The flow properties and presence of crystals in drug-polymer mixtures: Rheological investigation combined with light microscopy

FDM 3D-Printed Sustained-Release Gastric-Floating Verapamil Hydrochloride Formulations with Cylinder, Capsule and Hemisphere Shapes, and Low Infill Percentage

The aim of this work was to design and fabricate fused deposition modeling (FDM) 3D-printed sustained-release gastric-floating formulations with different shapes (cylinder, capsule and hemisphere) and infill percentages (0% and 15%), and to investigate the influence of shape and infill percentage on the properties of the printed formulations. Drug-loaded filaments containing HPMC, Soluplus^® and verapamil hydrochloride were prepared via hot-melt extrusion (HME) and then used to print the following gastric-floating formulations: cylinder-15, capsule-0, capsule-15, hemisphere-0 and hemisphere-15. The morphology of the filaments and the printed formulations were observed by scanning electron microscopy (SEM). The physical state of the drugs in the filaments and the printed formulations were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The printed formulations were evaluated in vitro, including the weight variation, hardness, floating time, drug content and drug release. The results showed that the drug-loaded filament prepared was successful in printing the gastric floating formulations. Verapamil hydrochloride was proved thermally stable during HME and FDM, and in an amorphous state in the filament and the printed formulations. The shape and infill percentage of the printed formulations effected the hardness, floating time and in vitro drug release.

Quality of FDM 3D Printed Medicines for Pediatrics: Considerations for Formulation Development, Filament Extrusion, Printing Process and Printer Design

3d printing is capable of providing dose individualization for pediatric medicines and translating the precision medicine approach into practical application. In pediatrics, dose individualization and preparation of small dosage forms is a requirement for successful therapy, which is frequently not possible due to the lack of suitable dosage forms. For precision medicine, individual characteristics of patients are considered for the selection of the best possible API in the most suitable dose with the most effective release profile to improve therapeutic outcome. 3d printing is inherently suitable for manufacturing of individualized medicines with varying dosages, sizes, release profiles and drug combinations in small batch sizes, which cannot be manufactured with traditional technologies. However, understanding of critical quality attributes and process parameters still needs to be significantly improved for this new technology. To ensure health and safety of patients, cleaning and process validation needs to be established. Additionally, adequate analytical methods for the in-process control of intermediates, regarding their printability as well as control of the final 3d printed tablets considering any risk of this new technology will be required. The PolyPrint consortium is actively working on developing novel polymers for fused deposition modeling (FDM) 3d printing, filament formulation and manufacturing development as well as optimization of the printing process, and the design of a GMP-capable FDM 3d printer. In this manuscript, the consortium shares its views on quality aspects and measures for 3d printing from drug-loaded filaments, including formulation development, the printing process, and the printed dosage forms. Additionally, engineering approaches for quality assurance during the printing process and for the final dosage form will be presented together with considerations for a GMP-capable printer design.

Enhanced Supersaturation via Fusion-Assisted Amorphization during FDM 3D Printing of Crystalline Poorly Soluble Drug Loaded Filaments

Filaments loaded with griseofulvin (GF), a model poorly water-soluble drug, were prepared and used for 3D printing via fused deposition modeling (FDM). GF was selected due to its high melting temperature, enabling lower temperature hot-melt extrusion (HME) keeping GF largely crystalline in the filaments, which could help mitigate the disadvantages of high HME processing temperatures such as filament quality, important for printability and the adverse effects of GF recrystallization on tablet properties. Novel aspects include single-step fusion-assisted ASDs generation during FDM 3D printing and examining the impact of tablet surface areas (SA) through printing multi-mini and square-pattern perforated tablets to further enhance drug supersaturation during dissolution. Kollicoat protect and hydroxypropyl cellulose were selected due to their low miscibility with GF, necessary to produce crystalline filaments. The drug solid-state was assessed via XRPD, DSC and FT-IR. At 165 °C HME processing temperature, the filaments containing ~80% crystalline GF were printable. Fusion-assisted 3D printing led to GF supersaturation of ~153% for cylindrical tablets and ~293% with the square-pattern perforated tablets, indicating strong monotonous impact of tablet SA. Dissolution kinetics of drug release profiles indicated Fickian transport for tablets with higher SA, demonstrating greater SA-induced drug supersaturation for well-designed 3D printed tablets.

Polymers in pharmaceutical additive manufacturing: A balancing act between printability and product performance

Materials and manufacturing processes share a common purpose of enabling the pharmaceutical product to perform as intended. This review on the role of polymeric materials in additive manufacturing of oral dosage forms, focuses on the interface between the polymer and key stages of the additive manufacturing process, which determine printability. By systematically clarifying and comparing polymer functional roles and properties for a variety of AM technologies, together with current and emerging techniques to characterize these properties, suggestions are provided to stimulate the use of readily available and sometimes underutilized pharmaceutical polymers in additive manufacturing. We point to emerging characterization techniques and digital tools, which can be harnessed to manage existing trade-offs between the role of polymers in printer compatibility versus product performance. In a rapidly evolving technological space, this serves to trigger the continued development of 3D printers to suit a broader variety of polymers for widespread applications of pharmaceutical additive manufacturing.

Solubilizing temperature of crystalline drug in polymer carrier: A rheological investigation on a posaconazole-copovidone system with low drug load

Measuring the solubility of a crystalline active pharmaceutical ingredient (API) in a polymer-rich system is challenging due to the high viscosity of the polymer which kinetically impedes reaching the solubility equilibrium. In this study, a rheological approach of determining the solubilizing temperature of a crystalline API in a polymeric carrier has been developed. To validate the method, a model physical mixture of crystalline posaconazole and copovidone with a relatively low API load (25 wt%) was utilized. First, a comparison between conventional differential scanning calorimetry (DSC) and a rheological temperature ramp was conducted to illustrate that the rheological method could capture the melting point depression behavior similarly to the more well-known DSC technique. Second, to further understand the dissolution process of the crystalline posaconazole into the copovidone carrier and precisely measure the solubilizing temperature, a series of isothermal rheological time sweeps were carried out at various temperatures selected based on the rheological temperature sweep. Because the dissolved API molecule imparted a plasticizing effect to the polymeric carrier, the complex viscosity of the API-polymer system decreased gradually over time and correlated well to an exponential decay function. Moreover, dependent on the applied temperature, the API-polymer system eventually accomplished distinct equilibrium states (complex viscosities) within different time frames. The obtained time constants at different temperatures were fitted to the Arrhenius equation, allowing the determination of the activation energy of the mixing process. The results indicated that once the processing temperature exceeded a critical point below the melting point of the crystalline API, the API-polymer solubilization process switched from a surface dominated dispersive mechanism to a molecular-level solubilization mode, manifested by the significantly increased activation energy. To the best of our knowledge, the currently developed rheological approach was the first successful measurement of the solubilizing temperature of a crystalline drug in a polymer-rich system.

Polymers for Extrusion-Based 3D Printing of Pharmaceuticals: A Holistic Materials-Process Perspective

Three dimensional (3D) printing as an advanced manufacturing technology is progressing to be established in the pharmaceutical industry to overcome the traditional manufacturing regime of 'one size fits for all'. Using 3D printing, it is possible to design and develop complex dosage forms that can be suitable for tuning drug release. Polymers are the key materials that are necessary for 3D printing. Among all 3D printing processes, extrusion-based (both fused deposition modeling (FDM) and pressure-assisted microsyringe (PAM)) 3D printing is well researched for pharmaceutical manufacturing. It is important to understand which polymers are suitable for extrusion-based 3D printing of pharmaceuticals and how their properties, as well as the behavior of polymer-active pharmaceutical ingredient (API) combinations, impact the printing process. Especially, understanding the rheology of the polymer and API-polymer mixtures is necessary for successful 3D printing of dosage forms or printed structures. This review has summarized a holistic materials-process perspective for polymers on extrusion-based 3D printing. The main focus herein will be both FDM and PAM 3D printing processes. It elaborates the discussion on the comparison of 3D printing with the traditional direct compression process, the necessity of rheology, and the characterization techniques required for the printed structure, drug, and excipients. The current technological challenges, regulatory aspects, and the direction toward which the technology is moving, especially for personalized pharmaceuticals and multi-drug printing, are also briefly discussed.

Exploring the Complexity of Processing-Induced Dehydration during Hot Melt Extrusion Using In-Line Raman Spectroscopy

The specific aim in this study was to understand the effect of critical process parameters on the solid form composition of model drug compounds during hot melt extrusion using in-line Raman spectroscopy combined with Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) modeling for semi-quantitative kinetic profiling. It was observed that the hydrate and anhydrate solid forms of two model drugs in the melts of nitrofurantoin (NF):polyethylene oxide (PEO) and piroxicam (PRX):PEO could be resolved from a MCR-ALS model without an external calibration dataset. Based on this model, the influence of two critical process parameters (shear and temperature) on the solid form composition could be evaluated in a real-time mode and the kinetics of complex transformation pathways could be explored. Additionally, the dehydration pathways of NF monohydrate and PRX monohydrate in molten PEO could be derived. It can be concluded that dehydration of both hydrates in PEO occurs via competing mechanisms—a solution-mediated transformation pathway and a solid–solid transformation, and that the balance between these mechanisms is determined by the combined effect of both temperature and shear. Another important observation was that the water released from these hydrate compounds has a detectable effect on the rheological characteristics of this mixture.

Holistic QbD approach for hot-melt extrusion process design space evaluation: Linking materials science, experimentation and process modeling

The aim of this work was to investigate the relationship between formulation material properties, process parameters and process performance for the manufacturing of amorphous solid dispersions via hot-melt extrusion (HME) using experimentation coupled with process modeling. Specifically, we evaluated the impact of the matrix copovidone melt rheology with and without the addition of a plasticizing surfactant, polysorbate 80, while also varying the process parameters, barrel temperature and screw speed, and keeping fill volume constant. To correlate the process performance to a critical quality attribute, we used telmisartan as an indicator substance by processing at temperatures below its solubility temperature in the polymeric matrix. We observed a broader design space of HME processes for the plasticized formulation with respect to screw speed than for the copovidone-only matrix formulation. This observation was determined by the range of observed melt temperatures in the extruder, both measured and simulated. The reason was not primarily linked to a reduced shear-thinning behavior, characterized by the power law index, n, but instead more to an overall reduced melt viscosity during extrusion and zero-shear rate viscosity, η₀, accordingly. We also found that the amount of residual crystallinity of telmisartan correlated with the simulated maximum melt temperature in the extruder barrel. This finding confirmed the applicability of the temperature-dependent API-matrix solubility phase diagram for HME to process development. Given the complex inter-dependent relationships between material properties, process and performance, process modeling combined with reduced laboratory experimentation was established as a holistic approach for the evaluation of Quality-by-Design-based HME process design spaces.

Roadmap to 3D-Printed Oral Pharmaceutical Dosage Forms: Feedstock Filament Properties and Characterization for Fused Deposition Modeling

Application of additive manufacturing techniques (3D printing) for mass-customized products has boomed in the recent years. In pharmaceutical industry and research, the interest has grown particularly with the future scenario of more personalized medicinal products. Understanding a broad range of material properties and process behavior of the drug-excipient combinations is necessary for successful 3D printing of dosage forms. This commentary reviews recent 3D-printing studies by fused deposition modeling (FDM) technique in pharmaceutical sciences, extending into the fields of polymer processing and rapid prototyping, where more in-depth studies on the feedstock material properties, modeling, and simulation of the FDM process have been performed. A case study of a model oral dosage form from custom-prepared indomethacin-polycaprolactone feedstock filament was used as an example in the pharmaceutical context. The printability was assessed in the different process steps: preparation of customized filaments for FDM, filament feeding, deposition, and solidification. These were linked with the rheological, thermal, and mechanical properties and their characterization, relevant for understanding the printability of drug products by FDM.

The application of temperature-composition phase diagrams for hot melt extrusion processing of amorphous solid dispersions to prevent residual crystallinity

Hot melt extrusion (HME) can be used to produce amorphous solid dispersions (ASDs) at temperatures below the drug's melting point if the drug and polymer exhibit melting point depression. However, the risk of residual crystallinity becomes significant. The purpose of this study was to apply the temperature-composition phase diagram to the HME process, correlating process conditions to ASD residual crystallinity, and identifying the formulation critical temperature, which defines the theoretical minimum processing temperature. The phase diagram of indomethacin (IDM) and polyvinylpyrrolidone/vinyl acetate copolymer (PVPVA) was generated using melting point depression measurements coupled with Flory-Huggins theory. Extrudates were manufactured above, at, and below the formulation critical temperature (T_c) as identified from the phase diagram, with a range of residence times, and characterized for crystallinity. Below the T_c, a fully amorphous sample could not be prepared. Above T_c, sufficient residence time led to amorphous samples. A processing operating design space diagram with three regimes was generated to correlate temperature and residence time factors with process outcome. In conclusion, phase diagrams provide a rational basis for designing hot melt extrusion processes of amorphous solid dispersions to minimize residual crystalline content, delineating the minimum processing temperature based on thermodynamic considerations.

Process optimization of spray-dried fanhuncaoin powder for pulmonary drug delivery and its pharmacokinetic evaluation in rats

The optimization of process parameters of spray-dried powder containing fanhuncaoin, a newly discovered anti-inflammatorily active phenolic acid isolated from Chinese herb, was conducted using response surface methodology (RSM). The experimental results were fitted into partial cubic polynomial model to describe and predict the response quality in terms of the final angle of repose, aerodynamic diameter, respirable fraction (RF), and yield. The recommended optimum spray-drying parameters for the development of fanhuncaoin powder with optimum quality were 110 °C inlet temperature, 0.50 m³/min aspiration speed, and 7.95 ml/min feed flow rate. The obtained optimum process parameters were employed for the production of spray-dried fanhuncaoin powder and to check the validity of the partial cubic model. Small and insignificant deviations were found between the predicted values and the experimental ones, showing the efficiency of the model in predicting the quality attributes of fanhuncaoin powder. The optimized powder was further examined for its pharmacokinetic properties in rats. A UPLC/MS assay was used to determine plasma fanhuncaoin concentration. Statistical analysis demonstrated that there was no significant difference in the t_1/2 and dose-normalized C_max and AUC as well as other pharmacokinetic parameters between the groups dosed differently following intratracheal administration (p > .05), indicating that fanhuncaoin followed linear kinetics. The pharmacokinetic parameters of fanhuncaoin after intratracheal administration differed significantly from the ones observed after intravenous administration (p < .05). The lower values of C_max and AUC_(0-∞) obtained following intratracheal administration may lead to effective drug concentrations at the target site with minimal systemic bioavailability and side effects.