Impact of Laser Structuring on Medical-Grade Titanium: Surface Characterization and In Vitro Evaluation of Osteoblast Attachment

Abstract

Improved implant osteointegration offers meaningful potential for orthopedic, spinal, and dental implants. In this study, a laser treatment was used for the structuring of a titanium alloy (Ti6Al4V) surface combined with a titanium dioxide coating, whereby a porous surface was created. The objective was to characterize the pore structure shape, treatment-related metallographic changes, cytocompatibility, and attachment of osteoblast-like cells (MG-63). The treatment generated specific bottleneck pore shapes, offering the potential for the interlocking of osteoblasts within undercuts in the implant surface. The pore dimensions were a bottleneck diameter of 27 µm (SD: 4 µm), an inner pore width of 78 µm (SD: 6 µm), and a pore depth of 129 µm (SD: 8 µm). The introduced energy of the laser changed the metallic structure of the alloy within the heat-affected region (approximately 66 µm) without any indication of a micro cracking formation. The phase of the alloy (microcrystalline alpha + beta) was changed to a martensite alpha phase in the surface region and an alpha + beta phase in the transition region between the pores. The MG-63 cells adhered to the structured titanium surface within 30 min and grew with numerous filopodia over and into the pores over the following days. Cell viability was improved on the structured surface compared to pure titanium, indicating good cytocompatibility. In particular, the demonstrated affinity of MG-63 cells to grow into the pores offers the potential to provide significantly improved implant fixation in further in vivo studies.

Antibiotic-loaded amphora-shaped pores on a titanium implant surface enhance osteointegration and prevent infections

“…The laser structuring results in minor metallographic changes of the titanium in that the microcrystalline structure is changed to a martensite structure within a depth of app. 66 μm, as demonstrated previously [ 17 ]. The loading with the drug of need is easy, reproducible, and can be done during the surgical procedure.…”

“…The bending modulus of 98 GPa for CTRL is close to the reported value of 110 GPa for solid titanium implants [ 38 ]. The reduced bending modulus of the Porous surface was expected due to the presence of multiple “notches” [ 17 ] and has to be considered in the implant design for load-bearing implants [ 39 ]. The application of an impact force on the porous surface resulted only in a surface scratch without coating loss or peeling, as reported by Duan et al for HA coatings [ 40 ].…”

“…The embedded metallic silver particles could result in long-term protection due to the very slow release [ 54 ]. A detailed characterization of the structured surface revealed amphora-shaped pores that can be loaded with gentamicin and killed bacterial in direct contact while not affecting osteoblast adhesion and vitality [ 17 , 18 ]. This shape is due to the bottleneck, which is optimal for drug loading and is assumed to improve the anchorage of newly formed bone.…”

“…A high-frequency sputtering chamber (Fraunhofer IFAM, Bremen, Germany) was then used to embed silver-nanoparticles (10–30 nm) in a porous titanium-dioxide coating (4 μg/cm 2 ) on top of the structure by magnetron sputtering. For a more detailed description of the surface modification and applied characterization methods, see recent publications [ 17 , 18 ]. The adhesion/cohesion of the generated structure (Porous) was evaluated against the control (CTRL) using the following tests: in regard to horizontal force, a lap-shear test (based on DIN EN 1465:2009–07), in regard to vertical force, a pull-off test (based on DIN EN ISO 4624:2016–08), and in regard to impact force, a scratch test (based on DIN 55656:2014–12).…”

“…To address these points, this study used laser-structuring technology. We already showed that the produced surface combines pores of the suggested size for bone ingrowth with undercuts for interlocking and the cell-attractive surface of titanium dioxide [ 17 ]. The amphora-shaped pores of the laser-structured surface can be loaded with antibiotics such as gentamicin without further equipment or post-coating, and the initial burst release will eradicate the bacteria contaminating the wound/bone or implant.…”