Background: Histological analysis of hyaluronic acid (HA) applied in the nasolabial fold (NLF) studied gel distribution into the dermis and subcutaneous fat, correlating density of NLF tissues, with cohesivity, concentration and degradation of HA.
Method: Ten patients received two injection points on each NLF. They were intradermal near the nasal ala and subcutaneous near the oral commissure. Injection points received 0.1 ml of 24 mg/ml HA cross-linked by BDDE 2.0 ppm through a bolus technique injection without retrograde backflow. Biopsies were taken 72 h and 9 months after application to histological analysis.
Results: Dermis density fragmented the gel into small nodules, spreading it into the reticular dermis. Seventy-two hours after application, average diameter of the small nodules was 0.30 mm and at month nine 0.05 mm. Softness of the subcutaneous fat and high concentration of HA created a single and compact nodule. Seventy-two hours after application, average of nodule diameters was 1.05 mm and at month nine 0.49 mm. HA biodegradation occurred on the external surface of the gel. The single nodule offered small contact surface to enzymes, slowing gel degradation. The sum average of the diameters of the small nodules offered a large contact surface to enzymes, accelerating gel degradation.
Conclusion: Permanence of the HA into the tissues depended on the relationship between the gel distribution and its degradation. Due to the small contact surface of the single nodule to enzymes, permanence of the HA into the subcutaneous fat was more extended than into the dermis.
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Keywords: HA cohesivity; HA integration; Hyaluronic acid (HA); Intradermal application; Nodules; Subcutaneous application.