Laser-Based Hybrid Manufacturing of Endosseous Implants: Optimized Titanium Surfaces for Enhancing Osteogenic Differentiation of Human Mesenchymal Stem Cells

Abstract

Additive manufacturing (AM) is becoming increasingly important in the orthopedic and dental sectors thanks to two major advantages: the possibility of custom manufacturing and the integration of complex structures. However, at smaller scales, surface conditions of AM products are not mastered. Numerous non-fused powder particles give rise to roughness values (Sa) greater than 10 μm, thus limiting biomedical applications since the surface roughness of, e.g., metal implants plays a major role in the quality and rate of osseointegration. In this study, an innovative hybrid machine combining AM and a femtosecond laser (FS) was used to obtain Ti6Al4V parts with biofunctional surfaces. During the manufacturing process, the FS laser beam "neatly" ablates the surface, leaving in its path nanostructures created by the laser/ matter interaction. This step decreases the Sa from 11 to 4 μm and increases the surface wettability. The behavior of human mesenchymal stem cells was evaluated on these new AM+FS surfaces and compared with that on AM surfaces and also on polished surfaces. The number of cells attached 24 h after plating is equivalent on all surfaces, but cell spreading is higher on AM+FS surfaces compared with their AM counterparts. In the longer term (days 7 and 14), fibronectin and collagen synthesis increase on AM+FS surfaces as opposed to AM alone. Alkaline phosphatase activity, osteocalcin production, and mineralization, markers of osteogenic differentiation, are significantly lower on raw AM surfaces, whereas on the AM+FS specimens they display a level equivalent to that on the polished surface. Overall, these results indicate that using an FS laser beam during the fabrication of AM parts optimizes surface morphology to favor osteoblastic differentiation. This new hybrid machine could make it possible to produce AM implants with functional surfaces directly at the end of AM, thereby limiting their posttreatments.

A comprehensive review on metallic implant biomaterials and their subtractive manufacturing

“…Regarding surface preparation, there are several promising non-conventional or hybrid methods to tailor micro or even nano-sized structures favorable to cell adhesion and proliferation. For instance, Bouet et al [ 300 ] has combined femtosecond laser with Selective Laser Melting to reduce product surface roughness and create periodic surface nanostructures due to laser-induced ablation. Additionally, IBM and EBM have been used as subtractive strategies for hard-to-cut metals, SMAs and Cermets, but the ongoing research aims to use these techniques for surface modification.…”

Delivering Mechanical Stimulation to Cells: State of the Art in Materials and Devices Design

“…Many physical processing methods have been used to develop surface topographies either in a bottom‐up or a top‐down manner. Surface treatments such as laser ablation, [ 49c,50a,57c,71 ] polishing and grit blasting, [ 72 ] and ion bombardment and drilling, [ 50b,73 ] create patterns by erosion of the substrate surface, while others, like physical vapor deposition (PVD) and electrohydrodynamic spraying deposit a layer of new material on the substrate. [ 53a,74 ] The majority of these methods including polishing, grit blasting, drilling, physical vapor deposition (PVD), and electrohydrodynamic spraying was suitable for generating only a limited range of topographical patterns (Table 3).…”

Influence of Successive Chemical and Thermochemical Treatments on Surface Features of Ti6Al4V Samples Manufactured by SLM

“…In the samples with acid etching at 40 • C (AECT-1 and AECT-2), macro, submicro and nanoscale structures were observed, while in the samples treated at 80 • C (AECT-3 and AECT-4), micropores were additionally seen. In recent years, the combination of micro-and nano-features has attracted the attention of researchers [14,18,19,37]. Xu et al have reported that the presence of micronano topography in SLM titanium allowed significantly higher osteoblast proliferation, total protein contents, bone-implant contact (BIC) and bone-bonding force than in as-built SLM [25].…”

“…One of the advantages of AM, is that it provides extensive customization for medical applications based on individual patient data and requirements, and enables the design and manufacture of patient-specific implants [12][13][14], which are modeled in 3D sections. For this reason, in recent years there has been notable progress in the implementation of AM in the field of biofabrication.…”