Bioprinted Stiffness‑Tunable Pancreatic Microniches to Decode Early Tumor Initiation Mechanisms

Pancreatic ductal adenocarcinoma (PDAC) remains one of the deadliest human cancers, driven in 90% of cases by KRAS mutations and characterized by an intense desmoplastic reaction, early metastasis, and therapy resistance. The mechanisms driving PDAC initiation, however, remain poorly understood because early acinar transformation is difficult to model in a controlled microenvironment. Here, we introduce a microvalve-bioprinted 3D pancreatic cancer initiation niche that supports culture of primary acini from wild-type and Kras-mutant mice, up to 14 days, within gelatin-methacryloyl (GelMA) hydrogels. Our printing strategy enables tuning of hydrogel stiffness to cover the range reported for healthy murine pancreas and early stages of desmoplastic remodelling. In this system, wild-type acini retain a predominantly acinar phenotype, whereas intermediate GelMA conditions cooperate with pre-existing oncogenic Kras to promote acinar-to-ductal metaplasia and proliferative programs associated with early neoplastic reprogramming. Multimodal readouts revealed a stiffness-permissive window in which mechanical cues cooperated with oncogenic Kras to promote acinar transdifferenciation, proliferation and distinct stiffness-dependent secretory programs, including inflammatory and stromal-associated factors with previously reported relevance to PDAC biology. The deterministic droplet geometry supported reproducible, high-throughput, and longitudinal analysis under conditions inaccessible to conventional extrusion or laser‑assisted bioprinting, providing an experimental framework to study early Kras-driven acinar reprogramming.