Application of Externally Applied Lower Punch Vibration and its Effects on Tablet Manufacturing.

PURPOSE: In the present study the influence and application of a newly developed external lower punch vibration system for an improved die filling on a running rotary tablet press was investigated. METHODS: Tablets were manufactured at different conditions (with and without vibration) and characterized regarding their direct compressibility and mechanical stability. Thus, two typical pharmaceutical binders for direct compression (Parmcel 102 and Tablettose® 80) were compared with two binders unsuitable for direct compression (Ceolus® KG1000 and GranuLac® 200). The powders were characterized by helium pycnometry, laser diffraction, scanning electron microscopy, and by determination of the powder flow. Furthermore, a novel technique to determine the occurrences of segregation within a tablet after manufacturing was introduced. For this purpose, a powder blend containing one spray-colored type of microcrystalline cellulose (Vivapur® 200) were prepared. RESULTS: It was shown that under application of externally applied lower punch vibration, the powder flow into the die increased and thus the die filling process was significantly improved. Hence, it was possible to manufacture tablets from powders, which are actually unsuitable for direct compression. In addition, the mechanical stability of the produced tablets was distinctly improved by application of lower punch vibration, whereby the occurrence of segregation was comparatively low. CONCLUSION: In summary, lower punch vibration allows a more efficient die filling, whereby the powder flow as well as mechanical stability of the tablets are improved.

Performance Characteristics of a Novel Vibration Technique for the Densification of a Powder Bed within a Die of a Rotary Tablet Press - a Proof of Concept.

The aim of this study was to investigate the concept of lower punch vibration as a possible approach to densify the powder bed within the die of a rotary tablet press. Therefore, a laboratory vibration equipment was developed to obtain a better understanding of the performance characteristics and effects of a pneumatically generated vibration system on pharmaceutical powders. For this purpose, two widely used pharmaceutical powders, basic magnesium carbonate (Pharmagnesia MC Type F) and microcrystalline cellulose (Ceolus® KG1000), both with different physical properties, were investigated. The powders were characterized by laser diffraction, scanning electron microscopy, helium pycnometry, ring shear testing, gas adsorption, and by determination of the powder flowability. Furthermore, the extent of densification within the die during vibration was visualized by a high-speed camera system and analyzed by an image-analyzing software. It was observed that lower punch vibration was able to densify the powder bed to a sufficient extent and within an adequate time period. Consequently, the presented results revealed that lower punch vibration may be a promising technique to remove entrapped air from powder beds, thus obtaining a denser powder bed within the die, which might potentially improve the tableting process and prevent complications during tablet manufacture.

Comparison of two paddle wheel geometries within the filling chamber of a rotary tablet press feed frame with regard to the distribution behavior of a model powder and the influence on the resulting tablet mass.

Objective: The purpose of this study was to compare the influence of two different paddle wheel geometries on the distribution behavior of a model powder within the filling chamber of the modified feed frame of a rotary tablet press. Moreover, both paddle wheels were compared regarding their influence on the resulting tablet mass during the tableting process. Significance: Insights are provided regarding the influence of the paddle wheel geometry on the powder distribution to optimize the die filling process. Materials and methods: Avicel PH 102 served as model powder. A laser triangulator was used to scan the powder surface level within the feed frame and, combined with the determination of the angle position of the paddle wheel, an in-house written software was used to calculate the powder surface profiles and filling levels. Two experimental setups, one based on the filling chamber filled with a defined amount of powder (offline) and one using the filling chamber during tableting (inline) were applied. Results: Both paddle wheel geometries caused a significantly different distribution behavior of the powder within the filling chamber. The tablets obtained with the round rod filling wheel showed significantly higher tablet masses and significantly lower standard deviations. The inflow of powder into the filling chamber appeared to be improved with the round rod filling wheel. Conclusions: Under the applied experimental conditions, the round rod filling wheel showed obvious advantages compared to that with flat rods in terms of the uniformity of tablet masses and the extent of die filling.

Micromechanical characterization of prismless enamel in the tuatara, Sphenodon punctatus.

Dental enamel - a naturally occurring biocomposite of mineral and protein - has evolved from a simple prismless to an advanced prismatic structure over millions of years. Exploring the mechanical function of its structural features with differing characteristics is of great importance for evolutionary developmental studies as well as for material scientists seeking to model the mechanical performance of biological materials. In this study, mechanical properties of prismless tuatara Sphenodon punctatus enamel were characterized. Using micro-cantilever bending samples the fracture strength and elastic modulus were found to be 640 ± 87 MPa and 42 ± 6 GPa, respectively in the orientation parallel to the crystallite long axis, which decreased in the orthogonal direction. The intrinsic fracture toughness of tuatara enamel ranged from 0.21 MPa m(1/2) and 0.32 MPa m(1/2). These values correspond to the lower limit of the range of values observed in prismatic enamel at the hierarchical level 1.

Biomechanical adaptation of the bone-periodontal ligament (PDL)-tooth fibrous joint as a consequence of disease.

In this study, an in vivo ligature-induced periodontitis rat model was used to investigate temporal changes to the solid and fluid phases of the joint by correlating shifts in joint biomechanics to adaptive changes in soft and hard tissue morphology and functional space. After 6 and 12 weeks of ligation, coronal regions showed a significant decrease in alveolar crest height, increased expression of TNF-α, and degradation of attachment fibers as indicated by decreased collagen birefringence. Cyclical compression to peak loads of 5-15N at speeds of 0.2-2.0mm/min followed by load relaxation tests showed decreased stiffness and reactionary load rate values, load relaxation, and load recoverability, of ligated joints. Shifts in joint stiffness and reactionary load rate increased with time while shifts in joint relaxation and recoverability decreased between control and ligated groups, complementing measurements of increased tooth displacement as evaluated through digital image correlation. Shifts in functional space between control and ligated joints were significantly increased at the interradicular (Δ10-25µm) and distal coronal (Δ20-45µm) regions. Histology revealed time-dependent increases in nuclei elongation within PDL cells and collagen fiber alignment, uncrimping, and directionality, in 12-week ligated joints compared to random orientation in 6-week ligated joints and to controls. We propose that altered strains from tooth hypermobility could cause varying degrees of solid-to-fluid compaction, alter dampening characteristics of the joint, and potentiate increased adaptation at the risk of joint failure.

Biomechanics of a bone-periodontal ligament-tooth fibrous joint.

This study investigates bone-tooth association under compression to identify strain amplified sites within the bone-periodontal ligament (PDL)-tooth fibrous joint. Our results indicate that the biomechanical response of the joint is due to a combinatorial response of the constitutive properties of organic, inorganic, and fluid components. Second maxillary molars within intact maxillae (N=8) of 5-month-old rats were loaded with a µ-XCT-compatible in situ loading device at various permutations of displacement rates (0.2, 0.5, 1.0, 1.5, 2.0 mm/min) and peak reactionary load responses (5, 10, 15, 20 N). Results indicated a nonlinear biomechanical response of the joint, in which the observed reactionary load rates were directly proportional to displacement rates (velocities). No significant differences in peak reactionary load rates at a displacement rate of 0.2mm/min were observed. However, for displacement rates greater than 0.2mm/min, an increasing trend in reactionary rate was observed for every peak reactionary load with significant increases at 2.0mm/min. Regardless of displacement rates, two distinct behaviors were identified with stiffness (S) and reactionary load rate (LR) values at a peak load of 5 N (S(5 N)=290-523 N/mm) being significantly lower than those at 10 N (LR(5 N)=1-10 N/s) and higher (S(10 N-20 N)=380-684 N/mm; LR(10 N-20 N)=1-19 N/s). Digital image correlation revealed the possibility of a screw-like motion of the tooth into the PDL-space, i.e., predominant vertical displacement of 35 µm at 5 N, followed by a slight increase to 40 µm at 10 N and 50 µm at 20 N of the tooth and potential tooth rotation at loads above 10 N. Narrowed and widened PDL spaces as a result of tooth displacement indicated areas of increased apparent strains within the complex. We propose that such highly strained regions are "hot spots" that can potentiate local tissue adaptation under physiological loading and adverse tissue adaptation under pathological loading conditions.

Hierarchical flexural strength of enamel: transition from brittle to damage-tolerant behaviour.

Hard, biological materials are generally hierarchically structured from the nano- to the macro-scale in a somewhat self-similar manner consisting of mineral units surrounded by a soft protein shell. Considerable efforts are underway to mimic such materials because of their structurally optimized mechanical functionality of being hard and stiff as well as damage-tolerant. However, it is unclear how different hierarchical levels interact to achieve this performance. In this study, we consider dental enamel as a representative, biological hierarchical structure and determine its flexural strength and elastic modulus at three levels of hierarchy using focused ion beam (FIB) prepared cantilevers of micrometre size. The results are compared and analysed using a theoretical model proposed by Jäger and Fratzl and developed by Gao and co-workers. Both properties decrease with increasing hierarchical dimension along with a switch in mechanical behaviour from linear-elastic to elastic-inelastic. We found Gao's model matched the results very well.