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Adjuncts in Vitreoretinal Surgery
Published in Pradeep Venkatesh, Handbook of Vitreoretinal Surgery, 2023
The viscosity of a substance is the resistive force that is encountered when a liquid is forced through a narrow tube. It is dependent on the molecular weight and degree of polymerization of the substance. It is measured as centistoke (cs). Generally, the higher the molecular weight, the greater the viscosity. During vitreoretinal surgery, the role of viscosity is most evident during injection and removal of silicone oil. The higher the viscosity of silicone oil, the greater the force necessary to inject and remove the oil from the vitreous cavity. This is the reason that 5000 cs of silicone oil is more difficult to inject and remove than 1000 cs of oil. Hence, 1000 cs of oil is preferred during uncomplicated surgery. However, higher viscosity oil has a lower risk of emulsification. Hence, in situations wherein it is deemed necessary to retain oil for longer periods [e.g., resurgery in one-eyed patients, choroidal coloboma–associated retinal detachment, retinal detachment in patients with oculocutaneous albinism], 5000 cs of oil is preferred.
Uro-Angiographic Contrast Agents—The Holy Grail
Published in Christoph de Haën, X-Ray Contrast Agent Technology, 2019
Polypaque, a particular realization of a certain chemical class of polymers, merit some critical evaluation not only as focal points for human group dynamic phenomena in technology shaping but also as molecules and contrast agents. Polypaque was described as a polymer of presaponified metrizoic acid of unrevealed exact chemical constitution (Almén and Fondberg [1966] 1967; Almén 1966a). Its degree of polymerization lay between 150 and 300 and the corresponding molecular weight between 100,000 and 200,000 (Almén 1966a). Fondberg let me know that the macromolecules were weakly cross-linked. A solution of the compound at a concentration of 440 mg (Iodine)/mL was reported to have a dynamic viscosity of 0.013 Pa·s. Almén did not question this puzzlingly small value since, as already pointed out, on erroneous theoretical grounds, he was not expecting viscosity to be a problem. Most notably, Almén described rudimentary observations on a single, unnamed human volunteer who had been injected with the compound. In the aforementioned contacts, I had with Fondberg he declared the viscosity data in error and himself as the volunteer. The polymer was reportedly degraded in the volunteer’s blood and was excreted completely within 24 h. Similar observations in animals were also reported on some other members of the polypaque family (Almén and Fondberg [1966] 1967). No radiographs obtained with these contrast agent solutions were made available.
Unlocking scaffold mechanical properties
Published in Yoshinobu Onuma, Patrick W.J.C. Serruys, Bioresorbable Scaffolds, 2017
John J. Scanlon, Yoshinobu Onuma, Patrick W.J.C. Serruys, Joseph M. Deitzel
It also appears that opportunity exists to preserve the molecular weight of polymers during fabrication of scaffolds. Various sources highlight that polymer molecular weight is reduced during thermal processing and sterilization. Alternative manufacturing processes that enable use of higher starting molecular weight materials and retaining more degree of polymerization may hold a second key to unlocking greater mechanical property performance.
Impact of adhesive application errors on dentin bond strength of resin composite
Published in Biomaterial Investigations in Dentistry, 2022
Benjamin Michael Schärer, Anne Peutzfeldt
For the Scotchbond Universal adhesive system, both deviations from the instructions for use led to a decrease in bond strength and an increase in the percentage of adhesive failures at the dentin surface. Failure to evaporate the solvents in the adhesive (Group 2) had the most detrimental effect. Like OptiBond FL, Scotchbond Universal contains ethanol as well as water as solvents. Lack of the evaporation step may be assumed to result in increased residual moisture on the dentin surface. This moisture has been found to not affect the thickness of the adhesive nor of the hybrid layer, but to shorten the resin tags [21]. A number of studies have shown that shortened resin tags can negatively affect the performance of Scotchbond Universal [21,22]. In contrast, other studies have found no negative impact of increased residual moisture [23,24]. Failure to light-cure (group 3) also led to lower bond strength. The light-curing of an adhesive or a resin composite converts the monomers to stable high-molecular weight polymers [25], and the higher the degree of conversion, the better the mechanical properties [26]. Although some degree of polymerization of the adhesive might have occurred during the subsequent light-curing of the resin composite, the layer thickness of the composite of 2 mm, is likely to have reduced the degree of polymerization significantly [27,28] and thus to have caused a reduction in bond strength.
Co-processing of small molecule excipients with polymers to improve functionality
Published in Expert Opinion on Drug Delivery, 2021
Prashantkumar K. Parmar, Srilaxmi G. Rao, Arvind K. Bansal
The degree of polymerization and substitution of the polymer can affect disintegration property. Sodium carboxymethyl cellulose (NaCMC) with high molecular weight and lower level of carboxymethylation exhibited better disintegration potential [16]. Corn starch contains different ratio of amylose (linear chain) and amylopectin (complex-branched chain), which is responsible for disintegrant and binding properties, respectively. Besides, porosity of the tablet was not affected by varying the ratio of amylose to amylopectin [17]. The degree of cross-linking and extent of substitution of the polymer can affect disintegration action. The swelling of sodium starch glycolate (SSG) was inversely proportional to a major extent on the degree of cross-linking and a lesser extent on the level of substitution [18].
A novel multi-stimuli-responsive theranostic nanomedicine based on Fe3O4@Au nanoparticles against cancer
Published in Drug Development and Industrial Pharmacy, 2020
Bakhshali Massoumi, Amir Farnudiyan‐Habibi, Hossein Derakhshankhah, Hadi Samadian, Rana Jahanban-Esfahlan, Mehdi Jaymand
The successful block copolymerization of acrylic acid monomer onto (S-PNIPAAm)2 was confirmed through the appearance of a broad chemical shift at 12.35–12.65 ppm related to –COOH group (l). It is worth noting that the chemical shifts of methylene and methine groups (j and k) of PAA backbone were overlapped with the methylene and methine groups of PNIPAAm backbone and appeared at 1.35–2.20 ppm. The degree of polymerization (DPn) and number-average molecular weight (Mn) of the synthesized polymers were calculated from the 1H NMR data through the following equations: