Stability of cross-linked collagen

Teoretická část této bakalářské práce pojednává o obecných vlastnostech kolagenu, který je nejčastěji rozšířeným vláknitým proteinem v těle, o síťování kolagenu, které vede ke zlepšení mechanických i chemických vlastností, a o široce využívaných síťovacích činidlech, především 1-ethyl-3-(3-dimethylaminopropyl) karbodiimidu (EDC). Dále se zabývá několika metodami stanovení EDC ve vodném roztoku. Experimentální část je zaměřena na praktické stanovení množství EDC, které zůstalo ve vodě použité k promývání vzorků po síťování. Cílem bylo zjistit, jestli současně používaná metoda promývání je dostatečná pro jisté aplikace nebo je potřeba ji upravit. I přesto, že sloučenina EDC je prakticky netoxická, může způsobovat zbarvení kolagenních materiálů po sterilizaci ozařováním. Vzhledem k tomu, že nebylo zjištěno jaké množství EDC může ve vzorku zůstat nebo jestli je nezbytné vymýt veškeré EDC, je obtížné rozhodnout jestli je promývací metoda dostatečná nebo není. Navíc je potřeba brát do úvahy i ostatní vedlejší produkty síťování kolagenu. Nicméně cílem této práce bylo pouze zhodnotit účinnost vymývání EDC z kolagenních vzorků. Pro síťování byly použity tři různé koncentrace EDC a následně byly vzorky vymývány po různě dlouhou dobu. Takto bylo získáno 48 vodných vzorků, které byly následně třikrát spektrofotometricky stanoveny. Výsledně bylo zjištěno, že pro běžně používanou koncentraci síťovacího činidla (50 mmol.l 1 EDC) postačuje promývat vzorky po dobu 30 minut v roztoku hydrogenfosforečnanu sodného (Na2HPO3) a následně promývat ve vodě čtyřikrát po dobu 15 minut s výměnou vody při každém kroku. Po těchto krocích klesla koncentrace EDC v promývací vodě pod 1 mol . l-1, pro nižší koncentrace síťovacího roztoku byla dostatečná i kratší doba promývání. Výsledky této bakalářské práce jsou pouze předběžné, a proto by mělo následovat další zkoumání této problematiky.Theoretical part of this bachelor thesis is based on general information about collagen, most common fibrous protein in body, collagen cross-linking; leading to its better mechanical and chemical properties; and widely used crosslinking agents, mainly based on 1-ethyl-3-(3 dimethylaminopropyl) carbodiimide (EDC). Furthermore it deals with several methods of quantifying EDC in aqueous solutions. Experimental part is concerned with the determination of EDC remained in water used for washing samples in order to purify them after the cross-linking. The goal is to find out if used washing method is adequate enough for certain application or if it needs some adjusting. Even if EDC is practically non-toxic, it provides side effects on colour of the collagenous material after the sterilization by irradiation. Since it has not been found in the literature what specific amount of EDC can stay in a sample or if it is necessary to be completely washed out. According the state-of-the-art, it is difficult to assessed if the washing method is sufficient or not. Moreover, there are also other side products of cross-linking collagen in the final collageneous products that have to be taken into account. However, the aim of this bachelor thesis is to evaluate washing EDC from the collagenous sample only. As for cross-linking method, three concentrations of EDC followed by washing samples for different periods of time were used. Following this method, 48 samples were prepared and three times measured using UV-VIS colorimetric assay. As a result it was found out that for commonly used concentration of cross-linking agent (50 mmol.l-1 of EDC) it is sufficient to wash samples for 30 min in solution of disodium phospnonate (Na2HPO3) followed by washing with water 4 times for 15 min with changing the water at each step. After these steps, the concentration of EDC in washing water was reduced up to 1 mol.l-1. For lower concentrations of cross-linking EDC solution it is sufficient even shorter washing time. Considering the preliminary results of this bachelor thesis, further investigation dealing with this topic should follow.

Poly(dimethylsiloxane)-poly(ethyleneoxide)-heparin block copolymers. I. Synthesis and characterization

Amphiphilic block copolymers containing poly(dimethylsiloxane), poly(ethylene oxide), and heparin (PDMS-PEO-Hep) have been prepared via a series of coupling reactions using functionalized prepolymers, diisocyanates, and derivatized heparins. All intermediate steps of the synthesis yield quantifiable products with reactive end-groups, while the final products demonstrate bioactive, covalently bound heparin moieties. Due to the solvent systems required, commercial sodium heparin was converted to its benzyltrimethyl ammonium salt to enhance its solubility. The same procedure was applied to heparin degraded by nitrous acid in order to covalently couple it in solutions with the semitelechelic copolymers. As might be expected, this derivatization reduces the apparent bioactivity of the heparin. However, preliminary findings suggest that the bioactivity can be restored by reforming the heparin sodium salt

Novel hydrogels based on polysaccharides for soft tissue regeneration: preparation and characterization

Předložená diplomová práce se zabývá přípravou, síťováním a fyzikálně-chemickou charakterizací hydrogelů na bázi polysacharidů. Cílem práce bylo vyvinout elastické filmy, které by mohly být použity pro vlhké hojení ran. Teoretická část shrnuje současné způsoby regenerace měkkých tkání a jejích náhradách (ať už se jedná o přírodní nebo syntetické materiály). Zároveň jsou zdůrazněny základní informace o přírodních polysacharidech (chemická struktura, rozpustnost, tepelná a pH stabilita atd.), jejich modifikace a chemické síťování. Experimentální část je zaměřena na modifikaci přírodní gumy Karaya tak, aby transparentní hydrogely měly nastavitelnou hydrolytickou stabilitu. Vzorky byly analyzovány pomocí FTIR, TGA následované vyhodnocením bobtnání a hydrolytické degradace. Z výsledků vyplynulo, že chemická modifikace zvýšila stabilizaci elastického filmu z přírodního polysacharidu ve vodě až na 25 dní. Díky řízené degradaci a vysoké absorpci vody (85 - 96%) jsou tyto nové hydrogely využitelné především pro vlhké hojení ran (např. popálenin).Presented diploma thesis deals with preparation, crosslinking and physico-chemical characterization of natural polysaccharide-based hydrogels. The aim of the work was to evolve elastic thin films with potential application for moist wound healing. The theoretical part summarizes the state-of-art about regeneration of soft tissues and their substitutes (synthetic or nature). There are pointed out the basic information about natural polysaccharide gums (chemical structure, solubility, heat and pH stability etc.), its modification and chemical crosslinking. The experimental part is focused on the modification of natural gum Karaya in order to make transparent hydrogels with adjustable hydrolytical stability. Samples were analyzed by FTIR, TGA followed by evaluation of swelling properties and hydrolytical degradation. Based on the results, chemical modification helped to stabilize polysaccharide hydrogels in water up to 25 days which is useful mainly for moist wound healing (e.g. after burns) because of high values of water uptake (from 85 up to 96%).

Reduction of Moisture Effects During the Cure of Epoxy Adhesives Used in Composite Repair

The requirements for repair work on Naval aircraft composite wing skins that can be performed under depot conditions (or still worse, under field conditions) are quite restrictive. Equipment that can be used is rather limited as are the available repair space and time. The procedures must be simple enough so that they can be performed satisfactorily by personnel without special knowledge in composite materials technology. Repairs of small holes should not require more than perhaps a short predrying cycle (with heat guns) and a subsequent patch bonding using a heating blanket, held in place by applying a vacuum. However, it has been observed during simulated experimental repair work that the glue lines frequently show a high content of pores and bubbles which are attributed to evaporation of moisture during the curing cycle. (Of course, other volatile materials such as residual solvent would act similarly). The purpose of this paper is to give some detailed analysis of the problem of moisture transport as a function of repair conditions, and to discuss some preliminary work to reduce the effect of moisture by removing moisture chemically with carbodiimides before it reaches a critical level for bubble formations

Catalysts for polyimide foams from aromatic isocyanates and aromatic dianhydrides

Polyimide foam products having greatly improved burn-through and flame-spread resistance are prepared by the reaction of aromatic polyisocyanates with aromatic dianhydrides in the presence of metallic salts of octoic acid. The salts, for example stannous octoate, ferric octoate and aluminum octoate, favor the formation of imide linkages at the expense of other possible reactions

Immunoadsorbents - Preparation and use of cellulose derivatives

Antibody isolation from blood by linking antigens to insoluble cellulose derivative

Unconventional Magnetism in a Nitrogen-Based Analogue of Cupric Oxide

We have investigated the magnetic properties of CuNCN, the first nitrogen-based analogue of cupric oxide, CuO. Our muon spin relaxation, nuclear magnetic resonance and electron spin resonance studies reveal that classical magnetic ordering is absent down to lowest temperatures. However, large enhancement of spin correlations and unexpected inhomogeneous magnetism have been observed below 80 K. We attribute this to a peculiar fragility of the electronic state against weak perturbations due to geometrical frustration, which selects between competing spin-liquid and more conventional frozen states.Comment: 4 pages + 1 page of supplementary information, accepted for publication in PR

Zinc-Catalyzed Guanylation Reaction of Amines to Carbodiimides/Isocyanate Leading to of Guanidines/Urea Derivatives Formation

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