On March 25th, 2015, the 10th Annual NC State University Graduate Student Research Symposium was held at the McKimmon Center. The Graduate School holds the Symposium each year to “showcase the outstanding quality and diversity of graduate-level research at NC State, in addition to providing students with the opportunity to practice their communication skills with those outside of their discipline.”
Abstracts of participants with Textile Engineering, Chemistry and Science faculty advisors or co-advisors:
Halil I. Akyildiz
Graduate Program: Fiber and Polymer Science; Materials Science and Engineering
Advisors: Jesse S. Jur and Gregory N. Parsons
Modification of Optical Properties of Polyethylene Terephthalate by Sequential Organometallic Vapor Infiltration
Polyethylene terephthalate (PET) is a recyclable thermoplastic polymer that has applications in textiles, packaging and insulating. PET shows weak photoluminescence by the excitation of the pi electrons on the backbone of the polymer upon UV absorption. This emission is identified by two adjacent band in the near UV region of the spectrum. Lower wavelength emission is attributed to the monomeric emission from the polymer and the other band is attributed to emission due to the interactions between the polymer chains. In this study the emission in the PET fibers are enhanced by infiltration of trimethylaluminum (TMA) precursors by sequential vapor infiltration (SVI) technique. TMA by reacting the ester groups in the polymer forms organic inorganic hybrid materials. In this study it is shown that SVI improves the higher wavelength emissions of the polymer is which is attributed to the enhanced interactions between the polymers. Furthermore the effect of the changes in the polymer structure on emission of the PET thin films is studied which showed SVI increases only certain emission bands. Emission bands improved by SVI is attributed to the amorphous regions of the polymer.
Chirag R. Gajjar, Bhavya Singhi, Melissa A. Pasquinelli and Martin W. King
Graduate Program: Fiber and Polymer Science
Advisors: Martin W. King and Melissa A. Pasquinelli
Experimental and Computational Study of Process-property Relationships for Bioabsorbable Polymers
Bioabsorbable polymers like poly(lactic acid) (PLA) are attractive biomaterials for regenerative medicine and tissue engineering applications due to their inherent property of in vivo resorption over time. However, the same useful property of hydrolytic degradation is a major concern from a manufacturer’s stand point. Melt-processing parameters such as higher processing temperatures, extrusion rate and the residence time in barrel, as well as material characteristics like residual moisture and monomer content influence the rate of degradation of the final product. Thus, the goal of our study is to determine the optimum processing conditions for bioabsorbable polymers in order to achieve the desired properties of extruded fibers while preventing excess degradation during processing. We propose the use of molecular dynamics (MD) simulations along with the experimental approach to understand the thermal degradation of PLA under the effect of various processing conditions (such as temperature and residence time) and the local environment (presence of oxygen, moisture and monomers). For the experimental study, we used different melt-spinning parameters to extrude PLA yarns, and characterized the changes in the physical and chemical properties as a result of processing conditions. MD simulations were performed on PLA chains using reaxFF force-field in LAMMPS. From the experimental study, it was seen that different temperatures and take-up speeds resulted in a difference in the orientation of the polymer chains and the crystalline content. The level of crystallinity also governs the tenacity, and a direct correlation was observed between them. MD simulation results showed that at slower rates for raising the temperature, the degradation started at relatively lower temperatures, whereas with prolonged exposure at higher temperatures, the extent of degradation increased. This combined approach provides a better understanding of process-induced degradation, which will help to design resorbable biomaterials, such as scaffolds, with better control of their in vivo performance.
Lauren A. Hunt
Graduate Program: Textile Engineering, Chemistry and Science
Advisors: Peter Hauser, Ahmed El-Shafei
Ultra-violet Curable Process Chemistry for Biofilm Resistant Finish on Textiles
A biofilm is a group of microorganisms in which cells stick to each other on a surface. They can grow virtually anywhere there is moisture, nutrients and a surface; as a result, they affect many natural and industrial environments. One example of a biofilm is bacterial growth on apparel and footwear. These biofilms not only cause unpleasant odors, but they can also lead to serious medical issues. Preventing the formation of biofilms on textile fibers has the potential to significantly improve the performance of textile products.
New technologies are needed within the textile industry to reduce environmental impacts and improve efficiency and economic feasibility. This study aims to develop a UV-cure process chemistry for coatings that impart biofilm resistant properties to textiles. As compared to traditional textile finishing, ultra-violet curing technology provides a customizable, rapid commercial process, with reduced energy consumption, that imparts value-added functional finishes to textile substrates. In previous research, a wide array of acrylate and methacrylate monomers was analyzed to determine their ability to support or hinder cell growth. This research examines five acrylate and methacrylate polymers previously identified to most efficiently inhibit cell propagation. Homopolymer/copolymer formulations and necessary curing parameters were optimized to achieve the most efficient UV induced polymerization and ideal biofilm resistant properties. Performance evaluation of each when applied to polyester fabric was conducted via FTIR analysis, contact angle testing, and antibacterial activity assessment using Streptoverticillium reticulum.
Graduate Program: Textile Chemistry
Advisor: Stephen Michielsen
Comparison of Wicking Behavior of Artificial Blood and Porcine Blood on Textile Surfaces
Bloodstain pattern analysis (BPA) is an important tool to help investigators have a better understanding of what happened at the crime scene. Most studies of bloodstains have been performed on hard surfaces, only a few on textiles. Due to the structural variety and liquid absorbing properties, BPA on textiles is more complicated and the different wicking behaviors lead to various bloodstain patterns. In this study, the wicking behavior of artificial blood (AB) and porcine blood (PB) on different textile surfaces were investigated. The area, perimeter and circularity changing over time during the wicking process of AB and PB were measured. The weight decrease of the blood drops was recorded continuously during the drying process. Two types of common fabric were used in this study: plain woven bed sheet fabric (both balanced and unbalanced) and jersey knit T-shirt fabric. All the fabrics used were 100% cotton fabric. Area of AB stains are approximately twice as large as that of PB stains. The drying time of PB is much longer than AB. The pattern of bloodstain were also affected by yarn structure. No obvious difference of bloodstain pattern caused by varying fabric structure (balanced or unbalanced) were observed. When wicking on ring spun woven fabric, bloodstains have a more circular shape (high circularity), while on air jet and open end woven fabric the bloodstains have low circularity. The wicking behaviors are similar between AB and PB. The difference in area and drying time are observed because PB contains red blood cells which do not exist in AB. The fabrics made of yarns with a more uniform structure result in a more circular pattern because liquid wicks evenly. These studies should assist bloodstain pattern analysts interpret stains on textiles.
Graduate Program: Textile Engineering
Advisor: Stephen Michielsen
Drip Bloodstain Patterns on Textile Surfaces
Bloodstain pattern analysis (BPA) is the examination of the shapes, and the categorization and distribution of bloodstain patterns in order to provide an interpretation of the physical events of a crime, which gave rise to their origin. These stains occur in a large proportion of homicide cases. They offer extensive information and are an important part of a functional, medically and scientifically based reconstruction of a crime. Many BPA studies have been published, however, most of them dealt with hard, non-absorbent surfaces. Although textiles are present in at most crime scenes, but BPA on textiles has not been developed to the same extent as on non-porous materials. This study focuses on the effect of yarn and fabric construction on drip bloodstains, and differences between porcine blood and artificial blood. Three types of yarn: ring spun, open end, and Murata vortex spun yarn, which are all from the same bale of cotton from Cotton, Inc., were converted into three types of fabric – 100×100, 130×70 woven and a similar jersey knit. In addition, a similar commercial woven and knit fabric were tested. Dripping single 30μL porcine and artificial blood drop from half meter high on these fabrics, which were placed 90° and 30° impact angle and videoed from top view and bottom view, resulted in stains that were analyzed for their area, perimeter, circularity, ellipticity, and number of spines and satellite drops. Analysis showed that yarn and fabric construction both effect on dripped bloodstain. Fabric construction is a more obvious factor when impact angle is 30°. The areas of porcine bloodstains are smaller than artificial blood because of the blood cells in porcine blood.
Harshini Ramakrishna1; Ting He1; Tieshi Li2; Joseph Temple2; Anna Spagnoli2; Martin W. King1,3
Graduate Programs: Textile Engineering, North Carolina State University1; Department of Pediatrics, University of North Carolina at
Chapel Hill2; Wilson College of Textiles, Donghua University, Shanghai, China3
Advisor: Martin W. King
Development of Degradable Scaffold for Tendon-bone Junction Regeneration and Evaluation of the Role of TgfbR2 Expressing Progenitor Cells on the Scaffold
Tendons play an important role in transferring stresses between muscles and bones and in maintaining the stability of joints. Tears in the joints have poor healing capacity and the lesions are associated with cartilage degeneration. Therefore, strategies are needed to promote repair and long-term regeneration of such joints. The ultimate goal of this study is to develop a biodegradable scaffold for tendon-bone junction regeneration. As a first step to achieve this, polylactic acid (PLA) yarns were braided into tubular scaffolds and cultured with unique TGF-β Type II receptor-expressing joint progenitor cells under static conditions. The scaffolds were designed to mimic the natural mice tendon-bone junction in terms of its structure, mechanical and immunochemical properties. Two types of PLA yarns were used. Those with round fibers had a 25μm diameter, while those fibers with a 4 deep grooved (4DG) cross-section had a thickness of 45μm. Three different tubular scaffolds measuring about 2 mm in diameter were braided on a Steeger 16-spindle braiding machine (Model K80/16-2008-SE) to mimic the tendon-bone junction by using these different yarns. The three different scaffold structures were: 1) PLA hollow tube using round fibers, 2) PLA hollow tube using grooved and round fibers, and 3) PLA multicomponent tube containing round fibers in the sheath and grooved core fibers inserted within the lumen. The biological and mechanical performance of the three scaffolds were evaluated, including cell viability using an Alamar Blue assay, cell attachment and proliferation using a live/dead assay, laser scanning confocal microscopy (LSCM) and dynamic tensile strength and initial Young’s modulus on an Instron mechanical tester. The results of this study showed that all three scaffolds exhibited good viability and cell attachment for the TGF-β Type II receptor- expressing progenitor cells. In view of these promising results further work is continuing with animal in vitro trials.
Graduate Program: Fiber and Polymer Science1, Chemical and Biomolecular Engineering2, Nuclear Engineering3
Advisors: Peter Hauser1, Michael Dickey2, Mohammed Bourham3
Plasma Induced Thiol-ene Addition for Polymeric Film Coating Applications
Deposition of metal oxides on different substrates has been an attractive topic due to its ability to render unique optical and electrical properties. However, common drawbacks of these films are undesirable chemical and mechanical robustness, which necessitates an additional stable protective layer to guarantee long term application of the product. Polymeric coatings can be used for this purpose, since they offer chemical and mechanical toughness. Photopolymerization of acrylate monomers and acrylated resins (such as epoxies, polyesters, polyurethanes) has been employed in the coating industry for years, due to the very fast reaction rate and large chemical diversity. Yet recent concerns about the toxicological activity of acrylate based chemicals, as well as processing challenges such as sensitivity of the reaction to air (specifically, oxygen), low conversion before gelation, high network shrinkage stress and light instability due to presence of photo-active components, have discouraged this approach. Thiol-ene systems, as an alternative, offer a set of unique properties not the least of which are toxicologically safer chemistry, low network shrinkage, oxygen insensitivity, and high conversion before gelation. Our proposed methodology for achieving the objective of this study is based on thiol-ene polymerization via atmospheric pressure plasma (APP). Use of APP as a source of excited species for initiation allowed the avoidance of photoactive components. Particular application of plasma sources for surface modification has motivated us to show reliability of this technology for polymer industry applications. The target of this study is a multilayered film containing a layer of sputtered metal oxide on top, which functions as an electromagnetic mirror for infrared range radiation. We sought to fabricate a polymeric protective coating on top of this layer. Using APP, we were able to carry out the thiol-ene reaction. Additionally, we tailored coating (mechanical and chemical) properties by altering the chemical composition of coating precursors.
Graduate Program: Fiber and Polymer Science
Advisors: Russell Gorga and Melissa Pasquinelli
A Systematic Investigation of How Antioxidants Prevent Thermal Degradation during the Processing of Industrially-relevant Polymers
During the formation of polymer products, thermal degradation has been an issue, which is also affected by the presence of oxygen and other impurities as well as the processing conditions. Thermal degradation not only impacts the physical and mechanical properties of the products, but also often leads to the failure of production lines. Antioxidants are often added to prevent thermal degradation during processing. An understanding of the molecular mechanisms that underlie thermal degradation can thus lead to the production of polymer materials with enhanced properties and can minimize waste during production. The goal of this work is to utilize both experiments and simulations to investigate how antioxidants reduce the loss of properties during thermal degradation. We studied two commercial antioxidants, Irganox 3114 (phenolic antioxidants) and Irgastab FS 042 (non-phenolic antioxidants), in polypropylene systems. From both simulations and experiments, antioxidants were observed to be most effective when the extrusion temperature is closer to melting temperatures but high enough to obtain effective melt flow. Both antioxidants were observed to have their own mechanisms and timescales to prevent thermal degradation. Chemical changes during melt extrusion and physical properties after extrusion will also be presented.
Graduate Programs: Textile Engineering
Advisor: Martin W. King
Small Diameter Vascular Prostheses for Coronary Artery Bypass Surgery
Coronary arterial diseases (CAD) is often a life threatening condition for patients suffering from cardio-vascular disease accounting for more than 385,000 deaths each year in the United States. The gold standard material for replacement or bypass surgery is the patient’s own autologous veins, which however may not be available due to aging, previous harvesting or the pre-existing arterial disease. Synthetic commercial ePTFE and polyester (PET) are not suitable for small diameter vessels (< 6 mm), mainly due to their poor circumferential compliance, thrombus formation and low endothelialization. In this study, we developed a bilayer tubular graft made of biodegradable polymers with the purpose of mimicking the multilayer structure of the native artery and provide adequate mechanical properties, reduced thrombogenicity and improved cell proliferation. Small diameter prototype vascular prostheses were fabricated by weft knitting polylactic acid (PLA) multifilament yarns into a tube and then electrospinning polylactide-co-caprolactone (PLCL) copolymer fibers onto the outer surface. The bilayer tube was then turned inside out so as to keep the knitted layer on the outside, followed by an impregnation of 0.5 wt% collagen/elastin (1:1 ratio) crosslinked with genipin. Both the mechanical and biological performances of the prototype scaffolds were determined, including circumferential tensile strength, suture retention, bursting strength, compliance, thrombogenicity and endothelial cells biocompatibility using an MTT assay and immunofluorescence. The results demonstrated that either adding an electrospun layer and/or impregnating with collagen/elastin improved the bursting strength, suture retention and circumferential tensile strength of the bilayer prosthesis. The graft with the electrospun layer inside has superior compliance compared to the graft with electrospun layer outside. We also found that the collagen/elastin impregnation reduced the level of thrombogenicity, and the electrospun layer promoted more uniform endothelial cell proliferation on the inner luminal surface. Work is continuing to evaluate the device using an in vivo animal study.
Graduate Program: Fiber and Polymer Science
Advisor: Martin W. King
Imaging Modalities to Visualize Polyester Fabric in Implantable Textiles
The treatment of aortic aneurysms with the deployment of an endovascular stent-graft has become a routine clinical procedure. While short term results are encouraging, the long term in situ biostability for these devices is still in question, particularly with the trend to use thinner graft materials, and with clinicians using chimney and sandwich approaches to insert more than one stent-graft into the same aneurysm. These trends are known to lead to fabric distortion, abrasion against metallic stents, tearing, ravelling and in situ yarn failure. The aim of this research study was to evaluate alternative visualizing modalities to determine which technique could be used to observe the integrity of polyester graft fabrics either in vivo or during accelerated in vitro fatigue testing. Nano-silver coatings and silicon based ink coatings were applied to polyester fabrics taken from commercial stent grafts so as to make them radio- opaque to x-rays. After coating, x-ray images, clinical computed tomography (CT) and micro CT scans were performed to visualize the polyester graft material inside a polyurethane phantom. The nano-silver particles could not provide sufficient radio-opacity to permit the polyester fabrics to be observed under x-ray. However, the silicon- based radio-opaque ink coating was able to provide adequate radio-opacity with x-ray imaging and CT modalities so as to identify locations but not for measuring dimensions to within ± 1mm. Clinical CT and micro CT scanning were found to be not suitable modalities for imaging the polyester component of a stent graft either with a contrast agent or in air. This is because the artifacts in the CT image created by the metal stent interfere with the ability to accurately locate the fabric.