Mechanical Property Characterization of Bilayered Tablets using Nondestructive Air-Coupled Acoustics

Abstract

Abstract. A noncontact/nondestructive air-coupled acoustic technique to be potentially used in mechanical property determination of bilayer tablets is presented. In the reported experiments, a bilayer tablet is vibrated via an acoustic field of an air-coupled transducer in a frequency range sufficiently high to excite several vibrational modes (harmonics) of the tablet. The tablet vibrational transient responses at a number of measurement points on the tablet are acquired by a laser vibrometer in a noncontact manner. An iterative computational procedure based on the finite element method is utilized to extract the Young's modulus, the Poisson's ratio, and the mass density values of each layer material of a bilayer tablet from a subset of the measured resonance frequencies. For verification purposes, a contact ultrasonic technique based on the time-of-flight data of the longitudinal (pressure) and transverse (shear) acoustic waves in each layer of a bilayer tablet is also utilized. The extracted mechanical properties from the air-coupled acoustic data agree well with those determined from the contact ultrasonic measurements. The mechanical properties of solid oral dosage forms have been shown to impact its mechanical integrity, disintegration profile and the release rate of the drug in the digestive tract, thus potentially affecting its therapeutic response. The presented nondestructive technique provides greater insight into the mechanical properties of the bilayer tablets and has the potential to identify quality and performance problems related to the mechanical properties of the bilayer tablets early on the production process and, consequently, reduce associated cost and material waste.

Evaluation of the Performance Characteristics of Bilayer Tablets: Part I. Impact of Material Properties and Process Parameters on the Strength of Bilayer Tablets

“…These tablets fractured along the interface upon axial loading, indicating that the interface is weaker than each individual layer. Delamination of these tablets upon axial loading can be attributed to the elastic mismatch between the brittle and plastic layers (19). Elastic mismatch is generated due to the differences in deformation histories and Young's modulus values of the adjacent layers.…”

“…Avicel is known to consolidate by plastic deformation and this will result in different deformation histories of both the layers and hence a substantial elastic mismatch between the layers to delaminate (19). The surface roughness of Avicel in the first layer was reduced significantly (at the first-layer forces: 2, 3, and 4 kN) thus resulting in a decrease in inter-particulate attraction and mechanical interlocking between the two adjacent layers.…”

Influence of Rate of Force Application During Compression on Tablet Capping

“…In the process perspective, identified causative factors in the formulation of tablets may be attenuated by modification of the tablet press operational attributes. Tablet capping has been associated to a number of causes, air entrapment, mechanism of volume reduction during compression, compression speed, viscoelastic recovery (VER), stress and density distribution, as well as internal shear stress because of die wall pressure . Several approaches have been tried to prevent capping by lowering compression force, reducing compression speed, or decreasing ejection path in die .…”

Real-time in-die compaction monitoring of dry-coated tablets

“…It is widely known that dwell-time is a key parameter defining the end-mechanical properties of the compacted tablet, such as hardness and porosity. For pharmaceutical applications, uses of a wide-spectrum of acoustic techniques for investigating the tablet hardness with ultrasonic methods (Lum and Duncan-Hewit, 1996), the effects of tablet porosity and particle size fraction of compacted on acoustic properties of tablets (Hakulinen et al, 2008), acoustic emission during compaction (Serris et al, 2002), their potential in identifying counterfeit tablets (Medendorp and Lodder, 2006), elasticity, integrity and defect states of tablets (Ketolainen et al, 1995;Varghese and Cetinkaya, 2007;Akseli et al, 2008bAkseli et al, , 2009, and mechanical characterization of multi-layer tablets (Akseli et al, 2010) have been reported.…”