## 3 Results and Discussion  
### Optimization of USM Processing Parameters  
The optimal processing window for ultrasonic micromolding (USM) was determined by two key parameters: plunger velocity and ultrasonic amplitude while maintaining the mold temperature at 60 \({}^{\circ}\)C as recommended by the material provider. Various combinations of these parameters were tested to achieve fully formed samples, minimal degradation, and high repeatability. Temperature and pressure were recorded during the filling step to identify the most suitable processing conditions. Initially, parameter combinations that failed to produce fully formed specimens or resulted in visible degradation were eliminated. The remaining conditions were assessed based on repeatability and mechanical performance. Four optimal combinations of amplitude and plunger velocity were identified, which were further evaluated for both neat P3 HB and a nanocomposite containing 5 wt% Cloisite 20. Detailed results, including the tested parameter combinations and the corresponding mechanical properties (e.g., tensile strength, strain at break), are provided in the Supplementary File (Table S1). From these tests, the condition of 36% amplitude and 2.5 mm/s plunger velocity were identified as the optimal processing conditions for both the neat polymer and the nanocomposite. This combination yielded the highest tensile strength (\(\sigma\)) and strain at break (\(\varepsilon\)), along with stable injection temperatures, which showed the lowest variability across trials. Furthermore, this combination was found to be suitable for processing nanocomposites with varying clay content (3-8 wt%) and for both Cloisite C20 and Cloisite C116 clays. In contrast, with conventional microinjection, where the specimen size is significantly larger than those produced by USM, the optimization of conditions can be effectively determined through visual assessment. The injection parameters, such as temperature, pressure, and cooling time, are adjusted until the product meets specific quality standards,such as smooth surfaces, perfect form, and absence of defects like burrs. Therefore, the detailed optimization process for conventional microinjection is not shown. Comparison of Molecular Integrity and Morphology of P3 HB Processed by USM and Conventional Injection  
3.2.1. Molecular Weight Retention: GPC Analysis  
GPC measurements provided valuable insights into the influence of ultrasonic processing parameters such as wave amplitude, plunger velocity, and switchover force (a parameter related to residence time) on the molecular weight of P3 HB. These parameters are critical in determining the extent of thermal and mechanical stress experienced by the polymer during processing. Figure 2 displays three representative chromatographs: the initial pellet, a specimen processed under optimal conditions, and a specimen showing clear signs of degradation. The chromatography of the optimally processed specimen aligned closely with that of the initial pellet, indicating minimal molecular weight loss during the USM process. In contrast, the degraded specimen exhibited a pronounced reduction in molecular weight, confirming significant polymer chain scission under suboptimal conditions. Table 1 further compares molecular weight data across samples processed under varying ultrasonic settings and samples processed with conventional microinjection. The results demonstrated that USM can effectively maintain molecular weight when parameters are carefully optimized, while conventional microinjection results in significant molecular loss due to prolonged thermal exposure and high shear stresses.