Screening for Polymorphs on Polymer Microarrays

Heterogeneous nucleation of polymorphs on polymer surfaces: polymer-molecule interactions using a Coulomb and van der Waals model

The nucleation processes of acetaminophen on poly(methyl methacrylate) and poly(vinyl acetate) have been investigated and the mechanisms of the processes are studied. This is achieved by a combination of theoretical models and computational investigations within the framework of a modified QM/MM method; a Coulomb-van der Waals model. We have combined quantum mechanical computations and electrostatic models at the atomistic level for investigating the stability of different orientations of acetaminophen on the polymer surfaces. Based on the Coulomb-van der Waals model, we have determined the most stable orientation to be a flat orientation, and the strongest interaction is seen between poly(vinyl acetate) and the molecule in a flat orientation in vacuum.

Rapid Nanogram Scale Screening Method of Microarrays to Evaluate Drug-Polymer Blends Using High-Throughput Printing Technology

A miniaturized, high-throughput assay was optimized to screen polymer-drug solid dispersions using a 2-D Inkjet printer. By simply printing nanoliter amounts of polymer and drug solutions onto an inert surface, drug/polymer microdots of tunable composition were produced in an easily addressable microarray format. The amount of material printed for each dried spot ranged from 25 ng to 650 ng. These arrays were used to assess the stability of drug/polymer dispersions with respect to recrystallization, using polarized light microscopy. One array with a panel of 6 drugs formulated at different ratios with a poly(vinylpyrrolidone-vinyl acetate) (PVPVA) copolymer was developed to estimate a possible bulk (gram-scale) approximation threshold from the final printed nanoamount of formulation. Another array was printed at a fixed final amount of material to establish a literature comparison of one drug formulated with different commercial polymers for validation. This new approach may offer significant efficiency in pharmaceutical formulation screening, with each experiment in the nanomicro-array format requiring from 3 up to 6 orders of magnitude lower amounts of sample than conventional screening methods.

Towards exhaustive and automated high-throughput screening for crystalline polymorphs

Methods capable of exhaustively screening for crystal polymorphism remain an elusive goal in solid-state chemistry. Particularly promising among the new generation of approaches is polymer-induced heteronucleation (PIHn), a tool utilizing hundreds of unique polymers for granting kinetic access to polymorphs. Here PIHn is redeployed in a high density format in which 288 distinct polymers, each acting as a heteronucleant, are arrayed on one substrate. This format allows determining the outcome of thousands of crystallizations in an automated fashion with only a few milligrams of sample. This technology enables the study of a broader range of targets, including preclinical candidates, facilitating determination of polymorphism propensity much earlier in the drug development process. Here the efficacy of this approach is demonstrated using four pharmaceutically relevant compounds: acetaminophen, tolfenamic acid, ROY, and curcumin.

Polymer templating of supercooled indomethacin for polymorph selection

Reported here is a relatively simple technique for polymorph screening of pharmaceutical compounds that are thermally stable. Polymer libraries have previously been used as surfaces to influence, or direct, the crystalline form adopted by an active pharmaceutical ingredient on crystallization from solution. In this current work, we demonstrate the polymorph-directing effect of homopolymer surfaces in the absence of solvent by recrystallization from the supercooled melt. When the nonsteroidal anti-inflammatory drug indomethacin is melted, cooled, and subsequently reheated above its glass transition temperature on an untreated surface, it has a proclivity to crystallize as its δ polymorph. On certain polymer surfaces, however, it preferentially crystallizes as the α polymorph, as a direct result of polymer templating. The method is well-suited to implementation in multiwell plate formats requiring only small amounts of material and enabling multiple experiments to be carried out in parallel with samples readily characterized using X-ray powder diffraction.

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.