Characterisation and modelling of the thermorheological properties of pharmaceutical polymers and their blends using capillary rheometry: Implications for hot melt processing of dosage forms

Role of rheology in formulation and process design of hot melt extruded amorphous solid dispersions

Hot melt extrusion (HME) has been widely used as a continuous and highly flexible pharmaceutical manufacturing process for the production of a variety of dosage forms. In particular, HME enables preparation of amorphous solid dispersions (ASDs) which can improve bioavailability of poorly water-soluble drugs. The rheological properties of drug-polymer mixtures can significantly influence the processability of drug formulations via HME and eventually the end-use product properties such as physical stability and drug release. The objective of this review is to provide an overview of various rheological techniques and properties that can be used to evaluate the flow behavior and processability of the drug-polymer mixtures as well as formulation characteristics such as drug-polymer interactions, miscibility/solubility, and plasticization to improve the HME processability. An overview of the thermodynamics and kinetics of ASD processing by HME is also provided, as well as aspects of scale-up and process modeling, highlighting rheological properties on formulation design and process development. Overall, this review provides valuable insights into critical rheological properties which can be used as a predictive tool to optimize the HME processing conditions.

3D printing of pharmaceutical oral solid dosage forms by fused deposition: the enhancement of printability using plasticised HPMCAS

3D printing (3DP) by fused deposition modelling (FDM) is one of the most extensively developed methods in additive manufacturing. Optimizing printability by improving feedability, nozzle extrusion, and layer deposition is crucial for manufacturing solid oral dosage forms with desirable properties. This work aimed to use HPMCAS (Affinisol^TM HPMCAS 716) to prepare filaments for FDM-3DP using hot-melt extrusion (HME). It explored and demonstrated the effect of HME-filament composition and fabrication on printability by evaluating thermal, mechanical, and thermo-rheological properties. It also showed that the HME-Polymer filament composition used in FDM-3DP manufacture of oral solid dosage forms provides a tailored drug release profile. HME (HAAKE MiniLab) and FDM-3DP (MakerBot) were used to prepare HME-filaments and printed objects, respectively. Two diverse ways of improving the mechanical properties of HME-filaments were deduced by changing the formulation to enable feeding through the roller gears of the printer nozzle. These include plasticizing the polymer and adding an insoluble structuring agent (talc) into the formulation. Experimental feedability was predicted using texture analysis results was a function of PEG concentration, and glass-transition temperature (T_g) values of HME-filaments. The effect of high HME screw speed (100 rpm) resulted in inhomogeneity of HME-filament, which resulted in inconsistency of the printer nozzle extrudate and printed layers. The variability of the glass-transition temperature (T_g) of the HME-filament supported by scanning electron microscopy (SEM) images of nozzle extrudates and the lateral wall of the printed tablet helped explain this result. The melt viscosity of HPMCAS formulations was investigated using a capillary rheometer. The high viscosity of unplasticized HPMCAS was concluded to be an additional restriction for nozzle extrusion. The plasticization of HPMCAS and the addition of talc into the formulation were shown to improve thickness consistency of printed layers (using homogeneous HME-filaments). A good correlation (R²=0.9546) between the solidification threshold (low-frequency oscillation test determined by parallel-plate rheometer) and T_g of HME-filaments was also established. Drug-loaded and placebo HPMCAS-based formulations were shown to be successfully printed, with the former providing tailored drug release profiles based on variation of internal geometry (infill).

Drug release from hydroxypropylcellulose gels cannot be statistically predicted from their viscometric and initial viscoelastic properties

This study questioned whether rheological properties can predict drug (metronidazole) release from Hydroxypropylcellulose (HPC) platforms. Viscometric and viscoelastic properties of aqueous, alcohols/diols and mixed solvent HPC solutions and gels were determined using viscometry and oscillatory analysis. Drug release was conducted at pH 7.4 under sink conditions. Relationships between rheological parameters and drug release were modelled using multiple linear stepwise regression. Viscometry identified ethanol and water as good solvents for HPC. Diol solvents were predicted to exhibit greater interactions with HPC (COSMO modelling) but possessed lowest intrinsic viscosities. Pentanediol or ethylene glycol prepared gels exhibited greatest elasticity. No relationships were observed between dilute solution properties and initial gel viscoelasticity. Drug release from HPC gels occurred via gel erosion and diffusion. No relationships were observed between initial gel viscoelasticity and drug release and thus, for gel platforms that undergo erosion in aqueous media, drug release cannot be predicted from initial gel viscoelasticity.

Mechanical properties and drug release of venlafaxine HCl solid mini matrices prepared by hot-melt extrusion and hot or ambient compression

Objective/significance: To elucidate the role of plasticizers in different mini matrices and correlate mechanical properties with drug release.

METHODS

Cylindrical pellets were prepared by hot-melt extrusion (HME) and mini tablets by hot (HC) and ambient compression (AC). Venlafaxine HCl was the model drug, Eudragit^® RSPO the matrix former and citric acid or Lutrol^® F127 the plasticizers. The matrices were characterized for morphology, crystallinity, and mechanical properties. The influence of plasticizer's type and content on the extrusion pressure (P_e) during HME and ejection during tableting was examined and the mechanical properties were correlated with drug release parameters.

RESULTS

Resistance to extrusion and tablet ejection force were reduced by Lutrol^® F127 which also produced softer and weaker pellets with faster release, but harder and stronger HC tablets with slower release. HME pellets showed greater tensile strength (T) and 100 times slower release than tablets. P_e correlated with T and resistance to deformation of the corresponding pellets (r² = 0.963 and 0.945). For both HME and HC matrices the decrease of drug release with T followed a single straight line (r² = 0.990) and for HME the diffusion coefficient (D_e) and retreat rate constant (k_b) decreased linearly with T (r² = 0.934 and 0.972).

CONCLUSIONS

Lutrol^® F127 and citric acid are efficient plasticizers and Lutrol^® F127 is a thermal binder/lubricant in HC compression. The different bonding mechanisms of the matrices were reflected in the mechanical strength and drug release. Relationships established between T and drug release parameters for HME and HC matrices may be useful during formulation work.

Development and optimization of ketoconazole oral strips by means of continuous hot-melt extrusion processing

Objectives

The aim of this study was to develop mucoadhesive oral strips using hot-melt extrusion as a continuous manufacturing process.

Methods

Powder blends of ketoconazole, a water-insoluble drug – either hydroxypropyl methylcellulose (HPMC) or soluplus (SOL), sorbitol (SRB) and magnesium aluminometasilicate (MAS) were extruded to manufacture thin strips with 0.5-mm thickness. The presence of the inorganic metasilicate facilitated smooth processing of the extruded strips as it worked as an absorbent directly impacting on the extensive mixing of the drug/excipients inside the extruder barrel.

Key findings

The use of MAS also favoured the rapid hydration, swelling and eventual disintegration of the strips. Differential scanning calorimetry and transmission X-ray diffraction analysis revealed the existence of the amorphous drug within the extruded strips. Scanning electron microscopy and energy dispersive X-ray undertaken on the formulations showed a homogeneous drug distribution within the extruded strips.

Conclusion

The strips produced via continuous hot-melt extrusion processing showed significantly faster release of ketoconazole compared to the bulk drug substance.