## 4 Conclusions  
In conclusion, despite great progress in the knowledge on insulin oral delivery using polymeric systems, there are still some limitations with respect to the stability and toxicity of the formulations. In this work, we demonstrated that insulin-loaded PEG-4000/mucin MPs can help to overcome some of these challenges. Such MPs display a smooth nonspherical morphology and can be prepared with more than 81% encapsulation efficiency via an emulsification-coacervation method followed by drug diffusion. The developed formulations exhibited good physicochemical performance and bioactivity. In vitro release studies at intestinal pH revealed significant insulin release, while maximum insulin was found to be retained within the MPs at stomach acid pH. Specifically, insulin-loaded MPs prepared with a 1:1 mucin/PEG ratio exhibited the highest prolonged drug release, while MPs containing higher PEG concentrations displayed faster drug release. Thus, insulin release was tuned within a range of 68%-92%. Furthermore, insulin-loaded MPs significantly (\(p<0.05\)) reduced the blood glucose level to 62 mg/dL after oral treatment. The blood glucose reduction effect was higher in animals that received orally administered insulin-loaded MPs than in those that were treated with insulin solution administered orally as a negative control. Interestingly, insulin-loaded MPs exhibited maximum glucose level reduction after 6 h, which was equivalent to that observed in the case of conventional subcutaneously administered insulin. Finally, no hepatotoxicity was observed after oral administration of insulin-loaded MPs. These results indicate that the use of insulin-loaded MPs based on the combination of PEG-4000 and mucin, without the use of organic crosslinkers, may be a promising alternative approach for diabetes treatment. Further pharmacokinetic studies to fully evaluate the potential of these polymeric carriers are underway in our laboratories, and the results will be published in due course.  
The following are available online at [[http://www.mdpi.com/2076-3417/10/8/2649/s1](http://www.mdpi.com/2076-3417/10/8/2649/s1)]([http://www.mdpi.com/2076-3417/10/8/2649/s1](http://www.mdpi.com/2076-3417/10/8/2649/s1)), Figure S1: DSC thermograms of mucin (_top_), insulin (_middle_), and PEG-4000 (_bottom_).  
Conceptualization, M.A.M.; Formal analysis, D.D.D.; Funding acquisition, M.A.M. and D.D.D.; Investigation, M.A.M., U.E.C., N.A., K.C.F., A.O.M., M.U., B.A., O.Y.J., K.C.O., A.A.A. and E.C.I.; Supervision, M.A.M.; Writing--original draft, M.A.M., K.C.O., A.A.A. and E.C.I.; Writing--review and editing, D.D.D. All authors have read and agreed to the published version of the manuscript.  
This study was funded by the Tertiary Education Trust Fund (TETFUND)-National Research Fund (NFR) of Nigeria with grant number TETFUND/DESS/NRF/STI/13/VOL_1.  
[PERSON] is very grateful to the Classical and Biomedical Laboratory (Naukka), InterCEDD Centre (Naukka), and Projex Biomedical Laboratory (Naukka). We are very thankful to [PERSON], from the Department of Chemical Engineering at the Ahmad Bello University Zaria, for assisting with thermal characterization of the materials. [PERSON] thanks the Deutsche Forschungsgemeinschaft (DFG) for the Heisenberg Professorship Award and the Spanish Ministry of Science, Innovation and Universities for the Senior Beatriz Galindo Award (Distinguished Researcher).  
The authors declare no conflict of interest.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Batch 2** & **SGPT (IU/L)** & **SGOT (IU/L)** & **ALP (IU/L)** \\ \hline A1 & 38.0 \(\pm\) 0.16 & 66 \(\pm\) 0.01 & 113 \(\pm\) 0.11 \\ A2 & 39.5 \(\pm\) 0.21 & 65 \(\pm\) 0.33 & 118 \(\pm\) 0.23 \\ A3 & 36.5 \(\pm\) 0.15 & 67 \(\pm\) 0.13 & 120 \(\pm\) 0.21 \\ A4 & 37.0 \(\pm\) 0.11 & 66 \(\pm\) 0.04 & 115 \(\pm\) 0.22 \\ A5 & 38.5 \(\pm\) 0.13 & 68 \(\pm\) 0.34 & 11