3D-Printed Sodium Alginate/Gelatin/Black Phosphorus Nanosheet Hydrogel Patches for Urethral Stricture Repair.

The urethral stricture is still a clinical challenge, where bioactive scaffold materials capable of providing critical biological hints are needed to help regenerate the function and also reduce excessive fibrosis. Black phosphorus nanosheets (BPNSs) have been identified as promising nanomaterials in tissue engineering; however, their effects on urethral repair, depending on their concentration, remain poorly understood. In this study, we fabricated a porous sodium alginate/gelatin/black phosphorus nanosheet (SA/Gel/BPNS) composite hydrogel patch based on extrusion-based 3D printing technology. The physicochemical properties and biocompatibility of the scaffolds were characterized. The biological effects of varying BPNS concentrations on human foreskin fibroblast (HFF) behaviors were systematically investigated in vitro. Furthermore, the regenerative potential of the patches was evaluated in a rabbit model of urethral injury through macroscopic and histological assessments. In vitro assays revealed that BPNS exerts a distinct biphasic regulatory effect on HFFs: Low concentrations (0.25 μg·mL-1) significantly promoted cell migration and the expression of pro-repair markers (fibronectin, COL1, and α-SMA), while high concentrations (4 μg·mL-1) inhibited fibrotic marker expression. Transcriptomic analysis further indicated that low-concentration BPNS was associated with the PI3K-Akt signaling pathway, whereas high-concentration BPNS mainly affected ECM-receptor interaction, focal adhesion, and Rap1 signaling pathways. In vivo results demonstrated that the SA/Gel/BPNS0.25 group had the best repair performance, characterized by an intact, smooth urethral surface, enhanced epithelial remodeling, and organized tissue regeneration with reduced fibrous scar deposition compared to the control groups. The SA/Gel/BPNS patch integrates mechanical scaffolding with concentration-dependent biomodulation. Through optimization of BPNS concentrations, this patch effectively facilitates functional urethral healing and mitigates secondary scarring, offering a potential bioengineering solution for the clinical treatment of urethral strictures.