Non-Destructive Characterization of Peripheral Arteries using Intravascular Ultrasound

Peripheral Artery Disease (PAD) is the chronic obstruction of blood flow to the extremities caused by plaque buildup. Poor circulation results in exertional pain, numbness, and weakness, and in severe cases, can manifest critical conditions, including gangrene and limb loss. PAD affects approximately 8.5 million Americans and costs the United States $21 billion annually in direct medical expenses. High expenditures are attributed to operation and intervention failures resulting in frequent need for revascularization. Treatment of PAD typically involves lifestyle/diet adjustments, bypass surgery, or angioplasty/stenting. Unfortunately, repeated limb deformation during locomotion often results in adverse repair device-artery interactions, which hinder the long-term efficacy of endovascular therapies. Patient and lesion-specific device selection guided by computational modeling can help improve clinical outcomes, but these models rely heavily on accurately recorded three-dimensional arterial geometry and plaque composition. Intravascular ultrasound (IVUS) is a minimally invasive method of endovascular imaging that allows evaluation of the geometry and composition of the arterial wall, but its two-dimensional nature is often insufficient to capture complex three-dimensional plaques. We have developed a method of obtaining three-dimensional arterial geometry from two-dimensional IVUS images to build Computer-Aided Design models of calcified human femoropopliteal arteries. Our imaging method will allow for the characterization of calcium, necrotic core, fibrofatty, and fibrous tissue using IVUS. Correlation of IVUS images with conventional histology, micro-CT imaging, and clinical CTA data will help inform computational models.https://digitalcommons.unmc.edu/surp2021/1025/thumbnail.jp

Multiphysics modeling of the electrospinning process

Continuous nanofibers represent an emerging new class of nanomaterials with dual nano- and macro-features that attracts rapidly growing interest due to its critical advantages for a broad range of nanotechnology applications. Electrospinning is a process producing ultrafine continuous nanofibers by jetting polymer solutions in high electric fields. Fine, electrically driven jets emanate from a polymer solution bath, get accelerated and stretched by the external electric field, experience electrohydrodynamic instabilities, and get deposited on substrates in the form of nanofiber mats or arrays. Despite substantial effort in the last decade, many features of this complex process are not yet fully understood. One such feature is solvent evaporation. Previous studies in our group at UNL as well as studies by others have treated electrospun jets as a coupled electromechanical process. Three-dimensional (3D) jet flow was reduced to one-dimensional (1D) by averaging over the jet cross-section. At the same time, solvent evaporation is expected to lead to substantial inhomogeneity over both jet cross-section and length. Solvent evaporation from the ultrafine jets occurs during jet flight and results in the deposition of nearly dry nanofibers on the substrate. Evaporation may have substantial effect on the jet motion in electrospinning and has to be taken into account in process analysis. The main objective of this dissertation was to develop a first comprehensive coupled 3D model of electrospun jets incorporating solvent evaporation and to study effects of evaporation on jet motion and nanofiber formation. The results show complex interdependence of different physical phenomena in the electrospun jets and demonstrate the need for 3D coupled modeling. The developed model and new insights gained in this work will have an impact on control and optimization of nanofiber formation in the electrospinning process

High-efficiency retention of ultrafine aerosols by electrospun nanofibers

Abstract The versatility of nanofibrous polymeric materials makes them attractive for developing respiratory protective equipment. Ultrafine nanofibers effectively trap the most penetrating aerosols and exhibit consistent performance compared to conventional electret filters. Advanced nanofiber manufacturing technologies such as electrospinning can functionalize filter materials, enhancing them with unique antibacterial, catalytic, sensory, and other properties. Much of the current research in nanofibrous air filtration focuses on using nanofibers for lightweight personal protective equipment such as N95 respirators, but their use for higher levels of respiratory protection required for chemical, biological, radiological, and nuclear (CBRN) protection has not yet been comprehensively explored. In this study, we tested the hypothesis that electrospun filters could provide the particle filtration efficiency and breathing resistance required by the National Institute for Occupational Safety and Health Standard for CBRN air-purifying respirators. Our manufactured nanofibrous filters demonstrated submicron aerosol retention efficiency of > 99.999999%, which is four orders of magnitude better than the requirements of the CBRN standard. They also had a breathing resistance of ~ 26 mmH2O, which is more than twofold lower than the maximum allowable limit. Although the filter material from the gas mask cartridge currently in service with the U.S. military demonstrated a higher quality factor than electrospun filters, the comparative analysis of filter morphology suggested ways of improving nanofibrous filter performance by tuning nanofiber diameter distribution

Histological evidence for the therapeutic effect of chitosan nanofibrous dressing on acute skin wounds in a rat model

Introduction: Large-area skin traumas, such as thermal burns, are among the most severe health issues that decrease patients’ quality of life and burden healthcare systems. The CDC estimates that there are 1.1 million burns requiring medical attention each year, with more than 20,000 cases involving at least 25% of the body surface, resulting in 4,500 deaths. In addition, about 10,000 people die from burn-related infections. A promising solution to alleviate this problem is using wound dressings based on biopolymers with inherent wound healing properties and biodegradability. One of these biopolymers is chitosan, which is derived from arthropod shells and exhibits antimicrobial activity. This study aims to assess the wound healing effects of nonwoven dressing made of chitosan nanofibers in an acute wound rat model. Methods: Thirty Sprague Dawley rats (3 mоnth old, 250-350g) were divided into three groups, and a full-thickness 2×2 cm skin wound was induced on the dorsal area of each rat, followed by splinting to reduce wound contraction. Treatments for three groups included our developed chitosan nanofibrous dressing, PriMatrix Dermal Repair Scaffold (Integra LifeSciences, positive control), Tegaderm (3M, negative control). Animals were sacrificed at three time points (days 7, 14, 21), and skin samples were used to evaluate histological parameters. Hematoxylin and eosin staining was used to measure wound closure, thickness and area of the epidermis and granulation tissue, and Masson’s trichrome staining was applied to assess collagen deposition in the granulation tissue. Results: Preliminary histological analysis demonstrated that wound closure rate in the rats treated with chitosan nanofibrous dressing was significantly (P \u3c 0.007) increased compared to PriMatrix at the day 21. We are currently analyzing other histological parameters to investigate whether our chitosan nanofibrous material has a more positive effect on the epidermis and dermis regeneration than commercial dressings

Modeling of solvent evaporation from polymer jets in electrospinning

Solvent evaporation plays a critical role in nanofiber formation in electrospinning. Here, we present a nonlinear mass diffusion-transfer model describing the drying process in dilute polymer solution jets. The model is used to predict transient solvent concentration profiles in polyacrylonitrile/ N,N-dimethylformamide (PAN/DMF) jets with the initial radii ranging from 50µm down to 100 nm. Numerical simulations demonstrate high transient inhomogeneity of solvent concentration over the jet cross-section in microscopic jets. The degree of inhomogeneity decreases for finer, submicron jets. The simulated jet drying time decreases rapidly with the decreasing initial jet radius, from seconds for microjets to single milliseconds for nanojets. The results demonstrate the need for further improved coupled multiphysics models of electrospinning jets