Publications by authors named "Daniel Swartz"

Competition during range expansions is of great interest from both practical and theoretical view points. Experimentally, range expansions are often studied in homogeneous Petri dishes, which lack spatial anisotropy that might be present in realistic populations. Here, we analyze a model of anisotropic growth, based on coupled Kardar-Parisi-Zhang and Fisher-Kolmogorov-Petrovsky-Piskunov equations that describe surface growth and lateral competition.

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In growing populations, the fate of mutations depends on their competitive ability against the ancestor and their ability to colonize new territory. Here we present a theory that integrates both aspects of mutant fitness by coupling the classic description of one-dimensional competition (Fisher equation) to the minimal model of front shape (Kardar-Parisi-Zhang equation). We solve these equations and find three regimes, which are controlled solely by the expansion rates, solely by the competitive abilities, or by both.

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In growing populations, the fate of mutations depends on their competitive ability against the ancestor and their ability to colonize new territory. Here we present a theory that integrates both aspects of mutant fitness by coupling the classic description of one-dimensional competition (Fisher equation) to the minimal model of front shape (KPZ equation). We solved these equations and found three regimes, which are controlled solely by the expansion rates, solely by the competitive abilities, or by both.

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Introduction: Porto-mesenteric venous thrombosis (PMVT) is a significant complication that occurs more frequently after laparoscopic sleeve gastrectomy (SG) than other bariatric procedures and presents later than other venous thromboembolic (VTE) events often 2 weeks after the operation. The common current practice in bariatric surgery of perioperative chemoprophylaxis until discharge may not adequately prevent PMVT. Therefore, a 30-day post-discharge chemoprophylaxis (PDC) might reduce the incidence of PMVT.

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First proposed as an empirical rule over half a century ago, the Richards growth equation has been frequently invoked in population modeling and pandemic forecasting. Central to this model is the advent of a fractional exponent γ, typically fitted to the data. While various motivations for this nonanalytical form have been proposed, it is still considered foremost an empirical fitting procedure.

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The eukaryotic cell's cytoskeleton is a prototypical example of an active material: objects embedded within it are driven by molecular motors acting on the cytoskeleton, leading to anomalous diffusive behavior. Experiments tracking the behavior of cell-attached objects have observed anomalous diffusion with a distribution of displacements that is non-Gaussian, with heavy tails. This has been attributed to "cytoquakes" or other spatially extended collective effects.

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Cell-free small diameter vascular grafts, based on small intestinal submucosa (SIS) functionalized with heparin and vascular endothelial growth factor (VEGF) manufactured and implanted successfully into the arterial system of neonatal lambs, where they remained patent and grew in size with the host to a similar extent and with similar rate as native arteries. Acellular tissue engineered vessels (A-TEV) integrated seamlessly into the native vasculature and developed confluent, functional endothelium that afforded patency. The medial layer was infiltrated by smooth muscle cells, showed no signs of calcification and developed contractile function.

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Recently our group demonstrated that acellular tissue engineered vessels (A-TEVs) comprised of small intestinal submucosa (SIS) immobilized with heparin and vascular endothelial growth factor (VEGF) could be implanted into the arterial system of a pre-clinical ovine animal model, where they endothelialized within one month and remained patent. Here we report that immobilized VEGF captures blood circulating monocytes (MC) with high specificity under a range of shear stresses. Adherent MC differentiate into a mixed endothelial (EC) and macrophage (Mφ) phenotype and further develop into mature EC that align in the direction of flow and produce nitric oxide under high shear stress.

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: Outpatient primary care clerkships are an important part of medical students' education.Traditional clerkships usually partner a student with a single preceptor in that physician's clinic. However, it can be quite difficult for the preceptor to balance the educational needs of the students, the expectations of the patients and the organizational demands of the clinic practice.

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Background: Use of liposomal bupivacaine (LB) in surgery is reported with decreased postoperative opioid requirements. The efficacy of LB versus standard bupivacaine injections at laparoscopic port sites during bariatric surgery is unknown.

Objectives: To determine whether there was a difference in postoperative hospital opioid requirements after port site injections of LB versus standard bupivacaine during laparoscopic bariatric surgeries.

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Recent advances in vascular tissue engineering have led to the development of cell-free grafts that are available off-the-shelf for on demand surgery. Challenges associated with cell-based technologies including cell sourcing, cell expansion and long-term bioreactor culture motivated the development of completely cell-free vascular grafts. These are based on decellularized arteries, decellularized cultured cell-based tissue engineered grafts or biomaterials functionalized with biological signals that promote tissue regeneration.

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The last two decades have seen many advances in regenerative medicine, including the development of tissue engineered vessels (TEVs) for replacement of damaged or diseased arteries or veins. Biomaterials from natural sources as well as synthetic polymeric materials have been employed in engineering vascular grafts. Recently, cell-free grafts have become available opening new possibilities for the next generation, off-the-shelf products.

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Background: The Neonatal Resuscitation Program (NRP) recommends close monitoring of oxygenation during the resuscitation of newborns using a pulse oximeter. However, there are no guidelines for monitoring carbon dioxide (CO2) to assess ventilation. Considering that cerebral blood flow (CBF) correlates directly with PaCO2, continuous capnography monitoring of end-tidal CO2 (ETCO2) may limit fluctuations in PaCO2 and, therefore, CBF during resuscitation of asphyxiated infants.

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Background: The Neonatal Resuscitation Program (NRP) recommends upper and lower limits of preductal saturations (SpO2) extrapolated from studies in infants resuscitated in room air. These limits have not been validated in asphyxia and lung disease.

Methods: Seven control term lambs delivered by cesarean section were ventilated with 21% O2.

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The large number of coronary artery bypass procedures necessitates development of off-the-shelf vascular grafts that do not require cell or tissue harvest from patients. However, immediate thrombus formation after implantation due to the absence of a healthy endothelium is very likely. Here we present the successful development of an acellular tissue engineered vessel (A-TEV) based on small intestinal submucosa that was functionalized sequentially with heparin and VEGF.

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The development of Tissue Engineered Vessels (TEVs) is advanced by the ability to routinely and effectively implant TEVs (4-5 mm in diameter) into a large animal model. A step by-step protocol for inter-positional placement of the TEV and real-time digital assessment of the TEV and native carotid arteries is described here. In vivo monitoring is made possible by the implantation of flow probes, catheters and ultrasonic crystals (capable of recording dynamic diameter changes of implanted TEVs and native carotid arteries) at the time of surgery.

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We demonstrate the ability of immobilized vascular endothelial growth factor (VEGF) to capture endothelial cells (EC) with high specificity under fluid flow. To this end, we engineered a surface consisting of heparin bound to poly-l-lysine to permit immobilization of VEGF through the C-terminal heparin-binding domain. The immobilized growth factor retained its biological activity as shown by proliferation of EC and prolonged activation of KDR signaling.

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Objective: To engineer and implant vascular grafts in the arterial circulation of a pre-clinical animal model and assess the role of donor medial cells in graft remodeling and function.

Approach And Results: Vascular grafts were engineered using Small Intestinal Submucosa (SIS)-fibrin hybrid scaffold and implanted interpositionally into the arterial circulation of an ovine model. We sought to demonstrate implantability of SIS-Fibrin based grafts; examine the remodeling; and determine whether the presence of vascular cells in the medial wall was necessary for cellular infiltration from the host and successful remodeling of the implants.

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Background: The oxygenation index (OI = mean airway pressure, MAP × FiO2 × 100 : PaO2) is used to assess the severity of hypoxic respiratory failure (HRF) and persistent pulmonary hypertension of the newborn (PPHN). An indwelling arterial line or arterial punctures are necessary to obtain PaO2 for the calculation of OI. Oxygenation can be continuously and noninvasively assessed using pulse oximetry.

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We examined the effects of senescence on the proliferation and leiomyogenic differentiation potential of mesenchymal stem cells (MSCs) isolated from bone marrow (BM-MSCs) or hair follicles (HF-MSCs). To this end, we compared ovine HF-MSCs and BM-MSCs in terms of their proliferation and differentiation potential to the smooth muscle cell lineage. We discovered that HF-MSCs are less susceptible to culture senescence compared with BM-MSCs.

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Background: Current neonatal resuscitation guidelines recommend tracheal suctioning of nonvigorous neonates born through meconium-stained amniotic fluid.

Methods: We evaluated the effect of tracheal suctioning at birth in 29 lambs with asphyxia induced by cord occlusion and meconium aspiration during gasping.

Results: Tracheal suctioning at birth (n = 15) decreased amount of meconium in distal airways (53 ± 29 particles/mm(2) lung area) compared to no suction (499 ± 109 particles/mm(2); n = 14; P < 0.

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Background: Cases of necrotizing enterocolitis occurring within 48 h of packed red blood cell (PRBC) transfusions are increasingly being described in observational studies. Transfusion-associated gut injury is speculated to result from an abnormal mesenteric vascular response to transfusion. However, the mechanism of disruption of the balance between mesenteric vasoconstriction and relaxation following transfusion is not known.

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We investigated the hypothesis that immobilizing TGF-β1 within fibrin hydrogels may act in synergy with cyclic mechanical stimulation to enhance the properties of vascular grafts. To this end, we engineered a fusion TGF-β1 protein that can covalently anchor to fibrin during polymerization upon the action of factor XIII. We also developed a 24-well based bioreactor in which vascular constructs can be mechanically stimulated by distending the silastic mandrel in the middle of each well.

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Because of rise in cardiovascular disease throughout the world, there is increasing demand for small diameter blood vessels as replacement grafts. The present review focuses on the animal models that have been used to test small-diameter TEVs with emphasis on the attributes of each model. Small animal models are used to test short-term patency and address mechanistic hypotheses; and large, preclinical animal models are employed to test long-term patency, remodeling and function in an environment mimicking human physiology.

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Synopsis of recent research by authors named "Daniel Swartz"

  • - Daniel Swartz's recent research focuses on the theoretical and experimental analysis of growing populations, particularly in the context of colony expansion and competition dynamics, incorporating advanced mathematical models such as the Kardar-Parisi-Zhang and Fisher-Kolmogorov-Petrovsky-Piskunov equations.
  • - His work explores the interplay between population morphology, mutation fitness, and competitive abilities, revealing multiple distinct regimes of influence based on rates of expansion and competition strength.
  • - In addition to theoretical aspects, Swartz has investigated practical applications in vascular tissue engineering, demonstrating successful development and integration of cell-free vascular grafts in preclinical models, which may hold significant implications for surgical practices and regenerative medicine.