3D Printing of Photocatalytic Filters Using a Biopolymer to Immobilize TiO2 Nanoparticles

Titanium oxide-based photocatalytic filters were produced by Fused Deposition Modelling (FDM) using biopolymers obtained from renewable biomass resources. The thermoplastic route allows shaping composites through the immobilization of photoactive TiO2 nanoparticles in an environmentally friendly bioplastic such as the polylactic acid (PLA). Composites with an inorganic charge of 30 wt% of TiO2 nanoparticles (NPs) exhibit a 100% methyl orange (MO) degradation after 24 h of light exposition due to the extremely uniform dispersion of the nanophase within the polymer matrix in the FDM feedstock. Surface modification of TiO2 NPs allows the optimization of the colloidal dispersion and stabilization of the inorganic charge in a PLA solution and hence, the optimal distribution of nano-photoactive points in the TiO2/PLA filaments and scaffolds. The proposed new route of processing improves the dispersion of nano-charges comparing with the traditional thermo-pressing routes used for mixing thermoplastics based composites, avoiding the thermal degradation of the polymer and providing a customised product. In this manuscript the evolution of photodegradation with the increase of TiO2 content in the composite and the variation of the filter geometry was evaluated.Authors acknowledge the support to the projects S2018/NMT-4411 (Comunidad de Madrid) and MAT2015-70780-C4-1 (MINECO/FEDER). Z. Gonzalez acknowledges the Spanish Ministry of Economy and Competitiveness for the Postdoctoral Fellowship: IJCI-2016-28538. J. Yus acknowledges to the Comunidad de Madrid the support from the Youth Employment Initiative, CAMPD17_ICV_002. The authors thank ECERS for funding on Mobility Project JECS Trust Contract number: 2017294.Peer Reviewe

Development of biocompatible and fully bioabsorbable PLA/Mg films for tissue regeneration applications

During recent years, Mg reinforced polylactic acid (PLA) composites have emerged as potential biocompatible and bioabsorbable materials for biomedical applications. It has been shown that Mg particles added to a matrix based on a biodegradable polymer can address the lack of bioactivity and the low mechanical properties of the polymers and, furthermore, it can counteract the detrimental effects associated to the high degradation rate of Mg, as alkalinization and elevated H release. Additionally, the polymer can protect the Mg particles, by tailoring their degradation rate. Former processing of these composites performed by extrusion, compression and injection molding employed Mg contents up to 10 wt%. Higher amounts of Mg resulted in heterogeneous materials and thermally degraded matrices, with the corresponding higher degradation rate. In the present work, Mg reinforced PLA films with Mg content as high as 50 wt% were obtained without compromising the thermal stability of the polymer. Firstly, a successful dispersion of Mg microparticles was achieved by a breakthrough in processing introducing a colloidal step where organic additives were added to modify the Mg particle surface and promote a chemically stable suspension. The resulting colloidal suspension was then used as feedstock to obtain composite films by tape casting. The films show advantageous in vitro behaviour in terms of degradation, hydrogen release and oxygen permeability. In addition, the viability with fibroblast cells (MEF) opens a window of opportunity for these composite films as bioabsorbable material for tissue engineering and wound dressing applications. Statement of Significance: Magnesium materials have extraordinary biodegradable properties and bioactive behavior due to release of Mg ions, which offer a promising opportunity for their applicability as biomaterials for tissue regeneration. However, Mg is one of the most reactive metals with a high degradation rate. In contact with water produces H, associated with a risk of failure of the implant. One alternative to minimize this drawback is the use of Mg particles surrounded by a biodegradable biocompatible polymer such as polylactic acid (PLA) to obtain PLA/Mg composites. In this work we processed Mg reinforced PLA in the shape of films that would be suitable for tissue regeneration. In vitro behavior of PLA/Mg films demonstrated that Mg ions increase the fibroblast cells growth.Financial support of MINECO: MAT2015-63974-C4-1, MAT2016-79869-C2-1-P, MAT2016-79869-C2-1-P (AEI/FEDER, UE), Comunidad de Madrid: ADITIMAT: S2018/NMT-4411, and M-ERA.NET PCIN-2017-036 (MINECO, Spain).Peer Reviewe

Impact of PLA/Mg films degradation on surface physical properties and biofilm survival

New biocompatible and bioabsorbable materials are currently being developed for bone regeneration. These serve as scaffolding for controlled drug release and prevent bacterial infections. Films of polylactic acid (PLA) polymers that are Mg-reinforced have demonstrated they have suitable properties and bioactive behavior for promoting the osseointegration process. However little attention has been paid to studying whether the degradation process can alter the adhesive physical properties of the biodegradable film and whether this can modify the biofilm formation capacity of pathogens. Moreover, considering that the concentration of Mg and other corrosion products may not be constant during the degradation process, the question that arises is whether these changes can have negative consequences in terms of the bacterial colonization of surfaces. Bacteria are able to react differently to the same compound, depending on its concentration in the medium and can even become stronger when threatened. In this context, physical surface parameters such as hydrophobicity, surface tension and zeta potential of PLA films reinforced with 10% Mg have been determined before and after degradation, as well as the biofilm formation capacity of Staphylococcus epidermidis. The addition of Mg to the films makes them less hydrophobic and the degradation also reduces the hydrophobicity and increases the negative charge of the surface, especially over long periods of time. Early biofilm formation at 8 h is consistent with the physical properties of the films, where we can observe a reduction in the bacterial biofilm formation. However, after 24 h of incubation, the biofilm formation increases significantly on the PLA/Mg films with respect to PLA control. The explosive release of Mg ions and other corrosion products within the first hours were not enough to prevent a greater biofilm formation after this initial time. Consequently, the Mg addition to the polymer matrix had a bacteriostatic effect but not a bactericidal one. Future works should aim to optimize the design and biofunctionality of these promising bioabsorbable composites for a degradation period suitable for the intended application.The authors gratefully acknowledge financial support from “Ministerio de Economía y Competitividad” (PCIN-2016-146, MAT2015-63974-C4-3-R, MAT2015-63974-C4-4-R, MAT2016-79869-C2-1-P, RTI2018-096862-B-I00 (AEI/FEDER;UE)) and “Junta de Extremadura-FEDER: European Regional Development Fund” (IB16117, IB16154, GR15089, GR15025, GR18153 and GR18096). Dr. María Carbajo Sánchez is also thanked for providing valuable technical assistance with SEM in the “Servicio de análisis y caracterización de sólidos y superficies (SACSS)” within the University of Extremadura