Biomedical subjects

A Muñoz-Ruiz

Publications and source records attributed to A Muñoz-Ruiz.

3 recordsLinked to original sources

PubMed1997

Frictional work in double-sided tablet compression.

The aim of this study was to evaluate the friction during double-sided tablet compression. Dicalcium phosphate dihydrate and lactose were tabletted with a compaction simulator with symmetrical and asymmetrical double-sided sawtooth punch displacement profiles. The estimation of force transmission in a powder column was based on an exponential equation, including the material parameter consisting of both the friction coefficient and Poisson's ratio. This parameter was predetermined from a single-sided compression. A novel equation was derived from a previously presented equation for friction work in single-sided tablet compression. The basic assumption was drawn from the linearly decreasing movement of infinitely thin particle layers, which are produced as the compressing punch surface approaches the other punch. This calculation was also based on the assumption that the equilibrium point, where the particles do not move, is halfway between the punches in the symmetrical profile and at a distance proportional to the amplitudes of the asymmetrical upper and lower sawtooth profiles. The tensile strength of tablets compressed with single-double-sided profiles was identical, and thus the behavior of the materials studied under compression was independent of the compression profiles. The friction work values that were calculated with the proposed expression for double-sided profiles were close to the theoretical values, as estimated by calculations based on compressions with single-sided profiles. In conclusion, the novel mathematical expression opens new possibilities for the evaluation of friction in double-sided compression; for example, in rotary press tabletting.

Friction↗

PubMed1996

Time-dependent densification behaviour of cyclodextrins.

Understanding of volume reduction mechanisms is a valuable aid in the development of robust cyclodextrin tablet formulations. The particle and powder properties of alpha-, beta-, gamma- and hydroxypropyl (HP)-beta-cyclodextrins and their behaviour under compression were examined. The cyclodextrins studied showed big differences in particle-size distribution and particle shape. The highest densification on tapping was found for cyclodextrins having the smallest particle size. Cyclodextrins were compressed using single-sided saw-tooth displacement-time profiles at rates of 3 and 300 mm s-1 with a compaction simulator. The densification of the powders was examined by Heckel treatment, using the tablet-in-die and ejected-tablet methods. The cyclodextrins were denser at the beginning of the tableting process (at low pressures) if high rather than low velocity was used. Ranking according to their tendency toward total deformation and permanent plastic deformation was: HP-beta-cyclodextrin > beta-cyclodextrin > gamma-cyclodextrin > alpha-cyclodextrin. The ranking order in strain-rate sensitivity (SRS) of total deformation was HP-beta-cyclodextrin > > gamma-cyclodextrin > or = alpha-cyclodextrin > or = beta-cyclodextrin. On the basis of yield pressure values and the Heckel plot profiles, all the cyclodextrins were highly prone to plastic deformation. Cyclodextrins showed time-dependent consolidation behaviour manifested as increased yield pressure with decreased contact time. A ratio was defined between the SRS of fast elastic recovery and total elastic recovery. The two materials with high ratios, HP-beta-cyclodextrin and beta-cyclodextrin, were especially prone to fast elastic recovery with increasing punch velocities; gamma-cyclodextrin and alpha-cyclodextrin had low values and were less prone. On the basis of this parameter it might be possible to categorize pharmaceutical materials according to capping tendency.

Chemical Phenomena↗

PubMed1994

Study of the compaction mechanisms of lactose-based direct compression excipients using indentation hardness and Heckel plots.

Indentation hardness of tablet surfaces has been used to determine the consolidation mechanisms of the lactose-based excipients Fast Flo Lactose, Ludipress, Cellactose and Tablettose. The Leuenberger equation has been modified to obtain values of compressibility and compactability by using a value of compactability obtained from a tablet at maximum applied force and by substituting deformation resistance by relative deformation resistance. Also, parameters obtained from plots of the Heckel tablet-indie and ejected-tablet methods were calculated in order to establish the comparative consolidation mechanisms in the lactose-based excipients under study. The possibility of using the absolute value of the difference between upper and lower surface hardnesses of the tablets made on an eccentric press is suggested as an alternative method to determine the comparative consolidation mechanisms of different substances.

Cellulose↗