Comb Architecture to Control the Selective Diffusivity of a Double Network Hydrogel

Abstract

Limiting the diffusion of small-sized substances (D h < 5 nm) through hydrogels is particularly difficult to achieve. Herein, we demonstrate the utility of a comb architecture to systematically reduce the mesh size of a double network (DN) hydrogel to between ∼1 and 3 nm, without loss of hydration. Combs of varying charge, length, and concentration were introduced during the formation of the first network of the DN hydrogel based on thermoresponsive N-isopropylacrylamide and negatively charged 2acrylamido-2-methylpropane sulfonic acid. The resulting hydrogels' mesh sizes were characterized with a size-exclusion test. Negatively charged combs were the most effective in reducing mesh size, attributed to electrostatic repulsive forces with the DN. Due to a lack of interaction and attractive forces to the first network, respectively, neutral and particularly positively charged combs were less effective.

Defect-controlled softness, diffusive permeability, and mesh-topology of metallo-supramolecular hydrogels

“…With this strategy, Grunlan et al controlled the mesh-size of a hydrogel with the introduction of thermoresponsive and charged dangling chains. 18 Their findings show that with negatively charged chains, smaller meshes are possible. 18 In an own previous work, we introduced poly( N -isopropylacrylamide) (pNIPAAm) dangling chains into a supramolecular polymer network and were able to similarly hinder the diffusion of small probes upon switching temperature above the lower critical solution temperature of pNIPAAm.…”

“…18 Their findings show that with negatively charged chains, smaller meshes are possible. 18 In an own previous work, we introduced poly( N -isopropylacrylamide) (pNIPAAm) dangling chains into a supramolecular polymer network and were able to similarly hinder the diffusion of small probes upon switching temperature above the lower critical solution temperature of pNIPAAm. 5 Similarly, we investigated how the network dynamics of gels, constituted by chains carrying sticky side-groups, changes with the introduction of sticky tracers having the same or lower connectivity than the network itself, thereby creating local connectivity defects.…”

A Glucose Biosensor Based on Phosphorescence Lifetime Sensing and a Thermoresponsive Membrane

“…Still, the E (≈0.44 MPa) and CS (≈0.37 MPa) of the DN‐ 0 prepared with the shorter cure time are similar to conventional hydrogels, such as those prepared from poly(ethylene glycol) diacrylate (PEG‐DA; M n = 3.4 kDa, 10% w/v; E = ≈0.33 MPa; CS = ≈0.48 MPa). [ 45 ] Even a slight increase in cure time from 10 to 14 min showed evidence of photo‐bleaching (Figure S2d, Supporting Information). Thus, the utilized 10 min UV cure protocol is judicious for the incorporation of HULK within the DN‐ x membranes.…”

“…A similar D eff value (at 37 °C) was observed for a non‐thermoresponsive PEG‐DA membrane. [ 45 ] The D eff of DN‐ x membranes was notably higher than that of subcutaneous tissue (≈2 ×10 −6 cm 2 s −1 ). [ 47 ] Thus, when used to prepare a glucose biosensor, the glucose diffusion lag time would be limited by the subcutaneous tissue, not the membrane.…”

Reversible Hydrogels with Switchable Diffusive Permeability

“…[ 8–10 ] In general, diffusion through a polymer‐network gel is determined by the mesh size, and this can be controlled in several ways, such as increasing the concentration of the polymer or by changing the structure of the polymer network, for example, through introduction of dangling chains. [ 11,12 ] Here, we employ thermoresponsive dangling chains to exquisitely control the mesh size on demand upon switch of temperature. On top of that, in polymer science, as well as in every other branch of materials science, there is an increasing demand for a sustainable footprint, here meaning a gel that is reversible.…”