High-Resolution, Multiplex Antibody Patterning using Micropillar-Focused Droplet Printing, and Microcontact Printing

Antibody arrays have great implications in many biomedical settings. However, commonly used patterning methods have difficulties in generating antibody arrays with both high resolution and multiplexity, limiting their applications. Here, a convenient and versatile technique for the patterning of multiple antibodies with resolution down to 20 µm is reported using micropillar-focused droplet printing and microcontact printing. Droplets of antibody solutions are first printed and stably confined on the micropillars of a stamp, and then the antibodies absorbed on the micropillars are contact-printed to the target substrate, generating antibody patterns faithfully replicating the micropillar array. The effect of different parameters on the patterning results is investigated, including hydrophobicity of the stamps, override time of the droplet printing, incubation time, and the diameters of the capillary tips and micropillars. To demonstrate the utility of the method, multiplex arrays of anti-EpCAM and anti-CD68 antibodies is generated to capture breast cancer cells and macrophages, respectively, on the same substrate, and successful capturing of individual cell types and enrichment among the cells are achieved. It is envision that this method would serve as a versatile and useful protein patterning tool for biomedical applications.

Selective Positioning of Different Cell Types on 3D Scaffolds via DNA Hybridization

Three-dimensional (3D) microscaffolds for cell biology have shown their potential in mimicking physiological environments and simulating complex multicellular constructs. However, controlling the localization of cells precisely on microfabricated structures is still complex and usually limited to two-dimensional assays. Indeed, the implementation of an efficient method to selectively target different cell types to specific regions of a 3D microscaffold would represent a decisive step toward cell-by-cell assembly of complex cellular arrangements. Here, we use two-photon lithography (2PL) to fabricate 3D microarchitectures with functional photoresists. UV-mediated click reactions are used to functionalize their surfaces with single-stranded DNA oligonucleotides, using sequential repetition to decorate different scaffold regions with individual DNA addresses. Various immortalized cell lines and stem cells modified by grafting complementary oligonucleotides onto the phospholipid membranes can then be immobilized onto complementary regions of the 3D structures by selective hybridization. This allows controlled cocultures to be established with spatially separated arrays of eukaryotic cells in 3D.

Integration of Biofunctional Molecules into 3D-Printed Polymeric Micro-/Nanostructures

Three-dimensional printing at the micro-/nanoscale represents a new challenge in research and development to achieve direct printing down to nanometre-sized objects. Here, FluidFM, a combination of microfluidics with atomic force microscopy, offers attractive options to fabricate hierarchical polymer structures at different scales. However, little is known about the effect of the substrate on the printed structures and the integration of (bio)functional groups into the polymer inks. In this study, we printed micro-/nanostructures on surfaces with different wetting properties, and integrated molecules with different functional groups (rhodamine as a fluorescent label and biotin as a binding tag for proteins) into the base polymer ink. The substrate wetting properties strongly affected the printing results, in that the lateral feature sizes increased with increasing substrate hydrophilicity. Overall, ink modification only caused minor changes in the stiffness of the printed structures. This shows the generality of the approach, as significant changes in the mechanical properties on chemical functionalization could be confounders in bioapplications. The retained functionality of the obtained structures after UV curing was demonstrated by selective binding of streptavidin to the printed structures. The ability to incorporate binding tags to achieve specific interactions between relevant proteins and the fabricated micro-/nanostructures, without compromising the mechanical properties, paves a way for numerous bio and sensing applications. Additional flexibility is obtained by tuning the substrate properties for feature size control, and the option to obtain functionalized printed structures without post-processing procedures will contribute to the development of 3D printing for biological applications, using FluidFM and similar dispensing techniques.

Dip-Pen Nanolithography(DPN): from Micro/Nano-patterns to Biosensing

Dip-pen nanolithography is an emerging and attractive surface modification technique that has the capacity to directly and controllably write micro/nano-array patterns on diverse substrates. The superior throughput, resolution, and registration enable DPN an outstanding candidate for biological detection from the molecular level to the cellular level. Herein, we overview the technological evolution of DPN in terms of its advanced derivatives and DPN-enabled versatile sensing patterns featuring multiple compositions and structures for biosensing. Benefitting from uniform, reproducible, and large-area array patterns, DPN-based biosensors have shown high sensitivity, excellent selectivity, and fast response in target analyte detection and specific cellular recognition. We anticipate that DPN-based technologies could offer great potential opportunities to fabricate multiplexed, programmable, and commercial array-based sensing biochips.

Evolution and applications of polymer brush hypersurface photolithography

Hypersurface photolithography creates arbitrary polymer brush patterns with independent control over feature diameter, height, and spacing between features, while controlling composition along a polymer chain and between features.

Recent progress in creating complex and multiplexed surface-grafted macromolecular architectures

Surface-grafted macromolecules, including polymers, DNA, peptides, etc., are versatile modifications to tailor the interfacial functions in a wide range of fields. In this review, we aim to provide an overview of the most recent progress in engineering surface-grafted chains for the creation of complex and multiplexed surface architectures over micro- to macro-scopic areas. A brief introduction to surface grafting is given first. Then the fabrication of complex surface architectures is summarized with a focus on controlled chain conformations, grafting densities and three-dimensional structures. Furthermore, recent advances are highlighted for the generation of multiplexed arrays with designed chemical composition in both horizontal and vertical dimensions. The applications of such complicated macromolecular architectures are then briefly discussed. Finally, some perspective outlooks for future studies and challenges are suggested. We hope that this review will be helpful to those just entering this field and those in the field requiring quick access to useful reference information about the progress in the properties, processing, performance, and applications of functional surface-grafted architectures.

Synergies between Surface Microstructuring and Molecular Nanopatterning for Controlling Cell Populations on Polymeric Biointerfaces

Polymeric biointerfaces are already being used extensively in a wide set of biomedical devices and systems. The possibility of controlling cell populations on biointerfaces may be essential for connecting biological systems to synthetic materials and for researching relevant interactions between life and matter. In this study, we present and analyze synergies between an innovative approach for surface microstructuring and a molecular nanopatterning procedure of recent development. The combined set of techniques used may be instrumental for the development of a new generation of functional polymeric biointerfaces. Eukaryotic cell cultures placed upon the biointerfaces developed, both before and after molecular patterning, help to validate the proposal and to discuss the synergies between the surface microstructuring and molecular nanopatterning techniques described in the study. Their potential role in the production of versatile polymeric biointerfaces for lab- and organ-on-a-chip biodevices and towards more complex and biomimetic co-culture systems and cell cultivation set-ups are also examined.

A Functioning Macroscopic "Rubik's Cube" Assembled via Controllable Dynamic Covalent Interactions

The dynamic behavior of a macroscopic adhered hydrogel stabilized through controllable dynamic covalent interactions is reported. These interactions, involving the cross-linked formation of a hydrogel through reaction of a diacylhydrazine precursor with a tetraformyl partner, increase as a function of time. By using a contact time of 24 h and different compounds with recognized aggregation-induced emission features (AIEgens), it proves possible to create six laminated acylhydrazone hydrogels displaying different fluorescent colors. Blocks of these hydrogels are then adhered into a structure resembling a Rubik's Cube, a trademark of Rubik's Brand Limited, (RC) and allowed to anneal for 1 h. This produces a 3 × 3 × 3 block (RC) wherein the individual fluorescent gel blocks are loosely adhered to one another. As a consequence, the 1 × 3 × 3 layers making up the RC can be rotated either horizontally or vertically to produce new patterns. Ex situ modification of the RC or application of a chemical stimulus can be used to produce new color arrangements. The present RC structure highlights how the temporal features, strong versus weak adhesion, may be exploited to create smart macroscopic structures.

Writing Behavior of Phospholipids in Polymer Pen Lithography (PPL) for Bioactive Micropatterns

Lipid-based membranes play crucial roles in regulating the interface between cells and their external environment, the communication within cells, and cellular sensing. To study these important processes, various lipid-based artificial membrane models have been developed in recent years and, indeed, large-area arrays of supported lipid bilayers suit the needs of many of these studies remarkably well. Here, the direct-write scanning probe lithography technique called polymer pen lithography (PPL) was used as a tool for the creation of lipid micropatterns over large areas via polymer-stamp-mediated transfer of lipid-containing inks onto glass substrates. In order to better understand and control the lipid transfer in PPL, we conducted a systematic study of the influence of dwell time (i.e., duration of contact between tip and sample), humidity, and printing pressure on the outcome of PPL with phospholipids and discuss results in comparison to the more often studied dip-pen nanolithography with phospholipids. This is the first systematic study in phospholipid printing with PPL. Biocompatibility of the obtained substrates with up to two different ink compositions was demonstrated. The patterns are suitable to serve as a platform for mast cell activation experiments.

Polymer Pen Lithography-Fabricated DNA Arrays for Highly Sensitive and Selective Detection of Unamplified Ganoderma Boninense DNA

There is an increasing demand for lithography methods to enable the fabrication of diagnostic devices for the biomedical and agri-food sectors. In this regard, scanning probe lithography methods have emerged as a possible approach for this purpose, as they are not only convenient, robust and accessible, but also enable the deposition of “soft” materials such as complex organic molecules and biomolecules. In this report, the use of polymer pen lithography for the fabrication of DNA oligonucleotide arrays is described, together with the application of the arrays for the sensitive and selective detection of Ganoderma boninense, a fungal pathogen of the oil palm. When used in a sandwich assay format with DNA-conjugated gold nanoparticles, this system is able to generate a visually observable result in the presence of the target DNA. This assay is able to detect as little as 30 ng of Ganoderma-derived DNA without any pre-amplification and without the need for specialist laboratory equipment or training.

Nanocombinatorics with Cantilever-Free Scanning Probe Arrays

The effectiveness of combinatorial experiments is determined by the rate at which distinct experimental conditions can be prepared and interrogated. This has been particularly limiting at the intersection of nanotechnology and soft materials research, where structures are difficult to reliably prepare and materials are incompatible with conventional lithographic techniques. For example, studying nanoparticle-based heterogeneous catalysis or the interaction between biological cells and abiotic surfaces requires precise tuning of materials composition on the nanometer scale. Scanning probe techniques are poised to be major players in the combinatorial nanoscience arena because they allow one to directly deposit materials at high resolution without any harsh processing steps that limit material compatibility. The chief limitation of scanning probe techniques is throughput, as patterning with single probes is prohibitively slow in the context of large-scale combinatorial experiments. A recent paradigm shift circumvents this problem by fundamentally altering the architecture of scanning probes by replacing the conventionally used cantilever with a soft compliant film on a rigid substrate, a substitution that allows a densely packed array of probes to function in parallel in an inexpensive format. This is a major lithographic advance in terms of scalability, throughput, and versatility that, when combined with the development of approaches to actuate individual probes in cantilever-free arrays, sets the stage for scanning-probe-based tools to address scientific questions through nanocombinatorial studies in biology and materials science. In this review, we outline the development of cantilever-free scanning probe lithography and prospects for nanocombinatorial studies enabled by these tools.

Super-resolution interference lithography enabled by non-equilibrium kinetics of photochromic monolayers

Highly parallelized optical super-resolution lithography techniques are key for realizing bulk volume nanopatterning in materials. The majority of demonstrated STED-inspired lithography schemes are serial writing techniques. Here we use a recently developed model spirothiopyran monolayer photoresist to study the non-equilibrium kinetics of STED-inspired lithography systems to achieve large area interference lithography with super-resolved feature dimensions. The linewidth is predicted to increase with exposure time and the contrast is predicted to go through a maximum, resulting in a narrow window of optimum exposure. Experimental results are found to match with high quantitative accuracy. The low photoinhibition saturation threshold of the spirothiopyran renders it especially conducive for parallelized large area nanopatterning. Lines with 56 and 92 nm FWHM were obtained using serial and parallel patterning, respectively. Functionalization of surfaces with heterobifunctional PEGs enables diverse patterning of any desired chemical functionality on these monolayers. These results provide important insight prior to realizing a highly parallelized volume nanofabrication technique.

The non-equilibrium kinetics of spirothiopyran monolayers are studied to enable large area interference lithography with feature dimensions that circumvent the diffraction barrier.

Guided protein/cell patterning on superhydrophilic polymer brushes functionalized with mussel-inspired polydopamine coatings

A simple approach for preparing bicomponent polymer patterns was developed by coating polydopamine (PDA) on superhydrophilic poly(2-acryl-amido-2-methylpropane sulfonic acid) (PAMPS) brushes. Well-defined and versatile arrays of proteins and cells were achieved without harm to proteins and cells.

Protein micropatterns printed on glass: Novel tools for protein-ligand binding assays in live cells

Micrometer-sized patterns of proteins on glass or silica surfaces are in widespread use as protein arrays for probing with ligands or recombinant proteins. More recently, they have been used to capture the surface proteins of mammalian cells seeded onto them, and to arrange these surface proteins into pattern structures. Binding of small molecule ligands or of other proteins, transmembrane or intracellular, to these captured surface proteins can then be quantified. However, reproducible production of protein micropatterns on surfaces can be technically difficult. In this review, we outline the wide potential and the current practical uses of printed protein micropatterns in a historical overview, and we detail some potential pitfalls and difficulties from our own experience, as well as ways to circumvent them.

Polymer Pen Lithography with Lipids for Large-Area Gradient Patterns

Gradient patterns comprising bioactive compounds over comparably (in regard to a cell size) large areas are key for many applications in the biomedical sector, in particular, for cell screening assays, guidance, and migration experiments. Polymer pen lithography (PPL) as an inherent highly parallel and large area technique has a great potential to serve in the fabrication of such patterns. We present strategies for the printing of functional phospholipid patterns via PPL that provide tunable feature size and feature density gradients over surface areas of several square millimeters. By controlling the printing parameters, two transfer modes can be achieved. Each of these modes leads to different feature morphologies. By increasing the force applied to the elastomeric pens, which increases the tip-surface contact area and boosts the ink delivery rate, a switch between a dip-pen nanolithography (DPN) and a microcontact printing (μCP) transfer mode can be induced. A careful inking procedure ensuring a homogeneous and not-too-high ink-load on the PPL stamp ensures a membrane-spreading dominated transfer mode, which, used in combination with smooth and hydrophilic substrates, generates features with constant height, independently of the applied force of the pens. Ultimately, this allows us to obtain a gradient of feature sizes over a mm² substrate, all having the same height on the order of that of a biological cellular membrane. These strategies allow the construction of membrane structures by direct transfer of the lipid mixture to the substrate, without requiring previous substrate functionalization, in contrast to other molecular inks, where structure is directly determined by the printing process itself. The patterns are demonstrated to be viable for subsequent protein binding, therefore adding to a flexible feature library when gradients of protein presentation are desired.