Comparison of the Influence of 45S5 and Cu-Containing 45S5 Bioactive Glass (BG) on the Biological Properties of Novel Polyhydroxyalkanoate (PHA)/BG Composites

Polyhydroxyalkanoates (PHAs), due to their biodegradable and biocompatible nature and their ability to be formed in complex structures, are excellent candidates for fabricating scaffolds used in tissue engineering. By introducing inorganic compounds, such as bioactive glasses (BGs), the bioactive properties of PHAs can be further improved. In addition to their outstanding bioactivity, BGs can be additionally doped with biological ions, which in turn extend the functionality of the BG-PHA composite. Here, different PHAs were combined with 45S5 BG, which was additionally doped with copper in order to introduce antibacterial and angiogenic properties. The resulting composite was used to produce scaffolds by the salt leaching technique. By performing indirect cell biology tests using stromal cells, a dose-depending effect of the dissolution products released from the BG-PHA scaffolds could be found. In low concentrations, no toxic effect was found. Moreover, in higher concentrations, a minor reduction of cell viability combined with a major increase in VEGF release was measured. This result indicates that the fabricated composite scaffolds are suitable candidates for applications in soft and hard tissue engineering. However, more in-depth studies are necessary to fully understand the release kinetics and the resulting long-term effects of the BG-PHA composites

In vitro characterization of a biodegradable chitosan/bioactive glass coating for Mg alloys

Magnesium and its alloys have already been proposed for biomedical applications in 1878. However, up to date no extended, successful medical Mg product is commercially available. The drawbacks of permanent implants, like stress-shielding or possible release of metal ions through wear, can be avoided with the use of biodegradable metals. Temporary implants as such could make a second surgical process to remove the implant unnecessary, not only decreasing the healthcare costs and associated risks of a surgery, but also reducing the trauma to the patient. Mg is an abundant cation in the human body and in part physiologically beneficial as the surrounding tissue can absorb and consume the ions. The main problems related to the usage of Mg and its alloys is its high chemical reactivity, a related low corrosion resistance, especially in chloride-containing environments and the accompanying fast hydrogen gas production. [1] In order to overcome these problems in this study a coating of a natural polymer/bioactive glass composite is applied using electrophoretic deposition. Additionally, functional properties like drug delivery characteristics and antibacterial capacity are added to these coatings. As natural, cationic polymer chitosan is taken which is the supporting material in the exoskeleton of crustaceans and insects (crab, butterfly) and in cell walls of fungi. It combines biodegradability and biocompatibility with the ability to promote cell adhesion. [1] To avoid dissolution of the Mg alloy substrate during the deposition, a pretreatment is used. The immersion in DMEM for 24 h is increasing the corrosion resistance to a level that the acidic, aqueous electrolyte during deposition is not corroding the Mg substrate. [2] A comparative study was performed on replacing part of the bioactive glass as ceramic part with silica particles in order to maintain a topography during dissolution of the glass. A constant solid content of 1 g/l was chosen, with 0.5 g/l chitosan in 1 vol% acetic acid, 20 vol% water and 79 vol% ethanol following previous studies. [3] For the cathodic deposition process 0.5 cm electrode distance with stainless steel as the counter electrode was used. The deposition was performed under constant current (50 V) and constant voltage (35 mA) with varying processing times. [1] Heise S, Virtanen S, Boccaccini AR. 2016. Tackling Mg alloy corrosion by natural polymer coatings—A review. J Biomed Mater Res Part A 2016:104A:2628–2641 [2] Wagener V, Virtanen S. 2016 Protective layer formation on magnesium in cell culture medium. Mater. Sci. Eng. C 63, 341–351 [3] Cordero-Arias, L. et al. 2013 Electrophoretic deposition of nanostructured-TiO2/Chitosan composite coatings on stainless steel. R. Soc. Chem. 3, 11247-11254 Acknowledgements: This study is supported by the German Science Foundation (DFG)

DEVELOPMENT OF A BIODEGRADABLE NATURAL POLYMER/CERAMIC COATING FOR MG ALLOYS USING ELECTROPHORETIC DEPOSITION

Magnesium and its alloys have already been proposed for biomedical applications in 1878. However, up to date no extended, successful medical Mg product is commercially available. The drawbacks of permanent implants, like stress-shielding or possible release of metal ions through wear, can be avoided with the use of biodegradable metals. Temporary implants as such could make a second surgical process to remove the implant unnecessary, not only decreasing the healthcare costs and associated risks of a surgery, but also reducing the trauma to the patient. Mg is an abundant cation in the human body and in part physiologically beneficial as the surrounding tissue can absorb and consume the ions. The main problems related to the usage of Mg and its alloys is its high chemical reactivity, a related low corrosion resistance, especially in chloride-containing environments and the accompanying fast hydrogen gas production. [1] In order to overcome these problems in this study a coating of a natural polymer/bioactive glass composite is applied using electrophoretic deposition. Additionally, functional properties like drug delivery characteristics and antibacterial capacity are added to these coatings. As natural, cationic polymer chitosan is taken which is the supporting material in the exoskeleton of crustaceans and insects (crab, butterfly) and in cell walls of fungi. It combines biodegradability and biocompatibility with the ability to promote cell adhesion. [1] To avoid dissolution of the Mg alloy substrate during the deposition, a pretreatment is used. The immersion in DMEM for 24 h is increasing the corrosion resistance to a level that the acidic, aqueous electrolyte during deposition is not corroding the Mg substrate. [2] A comparative study was performed on replacing part of the bioactive glass as ceramic part with silica particles in order to maintain a topography during dissolution of the glass. A constant solid content of 1 g/l was chosen, with 0.5 g/l chitosan in 1 vol% acetic acid, 20 vol% water and 79 vol% ethanol following previous studies. [3] For the cathodic deposition process 0.5 cm electrode distance with stainless steel as the counter electrode was used. The deposition was performed under constant current (50 V) and constant voltage (35 mA) with varying processing times. [1] Heise S, Virtanen S, Boccaccini AR. 2016. Tackling Mg alloy corrosion by natural polymer coatings—A review. J Biomed Mater Res Part A 2016:104A:2628–2641 [2] Wagener V, Virtanen S. 2016 Protective layer formation on magnesium in cell culture medium. Mater. Sci. Eng. C 63, 341–351 [3] Cordero-Arias, L. et al. 2013 Electrophoretic deposition of nanostructured-TiO2/Chitosan composite coatings on stainless steel. R. Soc. Chem. 3, 11247-11254 Acknowledgements: This study is supported by the German Science Foundation (DFG)

Editorial: Combating bacterial infections through biomimetic or bioinspired materials design and enabling technologies

Editorial on the Research Topic Combating Bacterial Infections Through Biomimetic or Bioinspired Materials Design and Enabling Technologie

Ag modified mesoporous bioactive glass nanoparticles for enhanced antibacterial activity in 3D infected skin model

Bioactive glasses (BG) are versatile materials for various biomedical applications, including bone regeneration and wound healing, due to their bone bonding, antibacterial, osteogenic, and angiogenic properties. In this study, we aimed to enhance the antibacterial activity of SiO2-CaO mesoporous bioactive glass nanoparticles (MBGN) by incorporating silver (Ag) through a surface modification approach. The modified Ag-containing nanoparticles (Ag-MBGN) maintained spherical shape, mesoporous structure, high dispersity, and apatite-forming ability after the surface functionalization. The antibacterial activity of Ag-MBGN was assessed firstly using a planktonic bacteria model. Moreover, a 3D tissue-engineered infected skin model was used for the first time to evaluate the antibacterial activity of Ag-MBGN at the usage dose of 1 mg/mL. In the planktonic bacteria model, Ag-MBGN exhibited a significant antibacterial effect against both Pseudomonas aeruginosa and Staphylococcus aureus in comparison to non-engineered (Ag-free) MBGN and the blank control. Moreover, Ag-MBGN did not show cytotoxicity towards fibroblasts at the usage dose. However, in the 3D infected skin model, Ag-MBGN only demonstrated antibacterial activity against S. aureus whereas their antibacterial action against P. aeruginosa was inhibited. In conclusion, surface modification by Ag incorporation is a feasible approach to enhance the antibacterial activity of MBGN without significantly impacting their morphology, polydispersity, and apatite-forming ability. The prepared Ag-MBGN are attractive building blocks for the development of 3D antibacterial scaffolds for tissue engineering

Modulation of neuronal cell affinity of composites scaffolds based on polyhydroxyalkanoates and bioactive glasses

Biocompatibility and neuron regenerating properties of various bioactive glass (BG)/Polyhydroxyalkanoate (PHA) blend composites were assessed in order to study their suitability for peripheral nerve tissue applications, specifically as lumen structures for nerve guidance conduits (NGCs). BG/PHA blend composites were fabricated using Bioactive glass® 45S5 (BG1) and BG 1393 (BG2) with the 25:35 poly(3-hydroxyoctanoate/poly3-hydroxybutyrate), 25:75 P(3HO)/P(3HB) blend (PHA blend). Various concentrations of each BG (0.5, 1.0 and 2.5 wt%) were used to determine the effect of BG on neuronal growth and differentiation, in single culture using NG108-15 neuronal cells and in a co-culture along with RN22 Schwann cells. NG108-15 cells exhibited good growth and differentiation on all the PHA blend composites showing that both BGs have good biocompatibility at 0.5, 1.0 and 2.5 wt% within the PHA blend. The Young's modulus values displayed by all the PHA blend/BG composites ranged from 385.6 MPa to 1792.6 MPa, which are able to provide the required support and protective effect for regeneration of peripheral nerves. More specifically, the tensile strength obtained in the PHA blend/BG1 (1.0 wt%) (10.0 ± 0.6 MPa) was found to be similar to that of rabbit peroneal nerve. This composite also exhibited the best biological performance in supporting growth and neuronal differentiation among all the substrates. The neurite extension on this composite was found to be remarkable with the neurites forming a complex connection network

3D melt-extrusion printing of medium chain length polyhydroxyalkanoates and their application as antibiotic-free antibacterial scaffolds for bone regeneration

In this work, we investigated, for the first time, the possibility of developing scaffolds for bone tissue engineering through three-dimensional (3D) melt-extrusion printing of medium chain length polyhydroxyalkanoate (mcl-PHA) (i.e., poly(3-hydroxyoctanoate-co-hydroxydecanoate-co-hydroxydodecanoate), P(3HO-co-3HD-co-3HDD)). The process parameters were successfully optimized to produce well-defined and reproducible 3D P(3HO-co-3HD-co-3HDD) scaffolds, showing high cell viability (100%) toward both undifferentiated and differentiated MC3T3-E1 cells. To introduce antibacterial features in the developed scaffolds, two strategies were investigated. For the first strategy, P(3HO-co-3HD-co-3HDD) was combined with PHAs containing thioester groups in their side chains (i.e., PHACOS), inherently antibacterial PHAs. The 3D blend scaffolds were able to induce a 70% reduction of Staphylococcus aureus 6538P cells by direct contact testing, confirming their antibacterial properties. Additionally, the scaffolds were able to support the growth of MC3T3-E1 cells, showing the potential for bone regeneration. For the second strategy, composite materials were produced by the combination of P(3HO-co-3HD-co-HDD) with a novel antibacterial hydroxyapatite doped with selenium and strontium ions (Se-Sr-HA). The composite material with 10 wt % Se-Sr-HA as a filler showed high antibacterial activity against both Gram-positive (S. aureus 6538P) and Gram-negative bacteria (Escherichia coli 8739), through a dual mechanism: by direct contact (inducing 80% reduction of both bacterial strains) and through the release of active ions (leading to a 54% bacterial cell count reduction for S. aureus 6538P and 30% for E. coli 8739 after 24 h). Moreover, the composite scaffolds showed high viability of MC3T3-E1 cells through both indirect and direct testing, showing promising results for their application in bone tissue engineering

MATERIALS SCREENING METHODOLOGY FOR ADDITIVE MANUFACTURING IN BIOREACTOR TECHNOLOGY

Biofabrication is used to fabricate complex tissues/organs inspired by their native structures using additive manufacturing (AM) techniques and bio-inks (biopolymers enriched with living cells). Electroactive cells such as skeletal muscle function via electrical signals and therefore, their optimum in vitro functionality requires electrical conductivity and electrical stimulations. AM can be used to precisely fabricate a bioreactor for a dynamic culture of cells and bioengineered tissues and electrical stimulation of them. In this study, we focused on a material selection methodology for AM of bioreactors with selective electrical conductivity based on Reuter [1]. The important material requirements for bioreactors are biocompatibility, chemical stability, electrical conductivity, and the capability of being sterilized. However, there is no standardized procedure for selecting materials, that are appropriate for AM of bioreactors. Our study comprises three phases which deductively narrowed down the material selection; these phases are the determination of material requirements, pre-selection, and fine selection of suitable materials. With the proposed method, a material selection for AM of functional bioreactors (consisting of bioreactor housing and integrated additively manufactured electrodes for electrical stimulation of the cells) could be efficiently made. For the bioreactor housing, two of the investigated materials, high-temperature polylactic acid (HTPLA) and polypropylene (PP) meet all requirements. The materials of the bioreactor electrodes could be narrowed down to polyethylene with copper particles (PE-Cu) and poly lactic acid with graphene nanoplates (PLA-GNP), where PE-Cu fulfilled all requirements besides the biocompatibility. PLA-GNP matches all requirements besides the high temperature resistance. For a final selection of the material for the bioreactor electrodes, further tests are required. However, this approach enabled to reduce the amount of biocompatibility testing from 16 different materials to only four (- 75%), saving material, time, capacity and costs.Mechanical Engineerin