Inflammation-Controlled Anti-Inflammatory Hydrogels

Abstract

While autoregulative adaptation is a common feature of living tissues, only a few feedback-controlled adaptive biomaterials are available so far. This paper herein reports a new polymer hydrogel platform designed to release anti-inflammatory molecules in response to the inflammatory activation of human blood. In this system, anti-inflammatory peptide drugs, targeting either the complement cascade, a complement receptor, or cyclophilin A, are conjugated to the hydrogel by a peptide sequence that is cleaved by elastase released from activated granulocytes. As a proof of concept, the adaptive drug delivery from the gel triggered by activated granulocytes and the effect of the released drug on the respective inflammatory pathways are demonstrated. Adjusting the gel functionalization degree is shown to allow for tuning the drug release profiles to effective doses within a micromolar range. Feedback-controlled delivery of covalently conjugated drugs from a hydrogel matrix is concluded to provide valuable safety features suitable to equip medical devices with highly active anti-inflammatory agents without suppressing the general immunosurveillance.

Keywords: drug delivery; elastase; feedback control; hydrogel; inflammation.

Figure 1

Schematic summary of the explored concept of inflammation‐responsive anti‐inflammatory hydrogels: Inflammatory processes activate granulocytes, followed by the release of cellular leukocyte elastase. A polymer hydrogel system of four‐armed poly(ethylene glycol) (starPEG) was crosslinked with heparin and contains linker peptides that are cleavable by leukocyte elastase in direct response to granulocyte activation. Anti‐inflammatory drugs are conjugated to the starPEG component of the hydrogel through the same cleavable linker peptide and released upon enzymatically controlled hydrogel cleavage. The amount of released drug can be adjusted via the degree of starPEG functionalization. Three different bioactives were applied to validate the adaptive anti‐inflammatory functionality of the hydrogel platform, targeting either the complement cascade, the leukocyte response to complement fragments, or the proinflammatory effects of extracellular cyclophilin A (CypA).

Figure 2

Release of a drug model compound (fluorescent dye Atto488) from a hydrogel. The model drug was conjugated to the amine term of the cleavable peptide at 2% of the starPEG arms. Nonresponsive control hydrogels were formed according to the same protocols using an amino‐terminated starPEG without the cleavable peptide. A) Molar release of the model compound by defined enzyme concentrations, rated to the hydrogel surface (mean ± SD of n  =  3). B) Release by resting and complement opsonized zymosan (OPZ)‐activated granulocytes normalized to the sample area (mean ± SD of n = 2).

Figure 3

Cleavage of inflammation‐responsive hydrogels in an in vitro inflammation model and assessment of the anti‐inflammatory effects of the released drugs. A) For hydrogel cleavage, isolated polymorphonuclear granulocytes (PMN) are activated with complement‐opsonized zymosan (OPZ) in cell culture media and incubated with the hydrogel over 2 h at 37 °C. The cell‐free supernatant containing the released bioactive is used to test the anti‐inflammatory effect in the corresponding system. B) 4W9A: Measurement of complement activation in whole blood activated with zymosan. C) PMX53: Activation of isolated PMN by zymosan activated serum, measured as CD11b expression (*P < 0.05, **P < 0.01 in t‐test). D) CsA: Cyclosporine A (CsA) release measured by the inhibitory effect on CypA.