IF 2.0×10⁶ day-30 purified iPSC-derived cardiomyocytes (>95% cTnT-positive) encapsulated in a 12% (w/v) gelatin hydrogel enzymatically crosslinked by microbial transglutaminase (Streptomyces mobaraensis) at a 20:1 mTG:gelatin ratio, delivered as a 50 μL intramyocardial bolus into the left ventricular free wall, are administered to C57BL/6J mice aged 20–24 months (both sexes),

THEN ≥30% donor cell retention at 8 weeks post-injection (quantified by human cardiac troponin T immunohistochemistry on serial sections spanning the injection site, corresponding to ≥6×10⁵ viable graft cells), combined with ≥8 percentage-point improvement in left ventricular ejection fraction versus saline-vehicle iPSC-CM controls and evidence of synchronized calcium transient propagation between donor and host cardiomyocytes on optical mapping at 12 weeks, will be observed,

BECAUSE the following causal chain links the intervention to outcome:

1. At a 20:1 mTG:gelatin ratio and 12% gelatin concentration, the precursor solution remains injectable through 28–30G needles at room temperature but undergoes a temperature-accelerated sol-gel transition upon reaching the 37°C intramyocardial environment, producing a crosslinked scaffold within 15–30 minutes post-injection that physically retains cells against the systolic ejection forces responsible for >90% early mechanical washout seen with saline vehicles (as synthesized in the Evidence Set, Physicochemical Properties section).

2. Gelatin's endogenous RGD cell-adhesive motifs provide immediate integrin-binding ligands for encapsulated iPSC-CMs, suppressing anoikis — the second major early cell-death mechanism — by restoring ECM-dependent survival signaling that is absent in saline delivery (Evidence Set, Introduction section).

3. [SPECULATIVE — critical novel link] The chronically inflamed, aged C57BL/6J myocardium (20–24 months) exhibits constitutively elevated matrix metalloproteinase (MMP) activity driven by the "inflammaging" secretory milieu — the same proteolytic environment described in the Evidence Set (Aged Myocardial Microenvironment section) as a barrier to engraftment — which paradoxically becomes an asset here: gelatin, as a collagen-derived substrate, is a native MMP-2/MMP-9 cleavage target, meaning the aged host myocardium's endogenous MMP burden is predicted to drive time-dependent scaffold resorption within a 2–4 week window, precisely when donor cells have stabilized through matrix-supported survival signaling and are primed to establish direct intercellular contact with host cardiomyocytes.

4. [SPECULATIVE] This MMP-mediated "niche opening" converts the hostile aged proteolytic microenvironment — identified as a liability in all prior engraftment literature — into a therapeutically programmed dissolution trigger: the higher the aged host's inflammatory MMP load, the faster the scaffold is resorbed, and the earlier the released iPSC-CMs are exposed to host cell surfaces for Connexin-43 (Cx43) ga...

SENS category: GlycoSENS