8 arm peg hydroxyl

8 arm PEG-hydroxyl (M_n = 20 kg mol⁻¹, tripentaerythritol core), 8 arm PEG-amine (M_n = 20 kg mol⁻¹, tripentaerythritol core), and 8 arm PEG-thiol (M_n = 20 kg mol⁻¹, tripentaerythritol core) were purchased from JenKem Technology USA. DBCO (dibenzylcyclooctyne) acid was purchased from Click Chemistry Tools (Scottsdale, AZ). All other chemicals were purchased from Sigma Aldrich (St. Louis, MO) or Thermo Fisher Scientific (Waltham, MA), and used as received unless otherwise noted.

PEG-norbornene was synthesized from 8-arm PEG hydroxyl (JenKem Technology, TX, USA) and 5-norbornene-2-carboxylic acid (Alfa Aesar, MO, USA) using N,N′-dicyclohexylcarbodiimide (Alfa Aesar) as the coupling agent[26 (link)]. Norbornene functionalization of PEG arms was determined with ¹H-NMR [CDCl3]: $\text{δ}$ = ~3.6 for PEG ether protons, $\text{δ}$ = 5.9–6.3 for norbornene vinyl protons, with PEG macromers having ≥90% functionality used for all experiments. The MMP-degradable peptide crosslinker GKKCGPQGIWGQCKKG, integrin-binding peptide peptides RGD (GCGRGDSG) and GFOGER (GCG(GPP)₅GFOGER(GPP)₅GCG), and scrambled control peptide (Ctrl, CGRDGSG) were synthesized using a Liberty 1 Microwave Assisted Peptide Synthesizer (CEM, NC, USA) or purchased from Genscript (NJ, USA) and characterized prior to use as previously described[28 ]. GFOGER triple helix formation in solution and stability at 37 °C was confirmed using a circular dichroism spectrophotometer (J-1000, Jasco, MD, USA) (Supplemental Figure 1).