Concave Punches Research Articles

Influence of the punch shape on the core and shell structure of press-coated tablets

Press-coated tablets are a key technology to achieve delayed releases in chronotherapeutics. The drug release properties of this kind of tablets are linked to its unique core–shell structure. It is thus important to understand the influence of the process parameters on this structure. As different shapes can be used in the industry, we focused, in this study, on understanding the influence of punch shape on the final structure of a press-coated tablet. Experiments were performed using flat, bevel-edged and concave punches for the coating-compression to study the effect of the punch shape on the final properties of the core but also on the density distribution in the shell. The experiments were supported by numerical simulation to understand the mechanical effects in the powder compression process. It was found that the radial and axial stress state in the shell and in the core during compression is very dependent on the punch shape. The use of concave punches results in a more hydrostatic stress state compared to flat punches. The consequences on the structure are a more homogenous shell and less deformation of the core, which confirms that the tooling shape is a critical parameter to consider for the production of press-coated tablets.

Preparation and Characterization of Hydrophilic Polymer Based Sustained-Release Matrix Tablets of a High Dose Hydrophobic Drug.

The objective of this study was the preparation and characterization of a sustained-release matrix tablet containing a high-dose hydrophobic drug and its comparison with marketed products. In the present study, HPMC was applied as the matrix-forming polymer for the sustained release of clarithromycin (500 mg). The compatibility of clarithromycin and excipients was studied using a binary mixture approach and compatible excipients were selected. Matrix tablets were prepared using the high-shear wet granulation technique. Tablets were compressed using oblong (19 mm), shallow concave punches, under a compression weight of 900 mg/tablet. The flow of granules was evaluated by determining their bulk density, tapped density, angle of repose, Hausner ratio, and Car’s index. Compressed tablets were tested for their physical parameters, mechanical characteristics, drug content, and in vitro drug release, as per United States Pharmacopeia (USP). Clarithromycin is a drug having poor water solubility and showed compatibility with all the excipients used in the formulation of polymeric matrix tablets. FTIR spectra of clarithromycin, before and after being subjected to the stress conditions, confirmed the compatibility of clarithromycin and other ingredients of the matrix tablets. All the formulations exhibited good rheological characteristics and all the parameters related to flow showed results in the acceptable range. Physically, matrix tablets were smooth and shiny, without any surface defects. Weight variation (±5%) and drug content of the tablets (95–102%) were within the pharmacopeial limits. HPMC successfully sustained the drug release for 24 h. It is concluded from the study that dissolution rate of clarithromycin can be sustained using hydrophilic polymer (HPMC) as a release-controlling agent.

Electromagnetic forming and perforation of Al tubes

Electromagnetic forming (EMF) is a high energy rate forming process which utilizes electromagnetic force to deform metal workpiece. In this research work, experiments have been conducted to establish the feasibility of electromagnetic forming and perforation (EMFP) of Al tubes. EMFP combines electromagnetic forming with electromagnetic perforation. For the feasibility study split die, pointed and concave punches were designed. The detailed study of the effect of process parameters on EMFP of Al tubes has been carried out. The optimum discharge energy was determined with experimental trials which lead to successful forming and perforation of the tube. In the case of 12-hole perforation with 5 mm stand-off distance, optimum discharge energy observed for pointed punch was 6.2 kJ whereas for the concave punch it reduced to 5.7 kJ. In the case of 36-hole perforation by a concave punch with 10 mm stand-off distance, optimum discharge energy observed was 6.2 kJ. Experimental results show that the concave punches were more suitable for perforation operation as complete removal of blank took place. EMFP overcomes the disadvantages of the formation of burrs and slivers in conventional shearing and perforation.

Effect of friction between powder and tooling on the die-wall pressure evolution during tableting: Experimental and numerical results for flat and concave punches

Tablet final properties are mainly determined during the compaction process by the evolution of the stresses applied to the powder. Any process or product parameter that may influence this stress evolution may have a direct impact on the tablet final properties. In this article, we studied the influence of the friction between the tooling and the powder on the evolution of the die-wall pressure during compaction using flat and concave punches.Experimental studies were performed on microcrystalline cellulose as well as numerical studies using finite element method (FEM) simulation. Both methodologies indicate that increasing the friction between the powder and the tooling promotes an increase in the die-wall pressure during tableting. This is in contradiction with results that can be found in the literature.Moreover, the results of this study showed that for flat punches, the stress evolution is mainly driven by the die/powder friction. On the contrary, for concave punches, changing the punches/powder friction have also a consequence in the evolution of the die-wall pressure. This could have practical consequences in sticking situations where, due film formation on the punches, the friction between the punches and the powder may change during tableting.

Interfacial strength of bilayer pharmaceutical tablets

The oral drug delivery system using bilayer (or multilayer) tablets has been more commonly used in therapeutic strategies. However, one of the most common problems associated with bilayer tablets is the insufficient interfacial strength between layers, which leads to product failure during manufacturing. Therefore, it is important to better understand the interfacial strength of bilayer pharmaceutical tablets. For this purpose, in this study, the interfacial strength of bilayer tablets made of microcrystalline cellulose (MCC PH 102) at various manufacturing conditions was systematically examined. Three cases were considered to explore: (1) the effect of interfacial curvature on the interfacial strength, for which the interfaces between two layers with different curvatures were produced using flat, convex and concave punches. (2) The effect of water content on the interfacial strength, for which the powder was conditioned at various relative humidity before being used to produce bilayer tablets. (3) The effect of the particle size of the powder used in first layer on the interfacial strength, for which the feed powder was sieved to obtain powders with specific particle sizes that were then used to produce the first layer of the bilayer tablets. For all cases considered, direct tensile tests were performed to measure the tablet interfacial strength. It is found that the interfacial curvature, the water content and the particle size in the first layer affected the interfacial strength significantly. It is also shown that the tablet interfacial strength was increased when larger particles were used in the first layer, or when curved punches (i.e. either convex or concave punches) were used to produce curved interfaces with increased interfacial areas. In addition, a higher interfacial strength can also be achieved by properly controlling water content in the powder.

Effect of the Curvature of the Punches on the Shape of the Interface and the Delamination Tendency of Bilayer Tablets

Bilayer tablets are of special interest in the pharmaceutical industry. The main problem during their manufacturing is the occurrence of delamination during or after the ejection from the die. This work studies the influence of using punches with a curvature on the interfacial strength and thus on the delamination tendency of bilayer tablets. Bilayer tablets were produced with a compaction simulator using different flat and concave punches with different radii of curvature. The main compaction pressure was kept constant but the tamping force was varied. Two bilayer model systems were studied. The interfacial strength was determined using a previously described indentation test. The factors studied were analyzed for statistical significance with respect to the responses. The curvature of the interface was found to be higher when the curvature of the punch and the tamping force increased. Breaking tests then demonstrated that, for bilayer tablets obtained using the same compression parameters, the interfacial strength was lower when the curvature of the interface increased. As a consequence, when producing bilayer tablets with concave punches, it is important to choose properly the tableting parameters in order to have an interface between the layers as flat as possible to avoid delamination issues.

Formulation Development and in-vitro Evaluation of Sulfasalazine and Dexamethasone Combination Tablets Containing Natural and Semi Synthetic Polymer for Colon Targeting

The present research was to develop oral sustained release tablets for colon targeting. Two drugs in combination form were used in this research to prepared tablets. Combination of sulfasalazine and dexamethasone used with natural and semi synthetic polymers (tragacanth and HPMC K15). Sustained release matrix tablets of sulfasalazine and dexamethasone were prepared by using different ratios of drug, HPMC K15 and tragacanth. Microcrystalline cellulose (MCC) and lactose were used as diluents. Both polymers were mixed with other ingredients and formed a matrix system using direct compression technique. All the ingredients of formulation were compressed using concave punches in ZP 19 compression machine. Compressed tablets were evaluated for assay, diameter, hardness, thickness, friability, weight variation and in vitro dissolution using USP dissolution apparatus type II. Different formulations were prepared and evaluated with respect to dissolution profile in 900 mL 0.1 N Hcl and phosphate buffer pH 6.8 and pH7.4 including microbial flora for 12 h at 37˚C. Rising the amount of polymer (HPMC K15) in the formulation led to slow release of drug and decreasing the amount of polymer gave enhanced release of sulfasalazine and dexamethasone. Different mathematical models used to evaluate the matrix system (Zero order, First order, Higuchi and Hixson-Crowell). T5, T7, T8 solid matrix formulations followed zero order and Higuchi. The results showed that the formulation T7 containing 17% HPMC K15 and 17% gum tragacanth gives better results in microbial flora with phosphate buffer. Key words: HPMC K15, Tragacanth gum, Sulfasalazine, Dexamethasone, Sustained release.

Formulation evaluation and stability studies of hydrogel tablets containing Cefditoren Pivoxil

AimCefditoren Pivoxil hydrogel tablets were prepared to achieve the gastro retentive effect in order to improve its absorption and bioavailability. MethodsThe formulations were made by varying the concentrations of carbopol and sodium alginate. The prepared blends were compressed directly using a 16-station rotary punch tablet machine (Cadmach, Germany) having caplet shaped concave punches. Stability studies for the selected formulation were performed as per the ICH protocol. ResultsThe pre-compression parameters and post compression parameters were within acceptable pharmacopeial limits. The tablets prepared with sodium carbonate showed good porosity in the swelling index studies. The in-vitro dissolution behavior shows that the formulations that contain carbopol (100 mg) and sodium alginate (30 mg) were found to have good controlled release of 95.012% at 24th hour. ConclusionBy preparing Cefditoren Pivoxil hydrogels with the above mentioned polymers gastro retentive effect was achieved, further the drug release can be controlled.

A concave indenter on a piezoelectromagneto-elastic substrate or a layer elastically supported

Indentation of piezoelectromagneto-elastic half-space or a layer on a two-parameter elastic foundation by a cylindrical indenter with a slightly concave base is considered. Full-field magnetoelectro-elastic solutions in elementary functions are obtained for the case of full contact and half-space. If the axial load is small, the contact area will be an annulus the outer circumference of which coincides with the edge of the punch. The inner circumference will shrink with increasing load and there will be a critical load above which the stratum makes contact with the entire punch base. The contact problem for high loads can therefore be treated by classical methods. The more interested case in which the load is less the critical value and the contact region is annulus remains. By use the methods of triple integral equations and series solution technique the solution for an indentured substrate over an annular contact region is also given. For parabolic and conical concave punches the exact or approximate solutions are obtained for full contact or annular contact region, respectively. For the layer on two-parameter elastic foundation and concave punch approximate solution is established.

Investigating the effect of punch geometry on high speed tableting through radial die-wall pressure monitoring

Dwell time mainly depends on punch geometry, so some tableting problems such as capping and lamination could occur at high speed compaction. Robust tools are required to monitor the interaction of punch tip and powder bed at these high speeds. Our aim was to investigate the effect of punch geometry (flat and standard concave) on powder compaction at high speed using radial die-wall pressure (RDWP) as a monitoring tool. Instrumented die guided by compaction simulation was applied for five materials with different compaction behaviors. Flat-faced punch showed higher residual, maximum die-wall pressures, and axial stress transmission than concave punches, p < 0.003. Moreover, flat-faced punches showed less friction upon ejection, p < 0.003. Flat compacts showed higher elastic recovery, tensile strength, and required less work of compaction than convex compacts, p < 0.05. RDWP monitoring was a useful tool to prove that flat-faced punch induced higher radial stresses and particle/particle interactions in comparison to concave punch.

On Adhesion Enhancement Due to Concave Surface Geometries

Recent experimental and theoretical work in literature has showed that several biological attachment devices are concave in shape and that such a shape enhances adhesion strength. In this paper, an analytical model is developed for the pull-off forces required to separate a rigid axisymmetric concave punch from an elastic half-space with the goal of understanding how concave shapes seen in both biological and man-made adhesive systems can outperform other geometries. Significant enhancement in adhesion strength compared with that of a flat punch was predicted for both spherical and elliptical concave punch profiles. Increasing the degree of the concavity initially increases the resulting pull-off force, but for higher depths the contact interface will separate before pull-off forces higher than those for the flat punch are achieved. Experiments performed with machined aluminum elliptical concave punches on gelatin qualitatively verified the trends predicted by the analytical model, and the maximum pull-off forces measured are within 80% of the predicted optimum pull-off force. These findings emphasize the benefits of concave geometries for designing interfaces which enhance adhesion through geometry alone.

Fast-Disintegrating Sublingual Epinephrine Tablets: Effect of Tablet Dimensions on Tablet Characteristics

ABSTRACTThe purpose of this study was to evaluate the effect of changing dimensions on the hardness (H), disintegration time (DT), and wetting time (WT) of fast-disintegrating epinephrine tablets for sublingual administration as potential first aid treatment for anaphylaxis. Tablet formulations I and II, containing 0% and 10% epinephrine bitartrate, respectively, and weighing 150 mg were prepared by direct compression. Formulations were compressed at a range of forces using an 8/32″ die with concave punches (CP); a 10/32″ and an 11/32″ die with CP and flat punches (FP). Tablet weight variation, content uniformity, thickness, H, DT, and WT were measured. The 8/32″, 10/32″, and 11/32″ dies resulted in tablet thickness of ranges 0.25–0.19″, 0.17–0.1″, and 0.16–0.08″, respectively. The DT and WT using the 8/32″ die were ≤10 and ≤30 sec, respectively, at H ≤5.4 ± 0.2 kg for formulation I, and H ≤5.4 ± 0.3 kg for formulation II. The DT and WT were ≤10 and ≤30 sec, respectively, using 10/32″ die/CP, 10/32″ die/FP, 11/32″ die/CP, and 11/32″ die/FP at H ≤6.2 ± 0.6 kg, ≤6.8 ± 0.4 kg, ≤4.9 ± 0.1 kg, and ≤7.2 ± 0.3 kg, respectively, for formulation I. For formulation II, the DT and WT were ≤10 sec and ≤30 sec, respectively, when H < 4 kg. No difference in DT and WT was observed between concave and flat tablets. The 11/32″ and 10/32″ dies resulted in more ideal tablet dimensions for sublingual administration, but H must be maintained <4 kg to ensure rapid DT and WT.

Effect of punch tip geometry and embossment on the punch tip adherence of a model ibuprofen formulation.

The sticking of a model ibuprofen-lactose formulation with respect to compaction force, punch tip geometry and punch tip embossment was assessed. Compaction was performed at 10, 25 or 40 kN using an instrumented single-punch tablet press. Three sets of 'normal' concave punches were used to evaluate the influence of punch curvature and diameter. The punches were 10, 11 and 12 mm in diameter, respectively. The 10-mm punch was embossed with a letter 'A' logo to assess the influence of an embossment on sticking. Flat-faced punches (12.5 mm) were used for comparison with the concave tooling. Surface profiles (Taylor Hobson Talysurf 120) of the upper punch faces were obtained to evaluate the surface quality of the tooling used. Following compaction, ibuprofen attached to the upper punch face was quantified by spectroscopy. Increasing punch curvature from flat-faced punches to concave decreased sticking. Altering punch diameter of the concave punches had no effect on sticking when expressed as microg mm(-2). The embossed letter 'A' logo increased sticking considerably owing to the probable concentration of shear stresses at the lateral faces of the embossed logo.

Influence of the punch diameter and curvature on the yield pressure of MCC-compacts during Heckel analysis

The volume reduction behaviour of powders has been quantified by means of the 'in-die' yield pressure (YP) using Heckel analysis. However, because different YPs are reported for the same material, the experimental conditions influencing this material-constant were investigated. Silicified microcrystalline cellulose was compressed into flat-faced and convex tablets using a compaction simulator instrumented with load and displacement transducers. During compression, upper and lower punch force and displacement data were recorded and corrected for punch deformation. A symmetrical triangle wave compression profile was used and the instantaneous punch velocity was kept constant (5mm/s). Individual tablet height and weight were used for Heckel analysis. The influence of the 'effective compression pressure' (P(EFF)) (ranging from 10 to 350 MPa), punch diameter (PD) (4, 9.5 and 12 mm) and filling depth (FD) (4.5, 7.5 and 10.5mm) on YP was statistically evaluated using Response Surface Modelling software. A quadratic surface response equation, describing the relationship between P(EFF), PD, FD and YP, was proposed for concave (Adj R(2): 0.8424; S.D.: 14.60 MPa) and flat-faced (Adj R(2): 0.8409; S.D.: 4.49 MPa) punches. YP and tensile strength were mainly determined by P(EFF), irrespective of punch curvature. FD and PD had only a minor influence on the YP, although more pronounced for the concave punches. The method used resulted in reproducible P(EFF) and tensile strength values and the flat-faced tablets showed less weight variation. Flat-faced punches are preferred over punches with a concave surface when investigating the volume reduction behaviour of a powder by means of Heckel analysis and the experimental parameters should be reported.

On all-optical laser cleaning and inspection of contaminated concave metal surfaces

A technique for all-optical laser cleaning and surface quality monitoring of concave metal surfaces is suggested. Contaminated pharmaceutical punches from a tablet compression machine were cleaned using high-energy laser pulses. Image information obtained from a diffractive-optical-element-based sensor was used in inspection of the surface quality change of the concave punches due to laser cleaning. Alternative method for mechanical cleaning of punches is introduced, which is based on simultaneous laser cleaning and surface quality inspection of the punches.

Diffractive optical element based sensor for surface quality inspection of concave punches

Optical surface quality of concave shaped punches was investigated with a diffractive optical element based sensor. Image information of the present sensor was studied for the purpose of surface roughness and reflectance inspection. The robust sensor is proposed for off-line optical inspection of concave punches.

Punch Geometry and Formulation Considerations in Reducing Tablet Friability and Their Effect on In Vitro Dissolution

The tablet friability resulting from formulation variations was studied under controlled granulation moisture content and tablet crushing strength. Tablets made with lactose were more friable than tablets made with microcrystalline cellulose. Replacement of 0.5% magnesium stearate with 0.5% stearic acid in the formula reduced tablet friability, whereas the combination of 0.5% stearic acid and up to 0.25% magnesium stearate did not increase tablet friability, decrease drug dissolution rate, or increase tablet-to-tablet variability in dissolution. Tablets compressed with extra deep concave punches resulted in lower friability compared with tablets compressed with standard concave or deep concave punches. The friabilities of the standard convex and deep convex tablets were similar, indicating that a critical level of punch tip curvature was important in reducing tablet friability. The dissolution rate was not affected by the punch tip geometry, but the tablet-to-tablet dissolution variability at the 0.5% stearic acid level for the extra deep convex tablets was higher compared with the standard convex tablets.

Contact Stresses of an Elastic Layer Indented by a Concave Rigid Punch

In this paper, the authors analyze exactly the stress state of an elastic layer indented by an axisymmetric concave rigid punch when the indented load is small and the contact region is an annulus. Numerical examples are presented for parabolic and conical concave punches. For each case, we show the distributions of surface displacements and contact stresses and clarify the relationships among the parameters of the indented load, the indented depth, the punch face confuguration and the layer's thickness.

Indentation of an Elastic Half‐Space by a Concave Rigid Punch

AbstractIn this paper, the author analyzes exactly the stress state of an elastic half‐space indented by an axisymmetric concave rigid punch when the indented load is small and the contact area is an annulus. Numerical examples are presented for parabolic and conical concave punches.