Vascular endothelial growth factor and dexamethasone release from nonfouling sensor coatings affect the foreign body response

Abstract

Vascular endothelial growth factor (VEGF) and dexamethasone (DX) release from hydrogel coatings were examined as a means to modify tissue inflammation and induce angiogenesis. Antibiofouling hydrogels for implantable glucose sensor coatings were prepared from 2-hydroxyethyl methacrylate, N-vinyl pyrrolidinone, and polyethylene glycol. Microdialysis sampling was used to test the effect of the hydrogel coating on glucose recovery. VEGF-releasing hydrogel-coated fibers increased vascularity and inflammation in the surrounding tissue after 2 weeks of implantation compared to hydrogel-coated fibers. DX-releasing hydrogel-coated fibers reduced inflammation compared to hydrogel-coated fibers and had reduced capsule vascularity compared to VEGF-releasing hydrogel-coated fibers. Hydrogels that released both VEGF and DX simultaneously also showed reduced inflammation at 2 weeks implantation; however, no enhanced vessel formation was observed indicating that the DX diminished the VEGF effect. At 6 weeks, there were no detectable differences between drug-releasing hydrogel-coated fibers and control fibers. From this study, hydrogel drug release affected initial events of the foreign body response with DX inhibiting VEGF, but once the drug depot was exhausted these effects disappeared.

Figure 1

A: Illustration of microdialysis probe. Glucose uptake occurs at the microdialysis probe tip. Dialysate flows slowly through an annular region between the inner cannula and the microdialysis membrane. Dialysate samples are collected from the outlet tubing and analyzed for analyte concentrations. B: Schematic illustration of microdialysis probe tip geometry. Microdialysis sampling occurred by analytes diffusing across the semipermeable membrane into the dialysate. The dialysate flowed through an annulus with inner radius of r_α and an outer radius of r_i adjacent to the microdialysis membrane and exits the probe through the inner cannula. The semipermeable microdialysis membrane was of thickness r_o − r_i and has length of L. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

Figure 2

The hydrogel-coated and bare PES probes were implanted for 8 days in rat subcutaneous tissue. After explantation, the tissue was sectioned and stained with Gomori’s Trichrome. (A): Explanted bare PES probe, (B) Explanted hydrogel-coated PES probe. The microdialysis probe membrane is 40 μm in thickness. The hydrogel coating stained green and is visible within the pores of the microdialysis probes. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

Figure 3

H&E stained images (60×) of implants in rat subcutaneous tissue after 2 and 6 week implantation periods from PES fibers (A and F), hydrogel-coated PES fibers (B and G), VEGF-releasing hydrogel-coated PES fibers (C and H), DX-releasing hydrogel-coated PES fibers (D and I) and VEGF-DX-releasing hydrogel-coated fibers (E and J). Panels (A–E) display tissue sections explanted at 2 weeks. Panels (F–J) display tissue sections explanted at 6 weeks. Asterisk (*) indicates position of implant in image. Scale bars are equal to 50 μm. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

Figure 4

Factor VIII-related antigen stained tissue sections from 2 to 6 week implantation studies in rat subcutaneous tissue from PES fibers (A and F), hydrogel-coated PES fibers (B and G), VEGF-releasing hydrogel-coated PES fibers (C and H), DX-releasing hydrogel-coated PES fibers (D and I) and VEGF-DX-releasing hydrogel-coated fibers (E and J). Panels (A–E) display tissue sections explanted at 2 weeks. Panels (F–J) display tissue sections explanted at 6 weeks. Asterisk (*) indicates position of implant in image. Scale bars are equal to 50 μm. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

Figure 5

Number of blood vessels within 40 μm of implant surface after 2 weeks implantation in rat subcutaneous tissue. The implanted materials were bare PES fibers (PES, n = 9), hydrogel-coated PES fibers (GEL, n = 10), VEGF-releasing hydrogel-coated PES fibers (VEGF GEL, n = 10), DX-releasing hydrogel-coated PES fibers (DX GEL, n = 10), and VEGF + DX-releasing hydrogel-coated PES fibers (VEGF + DX GEL, n = 10). VEGF-releasing hydrogels were shown to have a significantly increased blood vessel count compared to VEGF-DX-releasing hydro-gel-coated, hydrogel-coated, and bare fibers (p < 0.05).

Figure 6

Number of blood vessels within 40 μm of implant surface after 6 weeks implantation in rat subcutaneous tissue. The implanted materials were bare PES fibers (PES, n = 3), hydrogel-coated PES fibers (GEL, n = 4), VEGF-releasing hydrogel-coated PES fibers (VEGF GEL, n = 6), DX-releasing hydrogel-coated PES fibers (DX GEL, n = 5), and VEGF + DX-releasing hydrogel-coated PES fibers (VEGF + DX GEL, n = 4). Data were found to be inconclusive for statistical analysis.

Figure 7

Inflammation score of tissues surrounding implants after 2 weeks implantation in rat subcutaneous tissue. The implanted materials were bare PES fibers (PES, n = 9), hydrogel-coated PES fibers (GEL, n = 9), VEGF-releasing hydrogel-coated PES fibers (VEGF GEL, n = 6), DX-releasing hydrogel-coated PES fibers (DX GEL, n = 8), and VEGF + DX-releasing hydrogel-coated PES fibers (VEGF + DX GEL, n = 9). The tissues surrounding VEGF-releasing hydrogel-coated fibers were significantly inflamed compared to tissue surrounding hydrogel-coated and DX-releasing hydrogel-coated fibers (p < 0.05).

Figure 8

Inflammation score of tissues surrounding implants after 2 weeks implantation in rat subcutaneous tissue. The implanted materials were bare PES fibers (PES, n = 4), hydrogel-coated PES fibers (GEL, n = 5), VEGF-releasing hydrogel-coated PES fibers (VEGF GEL, n = 4), DX-releasing hydrogel-coated PES fibers (DX GEL, n = 4), and VEGF + DX-releasing hydrogel-coated PES fibers (VEGF + DX GEL, n = 3). Median score for VEGF-DX-releasing hydrogel-coated fibers was found to be zero. Data collected were found to be statistically inconclusive due to small sample size.