Biocompatibility of common implantable sensor materials in a tumor xenograft model

Abstract

Real-time monitoring of tumor microenvironment parameters using an implanted biosensor could provide valuable information on the dynamic nature of a tumor's biology and its response to treatment. However, following implantation biosensors may lose functionality due to biofouling caused by the foreign body response (FBR). This study developed a novel tumor xenograft model to evaluate the potential of six biomaterials (silicon dioxide, silicon nitride, Parylene-C, Nafion, biocompatible EPOTEK epoxy resin, and platinum) to trigger a FBR when implanted into a solid tumor. Biomaterials were chosen based on their use in the construction of a novel biosensor, designed to measure spatial and temporal changes in intra-tumoral O₂ , and pH. None of the biomaterials had any detrimental effect on tumor growth or body weight of the murine host. Immunohistochemistry showed no significant changes in tumor necrosis, hypoxic cell number, proliferation, apoptosis, immune cell infiltration, or collagen deposition. The absence of biofouling supports the use of these materials in biosensors; future investigations in preclinical cancer models are required, with a view to eventual applications in humans. To our knowledge this is the first documented investigation of the effects of modern biomaterials, used in the production of implantable sensors, on tumor tissue after implantation. © 2018 The Authors. Journal of Biomedical Materials Research Part B: Applied Biomaterials published by Wiley Periodicals, Inc. J Biomed Mater Res Part B, 2018. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1620-1633, 2019.

Keywords: biocompatibility; foreign body response; implantable biosensor; innate immune response; tumor microenvironment; tumor xenograft model.

Figure 1

Photographs depicting xenograft tumor processing and sectioning, along with representative H&E stained slides. (A–C) Photographs depicting the position of the biomaterial within a xenograft tumor following harvesting and processing for IHC. The dashed box is outlining an OG116‐31 resin biomaterial wire. To identify the implant site, sectioning of the tissue block continued until the tip of the biomaterial was found. If the biomaterial was approximately flush with the cut surface the wire was removed and sectioning continued; however, if the direction of the wire was further into the tumor, the paraffin was then melted, and the wire carefully removed. The tumor tissue was trimmed from its sectioned edge as parallel as possible to the path of the wire tract before being re‐embedded in paraffin. Once set, sectioning continued through the block. (D–G) Representative H&E stained sections from untreated and biomaterial implanted xenograft tumors harvested at day 7. (D, E) Untreated, (F) Nafion implanted, (G) SiO₂ implanted.

Figure 2

The effects of different biomaterials on mice body weights and tumor volumes. (Ai, Bi) Changes in mice body weights for untreated xenograft tumors and Cu, OG116‐31 resin, Parylene‐C, Nafion, Pt, Si₃N₄, and SiO₂ implanted xenograft tumors up to 7 days post‐implantation. Body weights were normalized to the day 0 value. (Aii, Bii) Mean tumor volumes for untreated and NT injury xenograft tumors, along with Cu, OG116‐31 resin, Parylene‐C, Nafion, Pt, Si₃N₄, and SiO₂ implanted xenograft tumors up to 7 days post‐implantation. Tumor volume at each time point was normalized to its day 0 measurement.

Figure 3

The effects of biomaterials on tumor necrosis and CA9 staining. (Ai, Aii) Representative H&E stained sections from xenograft tumors harvested at day 7. (Ai) Untreated, (Aii) Cu. (Bi, Bii) Percentage area of necrosis for untreated and NT injury xenograft tumors, along with Cu, OG116‐31 resin, Parylene‐C, Nafion, Pt, Si₃N₄, and SiO₂ implanted xenograft tumors up to 7 days post‐implantation. (Ci, Cii) Representative CA9 stained sections from xenograft tumors harvested at day 7. (Ci) Untreated, (Cii) Nafion. (Di, Dii) Percentage of CA9 positive staining cells for untreated and NT injury xenograft tumors, along with Cu, OG116‐31 resin, Parylene‐C, Nafion, Pt, Si₃N₄, and SiO₂ implanted xenograft tumors up to 7 days post‐implantation.

Figure 4

The effects of biomaterials on tumor proliferation and apoptosis. (Ai, Aii) Representative Ki67 stained sections from xenograft tumors harvested at day 7. (Ai) Untreated, (Aii) SiO₂. (Bi, Bii) Percentage of Ki67 positive staining cells for untreated and NT injury xenograft tumors, along with Cu, OG116‐31 resin, Parylene‐C, Nafion, Pt, Si₃N₄, and SiO₂ implanted xenograft tumors at 7 days post‐implantation. (Ci, Cii) Representative caspase 3 stained sections from xenograft tumors harvested at day 7. (Ci) Untreated, (Cii) Cu. (Di, Dii) Percentage of caspase 3 positive staining cells for untreated and NT injury xenograft tumors, along with Cu, OG116‐31 resin, Parylene‐C, Nafion, Pt, Si₃N₄, and SiO₂ implanted xenograft tumors at 7 days post‐implantation.

Figure 5

The effects of biomaterials on neutrophil (Ly‐6G/‐6C) and macrophage (F4/80) infiltration within tumor tissue. (Ai, Aii) Representative Ly‐6G/‐6C stained sections from xenograft tumors harvested at day 7. (Ai) Untreated, (Aii) Parylene‐C. (Bi, Bii) Percentage of Ly‐6G/‐6C positive staining cells for untreated and NT injury xenograft tumors, along with Cu, OG116‐31 resin, Parylene‐C, Nafion, Pt, Si₃N₄, and SiO₂ implanted xenograft tumors at 7 days post‐implantation. (Ci, Cii) Representative F4/80 stained sections from xenograft tumors harvested at day 7. (Ci) Untreated, (Cii) Si₃N₄. (Di, Dii) Percentage of F4/80 positive staining cells for untreated and NT injury xenograft tumors, along with Cu, OG116‐31 resin, Parylene‐C, Nafion, Pt, Si₃N₄, and SiO₂ implanted xenograft tumors at 7 days post‐implantation.

Figure 6

The effects of biomaterials on fibroblast (ER‐TR7) infiltration and collagen deposition within tumor tissue. (Ai–Aii) Representative ER‐TR7 stained sections from xenograft tumors harvested at day 7. (Ai) Untreated, (Aii) Pt. (Bi, Bii) Percentage of ER‐TR7 positive staining cells for untreated and NT injury xenograft tumors, along with Cu, OG116‐31 resin, Parylene‐C, Nafion, Pt, Si₃N₄, and SiO₂ implanted xenograft tumors up to 7 days post‐implantation. (Ci, Cii) Representative Masson's trichrome stained sections from xenograft tumors harvested at day 7. (Ci) Untreated, (Cii) SiO₂. (Di, Dii) Percentage area of collagen for untreated and NT injury xenograft tumors, along with Cu, OG116‐31 resin, Parylene‐C, Nafion, Pt, Si₃N₄, and SiO₂ implanted xenograft tumors up to 7 days post‐implantation. Data for (Di) graph is expressed as mean ± SEM; according to unpaired two sample t test. Data for (Dii) expressed as mean ± SEM; according to one‐way ANOVA followed by Tukey's multiple comparison test.

Figure 7

Macrophage (F4/80) distribution types within untreated xenograft tumors. (A) Macrophages are identified both at the periphery of the tumor and within the tumor tissue. (B) Macrophages are uniformly distributed within the tumor tissue.