Pentaerythritol

MPC was purchased from Sigma-Aldrich Japan Co., LLC. (Tokyo, Japan). BMA, pentaerythritol, and triethylamine were purchased from FUJIFILM Wako Pure Chemical Corporation (Osaka, Japan), while 2-Bromoisobutyryl bromide was obtained from Tokyo Chemical Industry Co., Ltd. (Tokyo, Japan). Ethylene bis(2-bromobutyrate), 2,2′-bipyridyl, copper(II) bromide, and l-ascorbic acid were purchased from Sigma-Aldrich Japan Co., LLC. (Tokyo, Japan). HeLa cells were obtained from the RIKEN Cell Bank (Saitama, Japan). RPMI-1640, Dulbecco’s modified Eagle medium (DMEM), fetal bovine serum (FBS), and phosphate-buffered saline (PBS) were purchased from Thermo Fisher Scientific, Inc. (Waltham, MA, USA). Cell counting kit-8 (CCK8) was purchased from Dojindo Laboratories Co., Ltd. (Kumamoto, Japan), LDH-Cytotoxic Test Wako from FUJIFILM Wako Pure Chemical Corporation (Osaka, Japan), Spectra/Por dialysis membrane from Spectrum Chemical Mfg. Corp. (New Brunswick, NJ, USA), and Methacryloxyethyl thiocarbamoyl rhodamine B from Polysciences Inc. (Warrington, PA, USA). The other solvents and reagents were of extra-pure grade and used without further purification.

PCL was prepared by cross-linking tetra-branched PCL with acrylate end groups in the presence of linear telechelic PCL with acrylate end groups according to a previously reported protocol^{28 (link)–30 (link)}. Briefly, linear and tetra-branched PCL were synthesized by ring-opening polymerization of ε-caprolactone (Tokyo Chemical Industry [TCI] Co., Tokyo, Japan) that was initiated with tetramethylene glycol (Wako Pure Chemical Industries, Osaka, Japan) and pentaerythritol (TCI) as initiators, respectively. Then, acryloyl chloride (TCI) was reacted to the hydroxyl end group of the branched chains to obtain the macromonomers. The structures and molecular weights were estimated by proton nuclear magnetic resonance spectroscopy (¹H NMR) (JEOL, Tokyo, Japan). The spectra of the reaction mixture is shown in Fig. 1 and Supplementary figure S1. The average degrees of polymerization of each branch for linear and tetra-branch PCL estimated by ¹H NMR were 20 and 45, respectively. The linear PCL with average degrees of polymerization of 20 was abbreviated as 2b20, and the tetra-branched PCL with average degrees of polymerization of 45 was abbreviated as 4b45 (Fig. 2).Figure 1

¹H NMR spectra of linear (a) and tetra-branched (b) PCL.

Figure 2

Schematic illustrations of (a) macromonomer synthesis and (b) cross-linking reaction.