Tuning Surface Wettability Through Volumetric Engineering

abstract: Many defense, healthcare, and energy applications can benefit from the development of surfaces that easily shed droplets of liquids of interest. Desired wetting properties are typically achieved via altering the surface chemistry or topography or both through surface engineering. Despite many recent advancements, materials modified only on their exterior are still prone to physical degradation and lack durability. In contrast to surface engineering, this thesis focuses on altering the bulk composition and the interior of a material to tune how an exterior surface would interact with liquids. Fundamental and applied aspects of engineering of two material systems with low contact angle hysteresis (i.e. ability to easily shed droplets) are explained. First, water-shedding metal matrix hydrophobic nanoparticle composites with high thermal conductivity for steam condensation rate enhancement are discussed. Despite having static contact angle <90° (not hydrophobic), sustained dropwise steam condensation can be achieved at the exterior surface of the composite due to low contact angle hysteresis (CAH). In order to explain this observation, the effect of varying the length scale of surface wetting heterogeneity over three orders of magnitude on the value of CAH was experimentally investigated. This study revealed that the CAH value is primarily governed by the pinning length which in turn depends on the length scale of wetting heterogeneity. Modifying the heterogeneity size ultimately leads to near isotropic wettability for surfaces with highly anisotropic nanoscale chemical heterogeneities. Next, development of lubricant-swollen polymeric omniphobic protective gear for defense and healthcare applications is described. Specifically, it is shown that the robust and durable protective gear can be made from polymeric material fully saturated with lubricant that can shed all liquids irrespective of their surface tensions even after multiple contact incidences with the foreign objects. Further, a couple of schemes are proposed to improve the rate of lubrication and replenishment of lubricant as well as reduce the total amount of lubricant required in making the polymeric protective gear omniphobic. Overall, this research aims to understand the underlying physics of dynamic surface-liquid interaction and provides simple scalable route to fabricate better materials for condensers and omniphobic protective gear.Dissertation/ThesisDoctoral Dissertation Mechanical Engineering 201

Carbon Nanotubes for Bone Tissue Engineering

Biological tissues are compositionally and structurally exquisite – a complex network of proteins and cells organised with molecular-precision. Unfortunately, in the absence of an organ transplant or tissue graft, there are no technologies that can completely repair or restore this complex system when it fails. With the hopes of regenerating failing tissue, tissue engineers have developed scaffold structures able to support cell life. As yet, these structures are unable to recreate the complexities of the biological environment, limiting the success of this approach. Nanotechnologies have realised methods to make materials with defined nanoscale properties. Continued research may lead to sophisticated nanobiomaterials, with properties that rival the complexities of biological environments and improve tissue regeneration. To this end, we explored the use of carbon nanotubes (CNTs) within the field of tissue engineering. We investigated the use of 3D CNT scaffolds in bone tissue engineering using strong and porous ceramic scaffold structures coated with CNTs. We abate limitations in previous fabrication methods limiting coating of CNTs throughout porous structures. We demonstrate these surfaces are high quality aligned CNTs, are non toxic and able to support attachment, spreading and proliferation of adipose derived stem cells (ASCs) and human osteoblasts. Following the development of a 3D CNT material, we investigated the potential for using CNTs to create well-defined nanoenvironments capable of regulating cell differentiation. This research is the first report of non-biased quantitative measurement of cell shape during long term differentiation. In contrast to previous techniques, it allows direct measurement of shape rather than that of the underlying substrate. This approach offers novel insights into the relationship between the nanoenvironment, cell shape and cell differentiation. The novel nanomaterials presented in this thesis, demonstrate the potential of nanotechnologies for artificially engineered tissues and organs. Continued research of nanomaterials promises to better recreate the complexities of the biological environment, instructing healthy regenerative processes and promoting tissue function

Phenotypic Modulation of Smooth Muscle Cells on Biodegradable Elastomeric Substrates

Cardiovascular disease is the number one killer in the U.S. Cardiovascular tissue engineering holds enormous potential by providing synthetic materials as vessel replacements. This dissertation focused on the development of novel biodegradable and photo-crosslinkable polymers with controlled surface chemistry, stiffness, and topographical features in regulating smooth muscle cell (SMC) adhesion, proliferation and phenotypic conversion for cardiovascular tissue engineering applications. Chapter II presents a facile synthesis route to obtain a series of photocrosslinkable poly(epsilon-caprolactone) triacrylates (PCLTA) with varied mechanical properties and further demonstrated tunable cell responses using these polymer system. Chapter III demonstrates a model polymer network from PCLTA that can gradually stiffen in 24 h through impeded crystallization at body temperature (37 ºC) and distinct SMC attachment, proliferation and spreading are found. Chapter IV presents the fabrication of a series of PCLTA networks with defined gradients in stiffness for regulation of SMCs behaviors. Chapter V fabricates cylindrical pillars with three different heights of 3.4, 7.4, and 15.1 micrometers by photo-crosslinking PCLTA in silicon molds with predesigned micropatterns. Chapter VI prepared photo-crosslinked PCLTA nanowire arrays with diameters of 20, 100 and 200 nanometers using inorganic nanoporous aluminum oxide (AAO) templates. Chapter VII reports a series of novel poly(L-lactic acid) triacrylates (PLLATAs) networks with same chemical composition but different crystallinity and surface roughness achieved by increasing the annealing time from 0 to 5, 7, 10, and 20 h at 70 ºC. Chapter VIII presents a method for tuning surface chemistry by grafting hydrophilic photocrosslinkable mPEGA chains into the hydrophobic PCLTA at various compositions and reports the smooth muscle cell responses. Chapter IX incorporates poly(L-lysine) (PLL) dangling chains into PCLTA networks at different PLL compositions of 0.5%, 1.0%, 1.5%, and 3%. The surface morphology, hydrophilicity and serum protein adsorption of all these polymer networks were characterized. Primary rat SMCs were cultured on these polymer networks and their attachment, spreading, proliferation, focal adhesions, expression of four contractile gene markers (SM-MHC, smoothlin, transgelin, and calponin) and contractile proteins were characterized systematically. Chapter X makes a summary of these separate investigations and draws general conclusions from the results obtained in these studies

The structure of spray-dried detergent powders

The complex multi-scale structure of spray-dried detergent granules has been characterized using a range of techniques including microscopy, wide-angle and small-angle X-ray scattering and X-ray microtomography. Four simple model formulations based on linear alkyl benzene sulphonate (NaLAS) and sodium sulphate were used to probe the influence of initial slurry water content and sodium silicate on the structure. The structure can be viewed as a porous matrix consisting of liquid crystalline NaLAS, sodium sulphate and binder in which large crystals of sodium sulphate are embedded. These large crystals were initially undissolved in the slurry and are consequently reduced in number in the product made from higher water content slurry. The both slurry water content and sodium silicate changed the polymorphs, and the d-spacing of the lamellae. The surface micro-structure and particle morphology can also be significantly affected with the high initial water content; particles having a distinct agglomerated and blistered structure

Bio-Interfaces Engineering Using Laser-Based Methods for Controlled Regulation of Mesenchymal Stem Cell Response In Vitro

The controlled interfacial properties of materials and modulated behaviours of cells and biomolecules on their surface are the requirements in the development of a new generation of high-performance biomaterials for regenerative medicine applications. Roughness, chemistry and mechanics of biomaterials are all sensed by cells. Organization of the environment at the nano- and the microscale, as well as chemical signals, triggers specific responses with further impact on cell fate. Particularly, human mesenchymal stem cells (hMSCs) hold a great promise in both basic developmental biology studies and regenerative medicine, as progenitors of bone cells. Their fate can be affected by various key regulatory factors (e.g. soluble growth factors, intrinsic, extrinsic environmental factors) that can be delivered by a fabricated scaffold. For example, when cultured on engineered environments that reproduce the physical features of the bone, hMSCs express tissue-specific transcription factors and consequently undergo an osteogenic fate. Therefore, producing smart bio-interfaces with targeted functionalities represents the key point in effective use of hierarchically topographical and chemical bioplatforms. In this chapter, we review laser-based approaches (e.g. Matrix-Assisted Pulsed Laser Evaporation (MAPLE), Laser-Induced Forward Transfer (LIFT), laser texturing and laser direct writing) used for the design of bio-interfaces aimed at controlling stem cell behaviour in vitro

Laser-fabricated porous alumina membranes (LF-PAM) for the preparation of metal nanodot arrays

We report on an efficient photonic-based method to prepare nanodot array of functional materials, independently of the nature of the substrate.Comment: Small (2008) Accepte

Development, Characterization of Mechanical Properties, Wear behaviour and Machining Analysis of Ceramic Composites for Bio-Medical Applications

Ceramic composites incorporating synthetic hydroxyapatite (HAp) particulate and thermoplastic polymer matrices are finding wide spread applications in bio-medical field. The fractured or damaged bone can be repaired or replaced by artificial bone materials. HAp has been tested many times as an artificial bone, especially as augmentation material in surgery work or as a coating material on bio-inert implants materials. It has shown excellent biocompatibility and bonding characteristics. Many implant materials used for last three decades are basically metals, alloys, ceramics and polymers etc. Most metals and ceramics are much stiffer than bone tissue resulting in mechanical mismatch (i.e. “stress shielding”) between the implant and the adjacent bone tissue. Metals are too stiff and pose other biocompatibility problems whereas ceramics are too brittle but polymers are too flexible and weak to meet the mechanical strength. However, polymers are popular due to their low density, good mechanical strength and easy formability. Therefore, polymeric bone implants are widely used. HAp particulates are mixed with polymer matrix through a series of processing stages involving melt compounding, granulating and micro-injection moulding. HAp is a suitable ceramic material for hard tissue replacement. In the present work, HAp is synthesized by wet chemical precipitation route. The mechanical properties such as tensile, compressive, flexural, impact and hardness are assessed for the composites varying HAp volume percentage in polycarbonate (PC) and polysulfone (PSU) polymers. The wear resistance of composites in abrasion, erosion, sliding and fretting mode is assessed in dry environment. Adaptive neuro-fuzzy inference system (ANFIS) model is proposed for prediction of wear behaviour of composites. The effect of drilling parameters on surface integrity of internal holes made on composite is assessed to provide insight into machinability (i.e. drilling) aspects of composites. The aim of this study is to develop material that has similar mechanical properties to that of human bone in order to achieve mechanical compatibility in the body, examine the various mechanical properties of ceramic composites, assess the performance of the ceramic composites under different wear modes and evaluate the performance of the composites in drilling operation. The samples were characterized by x-ray diffraction (XRD), fourier transform infrared test (FTIR), and scanning electron microscopy (SEM). Two-body abrasion wear behaviour of the composite is evaluated using pin-on-disc friction and wear test rig (ASTM G99). The experiment is conducted using three different water proof silicon carbide (SiC) abrasive papers of 400, 600 and 1000 grit size. Taguchi’s L27 orthogonal array is used to evaluate the tribological property with four control variables such as HAp volume percentage, load applied, sliding speed and track radius, each at three levels. The highest abrasive wear loss is noticed in the specimens worn with 400 grit size SiC paper. Erosion wear of ceramic composites is performed on air jet erosion test rig (ASTM G76). In this study, dry silica sand (spherical) of different particle size of 300μm, 400μm and 500μm are used as erodent. Taguchi’s L27 design is used to evaluate the tribological property with three control variables such as pressure, HAp volume, and impingement angle, each at three levels. The higher erosive wear loss is noticed in the specimens worn with 500μm erodent particle size as compared to both 300μm and 400μm erodent particle size. The sliding wear test of ceramic composites is performed on ball on plate wear tester (ASTM G194). Taguchi’s L27 design is designed to evaluate the tribological properties with three control variables such as HAp volume percentage, load applied and sliding speed, each at three levels. The fretting wear test of ceramic composites is performed on high frequency reciprocating rig (HFRR) testing machine (ASTM D6079). Taguchi’s L27 orthogonal array is used to evaluate the tribological properties with three control variables such as HAp volume, load applied and frequency, each at three levels. Since drilling is used to join the composite material with adjacent bone tissue in orthopaedic surgery, it is important to study drilling performance of the composite. Experiments have been conducted on a CNC milling machine using Taguchi’s L27 design with four control variables such as HAp volume percentage, drilling speed, feed rate and drill bit diameter, each at three levels. The responses considered are circularity at entry and exit, torque and thrust force. The circularity at both entry and exit is measured using the ratio of minimum diameter (Dmin) to maximum diameter (Dmax) of the drilled hole. The torque and thrust force are measured using drill dynamometer. Best parametric setting for simultaneous optimization of multiple performance measures such as circularity at entry, circularity at exit, torque and thrust in drilling operation is suggested using principal component analysis

Tuning Cell Fate on Self-assembled Structures

This dissertation presents novel biodegradable copolymers with dendritic architecture, classic polymers, and inorganic materials with controlled surface topography, stiffness, and surface energy for investigating cell-material interactions and targeting tissue engineering applications. Chapter I reviews the recent progress in bone and nerve regeneration, the key factors of materials influencing cell-material interaction, and self-assembled polymer structures. Chapter II presents a divergent method to synthesize biodegrable com-dendritic tri-block copolymers consisting of poly(ethylene glycol) and poly(L-lactide) or poly(e[epsilon]-caprolactone) and the MC3T3-E1 cell response to their spherulites. Chapter III presents the fabrication of deformable poly(e-caprolactone) honeycomb films prepared via a surfactant-free breath figure method in a water-miscible solvent and how the tunable topography regulates MC3T3-E1 cell functions. Chapter IV investigates the fabrication of photo-cured poly(e-caprolactone) triacrylate films with tunable pore size via breath figure method and how the pore size regulates MC3T3-E1 cell behavior. Chapter V invented a facile method to fabricate honeycomb films with submicron pores using monodisperse silica nanoparticle as template and studied the MC3T3-E1 cell functions on those honeycomb films. Chapter VI described a novel method to fabricate microgrooves with honeycomb patterns and investigated the MC3T3-E1 cell functions on this special topography. Chapter VII introduces a facile method to obtain controllable surface energy on poly(e-caprolactone) substrates via controlling the composition of edge-on and flat-on lamellae and how MC3T3-E1 cells behave on those substrates with different surface energy. Chapter VIII synthesizes biomimetic calcium carbonate concentric microgrooves with tunable width via self-assembly and studies the MC3T3-E1 cell response to those microgrooves. Chapter IX describes one method to fabricate controllable topographical features and mechanical properties on poly(e-caprolactone) substrates using uniaxial and biaxial stretching and how those substrates regulate MC3T3-E1 cell functions. Chapter X studies rat pheochromocytoma (PC12) response to the banded spherulites of poly(e-caprolactone) and polyhydroxybutyrate. Chapter XI presents the preparation of honeycomb-patterned copolymer films with tunable pore size and how the pore size regulates NPC cell attachment, proliferation, and differentiation