A morphological analysis of calcium hydroxylapatite and poly-l-lactic acid biostimulator particles.

Injectable fillers, pivotal in aesthetic medicine, have evolved significantly with recent trends favoring biostimulators like calcium hydroxylapatite (CaHA-CMC; Radiesse, Merz Aesthetics, Raleigh, NC) and poly-l-lactic acid (PLLA; Sculptra Aesthetics, Galderma, Dallas, TX). This study aims to compare the particle morphology of these two injectables and examine its potential clinical implications. Utilizing advanced light and scanning electron microscopy techniques, the physical characteristics of CaHA-CMC and PLLA particles were analyzed, including shape, size, circularity, roundness, aspect ratio, and quantity of phagocytosable particles. The findings reveal several morphological contrasts: CaHA-CMC particles exhibited a smooth, homogenous, spherical morphology with diameters predominantly ranging between 20 and 45 µm, while PLLA particles varied considerably in shape and size, appearing as micro flakes ranging from 2 to 150 µm in major axis length. The circularity and roundness of CaHA-CMC particles were significantly higher compared to PLLA, indicating a more uniform shape. Aspect ratio analysis further underscored these differences, with CaHA-CMC particles showing a closer resemblance to circles, unlike the more oblong PLLA particles. Quantification of the phagocytosable content of both injectables revealed a higher percentage of phagocytosable particles in PLLA. These morphological distinctions may influence the tissue response to each treatment. CaHA-CMC's uniform, spherical particles may result in reduced inflammatory cell recruitment, whereas PLLA's heterogeneous particle morphology may evoke a more pronounced inflammatory response.

In Vitro Cytocompatibility Analysis and Comparison of Different Hyaluronic Acid Fillers for Minimally Invasive Esthetics.

BACKGROUND/AIM: To overcome the natural visual consequences of the physiological aging process, the use of biodegradable fillers made of hyaluronic acid or sodium carboxymethyl cellulose is increasingly popular in modern esthetic medicine. Clinicians can choose from a wide range of fillers with variable compositions and rheological properties, and therefore with different application areas and injection depths. The aim of this study was to analyze and compare the most commonly used fillers for facial augmentation regarding their in vitro biocompatibility and to find potential correlations to their rheological properties. MATERIALS AND METHODS: In the present study, direct and indirect in vitro cytotoxicity analysis according to DIN EN ISO 10993-5 were performed on 39 different filler materials for facial augmentation. RESULTS: All fillers analyzed in this study overall showed satisfactory results in the direct and indirect cytocompatibility tests. While no material was outside the threshold values in the 2,3-bis-(2-methoxy-4-nitro-5-sulphenyl)-(2H)-tetrazolium-5-carboxanilide (XTT) cell viability and bromodeoxyuridine (BrdU) cell proliferation assays or in the live-dead staining, only 7 out of the 39 fillers reached the required values in the lactate dehydrogenase assay. CONCLUSION: All biodegradable fillers examined in this study were found to be sufficiently cytocompatible. Although the qualitative analysis of the test results showed differences between the fillers, no concrete correlation between test performance and composition or manufacturer of the fillers was found. Future efforts are required to provide clinicians with even better support in choosing the right filler for optimal outcome and patient satisfaction.

The rheology of injectable hyaluronic acid hydrogels used as facial fillers: A review.

Injectable hyaluronic acid (HA) hydrogels have been popularized in facial aesthetics as they provide a long-lasting effect, low risk of complications, allergenicity tests are not required before application and can be easily removed by the action of hyaluronidases. On the other hand, the development of these systems requires in-depth studies of chemical mechanisms involved in hydrogel formation. Ideal dermal fillers should temporarily fluidize during extrusion through the needle and quickly recover their original shape after application. Hydrogels with more elastic properties, for example, are difficult to inject while viscous materials are too liquid. A balance between both properties should be achieved. Each region of the face requires products with distinct rheological properties. High G' dermal fillers are preferable for deeper wrinkles whereas the counterpart with lower values of G' is more indicated in superficial wrinkles or lip augmentation. Factors such as molecular weight and concentration of HA, pH, type and concentration of the crosslinking agent, particle size, crosslinking reaction time and crosslinking agent/polysaccharide ratio should be modulated to achieve specific rheological properties. In this review, the effect of each variable is discussed in detail to guide the rational development of new dermal fillers.

Dilutional rheology of Radiesse: Implications for regeneration and vascular safety.

BACKGROUND: Calcium hydroxylapatite-carboxymethylcellulose (CaHA-CMC) injectables have emerged as dual-purpose fillers with bioregenerative and direct filling capabilities. AIMS: This study investigates the rheological properties of CaHA-CMC and its CMC carrier gel at various dilutions. METHODS: The storage modulus (G'), loss modulus (G″), complex viscosity (η*), loss factor (tan δ), cohesivity, and extrusion force were evaluated for a range of CaHA-CMC aqueous dilutions with an oscillatory rheometer, drop weight testing, and force analysis, respectively. RESULTS: Results revealed a significant decrease in G', η*, and increase in tan(δ) with increasing dilution, indicating a decline in the product's direct filling capabilities. Cohesivity decreased dramatically with dilution, potentially enhancing tissue biointegration and the product's biostimulatory effects. The CMC gel carrier displayed inelastic and non-resilient properties, with rheological changes differing from CaHA-CMC. Dilutional rheology was also correlated with previously published dilution-dependent biostimulatory data where hyperdiluted CaHA-CMC (>1:2) demonstrated a regenerative profile and diluted or hypodiluted mixtures retained meaningful filling properties and increased regeneration. CONCLUSIONS: These findings offer a continuum for tailoring the product's rheological profile to match specific tissue requirements. Customizable rheology allows CaHA-CMC to be tuned for either filling and contouring or optimal regenerative effects. Importantly, safety implications related to vascular occlusion suggest that dilutional rheomodulation decreases the risk of vascular events. In conclusion, this study highlights the significant impact of aqueous dilution on the rheological properties of CaHA-CMC and its carrier gel. The findings support the clinical application of tailored dilutions to achieve desired outcomes, providing versatility and safety for aesthetic applications.

Comparison of Hyaluronidase-Mediated Degradation Kinetics of Commercially Available Hyaluronic Acid Fillers In Vitro.

BACKGROUND: The ability to degrade hyaluronic acid (HA)-based fillers with hyaluronidase allows for better management of adverse effects and reversal of suboptimal treatment outcomes. OBJECTIVES: The aim of this study was to compare the enzymatic degradation kinetics of 16 commercially available HA-based fillers, representing 6 manufacturing technologies. METHODS: In this nonclinical study, a recently developed in vitro multidose hyaluronidase administration protocol was used to induce degradation of HA-based fillers, enabling real-time evaluation of viscoelastic properties under near-static conditions. Each filler was exposed to repeated doses of hyaluronidase at intervals of 5 minutes to reach the degradation threshold of G' ≤ 30 Pa. RESULTS: Noticeable differences in degradation characteristics were observed based on the design and technology of different filler classes. Vycross fillers were the most difficult to degrade and the Cohesive Polydensified Matrix filler was the least difficult to degrade. Preserved Network Technology products demonstrated proportional increases in gel degradation time and enzyme volume required for degradation across the individual resilient hyaluronic acid (RHA) products and indication categories. No obvious relationship was observed between gel degradation characteristics and the individual parameters of HA concentration, HA chain length, or the degree of modification of each filler when analyzed separately; however, a general correlation was identified with certain physicochemical properties. CONCLUSIONS: Manufacturing technology was the most important factor influencing the reversibility of an HA product. An understanding of the differential degradation profiles of commercially available fillers will allow clinicians to select products that offer a higher margin of safety due to their preferential reversibility.

Performance assessment of an injectable hyaluronic acid/polylactic acid complex hydrogel with enhanced biological properties as a dermal filler.

Injectable hyaluronic acid (HA) hydrogel plays an important role in dermal filling. However, conventional HA dermal fillers mostly lack bio-functional diversity and frequently cause adverse reactions because of the chemical stiffness of highly modified degree and crosslinker residues. In this study, polylactic acid (PLA) was embedded into HA hydrogel as a bioactive substance and 1,4-butanediol diglycidyl ether was used as a crosslinker to prepare the HA/PLA composite hydrogel with enhanced biocompatibility and biological performance. We aimed to investigate the properties of HA/PLA composite hydrogels as dermal fillers by assessing the rheological properties, surface microstructure, enzymolysis stability, swelling ratio, degradation rate, cytotoxicity, and anti-wrinkle effect on photo-aged skin. The results showed that the stability and stiffness of the composite hydrogel decreased with an increasing amount of PLA, while the in vivo safety of the HA/PLA hydrogel was enhanced, showing no adverse reactions such as edema, redness, or swelling. Moreover, the composite hydrogel with 2 wt% PLA exhibited excellent anti-wrinkle effects, showing the highest collagen production. Thus, the PLA-embedded HA composite hydrogel showed potential as a dermal filler with high safety, easy injectability, and excellent anti-wrinkle effects.

Effect of a New Hyaluronic Acid Hydrogel Dermal Filler Cross-Linked With Lysine Amino Acid for Skin Augmentation and Rejuvenation.

BACKGROUND: Hyaluronic acid (HA) fillers are the most popular filler agents for skin rejuvenation. Although 1,4-butanediol diglycidyl ether is regarded as a relatively safe cross-linker, it still exhibits certain cytotoxicity. OBJECTIVES: We presented here an amino acid-cross-linked HA (ACHA) which was obtained by an amidation reaction with lysine and HA. This study aimed to investigate ACHA's efficacy and safety for skin augmentation and rejuvenation. METHODS: Rheology, compressive tests, and swelling experiments were conducted to investigate ACHA's mechanical and viscoelastic properties. The effects of ACHA on the human keratinocytes (HaCaT) cells and the human dermal fibroblast (HDF) were investigated by Transwell and wound healing assays. Its impacts on the epithelial thickness and collagen synthesis were further examined in a mouse experimental model. We recruited 50 patients with moderate to severe nasolabial folds (NLFs). The patients were randomly allocated to receive ACHA or Restylane injections. The resulting retention rates of HA and the Wrinkle Severity Rating Scale and Global Aesthetic Improvement Scale outcomes were evaluated and compared. RESULTS: ACHA exhibited good viscoelasticity. It not only promoted migration and proliferation of HaCat and HDF and secretion of various growth factors but also increased skin thickness and promoted the generation of collagen. Patients who received ACHA had more residual volume 12 months after treatment. ACHA exhibited a promising augmentation effect in NLF correction with few adverse reactions. CONCLUSIONS: ACHA has shown promise as a biomaterial with excellent biocompatibility and viscoelastic characteristics in both research and the clinic.See the abstract translated into Hindi, Portuguese, Korean, German, Italian, Arabic, Chinese, and Taiwanese online here: https://doi.org/10.1093/asj/sjad169.

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.

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.

Safety of Cohesive Polydensified Matrix Cross-Linked Hyaluronic Acid Volumizing Gel in Temporal Hollows and Cheeks: A Prospective, Open-Label, Postmarket Study.

BACKGROUND: Facial aging is characterized by volume loss and progressive hollowing of temples and cheeks. Biodegradable filler materials are preferred over nonabsorbable materials; of these, hyaluronic acid (HA) fillers are the most often used because of their favorable effectiveness and safety profile. OBJECTIVE: To confirm the safety and effectiveness of Cohesive Polydensified Matrix (CPM)-HA26 gel in the treatment of volume deficiency. METHODS: Subjects received up to 2 treatments in the temples and/or cheeks. A blinded investigator assessed improvement according to the Merz Temple Volume Scale (MTVS) and Merz Cheek Fullness Assessment Scale (MCFAS). Subjects were followed for 48 weeks after the last treatment. RESULTS: In total, 87 healthy subjects were enrolled. The proportion of subjects achieving at least a 1-grade improvement on MTVS and/or MCFAS was above 70% for each (MTVS: Weeks 4, 24, and 48 = 95.4%, 94.2%, and 77.0%; MCFAS: Weeks 4, 24, and 48 = 92.3%, 83.1%, and 71.8%). Based on MTVS and MCFAS scores at Visit 5, improvement remained visible at up to 48 weeks. No treatment-related serious AEs occurred. CONCLUSION: CPM-HA26 demonstrated both a favorable safety and effectiveness profile, with improvement in facial volume evident for up to 48 weeks. It was well tolerated and had a positive, long-lasting effect.

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.

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.

Self-crosslinkable hyaluronate-based hydrogels as a soft tissue filler.

With increasing interest in aging and skin care, the use of fillers to increase the volume of soft tissue volume is increasing globally. However, the side effects caused by the residual chemical crosslinking agents present in these fillers limit the effective application of commercialized filler products. Therefore, the development of a novel crosslinking system with a non-toxic chemical crosslinking agent is required to overcome the limitations of commercial hyaluronate (HA)-based fillers. In this paper, a new injectable hydrogel with enhanced mechanical properties, tissue adhesion, injectability, and biocompatibility is reported. The HA derivatives modified with catechol groups (HA-DA) were crosslinked by self-oxidation under in vivo physiological conditions (pH 7.4) without chemical crosslinkers to form hydrogels, which can be further accelerated by the dissolved oxygen in the body. The fabricated HA-DA filler showed excellent mechanical properties and could be easily injected with a low injection force. Further, the HA-DA filler stably attached to the injection site due to the tissue adhesion properties of the catechol groups, thus leading to an improved displacement stability. In addition, the HA-DA filler showed excellent cell viability, cell proliferation, and biocompatibility. Therefore, the HA-DA hydrogel is a novel soft tissue filler with great potential to overcome the limitations of commercial soft tissue fillers.

Quantifying the Digestion of Cross-Linked Hyaluronic Acid Fillers With Hyaluronidase.

BACKGROUND: Adverse events due to hyaluronic acid fillers (HAFs) may be treated with hyaluronidase, an enzyme that cleaves bonds within hyaluronic acid. This study reviews the efficacy of currently available hyaluronidase preparations in breaking down commercial, cross-linked HAFs. METHODS: Three HAFs were used in this study (Restylane, Juvederm Voluma, and Belotero [BEL] Balance). A laser-based particle size analyzer (Malvern Mastersizer 3000) was used to calculate particle sizes in untreated HAFs (controls) and those treated with 450 units of hyaluronidase (Hylenex) for 5 and 30 minutes. RESULTS: Particle size analysis revealed that when Restylane was treated with hyaluronidase for 5 minutes, the average particle size reduced modestly, from 472 to 440 µm. At 30 minutes, the average particle size was 419 µm. For Juvederm, the average size of particles reduced from 703 µm in controls to 676 µm after treatment with hyaluronidase for 5 minutes and 635 µm after treatment for 30 minutes. For Belotero, the average size of control particles was 410 µm, reducing to 376 µm after treatment with hyaluronidase for 5 minutes and 345 µm after treatment for 30 minutes. CONCLUSION: After treatment with hyaluronidase for up to 30 minutes, there was only a modest breakdown of all 3 HAFs used. The results of this study raise questions regarding the efficacy of hyaluronidase in degrading cross-linked HAFs.

Influence of Rheological Properties and Needle Size on Extrusion Forces of Hyaluronic Acid Based Soft Tissue Fillers.

BACKGROUND: To date no precise data are available for extrusion forces related to the G-prime and G-double-prime of fillers in combination with different 27G and 30G needles. Therefore, the objective of this study was to analyze extrusion forces of various product-needle-combinations containing two different 27G and two different 30G needles in combination with fillers of a wide range of elastic moduli starting from 2.0 – 166.0 Pa. MATERIAL AND METHODS: Four different fillers with the following elastic moduli 1.87, 11.65, 61.80, 165.50 Pa were combined with four different needles: 27G ½”, internal diameter: 0.300 μm; 27G ½”, internal diameter: 0.241 μm; 30G ½”, internal diameter: 0.241 μm and 30G ½“, internal diameter: 0.240 μm. Product-needle-combination were subjected to uni-axial mechanical testing and the respective extrusion force was measured. RESULTS: The results of this study revealed that the G-prime and the G-double-prime of a product are statistically significantly related to their extrusion force, with higher G-prime/G-double-prime products requiring higher extrusion forces. The results additionally revealed that whether the size of the needle was described as 27G or 30G by the respective manufacturer statistically significant differences between the measured extrusion forces were detected. CONCLUSION: Injectors need to be aware that not every 27G/30G needle has the same extrusion force even though the external diameter is similar (27G or 30G); this might additionally influence the ability to withdraw blood during a pre-injection aspiration manoeuvre. J Drugs Dermatol. 20(5): doi:10.36849/JDD.5237.

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.

Chart Review Presenting Safety of Injectable PLLA Used With Alternative Reconstitution Volume for Facial Treatments.

BACKGROUND: Since the approval of Sculptra Aesthetic, the amount of sterile water used to reconstitute the product has gradually increased in clinical practice. A retrospective chart review was conducted to evaluate patient safety associated with a larger reconstitution volume, and to investigate specific parameters for how Sculptra Aesthetic is used in a real-world clinical setting. OBJECTIVE: The primary objective of the study was to evaluate the safety of Sculptra Aesthetic when using a reconstitution volume of 7 to 10 mL, via collection of adverse events related to the product or injection procedure reported in medical records. METHODS: This was a multi-center, retrospective chart review conducted in the US. Medical records for subjects treated in the facial area with Sculptra Aesthetic reconstituted to 7–10 mL were reviewed to obtain information about demographics, treatment data, and adverse events. Each injector completed a questionnaire regarding reconstitution and injection procedures generally used. RESULTS: There were 4483 treatments performed in 1002 subjects; nearly half (48%) had 3 or 4 treatments during the studied period. Subjects most commonly received treatment in the midface/cheek area (97%), temple (94%), and jawline (54%). All injectors indicated adding lidocaine to the solution, resulting in total volumes of 8–10 mL. Adverse events were reported by 3.6% of subjects, all mild in intensity. Nodules were reported by 4 subjects (0.4%). CONCLUSION: The low number of AEs reported in this retrospective chart review suggests that facial aesthetic treatment with PLLA reconstituted to a final volume of 8–10 mL, including anesthetics, is associated with a favorable risk benefit ratio. J Drugs Dermatol. 2021;20(1):18-22. doi:10.36849/JDD.5631.

Needle Manufacturing, Quality Control, and Optimization for Patient Comfort.

INTRODUCTION: There is an increasing rise of cosmetic injectables. We sought to understand the manufacturing, quality control process, and needle selection of hypodermic needles for fillers. OBJECTIVE: To understand the process of manufacturing and quality control of hypodermic needles and the relevance to an aesthetic clinician. METHODS: We conducted a search of the internet and contacted medical device companies to understand the manufacturing process. We then collaborated with the Executive director of global pharmaceutical technology from Abbvie as well as the packaging and device engineer at Galderma and summarized our findings. Finally, we reviewed the literature and summarized existing recommendations on techniques to minimize pain related to injection. RESULTS: Hypodermic needles undergo an extensive manufacturing and regulatory process. Many considerations are taken into account in needle manufacturing as well as the selection process with commercially available hyaluronic acid filler products. Needle manufacturers are held to universal standards though the International Organization for Standardization (ISO). Filler companies perform their own testing to evaluate suitability of needles for their product including leakage force, penetration force, extrusion force, etc. Finally, parameters such as needle length, needle diameter, and wall thickness are considered for selection of needle/hub with individual filler viscosity. CONCLUSION: There is extensive consideration that goes into needle manufacturing, quality control, and optimization for hyaluronic acid filler. Understanding the technical process helps inform the clinician and guide patient care for maximum comfort. J Drugs Dermatol. 2021;20(1):44-48. doi:10.36849/JDD.5591.

Rejuvenation of Aged Human Skin by Injection of Cross-linked Hyaluronic Acid.

BACKGROUND: Dermal injection of chemically cross-linked hyaluronic acid (CL-HA) is a common procedure to smooth wrinkles and add fullness to the face. Due to its physical properties, CL-HA both fills space and exerts mechanical forces within the dermis. Dermal fibroblasts produce the collagen-rich extracellular matrix (ECM), which comprises the bulk of skin. Attachment to the ECM allows fibroblasts to achieve a stretched, morphology, which confers a functional phenotype that maintains collagen production. In aged/photoaged skin, collagen fibril fragmentation impairs fibroblast attachment, resulting in a collapsed morphology and reduced collagen production. This article describes investigations of the impact of CL-HA injection on fibroblast morphology and function in the aged/photoaged human skin. METHODS: Fifty-three subjects, age 70 years or older, received a single injection of saline (vehicle control) and CL-HA (0.5 ml each) in separate adjacent skin sites on photodamaged forearm or sun-protected buttock skin. Full-thickness punch biopsies were obtained from injected skin sites at various times and analyzed for molecular and cellular changes. RESULTS: Injected CL-HA forms discreet pockets that localize to areas of the dermis that contain fragmented, loosely organized collagen fibrils. These CL-HA pockets fill space and apply mechanical forces on adjacent ECM that induce stretching of fibroblasts. This stretching is associated with increased collagen gene expression and deposition of mature collagen fibril bundles, which resemble those observed in young skin. CONCLUSIONS: CL-HA injected into aged/photoaged human dermis acts by both filling space and inducing production of collagen by dermal fibroblasts. Deposition of mature collagen, which remains in the skin for decades, likely confers long-term benefits. Reduced collagen production in aged/photoaged skin is an adaptive response of fibroblasts to ECM fragmentation, rather than inherent cellular aging mechanisms.

Transvascular Hydrolysis of Hyaluronic Acid Filler With Hyaluronidase: An Ex Vivo Study.

BACKGROUND: Despite the favorable safety profile of hyaluronic acid (HA) dermal fillers, side effects can occur. Skin necrosis is one of the most severe early-occurring complications resulting from accidental vascular impairment. Hyaluronidase (HYAL) is commonly used to degrade HA chains, allowing the degraded product to pass through vessels, and thus relieving the vascular obstruction. OBJECTIVE: The purpose of this study is to evaluate, in an ex vivo setting, the capability of HYAL to degrade crosslinked HA that was injected into human vessels. MATERIALS AND METHODS: During a neck dissection, a portion of the anterior jugular vein and facial artery was harvested. The vein and artery specimens were filled with 25 mg/mL of crosslinked HA filler. Each specimen was soaked in 0.5 mL of HYAL (300 IU/mL), in its own test tube, for 4 hours, after which the remaining HA was quantified. RESULTS: The remaining HA volume was found to be 0.02 mL in the vein segment and 0.002 mL in the artery segment. CONCLUSION: A single administration of HYAL may not be adequate to restore blood flow in the event of embolism, and relatively high doses of this enzyme must be injected hourly into the affected tissue until resolution is complete.