Tmeda

500 μL cell suspension (100 million per mL in PBS) was mixed with 500 μL hydrogel precursor solution (12% acrylamide, 1% BAC, 20 mM Tris, 0.6% sodium persulfate, and 20 mM NaCl in H₂O) in a 15 mL centrifuge tube. 1 mL HFE 7500 with 2% surfactant (008-FluoroSurfactant, RanBiotechnologies) was added to the cell/hydrogel precursor mixture. Emulsion was formed by passing the oil/aqueous mixture 5 times through the needle. 20 μL of TMEDA (tetramethylethylenediamine, Sigma) was added into the emulsion and the emulsion was incubated at 70 °C for 30 min and at room temperature for overnight for gelation. The emulsion can be stored at 4°C for up to 1 week.
The emulsion was centrifuged at 1000 RCF for 1 min and the bottom oil layer was removed by using a gel loading tip. 1 mL of 20% PFO (1H,1H,2H,2H-perfluoro-1-octanol, Sigma, 370533) and 5 mL of PBST buffer (0.4% tween 20 in PBS) were added into the emulsion. The mixture was vortexed at maximum speed for 1 min break the emulsion and centrifuged at 1000 RCF for 5 min. Any remaining oil was removed by pipetting through a gel-loading tip.

(3-Acrylamidopropyl)-trimethylammonium chloride
(AMPTMA, 75 wt % in H₂O, Sigma-Aldrich); methylene bis-acrylamide
(MBAAm, Sigma-Aldrich); poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide),
MW = 12,600 g·mol^–1; the so-called Pluronic
F-127, Sigma-Aldrich; ammonium persulfate (APS, Fluka); N,N,N′,N′-tetramethylethylenediamine (TMEDA, Sigma-Aldrich); ethanol (Sigma-Aldrich);
diethyl ether (Merck); and toluene (Merck) were all used as received.
Embryo axes of chickpea (Cicer arietinum L.) were used as initial explants (see the Supporting Information).

The three-step synthesis of the tert-butyldicumyl chloride bifunctional initiator was carried out, as described previously [78 (link),79 (link)]. Methacrylate-telechelic polyisobutylenes (MA-PIB-MAs) were obtained by quasiliving carbocationic polymerization of isobutylene (Messer Hungarogáz Kft., Budapest, Hungary) initiated by the tert-butyldicumyl chloride/TiCl₄ initiating system in the presence of N,N,N′,N′-tetramethylethylenediamine (TMEDA, 99.5%, Sigma-Aldrich, St. Louis, MO, USA) nucleophilic additive, followed by quantitative chain end derivatizations, as reported earlier [34 (link),77 ,78 (link),79 (link)]. Briefly, the polymerization of isobutylene was endquenched in situ by allyltrimethylsilane (ATMS, 97%, Honeywell Fluka, Charlotte, NC, USA) to obtain allyl-telechelic PIBs, and subsequent hydroboration/oxidation and esterification yielded the MA-PIB-MA macromonomers. The end products were purified by dissolving it in n-hexane (Molar Chemicals, Halásztelek, Hungary), passing through an alumina column, and precipitating in methanol (Molar Chemicals, Halásztelek, Hungary). Finally, the precipitated polymers were dried in a vacuum until constant weight at 30 °C.