Dear Colleague,

Viable alternatives to traditional materials are urgently needed. First, this is strictly related to climate change and the depletion of the Earth’s finite resources. Second, new functionalities are requested for metals and they can be achieved by coupling bio-based compounds to traditional metals. ‘Bio-based’ materials and compounds come from renewable biomass sources: plants, animals, marine, and forestry materials. Other possible sources include waste or by-products from the food industry. Coupling can occur through surface functionalization with a molecular layer, thin film or thick coatings, or composites. Bio-based materials often exhibit lower toxicity than traditional metals, alongside other novel characteristics, such as biodegradability. This is a new and interesting frontier for metal-based materials with the fast development of new alloys. The material processing and manufacturing of final products using bio-based materials are not inherently more sustainable than traditional materials, because the environmental impact of the entire production process must be considered via life cycle assessments.

The EU predicts and supports a steady growth in the uptake of bio-based materials: research can give a fundamental basis to this innovation and metals can be successfully integrated into this process.

In this Special Issue, we welcome articles that focus on:

• Metal-based materials with the addition of biobased materials (single compounds or extracts with a biological origin such as oils, chitosan, gelatin, algae, by-products, and/or waste from the food industry). Functionalized or coated metals and metal-matrix composites are included.
• New compositions or processing of biodegradable metals (such as magnesium, zinc, and iron alloys).
• Coatings or surface modifications for modulation of the corrosion rate and degradation of biodegradable metals.
• Methods for the characterization of biodegradable metals.
• LCA and LCC evaluation of the production and processing of bio-based and biodegradable metals.

Dr. Silvia Spriano
Prof. Dr. Takayoshi Nakano
Guest Editors

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• ferrous alloys
• non-ferrous alloys
• functionalization
• coatings
• surface modification
• biodegradation
• corrosion rate
• composites
• bio-based materials
• waste

Title: Development of the osteogenic phenotype in vitro on chemically produced titanium nanotopographies functionalized with GDF-5: the effect of etching time
Authors: Renan de Barros e Lima Bueno1, Lucas Novaes Teixeira1, William Marcatti Amarú Maximiano1, Adalberto Luiz Rosa1, Felippe José Pavinatto2, Osvaldo Novaes de Oliveira Junior2, Silvia Spriano3, Antonio Na
Affiliation: 1 Cell Culture Laboratory, Faculty of Dentistry of Ribeirão Preto, University of São Paulo, Av. do Café, s/n, CEP 14040-904, Ribeirão Preto, SP, Brazil 2 São Carlos Institute of Physics, University of São Paulo, Av. Trabalhador São-Carlense, 400, CEP 13566-590, São Carlos, SP, Brazil. 3 Politecnico di Torino, Torino, Italy. 4 Laboratory for the Study of Calcified Tissues and Biomaterials, Université de Montréal, Montréal, QC, Canada.
Abstract: This study evaluated the impact of a single variation in the etching time of H2SO4/H2O2-treated titanium (Ti) surfaces on the adsorption of growth and differentiation factor-5 (GDF-5) and their effects on the acquisition of the osteogenic phenotype in vitro. Rat calvarial osteogenic cells were grown for up to 14 days on the following Ti surfaces: 1) 30 min – nanotopography obtained with a 1:1 mixture of H2SO4/H2O2 for 30 min; 2) 30 min + GDF-5 – a 30 min-etched Ti sample adsorbed with recombinant human (rh) GDF-5; 3) 4 h – nanotopography obtained with a 1:1 mixture of H2SO4/H2O2 for 4 h; 4) 4 h + GDF-5 – a 4 h-etched Ti sample adsorbed with rhGDF-5. The adsorption procedure was carried out on the day before cell plating using 200 ng/mL rhGDF-5 overnight at 4°C. The 30 min- and 4 h-etched Ti samples exhibited a high hydrophilic network of nanopits with a tendency of larger nanopits for the 4 h group, which corresponded to an enhanced GDF-5 adsorption. For both etching times, functionalization with GDF-5 resulted in less hydrophilic surfaces that supported 1) a reduction in the proportion of spread cells and an enhanced extracellular OPN labeling at early time points of culture, and 2) increased ALP activity preceding an enhanced mineralized matrix formation compared with controls, with tendency for higher osteogenic activity for the 4 h + GDF-5. In conclusion, the interfacial stimulation of the osteogenic potential by GDF-5 can be tailored by subtle changes in the nanotopographic characteristics of Ti surfaces.