APPLICATIONS OF HYALURONAN – PART 2
Cosmetic Tissue Augmentation
HA fillers, most of which are based on the chemical cross-linked of hyaluronan for the relevance of the in vivo half-life, can be used to augment nasolabial folds, correct tear trough deformity, reduce wrinkles, as well as restore earlobe volume. Currently, there are several HA-derived dermal fillers, such as Restylane®, BioHyaluTM, Hylaform®, Perlane®, and Juvederm® that are sold for these purposes. Comparative clinical studies with bovine collagen product (Zyplast®) showed that cross-linked HA gel was as safe and effective as the control product, but unlike collagen products, HA products rarely cause a hypersensitivity reaction, because HA have the same chemical and physical properties regardless of the species or tissues.
HA-based products were considered ‘more effective in maintaining cosmetic correction’, and the local adverse reactions were very low (0.06–0.15%) based on data collected worldwide from 400,000 patients, which compared favorably with similar events after collagen skin augmentation.
Urinary Sphincter Viscoaugmentation
In 1993, an animal studies were carried out to demonstrate the usefulness of HA gel in viscoaugmentation as a tissue bulking agent for urinary sphincter muscle were completed (Biomatrix Inc., Ridgefield NJ). After that, some clinical trials confirmed that intramuscular injection of HA solution to augment the connective tissue between the sphincter urethra in incontinence patients have beneficial effect.
HA combined with dextran particles was also used in pilot clinical studies for endoscopic treatment of vesicoureteral reflux in children and women with stress incontinence. In this procedure, the dextran particles were suspended in 1% HA solution to decrease the foreign body reaction caused by the dextran.
Vocal Cord Augmentation
A study performed with rabbit vocal suggested that only HA solution had similar rheological properties to those of the intercellular matrix in the subepithelial space of the vocal fold compared with collagen and other material. For those properties, HA solution could be applied to restore or preserve the vibratory spacing of the vocal fold with injection treatment in glottal insufficiency.
Clinical observation showed that HA solution-treated patients showed better vocal fold status and longer maximum phonation time than collagen-treated patients at 12 months after treatment.
Viscoseparation
Viscoseparation means the use of hyaluronan (HA) to separate connective tissue surfaces to prevent adhesion and excessive scar formation caused by surgical procedures.
Postsurgical Visoseparation
The presence of large amounts of HA can make the healing process scarless and control the fibrosis in the early stage of postoperation. Most of the HA used for viscoseparation is chemically modified to increase the in vivo half-time, such as Seprafilm® , a poly film made of chemically modified HA and carboxymethylcellulose.
But the trouble is, that the effect of such a product may be limited only to the sites where HA is applied. Consequently, a large volume of the diluted solution was used to cover all tissue surface areas, which is called ‘lavage’. Intergel® (Lifecore Biomedical) is a ‘lavage’ product containing 0.5% ferric hyaluronate solution which was approved by the FDA in 2001.
Nasal and Otologic Viscoseparation
HA-containing products have extended their use to the nasal and otologic area, and serve to occupy the nasal or ontological spaces, separate mucosal surfaces, prevent adhesion, and control bleeding in surgeries. MeroGel® made by Fidia and generically known as HYAFF – a family of esterified HA derivatives, is a space-occupying dressing in nasal/sinus cavities and in the middle ear and external ear canal. HylaSine® (a crosslinked HA gel) is a similar product.
Viscoprotection
Viscoprotection means the application of HA solution to protect tissue surfaces from dehydration and noxious environmental agents (conjunctiva or cornea) or promote the wound healing of such surfaces.