Injectable biostimulatory agents such as poly-L-lactic acid (PLLA), polycaprolactone (PCL), and calcium hydroxyapatite (CaHA) have emerged as key tools in regenerative aesthetics due to their ability to stimulate adipogenesis and adipocyte metabolic activity, enhance collagen production, and improve dermal quality. This review aimed to provide an updated synthesis of the role of these agents in adipocyte stimulation, focusing on their mechanisms of action, clinical efficacy, and therapeutic applications. A comprehensive search of the MEDLINE, PubMed, and Ovid databases was conducted for studies published from 2018 onward, including in vitro and in vivo experiments, randomized controlled trials, and observational studies, which were evaluated according to the Oxford Centre for Evidence-Based Medicine hierarchy. The findings demonstrated that PCL promotes adipose-derived stem cell differentiation and extracellular matrix remodeling, while PLLA exhibits dual effects on collagen synthesis and adipocyte stimulation, with clinical trials such as the SPLASH study confirming significant improvements in dermal thickness and adipogenesis. CaHA provided immediate volumizing benefits with long-term tissue regeneration, and innovative approaches including combination therapies and novel injection protocols expanded clinical applications. Overall, PLLA, PCL, and CaHA represent effective and versatile biostimulatory agents that support natural and durable outcomes in aesthetic practice. Nevertheless, the absence of large-scale trials and standardized protocols highlights the need for further research to optimize safety, efficacy, and long-term treatment strategies.

Background: Collagen is the dominant structural protein of vertebrate connective tissues and a central biomaterial in skin, cornea, tendon, cartilage, bone, vessel, oral mucosa, and wound repair. Traditional collagen products have largely been extracted from bovine, porcine, fish, or other animal tissues. Although animal‐derived collagens have a long clinical history, they have limitations including batch variability, residual nonhuman epitopes, possible immunogenicity, pathogen‐related concerns, ethical constraints, and limited molecular engineering. Recombinant human collagen has emerged as a synthetic‐biology alternative designed to reproduce full‐length human collagen chains, selected human collagen domains, or engineered humanized collagen‐like sequences in controlled expression systems. Objective: This systematic review and narrative synthesis summarizes the biological basis, production methods, molecular types, benefits, clinical applications, aesthetic uses, safety considerations, and translational limitations of recombinant human collagen, with emphasis on dermatology, wound healing, corneal regeneration, tissue engineering, injectable aesthetics, and dermal rejuvenation. Methods: A PRISMA‐informed systematic search was performed across biomedical databases, publisher platforms, and regulatory sources for literature on recombinant human collagen, recombinant humanized collagen, recombinant type I collagen, recombinant type III collagen, recombinant collagen hydrogels, collagen‐based medical devices, dermal fillers, wound healing, corneal substitutes, tissue engineering, photoaging repair, and aesthetic applications. Because the evidence base includes heterogeneous manufacturing papers, in vitro studies, animal experiments, early clinical trials, case series, and regulatory documents, quantitative meta‐analysis was not performed. Results: Recombinant human collagen offers human‐sequence design, reduced animal‐origin risk, improved batch consistency, scalable manufacturing potential, and engineering flexibility. Type I and type III recombinant collagens are most relevant to dermal, wound, tendon, corneal, and aesthetic applications, whereas type IV, VII, and XVII collagens are increasingly relevant to basement membrane and epidermal adhesion biology. Production remains technically demanding because native collagen requires triple‐helix formation and post‐translational modifications such as proline hydroxylation. Current strategies include yeast expression with prolyl‐4‐hydroxylase co‐expression, microbial production of collagen‐like fragments, mammalian and insect cell systems, transgenic plants, chemical modification, cross‐linked microgels, and collagen‐based bioinks. Conclusion: Recombinant human collagen is a platform biomaterial rather than a single product class. Its clinical value depends on matching collagen type, molecular format, formulation, degradation profile, mechanical behavior, and biological indication. In aesthetic medicine, its strongest future role may be regenerative matrix restoration rather than simple volume replacement. Larger randomized trials, long‐term safety surveillance, and standardized quality‐control methods are required before broad equivalence with established animal collagens, hyaluronic acid fillers, or biostimulatory injectables can be assumed.

Background: Nasolabial folds are a prominent feature of facial aging and remain a frequent aesthetic concern. Poly-D,L-lactic acid and Hyaluronic Acid (PDLLA–HA; Juvelook, VAIM, Korea) has gained recognition as a biostimulatory filler with dual benefits of immediate volumization and long-term collagen induction. Objective: To evaluate the clinical efficacy and safety of PDLLA (Juvelook, VAIM, Korea) injection for the correction of nasolabial folds in 20 patients. Methods: Twenty patients with moderate-to-severe nasolabial folds were treated with PDLLA–HA (Juvelook; VAIM, Korea). Each vial was diluted with 6 mL of normal saline, with 1 mL administered per fold (intradermal injection). Treatments were performed in 3 sessions at 1-month intervals. Clinical outcomes were assessed at baseline and 3 months after the final session using standardized photography, the Global Aesthetic Improvement Scale (GAIS), and patient-reported satisfaction scores. Results: All patients showed progressive improvement in nasolabial fold severity across treatment sessions. At 3 months posttreatment, 85% of patients were rated as “improved” or “much improved” on the GAIS, while 90% reported high satisfaction. Standardized photography confirmed a visible reduction in fold depth and enhanced facial contour. The procedure was well tolerated, with only transient swelling and bruising reported; no nodules, granulomas, or delayed adverse events were observed. Conclusion: In this prospective case series, PDLLA–HA injections in intradermal injection were associated with clinically meaningful improvement of nasolabial folds and a favorable safety profile through 3 months after the final session.

Deoxycholic acid (DCA) occupies an unusual position at the boundary between endogenous metabolism and therapeutic tissue ablation. Under physiological conditions, DCA is a gut microbial secondary bile acid that enters the enterohepatic circulation, contributes to the composition of the bile-acid pool, and participates in receptor-dependent signaling. When delivered as a concentrated injectable drug into subcutaneous fat, however, DCA acts primarily as an amphipathic cytolytic molecule that disrupts cell membranes, initiates adipocyte death, and provokes an organized inflammatory and reparative response. These two biological identities are often conflated, leading to imprecise descriptions of injectable DCA as a lipolytic, receptor-targeted, or metabolically selective treatment. This critical review integrates evidence from bile-acid biochemistry, microbiology, membrane biophysics, adipose-tissue biology, human histology, pharmacokinetics, and clinical trials. We describe the microbial formation, transport, conjugation, and signaling actions of endogenous DCA; distinguish physiological receptor signaling from concentration-dependent detergent injury; and examine the temporal sequence of adipocytolysis, innate immune recruitment, lipid clearance, fibrovascular remodeling, and volume reduction after local injection. We also assess systemic exposure, clinical efficacy, anatomic determinants of safety, and the limitations of extrapolating submental data to large-volume or non-submental treatment. Finally, we propose a translational metabolomics and lipidomics framework that combines local interstitial sampling, plasma bile-acid profiling, lipid mediator analysis, imaging, and tissue phenotyping. The central conclusion is that injectable DCA is best understood as a controlled local cytolytic perturbation superimposed on a tightly regulated endogenous bile-acid system. Framing the intervention in this way clarifies terminology, identifies measurable biomarkers, and creates a rational path toward dose optimization, patient selection, and safer clinical translation.

Background: High-frequency ultrasound (HFUS) quantifies dermal skin density well, yet the low-echogenic (hypoechoic) regions in the image have not been treated as having informative value. Analyzing HFUS B-scans, we found that skins with near-identical aggregate density can differ markedly in their hypoechoic area fraction. To capture this, we introduce the dermal echo-void (DEV) area fraction index, a computer-assisted parameter measuring hypoechoic voids within a fixed 0.45 mm superficial-dermis band (T45), and assess its reproducibility and non-redundancy with skin density. Methods: In a single-arm proof-of-concept study of 23 Korean women, DEV and density were computed from the same 22 MHz B-scans. Results: DEV was reproducible across analysis-band depths (ICC = 0.93, 95% CI 0.86–0.97). Although DEV correlated inversely with density (r = −0.675), the two measures were non-redundant: among 39 density-matched pairs (Δ ≤ 1 percentage point), DEV differed by a mean of 5.6 percentage points. After one application, density rose +16.44% and DEV fell −35.75% (both p < 0.001). A secondary density–pigmentation association was non-significant (Spearman ρ = −0.224, p = 0.485). Conclusions: DEV is a reproducible, spatially resolved complement to HFUS skin density that captures dermal structure beyond an aggregate value. How the hypoechoic fraction relates to melanocyte-associated dermal processes warrants histologically validated study.

Peptides used in aesthetic dermatology differ in molecular identity, biological target, formulation, and route of administration. This critical narrative review classifies these agents and examines their direct or indirect relationships with dermal fibroblasts, integrating mechanistic, delivery, and clinical evidence. Matrikine-like and copper-binding peptides influence matrix-related responses in experimental systems, whereas neuromodulatory and pigment-modulating peptides primarily act through other cellular targets. Oral collagen hydrolysates provide amino acids and circulating hydroxyproline-containing peptides with fibroblast activity demonstrated mainly in preclinical models. Lipidation, encapsulation, and microneedles can modify exposure, but delivery-system effects complicate attribution to the peptide. Controlled human studies report improvements in selected skin endpoints, including wrinkles, hydration, elasticity, dermal density, and pigmentation; however, many trials are limited by small samples, short follow-up, industry sponsorship, or multi-ingredient formulations. Current evidence supports product-specific interpretation rather than interchangeability across peptide classes or administration routes. It does not establish universal purity thresholds, commercial shelf lives, or safety of degraded formulations. Future studies should connect characterized composition and verified exposure with cell-specific mechanisms, objective clinical outcomes, and route-appropriate safety assessment.