Study of the solvent-dependent crystal shape of theophylline using constant chemical potential molecular dynamics simulations

The crystal habit of an organic crystalline material impacts its properties, processing, and performance, especially in pharmaceuticals. In solution crystallization, solvents play a crucial role in modulating the crystal habits by interacting with the different growing facets - either enhancing or inhibiting the growth of specific facets. Thus, an in-depth understanding of the role of the solvent in crystal shape selection is of paramount importance for the design and growth of crystals. In this work, we used constant chemical potential molecular dynamics (CμMD) to simulate the growth of theophylline crystals in solvents with decreasing polarity, i.e. water, isopropyl alcohol, and dimethylformamide. Our results indicate that as the polarity of the solvent increases, theophylline crystallizes into rod-shaped crystals; the aspect ratio is modulated by the relative growth of the (001) and (010) facets. Furthermore, solvent profile analyses revealed that the desolvation of the crystal facets plays a major role in the growth process.

Ultrasound induced grain refinement of crystallization in evaporative saline droplets

We investigate the effect of ultrasound on the evaporation and crystallization of sessile NaCl solution droplets which were positioned in traveling or standing wave ultrasound field. The experimental results indicated that the ultrasound field can significantly accelerate the evaporation rate of the sessile droplets and refine the crystal grains. By adjusting the distance between the sessile droplets and the ultrasound emitter, it is found that, in traveling wave ultrasound field, the sessile droplet evaporation time and the time for the appearance of NaCl grains exhibited a fluctuating increase as the droplet-emitter distance increased. While in the standing wave ultrasound, the sessile droplet evaporation rate increases with the increasing droplet-emitter distance. Overall, the traveling wave ultrasound field has a stronger effect on grain refinement of the sessile droplets than the standing wave ultrasound field. The grain refinement is attributed to the decrease of critical nucleation radius caused by ultrasound energy and the increase of the nucleation rate caused by the accelerated evaporation rate. In addition, the breakage of grains caused by ultrasonic cavitation would also lead to grain refinement.

Separation performance and agglomeration behavior analysis of solution crystallization in food engineering

This study employed solution crystallization in food engineering to prepare a high-purity vitamin intermediate, optimize its crystal morphology and regulate its particle size distribution. Model analysis was performed to investigate the quantitative correlations between the process variables and target parameters, indicating the substantial effect of temperature on separation performance. Under optimal conditions, the product purity exceeded 99.5%, which meets the requirement of the subsequent synthesis process. A high crystallization temperature reduced the agglomeration phenomenon and increased particle liquidity. Herein, we also proposed a temperature cycling strategy and a gassing crystallization routine to optimize the particle size. The results illustrated that the synergistic control of temperature and gassing crystallization could substantially improve the separation process. Overall, based on a high separation efficiency, this study combined model analysis and process intensification pathways to explore the process parameters on product properties such as purity, crystal morphology, and particle size distribution.

Antisolvent Crystallization of Telmisartan Using Stainless-Steel Micromixing Membrane Contactors

Controlled continuous crystallization of the active pharmaceutical ingredient (API) telmisartan (TEL) has been conducted from TEL/DMSO solutions by antisolvent crystallization in deionized water using membrane micromixing contactors. The purpose of this work was to test stainless-steel membranes with ordered 10 μm pores spaced at 200 μm in a stirred-cell (batch, LDC-1) and crossflow (continuous, AXF-1) system for TEL formation. By controlling the feed flow rate of the API and solvent, through the membrane pores as well as the antisolvent flow, it was possible to tightly control the micromixing and with that to control the crystal nucleation and growth. Batch crystallization without the membrane resulted in an inhomogeneous crystallization process, giving a mixture of crystalline and amorphous TEL materials. The rate of crystallization was controlled with a higher DMSO content (4:1 DMSO/DI water), resulting in slower crystallization of the TEL material. Both membrane setups, stirred batch and the crossflow, yielded the amorphous TEL particles when deionized water was used, while a crystalline material was produced when a mixture of DI water and DMSO was used.

Machine Learning-Derived Correlations for Scale-Up and Technology Transfer of Primary Nucleation Kinetics

Scaling up and technology transfer of crystallization processes have been and continue to be a challenge. This is often due to the stochastic nature of primary nucleation, various scale dependencies of nucleation mechanisms, and the multitude of scale-up approaches. To better understand these dependencies, a series of isothermal induction time studies were performed across a range of vessel volumes, impeller types, and impeller speeds. From these measurements, the nucleation rate and growth time were estimated as parameters of an induction time distribution model. Then using machine learning techniques, correlations between the vessel hydrodynamic features, calculated from computational flow dynamic simulations, and nucleation kinetic parameters were analyzed. Of the 18 machine learning models trained, two models for the nucleation rate were found to have the best performance (in terms of % of predictions within experimental variance): a nonlinear random Forest model and a nonlinear gradient boosting model. For growth time, a nonlinear gradient boosting model was found to outperform the other models tested. These models were then ensembled to directly predict the probability of nucleation, at a given time, solely from hydrodynamic features with an overall root mean square error of 0.16. This work shows how machine learning approaches can be used to analyze limited datasets of induction times to provide insights into what hydrodynamic parameters should be considered in the scale-up of an unseeded crystallization process.

Effect of organic solvents on calcium minodronate crystal morphology in aqueous solution: an experimental and theoretical study

The influence of nine organic solvents on the crystal morphology of calcium minodronate (Ca(Min)₂) was investigated by experimental investigations and molecular simulations. Hirshfeld analysis was used to reveal the intermolecular interactions, and the modified attachment energy (AE) model was applied to constructing the Ca(Min)₂-organic-water model in different organic-water solvents. The surface structure and the mass density profile were demonstrated and analyzed. The results showed that there were different adsorption conditions in different organic-water solvents. Furthermore, it was found that the (2 0 0)/(1 1 0) side ratio of Ca(Min)₂ crystal had a linear relationship with the volume of organic solvent and had a certain correlation with some solvent properties. It is believed that the research developed in this work could have a promising application in prediction of Ca(Min)₂ crystal morphology and could give guidance in the selection of organic solvents to control the desirable crystal morphology.

Fractals for the Sustainable Design of Engineered Particulate Systems

The engineering properties of particulate materials are the collective manifestation of interactions among their constituent particles and are structures within which particles adopt their spatial arrangement. For the first time in the literature, this paper employs an extended concept of ‘fractals’ to show that materials constituting particles of a certain size can be rationalized in three universal fractals. Within each fractal, materials build repeatable, reproducible, and predictable traits, and exhibit the stress-strain behaviors of nondifferentiable, self-similar trajectories. We present experimental evidence for such repeatable traits by subjecting six different particulate materials to static undrained isotropic, static undrained anisotropic, and cyclic undrained isotropic stresses. This paper shows that universal fractals are associated with fractal structures; herein, we explore the matters that influence their spatial arrangement. Within the context of sustainable design, ways of engineering natural particulate systems to improve a product’s physical and hydromechanical properties are already well established. In this review, a novel extended concept of fractals is introduced to inform the biomimetic design of particulate systems, to show how biomimicry can benefit in preserving general behavioral traits, and how biomimicry can offer predicated forms, thereby enhancing the design efficiency. To pursue such an ideal, processes that lead to the engineering of natural materials should not compromise their loyalty to the parent universal fractal.

Integrated Purification and Formulation of an Active Pharmaceutical Ingredient via Agitated Bed Crystallization and Fluidized Bed Processing

Integrated API and drug product processing enable molecules with high clinical efficacy but poor physicochemical characteristics to be commercialized by direct co-processing with excipients to produce advanced multicomponent intermediates. Furthermore, developing isolation-free frameworks would enable end-to-end continuous processing of drugs. The aim of this work was to purify a model API (sodium ibuprofen) and impurity (ibuprofen ethyl ester) system and then directly process it into a solid-state formulation without isolating a solid API phase. Confined agitated bed crystallization is proposed to purify a liquid stream of impure API from 4% to 0.2% w/w impurity content through periodic or parallelized operations. This stream is combined with a polymer solution in an intermediary tank, enabling the API to be spray coated directly onto microcrystalline cellulose beads. The spray coating process was developed using a Design of Experiments approach, allowing control over the drug loading efficiency and the crystallinity of the API on the beads by altering the process parameters. The DoE study indicated that the solvent volume was the dominant factor controlling the drug loading efficiency, while a combination of factors influenced the crystallinity. The products from the fluidized bed are ideal for processing into final drug products and can subsequently be coated to control drug release.

Crystal Structure Determination and Hirshfeld Analysis of a New Alternariol Packing Polymorph

A new polymorph of the mycotoxin alternariol is reported and characterized by single crystal X-ray diffraction. Structural data, Hirshfeld surface analysis, and 2D fingerprint plots are used to compare differences in the intermolecular interactions of the orthorhombic Pca21 Form I (previously reported) and the monoclinic P21/c Form II (herein reported). The polymorphs have small differences in planarity-7.55° and 2.19° between the terminal rings for Form I and Form II, respectively-that brings about significant differences in the crystal packing and O-H … H interactions.

Significance of atomic-scale defects in flexible surfaces on local solvent and ion behaviour

Many factors can affect the course of heterogeneous nucleation, such as surface chemistry, flexibility and topology, substrate concentration and solubility. Atomic-scale defects are rarely investigated in detail and are often considered to be unimportant surface features. In this work, we set out to investigate the significance of atomic-scale defects in a flexible self-assembled monolayer surface for the behaviour of clusters of Ca²⁺ and CO₃^2- ions in water. To this end, we use molecular dynamics simulations to estimate the diffusion coefficients of ion clusters at different topological surface features and obtain ionic radial distribution functions around features of interest. Well-tempered metadynamics is used to gain insight into the free energy of ions around selected surface defects. We find that certain defects, which we refer to as active defects, can impair ionic surface diffusion, as well as affect the diffusion of ions in close proximity to the surface feature in question. Our findings suggest that this effect can result in an ability of such topological features to promote ion clustering and increase local ionic concentration at specific surface sites. The work reported here shows how the presence of small atomic-scale defects can affect the role of a surface in the process of heterogeneous nucleation and contributes towards a rational definition of surfaces as effective nucleating agents.

Investigation of Operation Strategy Based on Solution pH for Improving the Crystal Quality Formed during Reactive Crystallization of l-Aspartic Acid

The production of crystalline particles with a thick and low degree of agglomeration is required because the agglomerated crystals with thin primary particles, which are frequently formed during reactive crystallization, deteriorate the crystal size distribution (CSD) of the final product due to their fragile morphology. This study aimed to develop an operation strategy for improving the degree of agglomeration and thickness of crystalline particles in the reactive crystallization considering the effect of the solution pH using l-aspartic acid as an experimental system. The scanning electron microscopy observations showed that the thickness of primary particles which form agglomerated crystals could be increased by operating the crystallization under low solution pH conditions. In contrast, it was found that operating the crystallization under high solution pH led to a decrease in the nucleation rate of crystalline particles, which resulted in a decrease in the degree of agglomeration. Then, an operation method, that is, changing the addition method of feed solutions to overcome the trade-off between the thickness and degree of agglomeration, was proposed by considering the effect of solution pH. Consequently, crystalline particles with a narrow CSD could be successfully obtained using the proposed method due to the suppression of the agglomeration and increase of the thickness. Therefore, the development of the operation strategy based on the effect of the solution pH on the degree of agglomeration and thickness is important to produce crystalline particles with improved CSD in reactive crystallization.

The role of phosphoric acid in the crystallization of lenalidomide form DH–water system

In this work, we studied the effect of phosphoric acid (0–10 v%), acting as an additive, on the thermodynamics and nucleation kinetics of the lenalidomide (LDM) latest form (DH).

Energy framework and solubility: a new predictive model in the evaluation of the structure–property relationship of pharmaceutical solid forms

Crystal structures with lower interaction energy tend to present higher aqueous solubility.

Recent Progress of Antisolvent Crystallization

Antisolvent crystallization is a significant unit operation in the pharmaceutical industry, especially on drug crystal properties optimization. This paper firstly highlights the applications of antisolvent crystallization in crystal engineering. Antisolvent...

Optimal Operation of an Oscillatory Flow Crystallizer: Coupling Disturbance and Stability

In the process of industrial crystallization, it is always difficult to balance the secondary nucleation rate and metastable zone width (MSZW). Herein, we report an experimental and numerical study for the cooling crystallization of paracetamol in an oscillatory flow crystallizer (OFC), finding the optimal operating conditions for balancing the secondary nucleation rate and MSZW. The results show that the MSZW decreases with the increase of oscillation Reynolds number (Re _o). Compared to the traditional stirring system, the OFC has an MSZW three times larger than that of the stirring system under a similar power density of consumption. With the numerical simulation, the OFC can produce a stable space environment and instantaneous strong disturbance, which is conducive to the crystallization process. Above all, a high Re _o is favorable to produce a sufficient nucleation rate, which may inevitably constrict the MSZW to a certain degree. Then, the optimization strategy of the operating parameter (Re _o) in the OFC is proposed.

Ultrasound-assisted solution crystallization of fotagliptin benzoate: Process intensification and crystal product optimization

The ultrasound-assisted crystallization process has promising potentials for improving process efficiency and modifying crystalline product properties. In this work, the crystallization process of fotagliptin benzoate methanol solvate (FBMS) was investigated to improve powder properties and downstream desolvation/drying performance. The direct cooling/antisolvent crystallization process was conducted and then optimized with the assistance of ultrasonic irradiation and seeding strategy. Direct cooling/antisolvent crystallization and seeding crystallization processes resulted in needle-like crystals which are undesirable for downstream processing. In contrast, the ultrasound-assisted crystallization process produced rod-like crystals and reduced the crystal size to facilitate the desolvation of FBMS. The metastable zone width (MSZW), induction time, crystal size, morphology, and process yield were studied comprehensively. The results showed that both the seeding and ultrasound-assisted crystallization process (without seeds) can improve the process yield and the ultrasound could effectively reduce the crystal size, narrow the MSZW, and shorten the induction time. Through comparing the drying dynamics of the FBMS, the small rod-shaped crystals with a mean size of 9.6 μm produced by ultrasonic irradiation can be completely desolvated within 20 h, while the desolvation time of long needle crystals with an average size of about 157 μm obtained by direct cooling/antisolvent crystallization and seeding crystallization processes is more than 80 h. Thus the crystal size and morphology were found to be the key factors affecting the desolvation kinetics and the smaller size produced by using ultrasound can benefit the intensification of the drying process. Overall, the ultrasound-assisted crystallization showed a full improvement including crystal properties and process efficiency during the preparation of fotagliptin benzoate desolvated crystals.

Computer Aided Design of Solvent Blends for Hybrid Cooling and Antisolvent Crystallization of Active Pharmaceutical Ingredients

Choosing a solvent and an antisolvent for a new crystallization process is challenging due to the sheer number of possible solvent mixtures and the impact of solvent composition and crystallization temperature on process performance. To facilitate this choice, we present a general computer aided mixture/blend design (CAMbD) formulation for the design of optimal solvent mixtures for the crystallization of pharmaceutical products. The proposed methodology enables the simultaneous identification of the optimal process temperature, solvent, antisolvent, and composition of solvent mixture. The SAFT-γ Mie group-contribution approach is used in the design of crystallization solvents; based on an equilibrium model, both the crystal yield and solvent consumption are considered. The design formulation is implemented in gPROMS and applied to the crystallization of lovastatin and ibuprofen, where a hybrid approach combining cooling and antisolvent crystallization is compared to each method alone. For lovastatin, the use of a hybrid approach leads to an increase in crystal yield compared to antisolvent crystallization or cooling crystallization. Furthermore, it is seen that using less volatile but powerful crystallization solvents at lower temperatures can lead to better performance. When considering ibuprofen, the hybrid and antisolvent crystallization techniques provide a similar performance, but the use of solvent mixtures throughout the crystallization is critical in maximizing crystal yields and minimizing solvent consumption. We show that our more general approach to rational design of solvent blends brings significant benefits for the design of crystallization processes in pharmaceutical and chemical manufacturing.

Polymorphic forms of antiandrogenic drug nilutamide: structural and thermodynamic aspects

Attempts to obtain new cocrystals of nonsteroidal antiandrogenic drug nilutamide produced alternative polymorphic forms of the compound (Form II and Form III) and their crystal structures were elucidated by single-crystal X-ray diffraction. Apart from the cocrystallization technique, lyophilization was found to be an effective strategy for achieving polymorph control of nilutamide, which was difficult to obtain by other methods. The physicochemical properties and relative stability of the commercial Form I and newly obtained Form II were comprehensively investigated by a variety of analytical methods (thermal analysis, solution calorimetry, solubility, and sublimation), whereas for Form III, only a handful of experimental parameters were obtained due to the elusive nature of the polymorph. Form I and Form II were found to be monotropically related, with Form I being confirmed as the thermodynamically most stable solid phase. In addition, the performance of different DFT-D and semi-empirical schemes for lattice energy calculation and polymorph energy ranking was compared and analysed. Lattice energy calculations using periodic DFT at B3LYP-D3/6-31(F+)G(d,p) and PBEh-3c/def2-mSVP levels of theory were found to provide the most accurate lattice energy values for Form I against experimental data, while PIXEL and PBEh-3c/def2-mSVP were the only methods that predicted the correct order of stability of Forms I and II.

Controlling the aqueous growth of urea crystals with different growth inhibitors: a molecular-scale study

Molecular scale understanding of the mechanism of solution-mediated nucleation and the growth of crystalline materials in the presence of growth inhibitors together with the process parameters continues to attract the interest of the scientific community though much headway has been made in recent years. Growth inhibitors can be added to solution of a crystallizing parent molecule to alter the rate of growth of different crystal faces, size and shape of the crystalline materials. In this work, we investigated the effects of a number of shape-controlling inhibitors, such as acetone, biuret and biurea, on the growth kinetics of the various faces of aqueous-grown urea crystals as a means to predictably control the crystal growth morphology. We combined the adsorption energy landscape of various auxiliaries with the kinetics of the molecular growth processes to develop an analytical model to compute the rate of growth as a function of supersaturation and the additive concentration. The model relates the kinetic and thermodynamic aspects of the adsorption of the solute, solvent and additive to provide a quantitative description of the crystal growth. Ab initio periodic dispersion-corrected density functional theory using the hybrid exchange-correlation functional was employed to determine the interfacial structure of the adsorption of various auxiliaries at crystalline surfaces. The calculated adsorption energies of different auxiliaries were employed to examine the role played by these auxiliaries during the aqueous crystallization of urea crystals containing small amounts of additives. Our results showed that the growth of (110), (111) and (1̄1̄1̄) faces were nearly unaltered by the addition of moderate amounts of acetone as it has lower adsorption energies with the surfaces of these faces. Nevertheless, the presence of acetone in the solution reasonably impeded the growth of the (001) face. The addition of biuret or biurea in the solution led to a higher adsorption energy at (001) and (111) faces. Consequently, the low concentration of these additives severely obstructed the growth of (001) and (111) faces as most of the adsorption sites were occupied by these additives. On the other hand, these additives were weakly adsorbed at the (110) face and, hence, the growth of the (110) face largely remained unaltered. Moreover, unlike biuret, biurea considerably inhibited the growth of the (1̄1̄1̄) face. Our results are in agreement with the experimental and computational results reported in the literature.

Application of PAT-Based Feedback Control Approaches in Pharmaceutical Crystallization

Crystallization is one of the important unit operations for the separation and purification of solid products in the chemical, pharmaceutical, and pesticide industries, especially for realizing high-end, high-value solid products. The precise control of the solution crystallization process determines the polymorph, crystal shape, size, and size distribution of the crystal product, which is of great significance to improve product quality and production efficiency. In order to develop the crystallization process in a scientific method that is based on process parameters and data, process analysis technology (PAT) has become an important enabling platform. In this paper, we review the development of PAT in the field of crystallization in recent years. Based on the current research status of drug crystallization process control, the monitoring methods and control strategies of feedback control in the crystallization process were systematically summarized. The focus is on the application of model-free feedback control strategies based on the solution and solid information collected by various online monitoring equipment in product engineering, including improving particle size distribution, achieving polymorphic control, and improving purity. In this paper, the challenges of feedback control strategy in the crystallization process are also discussed, and the development trend of the feedback control strategy has been prospected.

Effect of Process Conditions on Particle Size and Shape in Continuous Antisolvent Crystallisation of Lovastatin

Lovastatin crystals often exhibit an undesirable needle-like morphology. Several studies have shown how a needle-like morphology can be modified in antisolvent crystallisation with the use of additives, but there is much less experimental work demonstrating crystal shape modification without the use of additives. In this study, a series of unseeded continuous antisolvent crystallisation experiments were conducted with the process conditions of supersaturation, total flow rate, and ultrasound level being varied to determine their effects on crystal size and shape. This experimental work involved identifying acetone/water as the most suitable solvent/antisolvent system, assessing lovastatin nucleation behaviour by means of induction time measurements, and then designing and implementing the continuous antisolvent crystallisation experiments. It was found that in order to produce the smallest and least needle-like particles, the maximum total flow rate and supersaturation had to be combined with the application of ultrasound. These results should aid development of pharmaceutical manufacturing processes where the ability to control particle size and shape would allow for optimisation of crystal isolation and more efficient downstream processing.

Component Quantification in Solids with the Mixture Analysis Using References Method

Quantifying components in solid mixtures composed of the same chemical species exhibiting different physical forms represents a difficult challenge in many areas of chemistry. The development of small-molecule active pharmaceutical ingredients (APIs) is a classic example. APIs predominantly exhibit polymorphism and the propensity to form solvates and hydrates. The various API phases typically display different physical properties affecting chemical stability, processability, and bioperformance. Accordingly, API development critically relies on characterizing and quantifying the relevant API forms in complex mixtures in the presence of each other and in the presence of excipients. Presented here is a new solid-state-NMR-based quantification method for components in solid mixtures: mixture analysis using references (MAR). The method utilizes weighted pure component reference spectra in a linear combination fitting procedure to reproduce the corresponding mixture spectrum. The results yield the respective component contributions to the mixture composition. Using several model systems of varying complexity, the applicability and performance of the MAR analysis utilizing ¹³C and ¹⁹F cross-polarization magic-angle-spinning data are evaluated. Finally, the MAR method is compared to one of the most commonly applied traditional quantification methods. The results demonstrate that MAR performs with the same high accuracy as conventional methods. However, MAR exhibits clear efficiency advantages over conventional methods by requiring significantly less overall time (experimental and computational) and displaying remarkable robustness and general applicability. The MAR quantification protocol as presented here can easily be applied to nonpharmaceutical molecular systems in other branches of chemistry.

Antimicrobial Activities of Highly Bioavailable Organic Salts and Ionic Liquids from Fluoroquinolones

As the development of novel antibiotics has been at a halt for several decades, chemically enhancing existing drugs is a very promising approach to drug development. Herein, we report the preparation of twelve organic salts and ionic liquids (OSILs) from ciprofloxacin and norfloxacin as anions with enhanced antimicrobial activity. Each one of the fluoroquinolones (FQs) was combined with six different organic hydroxide cations in 93-100% yield through a buffer-assisted neutralization methodology. Six of those were isomorphous salts while the remaining six were ionic liquids, with four of them being room temperature ionic liquids. The prepared compounds were not toxic to healthy cell lines and displayed between 47- and 1416-fold more solubility in water at 25 and 37 °C than the original drugs, with the exception of the ones containing the cetylpyridinium cation. In general, the antimicrobial activity against Klebsiella pneumoniae was particularly enhanced for the ciprofloxacin-based OSILs, with up to ca. 20-fold decreases of the inhibitory concentrations in relation to the parent drug, while activity against Staphylococcus aureus and the commensal Bacillus subtilis strain was often reduced. Depending on the cation-drug combination, broad-spectrum or strain-specific antibiotic salts were achieved, potentially leading to the future development of highly bioavailable and safe antimicrobial ionic formulations.

Antibiotic eluting poly(ester urea) films for control of a model cardiac implantable electronic device infection

Cardiac implantable electronic device (CIED) infections acquired during or after surgical procedures are a major complication that are challenging to treat therapeutically, resulting in chronic and sometimes fatal infections. Localized delivery of antibiotics at the surgical site could be used to supplement traditional systemic administration as a preventative measure. Herein, we investigate a cefazolin-eluting l-valine poly(ester urea) (PEU) films as a model system for localized antibiotic delivery for CIEDs. Poly(1-VAL-8) PEU was used to fabricate a series of antibiotic-loaded films with varied loading concentrations (2%, 5%, 10% wt/wt) and thicknesses (40 µm, 80 µm, 140 µm). In vitro release measurements show thickness and loading concentration influence the amount and rate of cefazolin release. Group 10%-140 µm (load-thickness) showed 22.5% release of active pharmaceutical ingredient (API) in the first 24 h and 81.2% of cumulative percent release through day 14 and was found most effective in bacterial clearance in vitro. This group was also effective in clearing a bacterial infection in a model in vivo rat study while eliciting a limited inflammatory response. Our results suggest the feasibility of cefazolin-loaded PEU films as an effective sustained release matrix for localized delivery of antibiotics. SIGNIFICANCE STATEMENT: Implant-associated infections acquired during surgical procedures are a major complication that have proven a challenge to treat clinically, resulting in chronic and sometimes fatal infections. In this manuscript, we investigate an antibiotic-eluting L-valine poly(ester urea) (PEU) films as a model system for localized delivery of cefazolin. Significantly, we demonstrate a wide variation in temporal delivery and dosing within this family of PEUs and show that the delivery can be extended by varying the film thickness. The in vivo results show efficacy in an infected wound model and suggest antibiotic loaded PEU films function as an effective sustained release matrix for localized delivery of antibiotics across a number of clinical indications.

The Steps from Batchwise to Continuous Crystallization for a Fine Chemical: A Case Study

Many processes to produce fine chemicals and precursors of pharmaceuticals are still operated in batchwise mode. However, recently, more producers have taken a change to continuous operation mode into consideration, performing studies and trials on such a change, while some have even already exchanged their production mode from batchwise to continuous operation. In this paper, the stepwise development from an initial idea to industrial implementation via laboratory testing and confirmation is revealed through the example of an organic fine chemical from the perspective of a crystallization plant manufacturer. We begin with the definition of the objectives of the project and a brief explanation of the advantages of continuous operation and the associated product properties. The results of the laboratory tests, confirming the assumptions made upfront, are reported and discussed. Finally, the implementation of an industrial plant using a draft tube baffled (DTB) crystallizer and the final product properties are shown. Product properties such as crystal size distribution, crystal shape, related storage stability and flowability have successfully been improved.

A high-throughput system combining microfluidic hydrogel droplets with deep learning for screening the antisolvent-crystallization conditions of active pharmaceutical ingredients

Crystallization of active pharmaceutical ingredients (APIs) is a crucial process in the pharmaceutical industry due to its great impact in drug efficacy. However, conventional approaches for screening the optimal crystallization conditions of APIs are usually time-consuming, labor-intensive and expensive. Recently, droplet microfluidic technology has offered an alternative strategy for high-throughput screening of crystallization conditions. Despite its many advantages such as low sample consumption, reduced operation time, increased throughput, etc., some challenges remain to be solved, such as instability of droplets in the long-term and tedious efforts required for extracting useful information from massive data. To solve these problems, a high-throughput system that combined microfluidic hydrogel droplets with deep learning was proposed for the first time to screen the antisolvent-crystallization conditions of APIs. In this system, stable hydrogel droplets containing different concentrations of indomethacin, its solvent and antisolvent were generated on a chip. Crystals of indomethacin with different morphologies were formed in hydrogel droplets, and their optical images were captured by a camera. Then, deep learning was applied to identify the hundreds of indomethacin crystal images and successfully classify the crystal morphologies in a short time; a ternary phase diagram was drawn by combining the experimental results with the recognition results of crystal morphologies, and was used to guide the scale-up preparations of indomethacin crystals as desired. This system, which integrated high throughput preparation, characterization and data analysis, is also useful for screening the crystallization conditions and processes of semiconductors, catalysts, agrochemicals, proteins and other specialty chemicals.

Seeded droplet microfluidic system for small molecule crystallization

A microfluidic approach to seeded crystallization has been demonstrated using abacavir hemisulfate, a nucleoside analog reverse transcriptase inhibitor, in droplet reactors to control polymorphism and produce particles with a low particle size distribution. Two techniques are introduced: (1) the first technique involves an emulsion system consisting of a dispersed phase solvent and a continuous phase, which holds slight solubility of the dispersed phase solvent. The dispersed phase contains both a dissolved active pharmaceutical ingredient (API) and seeds of the desired polymorph. While the continuous phase enables solvent extraction, the negligible solubility of the API allows for growth of seeds inside droplets via extraction and subsequent API saturation. This technique demonstrates the ability to crystallize the API in spherical agglomerates via slow extraction of droplets. (2) The second technique utilizes a combined dispersed phase by joining in-flow a seed suspension stream with a supersaturated active pharmaceutical ingredient (API) stream. The combined dispersed phase is emulsified in a continuous phase for which the dispersed phase solvent and the API are both insoluble - droplets are incubated at temperatures below their saturation limit to induce crystal growth. Decreasing the concentration of seeds in its input stream resulted in a decreased number of crystals per droplet, increase in crystal size, and decrease in PSD. Temperature cycling was utilized as a proof of concept to demonstrate the ability to reduce the number of seeds per droplet where the optimal goal is to obtain a single seed per droplet for all droplets. Utilizing this approach in conjunction with the ability to produce monodispersed droplet reactors allows for enhanced control of particle size distribution (PSD) by precisely controlling the available mass for each individual seed crystal. The development of this technique as a proof-of-concept for crystallization can be expanded to manufacturing scales in a continuous manner using parallelized droplet generators and flow reactors to precisely control the temperature and crystal growth kinetics of individual droplets.

Visualising early-stage liquid phase organic crystal growth via liquid cell electron microscopy

Here, we show that the development of nuclei and subsequent growth of a molecular organic crystal system can be induced by electron beam irradiation by exploiting the radiation chemistry of the carrier solvent. The technique of Liquid Cell Electron Microscopy was used to probe the crystal growth of flufenamic acid; a current commercialised active pharmaceutical ingredient. This work demonstrates liquid phase electron microscopy analysis as an essential tool for assessing pharmaceutical crystal growth in their native environment while giving insight into polymorph identification of nano-crystals at their very inception. Possible mechanisms of crystal nucleation due to the electron beam with a focus on radiolysis are discussed along with the innovations this technique offers to the study of pharmaceutical crystals and other low contrast materials.