**5. Conclusions**

In this work the discreet kinetically-limited phase separation was identified as the main factor influencing the resistance of the modified gelatin films to disintegration in the acidic environment. The imaging techniques (SEM, CLSM, Raman microscopy) provided the information on the mechanism of film partial dissolution in acid. The QCM-D analysis proved the a ffinity of the latex particles to the surface-wetted gelatin structures, which may be important in regard to the film formation process. The lab-scale soft capsule formation process was performed, and the tested filling materials were proved to be compatible with the films, however the obtained capsules showed the sealing area as a weak spot, limiting the acid-resistance of the capsules during the disintegration test. On the other hand, a modified dissolution test with a paddle apparatus and di ffusion cell allowed to confirm that the films are hampering the drug release in acidic phase, while releasing the drug at pH 6.8. The drug release at pH 6.8 was possible, however, only when higher stirring rates (150 rpm) were applied.

**Author Contributions:** Conceptualization, B.M. and M.S.; methodology, B.M., M.S. and A.L.; validation, B.M., V.A.; investigation, B.M.; resources, M.S., A.L.; data curation, B.M., V.A.; writing—original draft preparation, B.M.; writing—review and editing, M.S., A.L.; supervision, M.S.; funding acquisition, B.M. All authors have read and agreed to the published version of the manuscript.

**Funding:** The work was supported by the National Science Centre Poland (Grant No. 2015/19/N/NZ7/03447).

**Acknowledgments:** The oxygen permeability test was performed by COBRO–Packaging Research Institute (Lukasiewicz Research Network, Warsaw, Poland). Katrina Logg and Archana Samanta from Chalmers University of Technology in Gothenburg are acknowledged for the support with the imaging techniques. Authors acknowledge funding from NordForsk for the Nordic University Hub project #85352 (Nordic POP, Patient Oriented Products).

**Conflicts of Interest:** The authors declare no conflict of interest.
