Pilot Histomorphometric Study of Combined Use of Poly-L-Lactic Acid and Calcium Hydroxyapatite to Improve Dermis Remodeling.

Injectable collagen biostimulators such as Calcium Hydroxyapatite and Poly-L-Lactic Acid are well-established in regenerative dermatology for their ability to induce neocollagenesis and improve skin quality. Despite their proven individual efficacy, the combined use of these biomaterials remains underexplored. This study aimed to evaluate the histological and stereological effects of Calcium Hydroxyapatite, Poly-L-Lactic Acid, and their combination on dermal remodeling and connective tissue deposition. A pilot histomorphometric study was conducted in patients undergoing abdominoplasty, allowing access to treated and untreated tissue. Injections of Calcium Hydroxyapatite, Poly-L-Lactic Acid, their combination (Composite), or saline were administered in infraumbilical areas, using intradermal and deep dermal planes according to the material. Tissue samples were collected at D-30 (before intervention), and at 60 and 120 days for analysis. Histological assessment included fiber density, organization, and inflammatory infiltrates. Stereological analysis was performed using the point-counting method to quantify extracellular matrix (ECM) content. Results showed that all active treatments induced significant dermal remodeling compared with controls. Calcium Hydroxyapatite and Poly-L-Lactic Acid individually led to increased fiber bundle thickness and reduced interstitial spaces. The Composite group demonstrated the most pronounced effects, with fiber compaction and enhanced ECM remodeling. The ECM content increased up to 1000% by 60 days, with slower gains between 60 and 120 days, suggesting early peak stimulation followed by stabilization. In conclusion, the combination of Calcium Hydroxyapatite and Poly-L-Lactic Acid resulted in superior histological outcomes compared with isolated applications. These findings support the potential of a dual-modality dermis biostimulation as a promising strategy for treating skin laxity.