Browsing by Subject "Collagen"

Now showing 1 - 12 of 12
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    A thermodynamic model for membrane transport.
    (Texas Tech University, 1975-12) Narayan, Raghu Subramani
    Not available
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    Collagen Films as Substrates for Flexible Electronics
    (2019-04-24) Moreno, Salvador
    With fast progress in the field of implantable electronics, pushing towards an integration of technology with humans, the biocompatibility of these electronics is a key issue. Collagen, one of the most abundant proteins in mammalian tissues, is a well-known biomaterial used in tissue engineering and bone scaffolds. Our preliminary studies showed that collagen could be used as a substrate for flexible electronics made using with E-Beam (electron beam) deposition by shadow mask. This allows you to make passive sensors with electrodes such as temperature sensors and strain sensors as well as active devices such as antennas and heaters. However, in order to make more advanced electronic devices, manufacturing strategies need to be developed in order to overcome limitations of collagen for these applications, namely processing temperature and mechanical stability in water. Transfer printing of electronics is one such strategy, using sacrificial layers of plastics, which also have their own temperature limitations. Germanium oxide is presented in this dissertation as novel water based sacrificial layer, which is amenable to high temperature processes such as the annealing and doping of Zinc Oxide (ZnO) via Pulse Laser Deposition (PLD). A number of devices presented in this dissertation include capacitors, transistors, and an integrated inverter transistor circuit. After etching in water overnight, devices made on wafers are lifted off and transferred to collagen films. By using crosslinkers, devices built on collagen films can be programmatically enhanced to resist enzymatic digestion. Cross-linked collagen was shown to have enhanced mechanical and thermal properties Encapsulated integrated electrical devices transferred onto collagen were shown to have minimal effects on cell viability on assays on MC3T3 osteoblast and A549 epithelial cells. Together, this dissertation demonstrates a manufacturing strategy of developing biocompatible integrated electrical devices on collagen.
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    Controlling neural cell behavior with electric field stimulation across a conductive substrate
    (2012-12) Nguyen, Hieu Trung 1980-; Schmidt, Christine E.
    Electrical stimulation of tissues induces cell alignment, directed migration, extended processes, differentiation, and proliferation, but the mechanisms involved remain largely unknown. To reveal effects of electric fields (EF) through the media on cell behavior, voltage (7.45 – 22 V), current density (36 – 106 mA/cm2), duration (2 – 24 hrs), and alternating currents (AC, 2 – 1000 Hz) were varied independently when exposed to cell cultures. It was determined that current density and duration are the primary attribute Schwann cells respond to when an EF is applied through the media. This implies that the number of charges moving across the cell surface may play a key role in EF-induced changes in cell behavior. Identical conditions were used to stimulate cells grown on the surface of a conductive substrate to examine if a scaffold can provide structural and EF cues. The effects of an EF through the substrate were examined by placing a protein gel on the surface during stimulation and observing the morphology of subsequent cell cultures and the physical topology of the gel. EFs were shown to create Ca2+ redistribution across gels and subtle changes in collagen I fibril banding. Stimulated gels were able to induce perpendicular Schwann cell alignment on newly seeded cultures days after initial EF exposure, and the cell response decreased when seeded at longer times, indicating the effects of EF on the matrix environment has a relaxation time. These findings were then integrated into a biodegradable, electrically conductive polypyrrole-poly-ε-caprolactone polymer developed by collaborators. Dorsal root ganglia placed in matrix gels on top of conducting polymer exhibited significantly longer axons when stimulated with DC and AC signals. The overall results demonstrate that EFs have a significant effect on the extracellular environment. The broad implication of this data grants researchers with the ability to physically and metabolically control cell behavior with EFs, including improved wound healing or reduced cancer metastasis.
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    Dynamic Changes in Collagen Organization Modulate Cervical Remodeling During Pregnancy and Parturtion: New Insights and the Potential for Improved Clinical Tools to Combat Preterm Birth
    (2012-07-17) Akins, Meredith Lynne; Mahendroo, Mala
    Preterm birth affects approximately 500,000 infants in the Unites States alone and is the second highest cause of infant morbidity in this country. Obstetricians still do not have reliable tools to diagnose or treat women presenting with premature labor. Understanding mechanisms by which the cervix remodels during term and preterm pregnancy is critical to formulate better methods for detection and treatment of preterm birth. The focus of this study was to identify how cervical collagen is reorganized throughout pregnancy to allow the cervix to become compliant for parturition. Beginning early in pregnancy a reduction in cervical collagen cross-links as well as a decline in matricellular proteins contribute to the changing cervical extracellular matrix environment. These cumulative changes result in increased collagen fibril diameter, as well as a progressive increase in tissue distensibility and a decline in tissue stiffness. Changes in collagen morphology over pregnancy can be visualized via non-invasive second harmonic generation (SHG). Quantification of specific morphological features such as collagen fiber diameter or porosity reveal progressive changes that allow one to distinguish stages in pregnancy. In addition, analysis of SHG images from two preterm birth models as well as one postterm pregnancy model validate the ability to use quantitative morphological measurements to distinguish normal from abnormal cervical remodeling. These findings suggest SHG technology is a powerful tool that may have potential clinically to predict preterm birth. In closing these studies have identified early and progressive changes in processing and assembly of collagen fibrils as well as changes in other ECM components that likely contribute to the incremental change in cervical tensile strength required for birth. [Keywords: cervix, partition, preterm birth, cervical remodeling, cervical softening, collagen, collagen cross-linking, cervical imaging]
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    Exploiting synergy in animal co-product bisolids processing: the cactus project
    (2006-05) Pasupuleti, Divya; Morse, Audra; Shelly, Dennis C.
    The current project is a feasibility study prepared for the Dumas Economic Development Corporation in Cactus, Texas for the purpose of evaluating the feasibility of constructing a facility that processes leather wastes to produce useful products. The project aims at developing a zero discharge strategy by fully utilizing the wastes from the leather making industry and converting them into value-added products. The model of the comprehensive animal co-product biosolids processing facility consists of six processing units namely the tannery, the keratin unit, the collagen unit, the biodiesel unit, the modular agriculture unit, and the biogasification unit. All the above units are linked to each other in such a way that the waste produced by one unit is used as input to another unit, leading to zero waste discharge. Simulation models of all the units were developed using the SuperPro Designer software. The tannery processes raw goatskins and converts them into wet blue leather. In the process, the tannery generates wastes like hair pulp, fleshing grease, wastewater, and waste biosolids. The hair sludge and fleshing grease produced from the sanitization of hides in the tannery are sent to the keratin unit and biodiesel unit to obtain useful products like keratin and bio-diesel, respectively. The collagen unit is used to produce gelatin, protein, and basic chrome sulfate from wet blue shavings. The chrome sludge produced in this process is sent to the tannery to enable sanitization of the hides. The wastewater produced from all the above processes is sent to a modular agriculture unit, to grow duckweed and baitfish. Virtually all the waste biosolids are sent to a biogasification unit to produce power, steam, and ash. The annual operating costs for all the units in the facility were determined based on current prices of equipment, raw materials, labor, and utilities. The revenues obtained from the product sales of each unit determined the profitability. The profítability of the entire facility was determined based on the economics of the individual units. The total capital investment on the facility was approximated at $8,890,000. The total annual operating costs were estimated to be $7,466,000. The total annual revenues were found to be $9,581,000. The total gross profit obtained from the entire facility was estimated to be $2,115,000. The total net profit was found to be $1,763,000. The payback time is just 5 years. The results of the study indicate that the Cactus facility provides economic benefits and reduces environmental impact by eliminating the discharge of wastes.
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    Extracellular matrix mechanics regulate cell signaling and migratory potential in cancer
    (2012-05) Srivastava, Jaya, active 2012; Ellington, Andrew D.; Zaman, Muhammad H. (Muhammad Hamid)
    The objective of the presented research is to examine the relationship between the cellular microenvironment and biochemical response of metastatic cells. Clinically recognized as a trait of cancer progression, the cellular microenvironment can have variable and distinct mechanical properties that are processed via cellular mechanosensing, resulting in a cellular biochemical response. A range of studies investigating the interactions between the cellular micromechanical environment and the cell's molecular response during disease progression have been made, yet remain absent of quantitative characterization of many of these coordinated responses. The fundamental inquiry that drives the following research attempts to elucidate how a cell perceives the physical microenvironment and converts that signal to a biochemical response. With the goal of providing insight to such responses, the presented research seeks to elucidate the following questions: (1) What are the integrated effects of ECM stiffness, ECM architecture, and breast cancer cell metastatic potential on cell migration? (2) How does endogenous tissue transglutaminase (tTG) cross-linking of the ECM scaffold effect ECM mechanical properties? (3) How does the architecture and stiffness of the extracellular matrix (ECM) effect the systems-level cellular migration and signaling response? (4) What are the integrated effects of ECM architecture and the targeted knockdown of integrin [beta]1 and MT1-MMP on cellular metastatic potential? The presented research utilizes an interdisciplinary approach, integrating experimental mechanics, biochemical analysis, cellular biology techniques, covalent chemistry, and various microscopy techniques, to investigate these events. In short, cancerous cells are cultured atop or within synthetic collagen type I ECMs of varying mechanical stiffness and structure. These cells are subsequently analyzed by molecular analysis and immunoassays, including quantitative PCR, Western blotting, and gelatin zymography, to acquire measures of the cellular response to perturbations of micromechanical environment. Time-lapse microscopy experiments and subsequent image analyses enable observations of cellular migratory potential through synthetic ECMs. Results indicate that cooperative synergy between ECM properties, cell-matrix adhesion, and pericellular proteolysis drive cell migratory potential of highly invasive tumorigenic cell populations. Collectively, these findings contribute to the cancer biology and mechanobiology fields by systematically extending current insights of matrix mechanics, cellular signaling, and cellular migratory potential in cancer.
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    Modeling and optimization of heparinized collagenous surfaces
    (Texas Tech University, 1987-08) Chen, Jyh-herng
    The primary objective of this research is to determine the optimal conditions of heparin immobilization on collagen powder by varying pretreatment methods, pH of reaction environment and l-ethyl-3(3-dimethylaminopropyl) carbodiimide (i.e., EDC) to heparin weight ratio. This research is part of a series of investigations, of which the ultimate purpose is to develop an implantable small diameter (less than 6 mm diameter) (Parsonnet, 1976) vascular prosthesis which will remain functional while serving as a suitable interposition in the circulatory system.
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    Optimization of a dual enzyme system and its effect on collagenous surfaces
    (Texas Tech University, 1985-12) Lokapur, A. K
    The main purpose of this thesis is to co-immobilize heparin and plasmin onto collagenous substrates in an effort to produce a biomaterial possessing both fibrinolytic and thromboresistant properties. The path followed in this research has been to immobilize heparin onto collagenous substrates such as collagen powder, human umbilical vein grafts (HUVG) and chymotrypsin treated goat carotid arteries (GCA), and optimize its activity and stability over a period of time. Several pretreatment procedures have been studied in the case of heparin, which include fibronectin. Endothelial cell growth factor (ECGF),* methanol and hydrazine, hydrogen peroxide, and ammonium hydroxide. The crosslink agent 1-ethy1-3(3-dimethy1-aminopropy1) carbodiimide (EDO has been used to activate the carboxyl groups of the heparin structure. Heparin and plasmin have been co-immobi1ized on collagen powder and the activity of each has been studied in co-bound state. Experiments have shown that heparin in excess of 0.0 1 mg/sq cm can be immobilized on chymotrypsin treated GCA. that would remain stable for more than 3 weeks. In vivo studies have been performed on goats and dogs, the results of which show a patency rate of 807. after 1 week and 707« after 2 weeks, for the 10 samples that have been tested. Of all the pretreatment procedures, ammonium hydroxide appears to produce the most active and stable heparin complex. Co-immobi1ization of heparin and plasmin has shown that bound plasmin activity is increased if collagen powder is preimmobi1ized with heparin. Heparin, however, loses its activity. On the other hand, heparinization of plasmin bound collagen has not been successful. Furthermore, originally bound plasmin loses part of its activity. Experiments have been performed to determine the constants V^g>^ and K^j^ assuming M i chael i s-Menten kinetics for plasmin. The activation energy Eg has also been estimated for plasmin in soluble as well as immobilized form.
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    Optimization of co-immobilization of heparin and plasmin
    (Texas Tech University, 1987-08) Wu, Dauh-rurng
    Not available
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    Permeabilities to low molecular weight solutes of collagen and regenerated cellulose dialysis membranes.
    (Texas Tech University, 1974-08) Dearden, Craig Lee
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    Photopolymerizable scaffolds of native extracellular matrix components for tissue engineering applications
    (2010-05) Suri, Shalu; Schmidt, Christine E.; Chen, Shaochen; Roy, Krishnendu; Suggs, Laura J.; Shear, Jason B.
    In recent years, significant success has been made in the field of regenerative medicine. Tissue engineering scaffolds have been developed to repair and replace different types of tissues. The overall goal of the current work was to develop scaffolds of native extracellular matrix components for soft tissue regeneration, more specifically, neural tissue engineering. To date, much research has been focused on developing a nerve guidance scaffold for its ability to fill and heal the gap between the damaged nerve ends. Such scaffolds are marked by several intrinsic properties including: (1) a biodegradable scaffold or conduit, consisting of native ECM components, with controlled internal microarchitecture; (2) support cells (such as Schwann cells) embedded in a soft support matrix; and (3) sustained release of bioactive factors. In the current dissertation, we have developed such scaffolds of native biomaterials including hyaluronic acid (HA) and collagen. HA is a nonsulphated, unbranched, high-molecular weight glycosaminoglycan which is ubiquitously secreted by cells in vivo and is a major component of extracellular matrix (ECM). High concentrations of HA are found in cartilage tissue, skin, vitreous humor, synovial fluid of joints and umbilical cord. HA is nonimmunogenic, enzymatically degradable, non-cell adhesive which makes HA an attractive material for biomedical research. Here we developed new photopolymerizable HA based materials for soft tissue repair application. First, we developed interpenetrating polymer networks (IPN) of HA and collagen with controlled structural and mechanical properties. The IPN hydrogels were enzymatically degradable, porous, viscoelastic and cytocompatible. These properties were dependent on the presence of crosslinked networks of collagen and GMHA and can be controlled by fine tuning the polymer ratio. We further developed these hydrogel constructs as three dimensional cellular constructs by encapsulating Schwann cells in IPN hydrogels. The hydrogel constructs supported cell viability, spreading, proliferation, and growth factor release from the encapsulated cells. Finally, we fabricated scaffolds of photopolymerizable HA with controlled microarchitecture and developed designer scaffolds for neural repair using layer-by-layer fabrication technique. Lastly, we developed HA hydrogels with unique anisotropic swelling behavior. We developed a dual-crosslinking technique in which a super-swelling chemically crosslinked hydrogel is patterned with low-swelling photocrosslinked regions. When this dual-crosslinked hydrogel is swelled it contorts into a new shape because of differential swelling among photopatterned regions.
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    Region-specific role of water in collagen unwinding and assembly
    (Texas A&M University, 2008-10-10) Mayuram Ravikumar, Krishnakumar
    Conformational stability of the collagen triple helix affects its turnover and determines tissue homeostasis. Although it is known that the presence of imino acids (prolines or hydroxyprolines) confer stability to the molecule, little is known regarding the stability of the imino-poor region lacking imino acids, which plays a key role in collagen cleavage. In particular, there have been continuing debates about the role of water in collagen stability. We addressed these issues using molecular dynamics simulations on 30-residue long collagen triple helices, including a structure that has a biologically relevant 9-residue imino-poor region from type III collagen (Protein Data Bank ID: 1BKV). We characterized the conformational motion of the molecule that differs between imino-rich and imino-poor regions using a torsional map approach. At temperatures of 300 K and above, unwinding initiates at a common cleavage site, the glycine-isoleucine bond in the imino-poor region. This provides a linkage between previous observations that unwinding of the imino-poor region is a requirement for collagenase cleavage, and that isolated collagen molecules are unstable at body temperature. Unwinding of the imino-poor region is controlled by dynamic water bridges between backbone atoms with average lifetimes on the order of a few picoseconds, as the degree of unwinding strongly correlated with the loss of water bridges, and unwinding could be either prevented or enhanced, respectively by enforcing or forbidding water bridge formation. While individual water bridges were short-lived in the imino-poor region, the hydration shell surrounding the entire molecule was stable even at 330 K. The diameter of the hydrated collagen including the first hydration shell was about 14 ?, in good agreement with the experimentally measured inter-collagen distances. These results elucidate the general role of water in collagen turnover: water not only affects collagen cleavage by controlling its torsional motion, but it also forms a larger-scale lubrication layer mediating collagen self-assembly.