Hyaluronan-based hydrogels as dermal fillers: The biophysical properties that translate into a "volumetric" effect

Efficacy and Safety of Cell-Assisted Acellular Adipose Matrix Transfer for Volume Retention and Regeneration Compared to Hyaluronic Acid Filler Injection

BACKGROUND

Cell-assisted acellular adipose matrix (AAM) transfer is a novel technique for soft tissue volume restoration, where AAM acts as a scaffold for tissue proliferation and promotes host cell migration, vascularization, and adipogenesis. This study aimed to evaluate the efficacy and safety of in vivo cell-assisted AAM transfer compared to hyaluronic acid (HA) filler injection.

METHODS

Human adipose tissue was used to manufacture AAM, and murine adipose-derived stem cells (ASCs) were prepared. Nude mice were divided into four groups: AAM transfer (AT), ASC-assisted AAM transfer (CAT), HA filler injection (HI), and ASC-assisted HA filler injection (CHI). Eight weeks post-transfer, in vivo graft volume/weight, histology, and gene expression were analyzed to assess efficacy and safety.

RESULTS

The AAM retained its three-dimensional scaffold structure without cellular components. AT/CAT showed lower volume retention than HA/CHA; however, CAT maintained a similar volume to HA. Histologically, adipogenesis and collagen formation were increased in AT/CAT compared to HA/CHA, with CAT showing the highest levels. CAT also demonstrated superior angiogenesis, adipogenesis, and gene expression (Vegf and Pparg), along with lower Il-6 expression, higher Il-10 expression, and reduced capsule formation, indicating better biocompatibility.

CONCLUSIONS

Cell-assisted AAM transfer is a promising technique for volume retention and tissue regeneration, offering a safe and effective alternative to HA filler injections.

LEVEL OF EVIDENCE III

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 .

Efficacy of an Innovative Poly-Component Formulation in Counteracting Human Dermal Fibroblast Aging by Influencing Oxidative and Inflammatory Pathways

Skin aging is characterized by reactive oxygen species (ROS) accumulation, principal players in triggering events associated with aging. Our recent data on the ability of an innovative poly-component formulation (KARISMA Rh Collagen® FACE: K formulation) to suppress the biomolecular events associated with oxidative stress-induced aging prompted us to deepen the mechanisms underlying the observed effects on aged human dermal fibroblasts (HDFs). Here, we evaluated K's ability to perform a direct free radical-scavenging action and modulate anti-oxidant systems by counteracting the inflammatory process in an H2O2-induced cellular senescence model. Standard methods were used to measure scavenging capacity and enzymatic anti-oxidant system activities. Nuclear factor E2-related factor 2 (Nrf2) and nuclear factor kappa-B (NF-κB) levels were analyzed by Western blot. We assessed pro-inflammatory cytokines, matrix metalloproteinases (MMPs), and advanced glycation end-products (AGEs). Our results show that K counteracted stress-induced aging in a dose-dependent manner by exerting a direct scavenging action and increasing anti-oxidant systems, such as superoxide dismutase (SOD) and catalase (CAT) up to control values. These findings could be associated with increased phospho-Nrf2 (p-Nrf2) expression, generally reduced in aged HDFs following exposure to different concentrations of K formulation. Moreover, K formulation caused a reduction of pro-inflammatory cytokines, interleukin-1β and -6, MMP-1 and -9, and AGE levels, events related to a downregulation of p-NF-κB level. The results indicate that K formulation re-established the normal physiology of HDFs by reducing p-NF-κB expression and restoring Nrf2 activation, thus supporting its efficacious reparative and regenerative action in treating skin aging.

The Impact of Gel Parameters on the Dispersal and Fragmentation of Hyaluronic Acid Gel Fillers within an Artificial Model of Arterial Embolism

Accidental arterial embolization of hyaluronic acid (HA) fillers can lead to severe complications, including skin ischemia, blindness, and stroke. Currently, the intra-arterial dispersal and fragmentation behavior of HA gels is unknown but critical to our understanding of the pathomechanism of these injuries. This work introduces the Pulsatile Unit for the Laboratory Simulation of Arterio-embolic Restrictions (PULSAR) and evaluates the intravascular behavior of different HA gels. The fragmentation and dispersal behaviors of four HA gels with distinct rheological properties were evaluated via high-resolution videography and ImageJ particle size and morphology analysis. The gels' elastic modulus (G'), loss modulus (G″), tan(δ), and HA concentration were subsequently correlated with their intra-arterial behaviors. This study effectively confirms the extensive fragmentation of HA gels upon arterial inoculation, with particle sizes ranging from <50 µm to >1 mm. Gel particle size and morphology correlated most significantly with tan(δ). Conversely, arterial flow rates did not significantly influence gel fragmentation behavior, though the probability of proximal, macrovascular obstruction was affected. Overall, this study validates the PULSAR model for simulation of arterial dynamics and the testing of intravascular filler kinematics. The findings demonstrate the ability of gels to microfragment and disseminate distally, as well as induce partial proximal occlusion depending on gel rheology and arterial flow parameters.

Dual Functionalization of Hyaluronan Dermal Fillers with Vitamin B3: Efficient Combination of Bio-Stimulation Properties with Hydrogel System Resilience Enhancement

Hyaluronic acid (HA) hydrogels are commonly used for facial dermal filling and for alternative medical aesthetic purposes. High diversity exists in commercial formulations, notably for the optimization of finished product stability, functionality, and performance. Polyvalent ingredients such as calcium hydroxylapatite (CaHA) or vitamin B3 (niacinamide) are notably used as bio-stimulants to improve skin quality attributes at the administration site. The aim of the present study was to perform multi-parametric characterization of two novel cross-linked dermal filler formulas (HAR-1 "Instant Refine" and HAR-3 "Maxi Lift") for elucidation of the various functional impacts of vitamin B3 incorporation. Therefore, the HAR products were firstly comparatively characterized in terms of in vitro rheology, cohesivity, injectability, and resistance to chemical or enzymatic degradation (exposition to H2O2, AAPH, hyaluronidases, or xanthine oxidase). Then, the HAR products were assessed for cytocompatibility and in vitro bio-stimulation attributes in a primary dermal fibroblast model. The results showed enhanced resilience of the cohesive HAR hydrogels as compared to JUVÉDERM® VOLBELLA® and VOLUMA® reference products in a controlled degradation assay panel. Furthermore, significant induction of total collagen synthesis in primary dermal fibroblast cultures was recorded for HAR-1 and HAR-3, denoting intrinsic bio-stimulatory effects comparable or superior to those of the Radiesse® and Sculptra™ reference products. Original results of high translational relevance were generated herein using robust and orthogonal experimental methodologies (hydrogel degradation, functional benchmarking) and study designs. Overall, the reported results confirmed the dual functionalization role of vitamin B3 in cross-linked HA dermal fillers, with a significant enhancement of hydrogel system stability attributes and the deployment of potent bio-stimulatory capacities.

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.

LEVEL OF EVIDENCE: 4

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.

Strengthening the Key Features of Volumizing Fillers: Projection Capacity and Long-Term Persistence

Volumizing fillers aim to create or restore facial volume in fat layers. To provide strong tissue lifting and long-term persistence, gels are generally designed with stiff properties, characterized by a high storage modulus (G'). However, clinical evidence shows a discrepancy between high G' and good lifting capacities, especially after skin tension has been exerted on the gel. To better explore the in vivo behavior of a gel, we first evaluated the elastic moduli of five commercial volumizers (RHA4, JUVVOL, RESVOL, RESLYFT, and BELVOL) in dynamic compression mode, E'. We further developed a Projection Index score based on the rheological assessment of creep in compression to mimic skin tension-induced stress relaxation (flattening). Finally, the ability of a gel to resist enzymatic degradation was analyzed with a multidose approach. Despite similar clinical indications, volumizers exhibited distinct behaviors. RHA4 and BELVOL showed the highest E' values (resistance to strain), RHA4, JUVVOL, and RESVOL exhibited the greatest projection capacities, while JUVVOL and RHA4 offered the largest persistence to enzymatic degradation. In this article, we introduce the use of the Projection Index to efficiently assess the ability of a gel to lift tissues, thus increasing preclinical models' efficiency and reducing the need for animal studies.

Investigation of Crosslinking Parameters and Characterization of Hyaluronic Acid Dermal Fillers: From Design to Product Performances

Despite process similarities, distinctive manufacturing technologies offer hyaluronic acid dermal fillers with different in vitro physicochemical and rheological properties due to peculiar crosslinked hydrogel networks. A better understanding of dermal filler properties could provide specific clinical indications and expectations with more accurate performance correlations. In this study, with an emphasis on the degree of modification, hyaluronic acid concentration and molecular weight, these process parameters were able to modulate dermal filler properties, especially rheology. Moreover, an extensive characterization of commercial hyaluronic acid injectables of the Hyal System line was described to present product properties and help to elucidate related clinical effects. Standardized methodologies were applied to correlate in vitro parameters with feasible clinical indications. In view of an optimized dermal filler design, the results of the extrudability measurements allowed the quantification of the effect of hydrogel composition, rheological properties and needle size on injectability. Composition, dynamic viscosity and needle size showed an impactful influence on hydrogel extrudability. Finally, the positive influence of 200 KDa hyaluronic acid in comparison to fragments of ether-crosslinked hyaluronic acid on fibroblast recognition were shown with a migration assay.

Skin Cell and Tissue Responses to Cross-Linked Hyaluronic Acid in Low-Grade Inflammatory Conditions

Hyaluronic acid (HA), used in a variety of medical applications, is associated in rare instances to long-term adverse effects. Although the aetiology of these events is unknown, a number of hypotheses have been proposed, including low molecular weight of HA (LMW-HA) in the filler products. We hypothesized that cross-linked HA and its degradation products, in a low-grade inflammatory microenvironment, could impact immune responses that could affect cell behaviours in the dermis. Using two different cross-linking technologies VYC-15L and HYC-24L+, and their hyaluronidase-induced degradation products, we observed for nondegraded HA, VYC-15L and HYC-24L+, a moderate and transient increase in IL-1β, TNF-α in M1 macrophages under low-grade inflammatory conditions. Endothelial cells and fibroblasts were preconditioned using inflammatory medium produced by M1 macrophages. 24 h after LMW-HA fragments and HA stimulation, no cytokine was released in these preconditioned cells. To further characterize HA responses, we used a novel in vivo murine model exhibiting a systemic low-grade inflammatory phenotype. The intradermal injection of VYC-15L and its degradation products induced an inflammation and cell infiltration into the skin that was more pronounced than those by HYC-24L+. This acute cutaneous inflammation was likely due to mechanical effects due to filler injection and tissue integration rather than its biological effects on inflammation. VYC-15L and its degradation product potentiated microvascular response to acetylcholine in the presence of a low-grade inflammation. The different responses with 2D cell models and mouse model using the two tested cross-linking HA technologies showed the importance to use integrative complex model to better understand the effects of HA products according to inflammatory state.

Oligochitosan and oxidized nucleoside-based bioderived hydrogels for wound healing

Herein, we report biocompatible hydrogel for wound healing that was prepared using nature-sourced building blocks. For the first time, OCS was employed as a building macromolecule to form bulk hydrogels along with the nature-sourced nucleoside derivative (inosine dialdehyde, IdA) as the cross-linker. A strong correlation was obtained between the mechanical properties and stability of the prepared hydrogels with a cross-linker concentration. The Cryo-SEM images of IdA/OCS hydrogels showed an interconnected spongy-like porous structure. Alexa 555 labeled bovine serum albumin was incorporated into the hydrogels matrix. The release kinetics studies under physiological conditions indicated that cross-linker concentration could also control the release rate. The potential of hydrogels in wound healing applications was tested in vitro and ex vivo on human skin. Topical application of the hydrogel was excellently tolerated by the skin with no impairment of epidermal viability or irritation, determined by MTT and IL-1α assays, respectively. The hydrogels were used to load and deliver epidermal growth factor (EGF), showing an increase in its ameliorating action, effectively enhancing wound closure inflicted by punch biopsy. Furthermore, BrdU incorporation assay performed in both fibroblast and keratinocyte cells revealed an increased proliferation in hydrogel-treated cells and an enhancement of EGF impact in keratinocytes.

The Intrinsic Relation between the Hydrogel Structure and In Vivo Performance of Hyaluronic Acid Dermal Fillers: A Comparative Study of Four Typical Dermal Fillers

BACKGROUND

Hyaluronic acid dermal fillers are composed of cross-linked viscoelastic particles with high biocompatibility. The performance of the fillers is determined by the viscoelastic properties of particles and the connecting force between particles. However, the relationships among the properties of fillers, the interaction of the gels and the surrounding tissue are not clear enough.

METHOD

Four kinds of typical dermal filler were selected in this research to reveal the interaction between the gels and cells. A series of analytical tools was applied to characterize the structure and physicochemical properties of the gel, as well as observing their interaction with the surrounding tissues in vivo and discussing their internal mechanism.

RESULT

The large particles internal the gel and the high rheological properties endow the Restylane2 with excellent support. However, these large-size particles have a significant impact on the metabolism of the local tissue surrounding the gel. Juvéderm3 present gel integrity with the high cohesiveness and superior support. The rational matching of large and small particles provides the Juvéderm3 with supporting capacity and excellent biological performance. Ifresh is characterized by small-size particles, moderate cohesiveness, good integrity, lower viscoelasticity and the superior cellular activity located the surrounding tissues. Cryohyaluron has high cohesion and medium particle size and it is prominent in cell behaviors involving localized tissues. Specific macroporous structure in the gel may facilitate the nutrients delivering and removing the waste.

CONCLUSION

It's necessary to make the filler both sufficient support and biocompatibility through the rational matching of particle sizes and rheological properties. Gels with macroporous structured particle showed an advantage in this area by providing a space inside the particle.

From crosslinking strategies to biomedical applications of hyaluronic acid-based hydrogels: A review

Hyaluronic acid (HA) is not only a natural anionic polysaccharide with excellent biocompatibility, biodegradability, and moisturizing effect, but also an essential factor that can affect angiogenesis, inflammation, cell behavior, which has a wide range of applications in the biomedical field. Among them, HA-based hydrogels formed by various physical or chemical crosslinking strategies are particularly striking. They not only retain the physiological function of HA, but also have the skeleton function of hydrogel, which further expands the application of HA. However, HA-based natural hydrogels generally have problems such as insufficient mechanical strength and susceptibility to degradation by hyaluronidase, which limits their application to a certain extent. To solve such problems, researchers have prepared a variety of HA-based multifunctional hydrogels with remarkable properties in recent years by adopting various structural modification methods or novel crosslinking strategies, as well as introducing functionally reactive molecules or moieties, which have extended the application scope. This manuscript systematically introduced common crosslinking strategies of HA-based hydrogels and highlighted the development of novel HA-based hydrogels in anticancer drug delivery, cartilage repair, three-dimensional cell culture, skin dressing and other fields. We hope to provide some references for the subsequent development of HA-based hydrogels in the biomedical field.

Multidose Hyaluronidase Administration as an Optimal Procedure to Degrade Resilient Hyaluronic Acid Soft Tissue Fillers

Minimally invasive hyaluronan (HA) tissue fillers are routinely employed to provide tissue projection and correct age-related skin depressions. HA fillers can advantageously be degraded by hyaluronidase (HAase) administration in case of adverse events. However, clear guidelines regarding the optimal dosage and mode of administration of HAase are missing, leaving a scientific gap for practitioners in their daily practice. In this study, we implemented a novel rheological procedure to rationally evaluate soft tissue filler degradability and optimize their degradation kinetics. TEOSYAL RHA^® filler degradation kinetics in contact with HAase was monitored in real-time by rheological time sweeps. Gels were shown to degrade as a function of enzymatic activity, HA concentration, and BDDE content, with a concomitant loss of their viscoelastic properties. We further demonstrated that repeated administration of small HAase doses improved HA degradation kinetics over large single doses. Mathematical analyses were developed to evaluate the degradation potential of an enzyme. Finally, we tuned the optimal time between injections and number of enzymatic units, maximizing degradation kinetics. In this study, we have established a scientific rationale for the degradation of HA fillers by multidose HAase administration that could serve as a basis for future clinical management of adverse events.

Silica Hydrogels as Platform for Delivery of Hyaluronic Acid

Hyaluronic acid (HA) is chondroprotective and anti-inflammatory drug used clinically for treatment of inflammatory disorders (arthritis, skin diseases, bowel diseases, etc.). In addition, HA is a crucial ingredient in the cosmetic products used to eliminate the unpleasant consequences of inflammatory skin diseases. The main disadvantages that limit its use are its low mechanical properties and its rapid biodegradation. In this paper, silica hydrogels are considered as a promising matrix for HA to improve its properties. The hybrid HA-silica hydrogels were synthesized by the sol-gel method. Morphology of the hydrogels was investigated by optical microscopy and scanning electron microscopy methods. Taking into account their potential applications for topical and injectable delivery, much attention was paid to investigation of deformation properties of the hydrogels under shear, compression, and tension. Their resistance to enzymatic degradation in vitro was estimated. Kinetics and mechanisms of HA release from the hybrid hydrogels in vitro were also studied. It was found that the indicated properties can be controlled by synthesis conditions, HA molecular weight, and its loading in the hydrogels. Silica hydrogels are a prospective platform for the development of new soft formulations and cosmetic compositions of HA with improved pharmacological and consumer properties.

Investigation of the Sorption Capacity of Polyvinylpyrrolidone Copolymers As the Basis of Hydrogel Cosmetic Masks with Plant Biomass Extracts

The possibility of using hydrogels based on copolymers of polyvinylpyrrolidone with 2 hydroxyethylmethacrylate to saturate them with plant extracts was established. Hydrogel materials were obtained with extracts of Calendula officinalis and Arnica montana. The sorption capacity of the hydrogels regarding the extract data was determined. The bactericidal and fungicidal activity of the obtained hydrogel materials with extracts of Calendula officinalis and Arnica montana on bacterial strains of Escherichia coli, Staphylococcus aureus and fungal strains of Candida tenuis, Aspergilus niger were investigated.

Hyaluronic Acid in Biomedical Fields: New Trends from Chemistry to Biomaterial Applications

The aim of this review is to give an updated perspective about the methods for chemical modifications of hyaluronic acid (HA) toward the development of new applications in medical devices and material engineering. After a brief introduction on chemical, structural and biological features of this important natural polysaccharide, the most important methods for chemical and physical modifications are disclosed, discussing both on the formation of new covalent bonds and the interaction with other natural polysaccharides. These strategies are of paramount importance in the production of new medical devices and materials with improved properties. In particular, the use of HA in the development of new materials by means of additive manufacturing techniques as electro fluid dynamics, i.e., electrospinning for micro to nanofibres, and three-dimensional bioprinting is also discussed.

Benefit of Hyaluronic Acid to Treat Facial Aging in Completely Edentulous Patients

Hyaluronic acid (HA) is widely used in aesthetic medicine for its moisturizing and anti-aging action. This molecule, which is naturally present in the body, has an interesting response to aging, accentuated in totally edentulous patients. While its aesthetic benefits for facial rejuvenation are well-documented, there is a lack of description and investigation on its therapeutic usefulness for edentulous patients. The management of completely edentulous patients is a daily reality in dental practice and requires specific attention. The aesthetic and functional challenge is considerable. The displacement of the bone base, which is often marked, and lack of soft tissue support are sometimes difficult to correct with prosthetic reconstruction. This review aims to present the physiological processes appearing in completely edentulous patients and prosthetic solutions available to recreate oral functions and counteract facial aging. As prosthetic rehabilitations are not fully satisfying for counterbalancing the impression of excessive facial aging, we investigated the applications of HA injection in the perioral area, in order to improve edentulism treatment, and discussed the advantages and disadvantages, compared to other dermal fillers and rejuvenation therapies. Considering the specific situations of edentulous patients, dermal HA injections help to correct uncompensated bone losses and mucous volume losses and appear to be a therapeutically beneficial for treating completely edentulous patients, without the requirement to full rejuvenation therapy.

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.

Hyaluronan Hydrogels: Rheology and Stability in Relation to the Type/Level of Biopolymer Chemical Modification

BDDE (1,4-butanediol-diglycidylether)-crosslinked hyaluronan (HA) hydrogels are widely used for dermo-aesthetic purposes. The rheology and stability of the gels under physiological conditions greatly affect their clinical indications and outcomes. To date, no studies investigating how these features are related to the chemistry of the polymeric network have been reported. Here, four available HA-BDDE hydrogels were studied to determine how and to what extent their rheology and stability with respect to enzymatic hydrolysis relate to the type and degree of HA structural modification. ¹H-/¹³C-NMR analyses were associated for the quantification of the “true” HA chemical derivatization level, discriminating between HA that was effectively crosslinked by BDDE, and branched HA with BDDE that was anchored on one side. The rheology was measured conventionally and during hydration in a physiological medium. Sensitivity to bovine testicular hyaluronidase was quantified. The correlation between NMR data and gel rheology/stability was evaluated. The study indicated that (1) the gels greatly differed in the amounts of branched, crosslinked, and overall modified HA, with most of the HA being branched; (2) unexpectedly, the conventionally measured rheological properties did not correlate with the chemical data; (3) the gels’ ranking in terms of rheology was greatly affected by hydration; (4) the rheology of the hydrated gels was quantitatively correlated with the amount of crosslinked HA, whereas the correlations with the total HA modification level and with the degree of branched HA were less significant; (5) increasing HA derivatization/crosslinking over 9/3 mol% did not enhance the stability with respect to hyaluronidases. These results broaden our knowledge of these gels and provide valuable information for improving their design and characterization.

Drug Delivery from Hyaluronic Acid–BDDE Injectable Hydrogels for Antibacterial and Anti-Inflammatory Applications

Hyaluronic acid (HA) injectable biomaterials are currently applied in numerous biomedical areas, beyond their use as dermal fillers. However, bacterial infections and painful inflammations are associated with healthcare complications that can appear after injection, restricting their applicability. Fortunately, HA injectable hydrogels can also serve as drug delivery platforms for the controlled release of bioactive agents with a critical role in the control of certain diseases. Accordingly, herein, HA hydrogels were crosslinked with 1 4-butanediol diglycidyl ether (BDDE) loaded with cefuroxime (CFX), tetracycline (TCN), and amoxicillin (AMX) antibiotics and acetylsalicylic acid (ASA) anti-inflammatory agent in order to promote antibacterial and anti-inflammatory responses. The hydrogels were thoroughly characterized and a clear correlation between the crosslinking grade and the hydrogels’ physicochemical properties was found after rheology, scanning electron microscopy (SEM), thermogravimetry (TGA), and differential scanning calorimetry (DSC) analyses. The biological safety of the hydrogels, expected due to the lack of BDDE residues observed in ¹H-NMR spectroscopy, was also corroborated by an exhaustive biocompatibility test. As expected, the in vitro antibacterial and anti-inflammatory activity of the drug-loaded HA-BDDE hydrogels was confirmed against Staphylococcus aureus by significantly decreasing the pro-inflammatory cytokine levels.

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.

Potential of Biofermentative Unsulfated Chondroitin and Hyaluronic Acid in Dermal Repair

Chondroitin obtained through biotechnological processes (BC) shares similarities with both chondroitin sulfate (CS), due to the dimeric repetitive unit, and hyaluronic acid (HA), as it is unsulfated. In the framework of this experimental research, formulations containing BC with an average molecular size of about 35 KDa and high molecular weight HA (HHA) were characterized with respect to their rheological behavior, stability to enzymatic hydrolysis and they were evaluated in different skin damage models. The rheological characterization of the HHA/BC formulation revealed a G’ of 92 ± 3 Pa and a G″ of 116 ± 5 Pa and supported an easy injectability even at a concentration of 40 mg/mL. HA/BC preserved the HHA fraction better than HHA alone. BTH was active on BC alone only at high concentration. Assays on scratched keratinocytes (HaCaT) monolayers showed that all the glycosaminoglycan formulations accelerated cell migration, with HA/BC fastening healing 2-fold compared to the control. In addition, in 2D HaCaT cultures, as well as in a 3D skin tissue model HHA/BC efficiently modulated mRNA and protein levels of different types of collagens and elastin remarking a functional tissue physiology. Finally, immortalized human fibroblasts were challenged with TNF-α to obtain an in vitro model of inflammation. Upon HHA/BC addition, secreted IL-6 level was lower and efficient ECM biosynthesis was re-established. Finally, co-cultures of HaCaT and melanocytes were established, showing the ability of HHA/BC to modulate melanin release, suggesting a possible effect of this specific formulation on the reduction of stretch marks. Overall, besides demonstrating the safety of BC, the present study highlights the potential beneficial effect of HHA/BC formulation in different damage dermal models.

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.

Hyaluronan and Derivatives: An In Vitro Multilevel Assessment of Their Potential in Viscosupplementation

In this research work, viscosupplements based on linear, derivatized, crosslinked and complexed HA forms were extensively examined, providing data on the hydrodynamic parameters for the water-soluble-HA-fraction, rheology, sensitivity to enzymatic hydrolysis and capacity to modulate specific biomarkers’ expression in human pathological chondrocytes and synoviocytes. Soluble HA ranged from 0 to 32 mg/mL and from 150 to 1330 kDa MW. The rheological behavior spanned from purely elastic to viscoelastic, suggesting the diversity of the categories that are suitable for restoring specific/different features of the healthy synovial fluid. The rheological parameters were reduced in a diverse manner upon dilution and hyaluronidases action, indicating different durations of the viscosupplementation effect. Bioactivity was found for all the samples, increasing the expression of different matrix markers (e.g., hyaluronan-synthase); however, the hybrid cooperative complexes performed better in most of the experiments. Hybrid cooperative complexes improved COLII mRNA expression (~12-fold increase vs. CTR), proved the most effective at preserving cell phenotype. In addition, in these models, the HA samples reduced inflammation. IL-6 was down-regulated vs. CTR by linear and chemically modified HA, and especially by hybrid complexes. The results represent the first comprehensive panel of data directly comparing the diverse HA forms for intra-articular injections and provide valuable information for tailoring products’ clinical use as well as for designing new, highly performing HA-formulations that can address specific needs.

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.

Hyaluronan as a Prominent Biomolecule with Numerous Applications in Medicine

Hyaluronan (HA) is a natural glycosaminoglycan present in many tissues of all vertebrates. HA has various biological functions, which are dependent on its molar mass. High-molar-mass HA has anti-angiogenic, immunosuppressive and anti-inflammatory properties, while low-molar-mass HA has opposite effects. HA has also antioxidative properties, however on the other hand it can be readily degraded by reactive oxygen species. For many years it has been used in treatment of osteoarthritis, cosmetics and in ophthalmology. In the last years there has been a growing interest of HA to also be applied in other fields of medicine such as skin wound healing, tissue engineering, dentistry and gene delivery. In this review we summarize information on modes of HA administration, properties and effects of HA in various fields of medicine including recent progress in the investigation of HA.

Hyaluronan Hydrogels for Injection in Superficial Dermal Layers: An In Vitro Characterization to Compare Performance and Unravel the Scientific Basis of Their Indication

Background: Skinboosters represent the latest category of hyaluronan (HA) hydrogels released for aesthetic purposes. Different from originally developed gels, they are intended for more superficial injections, claiming a skin rejuvenation effect through hydration and possibly prompting biochemical effects in place of the conventional volumetric action. Here, three commercial skinboosters were characterized to unravel the scientific basis for such indication and to compare their performances. Methods: Gels were evaluated for water-soluble/insoluble-HA composition, rheology, hydration, cohesivity, stability and effect, in vitro, on human dermal fibroblasts towards the production of extracellular matrix components. Results: Marked differences in the insoluble-hydrogel amount and in the hydrodynamic parameters for water-soluble-HA chains were evidenced among the gels. Hydration, rigidity and cohesivity also varied over a wide range. Sensitivity to hyaluronidases and Reactive Oxygen Species was demonstrated allowing a stability ranking. Slight differences were found in gels’ ability to prompt elastin expression and in ColIV/ColI ratio. Conclusions. A wide panel of biophysical and biochemical parameters for skinboosters was provided, supporting clinicians in the conscious tuning of their use. Data revealed great variability in gels’ behavior notwithstanding the same clinical indication and unexpected similarities to the volumetric formulations. Data may be useful to improve customization of gel design toward specific uses.

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.

[Paradigm shift in understanding hyaluronic acid filler effects]

Hyaluronic acid (hyaluron; HA) is an important constituent of the extracellular matrix and has an age-dependent decrease in tissue concentration. While natural HA is rapidly degraded, filler cross-linked HA achieve a half-life of 6-12 months. Such fillers enjoy increasing popularity in esthetic medicine and are versatile tools. Although HA fillers can activate fibroblasts it is of minor importance for long-term results. Fillers are injected into subcutaneous adipose tissue. Their interaction with somatic stem cells and mature adipocytes has gained increasing interest. Cross-linked HA can indeed support proliferation of pre-adipocytes, stimulate their differentiation into mature adipocytes and protect the mature cells from senescence, apoptosis and lipolysis. This view offers a new perspective on the development of future fillers for esthetic medicine.

Biopolymer-based Scaffolds for Tissue Engineering Applications

Tissue engineering is governed by the use of cells and polymers. The cells may be accounted for the type of tissue to be targeted, while polymers may vary from natural to synthetic. The natural polymers have advantages such as non-immunogenic and complex structures that help in the formation of bonds in comparison to the synthetic ones. Various targeted drug delivery systems have been prepared using polymers and cells, such as nanoparticles, hydrogels, nanofibers, and microspheres. The design of scaffolds depends on the negative impact of material used on the human body and they have been prepared using surface modification technique or neo material synthesis. The dermal substitutes are a distinctive array that aims at the replacement of skin parts either through grafting or some other means. This review focuses on biomaterials for their use in tissue engineering. This article shall provide the bird's eye view of the scaffolds and dermal substitutes, which are naturally derived.

Hyaluronidase Inhibitor-Incorporated Cross-Linked Hyaluronic Acid Hydrogels for Subcutaneous Injection

Hyaluronidase (HAase) inhibitor-incorporated hyaluronic acid (HA) hydrogel cross-linked with 1,4-butanediol diglycidyl ether (BDDE) was designed to reduce the toxicity risk induced by BDDE and its biodegradation rate in subcutaneous tissue. The formulation composition of hydrogel and its preparation method were optimized to have a high swelling ratio and drug content. Quercetin (QCT) and quetiapine (QTP), as an HAase inhibitor and model drug, respectively, were incorporated into the cross-linked hydrogel using the antisolvent precipitation method for extending their release after subcutaneous injection. The cross-linked HA (cHA)-based hydrogels displayed appropriate viscoelasticity and injectability for subcutaneous injection. The incorporation of QCT (as an HAase inhibitor) in the cHA hydrogel formulation resulted in slower in vitro and in vivo degradation profiles compared to the hydrogel without QCT. Single dosing of optimized hydrogel injected via a subcutaneous route in rats did not induce any acute toxicities in the blood chemistry and histological staining studies. In the pharmacokinetic study of rats following subcutaneous injection, the cHA hydrogel with QCT exhibited a lower maximum QTP concentration and longer half-life and mean residence time values compared to the hydrogel without QCT. All of these results support the designed HAase inhibitor-incorporated cHA hydrogel being a biocompatible subcutaneous injection formulation for sustained drug delivery.

Evaluation of the Volumizing Performance of a New Volumizer Filler in Volunteers with Age-Related Midfacial Volume Defects

Purpose

The primary aim of this study was to evaluate the performance of the study product, in terms of volumizing activity as well as the duration of the effect, in women with age-related midfacial volume defects. In addition, the study allowed the evaluation of the tolerability of the product by both volunteers and investigators.

Patients and Methods

Twenty-two female volunteers, aged 42–60 years, participated in this study, which was performed under dermatological control in a single center. After an initial visit at baseline to verify adherence to the protocol criteria, volunteers received an injection of Aliaxin^® SV (IBSA Farmaceutici Italia Srl), followed 3–4 weeks later by a second touch-up treatment to treat eventual asymmetries. Four subsequent visits, the last performed 9 months from the first injection, were performed to evaluate clinically and instrumentally the efficacy of the treatment.

Results

Clinical and statistically significant improvement in cheek volume was recorded after the first postinjection visit, and the effect was maintained until the end of the study period. A clinically measurable amelioration of wrinkle severity was also observed. By 3D picture recording and subsequent quantitative analysis, it was possible to determine the efficacy in terms of increased facial volume, which was already appreciable at the first visit, was further increased at the second and third visits and was maintained at the fourth and last visits. The injections were very well tolerated by the volunteers, as determined by their self-evaluation questionnaires.

Conclusion

The results of the study confirm the esthetic performance of the study product on age-related midfacial volume defects. The very strong high-volumizing activity of the study product was not only properly determined by the investigators but also confirmed by self-evaluation by the volunteers. These effects were obtained with no appreciable undesired effects.

Biochemical and physical actions of hyaluronic acid delivered by intradermal jet injection route

Administration of exogenous hyaluronic acid (HA) by liquid jet injection is considered as a beneficial therapy for dermatology conditions. This paper reviews variety of the factors which would optimize the clinical output of hyaluronic acid in this treatment modality. A pneumatically accelerated jet penetrates the epidermis and spherically spreads micro-droplets of HA in the dermis without significant damage to the tissue and blood vessels. Kinetic energy of the jet activates two parallel mechanisms of action-mechanical and biological-which act synergistically to initiate and augment the regenerative effect. Jet-induced micro-trauma stimulates collagen synthesis and tissue repair without inflammation. Aside from the biophysical stimulation of dermal fibroblast, the biomolecular properties of exogenous HA provide excellent clinical results for skin atrophy, remodeling of dermal scarring, and reverse formation of fibrotic tissue. The effect is mediated by HA-specific cell receptors and depends on molecular weight and the rheological properties of HA polymer. Skin mechanical properties play a key role in predicting HA dispersion patterns. Tolerability and safety of the treatment approach are determined by the jet's physical impact on the tissue and/or by the safety profile of the injected material. Although pneumatic jet delivery of a hyaluronic acid has a limited use in clinical practice, this treatment approach has a strong potential for extended implementation in esthetic dermatology. The synergistic mechanism has significant advantages of predictable and rapid clinical outcomes with a low discomfort. Additional well-designed investigations are required for establishing a scientific foundation and guidelines for this treatment modality.

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.

Improvements in Skin Quality Biological Markers in Skin Explants Using Hyaluronic Acid Filler VYC-12L

Hyaluronic acid (HA), both crosslinked and uncrosslinked, is used clinically to treat fine lines and provides additional improvements in skin quality attributes. The purpose of this study was to assess potential early differences in the expression of biological markers of skin quality in living human skin explants injected with uncrosslinked and crosslinked HA gels.

Methods

Living human skin explants injected with VYC-12L or noncrosslinked HA with mannitol (HYD) and noninjected controls were assessed via microscopy, histology, and immunohistochemistry on days 3 and/or 8 for biological markers of elasticity (collagen density, elastin, fibrillin-1) and hydration [aquaporin-3, acidic glycosaminoglycans (GAGs), HA]. Hydration was also assessed via a corneometer probe on days 0, 1, 2, and 8.

Results

On day 3 versus controls, VYC-12L moderately increased collagen density in the upper reticular dermis and clearly increased fibrillin-1 expression, with slight increases persisting on day 8. Increases with HYD were smaller and did not persist on day 8. Both VYC-12L and HYD increased aquaporin-3 expression and GAG content on days 3 and 8, but VYC-12L produced greater GAG increases in the reticular dermis. Day 8 instrument-assessed hydration increased by 49% and 22% for VYC-12L and HYD, respectively. Elastin expression in oxytalan and elaunin fibers was unchanged. Upper-dermal HA reductions suggested HA injection-induced hyaluronidase expression.

Conclusion

VYC-12L produced greater, more lasting improvements in biological markers of skin quality than HYD.

Breaking the Glass Ceiling

Over the past century, the life expectancy in industrialized countries has rapidly risen by over 30 years due to improvements in standards of medical care, sanitation, and lifestyle. Estimation of life expectancy has traditionally been viewed through a lens of epidemiology and public health. However, this data, while considered the "gold standard" of measuring healthy life expectancy, may soon find itself redundant in the face of advancing medical technology. Even as average life expectancy has increased, there has not been an equivalent increase in healthy life expectancy, or "healthspan"; furthermore, there is a current trend of stagnation in life expectancy, as the supposed increases are estimated to be drastically slowing down, in part due to exhaustion of our current ability to extend the human lifespan. In this viewpoint, we will examine the developing fields of medicine and life sciences which will reshape our current approach to life expectancy prediction.

Hyaluronan Dermal Fillers: Efforts Towards a Wider Biophysical Characterization and the Correlation of the Biophysical Parameters to the Clinical Outcome

Introduction

Hyaluronic Acid (HA) fillers are among the most used products in cosmetic medicine. Companies offer different formulations to allow full facial treatment and/or remodeling. Gels are being studied to establish the biophysical properties behind the specific clinical use and a correlation between the gel biophysical properties and their clinical performance. Clinicians' awareness is growing about the potential benefit deriving from such biophysical characterization.

Aim

The Aliaxin^® line of HA dermal fillers is the object of this study. The study aimed to widen the biophysical characterization of these gels by investigating a variety of properties to better support their optimal use. Further, we aimed to provide some clinical findings to gain a deeper insight into the correlation between filler features and clinical outcome.

Methods

The four gels of the line were investigated, for the first time, for their cohesivity and stability to Reactive Oxygen Species (ROS). Additional secondary rheological parameters; evidence of relative water-uptake ability; and some clinical findings on product safety, palpability and duration of the aesthetic effect are provided.

Results and conclusion

The gels proved highly cohesive and sensitive to ROS action with stability declining with the decrease in the overall gel elasticity. The G* and complex viscosity values at clinically relevant frequencies and gel water-uptake ability are consistent with the relative clinical indication related to gel projection and hydration capacity. Clinical outcomes showed the safety of the products and a perception of palpability well correlating with the cohesive/viscosity properties of the gels. A similar duration of the aesthetic effect (up to 1 year) was observed despite the diverse in vitro gel stability. The results broaden our knowledge of these gels and may contribute to optimize their clinical use towards the improvement of patient safety and satisfaction. Initial clinical observation indicated that gel biophysical properties allow for a reliable prediction of gel palpability, while in vitro data on gel stability cannot be related to the duration of the observed skin improvement. The latter finding further corroborates the idea of a skin restoration process activated by the gels besides the physical volumetric action.

Hyaluronan-based hydrogels via ether-crosslinking: Is HA molecular weight an effective means to tune gel performance?

Hyaluronan (HA)-based hydrogels obtained by crosslinking the biopolymer via ether bonds are widely used in clinical practice. There is interest in improving the design of these gels to match specific properties. Here, the possibility to tune HA-hydrogel behavior by adjusting the molecular weight distribution of the biopolymer undergoing crosslinking was investigated. Three HA samples (500, 1100 and 1600 kDa) underwent reaction with 1,4-butandioldiglycidyl-ether(BDDE) under reported conditions and the crosslinked products were characterized for chemical modification extent, swelling, rheological behavior, cohesivity, sensitivity to enzymatic degradation and effect on Human Dermal Fibroblasts (HDF). HA hydrolysis, under the highly alkaline crosslinking conditions, was also studied for the first time. The main achievements are that 1) varying HA chain length affects hydrogel behavior less than expected, due to the de-polymerization occurring alongside crosslinking, that reduces the differences in sample size 2) when differences in chain length persist notwithstanding hydrolysis, lowering HA size is a means to prepare more concentrated formulations, expected to exhibit longer duration and better cohesivity in vivo, while retaining a certain rigidity, preserving biocompatibility and slightly influencing HDF behavior in relation to CollagenI production. The study shed light on aspects concerning BDDE-HA gel manufacturing and contributed to the improvement of their design.