# Functionalization Strategies and Fabrication of Solvent-Cast PLLA for Bioresorbable Stents
## 4 Conclusions  
PLLA is a biodegradable polymer with no reactive side-chain groups making its surface modifications a challenging task. In this work, we evaluate the potential of the solvent-cast PLLA functionalized by oxygen plasma, NaOH solution, or cutinase enzymes to enhance ECs adhesion and to be used for 3D printed BRS fabrication. Solvent casting of PLLA with chloroform leaves residues on the surface inducing cytotoxicity of the material and obtaining a low crystallinity and mechanical properties (i.e., Young's modulus and  
Figure 8: PLLA BRS obtained by the solvent-cast direct-write technique. Upper image: General image of PLLA BRS by optical microscopy. Lower images: Detailed optical microscopy images of the PLLA BRS struts.  
UTS). After the thermal treatment, solvent-cast PLLA presented full biocompatibility, increased mechanical properties, and degradation rates similar to the commercial REMEDY BRS. It was characterized the quantity and effectiveness of surface functional groups obtained after chemical hydrolysis of ester bonds or by grafting of reactive species, obtained by oxygen plasma, with the polymer chains. The plasma and enzyme functionalization did not affect the physical properties of 2D planar PLLA surfaces, such as crystallinity or degradation, or significantly increase their hydrophilicity and the density of surface functional groups, which reverted in enhanced ECs adhesion and spreading. On the contrary, NaOH etching induced surface roughness and was proven to be less efficient than the plasma and enzymes in terms of creating functional groups and improving the ECs response. The solvent cast direct writing technique allowed the seamless 3D printing of PLLA BRS. Consequently, the combined use of the solvent cast direct writing technique and plasma or enzyme functionalization holds great potential to fabricate 3D printed PLLA BRS with the capacity to accelerate the surface endothelialization.  
Conceptualization, R.S., C.C. ([PERSON]), C.C. ([PERSON]), and M.P.; methodology, R.S. and M.P.; software, R.S.; validation, R.S., C.C. ([PERSON]), and R.S.; formal analysis, R.S. and C.C. ([PERSON]); investigation, R.S., C.C. ([PERSON]), and Y.R.; resources, J.B., E.H.A., and G.M.G.; data curation, R.S.; writing--original draft preparation, R.S.; writing--review and editing, R.S. and M.P.; visualization, R.S. and M.P.; supervision, C.C. ([PERSON]), C.C. ([PERSON]), and M.P.; project administration, M.P.; funding acquisition, C.C. ([PERSON]), C.C. ([PERSON]), and M.P. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Spanish Government for financial support through project RTI2018-67183-R (MINECO/FEDER). Authors acknowledge the Agency for Administration of University and Research Grants of the Government of Catalonia (2017 SGR-1165), and the project (BASE3D 001-P-001646) co-financed by the European Union Regional Development Fund within the framework of the ERDF Operational Program of Catalonia 2014-2020 with a grant of 50% of the total cost eligible and MINECO for PID2019-103892 RB-I00 project. R.S. acknowledges the Erasmus Mundus Doctoral Programme DocMASE of the European Commission (FPA 2011 0020).  
Authors acknowledge [PERSON] for helping in the XPS measurement and analysis and [PERSON] for helping in the SEM measurement and analysis.  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.