Magnetic, Fluorescent, and Copolymeric Silicone Microspheres

Abstract

Silicone microspheres are exceedingly difficult to make. Here, polydimethylsiloxane microspheres (≈1 μm diameter) are synthesized using ultrasonic spray pyrolysis, the first demonstration of a scalable synthetic procedure for crosslinked silicone microspheres. This continuous, aerosol process is also used to directly produce fluorescent, magnetic, and copolymeric derivatives; the potential biomedical applications of these microspheres are explored.

Keywords: aerosol polymerization; drug delivery; microencapsulation; polydimethylsiloxane; sonochemistry.

Figure 1

Polydimethylsiloxane (PDMS) microspheres prepared using ultrasonic spray pyrolysis. a) SEM of microspheres. The inset shows expanded view of microsphere. b) ATR‐FTIR spectrum of resulting product; peaks match literature values for PDMS.10, 24 c) Raman spectrum of product, C—H stretching peaks (2906 and 2963 cm⁻¹) for PDMS are clearly evident.26 d) Optical image of PDMS microspheres overlaid with Raman mapping showing the relative intensity of the C—H stretching peak (2906 cm⁻¹, highlighted in (c)) as the intensity of red coloration.

Figure 2

Size control of polydimethylsiloxane (PDMS) microspheres. a,c,e) SEMs of PDMS microspheres obtained with a) 4 mg mL⁻¹, c) 20 mg mL⁻¹, and e) 100 mg mL⁻¹ PDMS in hexanes. b,d,f) Size distributions of microspheres shown in (a,c,e), respectively. Size distributions were determined using the Image J software package, with total number of microspheres counted given as N.

Figure 3

Magnetic core‐shell polydimethylsiloxane (PDMS) microspheres prepared using ultrasonic spray pyrolysis. a) Image of magnetic PDMS microspheres showing (left) microspheres dispersed in hexanes and (right) microspheres pulled from solution using a magnet. b) SEM of magnetic PDMS microsphere on copper foil showing path of energy‐dispersive X‐ray spectral (EDS) line scan. c) EDS line scan showing Si and Fe concentrations along the path line shown in (b). d) TEM of PDMS microsphere (prepared without Fe₃O₄) showing uniform density and composition throughout the sphere. e) TEM of magnetic microsphere showing core‐shell structure.

Figure 4

Fluorescent polydimethylsiloxane (PDMS) microspheres, cell uptake, and small molecule release. a) Diffuse reflectance spectrum of Nile red doped PDMS microspheres (red) and nonfluorescent PDMS microspheres (black). Peak at 522 nm indicates successful inclusion of Nile red. b) Fluorescence image of Nile red doped PDMS microspheres. c) Bright field image of cell that has taken up microspheres. d) Fluorescent image of cell in (c). The cell membrane has been stained green, the cell nucleus has been stained blue, and the Nile red doped microspheres appear red. e) Extended release of a small molecule, Rhodamine 6G, from PDMS microspheres into phosphate buffered saline; release reported as percent R6G released of total loaded R6G.