Browsing by Author "Tan, George Z."
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Item Development of Hybrid Microfabrication Techniques for Biomedical Applications(2020-08) Sooriyaarachchi, Dilshan C.; Tan, George Z.; Du, Dongping; Xu, Changxue; Li, WeiLatest tissue engineering strategies for musculoskeletal tissues regeneration focus on creating a biomimetic microenvironment closely resembling the natural topology of extracellular matrix. Proceeding work presents a novel meniscus tissue scaffold fabricated by a hybrid additive manufacturing technology to closely resemble the natural topology of extracellular matrix. A skeletal scaffold was 3D printed and a layer of random or aligned polycaprolactone and collagen nanofibers were embedded between two frames. A compression test was performed to study the mechanical properties of the system. Human osteosarcoma cells were cultured in the scaffold for 7 days to evaluate the effect of scaffold microstructure on cell growth. With reinforced nanofibers, the hybrid scaffold showed superior compression strength compared to 3D printed scaffold without nanofibers. The hybrid scaffold induced the cells to organize into an aligned structure. The study shows the potential of hybrid bio fabrication process to be developed as a scalable platform for biomimetic scaffolds with patterned fibrous microstructure. It will facilitate future development of clinical solutions for musculoskeletal tissue regeneration. Integration of nanomaterials in microfluidic devices has emerged as a new research paradigm. Microfluidic devices composed of ZnO nanowires have been developed for the collection of urine extracellular vesicles (EVs) at high efficiency and in situ extraction of various microRNAs (miRNAs). The devices can be used for diagnosing various disease including kidney diseases and cancers. One of the research needs for developing micro-total-analysis systems is to enhance extraction efficiency. This paper presents a novel fabrication method for a herringbone patterned microfluidic device anchored with ZnO nanowire arrays. The substrates with herringbone patterns were created by maskless photolithography. The ZnO nanowire arrays were grown on the substrates by chemical bathing. The patterned design was to introduce spiral circulation as opposed to laminar flow in traditional devices to increase the mixing and contact of the urine sample with ZnO nanowires.Item Development of Silver Integrated Polymer Composites and Alloys for Antimicrobial Applications(2020-08) Maharubin, Shahrima; Tan, George Z.; Du, Dongping; Millerick, Kayleigh; Xu, ChangxueThe superior antimicrobial properties and low toxicity make silver a suitable antimicrobial agent for use in various industries, including water purification and biomedical applications. However, the critical challenges to solve before their large-scale industrial implementation are- (1) the stability of silver (oxidation and the release of Ag+ ion to the environment) and (2) the toxicity (to mammal cell and ecosystem). These issues limit their long-term antimicrobial efficiency and cause enormous difficulty for human health and the environment. This research has proposed three different approaches to stabilize silver for prolonged antimicrobial performance without compromising toxicity or other properties required for a specific application. These methods include (a) Micro-current activation of silver, (b) Covalent attachment of silver to a substrate surface, and (c) Additive manufacturing of titanium-silver alloy through the LENS process. Micro-current activation of silver demonstrated significantly improved biofilm resistance and prevented silver leaching and oxidation. Covalent Attachment of silver to a substrate surface allows strong chemical bond formation between silver and thiol group that ensures stable attachment of silver to the film surface. This method effectively reduced bacterial attachment in short term exposure. Additive Manufacturing of titanium-silver alloy through the LENS Process allows the benefit of easy fabrication of antimicrobial and bio-compatible alloy. These three approaches address the critical issues limiting the widespread application of silver for biofilm control with reduced the toxic impact on human health and the environment. This research will provide a valuable resource for future studies regarding the chemical stabilization of antimicrobial silver for long-lasting performance.Item Fabrication of biomimetic scaffolds by electrospinning for tissue engineering applications(2020-08) Zhou, Yingge; Tan, George Z.; Zhang, Hong-Chao; Xu, Changxue; Du, DongpingTissue engineering has emerged as an alternative cell-based approach, aiming at replacement of damaged organs with in vitro generated tissue equivalents. Electrospinning has shown great potential in tissue engineering due to its versatile capabilities to create fibrous assemblies with structures mimicking extracellular matrix (ECM). This technique enables engineering scaffolds with multiple unique properties including micro to nanoscale topography, high porosity, and high surface to volume ratio. These properties are critical for enhancing cell attachment, regulating drug release, and promoting mass transfer properties. Fabrication of biomimetic cell microenvironment closely resembling the native tissues has become the latest strategy for regenerative medicine. However, it remains challenging to create scaffolds with tunable biomimetic microstructure close to native fibrous extra-cellular matrix on a clinically relevant scale. This research presented three novel electrospinning strategies to address this challenge. First, a rotation electrospinning system with a cone collector was developed to generate 2D fibrous mat with microtopology gradient. Multivariate analysis of variance (MANOVA) showed that the tip-to-axis distance (TAD) and rotation speed (RS) significantly influenced the gradient features including fiber diameter and fiber alignment. Second, a divergence electrospinning system was developed to create 3D scaffold comprising of aligned nanofibers. Factorial experiment revealed that inclination angle and length-to-width ratio influenced the electric field distribution and fiber gradients. The scaffolds provided topographical cues to promote human fibroblast cell adhesion, proliferation, and morphogenesis in 3D space. Future parametric and mechanism studies on materials properties such as viscosity, conductivity, and ambient parameters such as temperature are needed to establish quantitative relationships between process parameters and attribute gradients. In addition, a statistical model will be developed to predict the fiber distribution and geometry within the divergence electrospun scaffold. Thirdly, a novel electrospinning approach was developed to fabricate nanoporous polycaprolactone microtubes as potential functional capillaries. Our results showed that ambient environment parameters and solution properties affected the pore formation and tube morphology. The optimal tubular structure was obtained with consistent viscosities between the core and the sheath solutions. The biomimetic nanoporous microtubes hold great potential for vascularization in tissue engineering.Item Fabrication of Nanopores Polylactic Acid Microtubes by Core-Sheath Electrospinning for Capillary Vascularization(MDPI, 2021) Zhou, Yingge; Sooriyaarachchi, Dilshan; Tan, George Z.There has been substantial progress in tissue engineering of biological substitutes for medical applications. One of the major challenges in development of complex tissues is the difficulty of creating vascular networks for engineered constructs. The diameter of current artificial vascular channels is usually at millimeter or submillimeter level, while human capillaries are about 5 to 10 µm in diameter. In this paper, a novel core-sheath electrospinning process was adopted to fabricate nanoporous microtubes to mimic the structure of fenestrated capillary vessels. A mixture of polylactic acid (PLA) and polyethylene glycol (PEO) was used as the sheath solution and PEO was used as the core solution. The microtubes were observed under a scanning electron microscope and the images were analyzed by ImageJ. The diameter of the microtubes ranged from 1–8 microns. The diameter of the nanopores ranged from 100 to 800 nm. The statistical analysis showed that the microtube diameter was significantly influenced by the PEO ratio in the sheath solution, pump rate, and the viscosity gradient between the sheath and the core solution. The electrospun microtubes with nanoscale pores highly resemble human fenestrated capillaries. Therefore, the nanoporous microtubes have great potential to support vascularization in engineered tissues.Item Laser Directed Energy Deposition of Metal-based Wear-resistant Coating(2023-12) Li, Yunze; Cong, Weilong; Du, Dongping; Tan, George Z.; Li, WeiWear-resistant coatings are commonly applied to metal surfaces to enhance their tribological characteristics and extend the lifespan of machinery and equipment. Laser Directed Energy Deposition (DED) technology represents a pivotal advancement in advanced manufacturing techniques, offering distinct advantages over conventional processing methods. These advantages encompass high energy density, minimal heat-affected zones, controllable thickness, dense cladding layers, particularly noteworthy metallurgical bonds between the cladding and substrate, as well as the capacity to selectively treat specific workpiece surfaces. In this dissertation, novel insights into the laser DED process for wear-resistant coatings were generated. The metal matrix composites (MMC) coatings and high entropy alloy (HEA) coatings were fabricated by laser DED process. The study delved into the impact of nanomaterials such as graphene oxide, as well as ceramics like TiC and B4C, on the wear resistance and hardness of MMC coatings. Additionally, the dissertation explored existing challenges associated with MMC coatings fabricated through laser DED and proposed corresponding solutions. Furthermore, it investigated the strengthening mechanisms in CoCrFeNiTi HEA coatings. The findings presented in this dissertation serve as a valuable reference for controlling the microstructure, phase composition, and elemental distribution of wear-resistant coatings. This knowledge is instrumental in further improving the mechanical properties, such as hardness and wear resistance, of coatings fabricated by laser DED process.Item Nanoassembly of photoactive materials towards designing visible light heterostructured photocatalysts(2019-08) Moniruddin, Md; Nuraje, Nurxat; Wiesner, Theodore F.; Malmali, Mahdi; Casadonte, Dominick J., Jr.; Tan, George Z.Currently, the low efficiency of photocatalytic water splitting is mainly attributed to limited light harnessing and high charge recombination phenomena of photocatalysts. Several strategies have been developed on designing photocatalysts for water splitting to address these issues. However, there is still a lot of scope in designing photocatalysts to prevent charge recombination problem using unique nanoassembled strategies. The aim of this work is to develop nanoassembled fabrication strategies for photoactive materials to enhance the photoexcited charge separation as well as improve light harnessing capabilities of photocatalysts in photocatalysis. Assembled nanostructures influence the catalytic activity of a photocatalyst; however, controlling the surface morphology and crystal structure of the photocatalysts during the formation of nanoasembly is challenging. In this work, nanoassembled SrTiO3 nanofibers are synthesized using a polymeric nanofiber template with controlled surface morphology and crystallite size. In addition, the crystal growth mechanism is explained in the nanoconfined system (composite nanofiber) during the formation of ordered nanoassembled structures which support our experimental data. Nanoassembled structures provide an ideal platform on which multifunctional materials can be deposited to fabricate nanoasembled heterostructures. It is found that nanoassembled SrTiO3-based heterostructures demonstrate enhanced photocatalytic H2 evolution rate when compared to their respective unassembled heterostructures. The advantageous SrTiO3 interparticle nanoassembly facilitates faster electron transport and high photoexcited charge separation, resulting in enhanced photocatalytic H2 evolution. Further to demonstrate the heterostructure concept in improving charge separation issue, a novel Co metal incorporated ternary heterostructured photocatalyst, CdS/CoOx/Co-metal, is developed which increases photocatalytic H2 evolution 30.5 folds compared to pure CdS under visible light. This work demonstrates for the first time the effect of the Co metal on photocatalytic H2 evolution using CdS-based ternary heterostructure. The synergistic charge separation improvement achieved by the combined cocatalytic effect of CoOx and the Co metal is found to be the reason for enhanced photocatalytic H2 evolution.