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Electron Spectroscopy For Chemical Analysis: Applications in the Biomedical Sciences
Published in R. Michael Gendreau, Spectroscopy in the Biomedical Sciences, 1986
Buddy. D. Ratner, Brien. J. McElroy
Polyurethanes of the type that are used in biomedical devices are usually synthesized in a two-stage process. First, a prepolymer is formed by the reaction of a diisocyanate with a low-molecular-weight (500 to 4000), dihydroxy-terminated polyether:
Ophthalmic lenses
Published in Pablo Artal, Handbook of Visual Optics, 2017
Most current ophthalmic lenses are made with plastics due to several factors, mainly that they are safer, since they do not break like glass and they are also lighter. The only disadvantage is that they scratch more easily. The main plastics for ophthalmic uses, whose characteristics are in Table 10.2, are as follows: CR-39. This plastic is a polymerizable thermosetting resin, formed by allyl diglycol carbonate. The name comes from Columbia Resin No. 39, because it was the 39th formula of a thermosetting plastic developed by the Columbia Resins Project at the Pittsburgh Plate Glass Company in 1940. Their most important characteristic is a high degree of scratch resistance, but lower than that of glass.Trivex, which is a urethane-based prepolymer. PPG named the material Trivex because of its three main performance properties, that is, superior optics, ultra-lightweight, and extreme strength. This plastic has the same UV blocking properties and shatter resistance of polycarbonate. Its low refractive index of 1.532 may result in slightly thicker lenses. It can be easily tinted.Polycarbonate is a thermoplastic, lighter than other plastics. This material blocks UV rays and it is shatter resistant and it is better than CR-39, and it is used in sports glasses and glasses for children and teenagers. Because polycarbonate is soft and will scratch easily, scratch-resistant coating is typically applied after shaping and polishing the lens. Standard polycarbonate has a high Abbe value of 30, thus producing lenses with a high chromatic aberration.High-index plastics (thiourethanes) are high-index plastics, producing thin lenses, but not lighter, than most plastics due to the high density. As most with high-index plastics, lenses have a high level of chromatic aberration. Another advantage of high-index plastics is their strength and shatter resistance, although not as shatter resistant as polycarbonate.
Fluorescent melamine-formaldehyde/polyamine coatings for microcapsules enabling their tracking in composites
Published in Journal of Microencapsulation, 2022
Christian Neumann, Sophia Rosencrantz, Andreas Schmohl, Latnikova Alexandra
The ratio of the reactive groups is known to have a great influence on the formation of the MF condensates. Therefore, the influence of the ratio between the reactive (primary + secondary) amine groups of the polyamine [AMINE] and the hemiaminal ether groups [HAE] was systematically investigated. The polymerisation of the MF prepolymer and the PEI (Mw = 2000 g/mol) was carried out with a deficit of reactive amine groups (1:0.1) up to an excess of amines (1:2) as shown in Table 1. All synthesised MF/PEI polymers precipitated in the form of particulate condensates from the aqueous phase. The [HAE]:[AMINE] ratio of 1:0.1 to 1:0.5 led to higher yields (75–85% w/w) while MF/PEI (1:1)* and MF/PEI (1:2)* led to considerably lower yields. It can be assumed that the loss in yield with excess of amines is caused by the lower cross-linking density, the increase of the water solubility of the polycondensates and the high polymer concentration that could affect the polycondensation.
Two Polyurethane Adhesives for PVDF Fixation Show Superior Biocompatibility in a Rat Model
Published in Journal of Investigative Surgery, 2022
Daniel Heise, Yelyzaveta Mirlas, Marius Helmedag, Roman Eickhoff, Andreas Kroh, Andreas Lambertz, Christian Daniel Klink, Ulf Peter Neumann, Uwe Klinge, Rene Tolba
Two experimental polyurethane/urea-based adhesives (Adhesive-A and Adhesive-B, Adhesys Medical GmbH, Germany) were tested with respect to their biomechanical features and biocompatibility compared to conventional cyanoacrylatic adhesive (Glubran2®,Dahlhausen GmbH, Germany) as well as an untreated control group. The newly developed adhesives consist of two main components, an isocyanate-functionalized prepolymer and a curing agent mixture mainly based on amine functionalized aspartic acid ester and filling agents. The two main components are mixed by a static mixing unit and the polymerization reaction starts immediately upon mixing. The pre-filled syringes are ready to use, sterile and can be stored at room temperature. The adhesives are designed to be biodegradable and biocompatible. The formulation of Adhesive-A and Adhesive-B differs in its composition and performance characteristics, as Adhesive B has a higher initial viscosity and the curing time is slightly longer than for Adhesive A.
Release mechanisms and applications of drug delivery systems for extended-release
Published in Expert Opinion on Drug Delivery, 2020
Shuying Wang, Renhe Liu, Yao Fu, W. John Kao
Also important is to smooth the release profile over an extended period to reduce potential negative side effect. When employing polymers for controlled release, the manipulation of their comonomer ratio, end groups and molecular weight is always useful to modify the degradation rate so as to smooth the release profile. A typical example was reported by Amsden group [66] for the extended delivery of corticosteroid triamcinolone. To prolong the release, triamcinolone diffusivity (highly dependent on glass transition temperature Tg of the polymer [70]) was reduced via adjusting the monomer composition of hydrophobic prepolymer to increase Tg accordingly. Concurrently, a faster secondary release phase, caused by bulk erosion of the matrix with time [71], was eliminated by manipulating polymer degradation rate to achieve mass loss in a nearly linear fashion with time. Thus, the formulation design was based on the incorporation of trimethylene carbonate (TMC) and D,L-lactide (DLLA) into the prepolymer. The data demonstrated that a nearly constant, prolonged release for over 250 days was achieved using a network consisting of a hydrophobic prepolymer (TMC:DLLA 3:1) co-cross-linked with hydrophilic PEGDA, which was completely different from the ‘S’ shaped release pattern when equimolar ratios of TMC with DLLA was used (Figure 4).