The effect of temperature on the plasto-elasticity of some pharmaceutical powders and on the tensile strengths of their tablets

The effect of ultrasonic vibration on the compaction characteristics of ibuprofen

An ultrasonic (US) compaction rig has been developed, capable of providing compaction pressure together with high-power ultrasonic vibrations of 20 kHz to a powder or granular material in a die. The rig has been used to investigate the effect of ultrasound on the compaction properties of ibuprofen, a drug with poor compaction properties which produces tablets that are weak and frequently exhibit capping. It was found that coherent ibuprofen tablets could be prepared by ultrasound-assisted compaction at pressures as low as 20-30 MPa. Application of ultrasound before and after compaction was found not to be as effective as ultrasound applied during compaction. The breaking forces of the tablets produced with ultrasound applied during compaction were found to be consistently significantly higher than when compaction was performed conventionally, or with ultrasound applied before or after compaction. Application of ultrasound during compaction made it possible to increase tablet mechanical strength, typically by a factor of 2-5. It was concluded that pressure should be applied together with ultrasound in order to achieve a better acoustical contact, which is required to transmit vibrations from the horn to the material, and also to bond the surfaces of the particles. Ultrasound application during ibuprofen compaction also resulted in an increase in the apparent density, in relation to the apparent density of conventionally prepared tablets, of up to 14.4%. Ultrasound appears to improve particle rearrangement and provides energy for partial melting of particle asperities and subsequent fusion of particle surfaces, so as to increase interparticulate bonding. Solid bridge formation was thought to result in a reduction of void space, which in turn reduced the rate of water penetration into the compacts and consequently increased disintegration and dissolution times. It was found that the results of ultrasound-assisted compaction are influenced by formulation and US time. When ibuprofen was mixed with a second material, such as dibasic calcium phosphate dihydrate (DCP) or microcrystalline cellulose (MCC), stronger tablets were prepared by ultrasound-assisted compaction compared to the compacts containing no filler. Positive interactions were considered to have occurred due to ultrasound-induced bonding between the two materials. With an increase in DCP and MCC concentration in ibuprofen formulations, disintegration and drug dissolution rates of the tablets produced with ultrasound significantly increased. Using temperature-sensitive labels it was found that thermal changes occurred in powdered solids undergoing ultrasound-assisted compaction. Increases in the temperature of tablets were related to US amplitude and US time. With an increase in US amplitude from 5 to 13 microns, the temperature of the DCP tablet surface increased from 40 to 99 degrees C. With an increase in US time from 1 to 5 sec, the temperature of the surface of ibuprofen tablets increased from 43 to 60 degrees C. Increased tablet temperature was thought to be due to ultrasonic energy dissipation turned into heat. X-ray powder diffraction (XRD) studies of ibuprofen tablets prepared by ultrasound-assisted compaction at 32 MPa revealed that no changes in chemical or/and crystalline structure of the material occurred when ultrasound was applied for up to 5 sec (US amplitude 7 microns). An XRD study of DCP tablets produced by ultrasound-assisted compaction at 32 MPa with ultrasound of different amplitudes (5, 7, 13 microns) applied for 2 sec indicated that no material deterioration occurred in all the tested samples.

The effect of ultrasonic vibration on the compaction characteristics of paracetamol

An ultrasonic (US) compaction rig has been developed that is capable of providing compaction pressure together with high-power ultrasonic vibrations of 20 kHz to a powder or granular material in a die. The rig has been used to investigate the effect of US on the compaction properties of paracetamol, a drug that produces tablets that are weak and frequently exhibit capping. It was found that coherent paracetamol tablets could be prepared by US-assisted compaction at pressures as low as 20 to 30 MPa. Application of US before and after compaction was not found to be as effective as US applied during compaction. The breaking forces of the tablets produced with US applied during compaction were found to be consistently significantly higher than when compaction was performed conventionally or with US applied before or after compaction. The application of US during compaction made it possible to increase tablet breaking force, typically by a factor of 2 to 5. It was concluded that pressure should be applied together with US to achieve a better acoustical contact, which is required to transmit vibrations from the horn to the material and also to bond the surfaces of the particles. US application during compaction also resulted in an increase in apparent density, in relation to the apparent density of conventionally prepared paracetamol tablets, of up to 12.8%. US appears to improve particle rearrangement and provide energy for partial melting of particle asperities and subsequent fusion of particle surfaces, thus increasing interparticulate bonding. Development of solid bridges between the particles during US-assisted compaction was observed on scanning electron photomicrographs. Solid bridge formation was thought to result in a reduction of void space, which in turn reduced the rate of water penetration into the compacts and consequently increased tablet disintegration and drug dissolution times. It was found that the results of US-assisted compaction are influenced by formulation and US time. An increase in binder (polyvinylpyrrolidone) concentration and/or US time resulted in a significant increase in the breaking forces of paracetamol tablets produced with US. When paracetamol was mixed with a second material, such as dicalcium phosphate dihydrate and microcrystalline cellulose, stronger compacts were prepared by US-assisted compaction compared with the tablets containing no filler. Positive interactions were considered to have occurred as a result of US-induced bonding between the two materials. Overall, the application of US was found to significantly improve the compaction properties of paracetamol.

Principles and application of ultrasound in pharmaceutical powder compression

The use of ultrasound during the tableting of pharmaceutical powders is a new concept. However, in the metallurgy, plastic, and ceramic industries, ultrasound-assisted compression of materials has been known for some years. Ultrasound improves the characteristics of the compression process leading to optimized mechanical strength of the compacts without applying excessive compression force. Therefore, problems associated with high-pressure compression in tableting can be overcome and tablets may be manufactured more economically and consistently with the aid of ultrasound compared to conventional pressure processes. Although great progress in the theoretical understanding of the ultrasound-assisted powder compression process has been made since the late 1960s, the need for further research in the area of ultrasound application during pharmaceutical powder compression is essential. Further investigations on a wide range of drugs and excipients, to expand the usefulness and scope of the ultrasound-assisted technique, and to understand the complex phenomena involved in the process, are needed. In this article the principles, advantages, and limitations of the application of ultrasonic vibrations during pharmaceutical powder compression is reviewed with the hope that this article can contribute to, and stimulate research in the area.

The effects of interacting variables on the tensile strength, disintegration and dissolution of paracetamol tablets

A factorially designed scheme has been used to analyse the separate and combined effects of packing fraction (P), nature of binder (N) and concentration of binder (C) on the tensile strength, disintegration and dissolution (t50%) times of paracetamol tablets. In general, P has the greatest effect on tensile strength, disintegration and dissolution times followed by C then N. For the variables in combination, the ranking of the effects on tensile strength, for the PVP/gelatin formulations, are P x N greater than N x C greater than P x C and for the PVP/tapioca formulations are P x C = N x C greater than P x N. For disintegration and for dissolution, the ranking for the PVP/gelatin formulations are P x C greater than P x N = N x C and P x N greater than P x C greater than N x C, respectively, and for the PVP/tapioca formulations are P x N greater than N x C = P x C. The results also show that tapioca acts as a binding agent when included in paracetamol tablet formulations, but it is a weaker binder than either PVP or gelatin. It is thus required in a higher concentration to produce tablets of comparable physical properties with those formulated with PVP or gelatin.

Effects of applied load and particle size on the plastoelasticity and tablet strength of some directly compressible powders

Correlations have been established between the particle size and packing fraction of microcrystalline cellulose, calcium phosphate dihydrate, corn starch and lactose, and the elastic recovery, stress relaxation, and tensile strengths of their tablets.