A mechanistic study of the formation of polymer nanoparticles by the emulsification-diffusion technique

The mechanism of formation of polymer nanoparticles prepared by the emulsification-diffusion method was evaluated under different preparation conditions and by turbidimetry measurements. Biodegradable poly (D,L-lactic acid) was used as the polymer model. The results show that each emulsion droplet will form several nanoparticles and that the interfacial phenomena during solvent diffusion determine the size properties of the resulting colloid particles. These phenomena cannot be entirely explained by the convection effects caused by interfacial turbulence. We suggest that nanoparticle formation is due to diffusion alone, and we propose a mechanism based on the "diffusion-stranding” mechanism for spontaneous emulsification. In this mechanism, the diffusion of solvent causes local supersaturation near the interface, and nanoparticles are formed, due to the phase transformation and polymer aggregation that occur in these regions. This interpretation is supported by the turbidity measurements made at different polymer concentrations and stirring rate

Novel injectable urethral bulking agents for the treatment of urinary incontinence

Stress urinary incontinence is a highly prevalent disorder resulting from weak urethral closure mechanisms. Endoscopic injection of a urethral bulking agent (UBA) under the urethral mucosa increases coaptation, which improves continence. Collagen is an efficient agent, although its effects are limited in time. Other materials still suffer either from a short-lasting effect or migration in distant organs. We evaluated here novel UBAs using an ex vivo model, with respect to criteria of ease of injection, ability to form a high and stable tissue bulking, implant elasticity and tissue reaction. One approach involves solutions of polymers in water-miscible organic solvents that precipitates in situ. In this manner, high and stable bulks were routinely obtained using various commercial polymers. Selected solvents reduced the tissue reaction to the implant. Microsphere suspensions in hydrogels also proved to be efficient UBA, although less stable bulks were obtained. Thermosetting chitosan hydrogels showed promising results with respect to bulk stability and isoelasticity with surrounding tissues. Different strategies have thus been compared and optimised ex vivo. Further experiments are required to compare the ability of these materials to induce a sustained in vivo bulking effec

Influence of the Organization of Binary Mixes on Their Compactibility

Purpose. Elucidate the compactibility of binary mixes from their organization as compared to the traditional approach involving the different behavior of the materials under compression (plastic or brittle). Methods. Several materials were selected from their surface energies. Binary mixes 50/50 v/v were prepared from different sieved or freeze-milled fractions. The tensile strengths of the tablets obtained at two compression forces were compared with those of series of compacted binary mixes containing different proportions of the raw materials (concept of equivalent media). Results. In the case of interacting mixes, when the differences in particle size between the fractions blended increased, the material with the lowest particle size coated the largest particles more efficiently. Consequently, the tensile strengths of the tablets obtained became closer to the tensile strengths obtained from the pure coating material. For the non-interacting systems, the experimental tensile strengths were very close to the values calculated from the tensile strengths of the pure materials. Conclusions. This study clearly demonstrates the influence of the organization of binary mixes on their compactibility. The adhering material makes a percolating network governing the tensile strength of the tablet. From an industrial point of view, it is possible to improve the compactibility of binary mixes without changing their composition by selecting the appropriate organizatio