Temporal Pulse Structure of a 1550-nm Nonablative Fractional Laser Differentially Modulates Fibroblast...

Nonablative fractional laser (NAFL) therapy is a widely used energy-based device (EBD) modality for dermal remodeling and photorejuvenation. Pulse temporal structure-the combination of peak power and pulse duration at constant total fluence-represents an underexplored determinant of cellular response. Type-N (normal mode) and Type-T (thermal mode) pulse configurations of a 1550-nm NAFL system induce distinct pathway-level transcriptional responses in human dermal fibroblasts. The fibroblast subpopulation-level correlates and functional tissue consequences of these differences remain unknown.

Bulk RNA sequencing (n = 3 per group) was performed on human dermal fibroblasts at three days post-irradiation. Transcriptome-wide correlation scores were calculated against four reference fibroblast subpopulation clusters: secretory-reticular (cluster 1), pro-inflammatory (cluster 2), secretory-papillary (cluster 3), and mesenchymal (cluster 9). Subpopulation marker gene expression and collagen family profiles were visualized using z-score-normalized heat maps. Bioprinted three-dimensional (3D) dermal constructs were irradiated in Type-N or Type-T mode under matched parameters and assessed by uniaxial compression testing on Day 8.

Control fibroblasts showed transcriptional resemblance to the secretory-reticular subpopulation, consistent with a stable homeostatic baseline. Type-N mode-irradiated fibroblasts showed a broad, non-specific transcriptional activation pattern with signals consistent with pro-inflammatory, mesenchymal, and secretory-reticular subpopulation programs, without a single dominant subpopulation tendency, accompanied by broad induction across all collagen structural classes and, most prominently, fibrillar collagens. Type-T mode-irradiated fibroblasts showed preferential transcriptional resemblance to the pro-inflammatory subpopulation, consistently supported across replicates and marker gene analysis, with overall attenuation of fibrillar collagen expression and selective enrichment of basement membrane-associated collagens. Type-N mode-irradiated constructs showed directionally higher compressive modulus than Type-T mode and controls.

Pulse temporal structure is associated with distinct transcriptional tendencies in human dermal fibroblasts at equivalent total fluence. Type-T mode irradiation was associated with a robustly supported pro-inflammatory transcriptional tendency, while Type-N mode irradiation engaged a broad, non-specific activation pattern without preferential enrichment of a single subpopulation state. These molecular differences are directionally reflected in early biomechanical responses in the 3D dermal model and provide a framework for the mechanistic optimization of NAFL pulse parameters.