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The load necessary to fracture lactose monohydrate tablets under diametral compression has been determined using an Instron physical testing instrument, so that true tensile failure was obtained in all cases, leading to improved reproducibility. Four ranges of tablet thickness were examined at 12.7 mm diameter. All tablets gave a linear increase of breaking load with compaction pressure up to 310 MN/m2. Expressing the tablet strength as the breaking load gave a separate regression line for each range of tablet thickness, whereas the use of tensile strength provided a common regression line, within given statistical limits, for all but the lowest range of tablet thickness. The fact that such a correlation is possible shows that the tensile strength is a property of the "as compacted" material and provides a new and useful parameter to maintain constancy of properties when tablet size is changed.Pharmaceutical tablets, when compressed diametrically, as in any of the tablet crushing tests normally applied, may fracture in any of the five ways shown in the upper part of Fig. 1. Failure by any of the first four mechanisms (a-d) will lead to greater variability in the crushing strength measurements than will failure by mechanism 1 (e). This is purely tensile fracture, giving a straight crack dividing the tablet into two semi-circular parts. It occurs only when the force applied to break the tablet is carefully controlled: in such circumstances the stress distribution within the tablet is calculable (Frocht, 1948) and is as shown in the lower part of Fig. 1. The vertical stress component my varies along the vertical diameter, as does the maximum shear stress T. The horizontal stress component mx, however, is virtually constant along the vertical diameter and tends to split the tablet into two equal halves. The value of this uniform horizontal stress is, at failure, the ultimate tensile strength of the "as compacted" material forming the tablet, and is given by 2P nDtwhere P is the load necessary to cause fracture, D is the tablet diameter and t is its thickness. The various versions of the crushing strength tests have been compared by . To ensure correct load application, it is sometimes necessary to have packing pieces between the tablet and the loading platens, and experiment appears to be the only method of assessing the nature and quantity of padding required. Recognition of tensile failure is, however, readily made by inspection of the tablets after fracture.

Triboelectri®cation of pharmaceutical powder systems during various processing operations may give rise to adhesion and cohesion effects. The aim of this work was to investigate the electrostatic charging of size-fractionated lactose after contact with materials used in pharmaceutical processing and manufacturing operations.Triboelectri®cation of fractionated lactose samples was effected through transport at a known gas velocity to make contact with the surface of a cyclone separator constructed from materials typically used for the manufacture of pharmaceutical processing equipment and drug delivery devices. Generally, for all contact surfaces, the magnitude of charge on the lactose samples increased with decreasing particle size, over the range 90±1000 mm, and increasing gas velocity. The charge was electronegative for stainless steel and acetal but electropositive for PVC and polypropylene. The results indicate that a triboelectric series could be proposed by ranking materials in order of increasing work function (i.e. stainless steel, acetal, lactose, polypropylene and PVC).The results show the dependence of electrostatic charge on particle size and type of contact material, which has important implications for pharmaceutical processing and drug delivery.

Triboelectrification affects particle adhesion and agglomeration and hence the formulation, manufacture, and use of dry powder inhaler (DPI) devices. Electrostatic charge measurement of two component mixes of spray-dried or crystalline lactose fine particles (< 10 microns) 0, 5, 10, 15, 20, and 30% w/w with spray-dried or crystalline lactose 63-90 microns, respectively, has been undertaken using a system incorporating pneumatic transport of the mixed powders to a stainless steel cyclone charging device. The magnitude of charge on the mixes was shown to decrease with increased fine particle content, and there was no significant difference in charge for each concentration between spray-dried and crystalline lactose. Both the variation of charge and powder adhesion to the cyclone surface increased with increase in fine particle content. The proportion of fine particles in carrier systems in DPIs may thus have an important role where triboelectrification is involved.

A method previously described was used to determine the hyaluronic acid concentration in synovia from normal and arthritic horse joints. The concentration of hyaluronic acid in the synovia from arthritic joints was found to be significantly lower than the concentration in fluid from normal joints.