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Technical Briefs

# Formation of Uniform Microspheres Using a Perforated Silicon Membrane: A Preliminary Study

[+] Author and Article Information
K.-Y. Song, M. M. Gupta

M. Chiao, B. Stoeber, U. Häfeli

University of British Columbia, Vancouver, BC V6T 1Z4, Canada

W. J. Zhang1

1

Corresponding author.

J. Med. Devices 3(3), 034503 (Sep 01, 2009) (3 pages) doi:10.1115/1.3212556 History: Received July 24, 2008; Revised June 02, 2009; Published September 01, 2009

## Abstract

This paper presents a new method to generate uniform microspheres with biodegradable poly(lactic-co-glycolic acid) (PLGA) material using microelectromechanical system technology. The general idea with this method is such that a liquid phase containing the dissolved microsphere matrix material reaches a continuous phase after a silicon membrane with micron-sized perforations, where microdroplets are formed. After the droplet is detached from the membrane, the solvent diffuses out of the droplets into a continuous phase leading to the formation of solid microspheres. The experiment was performed to verify this method with some promising result. It has been shown that with this method, about 90% of the microspheres are in the range from 1 to $2 μm$, which seems to be better than the result obtained with other methods using glass or ceramic membranes. The microsphere with such a size range is useful for intravascular applications and pharmaceutical drug delivery with a slow release of the drug at narrowly defined rates.

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## Figures

Figure 1

A SEM image of the perforated Si membrane after the fabrication. The square perforations were fabricated by conventional photolithography processes and a focused ion beam patterning. The perforations were positioned far enough to avoid merging of the droplets.

Figure 2

Schematic view of the fabrication process (not drawn to scale). (a)–(d): The first conventional photolithography process with ultraviolet (UV) light and a wet chemical etching process with Tetramethylammonium hydroxide (TMAH). (e): The focused ion beam pattern squares on the exposed silicon dioxide. (f)–(g): The second conventional photolithography process with UV light and a wet chemical etching process.

Figure 3

Schematic view of the experimental setup. The PLGA is injected by a syringe pump, and passes through the perforations on the silicon membrane. The PLGA microsphere is forming when the droplet on the membrane is off by the cross flow on the membrane. The speed of the agitator determines the speed of the cross flow.

Figure 4

Simplified acting forces on a droplet formed at perforation

Figure 5

The optical image of the droplets on the membrane without agitation. The white bar represents 25 μm.

Figure 6

Size distribution of the microspheres by two different agitation speeds (400 rpm and 500 rpm). Optical and SEM images of the microsphere are shown on the side.

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