# Magnetic-Responsive Microparticles that Switch Shape at 37 \({}^{\circ}\)[PERSON]
## Materials and Methods  
\(\varepsilon\)-Caprolactone was purchased from Tokyo Kasei (Tokyo, Japan), and purified by distillation over calcium hydride under reduced pressure. Pentaerythnitol, 1,4-butanediol, and acryloyl chloride were also purchased from Tokyo Kasei and used as received. Triethylamine was purchased from Wako Pure Chemical Industries, Ltd. (Osaka, Japan), and dehydrated by distillation over potassium hydroxide for overnight. Tin octanoate and other chemicals were also purchased from Wako Pure ChemicalIndustries, Ltd. (Osaka, Japan), and used as received. Pluronic(r) F-127 and benzoyl peroxide (BPO) was purchased from Sigma (St. Louis, MO, USA) and used as received. Magnetic nanoparticles (EMG1300, Fe\({}_{3}\)O\({}_{4}\)) were purchased from Ferrotec and used as received.  
Linear telechelic and tetra-branched PCLs were synthesized by ring-opening polymerization from 1,4-butanediol and pentaerythnitrol, respectively (Figure S1). The average degrees of polymerization of each branch in two-branched and four-branched PCLs were 20 and 10, respectively. Then, acryloyl chloride was reacted to the hydroxyl end group of the branched chains. Microparticles were prepared by an in situ oil-in-water (o/w) emulsion polymerization using xylene solutions containing PCL macromonomers having acrylate end groups and BPO as an initiator with or without magnetic nanoparticles as oil phase and emulsifying 1390 \(\upmu\)L of this solution in 20 mL of an aqueous stabilizer solution containing 5 wt/v % Pluronic(r) F-127. Here, the equimolar amounts of linear telechelic and tetra-branched PCL macromonomers in the presence or absence of MNPs were dissolved at 50 wt % in xylene containing two-fold molar excess benzoyl peroxide (BPO) to the end-group of macromonomers. The mixed solution was vigorously stirring for 5 min and then increased solution temperature to 80 \({}^{\circ}\)C with oil bath and reacted for overnight to allow for in situ polymerization. The reacted microparticles were washed with a large amount of distilled water, acetone, and methanol, and collected by centrifugation after each washing. Each washing process repeated three times, and finally the purified particles were dispersed in distilled water (Figure 1a). To program temporary particle shape, the purified particles were casted on a solid substrate and compressed (compressive stress of 1 MPa) by heating at 40 \({}^{\circ}\)C for 10 min. The thermal treatment of samples and measurement temperature was controlled using hotplate (Microwarm plate, KM-3, Kitazato, Shizuoka, Japan) or thermos chamber (Chromato chamber M-600 FN, TAITEC, Saitama, Japan). The compressive stress was then released at 4 \({}^{\circ}\)C after 15 min of cooling. Samples had a temporary shape that could be triggered to transition to permanent sphere shape by heat at 37 \({}^{\circ}\)C for a period of 15 min.  
Particle shape was observed by using a scanning electron microscope (SEM, JCM-5000, JEOL, Tokyo, Japan). The actual content of magnetic nanoparticles in the microparticles were evaluated  
Figure 1: (**a**) Schematic illustration of preparation procedure of shape-memory PCL microparticles by in-situ oil-in-water (o/w) emulsion polymerization technique; (**b**) Top view (Left) and tilt view (Right) SEM images of prepared shape-memory PCL microparticles with acceleration voltage of 5 kV. Scale bars, 500 \(\upmu\)m (Left) and 200 \(\upmu\)m (Right).  
by thermogravimetric analysis (EXSTAR6000 TG/DTA, SII Nanotechnology, Northridge, CA, USA). The melting temperature as well as endothermic enthalpy change (\(\Delta H\)) were determined by differential scanning calorimetry (DSC 6100, SEIKO Instruments, Chiba, Japan). To examine the magnetic attractivity of the microparticles hybridized with magnetic nanoparticles, the transmittance of the dispersed solutions at wavelength of 500 nm were measured by a UV-vis spectrometer (V-650, JASCO, Tokyo, Japan).