Pluronic f108

Monoolein (MO; 1-oleoyl-rac-glycerol;
purity ≥99%) and Pluronic F108 (PF108) used for mesophase synthesis
were purchased from Sigma-Aldrich. The lipids used in the experiments,
1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine
(POPC), 1,2-dimyristoyl-sn-glycero-3-phospho-l-serine (sodium salt) (DMPS), and cholesterol (Chol), were
of high purity (≥99%) and purchased from Avanti Polar Lipids.
Stock solutions were prepared by dissolving either POPC and cholesterol
in chloroform or DMPS in a 4:1 v/v chloroform/methanol mixture. HPLC
grade organic solvents were purchased from Sigma-Aldrich. The subphase
used in the Langmuir experiments was a MES buffer solution (0.01 M;
pH 5.5; Sigma-Aldrich) and TRIS buffer solution (0.01 M; pH 9.0; Sigma-Aldrich)
or buffer solutions with doxorubicin hydrochloride (DOX) (AK Scientific)
and/or simvastatin (lactone) (SIM) (Sigma-Aldrich) at a concentration
of 10^–6 M for both DOX and SIM. The buffer solutions
were prepared using Milli-Q water with a resistivity of 18.2 MΩ·cm.

Graphite flakes (100 mesh,
≥75% min), sulfuric acid (H₂SO₄, 98%),
phosphoric acid (H₃PO₄, 85%), potassium permanganate
(KMnO₄, 99%), hydrogen peroxide (H₂O₂, 35%), hydrochloric acid (HCl, 37%), N-methyl-2-pyrrolidone
(NMP, C₅H₉NO, anhydrous, 99.5%), ethanol (C₂H₅OH, ≥99.9%), methanol (CH₃OH,
≥99.9%) tetraethyl orthosilicate (Si(OC₂H₅)₄, 98%), Pluronic F108 (∼14 600, PEG–PPG–PEG),
dimethoxydimethylsilane (DMDMS, 95%), ammonia solution (NH₄OH, 25%), ethylene glycol (C₂H₆O₂, 99.8%, anhydrous), potassium chloride (KCl), dipotassium hydrogen
phosphate (K₂HPO₄, anhydrous), lithium perchlorate
(LiClO₄, 99.9%, anhydrous), tetraglyme (TEGDME, 99.9%,
anhydrous), and lithium iodide (LiI, anhydrous) were purchased from
Sigma-Aldrich. Carbon black (Super P, >99%), poly(vinylidene fluoride)
(PVDF), palladium(II) chloride (solution 20–25%, w/w), and
melamine (C₃H₆N₆, 99%) were purchased
from Alfa Aesar. Lithium chips (16 × 0.25 mm², 99.9%)
were purchased from MTI Corporation.

SPMBs were suspended in a filtered phosphate buffer saline (PBS, Sigma-Aldrich, Saint-Louis, MO, USA) solution with 2% pluronic F-108 (Sigma-Aldrich, Saint-Louis, MO, USA) at a concentration of 50 SPMBs/µL and injected into the microchannel using a pressure-driven flow controller (Flow-EZ™, Fluigent, Le Kremlin-Bicêtre, France). A picture of the experimental set-up is provided in Supporting Information (Figure S3).

We designed and micromachined a microwell array to keep the tumour models in place at the PCD interface during the experiment. The microwell array features 9 groups of 16 microwells for a total of 144 microwells on a polymethylmethacrylate (PMMA) slab (Figure 1c). Each microwell is a cylinder of 700 µm in diameter and 900 µm in depth. Similar to PDMS devices [33 (link)], the microwell arrays were wetted and rendered hydrophilic by plasma treatment and rinsed with 100% ethanol. They were then sterilized by soaking in 70% ethanol for 15 min and prepared by incubation with a triblock copolymer (Pluronic^® F-108, Sigma-Aldrich, St. Louis, MO, USA) overnight (at least 16 h) at 37 °C in a 5% CO₂ incubator. The microwell arrays were then rinsed with PBS 1X three times to purge the Pluronic^® F-108 solution. We adapted the previously published method of our laboratory to load the MDTs in microwells [18 (link),19 (link)]. Briefly, the overlay liquid over the microwells was removed. 16 MDTs were picked using a 20 µL pipette and emptied over a microwell group. MDTs were diverted towards empty microwells using the pipette tip where they would fall into the microwells. In the case of more than one MDT falling in a microwell, the extra MDTs were pipetted out of the well and transferred to empty wells. This process was repeated for all 9 microwell groups.