1,720,980 research outputs found
Polyelectrolyte multilayers and capsules: S-layer functionalization for improving stability and biocompatibility
No full textRecent advances in medicine and biotechnology have brought about the need to develop nano-engineered delivery systems that can encapsulate a wide variety of therapeutics and that could allow their targeted delivery and sustained release. Nanostructured polyelectrolyte multilayers (NPMs) and capsules (NPCs), fabricated by electrostatic layer-by-layer (LbL) technique have been proposed for the functionalization of biomaterials and as delivery systems. This paper focuses on the degradation and biocompatibility characterization of NMPs and NPCs functionalized with bacterial self-assembled proteins (S-Layers). S-layers have been proposed as an efficient strategy for the functionalization of NPMs and NPCs. In present work, S-layers were recrystallized on mica and imaged by atomic force microscopy. The LbL assembly and the stability of cationic poly (allylamine hydrochloride) and anionic sodium poly (styrene sulfonate) multilayers functionalized with a terminal S-Layer were investigated by means of quartz crystal microbalance. In order to evaluate the impact of S-layer functionalization on the degradation of NPCs, S-Layer functionalized NPCs were characterized in vitro in terms of cell morphology and viability. The results revealed the role of S-layers in decreasing component release from NPMs and thus in increasing release time from NPCs
ESTABLISHMENT OF A COMPUTATIONAL FRAMEWORK FOR ANGIOGENESIS UNDER VARYING SCAFFOLD-HYDROGEL CONDITIONS
No full textThe full text of this item is not available at this time because the author has placed this item under an embargo until December 11, 2030.The success of regenerative medicine strategies for critical-sized bone defects depends on the rapid vascularization of biomaterial scaffolds. While biochemical cues are well researched, the role of the mechanical microenvironment remains less understood. The goal of this thesis is to investigate the inherent kinetics of vessel growth and the properties of a biomaterial scaffold-hydrogel combination that further direct it. A finite element model was developed to stimulate angiogenesis within hydroxyapatite scaffolds to systematically vary the growth segment velocity parameter to determine its influence on blood vessel maturation. Additionally, rigid constraints to the hydrogel at pore walls were applied to compare the fixed-boundary conditions against the free-boundary conditions, which allow unconstrained deformation. Results demonstrated that comparison between unconstrained and fixed boundary conditions showed no significant relative difference in vascular network evolution over time, indicating that geometric confinement dominates over the specific mechanical compliance of the pore walls. Furthermore, analysis of growth segment velocity revealed that increased velocity consistently enhanced network formation across all boundary conditions, with an observable optimum. These findings provide an understanding of the mechanical rules governing vascularization, enabling a refined predictive design of scaffolds optimized for rapid blood vessel growth using a computational model.Biomedical Engineerin
MATERIALS CHARACTERIZATION FOR ZONE-CONTROLLED DEGRADATION OF BONE TISSUE SCAFFOLDS AND PRODUCTION FACTORS APPERTAINING THERETO
No full textThe full text of this item is not available at this time because the author has placed this item under an embargo until May 15, 2028.Despite decades of medical advancement in orthopedic reconstructive medicine, unbridgeable “critical sized defects” remain an obstacle in the treatment of traumatic bone injuries. A novel approach to treating these injuries with osteogenic scaffolds composed of multiple layers with alternating mechanical properties has been proposed stimulate bone growth over larger gaps.
This study developed suitable materials for this device. 3-D printed scaffolds with varying ratios of hydroxyapatite and β-tricalcium phosphate, and varying ratios of mineral phase to binder, in sintered and unsintered states, were tested for weight, density/porosity, elastic modulus, and fluid permeability, over 28 days of aging in phosphate buffered saline at pH 7.4 and 6.0, at 37°C. Weight and elastic modulus were tested weekly; permeability and porosity were tested at the end.
Results indicated statistically significant differences in stiffness between sintered hydroxyapatite and β-tricalcium phosphate scaffolds, but failed to conclusively prove differences between the binder fractions, and showed no appreciable degradation in either weight or stiffness over time. Permeability was within acceptable margins for bioactive scaffolds. Unexpectedly, the expected ratio of stiffnesses between materials was reversed; which was attributed to differences in the sintering characteristics of the initial powders.
Unsintered scaffolds showed immediate degradation via hydration of the binder component, and were not structurally stable. The materials developed indicate that production of a multilayer scaffold with varying stiffnesses is possible.Electrical and Computer Engineerin
Solutions to the First-order Buckling Equations of a Fung Hyperelastic Cylindrical Shell Subjected to Torsion, Internal Pressure, and Axial Tension
No full textThe author has granted permission for their work to be available to the general public.In this study a theoretical model is proposed for the buckling of a vein subjected to torsion, internal pressure, and axial tension using a formation of elasticity theory for shells. The vein is assumed to be an anisotropic hyperelastic cylindrical shell which obeys the Fung constitutive model.
The approach uses finite deformation theory for thick-walled blood vessels to characterize the vessel dilation in the pre-buckling state. The pre-buckling state is identified by its midpoint and then perturbed by a displacement vector field dependent on the circumferential and axial directions to define the buckled state. The buckling equations of static equilibrium are derived using the nominal stress measure and traction boundary conditions are applied. A side result is shown proving the existence of a moment traction although typically taken to be zero for torsional problems. Perturbational displacements raised to the power of two or greater are assumed negligible thereby linearizing the coupled partial differential equations of equilibrium. The coupled equations are solved by supposing first-order and single Fourier term trigonometric forms for the displacement field components.
The model and the assumptions used are validated by experimental data for five human great saphenous vein (GSV) samples taken from a previous study. The theoretical model is unstable but using an eigenvalue compatibility condition as a selection method yields strong quantitative results for three out of five GSVs in the entire tested pressure range (6-100 mmHg). The other two sampless showed excessive stiffening upon loading and may indicate limitations of the model although quantitative predictions were still moderately accurate. The strongest results are in the 6-20 mmHg pressure range where all vessels matched well with predicted values. In general the model showed increased error as pressure increased hinting that effects of vessel stiffening are poorly predicted. The eigenmodes predicted were consistently inaccurate indicating the assumptions used in this solution method are inadequate to characterize the buckling modes of a nonlinear material. It may suggest that nonlinear buckling conformation is determined by nonlinear perturbation terms.Biomedical Engineerin
Effects of Electrical Stimulation and Growth Factor Levels on a Tunable Drug Delivery System Used in Tissue Regeneration
No full textThis study aimed to optimize a biomaterial graft with a tunable drug delivery system to be used as an intervention for preventing vocal fold fibrosis and atrophy. The design of the biomaterial patch previously developed patented design, with a different growth factor and processing parameter to conform to the targeted application in the vocal fold. Polyvinylidene fluoride (PVDF) is electrospun and coated with an in-situ polymerized polypyrrole (PPy). The PVDF fibers were spun at three different thicknesses, and their polypyrrole coatings were loaded with two different concentrations of biotinylated basic fibroblast growth factor. After PVDF-PPy fiber synthesis, polymerization, and loading, they were mechanically and electrically characterized. Small-sized grafts were also subjected to an electrical stimulation regime and evaluated for drug elution. Finally, graft morphology was reviewed with scanning electron microscopy and attenuated total reflectance-Fourier transform infrared spectroscopy. It was observed that coating was uniform in the generation of the composite grafts. Further, it was observed that the thickness of the graft needed to be ≤ 700 µm to ensure compliance suitable for functional preservation adjacent to the vocal folds and that stimulation voltages needed to be > 500 mV for effective drug delivery.Electrical and Computer Engineerin
Electrospun scaffold development for periodontal ligament regeneration
No full textThis item is available only to currently enrolled UTSA students, faculty or staff. To download, navigate to Log In in the top right-hand corner of this screen, then select Log in with my UTSA ID.Periodontitis is a major chronic inflammatory disorder that can lead to the destruction of the periodontal tissues and, ultimately, tooth loss. It is a major cause of tooth loss in adults and a substantial public-health burden worldwide. There is thus a significant need for periodontal ligament (PDL) regeneration to enable functional mechanical support of tooth prostheses and prevent occlusal overloading. The goal of stem cell-based dental tissue engineering, is to create tooth-like structures using scaffold materials to guide the dental stem cells. Current resorbable membranes act as an epithelial tissue down-growth into the defect, favoring the regeneration of periodontal tissues. In order to develop synthetic grafts for these applications, different biocompatible materials have been used to fabricate fibers with different structures and morphologies. This study demonstrated the feasibility of using a composite material that combines the advantage of multiple materials to synthesize polyvinyl alcohol/ chitosan blend fiber scaffolds to promote PDL regeneration and to achieve a synthetic composite that match the native PDL modulus. Morphology, dispersibility, and mechanical properties of blend nanofibrous mats were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and tensile test.Biomedical Engineerin
Quantifying the transport of pathogenic and nonpathogenic Escherichia coli in Magnesium and Nitrogen doped biochar amended sand columns
No full textThis item is available only to currently enrolled UTSA students, faculty or staff. To download, navigate to Log In in the top right-hand corner of this screen, then select Log in with my UTSA ID.The present study quantifies the transport of Escherichia coli pathogenic O157:H7 and nonpathogenic E. coli k12 strains in water-saturated sand columns amended with Magnesium and Nitrogen-doped biochars produced by pyrolysis at 400, 500, 600, and 7000C. Overall, the addition of the doped biochar to sand at 2% weight ration enhanced the retention of the bacterial cells in the sand/biochar columns. Our results show that: 1) the use of 2% doped biochar to sand had a similar retention of the E. coli O157:H7 compared to that quantified when 20% ratio of un-doped biochar to sand was used in our previous work 1; 2) the retention of E. coli O157:H7 was about 3-fold higher than that of E. coli k12 in all biochar amended sand columns; 3) biochar is hydrophobic while sand and bacteria are hydrophilic; and 4) all kinds of forces investigated (van der Waals, electrostatic, and acid-base interactions) played a role in governing the interactions between bacteria and biochar. In summary, when all physiochemical factors affecting the retention of E. coli in biochar/sand amended columns were considered, the biochar produced at 6000C was the most effective (Figure 1). Our results suggest that designing effective biochar filters includes considering the roles of all the forces that may have a role in governing the transport of bacteria in biochar/sand columns and needs to be tailored based on sand and biochar type used, bacteria involved as well as environmental chemistry.
Figure 1. Visual representation of retention of pathogenic and nonpathogenic E. coli with different porous mediaBiomedical Engineerin
Tissue Mechanics, Microbiome, and Inflammation Modulate Post-injury Rehabilitation in the Upper Airway
No full textThe full text of this item is not available at this time because the author has placed this item under an embargo until August 26, 2030.Upper airway injury from nerve denervation, inhalation injury, or traumatic/prolonged intubation can lead to long-term complications in laryngeal function, affecting voice, swallowing, and breathing outcomes. This dissertation investigates how changes in airway biomechanics, inflammatory response, and the local microbiome contribute to airway injury and healing. Emphasis is placed on characterizing how these biological systems interact across different forms of upper airway injury.
Using swine models that replicate recurrent laryngeal nerve injury, inhalation burn injury, traumatic intubation injury, we characterized injury-specific changes across multiple areas. Biomechanical properties were quantitatively assessed in the denervation model to evaluate vocal fold atrophy and recovery. Inflammatory, microbial, and biomechanical outcomes were assessed in intubation and inhalational burn models using immunoassays, immunohistochemistry, 16S rRNA sequencing, and indentation-based mechanical testing. We also evaluated the therapeutic potential of drug eluting endotracheal tubes designed to modulate local inflammation, reduce fibrotic remodeling, and preserve mucosal integrity.
Across models, airway injury was associated with mechanical stiffening, epithelial disruption, immune dysregulation, and microbial imbalance. Localized drug delivery via endotracheal tubes impacted these outcomes to varying degrees, with composite coatings demonstrating the greatest potential to reduce fibrosis and promote reparative immune phenotypes. This work offers an integrative framework for understanding the multifactorial nature of airway injury and recovery. The findings provide a foundation for future strategies that target mechanical, immunological, and microbial pathways for improving patient outcomes.Biomedical Engineerin
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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