crosslinking reaction can be reversed under aqueous conditions. Therefore cathecol was proposed as a solution. This structure is a benzenediol functional group and it is used on different applications since it is the responsible for the adhesion of mussels to organic and inorganic surfaces at sea on strong turbulence conditions[10, 11].
In this study, chitosan is functionalized with catechol for different reaction times of 15, 45, 90, 180 and 360 min. This functionalized compounds are characterized by themselves and used to form adhesives. It is determined that it is not possible to produced hydrogels with this polymer. As a result, mixtures between chitosan and catechol-chitosan were proposed as a solution. An analysis of rheological and adhesive properties is conducted in order to determine the combination with more promising results to the proposed application. A reaction time of 15 minutes and a catechol-chitosan proportion of 10% resulted in the most promising gels. This formulation showed adhesion when completely submerged and TBS values close to the obtained in the previous works.
Additionally, the use of polydopamine (a compound with a catechol group) as a crosslinker was evaluated for this formulation and the change in adhesion was analyzed. These adhesives did not show a significant difference in adhesion compared to the glutaraldehyde-crosslinked counterpart. Nevertheless, they were easier to apply when completely submerged given their higher density and lack the toxic disadvantage that glutaraldehyde entails.
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