Using the layer-by-layer (LbL) assembly technique to deposit mechanically reinforcing coatings onto porous templates is a route for fabricating engineered bone scaffold materials with a combination of high porosity, strength, and stiffness. LbL assembly involves the sequential deposition of nano-to micro-scale multilayer coatings from aqueous solutions. Here, a design of experiments (DOE) approach was used to evaluate LbL assembly of polyethyleneimine (PEI), polyacrylic acid (PAA), and nanoclay coatings onto open-cell polyurethane foam templates. The thickness of the coatings, and the porosity, elastic modulus and collapse stress of coated foam templates were most strongly affected by the pH of PAA solutions, salt concentration, and interactions between these factors. The mechanical properties of coated foams correlated with the thickness of the coatings, but were also ascribed to changes in the coating properties due to the different assembly conditions. A DOE optimization aimed to balance the trade-off between higher mechanical properties but lower porosity of foam templates with increasing coating thickness. Micromechanical modelling predicted that deposition of 116 QLs would achieve mechanical properties of cancellous bone (>0.05 GPa stiffness and >2 MPa strength) at a suitable porosity of >70%. When capped with a final layer of PAA and cross-linked via thermal treatment, the PEI/PAA/PEI/nanoclay coatings exhibited good indirect cytotoxicity with mesenchymal stem cells. The ability of LbL assembly to deposit a wide range of functional constituents within multilayer-structured coatings makes the general strategy of templated LbL assembly a powerful route for fabricating engineered tissue scaffolds that can be applied onto various porous template materials to achieve a wide range of properties, pore structures, and multifunctionality.

Control of the corrosion that occurs in magnesium alloys in vivo is a significant challenge for their use as resorbable orthopaedic implants. In this work, we report on the provision of bioactive calcium phosphate (CaP) coatings on magnesium alloys that can delay substrate corrosion while offering an attendant physiochemical environment with properties known to promote an osteoinductive response in vivo. RF magnetron sputtering from hydroxyapatite (HA) powder targets has been employed to create CaP coatings on AZ31 magnesium alloy substrates. Coatings of 70 and 210 nm thickness were achieved via regulation of sputtering parameters, in particular deposition time. XPS and ToF-SIMS were used to investigate the chemistry of the coating alloy interface and also to confirm composition and thickness. The Ca/P atomic ratio of the coatings was determined by EDX to be 1.54. μCT analysis showed a substrate volume loss after 14 days exposure to SBF of 5.89 ± 3.15 mm 3 for the un-coated alloy while the presence of the ~70 nm CaP coating reduced this to 3.42 ± 0.48 mm 3 and the ~210 nm coating to 0.30 ± 0.28 mm 3. The corrosion rates were calculated to be 1.74 ± 0.06 mmpy for the AZ31 control; 1.57 ± 0.09 mmpy for the ~70 nm CaP coated alloy and 1.01 ± 0.07 mmpy for the ~210 nm thick CaP coating. These data confirm that CaP coating

Polyetheretherketone (PEEK) has emerged as the material of choice for spinal fusion devices, replacing conventional materials such as titanium and its alloys due to its ability to easily overcome a lot of the limitations of traditional metallic biomaterials. However, one of the major drawbacks of this material is that it is not osteoinductive, nor osteoconductive, preventing direct bone apposition. One way to overcome this is through the modification of the PEEK with bioactive calcium phosphate (CaP) materials, such as hydroxyapatite (HA–Ca10(PO4)6(OH)2). RF magnetron sputtering has been shown to be a particularly useful technique for the deposition of CaP coatings due to the ability of the technique to provide greater control of the coating’s properties. The work undertaken here involved the deposition of HA directly onto PEEK via RF magnetron at a range of deposition times between 10–600 min to provide more bioactive surfaces. The surfaces produced have been extensively characterised using X-Ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), stylus profilometry, and Time of Flight Secondary Ion Mass Spectrometry (ToFSIMS). XPS results indicated that both Ca and P had successfully deposited onto the surface, albeit with low Ca/P ratios of around 0.85. ToFSIMS analysis indicated that Ca and P had been homogeneously deposited across all the surfaces. The SEM results showed that the CaP surfaces produced were a porous micro-/nano-structured lattice network and that the deposition rate influenced the pore area, pore diameter and number of pores. Depth profiling, using ToFSIMS, highlighted that Ca and P were embedded into the PEEK matrix up to a depth of around 1.21 µm and that the interface between the CaP surface and PEEK substrate was an intermixed layer. In summary, the results highlighted that RF magnetron sputtering can deliver homogenous CaP lattice-like surfaces onto PEEK in a direct, one-step process, without the need for any interlayers, and provides a basis for enhancing the potential bioactivity of PEEK.

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