Raymond Dunn

Engraftment of human HSCs in nonirradiated newborn NOD-scid IL2rγ null mice is enhanced by transgenic expression of membrane-bound human SCF.

Immunodeficient mice engrafted with human HSCs support multidisciplinary translational experimentation, including the study of human hematopoiesis. Heightened levels of human HSC engraftment are observed in immunodeficient mice expressing mutations in the IL2-receptor common γ chain (IL2rg) gene, including NOD-scid IL2rγ(null) (NSG) mice. Engraftment of human HSC requires preconditioning of immunodeficient recipients, usually with irradiation. Such preconditioning increases the expression of stem cell factor (SCF), which is critical for HSC engraftment, proliferation, and survival. We hypothesized that transgenic expression of human membrane-bound stem cell factor Tg(hu-mSCF)] would increase levels of human HSC engraftment in nonirradiated NSG mice and eliminate complications associated with irradiation. Surprisingly, detectable levels of human CD45(+) cell chimerism were observed after transplantation of cord blood-derived human HSCs into nonirradiated adult as well as newborn NSG mice. However, transgenic expression of human mSCF enabled heightened levels of human hematopoietic cell chimerism in the absence of irradiation. Moreover, nonirradiated NSG-Tg(hu-mSCF) mice engrafted as newborns with human HSCs rejected human skin grafts from a histoincompatible donor, indicating the development of a functional human immune system. These data provide a new immunodeficient mouse model that does not require irradiation preconditioning for human HSC engraftment and immune system development.

Flexible sensor for measurement of skin pressure and temperature in a clinical setting

A flexible, wearable sensor patch for simultaneous monitoring of local skin pressure and temperature is described. Measurement can be collected for a period of time extending over several hours, suitable for monitoring in a clinical setting, for example during surgery, in the home, or in a long-term care facility. Experimental results are presented demonstrating pressure and temperature measurement at multiple locations on an anesthetized animal during a seven hour surgical procedure.

Possible mechanisms of screw loosening of rigid sternal fixation

The goal of this study was to compare the performance of cancellous and cortical screws for plate and screw fixation of the sternum. Pelvic bone plates were fixated to osteoporotic sternum in both unicortical and bicortical configurations and then loaded transversely (0–50N at 2Hz) for 15,000 cycles. The resulting plate displacement was measured continuously. In the first 10 cycles bicortical screw purchase demonstrated less loosening (p=0.015), while differences between screw type was insignificant. After the 15,000 cycles, cortical screws had less loosening (p=0.039) than cancellous, while the number of cortices fixated was insignificant to loosening. These initial findings indicate that both number of cortices fixated and type of screw are both important in designing and optimized system for sternal fixation. It appears that the cortical shell regions allow more screw purchase than the osteoporotic cancellous regions, while bicortical screw purchase appears to minimize the loosening of the screws.

Design of a novel elliptical skin biopsy punch device

Current skin biopsy techniques utilizing a punch biopsy device can leave raised scars that are cosmetically unappealing. With 3.8 million procedures per year, the potential marketability of a superior device is substantial. The goal of this study is to design a novel elliptical punch biopsy device that maintains the simplicity of existing products while minimizing scarring. Mechanical testing was performed on porcine skin to determine the force required to breach the dermal layer using a single #11 scalpel blade (comparable to the excision biopsy technique), the traditional biopsy punch, and a novel blade design. The force required to penetrate the skin using the novel design (81.72 N) prototype was considerably higher than the single #11 blade (1.89 N–2.42 N) as well as the punch biopsy (4.61 N). Initial force data and mathematical analysis has resulted in a final blade design that requires less force than the initial prototype and includes fail-safes to prevent excessive depth of penetration. Clinicians will ultimately test these devices, and their feedback will be used to create a final production design. Finally, a proposed mass manufacturing technique was created.

Wearable wireless sensor patch for continuous monitoring of skin temperature, pressure, and relative humidity

This paper describes system design issues involved in the development of a wearable wireless sensor system for continuous monitoring of skin pressure, temperature, and relative humidity. The system is intended for prevention of pressure ulcers (bedsores), and would alert a patient or caregiver to a potentially harmful level of contact pressure or adverse microclimate that could cause tissue damage. Implementation of this system would reduce health care costs by improving pressure ulcer prevention, enabling patient treatment and monitoring outside a hospital setting, and easing workload on caregivers.

Incisional Hernia: Plastic Aspects, Component Separation, Technical Details & Pediatrics.

Methods: A retrospective review of patients with large midline abdominal hernia treated using component separation technique from 2009 to 2013 at General Surgery Department of Kipshidze Central University Hospital was performed. The scoring criteria were wound complications (infection, hematoma, seroma, scin necrosis, secondary healing), time to return to work/normal activities and recurrent hernia. The mean follow-up time was 21 months.

Comparison of Cortical and Cancellous Screws for Sternal Fixation

The goal of this study is to compare the performance of currently available screw types and configurations for rigid sternal fixation. Bone fixation plates were attached to osteoporotic human sternum with cortical or cancellous screws in either a unicortical or bicortical manner. The plates were cyclically loaded transversely (0–50N at 2Hz) for 15,000 cycles; the resulting lateral screw displacement was measured continuously. Bicortical attachment allowed significantly lower initial displacement than unicortical (p = 0.015), whereas cortical screws allowed significantly lower displacement than cancellous screws after long term cycling (p = 0.039). These initial findings indicate that both screw type and cortical purchase are important parameters in the design of a rigid plating system for sternal closure. Cortical screws appear to be more applicable to the osteoporotic sternum, as the cortical shell regions support more screw purchase than the degenerated cancellous part, and bicortical screw purchase appears to decrease screw loosening.Copyright

Characterization of the In Vivo Forces on the Sternum in Pigs

Approximately 15,000 Americans suffer complications associated with inadequate sternal fixation after open-heart surgery each year [1]. Although alternative fixation methods exist, limitations of current device evaluation systems have led to uncertainty about the relative increase in stability that these novel devices provide, thereby diminishing their widespread clinical use. Sternal closure techniques are typically evaluated in situ where estimated sternal forces (180–400N) are applied to an intact chest [2] or in vitro on isolated sternal models [3]. The mechanical stability afforded by each technique is quantified as the resultant separation along the bisected sternal midline. This displacement is assumed to reflect micro-motion that would occur at the wound site under physiological loading, a critical factor during bony healing [4]. However, the loading in these studies is hardly physiological; it is generally simplified to a single direction and applied quasistatically to only a few discrete locations along the sternum without regard for the in vivo distribution of forces. It is also unclear whether the transfer of loads from sternum to fixation device during in situ tests [5](cadavers) accurately reflects loading in vivo due to the potential effects of rigor mortis and/or embalming. To improve the accuracy of current in situ and in vitro sternal fixation test methods it is essential to advance our knowledge of in vivo dynamic multi-directional sternal loading.Copyright

A preliminary in-vitro evaluation and comparative study of various tissue pH sensors

An investigation is being pursued to determine the best pH sensor for assessing tissue viability during the process of reconstructive surgery. Two different pH sensors are being evaluated in a preliminary study designed to improve upon the standard glass pH electrode: an ion-selective field effect transistor (ISFET) sensor and a conventional glass electrode. Preliminary test results show that the ISFET sensor responds more quickly to changes in pH than the glass electrode does. Each electrode responds quickly enough to adequately monitor physiological pH changes. However, more importantly, the glass electrode displayed very little drift over a 72 hour period, whereas the ISFET sensor displayed an unacceptably large drift for patient monitoring. The accuracy of both the ISFET and the glass electrodes in the 7.0 pH buffer was found to be satisfactory for tissue monitoring. The accuracy tests in the 6.84 and 7.38 buffers showed a less than ideal accuracy for tissue monitoring. However, the results may be a result of using weak ionic strength buffers and not due to electrode inaccuracy at particular pH levels.<<ETX>>