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Biomedical subjects

J G Thacker

Publications and source records attributed to J G Thacker.

At least 37 records · Page 2Linked to original sources
PubMed1995

Strain-based fatigue analysis of wheelchairs on a double roller fatigue machine.

Results are presented from an experimental program that recorded the outputs of strain gages mounted on two wheelchair frames (one manual, one power) as the wheelchairs were run on a double roller fatigue machine. Rectangular strain gage rosettes were attached to the frames near the cross tube center pin and on the side frame behind a front caster. Thirty data sets were recorded from each rosette on each wheelchair frame. The fatigue test machine and test protocol were in substantial conformance with the recently published ANSI/RESNA Standard for wheelchair fatigue testing. Two analyses have been performed on the recorded strain data. The von Mises stress histories were computed from the strain data and show that peak stresses are frequently twice the mean value. Also, estimates of the number of fatigue machine cycles to failure have been made using a strain-based fatigue analysis. These data will provide wheelchair designers with useful data to incorporate into their design process.

Mathematics↗
PubMed1994

Some biomechanical considerations in microsutures.

The purpose of this study was to measure the biomechanical performance for commercially available microsutures, nylon polypropylene, polyester, and polyglactin 910. The biomechanical performance was determined by reproducible, biomechanical parameters that included stiffness, elasticity, resistance to creep, secure knot construction, and knot breaking strength. On the basis of these comprehensive studies, the handling characteristics of the nylon microsutures were judged to be superior over the other microsutures. Knot security was achieved with a three-throw square (1 = 1 = 1) knot that allowed a preview of the ultimate apposition of the divided tissue. In addition, nylon microsutures were more supple than the other microsutures. The breaking strength of the knotted nylon microsutures was comparable with those of the knotted polyglactin 910 and polyester microsutures, and significantly greater than that of the knotted polypropylene sutures. Its resistance to creep was significantly greater than that of the polypropylene microsutures but less than those of polyglactin 910 and polyester microsutures.

Biomechanical Phenomena↗
PubMed1994

Biomechanics of surgical glove expansion.

The purpose of this study was to correlate the latex gloves' susceptibility to hydration to its development of glove expansion or irreversible elongation of the latex glove. During hydration, the Micro-Touch glove exhibited significantly more creep strain than did the Biogel gloves. Similarly, the Micro-Touch glove exhibited glove growth, while the Biogel glove maintained a uniform fit during hydration.

Biomechanical Phenomena↗
PubMed1994

Modern concepts of packaging surgical needles and suture.

A new, innovative packaging system for surgical needles and sutures has been developed that meets the special needs of surgical technologists. This packaging system consists of an overwrap, or breather pouch, as well as an innerwrap containing the suture swaged to a surgical needle. The flaps of the overwrap are offset and serrated to facilitate the opening and sterile transfer of the inner packet to the sterile field. The inner packet contains either a plastic labyrinth, or craft board that maintains the suture as straight as possible until knot construction. The needle swaged to a suture is 'parked' in foam to protect its sharp cutting edges and point.

Drug Packaging↗
PubMed1994

Three-dimensional computer model of the human buttocks, in vivo.

In an effort to reduce the incidence of decubitus ulcers among wheelchair users, current work in cushion design concentrates on minimizing the pressure at the buttock-cushion interface. Finite element analysis can show the stress levels throughout the soft tissue between the cushion and the ischial tuberosity and give designers a better indication of the effects of a particular cushion. Finite element models were generated of the tissues around the ischial tuberosities of male and female subjects. Linear three-dimensional models were generated using a 386 computer and solved with infinitesimal deflection theory. The resulting minimal principal stresses were 17 kPa and 15 kPa at the buttock-cushion interface for seated male and female subjects, respectively. Computational results were verified experimentally with magnetic resonance imaging and interface pressure measurements.

Biomechanical Phenomena↗
PubMed1993

A synthetic membrane for testing needle penetration.

Needle performance is primarily judged by its penetration through tissue. For detailed studies of needle performance, tissue is too heterogeneous and unstable and difficult to obtain. A homogeneous, stable, and readily available polyurethane substrate has been evaluated as a suitable alternative to biological tissue for evaluation of needle penetration. The needle penetration profiles through the synthetic substrate correlated very well with those through natural tissue. In addition, the synthetic substrate was sensitive enough to easily detect a 20% increase in the force necessary to penetrate natural tissue. This polyurethane substrate offers a valid alternative to biological tissue for the testing of needle penetration performance.

Animals↗
PubMed1993

Influence of surgeon's tying technique on knot security.

The purpose of this study was to determine the influence of the surgeon's tying technique on knot security using 0 and 2-0 monofilament and multifilament nylon sutures. Using an Instron Tensile Tester and a portable tensiometer, knot security was achieved with these sutures using four-throw square knots (1 = 1 = 1 = 1). After didactic and psychomotor skill training, medical students were taught to construct the four-throw square knot using either a two-hand tie or an instrument tie. Using the portable tensiometer, their knot tying techniques were judged to be superior to those used by surgeons. The surgeon's faulty technique can easily be corrected by didactic information and psychomotor skill training.

Clinical Competence↗
PubMed1993

New advances in automatic disposable rotating cartridge skin staplers.

This report describes the design, operation, and mechanical performance of Auto Suture Multifire Premium disposable skin staplers and staples in a biomechanical laboratory investigation and a clinical evaluation. The performance of this reloadable stapler has been compared with that of a new disposable skin stapler with a rotating cartridge, the Proximate RH stapler. The latter exemplifies a disposable skin stapler whose cartridge cannot be reloaded. The Auto Suture Multifire Premium disposable skin stapler has been designed so that its cartridge can be reloaded during a single surgical procedure. The most obvious advantage of this new device is that it substantially reduces the cost of skin stapling during surgery. Another unique benefit of this stapler is that it can accommodate either regular or wide staples, allowing the surgeon to use both size of staples without discarding the stapler. On the basis of this investigation, the Auto Suture Multifire Premium disposable skin stapler is recommended for skin incision and graft closure, since it provides maximal visualization of the wound as well as the staple during its formation. It delivers the staple into the skin or skin graft so that the topspan of the staple is above the skin or wound surface. In addition, the Auto Suture Multifire Premium disposable skin stapler has a prepositioning (precocking mechanism) that is controlled by the surgeon with minimal force, a mechanism which allows the stapler to hold its staple securely, even when its pointed legs extend beyond the delivery end of the stapler. The force required to form its staples is so low that the surgeon can staple repetitively without fatigue.(ABSTRACT TRUNCATED AT 250 WORDS)

Disposable Equipment↗
PubMed1993

Past, present, and future for surgical needles and needle holders.

During the last two decades, major advances in surgical needle and needle holder technology have markedly improved surgical wound repair. These advances include quantitative tests for surgical needle and needle holders performance, high nickel maraging stainless steels, compound curved needles, needle sharpening methods, laser-drilled holes for swages, needle:suture ratios of 1:1, and the atraumatic needle holder.

Animals↗
PubMed1993

Characterization of the dynamic stress response of manual and powered wheelchair frames.

Two wheelchairs, one manual, one electrically powered, were instrumented with strain gages and operated over various laboratory terrains. Both wheelchairs were folding models with cross tubes pinned together at the center. The wheelchairs were operated on a constant speed treadmill with no bump, and with 0.953 cm (0.375 in) and 1.6 cm (0.625 in) dowels simulating bumps. The wheelchairs were also rolled off a 10.8 cm (4.25 in) platform to simulate a curb drop. The von Mises stresses were computed from the recorded strains, and statistical hypothesis tests were performed to determine whether the stresses were consistent with a stationary, narrow-band Gaussian random process. Such a stress history has been used in random fatigue analyses. Summary data for two strain gage locations on each wheelchair, for the four different test terrains, suggest that the von Mises stress can be considered stationary, but neither narrow-banded, nor Gaussian distributed.

Humans↗
PubMed1992

Biomechanical performance of ophthalmic surgical needles.

The mechanical performance of ophthalmic surgical needles is studied. Standard biomechanical tests, devised to evaluate the performance of ophthalmic surgical needles, are presented. Four comparable groups of ophthalmic surgical needles were selected from two different manufacturers for these biomechanical studies. The results of this testing demonstrate that needle point geometry and needle composition are important determinants of needle performance. When comparable size needles were evaluated, the biomechanical performance of the recently introduced CS160-6 ophthalmic needle (Ethicon, Inc) was superior to the AU-5, CU-5, and SU-5 needles (Alcon, Inc). Whereas the development of these biomechanical tests has allowed the evaluation of these ophthalmic needles, these same tests can be used to assess the performance of other new ophthalmic surgical needles.

Alloys↗
PubMed1991

Mechanical performance of surgical needle holders.

A new quantitative measurement of surgical needle holder performance has been described that records the forces (clamping moment) applied by the needle holder jaws to curved surgical needles. This test has been used to determine the applied clamping forces of four different surgical needle holders made by one manufacturer. By relating the magnitude of the clamping moment of needle holder to the resistance to bending of curved surgical needles, we propose a new scientific basis for selecting surgical needle and needle holders for wound closure.

Elasticity↗
PubMed1991

A new compound-curved needle for microvascular surgery.

A new compound-curved needle has been designed and developed for microvascular surgery from a unique stainless steel alloy, American Society for Testing Materials 45500. This needle has two distinct radii of curvature and a short tapered point, followed by a curved distal section. Despite its geometry, it exhibits similar resistance to bending and breakage as a curved needle with a single radius of curvature manufactured from the same alloy. The design of this new needle enables plastic surgeons to pass it through vessel walls with greater accuracy to a controlled depth and length of bite than a curved needle with a single radius of curvature.

Humans↗
PubMed1991

Biochemical performance of tapercut cardiovascular needles.

Standardized reproducible tests have been developed to determine the biomechanical performance of cardiovascular needles. The parameters used to assess performance were: 1) sharpness, 2) resistance to bending, and 3) ductility. Four comparable groups of tapercut and taper point cardiovascular needles were selected from different manufacturers for these biochemical studies. The results of this testing demonstrated that needle geometry, needle composition, and the manufacturer were important determinants of needle performance. When comparable needles were evaluated, the biochemical performance of cardiovascular needles manufactured by Ethicon, Inc. (Somerville, NJ) were superior to needles produced by other manufacturers. The superior performance characteristics of the cardiovascular needles produced by Ethicon, Inc. were related to their unique stainless steel alloy, American Society for Testing Materials 45500, which has greater yield and tensile strengths than the alloy used by the other manufacturers. This stainless steel alloy was ideal for the production of tapercut needles, which combined some of the features of a reverse cutting edge needle and taper point needle. Its very short cutting edges allowed it to penetrate the membrane at considerably lower penetration forces than were encountered with comparable taper point needles. In addition, the investigation indicated that the trocar point cardiovascular needles produced a large triangular defect whose diameter was much larger than that of the needle body. For this reason, the use of the trochar point needle is not recommended in cardiovascular surgery.

Biomechanical Phenomena↗
PubMed1990

Some biomechanical considerations of polytetrafluoroethylene sutures.

The biomechanical performance of polytetrafluoroethylene (PTFE) sutures has been compared with that of polypropylene sutures, the standard to which other sutures used in vascular and cardiac surgery are compared. The PTFE is supple and has no plastic memory, while the polypropylene suture is stiff and retains its plastic memory. In addition, the rate of creep encountered in the PTFE suture was significantly less than that of the polypropylene suture. The knotting profiles for knot security for either a square, granny, or surgeon's knot for polypropylene sutures were three throws each. In contrast, knot security with either a square or granny PTFE knot was accomplished with seven throws; six throws were needed for a secure surgeon's knot. The breaking strength of the unknotted and knotted PTFE sutures was approximately one half as great as that for the unknotted and knotted polypropylene sutures. Knot construction significantly reduced the breaking strength of polypropylene sutures but did not alter the breaking strength of PTFE sutures. The percent elongation experienced by both sutures before breakage did not differ significantly. The elasticity, as measured by work recovery, for the polypropylene suture was greater than that for the PTFE suture. On the basis of its unique biomechanical performance characteristics, the PTFE suture should have an important place in vascular and cardiac surgery.

Physical Phenomena↗
PubMed1990

Scientific basis for selecting staple and tape skin closures.

Use of tape and skin staples has many important clinical applications for surgical wounds. During the past two decades, our research program has identified the optimal performance parameters of these wound closure devices. On the basis of their unique performance characteristics, specific staplers and tapes are recommended for wound closure. The scientific basis for selecting staples and tapes for wound closure is based on their influences on the biology of wound repair and infection.

Bandages↗