Sponge-like Microspheres Research Articles

Simple emulsion technique as an innovative template for preparation of porous, spongelike poly(lactide-co-glycolide) microspheres with pore-closing capability

The objective of this study was to develop a new oil-in-water emulsion template for the preparation of highly porous poly(lactide-co-glycolide) (PLGA) microspheres having a spongelike skeleton and a pore-closing functionality. A dispersed phase consisting of isopropyl formate and PLGA was emulsified in an aqueous phase. Ammonia was added toward this emulsion, in order to induce ammonolysis in the dispersed phase. Subsequently, isopropyl formate was broken into water-soluble isopropanol and formamide. As they functioned as anti-solvents against PLGA, microsphere hardening occurred. Also, their leaching into the aqueous phase led to the formation of highly porous, spongelike microspheres. The microsphere porosity was found to be controlled by adjusting isopropyl formate volume, PLGA type and concentration, ammonia volume, and ammonia–isopropyl formate molar ratio. When these dried microspheres were dispersed into an aqueous phase, the pores closed themselves autonomously. Herein, the self-closing capability of the microspheres was greatly influenced by microsphere Tg and the aqueous phase temperature. FITC-dextran and lysozyme were successfully encapsulated into the microspheres by simply equilibrating their aqueous solutions with the self-closing microspheres. In conclusion, the new emulsion template did not use either a halogenated organic solvent or conventional porogens. It did not require high-shear or high-energy mixing devices that must be used in the practice of most contemporary microencapsulation techniques. Despite these facts, this new technique was able to fabricate spongelike microspheres with an extremely high porosity and an outstanding pore-closing functionality.

Guidelines for Ultrasonic Cement-Sheath Evaluation

Summary The primary objective of cement-sheath evaluation devices is to define the presence of set cement in the annulus, regardless of its density, compressive strength, or quality. Accepting the premise that any set cement in the annulus with a compressive strength greater than 0 psi cannot be replaced by squeeze cementing emphasizes the necessity of recognizing ultralow-compressive-strength cement (< 100 psi) from cement-sheath evaluation devices. Typically, most bond logging instruments cannot define satisfactorily the presence of these generally low-density, low-compressive-strength cements (such as foamed cement, cements filled with sponge-like microspheres, cements containing hydrogen for control of annular influx, or any cement contaminated with gas percolation). The ultrasonic cement evaluation instruments can define these gas contaminated, unset, or low-quality cements, provided the computing parameters are set and the tools calibrated correctly. This paper provides the mechanisms and data required to calibrate the ultrasonic cement evaluation devices correctly and the correct computing parameters for cement-sheath evaluation. Correct interpretation of the cement quality and quantity in the annulus permits the formulation of intelligent annular squeeze decisions.