Limitation observed in the application of the three dimensional solubility parameters to the coating formulation of poly (3-hydroxybutyrate-hydroxyvalerate) systems

Purpose: Poly (3-hydroxybutyrate-hydroxyvalerate) displayed high dipole-dipole interaction, a high hydrogen bonding but low polar interaction, and was therefore expected to be miscible with solvents/plasticizers that exhibit similar pattern of cohesive interaction. To determine the applicability, or otherwise of the theory of the three dimensional solubility parameters to the formulation of poly (3-hydroxybutyrate-hydroxyvalerate) polymeric coating system, and hence identify any limitation in the application of the theory. This aspect was investigated in the study. Method: The structural group contribution method was employed to compute the partial and total solubility parameters of the compounds – the biopol polymer, a series of organic solvents and plasticizers. The computed partial solubility parameters included: dipole-dipole (dd), polar (dp) and hydrogen bonding (dh). Following a standard procedure in the literatures, the dd and dp values were combined to form a composite solubility parameter, dv: where dv = &#8730 &#948d 2+&#948p 2. A plot of dh versus dv gave the energy maps, which depicted the energy levels of the various compounds and from which the miscibility of the compounds were predicted. The closer the position of the solvent or plasticizer to the polymer in the map, the greater, the probability of mixing. Cast films of the various polymeric formulations were made and examined for homogeneity by scanning electron microscopy. Results: It was possible to select suitable plasticizers that were miscible with the polymer by applying theory of solubility parameters. The prediction for the solvents was, however, erroneous and this may be attributable to the inability of the dv parameter to clearly reflect the differences between the dd and dp interactions of the polymer on the one hand and those of the various solvents in all situations on the other hand. This means that in certain instances, the dv values of the polymer and the solvents were similar even though their dd and dp interactions were dissimilar. Conclusion: The analysis of the data showed that the composite solubility parameter dv of compounds could be similar even though the actual energies of dd and dp interactions are different. This is a limitation in the application of the theory of the three dimensional solubility parameters. Keywords: keyword; keyword; keyword > Tropical Journal of Pharmaceutical Research Vol. 4 (1) 2005: pp. 355-36

Relationship Between Slugging Pressure and Brittle Fracture Tendency – A Case Study for Aspirin Tablets

Objective – Slugging is a pre-compression technique for the dry granulation of hydrolysable drugs (e.g. aspirin). The study was carried out to relate the slugging load to the hardness of the granules and the brittle fracture tendency of the final (recompressed) tablets. Method – Varying compression load were applied to aspirin powder to form slugs, which were subsequently broken down to form granules. These were recompressed to give the final tablets. The hardness of the slugs was determined and taken as measure of the hardness of the resulting granules. The following tableting parameters were measured for the final tablets - tensile strength (T), packing fraction (Pf) and the brittle fracture index (BFI). Results - A high slugging load was associated with the formation of hard slugs and hence hard granules. Upon recompression the hardest granules formed the hardest tablets (T = 3.29MN m-2) while the softest granules formed the softest tablets (T=1.09MN m-2). In turn, the hardest tablets displayed the highest brittle fracture tendency (BFI = 0.59) compared with the softest tablets (BFI= 0.21). A positive linear correlation existed between tablet hardness (T) and BFI values (r = 0.98). Keywords: Slugging pressure, aspirin granules, tablet tensile strength, brittle fracture index > Tropical Journal of Pharmaceutical Research Vol. 4 (2) 2005: pp. 483-48

Current trends in the production and biomedical applications of liposomes: a review

A review of literature was carried out to determine methods of production of liposomes, their stability, biodistribution and their uses as drug delivery systems. The conventional method of preparing liposomes is basically for the multilamellar vesicles (MLVs). However, other methods are used to reduce the size of these MLVs to small unilamellar vesicles (SUVs) so as to increase their plasma lifetime and consequently increase the possibility of achieving greater tissue localisation. Some of these methods of size reduction are sonication and high pressure extrusion. Each of these methods has its own advantages and disadvantages. Large unilamellar vesicles (LUVs), on the other hand, are prepared mainly by detergent removal method and reverse phase extrusion technique. There are also improved pharmacokinetic properties with liposomal drugs compared to free drugs, though some formulation factors affect the release kinetics of the liposomal drugs. The review also shows that liposomes have a lot of biomedical applications and uses. They have been used in drug targeting, oral delivery of vaccines, insulins, peptides and some compounds, which are usually degraded in the gastrointestinal tract. It has also found application in topical therapy especially in the eye and lungs. Other areas of application are in cancer chemotherapy and treatment of human immunovirus (HIV) infection. The control of the stability of liposomes is an essential pre-requisite for effective use as drug carriers. Leakage of the liposome is attributable mainly to differences in lamellar structure. For instance, MLVs are less prone to leakage than ULVs. The use of a combination of saturated phospholipid and cholesterol in the formulation of the liposomes has also been found to enhance stability with lower tendency to leakage

Characterization of coating systems

Polymeric film coatings have been applied to solid substrates for decorative, protective, and functional purposes. Irrespective of the reasons for coating, certain properties of the polymer films may be determined as a method to evaluate coating formulations, substrate variables, and processing conditions. This article describes experimental techniques to assess various properties of both free and applied films, including water vapor and oxygen permeability, as well as thermal, mechanical, and adhesive characteristics. Methods to investigate interfacial interactions are also presented