Multiscale porous titanium surfaces via a two-step etching process for improved mechanical and biological performance

Effect on osseointegration of dental implants treated with carboxyethylphosphonic acid and functionalized with BMP-2: preliminary study on a minipig model

Introduction: Rough titanium surfaces biofunctionalised by osteogenic proteins, such as BMP-2, have been shown to accelerate the osseointegration process and reduce waiting times for prosthetic loading. The preclinical study presented here compared the bone in contact with the implant and bone neoformation and density between titanium (Ti) implants with a conventional etched surface (SLA type) and others treated with carboxyethylphosphonic acid (CEPA) and bone morphogenetic protein 2 (BMP-2), after 4 weeks of implantation in the tibia of a minipig model. Methods: Sixteen implants (eight experimental and eight control) of Ti-Al16-V4 with a tapered screw design and internal hexagonal connection were randomly inserted into the tibiae of four minipigs, four in each tibia. The experimental implants were treated with CEPA and BMP-2 and sterilised with gamma radiation (25 KG). The insertion torque was 40 N and primary stability was measured with the Osstell® device (ISQ 64 ± 2.6). Five bone parameters were evaluated: bone in contact with the implant (BIC), bone in contact with the corrected implant (BICc), new bone formation (BV/TV), bone density between threads (BAI/TA) and peri-implant bone density (BAP/TA). A histomorphometric study was performed and the samples were digitised with Adobe Photoshop Cs6. Statistical analysis of the variables was performed using SAS 9.4. Results: After a period of 4 weeks, no significant clinical signs were observed and all implants were integrated. Light microscopy of the experimental group revealed an ICB with no signs of fiber tissue, but with areas of ectopic new bone in the medullary space. Statistical analysis showed significant results for BIC and BICc (p = 0.0001 and p = 0.001, respectively). No statistical signification was found for the other parameters evaluated. Conclusion: Despite the limitations of this study, our results demonstrated that dental implant surfaces treated with CEPA and BMP-2 improve their biological response to osseointegration.

Why Is Tantalum Less Susceptible to Bacterial Infection?

Periprosthetic infection is one of the trickiest clinical problems, which often leads to disastrous consequences. The emergence of tantalum and its derivatives provides novel ideas and effective methods to solve this problem and has attracted great attention. However, tantalum was reported to have different anti-infective effects in vivo and in vitro, and the inherent antibacterial capability of tantalum is still controversial, which may restrict its development as an antibacterial material to some extent. In this study, the polished tantalum was selected as the experimental object, the implant-related tibia osteomyelitis model was first established to observe whether it has an anti-infective effect in vivo compared to titanium, and the early studies found that the tantalum had a lower infectious state in the implant-related tibia osteomyelitis model in vivo than titanium. However, further in vitro studies found that the polished tantalum was not superior to the titanium against bacterial adhesion and antibacterial efficacy. In addition, we focus on the state of interaction between cells, bacteria and materials to restore the internal environment as realistically as possible. We found that the adhesion of fibroblasts to tantalum was faster and better than that of titanium. Moreover, what is more, interesting is that, in the early period, bacteria were more likely to adhere to cells that had already attached to the surface of tantalum than to the bare surface of it, and over time, the cells eventually fell off the biomaterials and took away more bacteria in tantalum, making it possible for tantalum to reduce the probability of infection in the body through this mechanism. Moreover, these results also explained the phenomenon of the "race for the surface" from a completely different perspective. This study provides a new idea for further exploring the relationship between bacteria and host tissue cells on the implant surface and a meaningful clue for optimizing the preparation of antibacterial implants in the future.

Improvement of osseointegration efficacy of titanium implant through plasma surface treatment

A novel plasma treatment source for generating cylindrical plasma on the surface of titanium dental implants is developed herein. Using the titanium implant as an electrode and the packaging wall as a dielectric barrier, a dielectric barrier discharge (DBD) plasma was generated, allowing the implant to remain sterile. Numerical and experimental investigations were conducted to determine the optimal discharge conditions for eliminating hydrocarbon impurities, which are known to degrade the bioactivity of the implant. XPS measurement confirmed that plasma treatment reduced the amount of carbon impurities on the implant surface by approximately 60%. Additionally, in vitro experiments demonstrated that the surface treatment significantly improved cell adhesion, proliferation, and differentiation. Collectively, we proposed a plasma treatment source for dental implants that successfully removes carbon impurities and facilitate the osseointegration of SLA implants.

Tailoring of TiAl6V4 Surface Nanostructure for Enhanced In Vitro Osteoblast Response via Gas/Solid (Non-Line-of-Sight) Oxidation/Reduction Reactions

An aging global population is accelerating the need for better, longer-lasting orthopaedic and dental implants. Additive manufacturing can provide patient-specific, titanium-alloy-based implants with tailored, three-dimensional, bone-like architecture. Studies using two-dimensional substrates have demonstrated that osteoblastic differentiation of bone marrow stromal cells (MSCs) is enhanced on surfaces possessing hierarchical macro/micro/nano-scale roughness that mimics the topography of osteoclast resorption pits on the bone surface. Conventional machined implants with these surfaces exhibit successful osseointegration, but the complex architectures produced by 3D printing make consistent nanoscale surface texturing difficult to achieve, and current line-of-sight methods used to roughen titanium alloy surfaces cannot reach all internal surfaces. Here, we demonstrate a new, non-line-of-sight, gas/solid-reaction-based process capable of generating well-controlled nanotopographies on all open (gas-exposed) surfaces of titanium alloy implants. Dense 3D-printed titanium-aluminum-vanadium (TiAl6V4) substrates were used to evaluate the evolution of surface nanostructure for development of this process. Substrates were either polished to be smooth (for easier evaluation of surface nanostructure evolution) or grit-blasted and acid-etched to present a microrough biomimetic topography. An ultrathin (90 ± 16 nm) conformal, titania-based surface layer was first formed by thermal oxidation (600 °C, 6 h, air). A calciothermic reduction (CaR) reaction (700 °C, 1 h) was then used to convert the surface titania (TiO₂) into thin layers of calcia (CaO, 77 ± 16 nm) and titanium (Ti, 51 ± 20 nm). Selective dissolution of the CaO layer (3 M acetic acid, 40 min) then yielded a thin nanoporous/nanorough Ti-based surface layer. The changes in surface nanostructure/chemistry after each step were confirmed by scanning and transmission electron microscopies with energy-dispersive X-ray analysis, X-ray diffraction, selected area electron diffraction, atomic force microscopy, and mass change analyses. In vitro studies indicated that human MSCs on CaR-modified microrough surfaces exhibited increased protein expression associated with osteoblast differentiation and promoted osteogenesis compared to unmodified microrough surfaces (increases of 387% in osteopontin, 210% in osteocalcin, 282% in bone morphogenic protein 2, 150% in bone morphogenic protein 4, 265% in osteoprotegerin, and 191% in vascular endothelial growth factor). This work suggests that this CaR-based technique can provide biomimetic topography on all biologically facing surfaces of complex, porous, additively manufactured TiAl6V4 implants.

A Review of Biomimetic Topographies and Their Role in Promoting Bone Formation and Osseointegration: Implications for Clinical Use

The use of metallic and polymeric materials for implants has been increasing over the past decade. This trend can be attributed to a variety of factors including a significant increase in basic science research focused on implant material characteristics and how various surface modifications may stimulate osseointegration and, ultimately, fusion. There are many interbody fusion devices and dental implants commercially available; however, detailed information about their surface properties, and the effects that various materials and surface modifications may have on osteogenesis, is lacking in the literature. While the concept of bone-implant osseointegration is a relatively recent addition to the spine fusion literature, there is a comparatively large body of literature related to dental implants. The purpose of this article is to summarize the science of surface modified bone-facing implants, focusing on biomimetic material chemistry and topography of titanium implants, to promote a better understanding of how these characteristics may impact bone formation and osseointegration. This manuscript has the following aspects: highlights the role of titanium and its alloys as potent osteoconductive bioactive materials; explores the importance of biomimetic surface topography at the macro-, micro- and nano-scale; summarizes how material surface design can influence osteogenesis and immune responses in vitro; focuses on the kinds of surface modifications that play a role in the process. Biomimetic surface modifications can be varied across many clinically available biomaterials, and the literature supports the hypothesis that those biomaterial surfaces that exhibit physical properties of bone resorption pits, such as roughness and complex hierarchical structures at the submicron and nanoscale, are more effective in supporting osteoblast differentiation in vitro and osteogenesis in vivo.

Preparation of Zirconium Hydrogen Phosphate Coatings on Sandblasted/Acid-Etched Titanium for Enhancing Its Osteoinductivity and Friction/Corrosion Resistance

Background

Sandblasted/acid-etched titanium (SLA-Ti) implants are widely used for dental implant restoration in edentulous patients. However, the poor osteoinductivity and the large amount of Ti particles/ions released due to friction or corrosion will affect its long-term success rate.

Purpose

Various zirconium hydrogen phosphate (ZrP) coatings were prepared on SLA-Ti surface to enhance its friction/corrosion resistance and osteoinduction.

Methods

The mixture of ZrCl₄ and H₃PO₄ was first coated on SLA-Ti and then calcined at 450°C for 5 min to form ZrP coatings. In addition to a series of physiochemical characterization such as morphology, roughness, wettability, and chemical composition, their capability of anti-friction and anti-corrosion were further evaluated by friction-wear test and by potential scanning. The viability and osteogenic differentiation of MC3T3-E1 cells on different substrates were investigated via MTT, mineralization and PCR assays.

Results

The characterization results showed that there were no significant changes in the morphology, roughness and wettability of ZrP-modified samples (SLA-ZrP0.5 and SLA-ZrP0.7) compared with SLA group. The results of electrochemical corrosion displayed that both SLA-ZrP0.5 and SLA-ZrP0.7 (especially the latter) had better corrosion resistance than SLA in normal saline and serum-containing medium. SLA-ZrP0.7 also exhibited the best friction resistance and great potential to enhance the spreading, proliferation and osteogenic differentiation of MC3T3-E1 cells.

Conclusion

We determined that SLA-ZrP0.7 had excellent comprehensive properties including anti-corrosion, anti-friction and osteoinduction, which made it have a promising clinical application in dental implant restoration.

Influence of porous tantalum scaffold pore size on osteogenesis and osteointegration: A comprehensive study based on 3D-printing technology

The emerging role of porous tantalum (Ta) scaffold for bone tissue engineering is noticed due to its outstanding biological properties. However, it is controversial which pore size and porosity are more conducive for bone defect repair. In the present work, porous tantalum scaffolds with pore sizes of 100-200, 200-400, 400-600 and 600-800 μm and corresponding porosities of 25%, 55%, 75%, and 85% were constructed, using computer aided design and 3D printing technologies, then comprehensively studied by in vitro and in vivo studies. We found that Ta scaffold with pore size of 400-600 μm showed stronger ability in facilitating cell adhesion, proliferation, and osteogenic differentiation in vitro. In vivo tests identified that porous tantalum scaffolds with pore size of 400-600 μm showed better performance of bone ingrowth and integration. In mechanism, computational fluid dynamics analysis proved porous tantalum scaffolds with pore size of 400-600 μm hold appropriate permeability and surface area, which facilitated cell adhesion and proliferation. Our results strongly indicate that pore size and porosity are essential for further applications of porous tantalum scaffolds, and porous tantalum scaffolds with pore size 400-600 μm are conducive to osteogenesis and osseointegration. These findings provide new evidence for further application of porous tantalum scaffolds for bone defect repair.

Osteoconductivity of Porous Titanium Structure on Implants in Osteoporosis

In compromised bone conditions such as osteoporosis, developments of the implant surface are necessary to secure the stability of implants. This study investigated the effect of the surface porous titanium structure (PS) on the osseointegration of implants in osteoporotic bone. Bilateral ovariectomy (OVX) was performed in 4 female beagle dogs to induce osteoporosis for 32 wk. Success of induction was based on the evaluation of bone mineral density by Hounsfield units (HU) in computed tomography images. Posterior teeth in both mandibles were extracted 1 wk after OVX, and a total of 30 implants (15 implants in each group) were placed after 32 wk of osteoporosis induction. The control group implant underwent resorbable blast media (RBM) surface treatment, whereas the test group underwent RBM surface treatment in the coronal two-thirds and a PS added to the apical 3-mm portion. HU values in the mandibular trabecular bone, lumbar, and femoral head significantly decreased 32 wk after OVX, confirming osteoporotic condition after induction. Resonance frequency analysis and removal torque test showed comparable values between the 2 groups at 4 wk after implant placement. The surface topography of the implant after removal showed hard tissue integration at the PS in the test group. Bone-to-implant contact length was greater in the apical portion of the test group, although statistical significance was not found between the groups. Interthread bone area in the apical portion of the test group showed a significant increase compared to the control group (control: 0.059 ± 0.041 mm², test: 0.121 ± 0.060 mm², P = 0.028) with the histological feature of bone ingrowth at the PS. The findings of the study demonstrated that the surface PS could improve osteoconductivity in the osteoporotic trabecular bone by bone ingrowth at the pore space, thereby enhancing the osseointegration and stability of the implants.

Characterization of Titanium Surface Modification Strategies for Osseointegration Enhancement

As biocompatible metallic materials, titanium and its alloys have been widely used in the orthopedic field due to their superior strength, low density, and ease of processing. However, further improvement in biological response is still required for rapid osseointegration. Here, various Ti surface-treatment technologies were applied: hydroxyapatite blasting, sand blasting and acid etching, anodic oxidation, and micro-arc oxidation. The surface characteristics of specimens subjected to these techniques were analyzed in terms of structure, elemental composition, and wettability. The adhesion strength of the coating layer was also assessed for the coated specimens. Biocompatibility was compared via tests of in vitro attachment and proliferation of pre-osteoblast cells.

Molecular Mechanisms of Topography Sensing by Osteoblasts: An Update

Bone is a specialized tissue formed by different cell types and a multiscale, complex mineralized matrix. The architecture and the surface chemistry of this microenvironment can be factors of considerable influence on cell biology, and can affect cell proliferation, commitment to differentiation, gene expression, matrix production and/or composition. It has been shown that osteoblasts encounter natural motifs in vivo, with various topographies (shapes, sizes, organization), and that cell cultures on flat surfaces do not reflect the total potential of the tissue. Therefore, studies investigating the role of topographies on cell behavior are important in order to better understand the interaction between cells and surfaces, to improve osseointegration processes in vivo between tissues and biomaterials, and to find a better topographic surface to enhance bone repair. In this review, we evaluate the main available data about surface topographies, techniques for topographies’ production, mechanical signal transduction from surfaces to cells and the impact of cell–surface interactions on osteoblasts or preosteoblasts’ behavior.

Three-Dimensional, MultiScale, and Interconnected Trabecular Bone Mimic Porous Tantalum Scaffold for Bone Tissue Engineering

To investigate the biocompatibility and bone ingrowth properties of a novel trabecular bone mimic porous tantalum scaffold which holds potential for bone tissue engineering, a novel three-dimensional, multiscale interconnected porous tantalum scaffold was designed and manufactured. The morphology of the novel scaffold was observed with the use of scanning electron microscopy (SEM) and industrial computerized tomography. Mesenchymal stem cells (MSCs) were cultured with novel porous tantalum powder, SEM was carried out for the observation of cell morphology and adhesion, and cytotoxicity was evaluated by the MTT assay. Canine femoral shaft bone defect models were established, and novel porous tantalum rods were used to repair the bone defect. Repair effects and bone integration were evaluated by hard tissue slice examination and push-out tests at the indicated time. We found that the novel porous tantalum scaffold is a trabecular bone mimic, having the characteristics of being three-dimensional, multiscaled, and interconnected. The MSCs adhered to the surface of tantalum and proliferated with time, the tantalum extract did not have a cytotoxic effect on MSCs. In the bone defect model, porous tantalum rods integrated tightly with the host bone, and new bone formation was found on the scaffold-host bone interface both 3 and 6 months after the implantation. Favorable bone ingrowth was observed in the center of the tantalum rod. The push-out test showed that the strength needed to push out the tantalum rod is comparable for both 3 and 6 months when compared with the normal femoral shaft bone tissue. These findings suggested that the novel trabecular bone mimic porous tantalum scaffold is biocompatible and osteoinductive, which holds potential for bone tissue engineering application.

Functionalization of a clustered TiO2 nanotubular surface with platelet derived growth factor-BB covalent modification enhances osteogenic differentiation of bone marrow mesenchymal stem cells

A multitude of micro- and nano-surface structures have been developed to improve the clinical performance of endosseous titanium (Ti) implants. However, most of these surface structures only simulate the topographic elements on a micro- or nano-scale. In this study, a nano-micro hierarchical TiO₂ clustered nanotubular structure was fabricated using anodization, and then functionalized with platelet derived growth factor-BB (PDGF-BB) using PhoA (11-hydroxyundecylphosphonic acid)/CDI (carbonyldiimidazole) chemistry. The resulting 3-dimensional spatial biomimetic structure, named NTPCP, exhibited negligible cytotoxicity and satisfactory bio-activity for host cells, and significantly enhanced the attachment as well as osteogenesis-related functions (early-stage proliferation, extracellular matrix synthesis and mineralization) of human bone marrow mesenchymal stem cells (bMSCs). We observed drastically elevated expression of osteocalcin (OCN), which mirrored prominent bone formation around the NTPCP implants in a rat model. This study establishes a novel strategy to improve the osseointegration of endosseous Ti implants via surface nano-topographic modification and bio-factor covalent functionalization.

Ta ion implanted nanoridge-platform for enhanced vascular responses

Bare metal stents are commonly used in interventional cardiology; they provide successful treatment because of their excellent mechanical properties, expandability ratios, and flexibility. However, their insufficient vascular affinity can induce the development of neointimal hyperplasia following arterial injury and subsequent smooth muscle cell overgrowth in the lumen of a stented vessel. Nanoengineering of the bare metal stent surface is a valuable strategy for eliciting favorable vascular responses. In this study, we introduce a target-ion-induced plasma sputtering (TIPS) technique to fabricate a platform with a favorable endothelial environment. This technique enables the simple single-step production of a Ta-implanted nanoridged surface on a stent with a complex 3D geometry that shows a clear tendency to become oriented parallel to the direction of blood flow. Moreover, the nanoridges developed show good structural integrity and mechanical stability, resulting in apparently stable morphologies under high strain rates. In vitro cellular responses to the Co-Cr, such as endothelialization, platelet activation, and blood coagulation, are considerably altered after TIPS treatment; endothelium formation is rapid and surface thrombogenicity is low. An in vivo rabbit iliac artery model is used to confirm that the nanoridged surface facilitates rapid re-endothelialization and limits the formation of neointima compared to the bare stent. These results indicate that the Ta ion implanted nanoridge platform fabricated using the TIPS technique has immense potential as a solution for in-stent restenosis and ensuring the long-term patency of bare metal stents.

Enhanced Osseointegration Ability of Poly(lactic acid) via Tantalum Sputtering-Based Plasma Immersion Ion Implantation

Poly(lactic acid) (PLA) is the most utilized biodegradable polymer in orthopedic implant applications because of its ability to replace regenerated bone tissue via continuous degradation over time. However, the poor osteoblast affinity for PLA results in a high risk of early implant failure, and this issue remains one of the most difficult challenges with this technology. In this study, we demonstrate the use of a new technique in which plasma immersion ion implantation (PIII) is combined with a conventional DC magnetron sputtering. This technique, referred to as sputtering-based PIII (S-PIII), makes it possible to produce a tantalum (Ta)-implanted PLA surface within 30 s without any tangible degradation or deformation of the PLA substrate. Compared to a Ta-coated PLA surface, the Ta-implanted PLA showed twice the surface roughness and substantially enhanced adhesion stability in dry and wet conditions. The strong hydrophobic surface properties and biologically relatively inert chemical structure of PLA were ameliorated by Ta S-PIII treatment, which produced a moderate hydrophilic surface and enhanced cell-material interactions. Furthermore, in an in vivo evaluation in a rabbit distal femur implantation model, Ta-implanted PLA demonstrated significantly enhanced osseointegration and osteogenesis compared with bare PLA. These results indicate that the Ta-implanted PLA has great potential for orthopedic implant applications.

Reduced fibrous capsule formation at nano-engineered silicone surfaces via tantalum ion implantation

Nano-engineered surface of silicone implant improves the biocompatibility and suppresses the fibrous capsule formation which is the most common side effect of polymeric implants.