Understanding the effects of PBF process parameter interplay on Ti-6Al-4V surface properties.

Ti-6Al-4V is commonly used in orthopaedic implants, and fabrication techniques such as Powder Bed Fusion (PBF) are becoming increasingly popular for the net-shape production of such implants, as PBF allows for complex customisation and minimal material wastage. Present research into PBF fabricated Ti-6Al-4V focuses on new design strategies (e.g. designing pores, struts or lattices) or mechanical property optimisation through process parameter control-however, it is pertinent to examine the effects of altering PBF process parameters on properties relating to bioactivity. Herein, changes in Ti-6Al-4V microstructure, mechanical properties and surface characteristics were examined as a result of varying PBF process parameters, with a view to understanding how to tune Ti-6Al-4V bio-activity during the fabrication stage itself. The interplay between various PBF laser scan speeds and laser powers influenced Ti-6Al-4V hardness, porosity, roughness and corrosion resistance, in a manner not clearly described by the commonly used volumetric energy density (VED) design variable. Key findings indicate that the relationships between PBF process parameters and ultimate Ti-6Al-4V properties are not straightforward as expected, and that wide ranges of porosity (0.03 ± 0.01% to 32.59 ± 2.72%) and corrosion resistance can be achieved through relatively minor changes in process parameters used-indicating volumetric energy density is a poor predictor of PBF Ti-6Al-4V properties. While variations in electrochemical behaviour with respect to the process parameters used in the PBF fabrication of Ti-6Al-4V have previously been reported, this study presents data regarding important surface characteristics over a large process window, reflecting the full capabilities of current PBF machinery.

Formulation and viscoelasticity of mineralised hydrogels for use in bone-cartilage interfacial reconstruction.

Articular cartilage is a viscoelastic tissue whose structural integrity is important in maintaining joint health. To restore the functionality of osteoarthritic joints it is vital that regenerative strategies mimic the dynamic loading response of cartilage and bone. Here, a rotating simplex model was employed to optimise the composition of agarose and gellan hydrogel constructs structured with hydroxyapatite (HA) with the aim of obtaining composites mechanically comparable to human cartilage in terms of their ability to dissipate energy. Addition of ceramic particles was found to reinforce both matrices up to a critical concentration (< 3w/v%). Beyond this, larger agglomerates were formed, as evidenced by micro computed tomography data, which acted as stress risers and reduced the ability of composites to dissipate energy demonstrated by a reduction in tan δ values. A maximum compressive modulus of 450.7±24.9 kPa was achieved with a composition of 5.8w/v% agarose and 0.5w/v% HA. Interestingly, when loaded dynamically (1-20Hz) this optimised formulation did not exhibit the highest complex modulus instead a sample with a higher concentration of mineral was identified (5.8w/v% agarose and 25w/v% HA). Thus, demonstrating the importance of examining the mechanical behaviour of biomaterials under conditions representative of physiological environments. While the complex moduli of the optimised gellan (1.0 ± 0.2MPa at 1Hz) and agarose (1.7 ± 0.2MPa at 1Hz) constructs did not match the complex moduli of healthy human cartilage samples (26.3 ± 6.5MPa at 1Hz), similar tan δ values were observed between 1 and 5Hz. This is promising since these frequencies represent the typical heel strike time of the general population. In summary, this study demonstrates the importance of considering more than just the strength of biomaterials since tissues like cartilage play a more complex role.

Osteoanabolic Implant Materials for Orthopedic Treatment.

Osteoporosis is becoming more prevalent due to the aging demographics of many populations. Osteoporotic bone is more prone to fracture than normal bone, and current orthopedic implant materials are not ideal for the osteoporotic cases. A newly developed strontium phosphate (SrPO4 ) coating is reported herein, and applied to Ti-29Nb-13Ta-4.6Zr (wt%), TNTZ, an implant material with a comparative Young's modulus to that of natural bone. The SrPO4 coating is anticipated to modulate the activity of osteoblast (OB) and osteoclast (OC) cells, in order to promote bone formation. TNTZ, a material with excellent biocompatibility and high bioinertness is pretreated in a concentrated alkaline solution under hydrothermal conditions, followed by a hydrothermal coating growth process to achieve complete SrPO4 surface coverage with high bonding strength. Owing to the release of Sr ions from the SrPO4 coating and its unique surface topography, OB cells demonstrate increased proliferation and differentiation, while the cellular responses of OC are suppressed, compared to the control case, i.e., bare TNTZ. This TNTZ implant with a near physiologic Young's modulus and a functional SrPO4 coating provides a new direction in the design and manufacture of implantable devices used in the management of orthopedic conditions in osteoporotic individuals.