Structural and property features of polymer compositions based on polyamide 6 and polyolefin functionalized mixtures

Изучена возможность получения полимер-полимерных композиций полиамида 6 (ПА6) с функционализированной смесью полибутена (ПБ) и сополимера этилена с октеном (СЭО), а также проанализированы особенности структуры и свойств полученных материалов. Показано, что функционализированные смеси ПБ/СЭО (ф(ПБ/СЭО)) по своим модифицирующим свойствам превосходят исходные и функционализированные ПБ и СЭО. При использовании в качестве модификаторов ф(ПБ/СЭО) микроструктура и степень гетерогенности в ПА6 композициях достигают такого уровня, при котором возможно получать смесевые полимер-полимерные композиции с улучшенным комплексом свойств: с повышенной ударной вязкостью, которая достигает 45–60 кДж/м 2 , и деформационно-прочностными характеристиками, близкими к исходному ПА6. Полученные результаты следует учитывать при разработке реальных материалов технического назначения с улучшенными свойствами на базе ПА6 и функционализированных полиолефинов.The possibility of obtaining polyamide 6 (PA6) polymer-polymer compositions with a functionalized mixture of polybutene (PB) and octene ethylene copolymer (OEC) has been studied. Structural and property features of the obtained materials have been analyzed. It has been shown that concerning the modifying properties functionalized PB/OEC mixtures (f(PB/OEC)) are superior to the initial and functionalized PB and OEC. When using f(PB/OEC) as modifiers, the microstructure and heterogeneity degree in PA6 compo- sitions reach a level at which it is possible to obtain mixed polymer-polymer compositions with an improved set of properties such as increased impact strength that reaches 45–60 kJ/m 2 , and deformation-strength characteristics close to the initial PA6. The results should be taken into account when developing real technical materials with improved properties based on PA6 and functionalized polyolefins

Dictated sequences and the pursuit of efficiency in the physical culture movement 1896-1939 : a filmic scrutiny

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Early effects of dexamethasone and anti-VEGF therapy in an inflammatory corneal neovascularization model

Inflammatory angiogenesis is the pathogenic mechanism of various sight-threatening eye diseases, among them corneal neovascularization. Current treatment options include steroids which have undesirable side effects, or anti-VEGF which has only limited efficacy. In an inflammatory environment, however, angiogenesis can be stimulated by numerous factors not directly targeted by anti-VEGF therapy. The aim of this study was to induce corneal inflammation leading to angiogenesis, and investigate the early, differential effects of steroid and anti-VEGF therapy at the cellular, tissue, and gene expression levels. Fifty-two Wistar rats received a single intrastromal corneal suture to induce a controlled inflammatory angiogenic response. Rats were subsequently treated with dexamethasone, rat specific anti-VEGF, or goat IgG (control), topically 4 times daily for 7 days. In vivo confocal microscopy of the cornea was performed longitudinally from 5 h up to 7 d to investigate morphology at the cellular and tissue-level. In vivo photographic vessel analysis and immunohistochemistry were also performed. RT-PCR for VEGF-A, FGF-2, IL-6, TNF-alpha, CXCL2, CCL2, CCL3 and DLL4 was performed at 24 h, and for VEGF-A, IL-6, TNF-alpha, FGF-2, CXCL2, CCL2, and CCL3 at 7 days. Early infiltration of CD11b + myeloid cells into the cornea at 5 h post-suture was delayed by both treatments relative to controls; however neither treatment was able to suppress accumulation of myeloid cells at day 2 or 7. Limbal vessel dilation was inhibited at 5 h by both treatments, but only dexamethasone showed sustained effect until day 2. Early macrophage recruitment was also suppressed by dexamethasone (but not by anti-VEGF) until day 2. Dexamethasone furthermore suppressed corneal neovascularization at day 7 by over 90%, whereas suppression by anti-VEGF was 14%. Despite differential suppression of vessel dilation, macrophage recruitment, and vascular invasion, anti-VEGF and dexamethasone both down-regulated VEGF-A and IL-6 expression at 24 h with sustained effect to 7 d. They also both down regulated FGF-2 and TNF-alpha at 24 h and CCL2 at 7 d. In conclusion, anti-angiogenic treatments influence early, pre-angiogenic tissue activity such as limbal vessel dilation, inflammatory cell infiltration of the stroma, and macrophage recruitment. Importantly, the differential effects of steroids and anti-VEGF treatment in suppressing neovascular growth could not be attributed to differential inhibition of several major angiogenic and inflammatory factors in the early pre-sprouting phase, including IL-6, VEGF-A, FGF-2, TNF-alpha, CCL2, CCL3, CXCL2, or DLL4.Funding Agencies|Crown Princess Margaretas Foundation; County Council of Ostergotland; Swedish Research Council [2012-2472]</p

Composite core-and-skirt collagen hydrogels with differential degradation for corneal therapeutic applications

Scarcity of donor tissue to treat corneal blindness and the need to deliver stem cells or pharmacologic agents to ensure corneal graft survival are major challenges. Here, new composite collagen-based hydrogels are developed as implants to restore corneal transparency while serving as a possible reservoir for cells and drugs. The composite hydrogels have a centrally transparent core and embedded peripheral skirt of adjustable transparency and degradability, with the skirt exhibiting faster degradation in vitro. Both core and skirt supported human epithelial cell populations in vitro and the skirt merged homogeneously with the core material to smoothly distribute a mechanical load in vitro. After in vivo transplantation in rabbit corneas over three months, composites maintained overall corneal shape and integrity, while skirt degradation could be tracked in vivo and non-invasively due to partial opacity. Skirt degradation was associated with partial collagen breakdown, thinning, and migration of host stromal cells and macrophages, while the central core maintained integrity and transparency as host cells migrated and nerves regenerated. IMPACT: This study indicates the feasibility of a collagen-based composite hydrogel to maintain corneal stability and transparency while providing a degradable peripheral reservoir for cell or substance release.Funding agencies:  Abbott Medical Optics Inc, Solna, Sweden</p

Enhanced Regeneration of Corneal Tissue Via a Bioengineered Collagen Construct Implanted by a Nondisruptive Surgical Technique

Severe shortage of donor corneas for transplantation, particularly in developing countries, has prompted the advancement of bioengineered tissue alternatives. Bioengineered corneas that can withstand transplantation while maintaining transparency and compatibility with host cells, and that are additionally amenable to standardized low-cost mass production are sought. In this study, a bioengineered porcine construct (BPC) was developed to function as a biodegradable scaffold to promote corneal stromal regeneration by host cells. Using high-purity medical-grade type I collagen, high 18% collagen content and optimized EDC-NHS cross-linker ratio, BPCs were fabricated into hydrogel corneal implants with over 90% transparency and four-fold increase in strength and stiffness compared with previous versions. Remarkably, optical transparency was achieved despite the absence of collagen fibril organization at the nanoscale. In vitro testing indicated that BPC supported confluent human epithelial and stromal-derived mesenchymal stem cell populations. With a novel femtosecond laser-assisted corneal surgical model in rabbits, cell-free BPCs were implanted in vivo in the corneal stroma of 10 rabbits over an 8-week period. In vivo, transparency of implanted corneas was maintained throughout the postoperative period, while healing occurred rapidly without inflammation and without the use of postoperative steroids. BPC implants had a 100% retention rate at 8 weeks, when host stromal cells began to migrate into implants. Direct histochemical evidence of stromal tissue regeneration was observed by means of migrated host cells producing new collagen from within the implants. This study indicates that a cost-effective BPC extracellular matrix equivalent can incorporate cells passively to initiate regenerative healing of the corneal stroma, and is compatible with human stem or organ-specific cells for future therapeutic applications as a stromal replacement for treating blinding disorders of the cornea