Chemical and mechanical characterization of hyaluronic acid hydrogel cross‐linked with polyethylen glycol and its use in dermatology

Clinical efficacy and safety of hyaluronic acid gel injection in the glans penis for treatment of premature ejaculation: systematic review and meta-analysis

BACKGROUND

In recent years, there has been growing interest in the use of hyaluronic acid (HA) for the treatment of premature ejaculation (PE). The efficacy of this treatment is quite controversial.

AIM

This study intended to evaluate the efficacy and safety of glans penis augmentation with HA gel for PE.

METHODS

This systematic review includes randomized controlled trials (RCTs), primary clinical trials, prospective and retrospective studies, case series, and case reports. Searches in Embase, PubMed, Cochrane, Web of Knowledge, and ClinicalTrials.gov were performed blindly by 2 reviewers.

OUTCOMES

Intravaginal ejaculation latency time (IELT), questionnaires about PE, glans circumference (millimeters), and adverse events.

RESULTS

Thirteen studies were included in the evaluation: 4 RCTs, 8 prospective observational studies, and 1 restrospective study. The number of patients who received HA gel on the glans penis was 706. According to the results of 2 placebo-controlled RCTs, HA gel treatment significantly improved IELT at the end of the first month (mean difference [MD], 65.44 seconds). In the first month after the HA gel injection procedure, IELT increased vs before the procedure (MD, 176.18 [95% CI, 146.89-205.48]; P < .001, I2 = 83%). When the IELT values ​​were compared at 6 months after HA gel application, IELT improved vs before the procedure (MD, 143.93 [95% CI, 124.78-163.09]; P < .001, I2 = 82). The glans circumference expanded by approximately 1.5 cm after the procedure (MD, 14.82 mm [95% CI, 12.75-16.90]; P < .001, I2 = 65%). When the side effect profile of other studies was examined, side effects were observed in 91 patients after HA gel injection applied to 598 patients (15.22%). Among these side effects, the most common were pain (n = 46, 7.69%), bulla/nodule formation (n = 25, 4.18%), and ecchymosis (n = 20, 3.34%).

CONCLUSION

While HA shows promise as a therapeutic option for PE, ongoing research is essential to elucidate its clinical utility, mechanisms of action, and comparative efficacy.

Efficacy and Safety of Neauvia Intense in Correcting Moderate-to-Severe Nasolabial Folds: A Post-Market, Prospective, Open-Label, Single-Centre Study

Purpose

 This prospective, single-center study aims to evaluate the safety and effectiveness of NEAUVIA Intense, a PEG cross-linked polymeric hydrogel, in correcting moderate-to-severe nasolabial folds (NLF) in a routine clinical setting. The study investigates the aesthetic outcomes, patient satisfaction, and adverse events associated with the injectable filler.

Patients and Methods

Seventy patients were initially enrolled, with 60 meeting study parameters. The post-market study involved a single session treatment, employing NEAUVIA Intense on each side of the NLF. Assessments utilized the Modified Fitzpatrick Wrinkle Scale (MFWS), Global Aesthetic Improvement Scale (GAIS), and Visual Analogical Scale (VAS).

Results

 The study demonstrated a statistically significant improvement in tissue depression immediately post-injection (p < 0.001), with sustained effects up to 6 months. MFWS assessments revealed that responder patients were 96.6% immediately after treatment, 76.6% one month, 48.3% after 3 months, and 28.3% at 6 months (p < 0.001). Additionally, there was a significant change in the frequency distribution of MFWS scores post-treatment (p < 0.001), with the majority of patients experiencing improvement in tissue depression. Maximum improvement was observed at 30- and 90-days post-treatment based on GAIS assessments. Patient and physician satisfaction, measured by VAS, remained stable over time, with fluctuations at 4 and 24 weeks after treatment (p < 0.001, Anova; p < 0.05, Wilcoxon). Throughout the entire follow-up duration of the patients enrolled in the study, no adverse effects related to the use of the product were observed.

Conclusion

 NEAUVIA Intense proved to be an effective solution for correcting NLF, providing significant and lasting improvements in tissue depression and aesthetic outcomes. The study underscores the necessity for continuous assessment in aesthetic medicine to align outcomes with evolving patient expectations and optimize long-term results. The findings contribute to the understanding of this specific hydrogel filler and highlight the broader context of injectable fillers in comprehensive facial aesthetic strategies.

Microneedles Based on a Biodegradable Polymer-Hyaluronic Acid

Transdermal transport can be challenging due to the difficulty in diffusing active substances through the outermost layer of the epidermis, as the primary function of the skin is to protect against the entry of exogenous compounds into the body. In addition, penetration of the epidermis for substances hydrophilic in nature and particles larger than 500 Da is highly limited due to the physiological properties and non-polar nature of its outermost layer, namely the stratum corneum. A solution to this problem can be the use of microneedles, which "bypass" the problematic epidermal layer by dispensing the active substance directly into the deeper layers of the skin. Microneedles can be obtained with various materials and come in different types. Of special interest are carriers based on biodegradable and biocompatible polymers, such as polysaccharides. Therefore, this paper reviews the latest literature on methods to obtain hyaluronic acid-based microneedles. It focuses on the current advancements in this field and consequently provides an opportunity to guide future research in this area.

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.

Glycosaminoglycans' Ability to Promote Wound Healing: From Native Living Macromolecules to Artificial Biomaterials

Glycosaminoglycans (GAGs) are important for the occurrence of signaling molecules and maintenance of microenvironment within the extracellular matrix (ECM) in living tissues. GAGs and GAG-based biomaterial approaches have been widely explored to promote in situ tissue regeneration and repair by regulating the wound microenvironment, accelerating re-epithelialization, and controlling ECM remodeling. However, most approaches remain unacceptable for clinical applications. To improve insights into material design and clinical translational applications, this review highlights the innate roles and bioactive mechanisms of native GAGs during in situ wound healing and presents common GAG-based biomaterials and the adaptability of application scenarios in facilitating wound healing. Furthermore, challenges before the widespread commercialization of GAG-based biomaterials are shared, to ensure that future designed and constructed GAG-based artificial biomaterials are more likely to recapitulate the unique and tissue-specific profile of native GAG expression in human tissues. This review provides a more explicit and clear selection guide for researchers designing biomimetic materials, which will resemble or exceed their natural counterparts in certain functions, thereby suiting for specific environments or therapeutic goals.

Hydrogel Based on Riclin Cross-Linked with Polyethylene Glycol Diglycidyl Ether as a Soft Filler for Tissue Engineering

Hydrogels composed of natural polysaccharides have been widely used as filling materials, with a growing interest in medical cosmetology and skin care. However, conventional commercial dermal fillers still have limitations, particularly in terms of mechanical performance and durability in vivo. In this study, a novel injectable and implantable hydrogel with adjustable characteristics was prepared from succinoglycan riclin by introducing PEG diglycidyl ether as a cross-linker. FTIR spectra confirmed the cross-linking reaction. The riclin hydrogels exhibited shear-thinning behavior, excellent mechanical properties, and cytocompatibility through in vitro experiments. Furthermore, when compared with subcutaneous injection of a commercial hyaluronic acid hydrogel, the riclin hydrogels showed enhanced persistence and biocompatibility in Balb/c mice after 16 weeks. These results demonstrate the great potential of the riclin-based hydrogel as an alternative to conventional commercial soft tissue fillers.

A novel hydrogel-based moisturizing cream composed of hyaluronic acid for patients with xerosis: An intraindividual comparative analysis

BACKGROUND

Hyaluronic acid (HA) is mainly used to treat xerosis. It also exerts wound-healing, moisturizing, and antiaging effects. Although HA is considered an effective and safe ingredient in cosmetics, there is a constant demand for a more money-saving and effective formulation. This study aimed to evaluate the safety and efficacy of a novel hydrogel-based moisturizer containing HA cross-linked with silicone polymers, produced solely through irradiation without the use of cross-linking agents.

MATERIALS AND METHODS

A safety study enrolled 30 participants with healthy skin to perform patch and photopatch tests while recording adverse events. For the efficacy study, 30 participants with xerosis were compared before and after using the novel hydrogel, evaluating the cutaneous barrier function, xerosis severity scale (XSS) score, participant's satisfaction, and Investigator's Global Assessment (IGA). Furthermore, the efficacy of the novel hydrogel-based moisturizer was evaluated by comparing it with a conventional moisturizer, Physiogel, in another 30 participants with xerosis.

RESULTS

In the safety study, no serious adverse events were observed. In the efficacy study before and after use, skin hydration and skin surface lipid increased (p < 0.05) whereas the XSS scores decreased (p < 0.05) with time. In the comparative efficacy study with Physiogel, skin hydration increased whereas the XSS scores decreased (p < 0.05) over time in both groups. Furthermore, IGA improved in 100% of participants in both groups. Also, 100% and 93% of participants were satisfied with the novel hydrogel-based moisturizer and Physiogel, respectively.

CONCLUSIONS

The novel hydrogel-based moisturizer proved to be safe and effective for xerosis, showing comparable results to the conventional moisturizer.

Efficacy of Pegylated Hyaluronic Acid Filler Enriched with Calcium Hydroxyapatite: A 24-Week Post-Market, Observational, Prospective, Open-Label, Single-Center Study

Recently, thanks to the greater discovery of the mechanisms of facial aging, an alternative to invasive plastic surgery has found space with less invasive aesthetic procedures, also based on an increasingly pressing request. We are specifically referring to dermal filler injection into or under the skin which leads to immediate rejuvenation and aesthetic improvements. In this study, we wanted to analyze the results obtained through the use of NEAUVIA Organic Stimulate, particularly with regard to its effectiveness, which is a cross-linked polymeric hydrogel, containing stabilized sodium hyaluronate 26 mg/mL and calcium hydroxyapatite (1%), glycine and L-proline in buffer pyrogen-free water, in its main indication, namely, the temporary correction of congenital and acquired deficiencies of the soft tissues of the face by intradermal injection. Initially, 70 patients were enrolled, but 10 did not complete the study due to non-observance of the investigation rules, so they were excluded from the protocol. The collected data demonstrate an efficient mechanical effect of the pegylated polymeric acid matrix enriched with low concertation of calcium hydroxyapatite and in accordance with other evidence in vitro and in vivo, and the mechanical support of the interstitial connective space improves the homestays of the anatomical layer rebalancing the physiological activity of the dermis cells.

Preparation and Properties of Self-Cross-Linking Hydrogels Based on Chitosan Derivatives and Oxidized Sodium Alginate

A self-cross-linking and biocompatible hydrogel has wide application potential in the field of tissue engineering. In this work, an easily available, biodegradable, and resilient hydrogel was prepared using a self-cross-linking method. This hydrogel was composed of N-2-hydroxypropyl trimethyl ammonium chloride chitosan (HACC) and oxidized sodium alginate (OSA). A stable and reversible cross-linking network was formed by the Schiff base self-cross-linked and hydrogen bonding. The addition of a shielding agent (NaCl) may weaken the intense electrostatic effect between HACC and OSA and solve the problem of flocculation caused by the rapid formation of ionic bonds, which provided an extended time for the Schiff base self-cross-linked reaction for forming a homogeneous hydrogel. Interestingly, the shortest time for the formation of the HACC/OSA hydrogel was within 74 s and the hydrogel had a uniform porous structure and enhanced mechanical properties. The HACC/OSA hydrogel withstood large compression deformation due to improved elasticity. What's more, this hydrogel possessed favorable swelling property, biodegradation, and water retention. The HACC/OSA hydrogels have great antibacterial properties against Staphylococcus aureus and Escherichia coli and demonstrated good cytocompatibility as well. The HACC/OSA hydrogels have a good sustained release effect on rhodamine (model drug). Thus, the obtained self-cross-linked HACC/OSA hydrogels in this study have potential applications in the field of biomedical carriers.

Evaluation of the Safety of Neauvia Stimulate Injectable Product in Patients with Autoimmune Thyroid Diseases Based on Histopathological Examinations and Retrospective Analysis of Medical Records

The aim of this study was to test the effect of hyaluronic acid cross-linked with polyethylene glycol containing micronized portions of calcium hydroxyapatite (Neauvia Stimulate) on both local tissue and systemic consequences, which are crucial from the perspective of long-term safety, in patients suffering from Hashimoto's disease. This most common autoimmune disease is a frequently mentioned contraindication to the use of fillers based on hyaluronic acid as well as biostimulants based on calcium hydroxyapatite. Broad-spectrum aspects of histopathology were analyzed to identify key features of inflammatory infiltration before the procedure and 5, 21, and 150 days after the procedure. A statistically significant effect on the reduction of the intensity of the inflammatory infiltration in the tissue in relation to the state before the procedure was demonstrated, combined with a reduction in the occurrence of both antigen-recognizing (CD4) and cytotoxic (CD8) T lymphocytes. With complete statistical certainty, it was demonstrated that the treatment with Neauvia Stimulate had no effect on the levels of these antibodies. All this corresponds with the risk analysis that showed no alarming symptoms during the time of observation. The choice of hyaluronic acid fillers cross-linked with polyethylene glycol should be considered justified and safe in the case of patients suffering from Hashimoto's disease.

Anatomy, molecular structures, and hyaluronic acid - Gelatin injectable hydrogels as a therapeutic alternative for hyaline cartilage recovery: A review

Cartilage damage caused by trauma or osteoarthritis is a common joint disease that can increase the social and economic burden in society. Due to its avascular characteristics, the poor migration ability of chondrocytes, and a low number of progenitor cells, the self-healing ability of cartilage defects has been significantly limited. Hydrogels have been developed into one of the most suitable biomaterials for the regeneration of cartilage because of its characteristics such as high-water absorption, biodegradation, porosity, and biocompatibility similar to natural extracellular matrix. Therefore, the present review article presents a conceptual framework that summarizes the anatomical, molecular structure and biochemical properties of hyaline cartilage located in long bones: articular cartilage and growth plate. Moreover, the importance of preparation and application of hyaluronic acid - gelatin hydrogels for cartilage tissue engineering are included. Hydrogels possess benefits of stimulating the production of Agc1, Col2α1-IIa, and SOX9, molecules important for the synthesis and composition of the extracellular matrix of cartilage. Accordingly, they are believed to be promising biomaterials of therapeutic alternatives to treat cartilage damage.

The Application of Hyaluronic Acid Injections in Functional and Aesthetic Andrology: A Narrative Review

Hyaluronic acid (HA) is a glycosaminoglycan widely utilised in different fields of medicine. We aimed to provide a comprehensive overview of the scientific evidence on the use of HA in andrology. A review of the literature to identify pertinent studies concerning the use of HA in andrology was carried out on the Medline, EMBASE, and the Cochrane databases, with no time restriction up to December 2022. Penile girth enlargement (PGE) using HA proved to be safe and effective in enhancing the diameter of the penis, with durable and satisfactory outcomes in long-term follow-up. Injection of HA in the glans seems to represent an alternative treatment option for those patients with premature ejaculation (PE) who fail to respond to conventional medications. HA intra-plaque injections represent a valid option which may contribute to restore sexual activity in patients with Peyronie's disease (PD). The adoption of HA filler injections should always be tailored to the patient's peculiar anatomy and underlying condition. More robust evidence is required to achieve a uniformed consensus regarding the use of HA in andrology, and further efforts should continue to improve the current injection techniques and HA products.

Safety and efficacy of a new hydrogel based on hyaluronic acid as cosmeceutical for xerosis

BACKGROUND

Hyaluronic acid (HA) is among the most effective and safe ingredients frequently used in cosmetics. However, a more economical and efficient formulation is still required.

OBJECTIVE

We sought to assess the safety and efficacy of a novel hydrogel manufactured only by irradiation containing cross-linked HA and polyethylene glycol polymers with addition of polysiloxane.

METHODS

The study included 30 people with normal skin and 30 patients with xerosis. In the normal skin group, to evaluate the safety, a patch test and a photopatch test were performed, and patients' discomfort was investigated. In those with xerosis, to assess the efficacy, a skin barrier function test was performed at baseline and at 2, 4, and 8 weeks after the application of the novel hydrogel. Additionally, the xerosis severity scale (XSS), patient satisfaction, Investigator's Global Assessment (IGA), and adverse responses were evaluated.

RESULTS

In the safety study, there was no significant discomfort in the experimental group compared with the control group. In the efficacy study, at 2, 4, and 8 weeks after the application of the novel hydrogel, the mean value of skin hydration and sebum content increased and the mean value of XSS decreased with time in the experimental group, and a difference was observed when compared with the control group. IGA showed improvement in 97%, 77%, and 80% at each visit and the proportions of satisfied patients were 90%, 87%, and 90%, respectively.

CONCLUSIONS

The novel HA-based hydrogel tested herein could be a safe and effective therapeutic remedy for xerosis.

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

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

Chitosan Cross-Linking with Acetaldehyde Acetals

Here we demonstrate the possibility of using acyclic diethylacetal of acetaldehyde (ADA) with low cytotoxicity for the fabrication of hydrogels via Schiff bases formation between chitosan and acetaldehyde generated in situ from acetals in chitosan acetate solution. This approach is more convenient than a direct reaction between chitosan and acetaldehyde due to the better commercial availability and higher boiling point of the acetals. Rheological data confirmed the formation of intermolecular bonds in chitosan solution after the addition of acetaldehyde diethyl acetal at an equimolar NH₂: acetal ratio. The chemical structure of the reaction products was determined using elemental analysis and ¹³C NMR and FT-IR spectroscopy. The formed chitosan-acetylimine underwent further irreversible redox transformations yielding a mechanically stable hydrogel insoluble in a broad pH range. The reported reaction is an example of when an inappropriate selection of acid type for chitosan dissolution prevents hydrogel formation.

Toxicity Assessment of a Single Dose of Poly(ethylene glycol) Diglycidyl Ether (PEGDE) Administered Subcutaneously in Mice

Poly(ethylene glycol) diglycidyl ether (PEGDE) is widely used to cross-link polymers, particularly in the pharmaceutical and biomaterial sectors. However, the subcutaneous toxicity of PEGDE has not yet been assessed. PEGDE samples (500–40,000 μg/mouse) were subcutaneously injected into the paraspinal dorsum of BALB/c male mice. Cage-side observations were carried out with measurement of organ weight, body weight variation, and feed intake, as well as histopathological characterization on day 28 post-exposure. Mice that received 40,000 μg of PEGDE showed severe toxic response and had to be euthanized. Subcutaneous injection of PEGDE did not alter feed intake and organ weight; however, the body weight variation of mice injected with 20,000 μg of PEGDE was significantly lower than that of the other groups. Exposure to 10,000 and 20,000 μg of PEGDE induced epidermal ulcer formation and hair loss. The histology of skin tissue in mice administered with 20,000 μg of PEGDE showed re-epithelialized or unhealed wounds. However, the liver, spleen, and kidneys were histologically normal. Collectively, PEGDE, particularly above 10,000 μg/mouse, caused subcutaneous toxicity with ulceration, but no toxicity in the other organs. These results may indicate the optimal concentration of subcutaneously injected PEGDE.

Crosslinking Hyaluronic Acid Soft-Tissue Fillers: Current Status and Perspectives from an Industrial Point of View

INTRODUCTION

Hyaluronan (HA)-based soft-tissue fillers are injectable crosslinked hydrogels aimed to counteract facial skin aging signs via minimally invasive procedures. The crosslinking step is required to drastically improve HA residence time in vivo and provide the gel with specific viscoelastic properties matching the clinical indications. While HA as a raw material and HA fillers are widely studied, little is reported about crosslinkers themselves used in commercial fillers.

AREAS COVERED

This article introduces the specifications of the ideal crosslinker in HA fillers. The properties of commercially used crosslinkers are reviewed. An up-to-date review of innovative hydrogel fabrication alternatives is conducted, and advantages and drawbacks are discussed.

EXPERT OPINION

HA fillers are predominantly manufactured using 1,4-butanediol diglycidyl ether (BDDE) which is considered as the gold standard crosslinker worldwide due to its proven and unrivalled clinical track record of more than 20 years. Extensive studies have been published covering BDDE-crosslinked HA fillers' chemistry, gel properties, and clinical effectiveness and safety. However, new hydrogel fabrication strategies have emerged, paving the way for innovative alternatives potentially bringing novel features to HA fillers. Nevertheless, major efforts must still be implemented to assess their safety, efficacy, stability and suitability for industrialization.

Clinical Experience with PEGylated Hyaluronic Acid Fillers: A 3-year Retrospective Study

BACKGROUND: Hyaluronic acid fillers are the most used worldwide, thanks to the high biocompatibility and safety profile of HA and it is also the only substance that can be “dissolved” due to the hyaluronidase effect. AIM: A retrospective clinical evaluation of the outcomes following PEG cross-linked HA-based filler injection was performed. METHODS: Data were collected from December 2017 to June 2020. A total of 65 patients (12 M, 53 F), age ranging 28–62 year’s old (mean age 42.3), were treated. Exclusion criteria were applied and in accord to treatment plan, were used specific site injections and fillers. Follow-up was evaluated between 6 months and 2 years. RESULTS: A total of 61 treatments using 124 vials of HA filler crosslinked with PEG were performed. CONCLUSION: In conclusion, from 2014, HA fillers having PEG as cross-linker agent have been introduced in the european market. Several papers have been published in order to evaluate the features of these fillers, although, to the best of our knowledge, this is the first clinical paper regarding their use.

Non-Surgical Touch-Up with Hyaluronic Acid Fillers Following Facial Reconstructive Surgery

The use of hyaluronic acid (HA) injectable fillers has become increasingly widespread in facial recontouring and rejuvenation. We report our experiences to emphasize the role of HA fillers as tools beyond aesthetic treatments in cases of post-surgical facial sequelae. HA fillers are generally used for aesthetic rejuvenation, but one potential new horizon could be their application in trauma, reconstructive, and craniofacial surgery. This study was conducted retrospectively, evaluating medical reports of patients treated at the Maxillofacial Surgery Unit, University of Campania “Luigi Vanvitelli”, Naples, for lip incompetence, trauma, oncological, reconstructive, and craniosynostosis surgery sequelae. Visual analog scale (VAS) evaluation was performed to assess patient satisfaction. No major complications (i.e., impending necrosis or visual loss) were reported. Bruising and swelling was reported for 48 h after lip injection. At the immediate VAS evaluation, 67% of the patients were “extremely satisfied” and 33% “satisfied”. In those 33%, VAS scores changed to “extremely satisfied” at 6–9 weeks and 3–6 months of VAS evaluation (contextually to improvement in tissue flexibility, elasticity, and aesthetic appearance). Results indicate that this minimally invasive approach achieves a high level of aesthetic enhancement, improving patient satisfaction. The concept of HA filler applications could be a frontier that may be applicable to other areas of reconstructive facial plastic surgery.

The Immunogenicity of Hyaluronic Fillers and Its Consequences

Hyaluronic acid (HA) is a glycosaminoglycan, a natural component of the extracellular matrix. The identical structure of the molecule in all living organisms is its main advantage, as it translates into the minimal probability of immunogenicity. Therefore, it is the closest to the ideal preparation used as a filler, due to its biocompatibility and stability at the site of implantation. This paper includes the discussion of the potential mechanisms of adverse immune reactions to HA along with the mechanisms of reaction following vaccinations against SARS-CoV-2. Based on the literature, we tried to systematize adverse immune reactions with systemic manifestations to HA. The occurrence of unpredictable reactions to hyaluronic acid indicates that they may not be treated as neutral or non-allergenic. The modifications of the chemical structure of HA, additives and individual tendencies in a patient may be the cause of unpredictable reactions, leading to serious health consequences. Preparations of unknown origin, poorly purified, or including bacterial DNA are particularly dangerous. Therefore, long-lasting follow-up of the patient and the selection of a preparation approved by the FDA or EMA are of high importance. Patients are often unaware of the consequences of cheaper procedures performed by persons without suitable knowledge with the use of unregistered products, so the public should be educated and legal regulations should be introduced.

Surgical Lip Remodeling Following Permanent Filler Injection: A Scoping Review

ABSTRACT

Over the years, several techniques have been introduced to obtain permanent lip enhancement, such as the use of silicone lip implants or the off-label use of permanent fillers. Although some reports indicate that permanent lip filler is safe, many others describe early- and late-onset complications. The main issue with permanent lip fillers is the lack of a standard technique to correct undesirable results. The aim of this scoping review was to list and evaluate the surgical pathways described in literature to correct lip deformity resulted from the injection of permanent fillers. The methods and the inclusion criteria of this work were specified in advance and documented in a protocol, according to the PRISMA 2009 checklist. The research was carried out on electronic databases PubMed, Cochrane Library, and Scopus databases identifying articles from March 1991 to December 2020 and conducted up to December 23rd, 2020. Articles language was limited to English. The selection process identified 3 retrospective studies eligible for inclusion. 73 patients and a total of 111 lips (72 upper and 39 lower) were considered. Two early complications were identified, 1 suture dehiscence and 1 total lip mucosa necrosis. Surgical lip remodeling following permanent filler injection seems to be an effective approach although the surgical pathway needs to be customized per each patient. Complication rate seems to be coherent to lip surgery performed with reconstructive purposes. To confirm these data case-control studies with much wider cohorts are needed to reach statistical significance.

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

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