Adhesion improvement and in vitro characterisation of 45S5 bioactive glass coatings obtained by atmospheric plasma spraying
Introduction
The global market for orthopaedic devices which include joint reconstructions, spinal devices, orthobiologics (substitutes and bone grafts) and trauma fixation among others reach every year higher values. Several factors are increasing the demand for orthopaedic implants. Mainly the ageing of the population that cause bone related diseases as osteoporosis and osteoarthritis. But also other diseases connected to lack of physical activity or poor diet intake and obesity have a growing trend in the last years that increment the requests of implants. Moreover, the increasing incidence of road traffic accidents and sports injuries have been an important factor for the market. The global orthopaedic device market is expected to rise in the following years.
Orthopaedic devices are very successful but there is a rate of implant failure that ends in revision surgery to correct. It is important to consider that revision surgery takes much longer, and is less successful than the primary procedure. Also the cost is higher than the primary intervention. For the patient it means more pain and the recovery takes weeks or months. In addition to the risk of a new surgery [1].
The main failures for orthopaedic devices are related to infections, being trauma devices more affected than joint replacements [2]. Other complications are associated to the implant-tissue interface due to a non-sufficient osteointegration or the stress shielding caused by the mismatch between the mechanical properties of bone tissue and the implanted materials.
Current biomaterials are reaching their limits and there is a need for study new opportunities that can satisfy biomechanical and biological requirements to improve the long-term success and to reduce the risk for revisions of artificial implants. One option is functionalizing current materials with bioactive glass coatings.
In the late 1960s Larry Hench developed the first composition of bioactive glass, named 45S5. It was composed of the following oxides wt%: sodium oxide (24.5%), calcium oxide (24.5%), silicon dioxide (45.0%) and phosphorus pentoxide (6.0%). Takes its name because the glass has 45 wt% of SiO2 and a calcium to phosphorus molar ratio of 5:1 [3,4].
Bioactive glass materials are different from conventional glasses. Their structure is quite more disrupted than the conventional ones. Bioactive glasses are characterized by their bioactivity and their unique bone bonding properties related to their surface reactivity when immersed in aqueous medium [1,4,5]. Depending on the composition, the glass can bond also to the soft tissue. The mechanism for bone bonding is in consequence of the formation of hydroxycarbonate apatite (HCA) layer on the surface of the glass, resulting from the initial glass dissolution. The biological apatite is partially replaced by the bone after long-term implantation. It is due because the ion release products from bioactive glasses stimulate expressions of several genes of osteoblastic cells and promotes its proliferation [[6], [7], [8]]. Moreover, bioactive glasses show osteoconductive and osteoinductive capabilities [5].
The properties of each glass (e.g. the dissolution and the HCA layer formation rate) are a result of atomic structure. So by varying the content and the kind of the oxides in the glass, a full range of stability can be produced, from soluble to nonresorbable [1]. The 45S5 composition, in particular, is highly reactive.
When bioactive glasses come in contact with water, an ion exchange occurs at the glass/water interface. This ion exchange between modifier ions and protons from the solution results in a fast pH increase, mainly occurring in the first hours [9].
The release of ions from bioactive glasses is continuous over time [10], which suggest there is a release of ions from the bulk because the open silicate network allows the water molecules enter easy.
The excellent bioactive properties of bioactive glasses make them suitable for use to replace or repair damaged tissue. However, due to their poor mechanical properties, these glasses cannot be used as a bulk for load-bearing applications as other biomaterials such as titanium and cobalt-chrome alloys. [6,11]. Otherwise, they are able to be used as bone grafts, scaffolds and coating materials.
The first clinical bioactive glass product, the “Bioglass® Ossicular Reconstruction Prosthesis”, was a device used to treat conductive hearing loss by replacing the bones of the middle ear. It was a structure intended to conduct sound from the tympanic membrane to the cochlea. For this product was used the 45S5 composition [3,12].
Nowadays, most of the bioactive glass products available in the market are bone grafts [[13], [14], [15]]. But there are some other applications like an absorbable composite interference screw of bioactive glass and PLLA-PDLLA or a component for toothpaste [16,17].
The current biomaterials used for load bearing applications meet the necessary mechanical requirements. However, they have an inert behaviour when implanted. For this reason is necessary to apply a superficial modification to improve their interaction with the body. There are several methods (physical, chemical or combined strategies) used to improve the bioactivity of the surfaces keeping at the same time the bulk properties unaltered. One of the strategies used to convert bioinert materials into bioactive ones is depositing a biomaterial that stimulates the implant and host bond integration by thermal spray techniques.
Plasma-sprayed HA coatings have been used as surface coatings on metallic implants since the 1980s [18]. Moreover, it is possible to find in the literature several studies of ceramics or glass coatings produced by different thermal spray techniques such as a coating of a HA and TiO2 mix (80–20% by weight) on Ti6Al4V by High-Speed Thermal Spray (HVOF) [19], biomimetic nanocrystalline apatites deposited by low pressure cold sprayed (LP-CS) on Ti6Al4V [20], apatite and wollastonite coatings by APS on Ti6Al4V [21], 45S5 bioactive glass by APS on AISI 304 metallic substrate [22], etc.
Several researchers have proposed bioactive glasses as an alternative to HA coatings because of their ability to create a stable interface that bond to bone strongly. Moreover, their dissolution products promote cells to differentiate to bone cells [7].
It is possible to find studies developing bioactive glasses coatings by different thermal spray processes [[23], [24], [25], [26], [27], [28], [29]]. Some of these studies use just the glass powder, others use suspensions, others solution precursors and there are also works were mix the glasses with other compositions. In most of the studies glass coatings are very defective and are weakly bonded to the substrate [30].
One of the major challenges of using bioactive glass as coatings is improving the adhesion of the coating [11]. In this article, different strategies were studied to develop plasma sprayed 45S5 bioactive glass coatings with better adhesion. First step was varying the spraying parameters to achieve the best adhesion directly from the technique. Then two different approaches were studied: a cooling process with carbon dioxide while spraying the powder and a heat treating of the samples after spraying. Achieving good adhesion of the coating to the substrate is essential for bioactive glasses to be considered candidates to replace current hydroxyapatite coatings.
Section snippets
Powder and substrate
The 45S5 bioactive glass powder was obtained from Denfotex research (United Kingdom). The powder was produced by the traditional melt-quenching route. To the milled powder 0.7 wt% of aerosil was added, as an extra in the standard formulation, mixing directly with the powder. This fumed silica (aerosil) serves as a universal anticaking agent in powders, to make powders capable of flowing during spray process.
Titanium grade V disks of 2 mm thick and 9 mm diameter (Tamec, Spain) were used as
Powder characterisation
The size distribution used for spray was micron-sized with D10 = 52 μm, D50 = 70 μm and D90 = 110 μm. The XRD pattern of the powder particles was the characteristic with amorphous structure.
The particles had irregular morphology as expected due to the route of fabrication. In addition, the cross section of the powders reveal full-dense particles (Fig. 1).
Coatings characterisation
Microstructure of the fabricated coatings can be observed in the cross-section micrographs showed in Fig. 2. Due to the low thermal
Conclusions
The effect of cooling with CO2 during spraying maintain the amorphous structure of the coating. Otherwise the post heat treatment generates sodium calcium silicate crystalline phase to the samples heated at 725 °C and 800 °C and sodium calcium phosphate silicate phase when heating at 800 °C.
The cooling process during spraying did not enhance the adhesion strength with the substrate, although with a post heat treatment high adhesion strengths were achieved due to the stress relaxation and the
CRediT authorship contribution statement
B. Garrido: Conceptualization, Funding acquisition, Methodology, Project administration, Resources, Supervision, Validation, Writing - review & editing. I.G. Cano: Data curation, Formal analysis, Investigation, Methodology, Validation, Visualization, Writing - original draft. S. Dosta: Funding acquisition, Investigation, Methodology, Resources, Supervision, Validation, Visualization, Writing - review & editing.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by Generalitat de Catalunya (SGR-1777) and Spanish Government (MAT2016-76928-C2-1-R).
References (38)
Review of bioactive glass: from Hench to hybrids
Acta Biomater.
(2013)- et al.
Mechanical properties of bioactive glasses, ceramics, glass-ceramics and composites: state-of-the-art review and future challenges
Mater. Sci. Eng. C.
(2019) - et al.
A review of the biological response to ionic dissolution products from bioactive glasses and glass-ceramics
Biomaterials
(2011) - et al.
Dissolution patterns of biocompatible glasses in 2-amino-2-hydroxymethyl- propane-1,3-diol (Tris) buffer
Acta Biomater.
(2013) - et al.
Bioactive glass coatings for orthopedic metallic implants
J. Eur. Ceram. Soc.
(2003) - et al.
Thermal and physical characterisation of apatite/wollastonite bioactive glass-ceramics
J. Eur. Ceram. Soc.
(2009) - et al.
Effect of processing on microstructure, mechanical properties and dissolution behaviour in SBF of Bioglass (45S5) coatings deposited by suspension high velocity oxy fuel (SHVOF) thermal spray
Surf. Coatings Technol.
(2019) - et al.
Functional bioactive glass topcoats on hydroxyapatite coatings: analysis of microstructure and in-vitro bioactivity
Surf. Coatings Technol.
(2014) - et al.
Solution precursor plasma spraying (SPPS): a novel and simple process to obtain bioactive glass coatings
Mater. Lett.
(2018) - et al.
Comparison between suspension plasma sprayed and high velocity suspension flame sprayed bioactive coatings
Surf. Coatings Technol.
(2015)
Different approaches to produce coatings with bioactive glasses: Enamelling vs plasma spraying
J. Eur. Ceram. Soc.
Structural transformations of bioactive glass 45S5 with thermal treatments
Acta Mater.
Ceramics for medical applications: a picture for the next 20 years
J. Eur. Ceram. Soc.
Low temperature spark plasma sintering of 45S5 bioglass®
J. Non-Cryst. Solids
Comprehensive biomaterials
Orthopedic prosthetic infections: diagnosis and orthopedic salvage
Semin. Plast. Surg.
The story of Bioglass®
J. Mater. Sci. Mater. Med.
History and trends of bioactive glass-ceramics
J. Biomed. Mater. Res. - Part A.
Gene-expression Profiling of Human Osteoblasts Following Treatment With the Ionic Products of Bioglass® 45S5 Dissolution
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