Low Viscosity Silicone Rubber Research Articles

Effect of the structure of hydrogen-containing silicone oil on the properties of silicone rubber

A series of methyl-terminated and hydrogen-terminated hydrogen-containing silicone oil with different hydrogen content and chain length were synthesized by ring-opening polymerization design. Silicone rubber was prepared with hydrogen-containing silicone oil and vinyl-terminated silicone oil with a viscosity of 8033 mPa s. The silicone rubber was reinforced with vinyl MQ resin with a viscosity of 6223 mPa s and a vinyl content of 0.9%. Then the structure, thermal stability, viscosity of the synthesized hydrogenated silicone oil were characterized and the crosslinking density, mechanical properties, aging properties of the silicone rubber were analyzed. It was found that the mechanical properties of hydrogen-containing silicone oil with hydrogen content of 0.50% and chain length of 50% were the best. The parameters of silicone rubber were obtained as follows: viscosity 35.6 Pa s, tensile strength 5.05 MPa, elongation at break 339.01%, tear strength 7.23 kN/m, hardness 44°, compressive modulus 7.43 MPa. This provides an efficient method for designing high strength and low viscosity silicone rubber materials.

Sedimentology and ichnology of the Mafube dinosaur track site (Lower Jurassic, eastern Free State, South Africa): a report on footprint preservation and palaeoenvironment.

Footprint morphology (e.g., outline shape, depth of impression) is one of the key diagnostic features used in the interpretation of ancient vertebrate tracks. Over 80 tridactyl tracks, confined to the same bedding surface in the Lower Jurassic Elliot Formation at Mafube (eastern Free State, South Africa), show large shape variability over the length of the study site. These morphological differences are considered here to be mainly due to variations in the substrate rheology as opposed to differences in the trackmaker’s foot anatomy, foot kinematics or recent weathering of the bedding surface. The sedimentary structures (e.g., desiccation cracks, ripple marks) preserved in association with and within some of the Mafube tracks suggest that the imprints were produced essentially contemporaneous and are true dinosaur tracks rather than undertracks or erosional remnants. They are therefore valuable not only for the interpretation of the ancient environment (i.e., seasonally dry river channels) but also for taxonomic assessments as some of them closely resemble the original anatomy of the trackmaker’s foot. The tracks are grouped, based on size, into two morphotypes that can be identified as Eubrontes-like and Grallator-like ichnogenera. The Mafube morphotypes are tentatively attributable to large and small tridactyl theropod trackmakers, possibly to Dracovenator and Coelophysis based on the following criteria: (a) lack of manus impressions indicative of obligate bipeds; (b) long, slender-digits that are asymmetrical and taper; (c) often end in a claw impression or point; and (d) the tracks that are longer than broad. To enable high-resolution preservation, curation and subsequent remote studying of the morphological variations of and the secondary features in the tracks, low viscosity silicone rubber was used to generate casts of the Mafube tracks.

Embolization of small vessels with a double-lumen microballoon catheter. Part II: Laboratory, animal, and histological studies. Work in progress.

A double-lumen microballoon catheter system measuring 0.5-0.85 mm in outer diameter (1.3-2.8 F) was fabricated for passage through standard 4.1 and 5 F catheters. By arresting circulation with the balloon, embolization with low-viscosity silicone rubber, ethanol, or isobutyl-2-cyanoacrylate can proceed in a methodical, unhurried manner, permitting precise control of tissue penetration and preventing paradoxical embolization of other vessels. Problems such as gluing the catheter in situ with cyanoacrylate did not occur. The catheter may also be inserted during surgery to control embolization at a remote site, which did result in the catheter being glued in situ in one case.

Embolization of small vessels with a double-lumen microballoon catheter. Part I: Design and construction.

Existing coaxial balloon catheters cannot be passed through the smaller catheters used for superselective angiography; nor can they be used by themselves for selective catheterization, as the balloons are easily damaged. The authors describe the principles and construction of double-lumen catheters ranging from 0.45 to 0.85 mm in outer diameter, which may be passed through 4.1-6.0 F catheters to engage smaller vessels. Double-lumen catheters with an outer diameter of 0.45-0.56 mm permit injection of ethanol or a mixture of isobutyl-2-cyanoacrylate, iophendylate, and tantalum powder. The 0.85-mm size is best suited for low-viscosity silicone rubber opacified with tantalum.

A new species of the conifer Frenelopsis from the Cretaceous of Sudan

Conifer fragments from the Lower Cretaceous of Sudan are preserved as internal and external silica moulds. Low viscosity silicone rubber has been used to prepare casts showing fine epidermal details which enable identification of the plants. One is I'seudofrenelopsis parceramosa (Fontaine) Watson, the other is described as a new species of Frenelopsis Schenk.

Transrenal ureteral occlusion with a detachable balloon.

Transrenal ureteral occlusion using a detachable balloon was successfully employed to stop urinary flow in seven patients. The balloon was filled with low-viscosity silicone rubber and released in the distal ureter. Percutaneous nephrostomy provided external drainage. Indications were painful dysuria and large urinary fistulas in advanced pelvic malignancy. The method is preferable to ureteral embolization with tissue adhesive.

Arteries of the antebrachium and manus of the tokay (Gekko gecko) (Reptilia: Gekkonidae)

The role of the circulatory system in the functioning of the subdigital adhesive pads of geckoes has been the subject of much discussion. However, the morphology and configuration of the blood system in the foot has remained poorly understood, rendering functional interpretation of the blood sinuses simplistic. Here the major arterial vessels of the manus are described for the first time and a discussion of their geometry is presented. Due to the paucity of information concerning the arterial system of the appendages of lizards a description of the major vessels of the antebrachium is also given.The data presented are based on the study of material injected with low-viscosity silicone rubber and then cleared so that vessels may be studied in situ. The data are pertinent to subsequent discussions of the microvasculature of the subdigital lamellae and of reconsiderations of their structure and form.

Evaluation of Low-Viscosity Intravascular Silicone Rubber with the Scanning Electron Microscope

A low-viscosity silicone rubber polymer used as an intravascular embolization material was studied with the aid of a scanning electron microscope. The silicone polymer became permanently affixed to the vessel endothelium without observable morphologic changes in the endothelium. No evidence of late recanalization of the embolized vessels was found in our experimental sections.

Visualization by scanning electron microscopy of the periodontal ligament in vivo in the macaque monkey

The incisors and their sockets of three adult monkeys were transected near to the socket margin. Impressions were made of the tissues with a low-viscosity silicone rubber from which replicas were prepared using a polyimide resin. With scanning electron microscopy a fine fibrillar pattern was evident. The form of the ligament changed when a horizontal or intrusive force of 2 newtons(N) was applied to the root for 4 min. Solutions of hyaluronidase or sodium hypochlorite applied to the tissue increased the clarity of the surface detail. This method thus enables the periodontal ligament to be examined repeatedly under different loading conditions.

Delivery System for Low Viscosity Silicone Rubber Through Small Co-axial Catheters

The authors describe a technique of infusing low viscosity silicone rubber through 1–4 French catheters using a commercially available Tuohy-Borst adaptor on the catheters and a Harvard pump for infusing silicone.

The embolization of vascular malformations of the spinal cord with low-viscosity silicone rubber.

Development of the low-viscosity silicone rubber has made possible the successful embolization and complete obliteration of 9 out of 11 vascular malformations of the spinal cord treated with this material. The procedure is particularly useful in patients where the malformation is fed by a limited number of posterior radicular feeders without any supply from the anterior spinal artery. One patient with a supply from the anterior spinal artery. One patient with a supply from both anterior and posterior feeders was successfully embolized after a temporary occlusion of the anterior spinal radicular feeder. Seven patients out of 11 embolized with silicone rubber showed a clinical improvement of their signs and symptoms.

Comparison of the renal medullary vascular systems of dog and chinchilla

Renal vascular structures of dogs and chinchillas were investigated, using a low viscosity silicone rubber arterial injection technique. Cortical and medullary thicknesses were measured and compared to measurements reported by Sperber. Cortical and juxtamedullary structural differences were found in the dog and chinchilla. The juxtamedullary glomeruli had larger diameters, longer afferent and efferent arterioles, and much larger efferent arteriole lumen diameters compared to cortical glomeruli of the same kidney. The vasa recta bundles of dogs are of larger over-all diameter but of approximately the same length and spacing as in the chinchilla. A model for the medullary circulation has been proposed. This model represents three major flow routes to convoluted tubule capillaries, frizzled zone capillaries, and medullary tip capillaries in series with the juxtamedullary glomeruli. The probable contribution of countercurrent exchange of diffusible solutes, occurring between the medullary venous drainage and inflowing blood and its role in the conservation of medullary solutes is discussed.