Development of additively manufactured Titanium based (Ti6Al4V) implants with different inclination angle and its implications on bio-interface for orthopaedic applications
Creators: name: Sarker, Avik
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400308
subject: Medical devices

description: Musculoskeletal injuries and defects are considered globally as some of the most critical types of injury in orthopaedic field and it often requires surgical intervention to deal with these problems. These injuries may occur in different way such as tumor resection, traumatic bone injury, and osteitis. Bone trauma or defect can significantly deteriorate on the status of human's life. The design of tissue engineering materials for both orthopaedic and dental implants is a great challenge in terms of desirable mechanical properties, biocompatibility, and improved osseo-integration. Titanium has been an effective implant material due to its excellent strength to weight ratio, corrosion resistance, toughness, and bio-inert oxide surface. Due to the recent progress of additive manufacturing technique it is possible to make patient-specific implants. Therefore, additive manufacturing has the huge potentiality to disrupt traditional orthopaedic implants to met up the demand of increasing population.<br> <br>Selective laser melting (SLM) is an additive manufacturing process that fabricates constructs based on CAD design by scanning powdered materials using the thermal energy supplied by a focused and computer-controlled laser beam. SLM allows the generation of complex 3D parts by a layer-wise material addition technique that selectively melts successive layers of metal powder on top of each other. <br><br>There have been several reports existed in the current literature which showed the relationship between different process parameters of additive manufacturing with its different surface properties, mechanical properties and microstructure. There have been also reported that there are several ways to improve the interface of additively manufactured by different surface treatments such as anodization, alkali treatment, surface modifications by coating, grafting and polishing. There has been only limited research has been carried out that how the build inclination angle can be used to improve the bio-interface of additively manufactured titanium implant surface for better osseo-integration without changing any process parameter of additive manufacturing. <br><br>Therefore, understanding and investigating the relationship between as manufactured parts and its different surface profile properties (surface texture both 2D and 3D), surface roughness (Ra, Rq), surface morphology, and surface wettability are so essential prior to successful clinical application. At the initial stage, we have manufactured Ti6Al4V parts by selective laser melting process (SLM) with different inclination angle with respect to the build plane from 5 to 90 degrees with 5 degrees interval. The upward and downward faces of as-manufactured parts have been investigated profoundly using optical microscopy (OM), profilometer scanning electron microscopy (SEM). Herein, we demonstrated how the surface roughness, surface morphology, and surface wettability are changed with the alteration of inclination angle of SLM parts. There is much more percentage of correlation of arithmetic average of roughness (Ra) value for 5 average data points is found on lower surface on the linear, exponential and logarithmic regression line than the upper surface of SLM plates in the change of inclination angle. This study provides us a deep insight in terms of understanding how the surface properties are influenced by the design angle of additive manufacture when the processing parameters are constant.<br><br>In the next stage, we have manufactured Ti6Al4V implants with three inclination angles (0 degree, 45 degrees and 90 degrees) and tried to establish a relationship between mammalian cell attachment with the surface properties of different inclination angle. It has been found that during the SLM process there is an increasing trend of partially melted particles with the increase of inclination angle which greatly influence the surface topography, surface chemistry and surface roughness. It has been found from the mammalian cell (CHO-GHP) attachment on different inclined surface that higher inclination angle induces the better cell attachment on implant surface with higher amount of spindle like shape with higher spindle dimension than lower inclination angle. <br> <br>Implant associated infection is also a major concern among orthopaedic research community. Different coating, grafting, surface modification approaches have been carried out on metallic implant surface in order to prevent against biofilm formation. In this study, we have printed three different inclination angle 10, 45, and 90 degrees and Staphylococcus aureus (S.aureus) were grown on all these samples. After 48 hours of incubation, it has been found that lower inclination angle 10 degrees surface can inhibit biofilm formation due to its lower hydrophobicity, lower roughness, higher surface energy, and fewer partially melted metal particles than 45, and 90 degrees surface. In addition, the bulk chemistry was not altered in both lower and higher inclination angle and mammalian cell growth was not compromised in any of the inclination angle. This work demonstrates us a novel one step method at additive manufacturing that without using any surface modification approach we can develop additively manufactured surface which can shield against implant associated infection with superior surface functionality.<br><br>In final stage, we have manufactured Ti6Al4V cylindrical single at three different inclination angles (30 degrees, 60 degrees and 90 degrees) with 0.2 mm, 0.6 mm, 1.0 mm diameter struts by selective laser melting process as a proof of concept of orthopaedic lattice implants. The surface properties (surface roughness) of individual cylindrical strut is dependent both with the inclination angle and diameter. In detailed porosity analysis of individual cylindrical strut has been conducted to understand how the pore size and pore orientation are changed with the inclination angle and strut diameter along the build height. The stress analysis and buckling behaviour have also been analysed for individual single strut. After that, rat primary osteoblast cells were grown on individual struts to understand how the bone cells are attached on strut surface after 3 &amp; 7 days of incubation by scanning electron microscope. This work gives us the deep understanding of utilising SLM technology for the development of customized metallic implants for orthopaedic application specially where lattice geometry is required for healing the bone trauma.