Green ultrasonic engineering of hierarchical microphase structures and enhanced properties in chitosan–silk blends across molecular weight ranges

Ultrasound processing offers a sustainable and non-chemical strategy for controlling molecular organization in soft materials. In this work, we show that ultrasonication can reorganize chitosan-silk blends into ordered microphase architectures similar to classical AB block copolymers without any chemical synthesis providing a novel strategy to control nanoscale morphology and enhance material functionality. Composite films were prepared using Bombyx mori silk fibroin and chitosan spanning low, medium, and high molecular weight ranges, followed by ultrasound treatment under optimized time and power conditions. The resulting materials were examined using scanning electron microscopy (SEM) to resolve microphase domains, Fourier-transform infrared spectroscopy (FTIR) to probe molecular interactions, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) to assess thermal behaviors, and X-ray diffraction (XRD) to analyze crystalline organization. Ultrasound treatment induced nanoscale structural ordering, enhanced intermolecular hydrogen bonding, and increased β-sheet formation in silk proteins, giving rise to distinct spherical, insular, and lamellar microdomains. These ultrasound-mediated structural transformations produced substantial improvements in thermal stability, mechanical performance, hydrophilicity, and morphological uniformity compared with untreated films. This study provides the first direct evidence that ultrasonic energy alone can drive biopolymer blends into ordered microphase patterns traditionally associated with block-copolymer chemistry. These findings position ultrasonication as a simple, green, and scalable platform for designing biomaterials with tunable hierarchical structures and multifunctional properties suitable for advanced biomedical and sustainable applications.