Rheologic and Physicochemical Properties Used to Differentiate Injectable Hyaluronic Acid Filler Products

Effect of relative centrifugal force on the biological properties of liquid platelet-rich fibrin produced via horizontal centrifugation

OBJECTIVES

Platelet-rich fibrin (PRF) in liquid form has shown advantages in tissue engineering including acting as injectable fillers and drug carriers. However, few studies have investigated the best relative centrifugal force (RCF) for preparing liquid PRF. The aim of the present study was to find out optimal centrifugation force for preparing liquid PRF.

MATERIALS AND METHODS

Liquid PRF was prepared using horizontal centrifugation (liquid H-PRF) with RCF ranging from 100 g, 300 g, 500 g, to 700 g for 8 min. The volume, weight, solidification time, and tensile properties were subsequently investigated. Scanning electron microscopy (SEM) and rheologic tests were carried out to investigate the microstructure and rheologic properties of liquid H-PRF after natural polymerization. The total number, concentration, and distribution of cells within each liquid H-PRF was evaluated by complete blood count (CBC) analysis and hematoxylin-eosin staining.

RESULTS

As RCF values increased, the volume and weight of liquid H-PRF both increased accordingly. SEM images revealed that as the centrifugal force increased, the fibrin bundles became thinner with a denser fibrin network, and rheologic tests revealed improved mechanical properties. CBC analysis demonstrated that 500 g group had the highest number of leukocytes and neutrophils, whereas 100 g group yielded the highest concentration of leukocytes and platelets. Furthermore, histological analysis suggests that cells obtained by 500 g for 8 min were most evenly distributed in liquid H-PRF.

CONCLUSIONS

In summary, the present study provided insights into the contents of liquid H-PRF prepared at different centrifugation forces, enabling clinicians to choose proper centrifugation forces based on their needs.

CLINICAL RELEVANCE

The present findings provide theoretical basis for clinical choice of liquid H-PRF protocol from mechanical, cell contents, and histological aspects.

How Much Does Filler Apparatus Influence Ease of Injection (and Hence, Potential Safety)?

PURPOSE

To document the relative contributions of intrinsic filler fluid dynamics versus delivery systems for ease of injection-specifically, to measure extrusion force variability across different syringes and needles (with the characterization of intrinsic rheological fluid properties vs. delivery apparatus contributions to ease of injection).

METHODS

Six different fillers were tested: Belotero balance (Bel), Juvederm Voluma XC (Vol), Revanesse Versa (Rev), Restylane Lyft (Res), Radiesse (Rad), and Teosyal RHA3 (RHA). Extrusion force was measured in Newtons (N) for each by testing using the provided injection apparatus (needle + syringe), and also by standardizing all fillers to the same syringe and then varying needle sizes (30-ga, 27-ga, 25-ga/1.5-inch, 25-ga/2-inch, and 22-ga). Five trials were conducted for each scenario, with comparison via t -test (2-tailed, unpaired, assuming unequal variance).

RESULTS

The following results were noted: (1) in order of least to highest extrusion force in box-provided syringe + needle at 0.2 ml volume, the following were noted: Vol < RHA = Bel (27-ga) < Bel (30-ga) < Rev < Res = Rad; (2) for each filler (except for Vol which was similar), the box-provided syringe involved greater extrusion force than the standardized syringe used in this study (each 1-cc, p < 0.05); (3) for 27-ga and 30-ga needles, after standardization of delivery syringe at 0.2 ml volume, a significant difference was noted (proportional to increasing resistance): Bel = Vol = RHA3 < Res < Rev < Rad (for needles of 30-ga [ p < 0.05] and 27-ga [ p < 0.01]); (4) for testing cannulas after standardization of syringes no reproducible order was noted with increasing resistance when using 25-ga/1.5-inch long, 25-ga/2-inch, and 22g/2-inch cannulae; and (5) confirming expectation (validating study technique), the extrusion force was significantly higher for smaller needles and longer needles.

CONCLUSIONS

The delivery apparatus appeared to be the most influential contributor to filler injection extrusion force, with significant changes in ease of injection correlated to the filler's intrinsic rheological properties, such as viscosity (when standardized to the same syringe for needles tested). Knowledge of such data could influence the injector's ability to maximize patients' safety and clinical results.

Effect of Stromal Vascular Fraction on Sustained Volume Retention of Five Different Hyaluronic Acid Fillers

BACKGROUND

The technology of manufacturing hyaluronic acid (HA) fillers is evolving to increase their safety and durability. This study aimed to compare the volume maintenance effect of stromal vascular fraction (SVF) on different types of HA fillers.

METHODS

In this controlled experiment, HA fillers mixed with SVF were injected into the right upper back and HA fillers alone were injected into the left upper back of each mouse. A total of 35 mice were separated into five groups according to the type of commercially used HA filler: Juvederm Voluma XC, Restylane Lyft, Restylane Skinboosters Vital, Giselle Ligne Signature 2, and Giselle Ligne Universal. Nodule size inspection was performed on post-injection days 0, 3, and 56. Ultrasonography for maximal two-dimensional area of filler nodule measurement and histology were performed on the last day of the inspection.

RESULTS

While most of the groups showed a volume reduction of over 50% on day 56, regardless of SVF administration, significant volume maintenance was observed when Giselle Ligne Signature 2 was injected with SVF. Ultrasonographic measurement of two-dimensional filler nodule size showed no significant difference regarding filler types and SVF injection. When compared with the histological results of other fillers mixed with SVF, Giselle Ligne Signature 2 showed marked increase in cell survival and extracellular matrix components in HA particles.

CONCLUSION

SVF showed different efficacies in terms of volume maintenance and cell survival for various HA filler types. The SVF mixture in selective HA filler injections may improve maintenance in clinical settings.

NO LEVEL ASSIGNED

This journal requires that authors assign a level of evidence to each submission to which Evidence-Based Medicine rankings are applicable. This excludes Review Articles, Book Reviews, and manuscripts that concern Basic Science, Animal Studies, Cadaver Studies, and Experimental Studies. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266.

NOT SO "HAPPY BUMP": A complication due to hyaluronic acid

INTRODUCTION

The use of hyaluronic acid (HA) as a dermal filler is considered safe. However, as new brands come to the market, reports of adverse events are becoming more and more common.

OBJECTIVE

To describe a particular type of adverse effect that, unlike the erythematous, indurated, and painful nodules described in the literature as "angry red bumps," is characterized by noninflammatory, stony-like nodules that appear in sites previously treated with HA.

METHODS

The report of four patients who presented this complication, and the occurrence of two HA syringes from the same batch that had hardened the product inside at the time of filling.

CONCLUSION

The authors propose the nomenclature "happy bump" to group adverse reactions to HA that translate into noninflammatory nodules, with a stony consistency, appearing up to 4 weeks (recent) or after one month (late) in sites previously treated with AH.

Dynamic ultrasound evaluation of body fillers and biostimulators in the buttocks of fresh-frozen specimen

BACKGROUND

Ultrasound imaging is a useful tool to study the injection of fillers and biostimulators in the body.

OBJECTIVE

Sonographically evaluate real-time injections of fillers and biostimulators and describe their behavior in the subcutaneous tissue of the buttocks of fresh-frozen specimen.

METHODS

injection of two brands of high-density hyaluronic acid (HA), one brand of calcium hydroxyapatite (CaHA), one brand of hybrid injectable (CaHa + HA), one brand of polycaprolactone (PCL) and three brands of poly-l-lactic acid (PLLA) were performed in the subcutaneous tissue of the gluteal region under ultrasonography visualization on a fresh-frozen specimen. Videos during injection and static images immediately after injection were obtained. The sonographic aspects of the substances and their dispersion and interaction with the surrounding tissues were described.

RESULTS

Real-time ultrasound showed different dispersion patterns of the two brands of HA, CaHA, hybrid injectable (CaHa + HA) and the three brands of PLLA. The sonographic aspects among the brands of PLLA were also different.

CONCLUSIONS

The dynamic ultrasound evaluation of the injection of HA, CaHA, hybrid injectable (CaHa + HA), PCL and PLLA in a fresh-frozen specimen shed some light on their aspects and dispersion pattern in the buttock. If these patterns are confirmed in further studies in vivo, there will be a positive impact on the selection and development of safer and more effective techniques to enhance buttock contour.

Five-point liquid rhinoplasty: Results from a retrospective analysis of a novel standardized technique and considerations on safety

BACKGROUND

Nonsurgical aesthetic improvement of the nose with hyaluronic acid (HA) fillers is becoming increasingly popular but comes with important safety considerations.

AIMS

To assess the safety and effectiveness of the standardized "five-point liquid rhinoplasty" approach.

METHODS

This was a retrospective, single-center analysis of consecutive adult patients undergoing nonsurgical aesthetic treatment of the nose. All had one of the three main indications (insufficient nasal projection, nasal hump, or deep glabella) and were injected using HA fillers with high elastic modulus. Treatments were given using some or all of the injection points of the "five-point liquid rhinoplasty" technique: P1 (nasal tip, 0.2-0.3 ml supracartilaginous); P2 (nasal root, 0.1-0.2 ml supraperiostal); P3 (cartilaginous dorsum, 0.1-0.2 ml supracartilaginous/supraperiostal); P4 (subnasal, 0.1-0.2 ml supraperiostal); and P5 (nasal alar, 0.1-0.2 ml per side supraperiostal). The risk of complications was minimized by injecting deep and staying in the midline as far as possible.

RESULTS

Twenty patients were enrolled (n = 15 female [75%]; mean age: 37.8 ± 11.7 years). The mean volume of filler used was 0.66 ± 0.35 ml per patient. Nineteen subjects (95%) said they were "very satisfied" with results, and the physician was also "very satisfied" with outcomes in 19 patients (95%). Two individuals experienced hematoma, which was managed conservatively; there were no other significant complications.

CONCLUSIONS

The "five-point liquid rhinoplasty" is a simple and effective method designed to maximize safety. It offers a good alternative to surgery in selected patients.

The Rheology and Physicochemical Characteristics of Hyaluronic Acid Fillers: Their Clinical Implications

Hyaluronic acid (HA) fillers have become the most popular material for facial volume augmentation and wrinkle correction. Several filler brands are currently on the market all around the world and their features are extremely variable; for this reason, most users are unaware of their differences. The study of filler rheology has become a wellspring of knowledge, differentiating HA fillers, although these properties are not described thoroughly by the manufacturers. The authors of this review describe the more useful rheological properties that can help clinicians understand filler characteristics and the likely correlation of these features with clinical outcomes.

Bridging a Century-Old Problem: The Pathophysiology and Molecular Mechanisms of HA Filler-Induced Vascular Occlusion (FIVO)-Implications for Therapeutic Interventions

Biocompatible hyaluronic acid (HA, hyaluronan) gel implants have altered the therapeutic landscape of surgery and medicine, fostering an array of innovative products that include viscosurgical aids, synovial supplements, and drug-eluting nanomaterials. However, it is perhaps the explosive growth in the cosmetic applications of injectable dermal fillers that has captured the brightest spotlight, emerging as the dominant modality in plastic surgery and aesthetic medicine. The popularity surge with which injectable HA fillers have risen to in vogue status has also brought a concomitant increase in the incidence of once-rare iatrogenic vaso-occlusive injuries ranging from disfiguring facial skin necrosis to disabling neuro-ophthalmological sequelae. As our understanding of the pathophysiology of these injuries has evolved, supplemented by more than a century of astute observations, the formulation of novel therapeutic and preventative strategies has permitted the amelioration of this burdensome complication. In this special issue article, we review the relevant mechanisms underlying HA filler-induced vascular occlusion (FIVO), with particular emphasis on the rheo-mechanical aspects of vascular blockade; the thromboembolic potential of HA mixtures; and the tissue-specific ischemic susceptibility of microvascular networks, which leads to underperfusion, hypoxia, and ultimate injury. In addition, recent therapeutic advances and novel considerations on the prevention and management of muco-cutaneous and neuro-ophthalmological complications are examined.

Construction of tissue-customized hydrogels from cross-linkable materials for effective tissue regeneration

Hydrogels are prevalent scaffolds for tissue regeneration because of their hierarchical architectures along with outstanding biocompatibility and unique rheological and mechanical properties. For decades, researchers have found that many materials (natural, synthetic, or hybrid) can form hydrogels using different cross-linking strategies. Traditional strategies for fabricating hydrogels include physical, chemical, and enzymatical cross-linking methods. However, due to the diverse characteristics of different tissues/organs to be regenerated, tissue-customized hydrogels need to be developed through precisely controlled processes, making the manufacture of hydrogels reliant on novel cross-linking strategies. Thus, hybrid cross-linkable materials are proposed to tackle this challenge through hybrid cross-linking strategies. Here, different cross-linkable materials and their associated cross-linking strategies are summarized. From the perspective of the major characteristics of the target tissues/organs, we critically analyze how different cross-linking strategies are tailored to fit the regeneration of such tissues and organs. To further advance this field, more appropriate cross-linkable materials and cross-linking strategies should be investigated. In addition, some innovative technologies, such as 3D bioprinting, the internet of medical things (IoMT), and artificial intelligence (AI), are also proposed to improve the development of hydrogels for more efficient tissue regeneration.

New Directions in Aesthetic Medicine: A Novel and Hybrid Filler Based on Hyaluronic Acid and Lactose Modified Chitosan

Fillers based on crosslinked hyaluronic acid (HA) are becoming increasingly important in the field of aesthetic medicine, for example for treating wrinkles or for volumizing purposes. However, crosslinking agents are usually associated with toxicity and adverse reactions. The aim of this study is the development of an innovative technology to manufacture high performance HA-based fillers using minimal amounts of crosslinking agent. In this work, new fillers based on HA, functionalized with different amounts of 1,4-butanediol diglycidyl ether (BDDE) (degree of modification ranging between 3.5% and 8.8%) and formulated with a lactose modified chitosan (CTL), were investigated. The relative quantities of these polymeric building blocks in the formulations were 20-25 and 5 mg/mL for HA and CTL, respectively. Due to its cationic nature, CTL could interact with the anionic HA and enhance the elastic properties of the filler. Fillers manufactured with this novel technology (HACL-CTL) were characterized and compared with several fillers available in the market. In particular, resistance against hyaluronidase, swelling, cohesivity and rheological properties were investigated. Cohesivity, resistance to hydrolysis and swelling of HACL-CTL were comparable to commercial products. However, HACL-CTL fillers showed excellent elastic performance that reached 94% of elasticity in response to shear stresses. Surprisingly, these fillers also showed a resistance to compression higher than that of currently marketed products, making them very promising for their lifting effect.

Evaluating hyaluronic acid dermal fillers: a critique of current characterization methods

Soft‐tissue augmentation has gained much popularity in recent years. Hyaluronic acid (HA) based dermal fillers; a non‐permanent injectable device, can restore volume loss, fill fine lines and wrinkles and add curves and contours. HA based dermal fillers entered the non‐surgical treatment market in the late 1990s, however there is a lack of data and literature comparing the range of products and detailing the complexities of these products and how it relates to tissue performance. Measuring the physico‐chemical properties of these dermal fillers provide key parameters to predict their performance after injection into the body. This article reviews the currently reported methods and parameters used to characterize dermal fillers. The review of these methods and data from the literature provides a useful guide to clinicians and injectors in selecting the optimal product suitable for the needs of each patient.

Rheologic and Physicochemical Characteristics of Hyaluronic Acid Fillers: Overview and Relationship to Product Performance

Injections with hyaluronic acid (HA) fillers for facial rejuvenation and soft-tissue augmentation are among the most popular aesthetic procedures worldwide. Many HA fillers are available with unique manufacturing processes and distinct in vitro physicochemical and rheologic properties, which result in important differences in the fillers' clinical performance. The aim of this paper is to provide an overview of the properties most widely used to characterize HA fillers and to report their rheologic and physicochemical values obtained using standardized methodology to allow scientifically based comparisons. Understanding rheologic and physicochemical properties will guide clinicians in aligning HA characteristics to the facial area being treated for optimal clinical performance.

Monophasic and Biphasic Hyaluronic Acid Fillers for Esthetic Correction of Nasolabial Folds: A Meta-Analysis of Randomized Controlled Trials

BACKGROUND

Hyaluronic acid (HA) fillers have become the most popular dermal fillers for esthetic nasolabial folds (NLFs) correction. Based on the cross-linking method, they can be classified as monophasic or biphasic types.

OBJECTIVES

The aim of this meta-analysis is to compare the efficacy and safety of monophasic HA fillers with that of biphasic HA fillers for treatment of NLFs. PubMed, Embase, Cochrane Library, Web of Science, ClinicalTrials.gov, and Chinese databases were searched from inception to January 2021.

METHODS

Randomized controlled trials (RCTs) that compared treatment outcomes of a monophasic HA filler with a biphasic HA filler for esthetic NLF correction were selected. Twenty-two RCTs with totally 1848 subjects were included to this meta-analysis. A significantly higher improvement of NLF severity score was seen for monophasic fillers than biphasic fillers at 2 (p = 0.005), 8 (p <0.0001), 12 (p = 0.03), 16 (p = 0.005), 24 (p <0.00001), 36 (p = 0.007), and 52 week (p <0.0001) after treatment.

RESULTS

The effect was retained regardless of ethnicity, total injection volume, and baseline NLF severity. More subjects preferred monophasic fillers over biphasic ones (≤7 months: RR = 3.45, 95% CI 1.17 to 10.11; >7 months: RR = 2.37, 95% CI 1.45 to 3.86). Rate of post-injection pain was significantly lower for monophasic fillers (RR = 0.85, 95% CI 0.78 to 0.92, p <0.0001), but no statistical difference was observed for other post-injection adverse events. Compared to biphasic HA fillers, monophasic HA fillers were associated with a greater and more durable esthetic NLFs improvement, a lower rate of post-injection pain, and were favored by more patients.

LEVEL OF EVIDENCE II

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

An Overview of Soft Tissue Fillers for Cosmetic Dermatology: From Filling to Regenerative Medicine

Hyaluronic acid (HA)-based injectable filling agents are at the forefront of the current demand for noninvasive dermatological procedures for the correction of age-related soft tissue defects. The present review aims to summarize currently available HA-based products and critically appraise their differences in rheological nature and clinical application. Linear HA (LHA) gels may be supplemented with amino acids, lipoic acid, vitamins, nucleosides, or minerals for synergistic antiaging and antioxidant benefits (polycomponent LHA). HA hydrogels can be generated via chemical or physical crosslinking, which increases their elasticity and decreases viscosity. The performance of crosslinked fillers depends on HA concentration, degree of crosslinking, elastic modulus, cohesivity, and type of crosslinking agent employed. PEG-crosslinked LHA displays improved elasticity and resistance to degradation, and lower swelling rates as compared to BDDE-crosslinked LHA. Physical crosslinking stabilizes HA hydrogels without employing exogenous chemical compounds or altering hyaluronans’ natural molecular structure. Thermally stabilized hybrid cooperative HA complexes (HCC) are a formulation of high- and low-molecular-weight (H-HA and L-HA) hyaluronans, achieving high HA concentration, low viscosity with optimal tissue diffusion, and a duration comparable to weakly cross-linked gel. Our critical analysis evidences the importance of understanding different fillers’ properties to assist physicians in selecting the most appropriate filler for specific uses and for predictable and sustainable results.

Approach to differentiate between hyaluronic acid skin quality boosters and fillers based on their physicochemical properties

BACKGROUND

The clinical indications, applications, and effect of the injectable hyaluronic acid range skin quality boosters (SQBs) are different than those of filler products. Material properties are increasingly being discussed for differentiation and in connection with clinical effects and esthetic indications.

AIMS

The aim of this study is to evaluate whether SQB products can be differentiated from filler products by their physicochemical material properties.

MATERIAL AND METHODS

Physicochemical properties (extrusion force, swelling degree, rheology, and cohesivity) of two SQBs (BEL_R , JUV_VE ) were compared with those of fillers (BEL_B , JUV_VT ) using the same manufacturing technology.

RESULTS

Cohesivity was almost equal for SQBs and fillers. Few statistically significant differences in physicochemical properties were found. Properties of SQBs differed from fillers mainly in their delta of rheological properties and extrusion force.

CONCLUSION

In this study, physicochemical differences between SQB and filler were determined and described, supporting the presence of two categories and their different clinical indications and applications.

Pharmacology of Aesthetic Medicines

The realm of aesthetic medicine is broad, and there are countless medications and topical agents used in the practice of aesthetic medicine. The most commonly used injectable medicines include botulinum toxin for mimetic lines and hyaluronic acid fillers for deeper facial rhytids and volume rejuvenation. Topical aesthetic medicines are useful adjuncts for facial rejuvenation and commonly include tretinoin, hydroquinone, growth factors, and vitamin C, as well as a wide range of chemical peels.

Comparison of the Rheological Properties and Structure of Fat Derivatives Generated via Different Mechanical Processing Techniques: Coleman Fat, Nanofat, and Stromal Vascular Fraction-Gel

Importance: Coleman fat, nanofat, and stromal vascular fraction-gel (SVF-gel) are three widely used fat derivatives. However, their rheological properties and structure remain unknown. Objectives: To disclose the rheological properties and structure of three different fat derivatives. Design, Settings, and Participants: Fat tissues obtained from eight different donors were processed into three separate groups: Coleman fat, nanofat, and SVF-gel (n = 8); their viscoelastic properties and structure were determined. Intervention: Oscillation measurements were performed in the context of serrated 25-mm parallel-plate geometry with a 1.2-mm gap at 25°C. In addition, fat samples were fixed using a patented protocol and observed under scanning electron microscopy. Main Outcomes and Measures: Comparison of the viscoelastic properties, microstructure, and particle size. Results: At 0.77 Hz, the elastic modulus of SVF-gel, Coleman fat, and nanofat was 201.6 ± 0.74, 69.94 ± 15.61, and 34.89 ± 3.484 Pa, respectively; their viscosity was 44.06 ± 3.038, 15.37 ± 2.0380, and 7.516 ± 0.7250 mPa, respectively. The particle size of SVF-gel, Coleman fat, and nanofat was 106.0 ± 4.796, 86.93 ± 3.597, and 12.61 ± 7.603 μm, respectively. Conclusion and Relevance: Mechanical processing may impact graft efficacy. The characterization of the rheological properties and structure of different fat derivatives in this study may help surgeons select the better type of tissue for a given intervention; however, further studies are still required.

Delayed Complications following Dermal Filler for Tear Trough Augmentation: A Systematic Review

Tear trough deformity is a popular target for the treatment with filler injections. The side effects are generally mild and transient. However, delayed complications may occur. We aim to perform a thorough systematic review of the published literature related to delayed complications after tear trough filler injections. A search of published literature was conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines in June 2021 and included PubMed, ScienceDirect, and Embase databases. The Medical Subject Headings (MeSH) terms used included the following terms: delayed complications, nodules, granulomas, swelling, discoloration, dermal filler, hyaluronic acid (HA), polyacrylamide, calcium hydroxyapatite (CaHA), poly-L-lactic acid (PLLA), eyelid, periorbital, periocular, and tear trough. Twenty-eight articles consisting of 52 individual cases were included in the final analysis. 98% (51/52) of patients were female and had an average age of 48.3 years. HA was the most reported product (71.2%, 37/52), followed by PLLA (4/52, 7.7%), and CaHA (4/52, 7.7%). The most common delayed complication with any dermal filler was swelling (42.3%, 22/52) followed by lumps or nodules (25.0%, 13/52). Xanthelasma-like reaction (17.3%, 9/52), migration (7.7%, 4/52), discoloration (3%, 3/52) also occurred. The average time of onset of any complication was 16.8 months with xanthelasma-like reaction appearing soonest (mean: 10 months) and discoloration appearing latest (mean: 52 months). Most swelling cases were caused by HA. Semi-permanent fillers such as PMMA and synthetic fillers such as PLLA were more likely to be associated with lumps and nodules than other complications. It is important that clinicians who perform tear trough augmentation with dermal fillers have a thorough understanding of the risks of the procedure to diagnose and manage them promptly as well as provide patients with accurate information regarding the potential adverse effects.

The Effects of Lipoaspirate-Derived Fibrous Tissue on Survival Quality and Mechanical Property of Fat Grafts

BACKGROUND

Fibrous connective tissue (referred to as fiber) in lipoaspirates would be discarded before lipotransfer in case of cannula blockage. However, the fiber contains extracellular matrix which provide structure support and is rich in stromal vascular fractions (SVFs). Removal of the fiber might theoretically affect the survival quality and mechanical properties of fat grafts. But there is few evidence in vivo and vitro about how the fiber affects the fat grafts.

OBJECTIVE

To assess the effect of fibers on the survival quality and mechanical property of fat grafts.

METHODS

The SVFs in both fat and fiber were obtained by collagenase digestion for cells counting and comparison. Three groups were designed according to the different proportions of fat and fiber: the fat group (100% fat), the mixed group (50% fat, 50% fiber in volume ratio), and the fiber group (100% fiber). Three groups of grafts were transplanted in vivo to evaluate the differences in volume retention rate, histological characteristics and mechanical properties.

RESULTS

The amount of SVF cells in fibers (3.47 ± 1.49 × 104 cells/mL) was significantly lower than that in fat (12.3 ± 4.95 × 104 cells/mL) (P < 0.05). Grafts in the mixed group and the fiber group showed an increase of volume retention at week 4, but the fiber content showed no significant effects on the volume retention of grafts in three groups at week 12. Elasticity modulus of grafts in the fat group was higher than that in the fiber group and the mixed group at week 4 and 8, the fiber content showed no significant effects on the elasticity modulus of grafts in three groups at week 12. The addition of the fiber reduced the inflammation, cysts, fibrosis, and capillaries density of the grafts.

CONCLUSIONS

There were few SVF cells in the fiber. When it was mixed with fat in different proportions and transplanted in vivo, the content of fiber showed no significantly different effects on the long-term volume retention and mechanical property of fat grafts. Due to the risk of blockage, it is recommended to discard the fiber in lipoaspirates.

Features to consider for mimicring tissues in orofacial aesthetics with optimal balance technology and non-animal stabilized hyaluronic acid (Restylane®): The MIMT concept

Nonsurgical cosmetic treatments have significantly increased over the last decade. Therefore, this study aims to review the features that should be considered in orofacial esthetic procedures, thorough of a proposal of a new concept called the tissue mimicry concept (MIMT concept) and filling techniques. The MIMT concept described in this article comprises knowledge about anatomy of the face and associated structures, understanding of aging and how this process affects the facial tissues interactions (skin, subcutaneous tissues, muscles, and bones), interpretation of facial analysis, comprehension of dermal fillers characteristics and discernment of the correct filling technique for each region. Based on these variables the MIMT concept proposes the implantation of the minimum-effective quantity of acid hyaluronic fillers (HA) with different physical, chemical and rheological properties (complex viscosity and elastic modulus) in the correct layers; in order to optimize their performance resulting in a natural appearance with fewer risks of adverse events. the versatility, acceptable safety profile, biocompatibility and greater patient compliance presented in the Restylane® line (by Galderma) should be taken in consideration, since the use of a proper HA is noteworthiness. The Non-Animal Stabilized Hyaluronic Acid Tecnology (NASHA®) and the Optimal Balance Technology (OBT®), which make up this line of fillers, allow us to have very firm to very flexible gels, with different particle sizes, with an optimal concentration of HA and with viscoelastic and biocompatible characteristics according to the region of the treated face.

Change in Rheologic Properties of Facial Soft-Tissue Fillers across the Physiologic Angular Frequency Spectrum

BACKGROUND

The number of soft-tissue filler injections performed in the United States is constantly increasing and reflects the high demand for enhanced facial and body attractiveness. The objective of the present study was to measure the viscoelastic properties of soft-tissue fillers when subjected to different testing frequencies. The range of tested frequencies represents clinically different facial areas with more [lips (high frequency)] or less [zygomatic arch (low frequency)] soft-tissue movement.

METHODS

A total of 35 randomly selected hyaluronic acid-based dermal filler products were tested in an independent laboratory for their values of G', G″, tan δ, and G* at angular frequencies between 0.1 and 100 radian/second.

RESULTS

The results of the objective analyses revealed that the viscoelastic properties of all tested products changed between 0.1 and 100 radian/second angular frequency. Changes in G' ranged from 48.5 to 3116 percent, representing an increase in their initial elastic modulus, whereas changes in G″ ranged from -53.3 percent (i.e., decrease in G″) to 7741 percent (i.e., increase in G″), indicating both an increase and a decrease in their fluidity, respectively.

CONCLUSIONS

The increase in G' would indicate the transition from a "softer" to a "harder" filler, and the observed decrease in G″ would indicate an increase in the filler's "fluidity." Changes in the frequency of applied shear forces such as those occurring in the medial versus the lateral face will influence the aesthetic outcome of soft-tissue filler injections.

A Reliable Method for Chin Augmentation by Mechanical Micronization of Lipoaspirates

BACKGROUND

Desire for improved aesthetic contour of the lower third of the face has resulted in an increase in chin augmentation. Although many fillers, including hyaluronic acid (HA), autologous fat and stromal vascular fraction gel (SVF-gel), have been used to improve facial morphology, chin augmentation requires fillers that provide greater support.

METHODS

The elastic and viscous moduli of SVF-gel and Coleman fat were assessed in vitro by rheological testing, whereas their elasticity were evaluated in vivo by ultrasonic elastography. Results in vitro were compared with those of highly elastic HA (HE-HA) and highly viscous HA (HV-HA), whereas results in vivo were compared with HE-HA. Changes in chin volume, SVF-gel retention rate and absorptivity for at least 12 months were measured by 3D white light scanning. Questionnaires were administered to assess patient satisfaction.

RESULTS

The elastic and viscous modulus of SVF-gel was, respectively, slightly lower than HE-HA and HV-HA but higher than the other two in vitro, with the elasticity of the three layers of SVF-gel lower than HE-HA but slightly higher than normal control in vivo. The average retention rate was 62.34±3.34% at 12 months. The absorptivity of 90% of the samples was <3% from 6 to 12 months, which was considered stable. Patients expressed satisfaction with their results.

CONCLUSION

SVF-gel has ideal rheologic characteristics in vitro, which has slightly higher elasticity than normal fat tissue of chin in vivo, and could keep well retention rate for chin augmentation in clinic.

LEVEL OF EVIDENCE IV

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Comparing Water Absorption of Food and Drug Administration-Approved Hyaluronic Acid Fillers

BACKGROUND

To compare the water absorption of 12 FDA-approved hyaluronic acid (HA) facial fillers in vitro in conditions relevant to in vivo injection.

OBJECTIVE

The goal of this study was to provide long-term insight into an improved, tailored facial rejuvenation approach and to understand sequelae that could affect preoperative surgical planning.

METHODS

In 2 experiments, 12 FDA-approved HA fillers were loaded into test tubes with nonpreserved normal saline and then placed in a 94.5°F-96°F environment for 1 month to allow water absorption by passive diffusion. The test tubes were centrifuged so that the hydrated filler could pass to the bottom of the tube. The tubes were centrifuged for 12 minutes at 1,200 revolutions per minute in the first experiment and for 7 minutes in the second experiment. A blue dye was then instilled to demarcate the filler/saline interface.

RESULTS

There was variation in the water absorption of different HAs. Low absorption occurred in non-animal-stabilized hyaluronic acid.

CONCLUSION

The pattern of water absorption was similar in the 2 experiments. The results inform us about in vivo conditions and provide guidance for filler selection.

Midface 3D restoration with an innovative high G' filler

BACKGROUND

In the evaluation of the facial aging, the midface certainly represents the part that undergoes the most modifications and in which the aging process is most evident. The filling and redefinition of this part are fundamental to modify the perception of the age of the face and create a global rejuvenation effect. In general, high G' fillers with a deep implant are used to treat the midface, taking advantage of the high lifting capacity and persistence of the implant in place.

METHODS

We report our experience in the treatment of 20 patients with a hyaluronic acid (HA) filler based on an innovative crosslinking technology (XTR™-eXcellent Tridimensional Reticulation) for midface treatment. GAIS (Global Aesthetic Improvement Scale) at 1 month and 3 months after treatment was evaluated as primary endpoint. Patient satisfaction with the overall appearance, repeatability of treatment, and also an instrumental evaluation of the improvement were performed.

RESULTS

Global Aesthetic Improvement Scale and patient satisfaction were very good 1 month and 3 months after treatment. The majority of patients said they would undergo treatment again. Clinical results were confirmed by instrumental evaluation.

CONCLUSION

The treatment of midface with this innovative HA high G' filler is really effective in restoration of the volumes and in reshaping the curves of zygomatic area.

Estimation of the Effect of Accelerating New Bone Formation of High and Low Molecular Weight Hyaluronic Acid Hybrid: An Animal Study

Osteoconduction is an important consideration for fabricating bio-active materials for bone regeneration. For years, hydroxyapatite and β-calcium triphosphate (β-TCP) have been used to develop bone grafts for treating bone defects. However, this material can be difficult to handle due to filling material sagging. High molecular weight hyaluronic acid (H-HA) can be used as a carrier to address this problem and improve operability. However, the effect of H-HA on bone formation is still controversial. In this study, low molecular weight hyaluronic acid (L-HA) was fabricated using gamma-ray irradiation. The viscoelastic properties and chemical structure of the fabricated hybrids were evaluated by a rheological analysis nuclear magnetic resonance (NMR) spectrum. The L-MH was mixed with H-HA to produce H-HA/L-HA hybrids at ratios of 80:20, 50:50 and 20:80 (w/w). These HA hybrids were then combined with hydroxyapatite and β-TCP to create a novel bone graft composite. For animal study, artificial bone defects were prepared in rabbit femurs. After 12 weeks of healing, the rabbits were scarified, and the healing statuses were observed and evaluated through micro-computer tomography (CT) and tissue histological images. Our viscoelastic analysis showed that an HA hybrid consisting 20% H-HA is sufficient to maintain elasticity; however, the addition of L-HA dramatically decreases the dynamic viscosity of the HA hybrid. Micro-CT images showed that the new bone formations in the rabbit femur defect model treated with 50% and 80% L-HA were 1.47 (p < 0.05) and 2.26 (p < 0.01) times higher than samples filled with HA free bone graft. In addition, a similar tendency was observed in the results of HE staining. These results lead us to suggest that the material with an H-HA/L-HA ratio of 50:50 exhibited acceptable viscosity and significant new bone formation. Thus, it is reasonable to suggest that it may be a potential candidate to serve as a supporting system for improving the operability of granular bone grafts and enhancing new bone formations.

Biocompatible hyaluronic acid-divinyl sulfone injectable hydrogels for sustained drug release with enhanced antibacterial properties against Staphylococcus aureus

Hyaluronic acid (HA) solutions were crosslinked with divinyl sulfone (DVS) and subsequently loaded with antibiotic molecules to obtain biocompatible and antibacterial injectable hydrogels. The crosslinking degree of the hydrogels was modulated by varying the reaction time and the HA:DVS weight ratio. Synthesized HA-DVS hydrogels were characterized by their rheological properties, pore size, swelling capacity and hydrolytic and thermal degradation. Biocompatibility was assessed by measuring pH, osmolality and by in vitro cytotoxic assay. Acetyl salicylic (AAS) loaded hydrogels display anti-inflammatory properties in vitro, whereas cefuroxime (CFX), tetracycline (TCN) and amoxicillin (AMX) loaded hydrogels show in vitro antibacterial activity against Staphylococcus aureus. The combine use of antibiotics and AAS produces a synergic effect that reduces the S. aureus population up to a log10 reduction (R) of 5.55. Overall results show that antibiotic/AAS loaded HA-DVS hydrogels could be effectively used to combat S. aureus infections and to increase the antibacterial activity of antibiotics commonly used against S. aureus.

Advanced Concepts in Rheology for the Evaluation of Hyaluronic Acid-Based Soft Tissue Fillers

BACKGROUND

Crosslinked hyaluronic acid (HA)-based soft tissue fillers possess unique viscoelastic properties intended to match specific product indications. Manufacturing has an impact on HA chain integrity and on filler properties.

OBJECTIVE

This study introduces 2 new rheological parameters to evaluate the macroscopic characteristics of fillers.

METHODS AND MATERIALS

A library of reference commercialized HA fillers was selected to cover the full spectrum of product indications. Gels were assessed in terms of size of released HA fragments as a readout of gel integrity, degree of modification, cohesivity, and rheological properties.

RESULTS

The elastic modulus G' often used to characterize fillers was shown not to follow macroscopic mechanical properties. To improve the mechanical characterization of fillers, Strength and Stretch scores were developed and tested. The Strength score defined the ability of a filler to sustain constant viscoelasticity over a wide range of constraints and represented the filler mechanical resilience. The Stretch score measured the propensity of a filler to deform in view to improve implant adaptation to facial animation for natural-looking results.

CONCLUSION

Strength and Stretch scores sorted rheological parameters to macroscopic cohesivity assays more accurately than G' and may thus help predict the gel behavior once implanted and submitted to facial dynamics.

Eyelid and Periorbital Dermal Fillers: Products, Techniques, and Outcomes

A retrospective observational case study and a literature review were conducted to evaluate how anatomic findings, especially those related to the periorbital zone, serve as a guiding compass for injectable implants. Treatment techniques and product selection will be discussed for patients with negative vector, shallow orbit, and deep set eyes. Versatility of injectables will be demonstrated on patients with peanut face, iatrogenically altered anatomy (after surgery), and trauma.

Toward Physicochemical and Rheological Characterization of Different Injectable Hyaluronic Acid Dermal Fillers Cross-Linked with Polyethylene Glycol Diglycidyl Ether

(1) Background: Injectable hyaluronic acid (HA) dermal fillers are used to restore volume, hydration and skin tone in aesthetic medicine. HA fillers differ from each other due to their cross-linking technologies, with the aim to increase mechanical and biological activities. One of the most recent and promising cross-linkers is polyethylene glycol diglycidyl ether (PEGDE), used by the company Matex Lab S.p.A., (Brindisi, Italy) to create the HA dermal filler PEGDE family. Over the last few years, several studies have been performed to investigate the biocompatibility and biodegradability of these formulations, but little information is available regarding their matrix structure, rheological and physicochemical properties related to their cross-linking technologies, the HA content or the degree of cross-linking. (2) Methods: Seven different injectable HA hydrogels were subjected to optical microscopic examination, cohesivity evaluation and rheological characterization in order to investigate their behavior. (3) Results: The analyzed cross-linked dermal fillers showed a fibrous "spiderweb-like" matrix structure, with each medical device presenting different and peculiar rheological features. Except for HA non cross-linked hydrogel 18 mg/mL, all showed an elastic and cohesive profile. (4) Conclusions: The comparative analysis with other literature works makes a preliminary characterization of these injectable medical devices possible.

High-velocity pneumatic injection of non-crosslinked hyaluronic acid for skin regeneration and scar remodeling: A retrospective analysis of 115 patients

BACKGROUND

Pneumatic-assisted high velocity jet injections are an alternative method for intradermal delivery of hyaluronic acid (HA) and demonstrated efficacy in dermal thickening and scar remodeling with minimal side effects.

AIMS

We aimed to investigate the clinical efficacy comparing non-crosslinked HA (NCL-HA) and crosslinked HA (CL-HA) for aesthetic skin concerns.

METHODS

We retrospectively analyzed charts of 115 patients treated with jet injected NCL-HA and CL-HA for skin rejuvenation, age-related laxity and rhytidosis, hypertrophic and acne scars and striae. Global Aesthetic Improvement Scale (GAIS) and the 5-grade patient satisfaction scale were used for assessment of the treatment efficacy at the 3-month follow-up. Efficacy was separately analyzed between patients receiving NCL-HA vs. CL-HA. Longevity of treatment effect was measured by the time to voluntary return for repeat treatment.

RESULTS

An average of 2.8 treatments was completed per patient with a low incidence of side effects including bruises (7%) and temporary local edema (1%). Patients were highly-satisfied with the treatment results in all categories with the average satisfaction scores of 3.68 (NCL-HA) and 3.76 (CL-HA). An average GAIS score of 1.7 ("much improved") was calculated for neck, décolleté and perioral areas. An overall GAIS score averaged as 1.78 (NCL-HA) and 1.6 (CL-HA). Longevity of the effect averaged 13.1 months for NCL-HA and 13.2 months for CL-HA groups.

CONCLUSION

Our retrospective data showed similar significant improvement of all aesthetic skin concerns in 115 subjects treated with either NCL-HA or CL-HA delivered intradermally by a high velocity jet-injector device with minimal downtime, pain or side-effects.

Response of twelve different hyaluronic acid gels to varying doses of recombinant human hyaluronidase

PURPOSE

Hyaluronic acid (HA) fillers can be reversed with hyaluronidase, but their dose responses are not well-characterized. We evaluated 12 fillers' in vitro responses to varying doses of recombinant human hyaluronidase (RHH).

METHODS

For the 12 HA gels, 0.2 mL aliquots were placed on six slides. Samples received no injection, saline injection, or RHH (2.5, 5, 10, or 20 units). The most resistant gels received 40 units of RHH on a seventh slide. Photos of gels were taken from bird's-eye and lateral views with a ruler at multiple time points.

RESULTS

Restylane-L and Restylane Lyft were the most easily dissolvable HA fillers. Both demonstrated a significant response to 2.5 units RHH/0.2 mL. Juvéderm Ultra, Belotero, Restylane Silk, and Restylane Defyne had moderate resistance to RHH. Restylane Refyne, Juvéderm Ultra Plus, Vollure, Versa, and Voluma were most resistant, requiring more than 20 units RHH/0.2 mL for complete dissolution. Volbella was moderately resistant up to 20 units RHH but demonstrated pronounced dissolution with 40 units RHH.

CONCLUSIONS

This study visually and objectively demonstrates the in vitro response of HA to dissolution by hyaluronidase. Fillers were categorized into least, moderate, and most resistant to RHH. Interesting findings include markedly different degrees of liquefaction for products used for similar indications (such as Restylane Lyft being more liquefied than Voluma), and Belotero easily flattening but retaining texture. Combined with in vivo data, this may help calculate hyaluronidase doses needed for controlled, partial reversal of commercially available HA gels.

Factors influencing pre-injection aspiration for hyaluronic acid fillers: A systematic literature review and meta-analysis

Pre-injection aspiration of hyaluronic acid filler is a well-recognized yet controversial safety technique. Many consider aspiration to be an important safety measure to prevent inadvertent intravascular filler injection. To assess factors influencing pre-injection aspiration by understanding the relationship between aspiration time and a range of product, needle, and procedural characteristics. We conducted a systematic review and meta-analysis of data, adopting the preferred reporting items for systematic reviews and metaanalyses guidelines. Our literature search identified four articles presenting data on variables associated with aspiration time for different HA filler brands. Statistical models pooling data from the four articles suggest a robust association between aspiration time and a filler's elastic modulus (G'), drop weight (cohesivity), and cross-sectional area of the needle lumen. However, there is insufficient evidence to confirm a robust association between aspiration time and HA concentration, viscous modulus (G″), needle length, and pullback volume. A deeper understanding of the relationship between product, needle, and procedural characteristics, and aspiration time can provide a sound base for discussing the role of pre-injection negative aspiration as a safety measure. The understanding of the effect of various factors on preinjection aspiration would further benefit from studies under clinical conditions.

Better Results in Facial Rejuvenation with Fillers

Facial rejuvenation is a rapidly advancing field in aesthetic medicine. Minimally invasive techniques represent a powerful tool for rejuvenation, and fillers are a popular modality with which to restore and optimize facial proportions. Currently, our filler armamentarium is characterized by products with an increasing variety of biochemical compositions warranting tailored injection approaches. An intimate knowledge of anatomy, product characteristics, and appropriate injection techniques is essential to achieve optimal results while maintaining patient safety. Here, we review facial anatomy, structural changes secondary to aging, appropriate filler selection, safe injection techniques, and complications.

Safety and Performance of Etermis 3 and 4 in Wrinkles/Folds Treatment and Facial Volume Enhancement: A Prospective, Evaluator-Blinded, Open-Label Study

Background

Facial aging is characterized by increased prominence of nasolabial folds (NLFs), marionette lines, and thinning of the lips. Cross-linked hyaluronic acid injection is a very effective method for the temporary correction of these areas.

Objective

To confirm the clinical performance and the safety of Etermis 3 (ET3) and/or Etermis 4 (ET4) in the treatment of moderate and severe wrinkles/folds, as well as lip volume enhancement.

Methods

Subjects were treated in at least two facial areas (NLFs, marionette lines, lips). ET3 was used in facial moderate wrinkles while ET4 was used in severe facial skin volume loss. An optional touch-up 1 month after treatment was possible. A blinded investigator assessed improvement on Merz Aesthetic Scales (MAS). Subjects were followed-up for 12 months after the last treatment.

Results

In total, 154 healthy subjects were enrolled. The proportion of subjects achieving ≥1 score improvement in MAS after treatment was above 60% for ET4 (Month 6/7: NLFs 94.9% and marionette lines 81.4%, p≤0.0004; Month 3/4: lips 63.0%, p=0.39) and ET3 (Month 6/7: marionette lines 79.4%, p=0.0005; Month 3/4: lips 65.5%, p=0.31). Facial improvement was still visible at Month 12/13 for ET4 (NLFs ≥76.6%, marionette lines ≥61%, lips ≥36%) and ET3 (marionette lines ≥50% and lips ≥21.9%). No treatment-related serious AEs occurred. The most frequent AEs were injection-site reactions.

Conclusion

Etermis 3 and Etermis 4 demonstrated good clinical performance and safety for NLFs and marionette lines volume enhancement for up to 12 months. Both products can also be used safely to treat lips for volume augmentation.

A randomized, split-face, double-blind, comparative study of the safety and efficacy of small- and large-particle hyaluronic acid fillers for the treatment of nasolabial folds

BACKGROUND

Injections of hyaluronic acid (HA) for tissue augmentation are one of the most common aesthetic treatments performed worldwide. However, few studies have compared the safety and efficacy of small- and large-particle HA (SP-HA; LP-HA).

AIM

To assess and compare the safety and efficacy of SP-HA and LP-HA for the correction of nasolabial folds (NLFs).

METHODS

A prospective, split-face, triple-blind study design was used. Ten female subjects were recruited. Patients underwent treatment at baseline, an optional touch up at Week 2, and a follow-up visit at Week 4. At weeks 2 and 4, a blinded reviewer assessed the patients using the Global Aesthetic Improvement Scale (GAIS) and Wrinkle Severity Rating Scale (WSRS); and subjects completed the Patient Satisfaction Questionnaire (PSQ). At all visits, 3-dimensional imagery and ultrasonography of patients' NLFs were captured. Adverse events (AEs) were evaluated by the Investigator and recorded by subjects in diaries.

RESULTS

The GAIS response rate, defined as ≥ "improved" from baseline, was between 90 (2 weeks) and 100% (1 month) for SP-HA and was 100% for LP-HA, at both visits. Paired-samples t tests revealed significant differences in the change in WSRS scores between groups, at both visits (P < .01). Differences in the clinical effect and lifting capacity of both products were observed in 3-dimensional imagery and ultrasonography. Treatment volumes varied, with 61.32% more SP-HA being required than LP-HA for achieving a ≥ one-grade WSRS improvement. There were no severe AEs throughout the trial, nor AEs related to the investigational device.

CONCLUSIONS

LP-HA demonstrates better efficacy for correcting bony resorption in the nasal pyriform region.

Rheologic properties of soft tissue fillers and implications for clinical use

BACKGROUND

The use of injectable soft-tissue fillers has become an essential tool in esthetic rejuvenation. Rheology, the study of flow of matter, helps to understand the function of these products.

AIMS

The purpose of this article is to review the rheologic properties of soft-tissue fillers currently available in the United States and to evaluate how these properties relate to clinical performance.

METHODS

This article explains basic rheologic terms and describes how rheologic properties of specific soft-tissue fillers affect filler performance.

RESULTS

The currently available soft-tissue fillers have unique rheologic and physicochemical properties that influence performance and cosmetic outcome. These properties determine that filler product is most appropriate based on degree of soft-tissue defect and anatomic location.

CONCLUSION

It is imperative for physicians to have an in-depth understanding of the rheologic properties of soft-tissue fillers in order to appropriately select and utilize these products for the desired cosmetic outcome.

Evaluation of the Rheologic and Physicochemical Properties of a Novel Hyaluronic Acid Filler Range with eXcellent Three-Dimensional Reticulation (XTR™) Technology

Soft-tissue fillers made of hyaluronic acid and combined with lidocaine have recently become a popular tool in aesthetic medicine. Several manufacturers have developed their own proprietary formulae with varying manufacturing tools, concentrations, crosslinked three-dimensional network structures, pore size distributions of the fibrous networks, as well as cohesivity levels and rheological properties, lending fillers and filler ranges their unique properties and degradability profiles. One such range of hyaluronic acid fillers manufactured using the novel eXcellent three-dimensional reticulation (XTR™) technology was evaluated in comparison with other HA fillers and filler ranges by an independent research laboratory. Fillers manufactured with the XTR™ technology were shown to have characteristic rheological, crosslinking and biophysical factors that support the suitability of this filler range for certain patient profiles.

Utility of Preinjection Aspiration for Hyaluronic Fillers: A Novel In Vivo Human Evaluation

Background

Hyaluronic acid (HA) fillers have increased in popularity. While complications are rare, practitioners should focus on their prevention. Preinjection aspiration remains controversial as an effective safety checkpoint.

Objectives

Our study investigated the utility of preinjection aspiration as a safety checkpoint for HA fillers through comparison of physiochemical and rheological properties in a novel in vivo human model.

Methods

An in vivo human model consisted of a cannula inserted into a peripheral vein. Preinjection aspiration was evaluated using syringes of 10 commonly used HA fillers. The time required to visualize a flash was recorded.

Results

Using a multivariable regression model, needle gauge, HA concentration, elastic modulus ( G′), viscous modulus ( G″), and complex modulus ( G*) had significant relationships with time to flash, whereas pullback volume did not. However, when comparing pullback volume using a more appropriate paired analysis, 0.5 cc pullback volume had a significantly decreased time to flash than 0.2 cc.

Conclusions

Preinjection aspiration for HA fillers has utility as a safety checkpoint. The times to visualize flashback decreased when using a human peripheral vein model compared to a previous in vitro model, suggesting that there may be real-time clinical utility of preinjection aspiration. Waiting times to visualize flashback may be affected by physiochemical and rheological properties. Additional studies would help to validate our results.