Hydrogels for tissue engineering.

Hydrogels, due to their unique biocompatibility, flexible methods of synthesis, range of constituents, and desirable physical characteristics, have been the material of choice for many applications in regenerative medicine. They can serve as scaffolds that provide structural integrity to tissue constructs, control drug and protein delivery to tissues and cultures, and serve as adhesives or barriers between tissue and material surfaces. In this work, the properties of hydrogels that are important for tissue engineering applications and the inherent material design constraints and challenges are discussed. Recent research involving several different hydrogels polymerized from a variety of synthetic and natural monomers using typical and novel synthetic methods are highlighted. Finally, special attention is given to the microfabrication techniques that are currently resulting in important advances in the field.

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Hydrogels in regenerative medicine

Designing of biologically active scaffolds with optimal characteristics is one of the key factors for successful tissue engineering. Recently, hydrogels have received a considerable interest as leading candidates for engineered tissue scaffolds due to their unique compositional and structural similarities to the natural extracellular matrix, in addition to their desirable framework for cellular proliferation and survival. More recently, the ability to control the shape, porosity, surface morphology, and size of hydrogel scaffolds has created new opportunities to overcome various challenges in tissue engineering such as vascularization, tissue architecture and simultaneous seeding of multiple cells. This review provides an overview of the different types of hydrogels, the approaches that can be used to fabricate hydrogel matrices with specific features and the recent applications of hydrogels in tissue engineering. Special attention was given to the various design considerations for an efficient hydrogel scaffold in tissue engineering. Also, the challenges associated with the use of hydrogel scaffolds were described.

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Hydrogel scaffolds for tissue engineering: Progress and challenges

Background Bovine collagen is extensively used for facial soft tissue augmentation but provides only temporary correction and can cause hypersensitivity reactions. Hyaluronic acid derivatives potentially offer improved longevity of correction and a reduced risk of immunogenicity and hypersensitivity. Objective To compare the efficacy and safety of nonanimal stabilized hyaluronic acid gel (Restylane; Q-Med, Uppsala, Sweden) with that of bovine collagen (Zyplast) for treatment of nasolabial folds. Methods One hundred thirty-eight patients with prominent nasolabial folds were randomized to treatment with hyaluronic acid gel and bovine collagen on contralateral sides of the face. Treatments were repeated at 2-week intervals, as required, to achieve "optimal cosmetic result" (baseline). Outcomes were evaluated by a blinded investigator at 2, 4, and 6 months after baseline. Results Less injection volume was required for "optimal cosmetic result" with hyaluronic acid gel than with bovine collagen, and patients and investigators judged hyaluronic acid gel to be more effective in maintaining cosmetic correction. The investigator-based Wrinkle Severity Rating Scale and Global Aesthetic Improvement Scale assessments at 6 months after baseline indicated that hyaluronic acid gel was superior in 56.9% and 62.0% of patients, respectively, whereas bovine collagen was superior in 9.5% and 8.0% of patients, respectively. The frequency, intensity, and duration of local injection-site reactions were similar for the two products. Conclusion Nonanimal stabilized hyaluronic acid provides a more durable aesthetic improvement than bovine collagen and is well tolerated.

A Randomized, Double-Blind, Multicenter Comparison of the Efficacy and Tolerability of Restylane Versus Zyplast for the Correction of Nasolabial Folds

background. Nonanimal hyaluronic acid gel was recently developed for soft tissue augmentation and volume expansion and has been shown to offer several advantages in comparison to other augmentation materials. There are rare reports of adverse events believed to be secondary to trace amounts of proteins in the hyaluronic acid raw material. objective. To determine the safety profile of nonanimal stabilized hyaluronic acid gel (Restylane, Perlane, Restylane Fine Lines, Q-Med AB, Uppsala, Sweden) for soft tissue augmentation using a retrospective review of all adverse events data from Europe, Canada, Australia, South American, and Asia from 1999 and 2000. results. Data from an estimated 144,000 patients treated in 1999 indicated the major reaction to injectable hyaluronic acid was localized hypersensitivity reactions, occurring in approximately 1 of every 1400 patients treated. In 1999 there was an adverse event reported for 1 of every 650 patients (0.15%) treated. These were temporary events that included redness, swelling, localized granulomatous reactions, bacterial infection, as well as acneiform and cystic lesions. For 2000 there was an estimated 262,000 patients treated with hyaluronic acid gel. The total number of adverse events was 144, corresponding to one adverse event for every 1800 patients (0.06%) treated. The major adverse event was again hypersensitivity, occurring in 1 of every 5000 patients treated. conclusion. According to the reported worldwide adverse events data, hypersensitivity to nonanimal hyaluronic acid gel is the major adverse event and is most likely secondary to impurities of bacterial fermentation. According to data from 2000, the incidence of hypersensitivity appears to be declining after the

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Safety data of injectable nonanimal stabilized hyaluronic acid gel for soft tissue augmentation.

background.Several biomaterials are available for the purpose of soft tissue augmentation, but none of them has all the properties of the ideal filler material. The recent development of hyaluronic acid gels for dermal implantation give the physician new possibilities of effective treatment in this

Mario Calandra

Papers

Injectable Hyaluronic Acid Gel for Soft Tissue Augmentation: A Clinical and Histological Study