(563f) Award Submission: Next-Generation Tattoo-Ink for Improved Endoscopic Imaging

Endoscopic tattooing (or commonly known as “colon tattooing”) is a routinely used clinical technique to mark colorectal lesions (i.e. polyps) for successive surgical resection or to facilitate follow-up of the endoscopic resection site. Colon tattooing procedures are typically recommended for lesions with evident or suspected colorectal cancers; lesions with dimensions ≥2cm in diameter with potential risk of cancer, and for flat broad lesions removed by endoscopic submucosal dissection (ESD) or endoscopic mucosal resection (EMR) procedures. This technique involves injecting a dark-colored (i.e., high contrast) ink directly into the submucosal layer of the colon; or the ink can also be delivered through a saline bleb created in the submucosa. Currently used tattoo inks in clinic are prone to many side effects including peritonitis, abscess formation and / or development of inflammatory bowel disease. Additionally, submucosal fibrosis associated with existing commercial inks can interfere with endoscopic resection techniques later and may increase the risk for incomplete resection. These products can rapidly and substantially diffuse throughout the submucosal tissue and also to other tissues, which complicates the approximation of a tattoo with the intended lesion of interest. Hence, there is an unmet clinical need for new endoscopic tattoo inks which can (1) retain localization for improved follow-up accuracy and (2) do not induce toxic, inflammatory and / or fibrotic responses in long-term. To address this medical problem, we generated novel biomaterial-based tattoo-ink, formulated by combining (1) metal-derived nanoparticles (such as polysaccharide-coated negatively charged iron oxide nanoparticles) as the contrast agent and (2) mucoadhesive polymer biomaterials as a bioprotective coating and retention-mediating carrier, for applications in endoscopic imaging of the gastrointestinal tract.

Polysaccharide-coated iron oxide nanoparticles were synthesized using a one-pot co-precipitation method. A library of cationic biomaterial derivatives was prepared based on variable molecular weight, terminal functional group, and chemical functionalization including thiolation, quaternization. All biomaterial derivatives were characterized using FTIR spectroscopy; amine and thiol contents were measured using ninhydrin and elman’s assay, respectively. A series of biomaterial-based tattoo-ink candidates were generated by modulating the ratio between the contrast agent and the biomaterial-based coating. Our tattoo-ink formulations, 0.25-2μm in hydrodynamic diameter, demonstrated near-equivalent contrast ex vivo with fresh porcine intestinal tissue as that shown by commercial inks, while also exhibiting substantially reduced diffusion in tissue, thus leading to better spot localization. The ability of these tattoo-ink constituents to induce IRF3 and NFκB inflammatory pathways in cells were evaluated in vitro using J774-DUAL mouse macrophage reporter cells and indicated minimal immunogenicity from these tattoo-ink constituents. Preclinical studies in immunocompetent Balb/c mice using subcutaneous injections indicate extensive diffusion of the commercial ink within the subcutis and significant leakage into the hypodermis. However, our formulations of biomaterial-based tattoo-ink demonstrated high contrast, effective spot localization in the subcutis and no leakage to other tissues, indicating better performance for visualization in vivo. Histopathology analyses on H&E-stained sections revealed lead tattoo-ink candidates with biomaterials chemistry-dependent biocompatibility responses and very minimal immune response in vivo. Additionally, our tattoo-ink formulation was visualized under clinical MR-imaging system which enhances its potential use in multimodal imaging capability with non-invasive follow-up procedure. These biomaterial-based tattoo-ink formulations represent a next generation biocompatible endoscopic ink which will have measurable impacts on patient quality of life and procedural outcomes with a clear path to clinical translation.