Brijesh S. Gill

Advances in Progenitor Cell Therapy Using Scaffolding Constructs for Central Nervous System Injury

Traumatic brain injury (TBI) is a major cause of morbidity and mortality in the United States. Current clinical therapy is focused on optimization of the acute/subacute intracerebral milieu, minimizing continued cell death, and subsequent intense rehabilitation to ameliorate the prolonged physical, cognitive, and psychosocial deficits that result from TBI. Adult progenitor (stem) cell therapies have shown promise in pre-clinical studies and remain a focus of intense scientific investigation. One of the fundamental challenges to successful translation of the large body of pre-clinical work is the delivery of progenitor cells to the target location/organ. Classically used vehicles such as intravenous and intra arterial infusion have shown low engraftment rates and risk of distal emboli. Novel delivery methods such as nanofiber scaffold implantation could provide the structural and nutritive support required for progenitor cell proliferation, engraftment, and differentiation. The focus of this review is to explore the current state of the art as it relates to current and novel progenitor cell delivery methods.

Evaluation of noninvasive hemoglobin measurements in trauma patients

BACKGROUNDnReliable, accurate, noninvasive, and continuous determination of hemoglobin would be an important advance in the care of trauma patients. The aim of this study was to evaluate the utility of the Masimo Radical 7 device in severely injured trauma patients.nnnMETHODSnHighest level trauma activation patients were enrolled over a 1-year period. Laboratory hemoglobin values were compared with Masimo hemoglobin values using Bland-Altman analysis.nnnRESULTSnA total of 525 patients were enrolled in the study. Comparison of 861 paired values from 418 patients showed a variance of 3.89 to -3.84 g/dL, showing a nonsignificant correlation between Masimo hemoglobin and laboratory hemoglobin values.nnnCONCLUSIONSnThe Masimo Radical 7 system evaluated in this study holds promise, but it is not ready to be used as an initial noninvasive evaluation tool in the acute treatment of severely injured trauma patients. There was a poor correlation between Masimo hemoglobin and laboratory hemoglobin and large numbers of missing data. On the basis of the poor correlation, the Masimo Radical 7 device cannot currently be used to guide transfusion therapy.

Bioimpedance Analysis: A Guide to Simple Design and Implementation

BACKGROUNDnBioimpedance analysis has found utility in many fields of medical research, yet instrumentation can be expensive and/or complicated to build. Advancements in electronic component design and equipment allow for simple bioimpedance analysis using equipment now commonly found in an engineering lab, combined with a few components exclusive to impedance analysis.nnnMATERIALS AND METHODSnA modified Howland bridge circuit was designed on a small circuit board with connections for power and bioimpedance probes. A programmable function generator and an oscilloscope were connected to a laptop computer and were tasked to drive and receive data from the circuit. The software then parsed the received data and inserted it into a spreadsheet for subsequent data analysis. The circuit was validated by testing its current output over a range of frequencies and comparing measured values of impedance across a test circuit to expected values.nnnRESULTSnThe system was validated over frequencies between 1 and 100 kHz. Maximum fluctuation in current was on the order of micro-Amperes. Similarly, the measured value of impedance in a test circuit followed the pattern of actual impedance over the range of frequencies measured.nnnCONCLUSIONSnContemporary generation electronic measurement equipment provides adequate levels of connectivity and programmability to rapidly measure and record data for bioimpedance research. These components allow for the rapid development of a simple but accurate bioimpedance measurement system that can be assembled by individuals with limited knowledge of electronics or programming.

Regional Differences in Cerebral Edema After Traumatic Brain Injury Identified by Impedance Analysis

OBJECTIVEnCerebral edema is a common and potentially devastating sequel of traumatic brain injury. We developed and validated a system capable of tissue impedance analysis, which was found to correlate with cerebral edema.nnnMETHODSnConstant sinusoidal current (50 microA), at frequencies from 500 to 5000 Hz, was applied across a bipolar electrode unit superficially placed in a rat brain after traumatic brain injury. Rats were randomized to three groups: severe controlled cortical injury (CCI), mild CCI, or sham injury. At 60 h post-CCI, cerebral voltage and phase angle were measured at each frequency at the site of injury, at the penumbral region, at the ipsilateral frontal region, and in the contralateral hemisphere. Impedance measurements were also obtained in vivo. The electrical properties of varied injuries and specified locations were compared using a repeated measures analysis of variance (RMANOVA), were correlated with regional tissue water percentage using regression analyses, and were combined to generate polar coordinates.nnnRESULTSnThe measured voltage was significantly different at the site of injury (P<0.0001), in the penumbra (P=0.002), and in the contralateral hemisphere (P=0.005) when severe, mild, and sham CCI rats were compared. Severely injured rats had statistically different voltage measurements when the various sites were compared (P=0.002). The ex vivo measurements correlated with in vivo measurements. Further, the impedance measurements correlated with measured tissue water percentage at the site of injury (R2=0.69; P<0.0001). The creation of a polar coordinate graph, incorporating voltage and phase angle measurements, enabled the identification of impedance areas unique to normal, mild edema, and severe edema measurements in the rat brain.nnnCONCLUSIONSnElectrical measurements and tissue water percentages quantified regional and severity differences in rat brain edema after CCI. Impedance was inversely proportional to the tissue water percentage. Thus, impedance measurement can be used to quantify severity of cerebral edema in real time at specific sites.

Hydrostatic intestinal edema induced signaling pathways: potential role of mechanical forces

BACKGROUNDnHydrostatic intestinal edema initiates a signal transduction cascade that results in smooth muscle contractile dysfunction. Given the rapid and concurrent alterations in the mechanical properties of edematous intestine observed with the development of edema, we hypothesize that mechanical forces may serve as a stimulus for the activation of certain signaling cascades. We sought to examine whether isolated similar magnitude mechanical forces induced the same signal transduction cascades associated with edema.nnnMETHODSnThe distal intestine from adult male Sprague Dawley rats was stretched longitudinally for 2 h to 123% its original length, which correlates with the interstitial stress found with edema. We compared wet-to-dry ratios, myeloperoxidase activity, nuclear signal transduction and activator of transcription (STAT)-3 and nuclear factor (NF)-kappa B DNA binding, STAT-3 phosphorylation, myosin light chain phosphorylation, baseline and maximally stimulated intestinal contractile strength, and inducible nitric oxide synthase (iNOS) and sodium hydrogen exchanger 1-3 messenger RNA (mRNA) in stretched and adjacent control segments of intestine.nnnRESULTSnMechanical stretch did not induce intestinal edema or an increase in myeloperoxidase activity. Nuclear STAT-3 DNA binding, STAT-3 phosphorylation, and nuclear NF-kappa B DNA binding were significantly increased in stretched seromuscular samples. Increased expression of sodium hydrogen exchanger 1 was found but not an increase in iNOS expression. Myosin light chain phosphorylation was significantly decreased in stretched intestine as was baseline and maximally stimulated intestinal contractile strength.nnnCONCLUSIONnIntestinal stretch, in the absence of edema/inflammatory/ischemic changes, leads to the activation of signaling pathways known to be altered in intestinal edema. Edema may initiate a mechanotransductive cascade that is responsible for the subsequent activation of various signaling cascades known to induce contractile dysfunction.

Inguinal Hernia Repair Using 3D Printed Surgical Instruments in the Cadaveric Model: A Feasibility Study

Background: 3D printing is an additive manufacturing process allowing the creation of solid objects directly from computer aided design (CAD). Design and fabrication of 3D printed surgical instruments has previously been performed with results indicating relevance to real surgical procedures. This study expands on previous work and investigates the feasibility of performing a cadaveric inguinal hernia repair using 3D printed surgical instruments. Methods: A CAD software package was used to design a general surgical set including hemostats, needle driver, scalpel handle, retractors and forceps. The digital models were manufactured on a 3D printer and used to perform a standard inguinal hernia repair on a human cadaver. Results: An acceptable inguinal hernia repair including mesh placement was successfully performed on a human cadaver using standard surgical techniques. Conclusions: General surgical procedures such as an inguinal hernia repair are feasible using 3D printed surgical instruments.

Progenitor Cell Tissue Engineering

A critical aspect of cell and tissue engineering is the design of non-cellular constructs that closely interact with cells to provide the necessary conditions for intended function. Properties such as surface chemistry, mechanical strength, porosity, and rates of degradation are important elements of a cellular support system and can deeply influence the fate of progenitor cells. To achieve the goal of successful implantation and proliferation of cells in a particular region, various biomaterials and fabrication processes have been explored. Lately, techniques with origins outside the field of biology or medicine have been used to create highly controlled morphologies. This chapter will review the fundamentals of scaffold design as it relates to brain-based therapies and give some examples of fabrication techniques.