Polymeric Materials Surfaces, Interfaces and Bioapplications Marta Fernández-García , Alexandra Muñoz-Bonilla, Coro Echeverría, Agueda Sonseca and Marina P. Arrieta www.mdpi.com/journal/materials Edited by Printed Edition of the Special Issue Published in Materials Polymeric Materials Polymeric Materials Surfaces, Interfaces and Bioapplications Special Issue Editors Marta Fern ́ andez-Garc ́ ıa Alexandra Mu ̃ noz-Bonilla Coro Echeverr ́ ıa Agueda Sonseca Marina P. Arrieta MDPI • Basel • Beijing • Wuhan • Barcelona • Belgrade Special Issue Editors Marta Fern ́ andez-Garc ́ ıa Instituto de Ciencia y Tecnolog ́ ıa de Pol ́ ımeros (ICTP-CSIC) Spain Alexandra Mu ̃ noz-Bonilla Instituto de Ciencia y Tecnolog ́ ıa de Pol ́ ımeros (ICTP-CSIC) Spain Coro Echeverr ́ ıa Instituto de Ciencia y Tecnolog ́ ıa de Pol ́ ımeros (ICTP-CSIC) Spain Agueda Sonseca Instituto de Ciencia y Tecnolog ́ ıa de Pol ́ ımeros (ICTP-CSIC) Spain Marina P. Arrieta Universidad Complutense de Madrid (UCM) Spain Editorial Office MDPI St. Alban-Anlage 66 4052 Basel, Switzerland This is a reprint of articles from the Special Issue published online in the open access journal Materials (ISSN 1996-1944) from 2018 to 2019 (available at: https://www.mdpi.com/journal/materials/ special issues/polymeric bioapplications). For citation purposes, cite each article independently as indicated on the article page online and as indicated below: LastName, A.A.; LastName, B.B.; LastName, C.C. Article Title. Journal Name Year , Article Number , Page Range. ISBN 978-3-03897-962-3 (Pbk) ISBN 978-3-03897-963-0 (PDF) c © 2019 by the authors. Articles in this book are Open Access and distributed under the Creative Commons Attribution (CC BY) license, which allows users to download, copy and build upon published articles, as long as the author and publisher are properly credited, which ensures maximum dissemination and a wider impact of our publications. The book as a whole is distributed by MDPI under the terms and conditions of the Creative Commons license CC BY-NC-ND. Contents About the Special Issue Editors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii Alexandra Mu ̃ noz-Bonilla, Coro Echeverr ́ ıa, ́ Agueda Sonseca, Marina P. Arrieta and Marta Fern ́ andez-Garc ́ ıa Polymeric Materials: Surfaces, Interfaces and Bioapplications Reprinted from: Materials 2019 , 12 , 1312, doi:10.3390/ma12081312 . . . . . . . . . . . . . . . . . . 1 Alexandra Mu ̃ noz-Bonilla, Coro Echeverria, ́ Agueda Sonseca, Marina P. Arrieta and Marta Fern ́ andez-Garc ́ ıa Bio-Based Polymers with Antimicrobial Properties towards Sustainable Development Reprinted from: Materials 2019 , 12 , 641, doi:10.3390/ma12040641 . . . . . . . . . . . . . . . . . . . 5 Mar ́ ıa Dolores Samper, David Bertomeu, Marina Patricia Arrieta, Jos ́ e Miguel Ferri and Juan L ́ opez-Mart ́ ınez Interference of Biodegradable Plastics in the Polypropylene Recycling Process Reprinted from: Materials 2018 , 11 , 1886, doi:10.3390/ma11101886 . . . . . . . . . . . . . . . . . . 57 Francesca Luzi, Luigi Torre, Jos ́ e Maria Kenny and Debora Puglia Bio- and Fossil-Based Polymeric Blends and Nanocomposites for Packaging: Structure–Property Relationship Reprinted from: Materials 2019 , 12 , 471, doi:10.3390/ma12030471 . . . . . . . . . . . . . . . . . . . 75 Marta Szekalska, Katarzyna Sosnowska, Anna Czajkowska-Ko ́ snik and Katarzyna Winnicka Calcium Chloride Modified Alginate Microparticles Formulated by the Spray Drying Process: A Strategy to Prolong the Release of Freely Soluble Drugs Reprinted from: Materials 2018 , 11 , 1522, doi:10.3390/ma11091522 . . . . . . . . . . . . . . . . . . 124 Ji-Dong Xu, Ya-Shuai Niu, Pan-Pan Yue, Ya-Jie Hu, Jing Bian, Ming-Fei Li, Feng Peng and Run-Cang Sun Composite Film Based on Pulping Industry Waste and Chitosan for Food Packaging Reprinted from: Materials 2018 , 11 , 2264, doi:10.3390/ma11112264 . . . . . . . . . . . . . . . . . . 138 Yunhai Ma, Siyang Wu, Jian Zhuang, Jin Tong, Yang Xiao and Hongyan Qi The Evaluation of Physio-Mechanical and Tribological Characterization of Friction Composites Reinforced by Waste Corn Stalk Reprinted from: Materials 2018 , 11 , 901, doi:10.3390/ma11060901 . . . . . . . . . . . . . . . . . . . 149 Iolanda Francolini, Elena Perugini, Ilaria Silvestro, Mariangela Lopreiato, Anna Scotto d’Abusco, Federica Valentini, Ernesto Placidi, Fabrizio Arciprete, Andrea Martinelli and Antonella Piozzi Graphene Oxide Oxygen Content Affects Physical and Biological Properties of Scaffolds Based on Chitosan/Graphene Oxide Conjugates Reprinted from: Materials 2019 , 12 , 1142, doi:10.3390/ma12071142 . . . . . . . . . . . . . . . . . . 163 Brody A. Frost, Sandra Camarero-Espinosa and E. Johan Foster Materials for the Spine: Anatomy, Problems, and Solutions Reprinted from: Materials 2019 , 12 , 253, doi:10.3390/ma12020253 . . . . . . . . . . . . . . . . . . . 180 v Ke Zhang, Bashayer Baras, Christopher D. Lynch, Michael D. Weir, Mary Anne S. Melo, Yuncong Li, Mark A. Reynolds, Yuxing Bai, Lin Wang, Suping Wang and Hockin H. K. Xu Developing a New Generation of Therapeutic Dental Polymers to Inhibit Oral Biofilms and Protect Teeth Reprinted from: Materials 2018 , 11 , 1747, doi:10.3390/ma11091747 . . . . . . . . . . . . . . . . . . 221 Monika Kurowska, Vania Tanda Widyaya, Ali Al-Ahmad and Karen Lienkamp Surface-Attached Poly(oxanorbornene) Hydrogels with Antimicrobial and Protein-Repellent Moieties: The Quest for Simultaneous Dual Activity Reprinted from: Materials 2018 , 11 , 1411, doi:10.3390/ma11081411 . . . . . . . . . . . . . . . . . . 238 Yubin Ji, Yuan Sun, Yanhe Lang, Lei Wang, Bing Liu and Zhizhou Zhang Effect of CNT/PDMS Nanocomposites on the Dynamics of Pioneer Bacterial Communities in the Natural Biofilms of Seawater Reprinted from: Materials 2018 , 11 , 902, doi:10.3390/ma11060902 . . . . . . . . . . . . . . . . . . . 253 Humberto Palza, Paula Andrea Zapata and Carolina Angulo-Pineda Electroactive Smart Polymers for Biomedical Applications Reprinted from: Materials 2019 , 12 , 277, doi:10.3390/ma12020277 . . . . . . . . . . . . . . . . . . . 265 Alexandra Mu ̃ noz-Bonilla, Roc ́ ıo Cuervo-Rodr ́ ıguez, F ́ atima L ́ opez-Fabal, Jos ́ e L. G ́ omez-Garc ́ es and Marta Fern ́ andez-Garc ́ ıa Antimicrobial Porous Surfaces Prepared by Breath Figures Approach Reprinted from: Materials 2018 , 11 , 1266, doi:10.3390/ma11081266 . . . . . . . . . . . . . . . . . . 289 Leire Ruiz-Rubio, Leyre P ́ erez- ́ Alvarez, Julia Sanchez-Bod ́ on, Valeria Arrighi and Jos ́ e Luis Vilas-Vilela The Effect of the Isomeric Chlorine Substitutions on the Honeycomb-Patterned Films of Poly(x-chlorostyrene)s/Polystyrene Blends and Copolymers via Static Breath Figure Technique Reprinted from: Materials 2019 , 12 , 167, doi:10.3390/ma12010167 . . . . . . . . . . . . . . . . . . . 299 Cristian Lavieja, Luis Oriol and Jos ́ e-Ignacio Pe ̃ na Creation of Superhydrophobic and Superhydrophilic Surfaces on ABS Employing a Nanosecond Laser Reprinted from: Materials 2018 , 11 , 2547, doi:10.3390/ma11122547 . . . . . . . . . . . . . . . . . . 312 Hongye Li, Bin Sheng, He Wu, Yuanshen Huang, Dawei Zhang and Songlin Zhuang Ring Wrinkle Patterns with Continuously Changing Wavelength Produced Using a Controlled-Gradient Light Field Reprinted from: Materials 2018 , 11 , 1571, doi:10.3390/ma11091571 . . . . . . . . . . . . . . . . . . 323 vi About the Special Issue Editors Marta Fern ́ andez-Garc ́ ıa is a research scientist at the Institute of Polymer Science and Technology. She belongs to the Spanish National Research Council (ICTP-CSIC) and is a leader of the Macromolecular Engineering Group (MacroEng). She is a co-author of ca. 160 articles and several book chapters and a co-editor of a book (Royal Society of Chemistry). She has supervised eight PhD theses and some minor theses. She has served as an international advisory board member of European Polymer Journal (Elsevier) and now is an editor member of International Journal of Molecular Sciences : Material Science (MDPI) and International Journal of Polymer Science (Hindawi). Her research interests include block copolymers, glycopolymers, antimicrobial and antifouling polymers, sustainable materials, and recycling. She is member of the Interdisciplinary Platform for Sustainable Plastics towards a Circular Economy (SusPlast-CSIC). Alexandra Mu ̃ noz-Bonilla completed her PhD in 2006 at the Institute of Polymer Science and Technology (ICTP-CSIC), in the area of controlled radical polymerization. During her PhD studies, she also held a one-year position at the University of Warwick, UK, as a Marie Curie visiting research student. Afterwards, she carried out postdoctoral research at the University of Bordeaux (France) in the field of polymer surfaces and interfaces and held a second postdoctoral position at the Eindhoven University of Technology (The Netherlands) in the field of colloidal systems. Currently, she is a tenured scientist at the ICTP-CSIC, having published nearly 90 articles and several book chapters and co-edited a RSC book. Now, she serves as editor for Coatings (MDPI) and Advances in Polymer Technology (Hindawi/Wiley). Her main research interests are the development of antimicrobial materials and bio-based and biodegradable polymeric systems, also participating in SusPlast-CSIC advancement. Coro Echeverria received her PhD in applied chemistry and polymeric materials in 2011 at the University of the Basque Country (EHU, Spain). Her main research area is in the field of polymeric materials, its characterization, and applications, and her scientific interest is the study and development of multifunctional stimuli-responsive polymeric systems. During her postdoctoral period, 2013–2017, she worked at the New University of Lisbon (UNL) and CENIMAT on the project “Cellulose in Motion”, which focused on the development of bio-based actuators from cellulosic liquid crystalline systems with an emphasis on the structure–properties relationship and flow behavior. Since 2018, she has been a Juan de la Cierva researcher at ICTP-CSIC. Her research is devoted to the development of multifunctional stimuli-responsive bio-based polymer systems with antimicrobial properties, aligned with the objectives of SusPlast-CSIC. Agueda Sonseca obtained her PhD in 2015 at the Polytechnic University of Valencia, supported by a FPU predoctoral fellowship in the field of biodegradable nanocomposites with shape memory properties and possible biomedical applications. Afterwards, she was hired as a postdoctoral researcher in the Division of Biomaterials and Microbiological Technologies of the West Pomeranian University of Technology (Poland), where she was involved in the development of new biodegradable elastomeric templates for heart tissue engineering. Since September 2017, she has been a part of MacroEng group at ICTP-CSIC, being financially supported by several postdoctoral contracts obtained in national and autonomic competitive calls. She is also member of SusPlast-CSIC, vii and her research interests are mainly oriented towards the development of multifunctional bio-based, biodegradable, and biocompatible polymers with well-defined structures by enzymatic polymerization. Marina P. Arrieta currently works at the Organic Chemistry Department of the Complutense University of Madrid (UCM, Spain). She holds a BS in biochemistry from the National University of C ́ ordoba (Argentina), a MS in food technology from the Catholic University of Cordoba (Argentina), a MS in polymer science and technology from UNED (Spain), and an international PhD in science, technology, and food management from the Polytechnic University of Valencia (Spain), awarded with the extraordinary PhD-Thesis award. She has been an AECID, Santiago Grisol ́ ıa, Juan de la Cierva, and UCM fellow. She has experience with the synthesis, processing (melt-blending, extrusion, injection molding, electrospinning, etc.), and characterization of bio-based and biodegradable polymers and their nanocomposites with active and multifunctional properties for sustainable food packaging or agricultural applications. She has published 42 papers with more than 1300 cites (h-index: 18) and several book chapters in the field of bio-based and biodegradable polymers. viii materials Editorial Polymeric Materials: Surfaces, Interfaces and Bioapplications Alexandra Muñoz-Bonilla 1,2 , Coro Echeverr í a 1,2 , Á gueda Sonseca 1,2 , Marina P. Arrieta 3 and Marta Fern á ndez-Garc í a 1,2, * 1 Instituto de Ciencia y Tecnolog í a de Pol í meros (ICTP-CSIC), C / Juan de la Cierva 3, 28006 Madrid, Spain; sbonilla@ictp.csic.es (A.M.-B.); cecheverria@ictp.csic.es (C.E.); agueda@ictp.csic.es (A.S.) 2 Interdisciplinary Platform for Sustainable Plastics towards a Circular Economy, SUSPLAST, 28006 Madrid, Spain 3 Facultad de Ciencias Qu í micas, Universidad Complutense de Madrid (UCM), Av. Complutense s / n, Ciudad Universitaria, 28040 Madrid, Spain; marina.arrieta@gmail.com * Correspondence: martafg@ictp.csic.es; Tel.: + 34-912587530 Received: 16 April 2019; Accepted: 21 April 2019; Published: 22 April 2019 Abstract: This special issue “Polymeric Materials: Surfaces, Interfaces and Bioapplications” was proposed to cover all the aspects related to recent innovations on surfaces, interfaces and bioapplications of polymeric materials. The collected articles show the advances in polymeric materials, which have tremendous applications in agricultural films, food packaging, dental restoration, antimicrobial systems and tissue engineering. We hope that readers will be able to enjoy highly relevant topics that are related to polymers. Therefore, we hope to prove that plastics can be a solution and not a problem. Keywords: surface modification / functionalization; surface segregation; micro- and nanopatterned films; blends and (nano)composites; coatings; surface wettability; stimuli-responsive materials / smart surfaces; bioapplications Polymeric materials have moved from making the progress of the twentieth century to becoming the materials of the future to be reviled and persecuted by problems that were mainly generated by the ignorance of citizens, businesses and governments. These problems have resulted in the planet being contaminated and the resulting consequences. A world without plastics is hardly imaginable and for this reason, the European Community is proposing some goals related to the production, use and recyclability of plastics: (1) 60% reuse and recycling of all plastic packaging by 2030; and (2) 100% reuse, recycling and / or recovery of all plastic packaging in the whole EU by 2040 [ 1 ]. Recently, Devasahayam et al. [2] pointed out the advantages of recycling polymers in mineral and metallurgical processing. For example, plastics in e-wastes can be used as fuels and reductants in recovering valuable metals. In another example, the epoxy resins can be used as a binder / reductant or fuel source, which o ff ers high compression strength under ambient conditions. This far exceeds the heat induration strength and provides savings in terms of costs, energy and emissions during the iron ore pelletization. Moreover, several review have focused on solid plastic waste recycling, discussing both mechanical and chemical recycling [ 3 , 4 ]. Of all types of waste, the largest amount of waste produced is packaging waste (near 40%), which has short life times. Therefore, EU has placed a limitation on single-use plastic to decrease this ratio. Another alternative to the recycling process and reducing the production of plastics from non-renewable resources is the use of biodegradable and / or bio-based polymers, respectively. One of the reviews in this special issue (SI) focuses on the use of natural and bio-based polymers as antimicrobial systems and their potential mainly in biomedical and food applications, but also in water purification and coating technology [ 5 ]. However, natural and bio-based materials frequently Materials 2019 , 12 , 1312; doi:10.3390 / ma12081312 www.mdpi.com / journal / materials 1 Materials 2019 , 12 , 1312 have lower performance than traditional synthetic polymers. Therefore, it is necessary to make modifications or adjustments during the processing steps in order to modulate their final performances. In one of the SI articles, Samper et al. [ 6 ] analyzed the influence of small amounts of biodegradable polymers, such as poly(lactic acid), polyhydroxybutyrate and thermoplastic starch in the recycled polypropylene. It is shown that the recycling of polypropylene blended with these bio-based and biodegradable polymers is hardly a ff ected when it is used at a proportion higher than 5 wt %. In this sense, the review of Luzi et al. [ 7 ] presents the blending of bio-based and / or biodegradable polymers with traditional synthetic polymers for packaging applications with an optional use of bio-based nanofillers. This nicely highlighted how these bio-based materials enhance the gas / water / light barrier properties and the compostability and migration performance of blends. Moreover, they also discuss the e ff ect of incorporating bio-based nanofillers on the overall behavior of nanocomposite systems that is constituted of synthetic polymers, which is combined with biodegradable and / or bio-based plastics. The use of natural polymers is also presented in another article wherein alginate crosslinking by CaCl 2 is obtained to create modified-release drug delivery systems with mucoadhesive properties [ 8 ]. The authors present the production of microparticles by the spray drying technique, which enables us to obtain microparticles with a low moisture content, high drug loading, a high production yield and a prolonged release of soluble drugs. Peng’s group [ 9 ] reported the use of chitosan with wood auto-hydrolysates that are obtained in the pulping process by hydrothermal extraction, which contains a considerable amount of hemicelluloses and slight lignin, in order to form films by the casting method. These films possess a higher tensile strength, better thermal stability, higher transmittances, lower water vapor permeability and superior oxygen barrier properties compared to those without chitosan due to the crosslinking interaction between the components, which occurs due to the Millard reaction. In another article, Ma et al. [ 10 ] used fibers from waste corn stalks as reinforcing materials in friction composites. They found that the incorporation of corn stalk fibers had a positive e ff ect on the friction coe ffi cients and wear rates of friction composites. The results revealed that the satisfactory wear resistance performances of these materials are associated with their worn surface morphologies and the formation of secondary contact plateaus. Moreover, another polysaccharide, chitosan, is applied for sca ff old preparation in tissue engineering. In more detail, Francolini et al. [ 11 ] analyzed the conjugation of chitosan with graphene oxide. Depending on its oxidation degree, the resulting sca ff olds present improved or reduced mechanical performance and best or worst cytocompatibility as tested in human primary dermal fibroblasts. Another review of Foster’s group [ 12 ] meticulously displays the problem of disc degeneration, which a ff ects a great part of population, by describing the anatomy of the spine, the functions and biological aspects of the intervertebral discs. They point out that although there are numerous studies focusing on tissue engineering for disc degeneration, more progress needs to be made. Focusing on some actual problems, dental restoration failures remain a major challenge in dentistry. In another review, Xu’s group [ 13 ] provided information on the development and properties of innovative antibacterial dental polymeric composites, antibacterial bonding agents, bioactive root caries composites, adhesives and antibacterial and protein-repellent endodontic sealers. These polymeric materials substantially inhibit biofilm growth and greatly reduce acid production and polysaccharide synthesis of biofilms. Following with antimicrobial polymeric materials, Lienkamp’s group [ 14 ] describes the development of amphiphilic copolymers of oxanorbornene monomer bearing N- tert -butyloxycarbonyl protected cationic groups with an oxanorbornene-functionalized poly(ethylene glycol) macromonomer. After this, these comb-like copolymers are surface-attached to polymer hydrogels, giving rise to a material that is simultaneously antimicrobial and protein-repellent. In another article, Ji et al. [ 15 ] analyzed the antifouling behavior directly in the natural seawater of di ff erent carbon nanotubes-modified polydimethylsiloxane nanocomposites by using the multidimensional scale analyses method. 2 Materials 2019 , 12 , 1312 Palza et al. [ 16 ] carefully reviewed the development of polymeric materials with electroactivity, such as intrinsically electric conductive polymers, percolated electric conductive composites and ionic conductive hydrogels. They evaluated their use in the electrical stimulation of cells, drug delivery, artificial muscles and as antimicrobial materials. On the other hand, the breath figures approach is presented as an e ffi cient method to obtain highly ordered porous materials with potential applications in cell culture and antimicrobial coatings, respectively [ 17 , 18 ]. These articles discuss the influence of the chemical nature of polymers, the solvent or the humidity in the preparation process on the final properties (porous size, surface energy, etc.). Another approach is presented in the article of Lavieja et al. [ 19 ], where the use of a green laser in the range of nanosecond pulses was an e ff ective method to obtain superhydrophobic and superhydrophilic surfaces on a white commercial acrylonitrile-butadiene-styrene copolymer and therefore, to control its wettability. The last article deals with the surface modification method to produce gradient wrinkles using a gradient light field. Li et al. [ 20 ] described the easy control of the gradient wavelength of wrinkles by modulating the distance between the lamp and the substrate. Finally, we would like to thank all authors for contributing to this collection in “Polymeric Materials: Surfaces, Interfaces and Bioapplications”. Funding: This research was funded by MINECO, Project MAT2016-78437-R, the Agencia Estatal de Investigaci ó n (AEI, Spain) and Fondo Europeo de Desarrollo Regional (FEDER, EU). Acknowledgments: C.E. and Á .S acknowledge the Juan de la Cierva contracts (IJCI-2015-26432 and FJCI-2015-24405, respectively) from the Spanish Ministry of Science, Innovation and Universities. M.P.A. thanks Universidad Complutense de Madrid for her postdoctoral contract (Ayuda posdoctoral de formaci ó n en docencia e investigaci ó n en los Departamentos de la UCM). Conflicts of Interest: The authors declare no conflict of interest. References 1. Europe, P. An analysis of european plastics production, demand and waste data. In Plastics—The facts 2018 ; PlasticsEurope: Brussels, Belgium, 2018. 2. Devasahayam, S.; Raman, R.K.S.; Chennakesavulu, K.; Bhattacharya, S. Plastics-villain or hero? Polymers and recycled polymers in mineral and metallurgical processing—A review. Materials 2019 , 12 , 655. [CrossRef] [PubMed] 3. Singh, N.; Hui, D.; Singh, R.; Ahuja, I.P.S.; Feo, L.; Fraternali, F. Recycling of plastic solid waste: A state of art review and future applications. Compos. Part B Eng. 2017 , 115 , 409–422. [CrossRef] 4. Ragaert, K.; Delva, L.; Van Geem, K. Mechanical and chemical recycling of solid plastic waste. Waste Manag. 2017 , 69 , 24–58. [CrossRef] [PubMed] 5. Muñoz-Bonilla, A.; Echeverria, C.; Sonseca, Á .; Arrieta, M.P.; Fern á ndez-Garc í a, M. Bio-based polymers with antimicrobial properties towards sustainable development. Materials 2019 , 12 , 641. [CrossRef] [PubMed] 6. Samper, M.D.; Bertomeu, D.; Arrieta, M.P.; Ferri, J.M.; L ó pez-Mart í nez, J. Interference of biodegradable plastics in the polypropylene recycling process. Materials 2018 , 11 , 1886. [CrossRef] [PubMed] 7. Luzi, F.; Torre, L.; Kenny, J.M.; Puglia, D. Bio- and fossil-based polymeric blends and nanocomposites for packaging: Structure–property relationship. Materials 2019 , 12 , 471. [CrossRef] [PubMed] 8. Szekalska, M.; Sosnowska, K.; Czajkowska-Ko ́ snik, A.; Winnicka, K. Calcium chloride modified alginate microparticles formulated by the spray drying process: A strategy to prolong the release of freely soluble drugs. Materials 2018 , 11 , 1522. [CrossRef] [PubMed] 9. Xu, J.-D.; Niu, Y.-S.; Yue, P.-P.; Hu, Y.-J.; Bian, J.; Li, M.-F.; Peng, F.; Sun, R.-C. Composite film based on pulping industry waste and chitosan for food packaging. Materials 2018 , 11 , 2264. [CrossRef] [PubMed] 10. Ma, Y.; Wu, S.; Zhuang, J.; Tong, J.; Xiao, Y.; Qi, H. The evaluation of physio-mechanical and tribological characterization of friction composites reinforced by waste corn stalk. Materials 2018 , 11 , 901. [CrossRef] [PubMed] 11. Francolini, I.; Perugini, E.; Silvestro, I.; Lopreiato, M.; Scotto d’Abusco, A.; Valentini, F.; Placidi, E.; Arciprete, F.; Martinelli, A.; Piozzi, A. Graphene oxide oxygen content a ff ects physical and biological properties of sca ff olds based on chitosan / graphene oxide conjugates. Materials 2019 , 12 , 1142. [CrossRef] [PubMed] 3 Materials 2019 , 12 , 1312 12. Frost, B.A.; Camarero-Espinosa, S.; Foster, E.J. Materials for the spine: Anatomy, problems and solutions. Materials 2019 , 12 , 253. [CrossRef] [PubMed] 13. Zhang, K.; Baras, B.; Lynch, C.D.; Weir, M.D.; Melo, M.A.S.; Li, Y.; Reynolds, M.A.; Bai, Y.; Wang, L.; Wang, S.; et al. Developing a new generation of therapeutic dental polymers to inhibit oral biofilms and protect teeth. Materials 2018 , 11 , 1747. [CrossRef] [PubMed] 14. Kurowska, M.; Widyaya, V.T.; Al-Ahmad, A.; Lienkamp, K. Surface-attached poly(oxanorbornene) hydrogels with antimicrobial and protein-repellent moieties: The quest for simultaneous dual activity. Materials 2018 , 11 , 1411. [CrossRef] [PubMed] 15. Ji, Y.; Sun, Y.; Lang, Y.; Wang, L.; Liu, B.; Zhang, Z. E ff ect of cnt / pdms nanocomposites on the dynamics of pioneer bacterial communities in the natural biofilms of seawater. Materials 2018 , 11 , 902. [CrossRef] [PubMed] 16. Palza, H.; Zapata, P.A.; Angulo-Pineda, C. Electroactive smart polymers for biomedical applications. Materials 2019 , 12 , 277. [CrossRef] [PubMed] 17. Muñoz-Bonilla, A.; Cuervo-Rodr í guez, R.; L ó pez-Fabal, F.; G ó mez-Garc é s, J.L.; Fern á ndez-Garc í a, M. Antimicrobial porous surfaces prepared by breath figures approach. Materials 2018 , 11 , 1266. [CrossRef] [PubMed] 18. Ruiz-Rubio, L.; P é rez- Á lvarez, L.; Sanchez-Bod ó n, J.; Arrighi, V.; Vilas-Vilela, J.L. The e ff ect of the isomeric chlorine substitutions on the honeycomb-patterned films of poly(x-chlorostyrene)s / polystyrene blends and copolymers via static breath figure technique. Materials 2019 , 12 , 167. [CrossRef] [PubMed] 19. Lavieja, C.; Oriol, L.; Peña, J.-I. Creation of superhydrophobic and superhydrophilic surfaces on abs employing a nanosecond laser. Materials 2018 , 11 , 2547. [CrossRef] [PubMed] 20. Li, H.; Sheng, B.; Wu, H.; Huang, Y.; Zhang, D.; Zhuang, S. Ring wrinkle patterns with continuously changing wavelength produced using a controlled-gradient light field. Materials 2018 , 11 , 1571. [CrossRef] [PubMed] © 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http: // creativecommons.org / licenses / by / 4.0 / ). 4 materials Review Bio-Based Polymers with Antimicrobial Properties towards Sustainable Development Alexandra Muñoz-Bonilla 1 , Coro Echeverria 1 , Á gueda Sonseca 1 , Marina P. Arrieta 2 and Marta Fern á ndez-Garc í a 1, * 1 Instituto de Ciencia y Tecnolog í a de Pol í meros (ICTP-CSIC), C/Juan de la Cierva 3, 28006 Madrid, Spain; sbonilla@ictp.csic.es (A.M.-B.); cecheverria@ictp.csic.es (C.E.); agueda@ictp.csic.es ( Á .S.) 2 Facultad de Ciencias Qu í micas, Universidad Complutense de Madrid (UCM), Av. Complutense s/n, Ciudad Universitaria, 28040 Madrid, Spain; marina.arrieta@gmail.com * Correspondence: martafg@ictp.csic.es; Tel.: +34-912587530 Received: 28 January 2019; Accepted: 15 February 2019; Published: 20 February 2019 Abstract: This article concisely reviews the most recent contributions to the development of sustainable bio-based polymers with antimicrobial properties. This is because some of the main problems that humanity faces, nowadays and in the future, are climate change and bacterial multi-resistance. Therefore, scientists are trying to provide solutions to these problems. In an attempt to organize these antimicrobial sustainable materials, we have classified them into the main families; i.e., polysaccharides, proteins/polypeptides, polyesters, and polyurethanes. The review then summarizes the most recent antimicrobial aspects of these sustainable materials with antimicrobial performance considering their main potential applications in the biomedical field and in the food industry. Furthermore, their use in other fields, such as water purification and coating technology, is also described. Finally, some concluding remarks will point out the promise of this theme. Keywords: bio-based polymers; antimicrobial; biodegradable; sustainable; eco-friendly 1. Introduction Nowadays, plastics have gone from being outstanding materials that make life easier for us to being a serious concern for our ecological system. The European Council has pointed out the need to reduce our dependency on fuel and gas imports and to create sustainable energy, that is, achieve sustainable development by 2030. The 17 goals that cover this sustainable development include food security, health, sustainable consumption and production, the sustainable management of natural resources, clean oceans, and climate change [ 1 ]. Bio-based polymers have emerged as a potent solution for replacing petroleum-based polymeric materials and reducing the dependence on the depleting crude oil reserve. Besides this, many of the existing bio-based polymers can be biodegradable; in particular, natural bio-based polymers, such as polysaccharides and proteins, but also several synthetic biopolymers, such as poly(lactic acid). Biodegradability is also an important and desired property in many applications, including food packaging and agricultural applications, and contributes to sustainability as it reduces the waste impact of oil-based polymers. Nowadays, although the bio-plastics market represents only about 1% of the 335 million tons of plastic that the world produces annually [ 2 , 3 ], their production is continuously growing [ 4 ]. In some of the uses of biopolymers, additional properties are also needed; for instance, antimicrobial properties are desired in food packaging and biomedical devices, wherein microbial contamination can cause serious problems for public health and safety. On account of this background, in this article we intend to show the capacities of bio-based polymers to be antimicrobial materials, centered on both natural and synthetic polymers. Materials 2019 , 12 , 641; doi:10.3390/ma12040641 www.mdpi.com/journal/materials 5 Materials 2019 , 12 , 641 There are extensive and excellent reviews about antimicrobial polymeric materials [ 5 – 12 ] in which the methodologies of encapsulation and blending with antimicrobial organic and inorganic compounds as well as their possible mechanisms of action are discussed [ 9 ]. However, most of them are mainly focused on fossil-oil derivatives. On the other hand, there are also many reviews about bio-based polymers [ 13 – 20 ]; however, only a few are related to antimicrobial activity [ 21 , 22 ]. Therefore, this review does not intend to gather all of the works performed to date but give hints on the subject and make the general public aware of the great possibilities of sustainable polymeric materials. First, we will mention polysaccharides, which are the most abundant and exploited family. Following the natural systems, the proteins with antimicrobial activity will be described. Then, synthetic systems based on natural products will be analyzed; specifically, polyesters and polyurethanes. Since the literature regarding natural and bio-based antimicrobial polymeric materials is significantly wide, we focus the analysis mainly on the research performed in the field during recent years. It is not our purpose to do an extensive review; instead, we will highlight some of these interesting materials. Finally, we will conclude with some reflections on this hot topic. 2. Polysaccharides Polysaccharides are the macromolecules that belong to the components of life, together with proteins and nucleic acids. They determine the functionality and specificity of species. Their functionalities divide them into structural, storage, and gel-forming polysaccharides. Due to their abundance and excellent properties, such as biodegradability, they are unique materials to develop interesting antimicrobial bio-based materials. 2.1. Chitosan Chitosan (CS) is a linear polysaccharide with inherent antimicrobial activity that is derived from naturally occurring chitin, which is, after cellulose, the most common biopolymer on earth. It is sourced mainly from crustacean shellfish and certain fungi. Chitosan is a partially or completely N -deacetylated derivative of chitin, chemically composed of N -acetylglucosamine and glucosamine units joined through β (1 − 4)glycosidic linkages, and has primary amino groups that provide a positive charge under acidic pH (pK a about 6.3) and decent antimicrobial properties against a wide range of micro-organisms (Figure 1) [23,24]. Figure 1. The chemical structure of chitin and chitosan and the protonated form of chitosan. Although the exact mechanism of action is still not completely understood, the most accepted mechanism is based on electrostatic interactions between positively charged chitosan and the negatively charged micro-organism membrane [ 25 ]. Nevertheless, other modes of action, such as interactions with DNA or the formation of complexes with metal ions, seem to be involved [ 26 ]. This antimicrobial activity is strongly affected by its structural characteristics, such as molecular weight or degree of deacetylation, and by environmental conditions, such as pH, temperature, or ionic strength [ 27 ]. Compared with other antimicrobial polymers, chitosan offers several advantages, as it has a natural origin, is biodegradable, biocompatible, and nontoxic for mammalian cells, and has been approved by the U.S. Federal Drug Administration (FDA) and the E.U. as safe (GRAS, Generally Recognized As Safe) for tissue engineering, drug delivery, wound dressing, dietary use, and plant protection applications. Besides this, chitosan has excellent film-forming ability and good mechanical and barrier properties; thus, it has great potential in food packaging [ 21 ]. However, its biocidal activity 6 Materials 2019 , 12 , 641 and solubility are reduced in neutral pH conditions [ 28 ], which limit its use in many applications. Therefore, chemical modifications of chitosan, typically either at amino (the secondary C2 NH 2 group) or hydroxyl groups (the primary C6 OH and secondary C3 OH groups), aim to produce derivatives with enhanced properties to widen its applications [ 29 , 30 ]. A huge number of studies have been carried out on the preparation of antimicrobial chitosan derivatives mainly via quaternization and carboxylation. However, all of these modifications propose to improve its solubility and antimicrobial activity while also maintaining its original biodegradability and biosafety. Next, the most common and recent functional groups and derivatives used to improve its antimicrobial activity without affecting its inherent properties are discussed viz. by chemical modification and blending with organic and inorganic antimicrobial agents. 2.1.1. Chitosan Modification Probably the most common method for introducing a permanent positive charge into chitosan chains is by the formation of quaternary ammonium groups by either direct quaternization of the primary amino group at the C2 position or by incorporating such groups at any of the reactive moieties (hydroxyl and amino groups). For instance, in a recent study, chitosan derivatives with triple quaternary ammonium groups were synthesized via Schiff-based reactions. Although the resulting samples with a high positive charge exhibit significantly enhanced antifungal activity, the preparation method required multiple steps [31]. In another study, chitosan derivatives were prepared by reaction with different quaternary ammonium salts containing a bromide end-group capable of reacting with the amino or hydroxyl groups of chitosan [ 32 ]. The ammonium salts benzalkonium bromide, pyridinium bromide, and triethyl ammonium bromide were previously obtained by a quaternization reaction between 1,4-dibromobutane and the respective tertiary amines. These chitosan derivatives with quaternary ammonium groups showed much lower minimum inhibitory concentration (MIC) values against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus bacteria than neat chitosan. Also, in the case of S. aureus , the type of substitution influences the activity, with better properties for the pyridinium derivative. Although an important improvement of the activity is generally obtained [ 33 ], these chemical modifications often lead to unselective reactions at the amine, the hydroxyl, or both, as occurred in the last example. For instance, the N -methylation with methyl iodide typically provokes partial O -methylation [ 34 ]. Similarly, chitosan derivatives only modified at the OH positions are exceptional. Besides this, it is difficult to obtain a high degree of substitution in most of the cases, in particular with long alkyl chains, as these syntheses normally need to be carried out in acidic conditions or heterogeneous media [35]. Recent studies have been directed at obtaining better selectivity and a high degree of substitution by using several protecting groups. Sahariah et al. [ 36 , 37 ] have developed an efficient method for the selective modification of chitosan with up to 100% substitution of the amino groups. They prepared protected di-tertbutyldimethylsilyl (TBDMS) chitosan and introduced quaternary ammonium groups with different alkyl chain lengths by reductive amination. All of the prepared derivatives showed bactericidal properties and good selectivity when tested with human red blood cells (RBCs). It was also shown that the activity was influenced by the length of the alkyl chain and by the tested micro-organisms; derivatives with a short alkyl chain presented high activity against S. aureus , while longer alkyl chains were more active against Gram-negative E. coli and Enterococcus faecalis bacteria [ 36 ]. These derivatives also demonstrated effectiveness towards S. aureus biofilms, especially those with short alkyl chains [37]. In another recent work, the quaternary ammonium groups were introduced exclusively at the hydroxyl groups by previous protection of the –NH 2 groups via a Schiff-based condensation reaction with benzaldehyde [ 38 ]. By this way, it is possible to prepare positively charged chitosan derivatives with free primary amino groups, which is important as these amino groups have a key role in the biological activity of chitosan, such as in its antioxidant activity. The obtained O -quaternized 7 Materials 2019 , 12 , 641 chitosans showed an improved water solubility and antibacterial activity against Gram-positive bacteria. Remarkably, the cytotoxicity for the AT2 cell line was significantly lower than that of the free quaternary ammonium sal