Rheologic properties of soft tissue fillers and implications for clinical use

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.

Nonsurgical Gluteal Volume Correction with Hyaluronic Acid: A Retrospective Study to Assess Long-term Safety and Efficacy

Background

Augmentation and reshaping of body volume, particularly in the gluteal area, presents a significant challenge in aesthetic surgery. Hyaluronic acid (HA) fillers have emerged as an effective and safe tool for such indications, but literature examining nonsurgical gluteal reshaping with HA remains limited. This study aims to evaluate the long-term safety of using recommended volumes of HA body fillers for nonsurgical gluteal augmentation.

Methods

A retrospective, observational study was carried out across multiple centers in Italy and the United Arab Emirates. The study involved participants between 22 and 53 years of age who underwent gluteal augmentation using HA body filler (HYAcorp MLF1/2) between 2017 and 2021, with up to 4 years and 7 months of follow-up. Participants and investigators independently evaluated the procedure's effectiveness by comparing pre- and posttreatment photographs. The Global Aesthetic Improvement Scale was used to assess posttreatment satisfaction by both participants and investigators. All adverse effects (AEs) were recorded.

Results

The study included a diverse group of 91 participants. No serious adverse events were reported, with the majority of AE occurring shortly after treatment and resolving in 1 week. AEs were more frequently observed in participants with previous treatments using different substances in the treatment area.

Conclusions

The real-world application of HA body filler (HYAcorp MLF1/2) for gluteal augmentation in the participants of this study showed the treatment's effectiveness, with no severe adverse events reported among the participants. High levels of satisfaction were reported among both participants and investigators.

A Covalently Cross-Linked Hyaluronic Acid/Carboxymethyl Cellulose Composite Hydrogel as a Potential Filler for Soft Tissue Augmentation

The use of fillers for soft tissue augmentation is an approach to restore the structure in surgically or traumatically created tissue voids. Hyaluronic acid (HA), is one of the main components of the extracellular matrix, and it is widely employed in the design of materials with features similar to human tissues. HA-based fillers already find extensive use in soft tissue applications, but are burdened with inherent drawbacks, such as poor thermal stability. A well-known strategy to improve the HA properties is to reticulate it with 1,4-Butanediol diglycidyl ether (BDDE). The aim of this work was to improve the design of HA hydrogels as fillers, by developing a crosslinking HA method with carboxymethyl cellulose (CMC) by means of BDDE. CMC is a water soluble cellulose ether, whose insertion into the hydrogel can lead to increased thermal stability. HA/CMC hydrogels at different ratios were prepared, and their rheological properties and thermal stability were investigated. The hydrogel with an HA/CMC ratio of 1/1 resulted in the highest values of viscoelastic moduli before and after thermal treatment. The morphology of the hydrogel was examined via SEM. Biocompatibility response, performed with the Alamar blue assay on fibroblast cells, showed a safety percentage of around 90% until 72 h.

Precision of Soft-Tissue Filler Injections: An Ultrasound-Based Verification Study

BACKGROUND

Uncontrolled product spread is an important issue to consider in facial filler injections. Lack of precision can result in reduced effectiveness and surface projection, as well as irregularities and product visibility.

OBJECTIVES

The authors sought to assess the precision of soft-tissue filler injections in the face by employing a cannula.

METHODS

This single-center observational study investigated soft-tissue filler distribution utilizing real-time non-invasive ultrasound imaging. Outcome parameters included (1) the tissue plane of product distribution, (2) the extent of horizontal as well as vertical product spread at the injection site, and (3) the product surface area taking into account the multifactorial influence of several independent variables. Participants were followed up to 30 days post-injection.

RESULTS

A total 100 facial injections were performed in 8 patients (2 males, 6 females) with a mean age of 37.20 (±6.34) years and a mean BMI of 22.21 (±1.39) kg/m.2. The plane of product distribution remained constant in approximately 90% of cases at day 0 (d0), d14, and d30. Mean horizontal product spread was higher compared with vertical spread, and both significantly decreased over all time points (P < .001). Mean product surface area was 22.51 ± 16.34 mm2 at d0, 15.97 ± 11.28 mm2 at d14, and 12.9 ± 9.15 mm2 at d30. Analysis employing generalized linear models revealed that injection volume and injection depth significantly influenced product surface area.

CONCLUSIONS

Injection of soft-tissue filler employing a cannula allows precise application of the product within the intended tissue plane. Precision can be improved by injecting less product into deeper tissue layers.

LEVEL OF EVIDENCE: 5

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.

COVID-19 vaccines and filler reactions: Should it be considered as a concern?

BACKGROUND

Any implant or external material used in the body tissues can potentially be followed by autoimmune or inflammatory reactions. With the global vaccination program against COVID-19, the reports of tissue filler reactions would be increasingly demonstrated.

AIM

To summarize the data regarding COVID vaccination and filler reactions.

METHOD

We reviewed the existing data in this regard through searching on PubMed, Google Scholar and Scopus. All of the relevant papers published until March 2022, which we could access to their fulltexts were included.

RESULTS

Here, we summarized the data regarding COVID-19 vaccination and filler reactions and discussed its etiopathogenesis, management, and importance.

CONCLUSION

Although the end of pandemic was announced, the necessity of continuing COVI-D19 vaccination in future mandates gathering data regarding safety of vaccines.

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.

Application Status of Sacrificial Biomaterials in 3D Bioprinting

Additive manufacturing, also known as three-dimensional (3D) printing, relates to several rapid prototyping (RP) technologies, and has shown great potential in the manufacture of organoids and even complex bioartificial organs. A major challenge for 3D bioprinting complex org unit ans is the competitive requirements with respect to structural biomimeticability, material integrability, and functional manufacturability. Over the past several years, 3D bioprinting based on sacrificial templates has shown its unique advantages in building hierarchical vascular networks in complex organs. Sacrificial biomaterials as supporting structures have been used widely in the construction of tubular tissues. The advent of suspension printing has enabled the precise printing of some soft biomaterials (e.g., collagen and fibrinogen), which were previously considered unprintable singly with cells. In addition, the introduction of sacrificial biomaterials can improve the porosity of biomaterials, making the printed structures more favorable for cell proliferation, migration and connection. In this review, we mainly consider the latest developments and applications of 3D bioprinting based on the strategy of sacrificial biomaterials, discuss the basic principles of sacrificial templates, and look forward to the broad prospects of this approach for complex organ engineering or manufacturing.

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.

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.

A mini-review of embedded 3D printing: supporting media and strategies

Embedded 3D printing is an additive manufacturing method based on a material extrusion strategy.