Albert R. Liberski

Inkjet fabrication of hydrogel microarrays using in situ nanolitre-scale polymerisation

Polymer hydrogel microarrays were fabricated by inkjet printing of monomers and initiator, allowing up to 1800 individual polymer features to be printed on a single glass slide.

Microarrays of over 2000 hydrogels--identification of substrates for cellular trapping and thermally triggered release.

In this paper we describe an approach whereby over 2000 individual polymers were synthesized, in situ, on a microscope slide using inkjet printing. Subsequent biological analysis of the entire library allowed the rapid identification of specific polymers with the desired properties. Herein we demonstrate how this array of new materials could be used for the identification of polymers that allow cellular adherence, proliferation and then mild thermal release, for multiple cell lines, including mouse embryonic stem (mES) cells. The optimal, identified hydrogels were successfully scaled-up and demonstrated excellent cell viability after thermal detachment for all cell lines tested. We believe that this approach offers an avenue to the discovery of a specific thermal release polymer for every cell line.

Reactive inkjet printing of calcium alginate hydrogel porogens—a new strategy to open-pore structured matrices with controlled geometry

Taking advantage of inkjets ability to dispense uniform droplets in the picolitre/nanolitre ranges of volumes, we have generated reversible hydrogel porogen beads using reactive printing, which we use as templates for creating networks of pores with monomodally distributed pore sizes.

A Practical Approach to the Development of Inkjet Printable Functional Ionogels—Bendable, Foldable, Transparent, and Conductive Electrode Materials

Ionic liquid gels, or ionogels, are semi-conductive, flexible materials, offering a host of tunable physical properties, gaining an increasing level of scientific interest. One of the challenges of this emerging category of materials is that the structure-process-property relationships are still empirically driven. In this study, a simple, practical approach is laid out to prepare standardized libraries of these materials, for the purpose of selecting transparent, flexible conductive formulations that can be dispensed using inkjet printing. The net result of this was the optimization of a PEG-DMA ionogel formulation exhibiting an optical transparency that was greater than 94% from near-UV to near-IR from a 150 µm thick films, and a resistivity of 12.4 Ω · m.

Screening for polymorphs on polymer microarrays.

ReceiVed June 29, 2007 Introduction. The way in which compounds crystallize has been the subject of study for many centuries with perhaps the most classical example relating to tartaric acid. A current focal point in this area is the phenomenon of polymorphism. This arises because of two main considerations; first in terms of patent law, new crystal forms of a solid compound can be considered as innovations and can be protected as intellectual property (this crucial issue has promoted the intense search for new polymorphs). Second, and of more practical consideration, is the fact that specific crystal forms can alter the dissolution rate of a compound, and thus, the pharmokinetics of any drug are partially determined by the specific crystal form, an issue that also supports the patentability of a polymorph. Many polymorphs have been discovered serendipitously, but traditional methods of discovery and selection of polymorphic forms usually involve the variation of crystallization parameters such as temperature and solvent, and current high-throughput screens generally rely on variation of these parameters. Examples of well-known compounds for which new polymorphic forms have been discovered, after many years of work, include maleic acid (120 years after it was first crystallized) and aspirin, confirming McCrone’s often quoted pronouncement. However, fewer than 5% of compounds in the Cambridge Structural Database are reported to be polymorphic, whereas it is known from other studies that do not provide a full structure (e.g., spectroscopic, thermal, and microscopy studies) that more than 35% of known compounds show polymorphic behavior. Therefore new developments in high-throughput platforms for primary polymorph screening would be a valuable tool for the discovery of, as yet, uncharacterized forms. The substrates upon which crystals grow play a pivotal role in allowing selective growth. For example, calcium carbonate crystal growth can be easily “tuned” by interaction with different surfaces, allowing a range of specific structures to be generated. Organic compounds, however, are typically difficult to tune because their “packing” is much more temperamental. In the approach presented here, control over specific factors involved in the crystallization processes such as concentration and temperature were used, but the main variable was the surface upon which crystallization occurred. It is well-known that polymers can support the growth of specific types of crystals. However, the nature of the interactions between the polymer and the compound under investigation are not understood, and it is not possible to predict the specific polymorphic form generated by crystallization on a specific polymeric support. The technique described here provides a tool to better understand these types of interactions, as well as to reduce the amount of material needed to carry out a “fullpolymorphic screen”. The approach developed, related to that described by Kazarian, used polymer microarrays onto which solutions of small-molecules were applied and allowed to crystallize, which because of the size of the arrays, required only tiny amounts of solution. The resultant crystals underwent direct characterization on the microarray by optical and Raman microspectroscopy (Raman spectroscopy has been proven to be a valid tool to differentiate between polymorphic forms.). It should be noted that even though different crystal habit forms were found within the array these did not always correspond to different polymorphic forms according to Raman shifts. In general, organic materials tend to crystallize in less symmetric space groups than inorganic materials, a phenomenon which makes crystal habit a less efficient indicator of different polymorphic forms in organic materials than it is for inorganic materials. The first step in the process consisted of fabrication of the polymer microarrays. This approach consisted of hydrophobic patterning of a glass slide into three grids, each consisting of 8 × 16 hydrophilic “features”. A specific polymer was then deposited by piezo jet-printing 800 drops of each of the polymer solutions onto a specific hydrophilic feature (each drop was ∼30 μm in diameter, and therefore, ∼0.9 μL of a 1% polymer solution was deposited, equating to approximately 9 μg of polymer per spot). The polymers used in this study were synthesized or obtained commercially (see Supporting Information for full experimental details). Two solvents were used for inkjet printing: NMP and toluene. NMP was the dominant solvent used because it efficiently dissolved the majority of the library of polymers, whereas toluene was used for the more hydrophobic polymers (see Supporting Information). Each slide thus contained three 8 × 16 grids giving a total of 128 polymer spots with the area of each spot approximately 1.76 mm. Three well-known and broadly studied small molecules were used in this study: carbamazepine, sulfamethoxazole, and 2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (often termed ROY (red/orange/yellow) from the well-known colors of the different polymorphic forms). This choice was the result of the large number of polymorphic studies previously carried out on these compounds, which allowed us to compare our approach to previous reports. Mother liquors of the small molecules were printed onto the polymer * To whom correspondence should be addressed. Phone: +44(0) 131 650 4820. Fax: +44 (0) 131 650 6453. E-mail: Mark.bradley@ed.ac.uk. † University of Edinburgh. ‡ University of Southampton. J. Comb. Chem. 2008, 10, 24–27 24

Inkjet fabrication of polymer microarrays and grids—solving the evaporation problem

Polymer microarrays, consisting of either discrete features or a matrix of inter-crossed lines were directly fabricated in situ by inkjet printing individual monomers and initiator solutions in organic solvents through a film of oil, thereby allowing the rapid generation of a broad range of co-polymers, while solving the problem of selective monomer evaporation.

Laser printing mediated cell patterning

An approach for complex cell patterning, using laser printing, is described allowing essentially any cellular image or pattern to be rapidly fabricated.

Printed conductive features for DNA chip applications prepared on PET without sintering

We present here an innovative and cheap alternative for the preparation of conductive tracks printed on flexible polymer substrates at room temperature. For this purpose, we applied a combination of a Tollens reagent-based silver deposition and printed mask, using an office laser printer. The as-prepared conductive structures were used for DNA chip fabrication. The great advantage of the presented method is that the conductive features can be fabricated in a facile and inexpensive way, while maintaining the high flexibility to tailor the design to its application. The DNA chips showed the same response as well as sensitivity compared to chips made conventionally by photolithography or screen printing.

In Situ Nanoliter-Scale Polymer Fabrication for Flexible Cell Patterning

Drug-testing technologies, biosensor fabrication, tissue engineering, and basic biological research depend strongly on the patterning of live animal cells. Current techniques for controlling cellular adhesion are restricted with two primary limitations. Firstly, the complexity of the available patterns is very limited and, secondly, the pallet of materials that induce cellular patterning is exhaustible. Here, we demonstrate a method for computer-aided control of cell patterning using a scientific inkjet printer that yields a highly complex cellular pattern suitable for applications in regenerative medicine and rapid prototyping, and a strategy for using in situ polymerization for fabrication polymeric patterns directly on-chip.