Non-adhesive PEG hydrogel nanostructures for self-assembly of highly ordered colloids

Current status and future developments in preparation and application of nonspherical polymer particles

Nonspherical polymer particles (NPPs) are nano/micro-particulates of macromolecules that are anisotropic in shape, and can be designed anisotropic in chemistry. Due to shape and surface anisotropies, NPPs bear many unique structures and fascinating properties which are distinctly different from those of spherical polymer particles (SPPs). In recent years, the research on NPPs has surprisingly blossomed in recent years, and many practical materials based on NPPs with potential applications in photonic device, material science and biomedical engineering have been generated. In this review, we give a systematic, balanced and comprehensive summary of the main aspects of NPPs related to their preparation and application, and propose perspectives for the future developments of NPPs.

Programmable Hydrogel Ionic Circuits for Biologically Matched Electronic Interfaces

The increased need for wearable and implantable medical devices has driven the demand for electronics that interface with living systems. Current bioelectronic systems have not fully resolved mismatches between engineered circuits and biological systems, including the resulting pain and damage to biological tissues. Here, salt/poly(ethylene glycol) (PEG) aqueous two-phase systems are utilized to generate programmable hydrogel ionic circuits. High-conductivity salt-solution patterns are stably encapsulated within PEG hydrogel matrices using salt/PEG phase separation, which route ionic current with high resolution and enable localized delivery of electrical stimulation. This strategy allows designer electronics that match biological systems, including transparency, stretchability, complete aqueous-based connective interface, distribution of ionic electrical signals between engineered and biological systems, and avoidance of tissue damage from electrical stimulation. The potential of such systems is demonstrated by generating light-emitting diode (LED)-based displays, skin-mounted electronics, and stimulators that deliver localized current to in vitro neuron cultures and muscles in vivo with reduced adverse effects. Such electronic platforms may form the basis of future biointegrated electronic systems.

Capillary assembly as a tool for the heterogeneous integration of micro- and nanoscale objects

During the past decade, capillary assembly in topographical templates has evolved into an efficient method for the heterogeneous integration of micro- and nano-scale objects on a variety of surfaces. This assembly route has been applied to a large spectrum of materials of micrometer to nanometer dimensions, supplied in the form of aqueous colloidal suspensions. Using systems produced via bulk synthesis affords a huge flexibility in the choice of materials, holding promise for the realization of novel superior devices in the fields of optics, electronics and health, if they can be integrated into surface structures in a fast, simple, and reliable way. In this review, the working principles of capillary assembly and its fundamental process parameters are first presented and discussed. We then examine the latest developments in template design and tool optimization to perform capillary assembly in more robust and efficient ways. This is followed by a focus on the broad range of functional materials that have been realized using capillary assembly, from single components to large-scale heterogeneous multi-component assemblies. We then review current applications of capillary assembly, especially in optics, electronics, and in biomaterials. We conclude with a short summary and an outlook for future developments.

Flexible transparent iontronic film for interfacial capacitive pressure sensing

A flexible, transparent iontronic film is introduced as a thin-film capacitive sensing material for emerging wearable and health-monitoring applications. Utilizing the capacitive interface at the ionic-electronic contact, the iontronic film sensor offers a large unit-area capacitance (of 5.4 μF cm(-2) ) and an ultrahigh sensitivity (of 3.1 nF kPa(-1) ), which is a thousand times greater than that of traditional solid-state counterparts.

Design, Fabrication, and In Vitro Testing of an Anti-biofouling Glaucoma Micro-shunt

Glaucoma, one of the leading causes of irreversible blindness, is a progressive neurodegenerative disease. Chronic elevated intraocular pressure (IOP), a prime risk factor for glaucoma, can be treated by aqueous shunts, implantable devices, which reduce IOP in glaucoma patients by providing alternative aqueous outflow pathways. Although initially effective at delaying glaucoma progression, contemporary aqueous shunts often lead to numerous complications and only 50% of implanted devices remain functional after 5 years. In this work, we introduce a novel micro-device which provides an innovative platform for IOP reduction in glaucoma patients. The device design features an array of parallel micro-channels to provide precision aqueous outflow resistance control. Additionally, the device's microfluidic channels are composed of a unique combination of polyethylene glycol materials in order to provide enhanced biocompatibility and resistance to problematic channel clogging from biofouling of aqueous proteins. The microfabrication process employed to produce the devices results in additional advantages such as enhanced device uniformity and increased manufacturing throughput. Surface characterization experimental results show the device's surfaces exhibit significantly less non-specific protein adsorption compared to traditional implant materials. Results of in vitro flow experiments verify the device's ability to provide aqueous resistance control, continuous long-term stability through 10-day protein flow testing, and safety from risk of infection due to bacterial ingression.

Novel functionalization of discrete polymeric biomaterial microstructures for applications in imaging and three-dimensional manipulation

Adapting ways to functionalize polymer materials is becoming increasingly important to their implementation in translational biomedical sciences. By tuning the mechanical, chemical, and biological qualities of these materials, their applications can be broadened, opening the door for more advanced integration into modern medical techniques. Here, we report on a method to integrate chemical functionalizations into discrete, microscale polymer structures, which are used for tissue engineering applications, for in vivo localization, and three-dimensional manipulation. Iron oxide nanoparticles were incorporated into the polymer matrix using common photolithographic techniques to create stably functional microstructures with magnetic potential. Using magnetic resonance imaging (MRI), we can promote visualization of microstructures contained in small collections, as well as facilitate the manipulation and alignment of microtopographical cues in a realistic tissue environment. Using similar polymer functionalization techniques, fluorine-containing compounds were also embedded in the polymer matrix of photolithographically fabricated microstructures. The incorporation of fluorine-containing compounds enabled highly sensitive and specific detection of microstructures in physiologic settings using fluorine MRI techniques ((19)F MRI). These functionalization strategies will facilitate more reliable noninvasive tracking and characterization of microstructured polymer implants as well as have implications for remote microstructural scaffolding alignment for three-dimensional tissue engineering applications.

Neural ECM mimetics

The consequence of numerous neurological disorders is the significant loss of neural cells, which further results in multilevel dysfunction or severe functional deficits. The extracellular matrix (ECM) is of tremendous importance for neural regeneration mediating ambivalent functions: ECM serves as a growth-promoting substrate for neurons but, on the other hand, is a major constituent of the inhibitory scar, which results from traumatic injuries of the central nervous system. Therefore, cell and tissue replacement strategies on the basis of ECM mimetics are very promising therapeutic interventions. Numerous synthetic and natural materials have proven effective both in vitro and in vivo. The closer a material's physicochemical and molecular properties are to the original extracellular matrix, the more promising its effectiveness may be. Relevant factors that need to be taken into account when designing such materials for neural repair relate to receptor-mediated cell-matrix interactions, which are dependent on chemical and mechanical sensing. This chapter outlines important characteristics of natural and synthetic ECM materials (scaffolds) and provides an overview of recent advances in design and application of ECM materials for neural regeneration, both in therapeutic applications and in basic biological research.

Print-to-print: a facile multi-object micro-patterning technique

In recent years, micropatterning techniques have gained increasing popularity from a broad range of engineering and biology communities for the promise to establish highly quantitative investigations on miniature biological objects (e.g., cells and bacteria) with spatially defined microenvironments. However, majority of the existing techniques rely on cleanroom-based microfabrication and cannot be easily extended to a regular biological laboratory. In this paper, we present a simple versatile printing-based method, referred to as Print-to-Print (P2P), to form multi-object micropatterns for potential biological applications, along with our recent efforts to deliver out-of-cleanroom microfabrication solutions to the general public (Zhao et al. 2009), (Xing et al. 2011), (Wang et al. 2009), (Pan and Wang 2011), (Zhao et al. 2011). The P2P method employs only a commercially available solid-phase printer and custom-made superhydrophobic films. The entire patterning process does not involve any thermal or chemical treatment. Moreover, the non-contact nature of droplet transferring and printing steps can be highly advantageous for sensitive biological uses. Using the P2P process, a minimal feature resolution of 229 ± 17 μm has been successfully demonstrated. In addition, this approach has been applied to form biological micropatterning on various substrates as well as multi-object co-patterns on the commonly used surfaces. Finally, the reusability of superhydrophobic substrates has also been illustrated.

From cleanroom to desktop: emerging micro-nanofabrication technology for biomedical applications

This review is motivated by the growing demand for low-cost, easy-to-use, compact-size yet powerful micro-nanofabrication technology to address emerging challenges of fundamental biology and translational medicine in regular laboratory settings. Recent advancements in the field benefit considerably from rapidly expanding material selections, ranging from inorganics to organics and from nanoparticles to self-assembled molecules. Meanwhile a great number of novel methodologies, employing off-the-shelf consumer electronics, intriguing interfacial phenomena, bottom-up self-assembly principles, etc., have been implemented to transit micro-nanofabrication from a cleanroom environment to a desktop setup. Furthermore, the latest application of micro-nanofabrication to emerging biomedical research will be presented in detail, which includes point-of-care diagnostics, on-chip cell culture as well as bio-manipulation. While significant progresses have been made in the rapidly growing field, both apparent and unrevealed roadblocks will need to be addressed in the future. We conclude this review by offering our perspectives on the current technical challenges and future research opportunities.

Cell confinement in patterned nanoliter droplets in a microwell array by wiping

Cell patterning is useful for a variety of biological applications such as tissue engineering and drug discovery. In particular, the ability to localize cells within distinct fluids is beneficial for a variety of applications ranging from microencapsulation to high-throughput analysis. However, despite much progress, cell immobilization and maintenance within patterned microscale droplets remains a challenge. In particular, no method currently exists to rapidly seed cells into microwell arrays in a controllable and reliable manner. In this study, we present a simple wiping technique to localize cells within arrays of polymeric microwells. This robust method produces cell seeding densities that vary consistently with microwell geometry and cell concentration. Moreover, we develop a simple theoretical model to accurately predict cell seeding density and seeding efficiency in terms of the design parameters of the microwell array and the cell density. This short-term cell patterning approach is an enabling tool to develop new high-throughput screening technologies that utilize microwell arrays containing cells for screening applications.