Cytocompatibility of boron nanoparticle-modified maxillofacial silicone elastomers: an in vitro study

Boron nanoparticles (BNPs) have attracted increasing interest as additives in dental biomaterials due to their antimicrobial activity, chemical stability, and reinforcing potential. Although various nanoparticles have been incorporated into maxillofacial silicone elastomers to improve mechanical and antimicrobial performance, the cytocompatibility of BNP-modified systems remains insufficiently investigated. This study evaluated the concentration-dependent effects of BNP incorporation on the cytocompatibility of two clinically used maxillofacial silicone elastomers.

Sixty disc-shaped specimens (2 mm × Ø 5 mm; n = 10/group) were fabricated from two room-temperature vulcanizing silicone elastomers (A-2000 and A-2006) incorporating BNPs at 0%, 1 wt%, and 3 wt%. Cytocompatibility was assessed using an MTT assay on human dermal fibroblasts (HDF), which were selected as the test model due to their direct and prolonged contact with maxillofacial prostheses. Material eluates were used for cellular exposure at 24 and 48 h of incubation. Surface morphology and nanoparticle distribution were evaluated by scanning electron microscopy (SEM) to correlate surface characteristics with biological responses.

At 24 h, cell viability in 1 wt% BNP groups was comparable to controls (A-2000-1%: 0.39 ± 0.04 vs. A-2000 control: 0.40 ± 0.04; p > 0.05), whereas 3 wt% BNP groups - particularly A-2006-3% (0.21 ± 0.02) - showed significantly reduced viability compared to controls (p < 0.001). At 48 h, no statistically significant differences were observed among any group (p = 0.26), and all groups exhibited cell viability above the ISO 10993-5 cytotoxicity threshold. A significant within-group decrease in viability from 24 to 48 h was observed in the A-2000 control and A-2000-1% groups (p < 0.001), attributable to cell-culture dynamics rather than material cytotoxicity. SEM revealed smooth surfaces in control groups, mild irregularities with dispersed nanoparticle clusters at 1 wt%, and pronounced surface roughness with particulate accumulations at 3 wt%, indicating concentration-dependent nanoparticle agglomeration.

BNP incorporation influenced cytocompatibility in a concentration-dependent manner. Incorporation at 1 wt% preserved cytocompatibility in both silicone systems, whereas 3 wt% was associated with a transient reduction in cell viability, likely related to nanoparticle agglomeration and early burst-release behavior. Differences observed between A-2000 and A-2006 suggest that polymer matrix characteristics modulate the biological effects of nanoparticle incorporation. These findings indicate that BNP concentration and matrix properties are key determinants of early cellular responses in nanoparticle-modified maxillofacial silicone systems.