Gelatin

A round microneedle mold (for 385 needles) with a diameter of 17.5 mm, tip distance of 700 μm, needle diameter of 270 μm and needle height of 500 μm is obtained from Engineering for Life (EFL-MMN-500, Suzhou, China). Novo Nordisk (0.454%, Tianjin, China) provides the insulin solution. Silk fibroin is from Shandong Qilu Biotechnology Group (Liaocheng, China). Food dye is from Lianyungang Xinai Food Technology Company (Lianyungang, China). OSTE is prepared according to a previous report [18 (link)]. Gelatin is from Shanghai Macklin Biochemical Co., Ltd. (Shanghai, China).

Ammonium persulfate (APS, 99.9%), gelatin (~250 g Bloom), and ethylene glycol (AR, 98%) were purchased from Macklin (Shanghai, China). Acrylamide (AAm, 99%), N,N′-MethylenebisAcrylamide (MBAA), and glycerol were purchased from Sigma-Aldrich (St. Louis, MO, USA). Deionized water (DI water) was used in all experiments.

Total proteins were extracted from culture supernatants and separated via PAGE on 7.5% polyacrylamide gels containing 0.5% gelatin (Macklin, Shanghai, China). Gels were then equilibrated with 2.5% Triton X-100 and incubated in substrate buffer (50 mmol/L Tris-HCl [pH 7.5], 150 mmol/L NaCl, and 10 mmol/L CaCl₂) for 24 h at 37 °C. Gels were stained with Coomassie Brilliant Blue G250 (BioFROXX, Guangzhou, China) for 2 h and washed until clear zones associated with MMP activity were observed.

BH (HPLC, ≥99%) was purchased from Meilun Biologics (Dalian, China). Gelatin (~250 g Bloom) and sodium metabisulfite (HPLC, ≥99%) were obtained from Macklin (Shanghai, China). Glutaraldehyde solution (50 wt. % in H₂O) and ethylenediaminetetraacetic acid (EDTA, HPLC, ≥99.5%) were purchased from Innochem (Beijing, China). Phosphate-buffered saline (PBS, 500 mL), 2-(4-amidinophenyl)-6-indolecarbamidine dihydrochloride (DAPI, 5 mg/mL), and the sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) gel quick preparation kit were obtained from Beyotime Biotechnology (Shanghai, China). Fluorescein isothiocyanate (FITC, 10 mg), Cy5-NHS (5 mg), and hydrophobic 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate (Dil, 10 mg) were purchased from Tianjin Biolite Biotech Co., Ltd. (Tianjin, China). A dialysis bag with a 3000 molecular weight cut off was purchased from Sigma-Aldrich Chemicals Private Ltd (Bangalore, India). All other chemicals were analytical grade.

CoCl₂·6H₂O, tannin, silver acetate, 3,3',5,5'-tetramethylbenzidine (TMB), o-phenylenediamine (OPD) and gelatin were obtained from Macklin Biochemical Co., Ltd. (Shanghai, China). Acrylic anhydride was purchased from Sigma (St Louis, MO, USA). Hydrogen peroxide (H₂O_2, 30%), aqueous ammonia, acetic acid and ethanol were the products of Tianjin Kermel Chemical Plant (Tianjin, China). 2,2-Dimethoxy-2-phenylacetophenone (DMPA), the live/dead (SYTO 9/PI) bacterial viability kit and PE anti-mouse CD45 (Cat# 12-0451-82) were received from Thermo Fisher Scientific (New Jersey, USA). The lactate dehydrogenase (LDH) cytotoxicity assay kit was obtained from Beyotime (Shanghai, China). 2',7'-Dichlorodihydrofluorescein diacetate (DCFH-DA) was obtained from Solarbio Life Science (Beijing, China). FITC anti-mouse F4/80 (Cat# 123108) and FITC anti-mouse Ly-6C/Ly-6C (Gr-1) (Cat# 108406) were obtained from Biolegend (San Diego, CA, USA). Anti-Ly6G + Ly6c (ab25377) and anti F4/80 (ab111101) were purchased from Abcam (Cambridge, UK). GTVisionTM I detection system/Mo&Rb (GK500510A) was received from Gene Tech (Shanghai) company limited. Four strains of MDR P. aeruginosa (21027, 20059, 21173, 21715) were kindly provided by Qingdao Municipal Hospital (China). Doubly deionized water was purified by a Unique-R20 purification system (Xiamen, China).

Analytical grade chemicals and reagents were used. Urea (CH₄N₂O), L-cysteine (C₃H₇NO₂S, molecular mass: 121.16 Dalton), sodium hydroxide (NaOH), hexafluoroisopropanol (C₃H₂F₆O), gelatin (gel, gel strength ~250 Bloom), and glycerol (gly, molecular mass: 92.09) were purchased from Shanghai Macklin Biochemical company (Shanghai, China, www. macklin.cn.qianyan.biz (accessed date on 8 September 2021)). Hydrochloric acid (HCl), barium chloride (BaCl₂), oxalic acid (H₂C₂O₄), curcumin (cur, molecular mass: 368.39), and phenolphthalein (C₂₀H₁₄O₄) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China, www.reagen.com.cn (accessed date on 10 September 2021)). Plate count agar (PCA) and nutrient broth (NB) were purchased from Shanghai Bio-way Technology Co., Ltd. (Shanghai, China, www.bw-bio.com (accessed date on 15 September 2021)).

Industrial SiC (D50 = 5 µm, 99.5% purity, Henan White Pigeon Group Co., Ltd., Henan, China) was used as the primary material, and Al₂O₃ (Purity: 99.9%, 5 μm, Taipeng Metal Material Co., Ltd., Jiangsu, China) and Y₂O₃ (Purity: 99.9%, 5 μm, Hebei Chuancheng Metal Material Co., Ltd., Hebei, China) were used as sintering aids (molar ratio of Al₂O₃ and Y₂O₃ was 5:3) [12 ]. Sodium polymethacrylate (PMMA-Na, 40 wt.% in water solution, Shanghai Macklin Biochemical Co., Ltd., Shanghai, China) was used as a dispersant. Gelatin (Shanghai Macklin Biochemical Co., Ltd., Shanghai, China) was used as an organic binder. The n-butanol solution (Shanghai Macklin Biochemical Co., Ltd., Shanghai, China) was used as a defoaming agent. The metal matrix in the composite was a commercial AZ91 magnesium alloy with the chemical composition shown in Table 1.