(311c) Effect of Fabrication Conditions On the Formation of Double-Walled Microspheres and Microfibers by Coaxial Electrospraying/Electrospinning Technique

Double-walled microspheres and microfibers, comprising of distinct core and shell phases, are useful and interesting devices for controlled drug release applications. The ability to form double-walled microspheres exhibiting a predefined core diameter and shell thickness may offer several additional advantages in drug delivery, including: i) drug encapsulated in the core of double-walled microspheres may overcome the problem of high initial burst release which is commonly encountered in traditional single-polymer microspheres, ii) higher drug loads with improved drug stability may be achieved by using materials in the core phase that offer increased drug solubility while stabilizing fragile therapeutics such as proteins and DNA, iii) advanced drug release schedules may be possible by selectively varying the shell material or thickness, and iv) drugs can be released in tandem by selectively loading them into the core or shell phase, thereby potentially enhancing drug efficacy. However, the controlled synthesis of double-walled microspheres and microfibers with specific core and shell phases still remain a challenge and the effect of fabrication conditions on the formation of double-walled microspheres and microfibers are not well-understood.

Based on previous works on the fabrication of double-walled microspheres via coaxial electrospraying process, we investigate the effect of various fabrication conditions, including polymer concentration, electrical voltage and volumetric flow rate ratio of shell to core phase, on the formation of double-walled microspheres and microfibers. In this study, double-walled PCL(PLLA) microspheres and microfibers consisting of poly(L-lactic acid) (PLLA) core surrounded by polycaprolactone (PCL) shell are used as a model for investigation.

Double-walled PCL(PLLA) microspheres and microfibers were synthesized and characterized. Positive encapsulation of the PLLA core by the PCL shell material was verified by energy dispersive X-ray (EDX) spectroscopy. The surface morphology of the double-walled microspheres and microfibers were examined using the scanning electron microscope (SEM). Results indicated that a critical polymer concentration of the core and shell phase was required to switch from the formation of double-walled microspheres to double-walled microfibers. Both electrical voltage and volumetric flow rate ratio of shell to core phase had a dominant effect on the overall size and occurrence of defects in the double-walled microspheres and microfibers.