Template synthesized Microneedle Arrays for Interfacing Microalgae Cells

Genetically engineered microalgae are gaining increased interest due to their potential use in biofuel production, and in protein and drug biosynthesis. However, the cell wall that surrounds its unicellular body acts as a formidable barrier to DNA delivery. In many cases, higher transformation efficiency cannot be achieved without removing or modifying the cell wall. However, cell walls of different species have large variance in their composition, hardness and thickness, and not every cell types are compatible with such pretreatments. This talk will discuss the first example of using microneedle-array technology to deliver genes to microalgae cells with intact cell walls. The microneedle-array was prepared by a template-synthesis method. Briefly, this entails depositing a desired material into a porous template, and then removing the template to expose the replica of the template pores. This method is highly attractive because the resulting structure can easily be controlled by manipulating the pores of the template. Details on how the microneedle array is developed using the template synthesis will be described, and results on using this needle array as a tool to interface with a model microalgae specimen, Chlamydomonas Reinhardtii, will be presented

Exploiting transport phenomena to synthesize functional materials within template nanomembranes

Thesis (Ph. D.)--University of Rochester. Department of Chemical Engineering, 2017.Template synthesis is a technique for producing materials with geometries that are defined by the geometry of their template – e.g., cylindrical wires are commonly synthesized from template membranes with cylindrical pores. This dissertation focuses on precise tuning of the template synthesized materials, enabling control over their dimensions without being limited by the shape of the template. Specifically, commercial track-etched polycarbonate filter membranes with non-parallel, cylindrical pores and in-house-prepared track-etched poly(ethylene terephthalate) (PET) membranes with parallel, conical pores are explored in this work. With the polycarbonate membrane, difference in the transport rates through the nanopore was exploited to localize template synthesis at only one surface of the membrane. This was demonstrated by using the membrane to separate a solution of small crosslinking molecules from a solution of larger oligomers. The crosslinkers diffuse faster through the membrane pores and react with the oligomer to form a hydrogel film at the surface of the nanopore membrane. A proof-of concept experiment is described using crosslinkers with imidoester moieties (dimethyl 3,3´-dithiobispropionimidate (DTBP) or dimethyl suberimidate (DMS)) and chitosan oligomers. The film’s formation is confirmed and its morphology examined with electron microscopy. Crosslinking with DTBP or DMS also confers degradability to the chitosan film. This was used to confirm successful crosslinking by monitoring the increase in transport of gold nanoparticles through the chitosan film as a function of the degradation treatment. The method presented here can potentially be used to prepare functional hydrogel thin films for biosensors, coatings, and drug delivery systems in an inexpensive, high-throughput manner. With the PET membrane, fabrication of an array of open-tipped tapered microtubes is demonstrated using a template with close-tipped conical pores, by controlling the depth of material penetration into the template pore. This was accomplished using atomic layer deposition (ALD) of Pt and pulsed-current electrodeposition (PCD) of Ni with the track-etched conical pores of a PET template membrane. The tapered microtube height is controlled by the Pt precursor pulse duration during ALD, and the microtube wall thickness is controlled by the number of cycles of Ni PCD. The microtubes’ lumen is confirmed to stay open even after 2000 cycles of Ni PCD. A potential application of the open-tipped tapered microtube array as a microinjection platform is demonstrated via successful injection of 10-nm-sized CdZnS/ZnS core/shell quantum dots into Chlamydomonas reinhardtii microalgae cells with intact cell walls. The direct delivery method demonstrated here offers novel opportunities for extending the growing interest in array-based microinjection platforms to microalgal systems. A model is also presented to simulate molecular transport during ALD in both cylindrical and conical nanopores. Using a Monte Carlo simulation method, the trajectory of particles is calculated within the pores under molecular flow, where interparticle interactions are negligible and only collisions with the pore walls are considered. Both cosine emission and diffuse elastic emission profiles from the pore wall surface are considered, and diffuse elastic emission is found to match Knudsen molecular flow theory to within 1%. To simulate ALD, a sticking probability is introduced that determines the likelihood of a reaction taking place upon collision with the pore wall. The simulation is shown to match literature-reported thickness profiles of ALD within cylindrical nanopores. In conical nanopores with a high sticking probability, it is shown that thicker deposition occurs near the pore entrance. However, with a low sticking probability the deposition is thicker near the pore end. This phenomenon is attributed to increased diffusion into the pore where the diameter is smaller and greater collision frequency takes place, providing more opportunity of reaction. This study offers theoretical understanding to ALD in closed-ended conical nanopores, and how the depth of penetration into the template pore may be controlled. Furthermore, these findings may have implications for other non-uniform geometries and may be important in estimating the minimum ALD exposure required for conformal coating therein

Cycle and rate properties of mesoporous tin anode for lithium ion secondary batteries

A mesoporous Sn anode was electrodeposited in the presence of lyotropic liquid crystals made of nonionic surfactants. The introduction of mesoporous structure was effective for the accommodation of volume change of Sn during charge and discharge cycling of Li ions. The discharge capacity of the mesoporous Sn anode at 1 C rate was as high as 425 mA h g(-1) at the 100th cycle, and that was as high as 320 mA It g(-1) at the 100th cycle even though at 5 degrees C rate

Fabrication of Tapered Microtube Arrays and Their Application as a Microalgal Injection Platform

A template-synthesis method that enables fabrication of tapered microtube arrays is reported. Track-etched poly­(ethylene terephthalate) membranes are used as the template, with closed-tipped conical pores having length and base diameter of 6.27 ± 0.28 and 1.21 ± 0.05 μm, respectively. A conductive layer of Pt is deposited by atomic layer deposition (ALD) to enable the successive electrodeposition of Ni. By decreasing the Pt precursor pulse duration from 10 to 1 s during the ALD step, the heights of the microtubes are controlled from the maximal full length (∼6 μm) to only a fraction (1–2 μm) of the template pore. Using a pulsed-current electrodeposition (PCD) method, a smooth and uniform Ni deposit is achieved with a thickness that can be controlled as a function of the PCD cycle. The microtubes’ lumen is confirmed to stay open even after 2000 cycles of Ni PCD. A potential application of the prepared array as a microinjection platform is demonstrated via successful injection of 10 nm sized CdZnS/ZnS core/shell quantum dots into Chlamydomonas reinhardtii microalgae cells with intact cell walls. The direct delivery method demonstrated in this paper offers novel opportunities for extending the growing interest in array-based microinjection platform to microalgal systems

Nanoindentation and nanowear study of Sn and Ni-Sn coatings

As potential high capacity anode materials for lithium ion batteries, the Sn and Ni-Sn alloy coatings have been investigated by many electrochemical researchers. However, their mechanical properties have not been extensively studied, despite the fact that such anode films may fail mechanically during service. Thus, in this study nanoindentation and nanowear tests have been performed. Nanoindentation tests reveal that the ability to carry the load dramatically reduces in the Sn coating after one charge-discharge cycle which makes the plastic strain accumulation in the copper substrate play a greater contribution to crack formation and propagation in repeated charge-discharge cycling. Upon the nanoindentation analysis, it also shows that the pores formed by lithiation/delithiation can easily collapse at low loads. Furthermore, nanowear tests explore that the damage resistance of the Sn-Ni alloy film significantly improves after one charge-discharge cycle but it decreases in the Sn film after the same charge-discharge cycle; this explains why the degradation rate of the Ni-Sn alloy is slow after the first charge-discharge cycle and why the high capacity is maintained in further cycling. The links between the mechanical characterization and the degradation in charge-discharge cycling are also discussed