Chwatko, M. | Search bioRxiv

bioRxiv2024

Design of PEG-based hydrogels as soft ionic conductors

Conductive hydrogels have gained interest in biomedical applications and soft electronics. To tackle the challenge of ionic hydrogels falling short of desired mechanical properties in previous studies, our investigation aimed to understand the pivotal structural factors that impact the conductivity and mechanical behavior of polyethylene glycol (PEG)-based hydrogels with ionic conductivity. Polyether urethane diacrylamide (PEUDAm), a functionalized long-chain macromer based on PEG, was used to synthesize hydrogels with ionic conductivity conferred by incorporating ions into the liquid phase of hydrogel. The impact of salt concentration, water content, temperature, and gel formation on both mechanical properties and conductivity was characterized to establish parameters for tuning hydrogel properties. To further expand the range of conductivity available in these ionic hydrogels, 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) was incorporated as a single copolymer network or double network configuration. As expected, conductivity in these ionic gels was primarily driven by ion diffusivity and charge density, which was dependent on hydrogel network formation and swelling. Copolymer network structure had minimal effect on the conductivity which was primarily driven by counter-ion equilibrium; however, the mechanical properties and equilibrium swelling was strongly dependent on network structure. The structure-property relationships elucidated here enables the rationale design of this new double network hydrogel to achieve target properties for a broad range of applications.

bioengineering↗

bioRxiv2021

Towards prevention of re-entrant arrhythmias: Injectable hydrogel electrodes enable direct capture of previously inaccessible cardiac tissues

Re-entrant arrhythmias--the leading cause of sudden cardiac death--are caused by diseased myocardial tissue and consequent delayed myocardial conduction. Access to the coronary veins that cross the "culprit" scar regions where re-entry originates can provide improved pacing to these delayed regions, offering a novel opportunity to prevent ventricular arrhythmias and circumvent the need for painful defibrillation, risky cardiac ablation, or toxic and often ineffective antiarrhythmic medications. However, there are no pacing electrodes which are small or focal enough to navigate these tributaries. To address this need, we have developed an injectable conductive hydrogel that can fill the epicardial coronary veins and their mid-myocardial tributaries. When connected to a standard pacing lead, these injected hydrogels can be converted into flexible electrodes that directly pace the previously inaccessible mid-myocardial tissue. In our two-component system, hydrogel precursor solutions can be injected through a dual lumen catheter in a minimally invasive deployment strategy to provide direct access to the diseased regions with precision and ease. Mixing of the two solutions upon injection into the vein activates redox-initiated crosslinking of the gel for rapid in situ cure without an external stimulus. An ex vivo porcine model was used to identify the requisite viscosity and cure rate for gel retention and homogeneity. Ionic species added to the hydrogel precursor solutions conferred conductivity above target myocardium values that was retained after implantation. Successful in vivo deployment demonstrated that the hydrogel electrode filled the anterior interventricular vein with extension into the septal (mid-myocardial) venous tributaries to depths far more distal and refined than any current technologies allow. In addition to successful capture and pacing of the heart, analysis of surface ECG tracings revealed a novel pacing observation highly specific for and suggestive of capture of extensive swaths of septal myocardial tissue. This is the first report of an injectable electrode used to successfully pace the mid-myocardium and mimic physiologic conduction. Furthermore, in vivo cardiac electroanatomical mapping studies in an ablation scar model showed uniform capture along the hydrogel in the vessels as well as increased capture area compared to point pacing. Collectively, these findings demonstrate that this injectable hydrogel electrode can be deployed to scarred regions of the heart to provide a reliable pacing modality that most closely resembles native conduction with the potential to eliminate delayed myocardial conduction and associated re-entry. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=179 SRC="FIGDIR/small/467102v2_ufig1.gif" ALT="Figure 1"> View larger version (50K): org.highwire.dtl.DTLVardef@1577526org.highwire.dtl.DTLVardef@cc510dorg.highwire.dtl.DTLVardef@1dd426eorg.highwire.dtl.DTLVardef@1346aab_HPS_FORMAT_FIGEXP M_FIG C_FIG One Sentence SummaryInjectable hydrogel electrodes achieve pacing that mimics physiologic conduction by capturing midmyocardial tissue

bioengineering↗