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Machines and Instrumentation
Published in Pradeep Venkatesh, Handbook of Vitreoretinal Surgery, 2023
General-purpose instruments that are required during vitreous surgery are a speculum [e.g., Barraquer standard wire, heavy (1 mm) wire or solid blade; Kratz-Barraquer (open blades); Kraff solid blade adjustable; Lieberman open blade adjustable]; Castroviejo calliper [straight or curved, measuring 1–20 mm in 1-mm increments]; scleral depressor [Schepens, Schokett, Packo (has marker)]; muscle hook [Gass, Green]; suture holding and tissue forceps [Lim, Bishop-Harman]; tissue forceps [serrated or non-serrated]; suturing forceps [Castroviejo]; tying forceps that are straight, angled, or curved [McPherson/ Jaffe]; needle holder [Castroviejo with or without a lock; Barraquer, McPherson, Sinskey]; conjunctival scissors; and tenotomy scissors [Westcott-spring handle, Stevens-ring handle]. Scleral plugs or cannula plugs and plug-holding forceps are rarely necessary with valved instrumentation. A 10-mm polyimide tip is necessary to inject viscous fluid [silicone oil] under high pressure.
Conventional Pressure Sensors
Published in J G Webster, Prevention of Pressure Sores, 2019
In order to solve this problem, Beebe et al (1990) explored a new packaging technique, as shown in figure 9.4. Starting with an unpackaged diaphragm sensor mounted temporarily on a Teflon disk, they applied several layers of polyimide. They then etched the polyimide to reveal the bonding pads on the diaphragm, and deposited thin film metal leads. After applying more polyimide layers to protect the leads, they removed the Teflon, and replaced it with a backing disk. The backing disk had the effect of increasing the contact area of applied force. They applied final layers of polyimide to yield a sensor which was totally encased. A similar technique has been used successfully in the packaging of temperature sensors. The output of the sensor would vary with the compliance of the tissue, so calibration procedures should include placing the sensor between layers of material with compliance similar to that of tissue. The main problem with this approach was the inability to planarize the die–substrate interface via spin coating. Another problem was the warping of the Teflon substrate at relatively low processing temperatures. Thus they are fabricating their own pressure sensors using micromachining. Silicon etching using KOH etches shallow (< 5 μm) cavities so the diaphragm will bottom out during overload. Silicon fusion bonding will bond the constraint and sensing wafers. Ion implantation will create a piezoresistive Wheatstone bridge in the diaphragm. Polyimide layers will encapsulate the sensor.
Surgical treatment of central retinal vein occlusion
Published in A Peyman MD Gholam, A Meffert MD Stephen, D Conway MD FACS Mandi, Chiasson Trisha, Vitreoretinal Surgical Techniques, 2019
Mohamed K Tameesh, Rohit R Lakhanpal, Mark S Humayun
Several materials have been tried, but our group at the Doheny Retina Institute has recently developed a micro-catheter system made of 44-gauge polyimide tubing, a material that we feel is the best for such a procedure (Fig. 41.2). We developed a flexible catheter that is mounted inside a modified metal microcannula system that protects the delicate tubing during insertion through the sclerotomy. The intraocular part of the catheter is composed of 44-gauge (60 μm) polyimide tube, which is small and flexible enough to be manipulated inside the eye. Attached to this polyimide tube is a glass pipette 1.5–2 mm in length with an outer diameter of 50μm and a tip beveled at 30° to make it sharper, thus allowing insertion of the cannula into the retinal vein with increasing ease. The extraocular part of the catheter is composed of a larger polyimide tube (600μm); this larger-diameter tubing also allows easy attachment to the tip of a syringe loaded with infusion fluid. Lastly, the plunger of the syringe loaded with fluid is attached to a motorized pump for fluid injection.
Long-acting ocular drug delivery technologies with clinical precedent
Published in Expert Opinion on Drug Delivery, 2022
Matthew N. O’Brien Laramy, Karthik Nagapudi
The core-shell implant design is likely manufactured via one of two processes: 1) simple extrusion and curation of the skin, followed by filling the drug core mixture in a non-extrusion process, or 2) co-extrusion of the core and shell materials [63]. The blended core composition of FA and PVA likely permits co-extrusion, provides mechanical integrity, and slows FA dissolution in the core [63]. If the implant ruptured, a blended core would slow possible burst release effects in vivo, as compared to a drug only core. Polyimide is a thermoset polymer that offers an impermeable barrier to drug dissolution and permeation, similar to EVA [12,14]. Unlike EVA, polyimide can be cured by methods other than heating, which can preserve core structure and minimize manufacturing-related degradation.
Ureteral anastomosis with a polyimide stent in rat kidney transplantation
Published in Renal Failure, 2020
Tong Wang, Zhou Yu, Chen Chen, Yajuan Song, Xianhui Zeng, Yingjun Su, Chenggang Yi
Polyimide is considered to be an ideal polymer material for stents on account of its high thermal stability, excellent chemical and physical properties, good adhesion properties, and good biocompatibility. Polyimide is currently used for the production of medical devices and implants, such as microelectrodes, chemical sensors, microchannels, and blood pressure sensors. In addition, a stent made from polyimide tubing has been successfully used for vascular anastomosis in vascularized skin transplantation performed in a mouse model [15], with no evidence of damage or thrombus formation. The ureter and blood vessels share similarities in terms of their composition and liquid transport function. Therefore, a polyimide stent may also be suitable for ureteral anastomosis during renal transplantation.
Pharmaceutical Formulation Methods for Improving Retinal Drug Delivery
Published in Seminars in Ophthalmology, 2019
Tomasz P. Stryjewski, James A. Stefater, Dean Eliott
Non-biodegradable polymers can be created by introducing bonds that are not susceptible to hydrolytic or enzymatic degradation. For example, the Iluvien device consists of a hollow polyimide tube with a porous polyvinyl alcohol cap. Polyimide is a polymer composed of repeating imide monomers and is inert and very mechanically stable. The end cap of the devices is composed of polyvinyl alcohol (PVA), an inert, porous, and biocompatible hydrophilic polymer. Depending on the density of the cross-links and molecular weight of the PVA, diffusion kinetics can be optimized.