Axial tensile fracture of microcrystalline cellulose compacts.

An adapted tensile stress methodology for the fracture of microcrystalline cellulose (MCC) tablets has been investigated and implemented. The application of the generally applied linear elastic fracture mechanic (LEFM) parameters used to describe the fracture behaviour of these porous systems has been discussed. The application of an effective crack length concept, comprising of the notch depth and a process zone length designated delta c, has enabled the localised non-linear response of the MCC tablets to be characterised in a quantified manner. The requirement of the composite value delta c is postulated to be a direct result of the internal properties of the tablet formed during the compaction process due to its strong dependence on porosity. The high compact relative density creates a greater possibility for both local small-scale plastic yielding at the crack tip, commonly found in polymer materials and microcracking ahead of the crack tip, typically observed in the fracture of ceramics. The extrapolated value of KIC0 of 0.72 MPa m0.5 found in this work lies within the range found in literature for this material indicating that the adopted procedure is acceptable for the determination of the resistance to fracture of MCC compacts.

A study on the coherence of compacted binary composites of microcrystalline cellulose and paracetamol.

This paper describes and interprets the coherence and the tensile strength of bi-component compacted tablets, composing a mixture of a poorly compactable drug, paracetamol and a very cohesive and ductile carrier, microcrystalline cellulose (MCC), Avicel PH 102, using the concepts of the stored elastic strain in conjunction with the particle size and the relative volume fraction of the powders. Cylindrical compacts of the bi-component tablets, at various compositions formed at a common ultimate stress of 99 MPa, were subsequently fractured using the indirect tensile test method (Brazilian test method) to obtain a measure of their tensile strength. Various inter-relations between the compaction and tensile rupture characteristics are described. A simple model, which may predict the required volume fraction of MCC to produce a cohesively viable tablet is suggested, and applied to the current system. The results show to some extent the consistency of the suggested model with the experimental results.

The effect of nasal patency on the clearance of radiolabeled saline in healthy volunteers.

PURPOSE: The objective of this study was to investigate the effect of nasal cavity patency on the penetration, deposition, and clearance of an aqueous isotonic saline solution. METHODS: The study was carried out as a single center, open, randomized, 2-way cross-over in healthy volunteers. Nasal patency was assessed using misting patterns on a cold metal surface at the beginning and end of study. 100 microl of technetium-99m radiolabeled saline solution was introduced into either the most or least patent nasal cavity using a purpose designed spray device. The distribution and residence time of the radiolabel was followed for 2 hours using gamma scintigraphy. RESULTS: The mean times to 50% clearance were 34+/-7 and 28+/-12 minutes (+/- s.d.) for the side view of the least and most patent nasal cavity respectively. Total clearance of the radiolabelled saline from the nose was not affected by patency. Between 7 and 35% of the radiolabelled saline solution remained in the nasal cavity at the end of imaging. Using endoscopy to track the clearance of an aqueous solution of food dye using the same delivery procedure, identified this region as hair in the nasal vestibule. The dye was seen to dry in this region along with the mucus. CONCLUSIONS: Nasal patency affects the initial, but not total clearance of solutions, however, the remaining solution may not be available for drug delivery.

Effects of compaction variables on porosity and material tensile strength of convex-faced aspirin tablets.

The porosity and tensile strength of convex-faced aspirin tablets formed under a compaction pressure in the range 40-320 MPa and at punch velocities in the range 0.008 to 500 mm s-1 have been determined. The material tensile strength, sigma f, was calculated from the observed fracture load, Ps, using the equation of Pitt et al (1988): sigma f = 10 Ps/pi D2(2.84 t/D - 0.126 t/W + 3.15 W/D + 0.01)-1 where D is the tablet diameter, t is the overall tablet thickness and W is the central cylinder thickness. Tablets formed at lower compaction pressures had a higher porosity and lower tensile strength than those formed at higher compaction pressures. Tablets of face curvature ratio (D/R) in the range 0.25-0.67 and a normalized cylinder length (W/D) of 0.2 had the optimum tensile strength. (R is the radius of curvature of the tablet face.) Tablets formed at high compaction rates were significantly weaker than those formed at lower compaction rates.

The material tensile strength of convex-faced aspirin tablets.

The material tensile strength of a range of convex-faced tablets, compacted under controlled conditions at pressures of 40 and 320 MPa from a size fraction of acetylsalicylic acid, has been assessed. The calculation of the tensile strength sigma 1, from observed fracture loads obtained in diametral compression testing, is based on the equation derived by Pitt et al (1988), namely: (formula; see text) where P is the fracture load, D is the tablet diameter, t is the overall tablet thickness and W is the central cylinder thickness. The strength of a tablet of a given shape compacted at 320 MPa was between two and four times greater than that of a similar tablet compacted at 40 MPa. For the thicker tablets (W/D greater than or equal to 0.2) the material tensile strength was practically independent of shape. For the thinner tablets (W/D = 0.1) the material tensile strength varied considerably with face-curvature, showing a maximum for each of the two compaction pressures at a D/R value of 0.67.