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Organo-Modified Siloxane Polymers for Conditioning Skin and Hair
Published in Randy Schueller, Perry Romanowski, Conditioning Agents for Hair and Skin, 2020
Formulators have come to trust the safety of silicones—a wide range of studies document a low order of toxicity (60), For this reason, the (poly)dimethylsiloxane backbone has become a key conditioning ingredient for both skin care and hair care applications. It was not too long ago that silicones were a strange and unique cosmetic additive, but today more than 50% of all new cosmetic and toiletry products have at least one silicone incorporated to aid in esthetics, improve delivery, or improve application ease to the skin and hair, or to provide a functionalized performance (e.g., nonwhitening/nonresidue, emulsification, enhanced substantivity, enhanced sun protection). Polyether functional siloxanes and amino-functional siloxanes will continue to play an important role in conditioning of hair, but branching and crosslinking of the basic (poly)dimethylsiloxane molecule will emerge as an important classification to improved deposition and measurable performance. Alkyl methyl siloxanes and copolymers will emerge as important classifications for improved deposition on skin. Polyether functional siloxanes (and copolymers) will continue their growth as important water-in-oil/silicone emulsifiers.
Selection Considerations for Membranes and Models for In Vitro/Ex Vivo Permeation Studies
Published in Tapash K. Ghosh, Dermal Drug Delivery, 2020
Pei-Chin Tsai, Tannaz Ramezanli, Dina W. Ameen, Sonia Trehan, Nathaly Martos, Zheng Zhang, Bozena Michniak-Kohn
Silicone membrane is based on silicone polymers whose backbone is composed of silicon-oxygen (Si-O) units. Among those silicone polymers, polydimethylsiloxane (PDMS) is the basic form, in which two methyl groups are linked to each silicon molecule. PDMS has unique properties such as high flexibility, low glass transition temperature and high gas permeability.74 The properties of silicone polymers can be tuned by modifying the chemical structure of PDMS. For example, an important modification to PDMS is the incorporation of vinyl groups, which significantly increases the cross-linking efficiency with organic peroxide. Methyl-vinyl silicone is a widely used silicone rubber.
Vulvar cancer and post-vulvectomy complications
Published in Miranda A. Farage, Howard I. Maibach, The Vulva, 2017
Christos Iavazzo, Ioannis D. Gkegkes
Another serious complication that has been reported after radical vulvectomy with a combined removal of a portion of the urethra is the probability of severe urinary incontinence, with incidence, according to the literature, ranging from 22% to 100% (136). However, in another study, de Melo Ferreira et al. showed that patients undergoing surgical treatment for vulvar cancer postoperatively showed no decrease in urinary function (137). The presence of urinary incontinence was correlated with patient age and number of deliveries, but not with a history of surgery for vulvar cancer. A study where patients with radical vulvectomy and partial urethra removal were compared with patients without urethra resection did not demonstrate any significant differences regarding urinary incontinence rates between the compared groups (138). During urethrectomy, the urethral length is reduced, causing a decrease in urethral closure pressure and leading to urinary incontinence. Also, paraurethral fibrosis after a radical surgical treatment leads to decreased urethral mobility, resulting in intrinsic sphincter deficiency in the majority of cases. Nevertheless, the management of this condition includes utilization of a pubovaginal sling, artificial sphincter implantation, insertion of mid-urethra tension-free vaginal tape, and injection of bulking agents (139–141). The use of a pubovaginal sling is correlated with high perioperative morbidity, while artificial sphincter implantation has a high risk of discontinuation and complications (such as infection, erosion, and mechanical failure) (140,141). Additionally, the use of a mid-urethra tension-free sling in patients with vulvar cancer seems to be unreasonable due to the fact that these patients generally present severe paraurethral fibrosis and a short urethra, combined with vulvar and vaginal retraction induced by previous radical vulvectomy. Nonetheless, only one case of the management of severe urinary incontinence after radical vulvectomy has been described in the literature (142). The presented case was treated with an Aldridge sling operation. Recently, the use of urethral bulking agents as a minimally invasive procedure for the treatment of urinary incontinence caused by intrinsic sphincter deficiency has also been proposed. The utility of these agents rests on narrowing the urethral lumen and inducing urethral coaptation during increased intra-abdominal pressure without variating the voiding pressure. Among the most common agents used are collagen, autologous fat, polytetrafluoroethylene, carbon-coated beads, and polydimethylsiloxane (141). The latter of these substances is a soft-textured, permanent implant of a safe, efficient, and longterm durable material (143). Also, polydimethylsiloxane can be implanted as an outpatient therapy with local anesthetic and with low morbidity, especially in patients with a high operative risk (ASA > 3) (American Society of Anesthesiologists [ASA] Physical Status classification) (141).
Drug eluting implants in pharmaceutical development and clinical practice
Published in Expert Opinion on Drug Delivery, 2021
Ashley R. Johnson, Seth P. Forster, David White, Graciela Terife, Michael Lowinger, Ryan S. Teller, Stephanie E. Barrett
Finally, silicones are a family of polymers defined by a long chain of alternating silicon and oxygen atoms [117,118]. The most commonly used silicone in medical devices is poly(dimethylsiloxane) (PDMS), which contains methyl groups as side chains. This polymer has been used in pacemaker leads, mammary prostheses, drainage implants for glaucoma, contact lenses, cochlear implant coatings, transdermal patch adhesives and denture liners. Silicones have found use in these applications due to their beneficial properties, including their biological and chemical inertness, resistance to oxidation, low modulus, low surface adhesion, high oxygen permeability and ability to be formulated in the absence of stabilizers. Unlike the previously described polymers, poly(dimethylsiloxane) is not a thermoplastic. Instead, silicones are extruded at low temperatures and then cured under heat or UV light [119].
Current treatments for female primary stress urinary incontinence
Published in Climacteric, 2019
A.-M. Itkonen Freitas, P. Rahkola-Soisalo, T. S. Mikkola, M. Mentula
A Cochrane review found some limited evidence that bulking agents can relieve SUI in women48, but further comparative randomized clinical trials are required. In a more recent randomized, prospective, multicenter North American study, 345 women with SUI were treated either with PAHG or collagen gel27. At 1-year follow-up, 47% of patients with PAHG and 50% with collagen gel were cured, and 77% and 70%, respectively, considered themselves cured or improved. Similar results in efficacy were detected after 1 year when polydimethylsiloxane and PAHG were compared, showing 66–89% subjective success rates46,47. However, the long-term efficacy of bulking treatments is not well established and thus further data on repeated injections and cost-effectiveness are warranted. Currently, one randomized trial comparing PAHG and TVT sling is being conducted (www.clinicaltrials.gov), eventually providing both short-term and long-term efficacy data on the primary SUI treatment. This trial may help to determine the subjective and objective efficacy of PAHG treatment, and whether it could have potential to become a first-line treatment for SUI. In addition, more studies comparing the different bulking agents, particularly with new products, are needed.
Maxillofacial prostheses challenges in resource constrained regions
Published in Disability and Rehabilitation, 2019
Sophia Tetteh, Richard J. Bibb, Simon J. Martin
Also new experimental materials have been developed with a formulation consisting of high and low molecular weight vinyl-end-blocked polydimethylsiloxane, surface treated hydrophobic silica; hydride functional silicone polymer and lastly a platinum complex [91]. The new experimental materials had superior tear strength, low hardness and comparable viscosity in contrast to commercially available materials. Furthermore, new poly-dimethylsiloxane material formulations comprising of a tin catalyst, silane cross-linking agents, hydrophobic silica filler and hydroxy-end-blocked poly-dimethylsiloxane with improved mechanical properties in comparison to commercially available materials. Additionally, silicone hollow microsphere composites were created utilising expancel hollow spheres and hollow silicone dioxide microspheres [92]. This new material revealed an improvement in the density, Shore A hardness and breaking elongation of the materials. However, there was degradation in tensile strength, tear strength and dynamic mechanical properties while the contrary was observed in the hollow silicon dioxide microspheres. The silicone materials and the additives remain expensive and difficult to obtain in resource-limited countries.