Immune‐Informed Mucin Hydrogels Evade Fibrotic Foreign Body Response In Vivo

Abstract

The immune‐mediated foreign body response to biomaterial implants can trigger the formation of insulating fibrotic capsules that can compromise implant function. To address this challenge, the intrinsic bioactivity of the mucin biopolymer, a heavily glycosylated protein that forms the protective mucus gel covering mucosal epithelia, is leveraged. By using a bioorthogonal inverse electron demand Diels–Alder reaction, mucins are crosslinked into implantable hydrogels. It is shown that mucin hydrogels (Muc‐gels) modulate the immune response driving biomaterial‐induced fibrosis. Muc‐gels do not elicit fibrosis 21 days after implantation in the peritoneal cavity of C57Bl/6 mice, whereas medical‐grade alginate hydrogels are covered by fibrous tissues. Further, Muc‐gels dampen the recruitment of innate and adaptive immune cells to the gel and trigger a pattern of very mild activation marked by a noticeably low expression of the fibrosis‐stimulating transforming growth factor beta 1 cytokine. Macrophages recruited to Muc‐gels upregulate the gene expression of the protein inhibitor of activated STAT 1 (PIAS1) and SH2‐containing phosphatase 1 (SHP‐1) cytokine regulatory proteins, which likely contributes to their low cytokine expression profiles. With this advance in mucin materials, an essential tool is provided to better understand mucin bioactivities and to initiate the development of new mucin‐based and mucin‐inspired “immune‐informed” materials for implantable devices subject to fibrotic encapsulation.

Mucin hydrogel glyco-modulation to investigate immune activity of mucin glycans

“…Using the Muc and tMuc gels, we characterized the interactions of non-polarized macrophages, both THP1-M0 and hPBMC-M0, with the materials' surface. The Muc gels have already shown to be non-cytotoxic and support the survival of cells seeded on or in the hydrogels for several days 26 . Both THP1-M0 and hPBMC-M0 poorly adhered to the surface of Muc and tMuc gels.…”

“…The resulting hydrogels have similar bulk elastic moduli (Figure 2) and nanomechanical surface properties (Figure 3) regardless of the sialic acid content, suggesting that sialic acid residues on mucins are not crucial for the formation of the crosslinking knots of Muc gels. We hypothesize that this is because the EDC/NHS chemistry applied to graft the Tz and Nb functionalities mainly targets carboxylic groups on the mucin-protein backbone 26 can affect a host of cell processes 39 and impurities in the material alone can activate macrophages 40,41 . Such glyco-modulation of mucins with glycolytic enzymes prior to the material formulation could also be expanded to other enzymes, including glycosyltransferases.…”

“…To prepare mucin hydrogels (Muc gels), we introduced tetrazine (Tz) and norbornene (Nb) functionalities to bovine submaxillary mucin (Muc) molecules as previously described 26 . After being mixed in solution, the Muc-Tz and Muc-Nb formed a covalently crosslinked hydrogel through an inverse electron demand Diels-Alder cycloaddition reaction (Figure 1A, B).…”

“…We have recently shown that covalently crosslinked mucin hydrogels (Muc gels) made of bovine submaxillary mucins (Muc) modulate the foreign body response in vivo. Those hydrogels caused a broad dampening effect of cytokine expression in macrophages harvested from the explanted gels and their corresponding peritoneal cavity, and the absence of fibrous encapsulation after 21 days 26 . This discovery suggests that biomaterials containing mucins or mucin-like molecules could be used as implantable hydrogels and coatings that can evade fibrosis and ensure the long-term function of the devices.…”

“…This discovery suggests that biomaterials containing mucins or mucin-like molecules could be used as implantable hydrogels and coatings that can evade fibrosis and ensure the long-term function of the devices. However, fibrous capsule formation is typically initiated after ~ 2 weeks of implantation 26 , and the earlier events that led to such effects are unknown. In addition, none of the features of mucins essential for their immune-modulating properties were clearly identified.…”