In vitro and in vivo studies of ultrafine-grain Ti as dental implant material processed by ECAP

Usability of the ECAP-Conform process for the production of dental implants material

This study addresses the applicability of the ECAP-Conform process for the production of strengthened titanium to produce dental implants. For this purpose, the commercially pure titanium (CP-Ti) grade 2 was subjected to the ECAP-Conform process with a square cross-section die (at a temperature of 240 °C). This process improved the mechanical properties of CP-Ti grade 2 after one pass, such that both strength and hardness have increased by 35%. The functional properties of dental implants produced from the strengthened titanium and the as-received CP-Ti were compared. It was found that the average grain was reduced from 8.35 μm to 2.35 μm after one pass ECAP-Conform process (i.e. about 72% reduction in grain size). Also, the strength and energy absorption of CP-Ti dental implants made after one pass ECAP-Conform increased by 53% and 139%, respectively.

Recent Progress on Nanocrystalline Metallic Materials for Biomedical Applications

Nanocrystalline (NC) metallic materials have better mechanical properties, corrosion behavior and biocompatibility compared with their coarse-grained (CG) counterparts. Recently, nanocrystalline metallic materials are receiving increasing attention for biomedical applications. In this review, we have summarized the mechanical properties, corrosion behavior, biocompatibility, and clinical applications of different types of NC metallic materials. Nanocrystalline materials, such as Ti and Ti alloys, shape memory alloys (SMAs), stainless steels (SS), and biodegradable Fe and Mg alloys prepared by high-pressure torsion, equiangular extrusion techniques, etc., have better mechanical properties, superior corrosion resistance and biocompatibility properties due to their special nanostructures. Moreover, future research directions of NC metallic materials are elaborated. This review can provide guidance and reference for future research on nanocrystalline metallic materials for biomedical applications.

Surface Modification Techniques to Produce Micro/Nano-scale Topographies on Ti-Based Implant Surfaces for Improved Osseointegration

Titanium and titanium alloys are used as artificial bone substitutes due to the good mechanical properties and biocompatibility, and are widely applied in the treatment of bone defects in clinic. However, Pure titanium has stress shielding effect on bone, and the effect of titanium-based materials on promoting bone healing is not significant. To solve this problem, several studies have proposed that the surface of titanium-based implants can be modified to generate micro or nano structures and improve mechanical properties, which will have positive effects on bone healing. This article reviews the application and characteristics of several titanium processing methods, and explores the effects of different technologies on the surface characteristics, mechanical properties, cell behavior and osseointegration. The future research prospects in this field and the characteristics of ideal titanium-based implants are proposed.

Impact of Preparation of Titanium Alloys on Their Abrasive Water Jet Machining

Several titanium alloys, i.e., grade 2 Ti, Ti6Al4V and NiTi alloy, prepared by selected deformation procedures were subjected to abrasive water jet (AWJ) cutting and subsequently analysed. The study describes samples’ preparations and respective material structures. The impact of deformation processing of the selected alloys on the declination angle during cutting, and the results of measurements of surface wall quality performed for the selected samples at the Department of Physics of Faculty of Electrical Engineering and Computer Science at VŠB–Technical University of Ostrava, are presented and discussed, as are also the influences of structural features of the processed titanium alloys on surface qualities of the investigated samples. The results showed that the highest resistance to AWJ machining exhibited the Ti6Al4V alloy prepared by forward extrusion. Its declination angle (recalculated to the thickness 10 mm to compare all the studied samples) was 12.33° at the traverse speed of 100 mm/min, pumping pressure of 380 MPa, and abrasive mass flow rate of 250 g/min.

The Effects of Chemical Etching and Ultra-Fine Grain Structure of Titanium on MG-63 Cells Response

In this work, we study the influence of the surface properties of ultrafine grained (UFG) and coarse grained (CG) titanium on the morphology, viability, proliferation and differentiation of osteoblast-like MG-63 cells. Wet chemical etching in H2SO4/H2O2 and NH4OH/H2O2 solutions was used for producing surfaces with varying morphology, topography, composition and wettability. The topography and morphology have been studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The composition was determined by time of flight mass-spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS). The results showed that it is possible to obtain samples with different compositions, hydrophilicity, topography and nanoscale or/and microscale structures by changing the etching time and the type of etching solution. It was found that developed topography and morphology can improve spreading and proliferation rate of MG-63 cells. A significant advantage of the samples of the UFG series in comparison with CG in adhesion, proliferation at later stages of cultivation (7 days), higher alkaline phosphatase (ALP) activity and faster achievement of its maximum values was found. However, there is no clear benefit of the UFG series on osteopontin (OPN) expression. All studied samples showed no cytotoxicity towards MG-63 cells and promoted their osteogenic differentiation.

Biological Applications of Severely Plastically Deformed Nano-Grained Medical Devices: A Review

Metallic materials are widely used for fabricating medical implants due to their high specific strength, biocompatibility, good corrosion properties, and fatigue resistance. Recently, titanium (Ti) and its alloys, as well as stainless steel (SS), have attracted attention from researchers because of their biocompatibility properties within the human body; however, improvements in mechanical properties while keeping other beneficial properties unchanged are still required. Severe plastic deformation (SPD) is a unique process for fabricating an ultra-fine-grained (UFG) metal with micrometer- to nanometer-level grain structures. SPD methods can substantially refine grain size and represent a promising strategy for improving biological functionality and mechanical properties. This present review paper provides an overview of different SPD techniques developed to create nano-/ultra-fine-grain-structured Ti and stainless steel for improved biomedical implant applications. Furthermore, studies will be covered that have used SPD techniques to improve bone cell proliferation and function while decreasing bacterial colonization when cultured on such nano-grained metals (without resorting to antibiotic use).

3D X-ray micro-computed tomography imaging for the microarchitecture evaluation of porous metallic implants and scaffolds

As an advanced microscopy technology with strong sample adaptability and non-destructive three-dimensional (3D) characteristics, X-ray micro-computed tomography (Micro-CT) can establish the overall connection between various microarchitecture parameters and accelerate the research process of porous metallic implants and scaffolds. In this review, the Micro-CT based quantitative evaluation methods of microarchitecture and bone formation are investigated. To ensure reliability of the results, the Micro-CT setup is discussed briefly and the essential image processing algorithms are introduced in detail. The significance and limitations of Micro-CT are analyzed in the context of research on porous metallic implants. We also discuss the future development of Micro-CT technology in the field of biological tissue engineering.

Surface Characteristics and Biocompatibility of Ultrafine-Grain Ti after Sandblasting and Acid Etching for Dental Implants

This study investigated the surface characteristics and biocompatibility of ultrafine-grain pure titanium (UFG Ti) after sandblasting and acid etching (SLA) treatment to determine an effective method for modification of UFG Ti dental implants. The UFG Ti was processed by equal-channel angular pressing (ECAP). The micromorphology, roughness, and wettability of its surface were studied after SLA modification in different conditions. Rat bone marrow mesenchymal stem cells were subsequently seeded onto the specimens to evaluate the biocompatibility of cell adhesion, proliferation, and differentiation compared with commercially pure titanium (CP Ti). The results showed that surface characteristics of UFG Ti were affected by the pressure of sandblasting and acid etching time in addition to material properties. The favorable hierarchical porous structure that would benefit cell adhesion was formed on the UFG Ti surface when the pressure of sandblasting was 0.6 MPa and the acid etching time was 5 min; at this time, UFG Ti promoted proliferation and differentiation to a greater extent than CP Ti because of its excellent wettability. From this study, it could be seen that UFG Ti can be used as a dental implant material after proper surface modification.

Review on titanium and titanium based alloys as biomaterials for orthopaedic applications

Variety of implant materials have been employed in various disciplines of medical science depending on the requirement of a particular application. Metals, alloys, ceramics, and polymers are the commonly used biomaterials. The main focus of this study is to review the various structural and microstructural properties of titanium and titanium based alloys used as orthopaedic implants. Orthopaedic implants need to possess certain important qualities to ensure their safe and effective use. These properties like the biocompatibility, relevant mechanical properties, high corrosion and wear resistance and osseointegration are summarized in this review. Various attempts to improve upon these properties like different processing routes, surface modifications have also been inculcated in the paper to provide an insight into the extent of research and effort that has been put into developing a highly superior titanium orthopaedic implant.

Outsmarting superbugs: bactericidal activity of nanostructured titanium surfaces against methicillin- and gentamicin-resistantStaphylococcus aureusATCC 33592

The colonisation of biomaterial surfaces by pathogenic bacteria is a significant issue of concern, particularly in light of the rapid rise of antibiotic resistance.

Comprehensive Evaluation of the Properties of Ultrafine to Nanocrystalline Grade 2 Titanium Wires

This paper describes the mechanical properties and microstructure of commercially pure titanium (Grade 2) processed with Conform severe plastic deformation (SPD) and rotary swaging techniques. This technology enables ultrafine-grained to nanocrystalline wires to be produced in a continuous process. A comprehensive description is given of those properties which should enable straightforward implementation of the material in medical applications. Conform SPD processing has led to a dramatic refinement of the initial microstructure, producing equiaxed grains already in the first pass. The mean grain size in the transverse direction was 320 nm. Further passes did not lead to any additional appreciable grain refinement. The subsequent rotary swaging caused fine grains to become elongated. A single Conform SPD pass and subsequent rotary swaging resulted in an ultimate strength of 1060 MPa and elongation of 12%. The achieved fatigue limit was 396 MPa. This paper describes the production possibilities of ultrafine to nanocrystalline wires made of pure titanium and points out the possibility of serial production, particularly in medical implants.

Osseointegration of ultrafine-grained titanium with a hydrophilic nano-patterned surface: an in vivo examination in miniature pigs

Advances in biomaterials science and implant surface technology have made dental implants more predictable and implant therapy more attractive to patients. Surgical interventions are becoming less invasive, and patients heal faster and suffer less morbidity. In this preclinical in vivo study, we compared a new ultra-fine grained titanium (ufgTi) implant material with a hydrophilic nano-patterned surface to commercially pure titanium (cpTi) in a well-established animal model. CpTi grade 4 was subjected to Equal Channel Angular Pressing (ECAP), followed by a cold drawing process that provided ultra-fine-grained titanium (ufgTi) with a mean grain size of 300 nm. After metallographic assessment, the surface topography was characterized by laser confocal microscopy and atomic force microscopy. UfgTi and cpTi implants were inserted in the mandible and maxilla of miniature pigs that healed for 4 and for 8 weeks. Osseointegration was assessed by biomechanical torque out analysis, histomorphometric evaluation, and micro-CT analysis. The metallographic properties of UfgTi were significantly better than those of cpTi. Their surface topographies had similar hydrophilic nano-patterned characteristics, with no significant differences in the nanometre range. Histomorphometric and biomechanical torque out analysis revealed no significant differences between ufgTi and cpTi in environments of either low (maxilla) or high (mandible) bone density. We obtained high bone-to-implant contact values irrespective of the bony microarchitecture even when the bone mineral density was low. Overall, this investigation suggests that ufgTi forms a hydrophilic nano-patterned surface with superior metallographic properties compared to cpTi and high levels of osseointegration. Thus, ufgTi has therapeutic potential as a future strategy for the development of small diameter implants to enable less invasive treatment concepts, reduce patient morbidity and may also lower the costs of patient care.

In vitro corrosion behavior and biocompatibility of nanostructured Ti6Al4V

Ti6Al4V (TC4) alloy has long been used as a bone interfacing implant material in dentistry and orthopedics due to its excellent biocompatibility and mechanical properties. The performance of TC4 can be further tailored by altering its grain structures. In this study, by means of sliding friction treatment (SFT), a nano-grained (NG) surface layer with an average grain size of ≤100 nm on the topmost surface was successfully generated on coarse-grained (CG) TC4 alloy sheet. It was shown that the NG surface possessed notably enhanced corrosion resistance in physiological solution compared to the CG surface, due to the formation of thicker and denser passive film facilitated by surface nanocrystallization. Additionally, the NG surface with stronger hydrophilicity favorably altered the absorption of anchoring proteins such as fibronectin (Fn) and vitronectin (Vn) that can mediate subsequent osteoblast functions. The in vitro results indicated that the NG surface exhibited remarkable enhancement in osteoblast adherence, spreading and proliferation, and obviously accelerated the osteoblast differentiation as compared to CG surface. Moreover, the NG surface also demonstrated good hemocompatibility. These findings suggest that SFT can endure bio-metals with advanced multifunctional properties for biomedical applications.

The Microdamage and Expression of Sclerostin in Peri-implant Bone under One-time Shock Force Generated by Impact

Osseointegration is the key to implant stability and occlusal support. Biomechanical response and remodeling of peri-implant bone occurs under impact loading. Sclerostin participates in bone formation and resorption through Wnt and RANKL pathways. However the mechanism of microdamage and expression of sclerostin in peri-implant bone under impact load is still unclear. In present study, specific impact forces were applied to the implants with favorable osseointegration in rabbits. The microdamage of peri-implant bone and the expression of sclerostin, β-catenin and RANKL during the process of bone damage and remodeling were investigated by micro-CT, histology, immunofluorescence and RT-qPCR analysis. Interface separation and trabecular fracture were found histologically, which were consistent with micro-CT analyses. Throughout remodeling, bone resorption was observed during the first 14 days after impact, and osseointegration and normal trabecular structure were found by 28 d. The expression of sclerostin and RANKL increased after impact and reached a maximum by 14 d, then decreased gradually to normal levels by 28 d. And β-catenin expression was opposite. Results indicated that sclerostin may involve in the peri-implant bone damage caused by impact and remodeling through Wnt/β-catenin and RANKL/RANK pathways. It will provide a new insight in the diagnosis and treatment for patients suffering impact.

Investigation of the mechanical and chemical characteristics of nanotubular and nano-pitted anodic films on grade 2 titanium dental implant materials

OBJECTIVE

The objective of this study was to investigate the reproducibility, mechanical integrity, surface characteristics and corrosion behavior of nanotubular (NT) titanium oxide arrays in comparison with a novel nano-pitted (NP) anodic film.

METHODS

Surface treatment processes were developed to grow homogenous NT and NP anodic films on the surface of grade 2 titanium discs and dental implants. The effect of process parameters on the surface characteristics and reproducibility of the anodic films was investigated and optimized. The mechanical integrity of the NT and NP anodic films were investigated by scanning electron microscopy, surface roughness measurement, scratch resistance and screwing tests, while the chemical and physicochemical properties were investigated in corrosion tests, contact angle measurement and X-ray photoelectron spectroscopy (XPS).

RESULTS AND DISCUSSION

The growth of NT anodic films was highly affected by process parameters, especially by temperature, and they were apt to corrosion and exfoliation. In contrast, the anodic growth of NP film showed high reproducibility even on the surface of 3-dimensional screw dental implants and they did not show signs of corrosion and exfoliation. The underlying reason of the difference in the tendency for exfoliation of the NT and NP anodic films is unclear; however the XPS analysis revealed fluorine dopants in a magnitude larger concentration on NT anodic film than on NP surface, which was identified as a possible causative. Concerning other surface characteristics that are supposed to affect the biological behavior of titanium implants, surface roughness values were found to be similar, whereas considerable differences were revealed in the wettability of the NT and NP anodic films.

CONCLUSION

Our findings suggest that the applicability of NT anodic films on the surface of titanium bone implants may be limited because of mechanical considerations. In contrast, it is worth to consider the applicability of nano-pitted anodic films over nanotubular arrays for the enhancement of the biological properties of titanium implants.

TiO2 nanorod arrays modified Ti substrates promote the adhesion, proliferation and osteogenic differentiation of human periodontal ligament stem cells

Nanostructure coating on titanium (Ti) implants is well known as a cue for directing osteoblast behavior and function. However, effects of nanostructure coatings on dental stem cells have been rarely explored. In this work, assembled TiO₂ nanorod arrays (TNRs) were fabricated on the polished Ti substrates using hydrothermal and sintering methods. The adhesion, morphology, proliferation and osteogenic differentiation of human periodontal ligament stem cells (PDLSCs) seeded onto TNRs substrates were evaluated. Ti substrates were used as control. Rougher TNRs showed better hydrophilicity and protein adsorption capacity compared with Ti control. When seeded on TNRs substrates, PDLSCs exhibited more stretched morphology and higher proliferation rate. Cytoskeletal F-actin expression was markedly promoted for PDLSCs cultured on TNRs substrates under osteogenic induction. Alkaline phosphatase (ALP) activity and mineral deposition were also enhanced by TNRs. Moreover, osteogenesis-related markers of ALP, runt related transcription factor 2 (Runx2) and osteopontin (OPN) of PDLSCs cultured on TNRs substrates were significantly up-regulated at both gene and protein levels when compared to Ti substrates. In conclusion, the unique structure of TNRs provided a biocompatible platform for modulating morphology and function of PDLSCs. The promotion of osteogenic differentiation indicated that the surface modification of implants with TNRs may improve the osteogenic activity of implants and the bone-implant integration in future clinical applications.