We describe a microfluidic platform comprised of 48 wells to screen for pharmaceutical salts. Solutions of pharmaceutical parent compounds (PCs) and salt formers (SFs) are mixed on-chip in a combinatorial fashion in arrays of 87.5-nanolitre wells, which constitutes a drastic reduction of the volume of PC solution needed per condition screened compared to typical high throughput pharmaceutical screening approaches. Nucleation and growth of salt crystals is induced by diffusive and/or convective mixing of solutions containing, respectively, PCs and SFs in a variety of solvents. To enable long term experiments, solvent loss was minimized by reducing the thickness of the absorptive polymeric material, polydimethylsiloxane (PDMS), and by using solvent impermeable top and bottom layers. Additionally, well isolation was enhanced via the incorporation of pneumatic valves that are closed at rest. Brightfield and polarized light microscopy and Raman spectroscopy were used for on-chip analysis and crystal identification. Using a gold-coated glass substrate and minimizing the thickness of the PDMS control layer drastically improved the signal-to-noise ratio for Raman spectra. Two drugs, naproxen (acid) and ephedrine (base), were used for validation of the platform's ability to screen for salts. Each PC was mixed combinatorially with potential SFs in a variety of solvents. Crystals were visualized using brightfield polarized light microscopy. Subsequent on-chip analyses of the crystals with Raman spectroscopy identified four different naproxen salts and five different ephedrine salts.
Here we present a microfluidic platform comprised of 48 wells to screen for polymorphs of active pharmaceutical ingredients (API) through antisolvent crystallization. API solutions and anti-solvents are precisely metered in various volumetric ratios (range from 50 : 10 to 10 : 50), and mixed via diffusive mixing on-chip. Optical microscopy and Raman spectroscopy were used to analyze the resultant solids. The small volumes (37 nL) and the ability to screen a wide range of supersaturations through diffusive mixing make this platform especially useful for solid form development at discovery and early development stages in pharmaceutical industry. To validate this microfluidic approach, we conducted on-chip antisolvent crystallization using indomethacin. Solvent choice, supersaturation level, and antisolvent-to-solution ratio were found to affect the resulting crystal form of the solids prepared on chip. We modelled the representative time-dependent concentration profiles during the mixing of the antisolvent and API solutions. Combining this analysis with solubility data yielded spatiotemporal supersaturation profiles, which we correlated with solid formation as observed experimentally. Experimental section Chip assemblyThe crystallization platform is comprised of a thin multilayer polydimethylsiloxane (PDMS, General Electric RTV 650 Part A/B) chip fabricated using standard multilayer soft lithographic procedures reported previously 23,24 with some modifications. The thickness of the control layer was reduced to 70 mm by spin
We describe a microfluidic approach to screen for the formation of cocrystalline solid forms of pharmaceutical parent compounds (PCs). Saturated solutions of PCs and of cocrystal formers dissolved in a variety of solvents are precisely metered in arrays of 48 wells to enable the combinatorial mixing of all possible combinations. Key characteristics of the microfluidic approach, including small quantities (∼240 μg/48 conditions), the ability to generate and screen 48 unique conditions per chip, and the ability to identify solid forms on-chip via Raman spectroscopy, enable solid form screening very early in the drug development process. In contrast, current approaches require on the order of ∼240 mg for 48 conditions, thus delaying solid form screening to later stages of the drug development. Sequential screening experiments using caffeine as the model compound were conducted to validate the on-chip approach reported here. Preliminary screens were executed to identify conditions with the highest propensity for crystallization and to identify the cocrystal formers (CCFs) resulting in formation of cocrystals via on-chip Raman spectroscopy. Next, the identified, promising conditions were replicated to confirm reproducibility and consistency of the on-chip outcomes. Nine cocrystals of caffeine were identified in this way.
We describe a microfluidic platform to screen for salt forms of pharmaceutical compounds (PCs) via controlled evaporation. The platform enables on-chip combinatorial mixing of PC and salt former solutions in a 24-well array (~200 nL/well), which is a drastic reduction in the amount of PC needed per condition screened compared to traditional screening approaches that require ~100 μL/well. The reduced sample needs enable salt screening at a much earlier stage in the drug development process, when only limited quantities of PCs are available. Compatibility with (i) solvents commonly used in the pharmaceutical industry, and (ii) Raman spectroscopy for solid form identification was ensured by using a hybrid microfluidic platform. A thin layer of elastomeric PDMS was utilized to retain pneumatic valving capabilities. This layer is sandwiched between layers of cyclic-olefin copolymer, a material with low air and solvent permeability and low Raman background to yield a physically rigid and Raman compatible chip. A solvent-impermeable thiolene layer patterned with evaporation channels permits control over the rate of solvent evaporation. Control over the rate of solvent evaporation (2-15 nL h(-1)) results in consistent, known rates of increase in the supersaturation levels attained on-chip, and increases the probability for crystalline solids to form. The modular nature of the platform enables on-chip Raman and birefringence analysis of the solid forms. Model compounds, tamoxifen and ephedrine, were used to validate the platform's ability to screen for salts. On-chip Raman analysis helped to identify six different salts each of tamoxifen and ephedrine.
Microfluidic platforms provide several advantages for liquid-liquid extraction (LLE) processes over conventional methods, for example with respect to lower consumption of solvents and enhanced extraction efficiencies due to the inherent shorter diffusional distances. Here, we report the development of polymer-based parallel-flow microfluidic platforms for LLE. To date, parallel-flow microfluidic platforms have predominantly been made out of silicon or glass due to their compatibility with most organic solvents used for LLE. Fabrication of silicon and glass-based LLE platforms typically requires extensive use of photolithography, plasma or laser-based etching, high temperature (anodic) bonding, and/or wet etching with KOH or HF solutions. In contrast, polymeric microfluidic platforms can be fabricated using less involved processes, typically photolithography in combination with replica molding, hot embossing, and/or bonding at much lower temperatures. Here we report the fabrication and testing of microfluidic LLE platforms comprised of thiolene or a perfluoropolyether-based material, SIFEL, where the choice of materials was mainly guided by the need for solvent compatibility and fabrication amenability. Suitable designs for polymer-based LLE platforms that maximize extraction efficiencies within the constraints of the fabrication methods and feasible operational conditions were obtained using analytical modeling. To optimize the performance of the polymer-based LLE platforms, we systematically studied the effect of surface functionalization and of microstructures on the stability of the liquid-liquid interface and on the ability to separate the phases. As demonstrative examples, we report (i) a thiolene-based platform to determine the lipophilicity of caffeine, and (ii) a SIFEL-based platform to extract radioactive copper from an acidic aqueous solution.
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