Influence of pores created by laser superfinishing on osseointegration of titanium alloy implants

In Vitro Biological Characterization of Silver-Doped Anodic Oxide Coating on Titanium

Despite the high biocompatibility and clinical effectiveness of Ti-based implants, surface functionalization (with complex osteointegrative/antibacterial strategies) is still required. To enhance the dental implant surface and to provide additional osteoinductive and antibacterial properties, plasma electrolytic oxidation of a pure Ti was performed using a nitrilotriacetic acid (NTA)-based Ag nanoparticles (AgNP)-loaded calcium–phosphate solution. Chemical and structural properties of the surface-modified titanium were assessed using scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) and contact angle measurement. A bacterial adhesion test and cell culture biocompatibility with collagen production were performed to evaluate biological effectiveness of the Ti after the plasma electrolytic process. The NTA-based calcium–phosphate solution with Ag nanoparticles (AgNPs) can provide formation of a thick, porous plasma electrolytic oxidation (PEO) layer enriched in silver oxide. Voltage elevation leads to increased porosity and a hydrophilic nature of the newly formed ceramic coating. The silver-enriched PEO layer exhibits an effective antibacterial effect with high biocompatibility and increased collagen production that could be an effective complex strategy for dental and orthopedic implant development.

In Vitro Bioactivity and Biocompatibility of Bio-Inspired Ti-6Al-4V Alloy Surfaces Modified by Combined Laser Micro/Nano Structuring

The bioactivity and biocompatibility play key roles in the success of dental and orthopaedic implants. Although most commercial implant systems use various surface microstructures, the ideal multi-scale topographies capable of controlling osteointegration have not yielded conclusive results. Inspired by both the isotropic adhesion of the skin structures in tree frog toe pads and the anisotropic adhesion of the corrugated ridges on the scales of Morpho butterfly wings, composite micro/nano-structures, including the array of micro-hexagons and oriented nano-ripples on titanium alloy implants, were respectively fabricated by microsecond laser direct writing and femtosecond laser-induced periodic surface structures, to improve cell adherence, alignment and proliferation on implants. The main differences in both the bioactivity in simulated body fluid and the biocompatibility in osteoblastic cell MC3T3 proliferation were measured and analyzed among Ti-6Al-4V samples with smooth surface, micro-hexagons and composite micro/nano-structures, respectively. Of note, bioinspired micro/nano-structures displayed the best bioactivity and biocompatibility after in vitro experiments, and meanwhile, the nano-ripples were able to induce cellular alignment within the micro-hexagons. The reasons for these differences were found in the topographical cues. An innovative functionalization strategy of controlling the osteointegration on titanium alloy implants is proposed using the composite micro/nano-structures, which is meaningful in various regenerative medicine applications and implant fields.

Osseointegration and current interpretations of the bone-implant interface

Complex physical and chemical interactions take place in the interface between the implant surface and bone. Various descriptions of the ultrastructural arrangement to various implant design features, ranging from solid and macroporous geometries to surface modifications on the micron-, submicron-, and nano- levels, have been put forward. Here, the current knowledge regarding structural organisation of the bone-implant interface is reviewed with a focus on solid devices, mainly metal (or alloy) intended for permanent anchorage in bone. Certain biomaterials that undergo surface and bulk degradation are also considered. The bone-implant interface is a heterogeneous zone consisting of mineralised, partially mineralised, and unmineralised areas. Within the meso-micro-nano-continuum, mineralised collagen fibrils form the structural basis of the bone-implant interface, in addition to accumulation of non-collagenous macromolecules such as osteopontin, bone sialoprotein, and osteocalcin. In the published literature, as many as eight distinct arrangements of the bone-implant interface ultrastructure have been described. The interpretation is influenced by the in vivo model and species-specific characteristics, healing time point(s), physico-chemical properties of the implant surface, implant geometry, sample preparation route(s) and associated artefacts, analytical technique(s) and their limitations, and non-compromised vs compromised local tissue conditions. The understanding of the ultrastructure of the interface under experimental conditions is rapidly evolving due to the introduction of novel techniques for sample preparation and analysis. Nevertheless, the current understanding of the interface zone in humans in relation to clinical implant performance is still hampered by the shortcomings of clinical methods for resolving the finer details of the bone-implant interface. STATEMENT OF SIGNIFICANCE: Being a hierarchical material by design, the overall strength of bone is governed by composition and structure. Understanding the structure of the bone-implant interface is essential in the development of novel bone repair materials and strategies, and their long-term success. Here, the current knowledge regarding the eventual structural organisation of the bone-implant interface is reviewed, with a focus on solid devices intended for permanent anchorage in bone, and certain biomaterials that undergo surface and bulk degradation. The bone-implant interface is a heterogeneous zone consisting of mineralised, partially mineralised, and unmineralised areas. Within the meso-micro-nano-continuum, mineralised collagen fibrils form the structural basis of the bone-implant interface, in addition to accumulation of non-collagenous macromolecules such as osteopontin, bone sialoprotein, and osteocalcin.

Controlled laser texturing of titanium results in reliable osteointegration

We have developed a laser-textured superhydrophilic Ti-6Al-4V surface with unique surface chemistry and topography that substantially promotes osteoblast adhesion in culture. Here we investigate the osteointegration of laser-textured implants in an ovine model. Our hypothesis was that laser-textured implants, without any surface coating (LT), would encourage comparable amounts of bone-implant contact and interfacial strength when compared with widely accepted hydroxyapatite (HA) coated implants. Additionally, we hypothesized that LT would significantly increase bony integration compared with machine-finished (MF) and grit-blasted (GB) implants. Forty-eight tapered transcortical pins were implanted into six sheep. Four experimental groups (LT, HA, MF, and GB) were investigated (n = 12) and implants remained in vivo for 6 weeks. Bone apposition rates, interfacial shear strength, and bone-implant contact (BIC) were quantified. The interfacial strength of LT and HA implants were found to be significantly greater than GB (p = 0.032 and p = 0.004) and MF (p = 0.004 and p = 0.004, respectively), but no significant difference between LT and HA implants was observed. Significantly increased BIC was measured adjacent to HA implants when compared with both LT and GB implant surfaces (p = 0.022 and p = 0.006, respectively). No significant difference was found when LT and GB implants were compared. However, all surface finishes encouraged significantly increased BIC when compared with the MF surface. Maximizing implant fixation to host bone is vital for its long-term success. The production of an LT surface is a simple and cheap manufacturing process and this study demonstrated that laser-textured implants are a very promising technical development that warrants further research. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:820-828, 2017.

Laser-treated stainless steel mini-screw implants: 3D surface roughness, bone-implant contact, and fracture resistance analysis

BACKGROUND/OBJECTIVES

This study investigated the biomechanical properties and bone-implant intersurface response of machined and laser surface-treated stainless steel (SS) mini-screw implants (MSIs).

MATERIAL AND METHODS

Forty-eight 1.3mm in diameter and 6mm long SS MSIs were divided into two groups. The control (machined surface) group received no surface treatment; the laser-treated group received Nd-YAG laser surface treatment. Half in each group was used for examining surface roughness (Sa and Sq), surface texture, and facture resistance. The remaining MSIs were placed in the maxilla of six skeletally mature male beagle dogs in a randomized split-mouth design. A pair with the same surface treatment was placed on the same side and immediately loaded with 200 g nickel-titanium coil springs for 8 weeks. After killing, the bone-implant contact (BIC) for each MSI was calculated using micro computed tomography. Analysis of variance model and two-sample t test were used for statistical analysis with a significance level of P <0.05.

RESULTS

The mean values of Sa and Sq were significantly higher in the laser-treated group compared with the machined group (P <0.05). There were no significant differences in fracture resistance and BIC between the two groups.

LIMITATION

animal study

CONCLUSIONS/IMPLICATIONS

Laser treatment increased surface roughness without compromising fracture resistance. Despite increasing surface roughness, laser treatment did not improve BIC. Overall, it appears that medical grade SS has the potential to be substituted for titanium alloy MSIs.

Bone-implant interface shear modulus and ultimate stress in a transcortical rabbit model of open-pore Ti6Al4V implants

This experimental study on laser-textured implants aimed to evaluate periimplant bone elasticity and ultimate stress of the bone-implant interface in a rabbit femur model. After randomization, two cylindrical Ti6Al4V samples (3.5 mm wide, 5.5 mm long) were transcortically implanted in each femur of 15 female New Zealand White Rabbits. Polished implants had been laser-textured with 100, 200, and 300 microm diameter pores, and another corundum blasted implant was additionally textured with 200 microm pores. Twelve weeks into the experiment, a modified push-out test was performed. The median shear modulus indicating the elasticity of the periimplant bone was 41.12 MPa for the proximal implant location and 25.38 MPa for the distal, without evidence for significant differences between implant types. Taking into account the median ultimate shear stress for 200 microm implants with and without corundum blasting, no significant difference could be demonstrated. However, for blasted 200 microm implants a statistically significant (p<0.025) relative gain in ultimate shear stress of 41% and 17% was proven in comparison with 100 and 300 microm implants, respectively. Non-blasted 200 microm implants reached 48% relative gain in respect of 100 microm samples.