To Evaluate the Synergistic Effect of Different Crosslinking Strategies on Collagen Derivatives to Develop Funcional Biomimetic Scaffolds

The preliminary objective of this work was to study how the effect of different crosslinking methodologies can functionally modify various characteristics of biological macromolecules relevant for scaffold development in bone tissue engineering. The research study was classified and studied in three different phases: (i) different crosslinking strategies in gelatin functionalization, (ii) ribose mediated crosslinking in collagen-hydroxyapatite scaffold (iii) different crosslinking mechanisms in functional modification of bone-like scaffold. The obtained results were highly positive in all the three investigated studies. Though the core aim of this research was to explore the available crosslinking strategies in different biological macromolecules, the present study generated significant findings, largely contributing to provide optimum solutions in understanding how the crosslinking density can fine-tune the overall performance of a scaffold, relevant for its functioning in vivo. In particular, this study demonstrated that different crosslinkers at different conditions (pH and temperature) can modify the functional properties of the scaffolds differently, therefore this optimization strategies on these crosslinkers as obtained from this study results will help material scientists in the design and development of bioactive hybrid biomaterials for hard tissue regeneration.

Development of new collagen cross-linkers for adhesive bonding stabilization

Aims: This thesis aimed to investigate the influence of different collagen cross-linkers, as separate primers or contained within desensitizing agents, on the longevity of dental restorations and on the dentinal enzymatic activity immediately, or after aging in vitro. Methods: A series of studies was conducted using several different cross-linking molecules and several adhesive systems. Four studies investigated the longevity of the hybrid layer by means of microtensile bond strength test, and the enzymatic activity using gelatin and in situ zymography, immediately or after 1 year of aging in the artificial saliva. The first study tested samples bonded with or without a cross-linking agent, that were previously aged for 5 years. The degradation of the hybrid layer was observed using transmission electron microscopy, the enzymatic activity in the hybrid layer using in situ zymography. Raman spectroscopy was used to investigate whether the active substance was still within the hybrid layer after 5 years. Results: The results of the studies showed that collagen cross-linkers were efficient in preserving bond strength after aging in vitro when used as separate primers on demineralized or partially demineralized dentin. In the cases when the cross-linker was utilized on mineralized dentin, bond strength results were higher than in the control groups immediately and after aging, however, no difference in enzymatic activity was detected after aging. Conclusions: The tested cross-linker molecules used as separate primers in etch-and-rinse and self-etch adhesives seem to be clinically applicable, since the procedure is not overly time-consuming and seems to preserve the hybrid layer over time. As for the cross-linkers contained in the desensitizing agent, when utilized before the adhesive procedures, it has shown to increase the bond strength of self-etch adhesives, but further studies are needed to better understand its effect on the enzymatic activity and crosslinking effects on mineralized dentin.