Changes in Dermal Thickness in Biopsy Study of Histologic Findings After a Single Injection of Polycaprolactone-Based Filler into the Dermis

Abstract

Background: During aging, facial skin thins, atrophies, and loses elasticity. Subdermal filler injections can volumize and treat wrinkles but cannot directly change dermal thickness. Polycaprolactone (PCL) fillers can improve skin texture and quality through dermal thickening and inducing neocollagenesis. Through biopsy study, evidence of neocollagenesis will be introduced.

Objectives: In this single-clinic prospective study, 13 patients received a single injection of diluted 0.5 cc of PCL filler in the facial dermis except the right temple area for intra-individual control study.

Methods: A biopsy was performed from temple skin at 1 year for all patients. An additional biopsy was performed at 2 weeks and 4 years posttreatment for 3 patients. Dermal thickness was measured with sonography after 1 year.

Results: On average, the mean rate of temporal skin thickness in biopsy specimens (n = 117 points in 13 patients) at 1 year posttreatment increased by 26.74% ± 9.26% from 1412.41 μm ± 69 μm to 1781.11 μm ± 110 μm (P < 0.001). On average, the mean thickness of facial skin (n = 39 points in 13 patients) measured by ultrasound at 1 year increased by 21.31% ± 4.34%. Around PCL particles, many fibroblasts, giant cells, new capillaries, new collagen, and elastic fibers were found in various stains.

Conclusions: Facial dermal thickness increased after intradermal injection of PCL filler by neocollagenesis to treat skin atrophy. PCL filler may last more than 4 years in the dermis.

Figure 1.

Changes of dermis thickness on the temporal area. In this study, the skin thickness was measured from the epidermis to the skin appendage. (A) One year after posttreatment, the dermal thickness of temple skin on the control (right) side was 1412.41 μm ± 69 μm. (B) One year after posttreatment, the dermal thickness of temple skin on the treated (left) side was 1781.11 μm ± 110 μm, a 26.7% increase from the control side. Black arrows, polycaprolactone particles.

Figure 2.

Tissue reaction after polycaprolactone injection into dermis with H&E stain (×400). (A) Two weeks after posttreatment, numerous macrophages and a number of foreign-body giant cells were found around polycaprolactone particles. (B) The carboxymethylcellulose portion was found 2 weeks after posttreatment, and foreign-body giant cells and macrophages engulfed the carboxymethylcellulose portion. (C) One year after posttreatment, numerous foreign-body giant cells, macrophages, and monocytes were found all around the polycaprolactone particles. (D) Many eosinophils were found 1 year after posttreatment. New capillaries with small lumen composed of thin endothelium were found 1 year after posttreatment. The polycaprolactone particle cleaved and had a rough surface and irregular shape 4 years after posttreatment. The polycaprolactone particle was 40 microns (A-C) 2 weeks and 1 year after posttreatment, whereas it had decreased 4 years after posttreatment (E). (F) Some eosinophils were found, and many new capillaries composed of thin endothelium were found 4 years after posttreatment. *, polycaprolactone particle; C, capillary; cf, collagen fiber; Cmc, carboxymethylcellulose carrier gel; EB, asteroid body; Eo, eosinophil; F, fibroblast; FGC, foreign-body giant cell; Mc, macrophage; Mo, monocyte; Nc, nuclei of foreign-body giant cell.

Figure 2.

Tissue reaction after polycaprolactone injection into dermis with H&E stain (×400). (A) Two weeks after posttreatment, numerous macrophages and a number of foreign-body giant cells were found around polycaprolactone particles. (B) The carboxymethylcellulose portion was found 2 weeks after posttreatment, and foreign-body giant cells and macrophages engulfed the carboxymethylcellulose portion. (C) One year after posttreatment, numerous foreign-body giant cells, macrophages, and monocytes were found all around the polycaprolactone particles. (D) Many eosinophils were found 1 year after posttreatment. New capillaries with small lumen composed of thin endothelium were found 1 year after posttreatment. The polycaprolactone particle cleaved and had a rough surface and irregular shape 4 years after posttreatment. The polycaprolactone particle was 40 microns (A-C) 2 weeks and 1 year after posttreatment, whereas it had decreased 4 years after posttreatment (E). (F) Some eosinophils were found, and many new capillaries composed of thin endothelium were found 4 years after posttreatment. *, polycaprolactone particle; C, capillary; cf, collagen fiber; Cmc, carboxymethylcellulose carrier gel; EB, asteroid body; Eo, eosinophil; F, fibroblast; FGC, foreign-body giant cell; Mc, macrophage; Mo, monocyte; Nc, nuclei of foreign-body giant cell.

Figure 3.

Dermis with Masson Trichrome stain at 100× magnification and collagen fibers stained blue. (A) One year after posttreatment. (B) Four years after posttreatment. (A,B) Stained in blue, newly made collagen fibers (new), which are extremely thin, were found between particles. The pink parts are inflammation cells including the foreign body giant cells. *, polycaprolactone particle; cf, collagen fiber; F, fibroblast; FGC, foreign-body giant cell.

Figure 4.

Dermis after polycaprolactone injection with special stainings. Elastin fiber stained black in Verhoeff’s Van Gieson stain and stained blue in Victoria Blue stain. (A) Irregular and short-patterned new elastic fibers were found more in Verhoeff’s Van Gieson stain (×400) 1 year after posttreatment. (B) Numerous new elastic fibers were located throughout at 4 years after posttreatment in Victoria Blue stain (×100). *, polycaprolactone particle; Ed, epidermis; Ef, elastic fiber; FGC, foreign-body giant cell.

Figure 5.

Ultrasound image demonstrates change in the dermal thickness after the injection of polycaprolactone filler for this 41-year-old female. Thickness of dermis on midpoint of nasolabial fold was (A) 2.15 mm before the procedure and (B) 2.69 mm 1 year after posttreatment. The dermal thickness increased by 25.11%.

Figure 6.

Changes in skin texture and skin pores for this 41-year-old female who was also featured in Figure 5. (A) Before the treatment and (B) 1 year after polycaprolactone injection, pore size (in the anterior malar area) was reduced. The nasolabial fold also showed significance. The appearance in both the increase of skin thickness and anteromedial cheek volume enhancement changed. Neocollagenesis in dermis and subdermis may led to skin tightening. The skin tightening seems to have elevated the depressed area and flattened the nasolabial fold. There was a redistribution effect.