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

Fabrication of hollow microtube arrays based on a femtosecond laser double-pulse multiphoton polymerization

Microtubes with widely varied dimensions and materials have great prospects in functional devices applied in microoptics, microrobot, and biomedicine. However, the fabrication of vertically protruding hollow microtubes with high diameter-to-thickness ratio is challenging and few reported. Femtosecond laser two-photon polymerization can solve this problem via point-by-point scanning or SLM-based parallel processing, but the low efficiency limits its high throughput fabrication. Here, we report a novel, to the best of our knowledge, femtosecond laser double-pulse multiphoton polymerization approach for high efficiency fabrication of hollow microtube arrays. We established a two-aperture laser beam reshaping system to generate a circular beam via two rounds of Fresnel diffraction. Based on the unique laser energy distribution, hollow microtubes with high diameter-to-thickness ratio can be generated by two successively laser pulses exposure, which can improve the fabrication efficiency significantly. With the optimized parameters, we can achieve repeatable and uniform microtube array fabrication in large scale, and the yield can be 94.9%. Defocus testing showed that the proposed approach has a high range of focusing tolerance. The proposed microtube fabrication approach is meaningful in providing some enlightenment for researchers in the field of microfabrication.

Advances in Cell-Conductive Polymer Biointerfaces and Role of the Plasma Membrane

The plasma membrane (PM) is often described as a wall, a physical barrier separating the cell cytoplasm from the extracellular matrix (ECM). Yet, this wall is a highly dynamic structure that can stretch, bend, and bud, allowing cells to respond and adapt to their surrounding environment. Inspired by shapes and geometries found in the biological world and exploiting the intrinsic properties of conductive polymers (CPs), several biomimetic strategies based on substrate dimensionality have been tailored in order to optimize the cell-chip coupling. Furthermore, device biofunctionalization through the use of ECM proteins or lipid bilayers have proven successful approaches to further maximize interfacial interactions. As the bio-electronic field aims at narrowing the gap between the electronic and the biological world, the possibility of effectively disguising conductive materials to "trick" cells to recognize artificial devices as part of their biological environment is a promising approach on the road to the seamless platform integration with cells.

Fabrication of Size- and Shape-Controlled Platinum Cones by Ion-Track Etching and Electrodeposition Techniques for Electrocatalytic Applications

The micro/nanocone structures of noble metals play a critical role as heterogeneous electrocatalysts that provide excellent activity. We successfully fabricated platinum cones by electrodeposition using non-penetrated porous membranes as templates. This method involved the preparation of template membranes by the swift-heavy-ion irradiation of commercially available polycarbonate films and subsequent chemical etching in an aqueous NaOH solution. The surface diameter, depth, aspect ratio and cone angle of the resulting conical pores were controlled in the ranges of approximately 70–1500 nm, 0.7–11 μm, 4–12 and 5–13°, respectively, by varying the etching conditions, which finally produced size- and shape-controlled platinum cones with nanotips. In order to demonstrate the electrocatalytic activity, electrochemical measurements were performed for the ethanol oxidation reaction. The oxidation activity was found to be up to 3.2 times higher for the platinum cone arrays than for the platinum plate. Ion-track etching combined with electrodeposition has the potential to be an effective method for the fabrication of micro/nanocones with high electrocatalytic performance.

Surface-Mediated Intracellular Delivery by Physical Membrane Disruption

Effective and nondestructive intracellular delivery of exogenous molecules and other functional materials into living cells is of importance for diverse biological fundamental research and therapeutic applications, such as gene editing and cell-based therapies. However, for most exogenous molecules, the cell plasma membrane is effectively impermeable and thus remains the greatest barrier to intracellular delivery. In recent years, methods based on surface-mediated physical membrane disruption have attracted considerable attention. These methods exploit the physical properties of the surface to transiently increase the membrane permeability of cells come in contact thereto, thereby facilitating the efficient intracellular delivery of molecules regardless of molecule or target cell type. In this Review, we focus on recent progress, particularly over the past decade, on these surface-mediated membrane disruption-based delivery systems. According to the membrane disruption mechanism, three categories can be recognized: (i) mechanical penetration, (ii) electroporation, and (iii) photothermal poration. Each of these is discussed in turn and a brief perspective on future developments in this promising area is presented.

High-Aspect-Ratio Nanostructured Surfaces as Biological Metamaterials

Materials patterned with high-aspect-ratio nanostructures have features on similar length scales to cellular components. These surfaces are an extreme topography on the cellular level and have become useful tools for perturbing and sensing the cellular environment. Motivation comes from the ability of high-aspect-ratio nanostructures to deliver cargoes into cells and tissues, access the intracellular environment, and control cell behavior. These structures directly perturb cells' ability to sense and respond to external forces, influencing cell fate, and enabling new mechanistic studies. Through careful design of their nanoscale structure, these systems act as biological metamaterials, eliciting unusual biological responses. While predominantly used to interface eukaryotic cells, there is growing interest in nonanimal and prokaryotic cell interfacing. Both experimental and theoretical studies have attempted to develop a mechanistic understanding for the observed behaviors, predominantly focusing on the cell-nanostructure interface. This review considers how high-aspect-ratio nanostructured surfaces are used to both stimulate and sense biological systems.

Cell Membrane Disruption by Vertical Micro-/Nanopillars: Role of Membrane Bending and Traction Forces

Gaining access to the cell interior is fundamental for many applications, such as electrical recording and drug and biomolecular delivery. A very promising technique consists of culturing cells on micro-/nanopillars. The tight adhesion and high local deformation of cells in contact with nanostructures can promote the permeabilization of lipids at the plasma membrane, providing access to the internal compartment. However, there is still much experimental controversy regarding when and how the intracellular environment is targeted and the role of the geometry and interactions with surfaces. Consequently, we investigated, by coarse-grained molecular dynamics simulations of the cell membrane, the mechanical properties of the lipid bilayer under high strain and bending conditions. We found out that a high curvature of the lipid bilayer dramatically lowers the traction force necessary to achieve membrane rupture. Afterward, we experimentally studied the permeabilization rate of the cell membrane by pillars with comparable aspect ratios but different sharpness values at the edges. The experimental data support the simulation results: even pillars with diameters in the micron range may cause local membrane disruption when their edges are sufficiently sharp. Therefore, the permeabilization likelihood is connected to the local geometric features of the pillars rather than diameter or aspect ratio. The present study can also provide significant contributions to the design of three-dimensional biointerfaces for tissue engineering and cellular growth.

Intracellular Delivery by Membrane Disruption: Mechanisms, Strategies, and Concepts

Intracellular delivery is a key step in biological research and has enabled decades of biomedical discoveries. It is also becoming increasingly important in industrial and medical applications ranging from biomanufacture to cell-based therapies. Here, we review techniques for membrane disruption-based intracellular delivery from 1911 until the present. These methods achieve rapid, direct, and universal delivery of almost any cargo molecule or material that can be dispersed in solution. We start by covering the motivations for intracellular delivery and the challenges associated with the different cargo types-small molecules, proteins/peptides, nucleic acids, synthetic nanomaterials, and large cargo. The review then presents a broad comparison of delivery strategies followed by an analysis of membrane disruption mechanisms and the biology of the cell response. We cover mechanical, electrical, thermal, optical, and chemical strategies of membrane disruption with a particular emphasis on their applications and challenges to implementation. Throughout, we highlight specific mechanisms of membrane disruption and suggest areas in need of further experimentation. We hope the concepts discussed in our review inspire scientists and engineers with further ideas to improve intracellular delivery.

Electrokinetically controlled fluid injection into unicellular microalgae

Electrokinetically controlled microinjection is reported as an effective transport mechanism for microinjection into the wild-type strain of the widely studied model microalga Chlamydomonas reinhardtii. A microinjection system using glass capillary pipettes was developed to capture and impale the motile cells. To apply an electric field and induce electrokinetic flow (e.g., electrophoresis and electroosmosis), an electrode was inserted directly into the solution inside the impaling injection pipette and another electrode was inserted into the external cell media. The viability of the impaled cells was confirmed for more than an hour under 0.01 V using the fluorescein diacetate/propidium iodide dual fluorescent dye based assay. The viability was also found to increase almost logarithmically with decreasing voltage and to depend strongly on the solution within the injection pipette. Successful electrokinetic microinjection into cells was confirmed by both an increase in cell volume under an applied voltage and electric field dependent delivery of fluorescent fluorescein molecules into an impaled cell. Our study offers novel opportunities for quantitative delivery of biomolecules into microalgae and advancing the research and development of these organisms as biosynthetic factories.