gms | German Medical Science

Objectives: Small and inaccessible bone fractures are difficult to treat with metallic implants. In such cases, an option to glue the affected fragments could have potential advantages. Such a glue would need to allow the bone regeneration on multiple levels, from providing a structural scaffold for new bone growth to promoting regenerative cell activity.

The aim of this project is to design and produce a biocompatible, artificial organic bone adhesive with low antigenicity that establishes a suitable biochemical environment and biomechanical support for the bone cells. To provide adhesion and extra mechanical strength, the polymer will contain a UV-light activated crosslinker, which would be ideal for small bone fracture fixation. For that purpose, an organic polymer functionalized with diazirine groups will be designed. Diazirines are photoactive chemical groups that are able to form rapid and stable crosslinks by applying UV light, with molecular nitrogen as the only side product. Diazirines have been demonstrated to be biocompatible and could provide the necessary mechanical strength to be a promising candidate for the creation of new biodegradable adhesives for bone healing.

Methods: Solid Phase Peptide Synthesis (SPPS) and High-Performance Liquid Chromatography (HPLC) were used to produce purely artificial peptide fragments of the polymeric scaffold. Chemical elongation of these fragments was achieved by EDC-NHS coupling and Circular Dichroism (CD) spectroscopy was performed to assess the secondary structure and denaturation temperature of the peptides. For the evaluation of their self-assembly and supramolecular structure, several characterization techniques including Confocal Laser Scanning Microscopy (CLSM) or Stimulated Emission Depletion (STED) microscopy were used with the suitable fluorescent tags. Viscoelastic properties of the self-assembled polymer matrix were quantified with Video Particle Tracking Microrheology.

Results and conclusion: Peptide fragments can be successfully synthesized and purified, and these could be used as building blocks in an elongation reaction for reaching a polymeric material with comparable size to extracellular matrix proteins. We could demonstrate by CLSM that our peptides hybridize with structural bone proteins. Microrheology experiments showed significant differences in the values of the shear modulus (G) before and after UV irradiation, suggesting a good crosslinking capacity of the diazirines, which will be crucial for a fast reaction time of the future hydrogel at the time of surgery. The next steps will include the optimization of self-assembly and polymerization into a mechanically stable hydrogel for better applicability.