We have developed plasmonic fibrin-based hydrogels that incorporate gold nanoparticles which transduce incident near-infrared (NIR) light into heat. Human adenovirus serotype type-5 vectors encoding a firefly luciferase (fLuc) coding sequence driven by a heat-inducible promoter were incorporated into the hydrogels. Transmission electronic microscopic analysis revealed that the adenoviral vectors were associated to the fibrin fibers. In vitro experiments in which human cells were cultured with plasmonic hydrogels showed that the adenoviral vectors can diffuse from the hydrogels, transduce the cells, and stimulate heat-induced transgene expression upon NIR irradiation. The hydrogels were implanted in 4.2 mm drill hole defects generated in the humerus of male rabbits. Three days after implantation, the defects were NIR-irradiated. Six h later, the animals were euthanized and samples from the bone defect zone were processed for immunohistochemical analyses using a specific fLuc antibody. The results showed strong expression of fLuc in tissues surrounding the implants of NIR-irradiated rabbits, while non- irradiated animals exhibited negligible expression. We next aimed to use the temperature increase to induce the production of transgenic bone morphogenetic protein 6 (BMP-6), using safe gene switches that can provide tighter control of in vivo transgene expression than heat-inducible promoters. These switches are only activated by heat in the presence of rapamycin and maintain a high level of targeted transgene expression for several days after heat activation. Adenoviral vectors encoding the safe switches that control the expression of BMP-6 were incorporated to the composites. The resulting NIR-responsive hydrogels were implanted in the bone defects generated in rabbits and used as a platform to transduce host cells, generate local hyperthermia and stimulate BMP-6 production.

Acknowledgements: This research was supported by grants RTI2018-095159-B-I00 and PID2021-126325OB-I00 (MCIN/AEI/10.13039/501100011033 and “ERDF A way of making Europe”), by grant P2022/BMD- 7406 (Regional Government of Madrid). M.A.L-J. is the recipient of predoctoral fellowship PRE2019-090430 (MCIN/AEI/10.13039/501100011033).

Bone-regenerative and biocompatible materials are indicated for the regeneration of bone lost in periodontology and maxillofacial surgery. Bio-Oss is a natural bone mineral for bone grafting of bovine origin and the most common used in this kind of interventions¹. Sil-Oss is a new synthetic nanostructured monetite-based material that is reabsorbed at the same time that is replaced by new bone tissue ². Bacterial infection is one of the complications related to this kind of material. Streptococcus oralis is the most associated oral infecting pathogen to oral surgery³ and Staphylococcus aureus is the most common infecting pathogen to maxillofacial non-oral interventions⁴. Here we evaluated bacterial adherence of two of the most common infecting bacteria of this kind of biomaterial: S. oralis and S. aureus, on Bio-Oss and Sil-Oss.

S. oralis ATCC 9811 and S. aureus 15981 strains were used. Bacterial adherence was evaluated using the modified previously described protocol of Kinnari et al.⁵ that was adapted to our biomaterial. The quantification was performed by the drop plate method⁶. The statistical data were analyzed by pairwise comparisons using the nonparametric Mann-Whitney test with a level of statistical significance of p<0.05. Values are cited and represented as medians.

Bacterial adherence decreased significantly on Sil-Oss compared to Bio-Oss. S. oralis ATCC 9811 adherence was between 11 and 13-fold less on Sil-Oss compared to Bio-oss. In the case of S. aureus15981, the adherence was between 4 and 6-fold less on Sil-Oss compared to Bio-Oss.

Sil-Oss nanostructured monetite-based biomaterial could be considered as a promising biomaterial to be used for the regeneration of bone defects since the bacterial adherence on it is lower than on another currently used material.