Non-Invasive Monitoring of Oxygen Tension and Oxygen Transport Inside Subcutaneous Devices After H2S Treatment

Abstract

Medical devices for cell therapy can be improved through prevascularization. In this work we study the vascularization of a porous polymer device, previously used by our group for pancreatic islet transplantation with results indicating improved glycemic control. Oxygen partial pressure within such devices was monitored non-invasively using an optical technique. Oxygen-sensitive tubes were fabricated and placed inside devices prior to subcutaneous implantation in nude mice. We tested the hypothesis that vascularization will be enhanced by administration of the pro-angiogenic factor hydrogen sulfide (H₂S). We found that oxygen dynamics were unique to each implant and that the administration of H₂S does not result in significant changes in perfusion of the devices as compared with control. These observations suggest that vascular perfusion and density are not necessarily correlated, and that the rate of vascularization was not enhanced by the pro-angiogenic agent.

Keywords: biophotonics; diabetes; islet transplantation; medical devices; oxygen monitoring; tissue engineering.

Figure 1.

(A) Oxygen-sensitive tubes (OSTs) shown as green cylinders (15 mm in length) are inserted into three empty channels of the porous PDLLCL device (5 mm × 10 mm × 15 mm) to quantify oxygen tension. (B) OSTs act as retrievable oxygen-monitoring sensors and are made of oxygen-permeable silicone tubing coated on the inner surface with a layer of PtTPTBPF and reinforced with stainless steel wire. Both ends are sealed using medical-grade silicone adhesive. (C) Oxygen monitor comprising a printed circuit board that houses two LEDs, photodetector and optical filter.

Figure 2.

(A) Three calibration cycles of a single oxygen-sensitive tube (PO₂: 160, 76, 38, and 0 mmHg, in order). Average lifetime values for each plateau (at each gas mixture) across the three cycles are 19.0 ± 0.07, 21.6 ± 0.08, 24.9 ± 0.04 and 34.1 ± 0.06 µs, respectively. (B) DIGT performed on an animal 3 days after device implantation. Risetime is defined as elapsed time between exchanging inhaled gas from 152 to 760 mmHg (left green circle) and steady state (right green circle).

Figure 3.

(A–C) DIGT Oxygen Risetime (minutes) and (D-F) PO₂ plateau value (mmHg) at the end of each DIGT experiment, measured for three groups: control (saline), low (25 μmol/kg body weight) and high (50 µmol/kg body weight) NaHS dosages (n = 6 per group). All groups underwent twice daily injections for the first 28 days followed by 35 days without injections (day 28 to 63). No statistical differences in Risetime or PO₂ plateau values were detected between groups.

Figure 4.

Histological analysis of blood vessels after 63 days of implantation. Blood vessels in the control (A), low H₂S dosage (B), and high H₂S dosage (C) treated groups were stained by using the endothelial cell marker CD31 (pink color). (D) Gene expression of the endothelial cell marker CD31 after 63 days of implantation and (E) the number of vessels per area (mm²) in each device was measured. Data is plotted as mean with the standard error of mean. Statistical analysis was carried out using a one-way ANOVA with a Tukey post-hoc test, p < 0.05 (*) and p < 0.001 (**).