With the increased requirement of miniaturization structures on hard and brittle substrates, micro abrasive air jet turning technology has become a promising machining technology for manufacturing miniaturization structures. This paper presents an investigation on multi-pass radial-mode micro abrasive air jet turning of fused silica. The effect of machining parameters on the depth of cut and materials removal rate was analyzed. The waviness and striation formation mechanisms were studied. It was found that increasing the number of passes significantly increases the depth of cut and materials removal rate. When the surface speed is reduced, the depth of cut and materials removal rate significantly increases. The waviness may be attributed to the intersection and overlap of the adjoint jet footprint. The crossed striations have been found, which may lead to the elimination of the striation. A predictive model of the material removal rate was developed using the dimensional analysis method. The model was assessed and shown to be able to give adequate predictions.

Biological bone screws play an important role in fixing fractures and bone defects. The machining of helical grooves on xenogenic materials is a key part of fabricating biological bone screws. The fabrication of helical grooves on bovine bone using micro-abrasive air jets was investigated in this paper. The helical groove shapes were classified and their formation mechanisms were studied. Analyses of the material removal mechanism and the effect of process parameters on the groove shapes were carried out. The results show that the helical grooves could be effectively machined using micro-abrasive air jets with a spring mask. The shapes of the helical grooves could be classified as U-, V-, and W-shaped. Cracks that propagated along the cement line may have led to the formation of a slot. Meanwhile, cracks that propagated in the interstitial lamella may have led to the formation of ridges. The slots and ridges resulted in the appearance of stripes on the groove bottom. The cracks propagated along the axial direction of the osteon at the same time as it propagated into the osteon, leading to the formation of dimples on the groove sidewall. The experimental method proposed in this study can be regarded as a suitable method to fabricate helical grooves on bones.

The inherent brittleness, retarded crystallization kinetics and insufficient melt strength of polylactic acid (PLA) severely limit its applications in foaming. This study proposed a reactive chain extender and compatibilizer strategy, which involved introducing the multifunctional epoxy-based chain extender KL-E4370 (0.6 wt%) into a PLA/polypropylene carbonate (PPC) blend system to simultaneously enhance melt strength and interfacial compatibility, with the aim of preparing high-expansion-ratio nano-cellular foams by means of the physical foaming assisted by supercritical CO₂. The impact of PPC loading and foaming temperature on the crystallization behavior, rheological properties, cell morphology, and compressive properties of the blends were systematically investigated. As a result, chemical interactions occurred between the chain extender and terminal carboxyl and hydroxyl moieties of PLA and PPC during ring-opening reactions, which produced a PLA–chain extender–PPC copolymer in situ. This significantly improved melt elasticity, reduced interfacial tension, and promoted the even distribution of the PPC phase. At the same time, the addition of PPC enhanced the CO₂ adsorption capacity of PLA. The PLA/PPC15-CE0.6 formulation exhibited the highest crystallinity (5.9%) and a refined spherulite morphology, providing abundant interfaces between crystalline and amorphous regions that serve as auxiliary nucleation sites. At the optimal foaming temperature of 115 °C, this formulation achieved an excellent foaming volume expansion ratio of 7.3 times, an average cell size of 660 nm, and a maximum cell density of 1.1 × 10¹³ cells/cm³. With further elevation of the foaming temperature to 117 °C and beyond, excessive softening of the matrix triggered cell coalescence, causing the cell sizes to increase sharply beyond the nanoscale range and the cell density to drop significantly. Samples foamed at 115 °C retained a compressive strength of 2.7 MPa under 70% strain, demonstrating a good balance between lightweight properties and mechanical integrity. This study provides a systematic mechanism understanding and operational directions for the sustainable fabrication of high-performance bio-based biodegradable polymer nanoporous materials.