Development and characterization of solid lipid-based formulations (sLBFs) of ritonavir utilizing a lipolysis and permeation assay

As a high number of active pharmaceutical ingredients (APIs) under development belong to BCS classes II and IV, the need for improving bioavailability is critical. A powerful approach is the use of lipid-based formulations (LBFs) that usually consist of a combination of liquid lipids, cosolvents, and surfactants. In this study, ritonavir loaded solid LBFs (sLBFs) were prepared using solid lipid excipients to investigate whether sLBFs are also capable of improving solubility and permeability. Additionally, the influence of polymeric precipitation inhibitors (PVP-VA and HPMC-AS) on lipolysis triggered supersaturation and precipitation was investigated. One step intestinal digestion and bicompartmental permeation studies using an artificial lecithin-in-dodecane (LiDo) membrane were performed for each formulation. All formulations presented significantly higher solubility (5 to >20-fold higher) during lipolysis and permeation studies compared to pure ritonavir. In the combined lipolysis-permeation studies, the formulated ritonavir concentration increased 15-fold in the donor compartment and the flux increased up to 71 % as compared to non-formulated ritonavir. The formulation with the highest surfactant concentration showed significantly higher ritonavir solubility compared to the formulation with the highest amount of lipids. However, the precipitation rates were comparable. The addition of precipitation inhibitors did not influence the lipolytic process and showed no significant benefit over the initial formulations with regards to precipitation. While all tested sLBFs increased the permeation rate, no statistically significant difference was noted between the formulations regardless of composition. To conclude, the different release profiles of the formulations were not correlated to the resulting flux through a permeation membrane, further supporting the importance of making use of combined lipolysis-permeation assays when exploring LBFs.

3D-printed prednisolone phosphate suppositories with tunable dose and rapid release for the treatment of inflammatory bowel disease

Established medicines are often not tailored to the needs of the pediatric population, causing difficulties with administration or dosing. Three-dimensional (3D) printing technology allows novel approaches for compounding of personalized medicine, as is exemplified in this study for the automated compounding of rectal preparations for children. We investigated the material requirements to print prednisolone phosphate-loaded suppositories with tunable dose and rapid drug release for the treatment of inflammatory bowel diseases. Three formulations containing 4 % w/w prednisolone sodium phosphate (PSP) and different amounts of hydroxypropyl cellulose (HPC) and mannitol as excipients were printed as suppositories with a fused deposition modeling (FDM) 3D-printer. Dissolution studies showed that the PSP release rate was increased when higher weight fractions of mannitol were added as a pore former, with 90 % drug release within 30 min for mannitol 48 % w/w. We further printed suppositories with 48 % mannitol with different infill densities and dimensions to tune the dose. Our findings demonstrated that 3D-printed suppositories with PSP doses ranging from 6 to 30 mg could be compounded without notably affecting the dissolution kinetics, ensuring equivalent therapeutic efficacies for different doses.

Exploring the use of modified in vitro digestion assays for the evaluation of ritonavir loaded solid lipid-based formulations

Solid lipid-based formulations (sLBFs) have the potential to increase the oral bioavailability of drugs with poor solubility in water, while counteracting some of the disadvantages of liquid LBFs. The most common experimental set-up to study the performance of LBFs in vitro is the lipolysis assay, during which the LBFs are digested by lipases in an environment mimicking the human small intestine. However, this assay has failed in many cases to correctly predict the performance of LBFs in vivo, highlighting the need for new and improved in vitro assays to evaluate LBFs at the preclinical stage. In this study, the suitability of three different in vitro digestion assays for the evaluation of sLBFs was assessed; the classic one-step intestinal digestion assay, a two-step gastrointestinal digestion assay and a bicompartmental assay permitting the simultaneous monitoring of digestion and permeation of the active pharmaceutical ingredient (API) across an artificial membrane (Lecithin in Dodecane - LiDo). Three sLBFs (M1-M3) with varied composition and ritonavir as model drug were prepared and examined. When comparing the ability of these formulations to keep the drug solubilized in the aqueous phase, all three assays show that M1 performs better, while M3 presents poor performance. However, the classic in vitro intestinal digestion assay fails to provide a clear ranking of the three formulations, something that is more evident when using the two modified and more physiologically relevant assays. Also, the two modified assays provide additional information about the performance of the formulations including the performance in the gastric environment and intestinal flux of the drug. These modified in vitro digestion assays are valuable tools for the development and evaluation of sLBFs to make better informed decisions of which formulations to pursue for in vivo studies.

Customizable 3D Printed Implants Containing Triamcinolone Acetonide: Development, Analysis, Modification, and Modeling of Drug Release

Three-dimensional-printed customizable drug-loaded implants provide promising opportunities to improve the current therapy options. In this study, we present a modular implant in which shape, dosage, and drug release can be individualized independently of each other to patient characteristics to improve parenteral therapy with triamcinolone acetonide (TA) over three months. This study focused on the examination of release modification via fused deposition modeling and subsequent prediction. The filaments for printing consisted of TA, ethyl cellulose, hypromellose, and triethyl citrate. Two-compartment implants were successfully developed, consisting of a shape-adaptable shell and an embedded drug-loaded network. For the network, different strand widths and pore size combinations were printed and analyzed in long-term dissolution studies to evaluate their impact on the release performance. TA release varied between 8.58 ± 1.38 mg and 21.93 mg ± 1.31 mg over three months depending on the network structure and the resulting specific surface area. Two different approaches were employed to predict the TA release over time. Because of the varying release characteristics, applicability was limited, but successful in several cases. Using a simple Higuchi-based approach, good release predictions could be made for a release time of 90 days from the release data of the initial 15 days (RMSEP ≤ 3.15%), reducing the analytical effort and simplifying quality control. These findings are important to establish customizable implants and to optimize the therapy with TA for specific intra-articular diseases.

Selective laser sintering additive manufacturing of dosage forms: Effect of powder formulation and process parameters on the physical properties of printed tablets

Large batches of placebo and drug-loaded solid dosage forms were successfully fabricated using selective laser sintering (SLS) 3D printing in this study. The tablet batches were prepared using either copovidone (N-vinyl-2-pyrrolidone and vinyl acetate, PVP/VA) or polyvinyl alcohol (PVA) and activated carbon (AC) as radiation absorbent, which was added to improve the sintering of the polymer. The physical properties of the dosage forms were evaluated at different pigment concentrations (i.e., 0.5 and 1.0 wt%) and at different laser energy inputs. The mass, hardness, and friability of the tablets were found to be tunable and structures with greater mass and mechanical strength were obtained with increasing carbon concentration and energy input. Amorphization of the active pharmaceutical ingredient in the drug-loaded batches, containing 10 wt% naproxen and 1 wt% AC, was achieved in-situ during printing. Thus, amorphous solid dispersions were prepared in a single-step process and produced tablets with mass losses below 1 wt%. These findings show how the properties of dosage forms can be tuned by careful selection of the process parameters and the powder formulation. SLS 3D printing can therefore be considered to be an interesting and promising technique for the fabrication of personalized medicines.

Investigation of the degradation and in-situ amorphization of the enantiomeric drug escitalopram oxalate during Fused Deposition Modeling (FDM) 3D printing

Hot-melt extrusion (HME) and subsequent FDM 3D printing offer great potential opportunities in the formulation development and production of customized oral dosage forms with poorly soluble drugs. However, thermal stress within these processes can be challenging for thermo-sensitive drugs. In this work, three different formulations were prepared to investigate the degradation and the solid state of the thermo-sensitive and poorly soluble drug escitalopram oxalate (ESC-OX) during the two heat-intensive processes HME and FDM 3D printing. For this purpose, hydroxypropyl methyl cellulose (HPMC) and basic butylated methacrylate copolymer (bPMMA) were chosen as polymers. DSC and XRD measurements revealed that ESC-OX is amorphous in the HPMC based formulations in both, extrudates and 3D printed tablets. In contrast, in-situ amorphization of the drug from crystalline state in bPMMA filaments was observed during FDM 3D printing. With regard to the content, it was found that degradation of ESC-OX in extrudates with bPMMA could be avoided and in 3D printed tablets almost fully reduced. Furthermore, a possible conversion into the R-enantiomer in the formulation with bPMMA could be excluded using a chiral column. Compared to the commercial product Cipralex®, drug release from extrudates and tablets with bPMMA was slower but still qualified as immediate drug release.

3D printing of amorphous solid dispersions: A comparison of fused deposition modeling and drop-on-powder printing

Nowadays, a high number of pipeline drugs are poorly soluble and require solubility enhancement by e.g., manufacturing of amorphous solid dispersion. Pharmaceutical 3D printing has great potential in producing amorphous solid oral dosage forms. However, 3D printing techniques differ greatly in terms of processing as well as tablet properties. In this study, an amorphous formulation, which had been printed via Fused Deposition Modeling and drop-on-powder printing, also known as binder jetting, was characterized in terms of solid-state properties and physical stability. Solid state assessment was performed by differential scanning calorimetry, powder X-ray diffraction and polarized microscopy. The supersaturation performance of the amorphous solid dispersion was assessed via non-sink dissolution. We further evaluated both 3D printing techniques regarding their processability as well as tablet uniformity in terms of dimension, mass and content. Challenges and limitations of each 3D printing technique were discussed. Both techniques are feasible for the production of amorphous formulations. Results indicated that Fused Deposition Modeling is better suited for production, as the recrystallization tendency was lower. Still, filament production and printing presented a major challenge. Drop-on-powder printing can be a viable alternative for the production of amorphous tablets, when a formulation is not printable by Fused Deposition Modeling.

Investigations into the use of machine learning to predict drug dosage form design to obtain desired release profiles for 3D printed oral medicines

Three-dimensional (3D) printing, digitalization, and artificial intelligence (AI) are gaining increasing interest in modern medicine. All three aspects are combined in personalized medicine where 3D-printed dosage forms are advantageous because of their variable geometry design. The geometry design can be used to determine the surface area to volume (SA/V) ratio, which affects drug release from the dosage forms. This study investigated artificial neural networks (ANN) to predict suitable geometries for the desired dose and release profile. Filaments with 5% API load and polyvinyl alcohol were 3D printed using Fused Deposition Modeling to provide a wide variety of geometries with different dosages and SA/V ratios. These were dissolved in vitro, and the API release profiles were described mathematically. Using these data, ANN architectures were designed with the goal of predicting a suitable dosage form geometry. Poor accuracies of 68.5% in the training and 44.4% in the test settings were achieved with a classification architecture. However, the SA/V ratio could be predicted accurately with a mean squared error loss of only 0.05. This study shows that the prediction of the SA/V ratio using AI works, but not of the exact geometry. For this purpose, a global database could be built with a range of geometries to simplify the prescription process.

Fused Deposition Modeling (FDM) 3D Printing of the Thermo-Sensitive Peptidomimetic Drug Enalapril Maleate

Fused deposition modeling (FDM) 3D printing was used to produce 3D printed tablets with the thermo-sensitive model peptidomimetic drug enalapril maleate (EM). Two different formulations were prepared to investigate the degradation of enalapril maleate during the FDM 3D printing process. Soluplus^® and Eudragit^® E PO were chosen as polymers. After hot-melt extrusion (HME) and FDM 3D printing, both formulations were characterised regarding their solid-state properties using DSC and XRD. The degradation of the drug was analysed by determination of the content in the extrudates and 3D printed tablets, and dissolution was assessed. Various approaches have been attempted to prevent degradation of enalapril maleate, including utilization of a larger nozzle diameter and higher printing speeds to reduce heat exposition. None of these approaches were successful in preventing drug degradation. However, significant differences in the amount of degradation between the two formulations with different polymers could be observed. Thus, the FDM 3D printing process was not feasible without any degradation for the thermo-sensitive drug enalapril maleate. A maximum of 85.55 ± 1.48% enalapril was recovered in Eudragit^® E PO tablets printed with a 0.4 mm nozzle at a temperature of 180 °C and with a speed of 30 mm/s.

Hot-Melt Extrusion of the Thermo-Sensitive Peptidomimetic Drug Enalapril Maleate

The aim of this research was the production of extrudates for the treatment of hypertension and heart failure and the investigation of the degradation of the peptidomimetic drug enalapril maleate (EM) during hot-melt extrusion (HME). A fast HPLC method was developed to quantify enalapril maleate and possible degradation products. Screening experiments revealed that the diketopiperazine derivative (Impurity D) was the main degradation product. Hot-melt extrusion of enalapril maleate with the polymer Soluplus^® enabled extrusion at 100 °C, whereas a formulation with the polymer Eudragit^® E PO could be extruded at only 70 °C. Extrusion at 70 °C prevented thermal degradation. A stabilizing molecular interaction between enalapril maleate and Eudragit^® E PO was identified via FT-IR spectroscopy. Dissolution studies were carried out to study the influence of the formulation on the dissolution behavior of enalapril maleate. These promising results can be transferred to other thermo-sensitive and peptidomimetic drugs to produce extrudates which can be used, for instance, as feedstock material for the production of patient-specific dosage forms via Fused Deposition Modeling (FDM) 3D printing.

Impact of alternative lubricants on process and tablet quality for direct compression

Internal lubrication with magnesium stearate (MgSt) is associated with a reduced tensile strength and prolonged disintegration and dissolution times. In the current study, alternative lubricants to MgSt were compared with regard to lubrication efficacy and their impact on tablet properties. The lubricants were combined in different concentrations (0.5-5% w/w) with three fillers (lactose, mannitol and microcrystalline cellulose (MCC)). The high lubrication efficiency of MgSt was associated with the highest reduction of tensile strength. The micronized stearic acid (SA) grades proved good alternatives as they showed a good lubrication efficiency in combination with a limited negative effect on tensile strength. The hydrophobic lubricants (e.g., MgSt and SA) did not prolong disintegration. In contrast, delayed disintegration was observed for sucrose monopalmitate combined with all three fillers and for several other hydrophilic lubricants (sodium lauryl sulfate, poloxamers 188 and P407) combined with MCC. These unexpected findings were explained by the competition-for-water hypothesis. The potential of alternative lubricants to MgSt was demonstrated in this study. Nevertheless, the impact of lubricant addition on process and tablet quality depended on lubricant (type and concentration) and formulation (lubrication need, deformation mechanism and disintegration behavior) properties. Therefore, lubricant selection should be carefully considered in formulation development.

3D Printed Mini-Floating-Polypill for Parkinson's Disease: Combination of Levodopa, Benserazide, and Pramipexole in Various Dosing for Personalized Therapy

Therapy for Parkinson’s disease is quite challenging. Numerous drugs are available for symptomatic treatment, and levodopa (LD), in combination with a dopa decarboxylase inhibitor (e.g., benserazide (BZ)), has been the drug of choice for years. As the disease progresses, therapy must be supplemented with a dopamine agonist (e.g., pramipexole (PDM)). Side effects increase, as do the required dose and dosing intervals. For these specific requirements of drug therapy, the 3D printing method fused deposition modelling (FDM) was applied in this study for personalized therapy. Hot melt extrusion was utilized to produce two different compositions into filaments: PDM and polyvinyl alcohol for rapid drug release and a fixed combination of LD/BZ (4:1) in an ethylene-vinyl acetate copolymer matrix for prolonged drug release. Since LD is absorbed in the upper gastrointestinal tract, a formulation that floats in gastric fluid was desired to prolong API absorption. Using the FDM 3D printing process, different polypill geometries were printed from both filaments, with variable dosages. Dosage forms with 15−180 mg LD could be printed, showing similar release rates (f2 > 50). In addition, a mini drug delivery dosage form was printed that released 75% LD/BZ within 750 min and could be used as a gastric retentive drug delivery system due to the floating properties of the composition. The floating mini-polypill was designed to accommodate patients’ swallowing difficulties and to allow for individualized dosing with an API release over a longer period of time.

Blind-Watermarking—Proof-of-Concept of a Novel Approach to Ensure Batch Traceability for 3D Printed Tablets

Falsified medicines are a major issue and a threat around the world. Various approaches are currently being investigated to mitigate the threat. In this study, a concept is tested that encodes binary digits (bits) on the surface of Fused Deposition Modelling (FDM) 3D printed geometries. All that is needed is a computer, a FDM 3D printer and a paper scanner for detection. For the experiments, eleven different formulations were tested, covering the most used polymers for 3D printing in pharma: Ethylene-vinyl acetate (EVA), polyvinyl alcohol (PVA), polylactic acid (PLA), Hypromellose (HPMC), ethyl cellulose (EC), basic butylated-methacrylate-copolymer (EPO), and ammonio-methacrylate-copolymer type A (ERL). In addition, the scanning process and printing process were evaluated. It was possible to print up to 32 bits per side on oblong shaped tablets corresponding to the dimensions of market preparations of oblong tablets and capsules. Not all polymers or polymer blends were suitable for this method. Only PVA, PLA, EC, EC+HPMC, and EPO allowed the detection of bits with the scanner. EVA and ERL had too much surface roughness, too low viscosity, and cooled down too slowly preventing the detection of bits. It was observed that the addition of a colorant or active pharmaceutical ingredient (API) could facilitate the detection process. Thus, the process could be transferred for 3D printed pharmaceuticals, but further improvement is necessary to increase robustness and allow use for more materials.

Dose-independent drug release from 3D printed oral medicines for patient-specific dosing to improve therapy safety

Fused deposition modelling (FDM) 3D printing provides the ability to address individual patients' therapeutic needs without having to change the formulation every time. This is particularly interesting for dosing and release modelling. In this study, a geometry model was developed that can represent variable dosages while keeping the surface area to volume (SA/V) ratio alike, so the drug release profiles remain similar. The model was tested on three different formulations. Two BCS I active pharmaceutical ingredients (API), pramipexole and levodopa, and one BCS II API, praziquantel, were used. Polyvinyl alcohol (PVA, water soluble) and a combination of vinylpyrrolidone-vinyl acetate copolymer (PVP-VA, water soluble) and ethylene-vinyl acetate (EVA, water insoluble) were used as the polymer matrix. The curves were compared using the similarity factor (f₂ value) and mean dissolution time (MDT). Using a hollow cylinder-based (HCb) geometry model, a dose-independent drug release could be realized. For the PVA formulations, an 8-fold dose change could be obtained and for the EVA-PVP-VA formulation a factor of 5.5 could be achieved, with f₂ > 50. Due to the layer structure of the printed objects, very fine dose variation of 0.13 mg per layer is possible within these models. This allows variable dosing in small steps with only one basis formulation.

Determination of feed forces to improve process understanding of Fused Deposition Modeling 3D printing and to ensure mass conformity of printed solid oral dosage forms

Fused Deposition Modeling is a suitable technique for the production of personalized solid oral dosage forms. For widespread application, it is necessary to be able to print a wide range of different formulations to address individual therapeutic needs. Due to the complexity of formulation composition (e.g., due to different compounds, excipients for enhancement of release and mechanical properties) and limited mechanical understanding, determination of suitable printing parameters is challenging. To address this challenge, we have developed a feed force tester using a Texture Analyser setup that mimics the actual printing process. Feed force data were compared to the mass of tablets printed from technical materials as well as pharmaceutical filaments of ketoconazole at high drug loads of 20 and 40% and polyvinyl alcohol. By determining a feed force limit for the 3D printer from feed force data of several formulations printed, it was possible to specify the operable printing range, where printing is reproducible and printed mass corresponds the target mass. Based on these results, rational optimization of the printing process in terms of speed, time and temperature for different materials and formulations is possible.

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.

Predicting Drug Release from 3D Printed Oral Medicines Based on the Surface Area to Volume Ratio of Tablet Geometry

3D printing offers the advantage of being able to modify dosage form geometry, which can be exploited to modify release characteristics. In this study, we investigated the influence of the surface area to volume ratio (SA/V) to change and predict release profiles of 3D printed dosage forms. Geometries with varying SA/V and dosages were designed and printed, and drug dissolution was investigated. Three drug substances were used: pramipexole, levodopa (both BCS I) and praziquantel (BCS II). Two polymers were chosen as matrix formers: polyvinyl alcohol (water-soluble) and ethylene vinyl acetate (inert). Drug release was characterized using the mean dissolution time (MDT) and established equations that describe complete dissolution curves were applied. Predictions were validated with previously un-printed dosage forms. Based on an identified MDT-SA/V correlation, the MDT can be predicted with a deviation of ≤5 min for a given SA/V. Using correlations of fit parameters and SA/V, RMSEP values of 0.6-2.8% and 1.6-3.4% were obtained for the BCS I formulations and RMSEP values of 1.0-3.8% were obtained for the BCS II formulation, indicating accurate prediction over a wide range of dissolution profiles. With this approach, MDT and release profiles of dosage forms with a given SA/V can be precisely predicted without performing dissolution tests and vice versa, the required SA/V can be predicted for a desired release profile.

Versatility on demand - The case for semi-solid micro-extrusion in pharmaceutics

Since additive manufacturing of pharmaceuticals has been introduced as viable method to produce individualized drug delivery systems with complex geometries and release profiles, semi-solid micro-extrusion has shown to be uniquely beneficial. Easy incorporation of actives, room-temperature processability and avoidance of cross-contamination by using disposables are some of the advantages that led many researchers to focus their work on this technology in the last few years. First acceptability and in-vivo studies have brought it closer towards implementation in decentralized settings. This review covers recently established process models in light of viscosity and printability discussions to help develop high quality printed medicines. Quality defining formulation and process parameters to characterize the various developed dosage forms are presented before critically discussing the role of semi-solid micro-extrusion in the future of personalized drug delivery systems. Remaining challenges regarding regulatory guidance and quality assurance that pose the last hurdle for large scale and commercial manufacturing are addressed.

Brittle polymers in Fused Deposition Modeling: An improved feeding approach to enable the printing of highly drug loaded filament

Brittleness is often described as a restricting material property for the processability of filaments via Fused Deposition Modeling. Especially filaments produced from approved pharmaceutical polymers often tend to fracture between feeding gears, the commonly employed feeding mechanism. In order to enhance their mechanical properties, usually extensive formulation development is performed. This study presents a different strategy to enable the printing of brittle filaments without the use of additional excipients by adapting the feeding mechanism to piston feeding. The polymers Soluplus®, Kollidon® VA64 and Eudragit® E PO were used, which have been reported to be brittle. Ketoconazole was used as model compound at 40% drug load and the influence on the mechanical properties was investigated using the three-point flexural test. In order to gain a better understanding of the mechanism affecting brittleness, filaments were analyzed in terms of crystallinity and miscibility of the components using polarized microscopy, differential scanning calorimetry and X-ray diffraction. Printing was performed with the aim to obtain immediate release tablets. The addition of Ketoconazole resulted in filaments even more brittle than placebo filaments. Nevertheless, the adaption of the feeding mechanism enabled the successful manufacturing of uniform tablets from all formulations.

Advancing the understanding of the tablet disintegration phenomenon - An update on recent studies

Disintegration is the de-aggregation of particles within tablets upon exposure to aqueous fluids. Being an essential step in the bioavailability cascade, disintegration is a fundamental quality attribute of immediate release tablets. Although the disintegration phenomenon has been studied for over six decades, some gaps of knowledge and research questions still exist. Three reviews, published in 2015, 2016 and 2017, have discussed the literature relative to tablet disintegration and summarised the understanding of this topic. Yet, since then more studies have been published, adding to the established body of knowledge. This article guides a step forward towards the comprehension of disintegration by reviewing, concisely, the most recent scientific updates on this topic. Initially, we revisit the mechanisms of disintegration with relation to the three most used superdisintegrants, namely sodium starch glycolate, croscarmellose sodium and crospovidone. Then, the influence of formulation, storage, manufacturing and media conditions on disintegration is analysed. This is followed by an excursus on novel disintegrants. Finally, we highlight unanswered research questions and envision future research venues in the field.

Fibrillated Cellulose via High Pressure Homogenization: Analysis and Application for Orodispersible Films

Powdered cellulose (PC) and microcrystalline cellulose (MCC) are common excipients in pharmaceuticals. Recent investigations imply that particle size is the most critical parameter for the different performance in many processes. High-pressure homogenization (HPH) was used to reduce fiber size of both grades. The effect of the homogenization parameters on suspension viscosity, particle size, and mechanical properties of casted films was investigated. PC suspensions showed higher apparent viscosities and yield stresses under the same process conditions than MCC. SLS reduced shear viscosity and thixotropic behavior of both cellulose grades probably due to increased electrostatic repulsion. Homogenization reduced cellulose particle sizes, but re-agglomeration was too strong to analyze the particle size correctly. MCC films showed a tensile strength of up to 16.0 MPa and PC films up to 4.1 MPa. PC films disintegrated within 30 s whereas MCC films did not. Mixtures of MCC and PC led to more stable films than PC alone, but these films did not disintegrate anymore. Diclofenac sodium was incorporated in therapeutic dose with drug load of 47% into orodispersible PC films. The content uniformity of these films fulfilled requirements of Ph.Eur and the films disintegrated in 12 s. In summary, PC and MCC showed comparable results after HPH and most differences could be explained by the smaller particle size of MCC suspensions. These results confirm the hypothesis that mainly the fiber size during processing is responsible for the existing differences of MCC and PC in pharmaceutical process, e.g., wet-extrusion/spheronization.

A Critical Review on 3D-printed Dosage Forms

BACKGROUND

In the last decades, 3D-printing has been investigated and used intensively in the field of tissue engineering, automotive and aerospace. With the first FDA approved printed medicinal product in 2015, the research on 3D-printing for pharmaceutical application has attracted the attention of pharmaceutical scientists. Due to its potential of fabricating complex structures and geometrics, it is a highly promising technology for manufacturing individualized dosage forms. In addition, it enables the fabrication of dosage forms with tailored drug release profiles.

OBJECTIVE

The aim of this review article is to give a comprehensive overview of the used 3D-printing techniques for pharmaceutical applications, including information about the required material, advantages and disadvantages of the respective technique.

METHODS

For the literature research, relevant keywords were identified and the literature was then thoroughly researched.

CONCLUSION

The current status of 3D-printing as a manufacturing process for pharmaceutical dosage forms was highlighted in this review article. Moreover, this article presents a critical evaluation of 3D-printing to control the dose and drug release of printed dosage forms.

Model-based approach to the design of pharmaceutical roller-compaction processes

This work presents a new model based approach to process design and scale-up within the same equipment of a roller compaction process. The prediction of the operating space is not performed fully in-silico, but uses low-throughput experiments as input. This low-throughput data is utilized in an iterative calibration routine to describe the behavior of the powder in the roller compactor and improves the predictive quality of the mechanistic models at low and high-throughput. The model has been validated with an experimental design of experiments of two ibuprofen formulations. The predicted sweet spots in the operating space are in good agreement with the experimental results.

Implementation of real-time and in-line feedback control for a fluid bed granulation process

The application of process analytical technologies (PAT) to monitor critical quality attributes (CQAs) provides an important approach to enhance process understanding and improve the reliability of pharmaceutical production processes. The present study focuses on the first PAT based feedback control system for a fluid bed granulation batch process. Real-time particle size measurement by in-line spatial filtering technique (SFT) using a modified time-based buffer system was applied to define a target particle size after spraying a specific amount of binder solution. After identifying an appropriate control variable, a suitable strategy for feedback control was established, followed by tuning of the control loop to obtain best performance of the integrated system. By adapting the final target particle size within a specified range good functionality of the system could be demonstrated. Investigations of the robustness further showed that the implemented system enables the production of a predefined target particle size also by varying process and formulation parameters. The effect of increasing spray rates and binder concentrations on the particle size could be compensated in a given range by feedback control ensuring a predefined product quality. The study provides an advanced approach for quality assurance of fluid bed granulation.

Formulation development of a continuously manufactured orodispersible film containing warfarin sodium for individualized dosing

Continuously manufactured orodispersible films (ODFs) offer a promising approach for individualized therapy with an easy to administer solid dosage form. The aim of this study was to develop a long ODF containing warfarin sodium to enable safe and more flexible dosing. Formulation development was conducted systematically for the continuous film coating process. A continuously working pilot-scale coating bench was used for film manufacturing and the viscosities of the polymer solutions were investigated to obtain processible formulations. The investigation of the mechanical properties of the long film was an integral part of the study, because the handling of the long film during flexible dosing differs distinctly from the handling of a single dosed ODF. The secant modulus and the yield stress were evaluated as parameters with high information value about the deformation behavior of the ODF. A long warfarin ODF was successfully produced using the pilot-scale coating bench equipped with an optical probe for in-line film thickness measurement. It was feasible to use the principle of a tape dispenser for flexible and, therefore, individualized dosing as proof of concept. Combining the long ODF with a dosing device allows individualized therapy with warfarin for all age groups manageable by the patient himself.

The influence of ethanol on superdisintegrants and on tablets disintegration

Disintegration of immediate release tablets originates from the volume expansion of disintegrants within the formulation. Here, we study the impact of ethanol on the disintegrant expansion and on tablets disintegration. The three most commonly used superdisintegrants, namely sodium starch glycolate (SSG), crospovidone (PVPP) and croscarmellose sodium (CCS) were investigated alone and incorporated in dicalcium phosphate and in drug-containing tablets. High (i.e. 40%), but not moderate (i.e. 10%), aqueous ethanol concentrations reduce the size expansion of the three disintegrants compared to water. This "ethanol effect" is the greatest for SSG, followed by CCS and then PVPP. Moreover, the presence of ethanol in the media can significantly influence the disintegration time of drug-containing tablets via affecting both the disintegrant action itself and the drug solubility. For example, the disintegration time of theophylline tablets containing SSG is 8.1-fold greater in 40% aqueous ethanol compared to water. Overall, this study brought to light the existence of a potentially significant interference of alcohol with the disintegration phenomenon, suggesting that the concomitant administration of tablets and intake of alcoholic beverages may affect, in some cases, tablets disintegration. More studies are now needed to verify the importance of the "ethanol effect" on disintegration of commercial dosage forms. Our findings also suggest that PVPP is the disintegrant that is the least affected by alcohol.

3D-Printed Network Structures as Controlled-Release Drug Delivery Systems: Dose Adjustment, API Release Analysis and Prediction

3D printing evolved as a promising technique to improve individualization of drug therapy. In particular, when printing sustained release solid dosage forms, as for instance implants, inserts, and also tablets, estimation of the drug release profile in vivo is necessary. In most cases, corresponding analyses cannot be performed at hospital or community pharmacies. Therefore, the present study aimed to develop a sustained release drug delivery system produced via 3D printing, which allows dose adaption and estimation of drug release at the same time. Filaments as feedstock for the printer were produced via hot-melt extrusion and consisted of Eudragit® RL as sustained release polymer, 30% theophylline as model active pharmaceutical ingredient, and stearic acid as solid plasticizer. Assuming that the surface/mass ratio was constant, network structures of different densities were printed as novel solid dosage form. Their weight (263 to 668 mg), thereby their dose, and surface area, determined using X-ray microcomputed tomography, showed a linear correlation with the fill density. The specific surface area of the network hardly varied with changing fill density. Dissolution studies showed a slower drug release for dosage forms with a denser network. Higuchi's model was used for prediction of drug release and showed limited applicability due to different release kinetics for different fill densities. However, using linear interpolation for the prediction resulted in good RMSEP values between 1.4 and 3.7%. These findings might be useful to enable customized production of sustained release solid dosage forms via 3D printing in hospital and community pharmacies in the future.

Application of a chromatic confocal measurement system as new approach for in-line wet film thickness determination in continuous oral film manufacturing processes

The key parameter of the oral film production process is the wet film thickness since it regulates the active pharmaceutical ingredient (API) content of the finished product. There is no general recommendation on how to adjust the gap height of the coating knife during the film manufacturing process to obtain the target content. Therefore, trial and error approaches are common to determine the surplus of drug for every newly developed formulation. This wastes resources, money and time and calls for an adequate in-line tool for wet film thickness measurement during the film manufacturing process to ensure consistent quality. In this work, a chromatic confocal optical probe was implemented into a continuous oral film manufacturing process on a pilot-scale coating bench. The optical probe allows a non-destructive and contactless wet film thickness measurement. The validation of the method showed good results. Linearity was demonstrated over a wide range of film thicknesses (R² = 0.999). A good precision between different films was revealed by a coefficient of variation smaller than 2%. The robustness investigations showed that the method is applicable for transparent and non-transparent film forming masses. Furthermore, coloring agents, particles in the polymer mass and different viscosities do not influence the thickness measurement.

Formulation development and process analysis of drug-loaded filaments manufactured via hot-melt extrusion for 3D-printing of medicines

Three dimensional(3D)-printing via fused deposition modeling (FDM) allows the production of individualized solid dosage forms. However, for bringing this benefit to the patient, active pharmaceutical ingredient (API)-loaded filaments of pharmaceutical grade excipients are necessary as feedstock and have to be produced industrially. As large-scale production of API-loaded filaments has not been described in literature, this study presents a development of 3D-printable filaments, which can continuously be produced via hot-melt extrusion. Further, a combination of testing methods for mechanical resilience of filaments was applied to improve the prediction of their printability. Eudragit RL was chosen as a sustained release polymer and theophylline (30%) as thermally stable model drug. Stearic acid (7%) and polyethylene glycol 4000 (10%), were evaluated as suitable plasticizers for producing 3D-printable filaments. The two formulations were printed into solid dosage forms and analyzed regarding their dissolution profiles. This revealed that stearic acid maintained sustained release properties of the matrix whereas polyethylene glycol 4000 did not. Analysis of the continuous extrusion process was done using a design of experiments. It showed that powder feed rate and speed of the stretching device used after extrusion predominantly determine the diameter of the filament and thereby the mechanical resilience of a filament.

A critical review on tablet disintegration

CONTEXT

Tablet disintegration is an important factor for drug release and can be modified with excipients called tablet disintegrants. Tablet disintegrants act via different mechanisms and the efficacy of these excipients is influenced by various factors.

OBJECTIVE

In this review, the existing literature on tablet disintegration is critically reviewed. Potential disintegration mechanisms, as well as impact factors on the disintegration process will be discussed based on experimental evidence.

METHODS

Search terms for Scopus and Web of Science included "tablet disintegration", "mechanism tablet disintegration", "superdisintegrants", "disintegrants", "swelling force", "disintegration force", "disintegration mechanisms", as well as brand names of commonly applied superdisintegrants. References of identified papers were screened as well.

RESULTS

Experimental data supports swelling and shape recovery as main mechanisms of action of disintegrants. Other tablet excipients and different manufacturing techniques greatly influence the disintegration process.

CONCLUSION

The use of different excipients, experimental setups and manufacturing techniques, as well as the demand for original research led to a distinct patchwork of knowledge. Broader, more systematic approaches are necessary not only to structure the past but also future findings.

Systematic classification of tablet disintegrants by water uptake and force development kinetics

Objective

Water uptake and force development of disintegrating tablets provide a high degree of information about the disintegration mechanisms and process itself. An apparatus for the simultaneous measurement of water uptake and force development of tablets is presented, and the gathered data are analysed.

Methods

Flat faced, 10 mm, dibasic calcium phosphate tablets containing 2% disintegrant are investigated with the newly constructed apparatus. The force is determined with a texture analyser, whereas the water uptake is recorded by a balance. Different measurement regimes are compared with each other. Measured curves are analysed according to their shape and fitted with a modified Hill equation.

Key findings

Known disintegration mechanisms can be confirmed with the newly constructed apparatus – swelling for sodium starch glycolate and croscarmellose sodium, and shape recovery for crospovidone disintegrants. Different brands of polacrilin potassium act by different mechanisms. All curves could be fitted successfully with a modified Hill equation. A novel classification to facilitate the appropriate disintegrant selection is presented on basis of the fit parameters.

Conclusion

The new apparatus allows the acquisition of water uptake and force data simultaneously. Parameters calculated with the modified Hill equation provide a simple way to classify disintegrants according to their behaviour.

Compaction behavior of isomalt after roll compaction

The suitability of the new isomalt grade galenIQ™ 801 for dry granulation and following tableting is evaluated in this study. Isomalt alone, as well as a blend of equal parts with dibasic calcium phosphate, is roll compacted and tableted. Particle size distribution and flowability of the granules and friability and disintegration time of the tablets are determined. Tensile strength of tablets is related to the specific compaction force during roll compaction and the tableting force. In all cases, the tensile strength increases with raising tableting forces. The specific compaction force has a different influence. For isomalt alone the tensile strength is highest for tablets made from granules prepared at 2 kN/cm and 6 kN/cm and decreases at higher values, i.e., >10 kN/cm. Tensile strength of the blend tablets is almost one third lower compared to the strongest tablets of pure isomalt. Friability of pure isomalt tablets is above the limit. Disintegration time is longest when the tensile strength is at its maximum and decreases with higher porosity and lower tensile strengths. Isomalt proves to be suitable for tableting after roll compaction. Even though the capacity as a binder might not be as high as of other excipients, it is a further alternative for the formulation scientist.