## 3 Results  
### Set Up of Molding Conditions  
As mentioned before, this new processing technique is based on the use of ultrasound as a heating source. Hence, molding parameters such as ultrasound intensity or wave amplitude do not have not a clear correlation with physical characteristics of processed specimens compared with the well-established knowledge concerning conventional micromolding machines. In this case, polymer properties, such as melting point or flow index, are easily related to heating and pumping intensity, whereas ultrasound micromolding needs further research to arrive to a similar know how [7]. Furthermore, new insights concerning ultrasound induced micromolding should be mentioned, which indicated the influence of additional effects such as acoustic streaming [25] and acoustic radiation forces [26].  
Therefore, an empirical study has been done to determine correct molding conditions for neat PLA before processing with the different drug loaded samples. Specifically, assays have been carried out to cover the following points:  
1. To find appropriate energy and molding force values to fill the whole mold. These were based with previous works carried out with neat PLA [7]. Through a visual inspection (the eight test specimens were fully molded or not), it could be concluded that working with an amplitude lower than 24 \(\upmu\)m was not enough to reach an appropriate flow of PLA (Table 1). In reference to the molding force, a value above 300 N was needed to get the eight specimens full. However, caution should be taken into account since forces around 500-600 N were not stable and, in some cases, the sonotrode was overloaded (i.e., it cannot vibrate) due to a high PLA compaction.
2. To compare the molecular weight of molded sample with the original polymer. One of the main issues of this process is the possibility of polymer degradation (i.e., rupture of the polymer chain in oligomers) that could compromise the final physical properties of the molded specimen [9]. GPC measurements of samples processed under different conditions are summarized in Table 1. PLA seems to be very flexible with the molding condition in comparison with other polymers [13]. Molecular weight variation was not detected for the applied range of force. However, the increase of the molding time caused a significant degradation. It can be assumed that a molding time equal or lower than 1.2 s may cause a minimum degradation of PLA.
3. To confirm that chemical structure of the polymer molded keeps the FTIR spectrum of a PLA specimen molded unaltered at the optimized condition of 300 N 1.2 s 24 \(\upmu\)m, according to the filling efficiency and GPC assay, were compared with the spectrum of commercial powdered PLA (Figure 3). It is clear that the ultrasonic source has not given rise to any significant modification of the chemical structure of the polymer. The typical bands of ester (1745, 1266 and 1108 cm\({}^{-1}\)) and methylene groups (1455 cm\({}^{-1}\) and 1380 cm\({}^{-1}\)) remained unchanged.
4. To check by visual inspection the presence of fissures and cracks inside the processed samples, features that may affect the final mechanical properties of specimens. Figure 4 shows SEM micrographs of the processed sample under optimal parameters where significant physical defects cannot be detected.