Composition and Mechanism of Action of Poly-L-Lactic Acid in Soft Tissue Augmentation

April 2014 | Volume 13 | Issue 4 | Supplement Individual Articles | 29 | Copyright © April 2014

Danny Vleggaar MD,a Rebecca Fitzgerald MD,b and Z. Paul Lorenc MD FACSc

aHead of Cosmetic Dermatology in Private Practice, Geneva, Switzerland
bDepartment of Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA
cLorenc Aesthetic Plastic Surgery Center, New York, NY, USA

Abstract
Poly-L-lactic acid (PLLA) is a synthetic, biocompatible, biodegradable polymer. For its use in soft tissue augmentation, it is supplied as a lyophilized powder containing PLLA microparticles, the size and chemical attributes of which are tightly controlled. As a biocompatible material, PLLA generates a desired subclinical inflammatory tissue response that leads to encapsulation of the microparticles, stimulation of host collagen production, and fibroplasia. Over time, the PLLA degrades, the inflammatory response wanes, and host collagen production increases. This response leads to the generation of new volume and structural support that occurs in a gradual, progressive manner, and which can last for years. Coupled with consistent, optimized injection methodology, the use of PLLA in soft tissue augmentation can result in a predictable cosmetic effect that is completely controlled by the treating clinician.

J Drugs Dermatol. 2014;13(suppl 4):s29-s31.

INTRODUCTION

Poly-L-lactic acid (PLLA) (Figure 1)1 is a synthetic, biocompatible, biodegradable polymer that has been used in various medical applications for more than 3 decades. 1,2 For its use in soft tissue augmentation, it is supplied in a sterile glass vial as lyophilized powder, which includes nonpyrogenic mannitol, sodium carboxymethylcellulose, and PLLA microparticles.3 The diameter of the microparticles is tightly controlled, measuring on average between 40 μm to 63 μm; particle size is key to product performance, as particles in this range are large enough to avoid both passage through capillary walls and phagocytosis by dermal macrophages, but small enough for easy injection.1 Prior to use, reconstitution of the lyophilized product through the addition of sterile water forms a hydrocolloid suspension.1,3
Poly-L-lactic acid is a relatable example of the clinical utility of biocompatible materials. The biocompatibility of a product pertains to its ability to generate a beneficial cellular or tissue response in a particular clinical application.4 Implanted polymeric biomaterial results in an inflammatory response (Figure 2), the nature of which is determined by many factors that can be broadly classified into 3 categories: the biomaterial’s properties, the host’s characteristics, and the methodology by which the biomaterial is introduced into the host.5 Consistency in each of these 3 parameters leads to a predictable host response and, in the case of collagen stimulators, to a predictable cosmetic effect that is completely controlled by the clinician.
The impact of the methodology of biomaterial introduction, as it relates to PLLA, will be explored in detail in “The History Behind the Use of Injectable Poly-L-Lactic Acid for Facial and Nonfacial Volumization: the Positive Impact of Evolving Methodology” section of this supplement.6
The properties of a biomaterial implant that affect host response include both physical attributes (shape, size, surface area) and chemical attributes (pH, charge, hydrophilic vs hydrophobic), in both its initial and degraded forms.5 The importance of such properties can be illustrated briefly by looking at one well-established example, the refinement of microparticle size during the development of polymethylmethacrylate (PMMA)-based collagen stimulators. Arteplast®, the first generation of injectable PMMA, had a broad range of particle sizes and a high level of particles below 20 μm, resulting in an unpredictable amount of inflammation and high incidence of granulomas.7 The second-generation agent, Artecoll®, had greater uniformity in particle size, and while the results with this agent were improved, further refinement was necessary to produce the third-generation product, Artefill®, the first to meet the United States Food and Drug Administration’s rigorous quality requirements.7
As this example illustrates, a great deal has been learned over time regarding how the many characteristics of collagen stimulators can affect their clinical behavior. With the tight control over the physical and chemical attributes of injectable PLLA microparticles, the tissue response with its use follows a controlled and predictable pattern.8 Although the injection of PLLA into the subcutaneous or the supraperiosteal plane creates the appearance of immediate volumization due to mechanical