Microgel reinforced zwitterionic hydrogel coating for blood-contacting biomedical devices

Abstract

Zwitterionic hydrogels exhibit eminent nonfouling and hemocompatibility. Several key challenges hinder their application as coating materials for blood-contacting biomedical devices, including weak mechanical strength and low adhesion to the substrate. Here, we report a poly(carboxybetaine) microgel reinforced poly(sulfobetaine) (pCBM/pSB) pure zwitterionic hydrogel with excellent mechanical robustness and anti-swelling properties. The pCBM/pSB hydrogel coating was bonded to the PVC substrate via the entanglement network between the pSB and PVC chain. Moreover, the pCBM/pSB hydrogel coating can maintain favorable stability even after 21 d PBS shearing, 0.5 h strong water flushing, 1000 underwater bends, and 100 sandpaper abrasions. Notably, the pCBM/pSB hydrogel coated PVC tubing can not only mitigate the foreign body response but also prevent thrombus formation ex vivo in rats and rabbits blood circulation without anticoagulants. This work provides new insights to guide the design of pure zwitterionic hydrogel coatings for biomedical devices.

Fig. 1. Design principle of mechanically robust pure zwitterionic pCBM/pSB hydrogel.

a Photograph of the preparation of the pCBM/pSB hydrogel. b Network structure and the preparation process of the pCBM/pSB hydrogel.

Fig. 2. Mechanical and anti-swelling properties of the pCBM/pSB hydrogels.

a Compressive and (c) tensile stress–strain curves of the pCBM/pSB hydrogel and the pSB hydrogel. b Compressive stress (n = 4) and (d) tensile stress (n = 4) of the pCBM/pSB hydrogel with varying pCBM concentrations. e Representative loading–unloading compression curves (100 runs) of the pCBM20/pSB hydrogel. f Equilibrium swelling ratios of the pCBM/pSB hydrogels with varying pCBM concentrations (n = 4). g Comparison diagram of the compressive stress at 80% strain and tensile stress at fracture of other pure zwitterionic hydrogels^,–. h Comparison of the preparation of other pure zwitterionic hydrogels between this work and other strategies^–,, and in terms of their mechanical strength, anti-swelling, and easy-to-prepare coating properties. Data presented as mean ± SD in (b, d, f). Source data are provided as a Source Data file.

Fig. 3. Formation of pCBM/pSB hydrogel coatings.

a Schematic illustration of the pCBM/pSB hydrogel coating preparation procedures. (i) The PVC substrates were treated with acetone containing 5 wt% hydrophobic initiators (benzophenone). (ii) PVC substrates were covered with pCBM/pSB pre-gel solution containing hydrophilic initiators (photoinitiator 1173). (iii) After UV-initiated polymerization, the pSB/PVC interpenetrating layer and pCBM/pSB hydrogel coating were formed on the PVC substrates. b Preparation process of ultrathin pCBM/pSB hydrogel coating. c X-ray photoelectron spectroscopy survey scan of PVC substrate, pSB hydrogel coating, and pCBM/pSB hydrogel coating. High-resolution spectra of N 1 s of (d) pSB and (e) pCBM/pSB hydrogel coating. f Fluorescence image of the cross-section of pCBM/pSB hydrogel coatings on PVC sheet by using a 0.1-mm thick pre-gel solution. Measurements in (f) were repeated three times independently with similar results. g Digital photo and SEM image of the cross-section of pCBM/pSB hydrogel coatings on PVC tubing. Measurements in (g) (right panel) were repeated three times independently with similar results. Source data are provided as a Source Data file.

Fig. 4. Surface properties of the pCBM/pSB hydrogel coatings.

a SEM images of PVC, PVC-BP, pSB hydrogel coating, and pCBM/pSB hydrogel coating. Measurements in (a) were repeated three times independently with similar results. (b) Hydrophilicity and (c) underwater superaerophobicity of the pCBM/pSB hydrogel coatings. The relative adhesion amount of (d) fibrinogen (n = 5), (e) lysozyme (n = 5), (f) L929 cells (n = 5), and (g) platelets (n = 5) of PVC substrate, pSB hydrogel coating, and pCBM/pSB hydrogel coating. Data presented as mean ± SD and analyzed using a one-way ANOVA with Tukey’s post hoc test in (d, e, f, g), ***P < 0.001, n.s.: no significant difference at P > 0.05. d P = 0.6198 (pSB vs pCBM/pSB, fibrinogen), P < 0.001 (PVC vs pCBM/pSB, PVC vs pSB, fibrinogen). e P = 0.1116 (pSB vs pCBM/pSB, lysozyme), P < 0.001 (PVC vs pCBM/pSB, PVC vs pSB, lysozyme). f P = 0.3095 (pSB vs pCBM/pSB, L929 cells), P < 0.001 (PVC vs pCBM/pSB, PVC vs pSB, L929 cells). g P = 0.4564 (pSB vs pCBM/pSB, platelets), P < 0.001 (PVC vs pCBM/pSB, PVC vs pSB, platelets). Source data are provided as a Source Data file.

Fig. 5. Mechanical stability and long-term antifouling properties of the pCBM/pSB hydrogel coatings.

a Schematic illustration of the peeling test on pCBM/pSB hydrogel coatings. b Force-displacement curves of the peeling tests of untreated PVC substrates, pSB, pCBM10/pSB, pCBM20/pSB, and pCBM30/pSB hydrogel coatings. c SEM image and S element mapping of (i) the side of the PVC substrate and (ii) the peeling film after undergoing the peel test. Measurements in (c) were repeated three times independently with similar results. d Water contact angle of the pSB and pCBM20/pSB hydrogel coatings after shearing for 7 d, 14 d, and 21 d (n = 3). e The force-displacement curves of the pCBM20/pSB hydrogel coating before and after 0.5 h of strong water flushing. f The friction coefficients of the pSB and pCBM20/pSB hydrogel coatings before and after 100 sandpaper abrasion tests (n = 5). Representative SEM images for biofilm formation of (g) Escherichia coli (E. coli) and (h) Staphylococcus aureus (S. aureus) adhesion on PVC and pCBM20/pSB hydrogel coatings after 1 d, 14 d, and 30 d of coculture. Measurements in (g, h) were repeated three times independently with similar results. Data presented as mean ± SD in (d, f) and analyzed using a one-way ANOVA with Tukey’s post hoc test in f, ***P < 0.001, n.s.: no significant difference at P > 0.05. f P = 0.1571 (pristine vs after 100 friction, pCBM20/pSB), P < 0.001 (pristine vs. after 100 friction, pSB). Source data are provided as a Source Data file.

Fig. 6. Antithrombogenicity of the pCBM/pSB hydrogel coatings in vitro and ex vivo blood circulation in rat model.

a Scheme of circulation calcified whole blood in vitro. b Cross-section, (c) photographs, and (d) thrombus weight of circuits of PVC tubing and pCBM/pSB hydrogel coating modified PVC tubing after circulation for 1 h (n = 3). e Scheme of an ex vivo perfusion experiment in SD rats. f Cross-section, (g) photographs, and (h) thrombus weight of circuits of PVC tubing and pCBM/pSB hydrogel coating modified PVC tubing after circulation for 1 h without anticoagulants (n = 3). Data presented as mean ± SD and analyzed using a one-way ANOVA with Tukey’s post hoc test in (d, h), **P < 0.01. d P = 0.0036 (PVC vs pCBM/pSB, in vitro blood circulation), h P = 0.0049 (PVC vs pCBM/pSB, ex vivo blood circulation). Source data are provided as a Source Data file.

Fig. 7. Antithrombogenicity and biochemical analysis of the pCBM/pSB hydrogel coatings in the rabbit model.

a Scheme of the New Zealand white rabbits veno-venous extracorporeal circuit. b Photographs, (c) cross-section, SEM images of (d) PVC tubing, and (e) pCBM/pSB hydrogel coating modified PVC tubing after 2 h of circulation. Measurements in (d, e) were repeated three times independently with similar results. The quantitative results of f occlusion rate (n = 9), (g) thrombus weight (n = 3), (h) blood flow rate (n = 3), coagulation test of (i) TT (thrombin time) (n = 3), (j) APTT (activated partial thromboplastin time) (n = 3), and (k) PT (prothrombin time) (n = 3). The inflammatory cytokines level of (l) TNF-α (tumor necrosis factor-α) (n = 4) and (m) creatinine (CRE) (n = 3) in PVC tubing with/without pCBM/pSB hydrogel coating at the end of the circulation experiments. Data presented as mean ± SD and analyzed using a one-way ANOVA with Tukey’s post hoc test in (f–m), *P< 0.05, **P < 0.01, ***P < 0.001, n.s.: no significant difference at P > 0.05. f P < 0.001 (PVC vs pCBM/pSB, occlusion rate). g P = 0.0087 (PVC vs pCBM/pSB, thrombus weight). h P =  0.0121 (PVC vs pCBM/pSB, blood flow rate). i P = 0.0055 (control vs PVC, APTT), P = 0.0002 (PVC vs pCBM/pSB, APTT). k P = 0.0076 (control vs PVC, PT), P = 0.0365 (PVC vs pCBM/pSB, PT). l P = 0.0478 (control vs PVC, TNF-α), P = 0.0099 (PVC vs pCBM/pSB, TNF-α). m P = 0.4031 (control vs PVC, CRE), P = 0.7922 (PVC vs pCBM/pSB, CRE), P = 0.1038 (control vs pCBM/pSB, CRE). Source data are provided as a Source Data file.