https://material.karlov.mff.cuni.cz/people/janecek/studenti/FyzMetNano/Estrin_AM61_2013_782.pdf

Extreme grain refinement by severe plastic deformation: A wealth of challenging science

Twenty-five years of ultrafine-grained materials: achieving exceptional properties through grain refinement

The influence of nano-scale surface roughness on bacterial adhesion to ultrafine-grained titanium

Metallic biomaterials are engineered systems designed to provide internal support to biological tissues and they are being used largely in joint replacements, dental implants, orthopaedic fixations and stents. Higher biomaterial usage is associated with an increased incidence of implant-related complications due to poor implant integration, inflammation, mechanical instability, necrosis and infections, and associated prolonged patient care, pain and loss of function. In this review, we will briefly explore major representatives of metallic biomaterials along with the key existing and emerging strategies for surface and bulk modification used to improve biointegration, mechanical strength and flexibility of biometals, and discuss their compatibility with the concept of 3D printing.

Metallic Biomaterials: Current Challenges and Opportunities.

It is now well established that the processing of bulk solids through the application of severe plastic deformation (SPD) leads to exceptional grain refinement to the submicrometer or nanometer level. Extensive research over the last decade has demonstrated that SPD processing also produces unusual phase transformations and leads to the introduction of a range of nanostructural features, including nonequilibrium grain boundaries, deformation twins, dislocation substructures, vacancy agglomerates, and solute segregation and clustering. These many structural changes provide new opportunities for fine tuning the characteristics of SPD metals to attain major improvements in their physical, mechanical, chemical, and functional properties. This review provides a summary of some of these recent developments. Special emphasis is placed on the use of SPD processing in achieving increased electrical conductivity, superconductivity, and thermoelectricity, an improved hydrogen storage capability, materials for use in biomedical applications, and the fabrication of high-strength metal-matrix nanocomposites.

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Producing Bulk Ultrafine-Grained Materials by Severe Plastic Deformation: Ten Years Later

Metallic materials, for example, stainless steel, titanium and its alloys, and tantalum, are widely used for medical implants in trauma surgery, orthopedic and oral medicine. Successful incorporation of these materials for design, fabrication and application of medical devices require that they meet several critical criteria. Paramount is their biocompatibility as expressed by their relative reactivity with human tissues. Another is their ability to provide sufficient mechanical strength, especially under cyclic loading conditions to ensure the durability of the medical devices made therefrom. Finally the material should be machinable and formable thereby enabling device fabrication at an affordable cost. In this paper we show that nanostructured commercial purity titanium produced by severe plastic deformation (SPD) opens new avenues and concepts for medical implants, providing benefits in all areas of medical device technology. Numerous clinical studies of medical devices fabricated from commercial purity (CP) titanium for trauma, orthopaedic and oral medicine has proven its excellent biocompatibility. However the mechanical strength of CP titanium is relatively low compared to other metals used in biomedical devices. Whereas the strength of this material can be increased by either alloying or secondary processing, for example rolling, drawing, etc., these enhancements normally come with some degradation in biometric response and fatigue behaviour. Recently it has been shown that nanostructuring of CP titanium by SPD processing can provide a new and promising alternative method for improving the mechanical properties of this material. This approach also has the benefit of enhancing the biological response of the CP titanium surface. This paper reports the results of the first developments and studies of nanostructured titanium (n-Ti), produced as long-sized rods with superior mechanical and biomedical properties and demonstrates its applicability for dental implants. The effort was conducted using commercially pure Grade 4 titanium [C – 0.052 %, O2 – 0.34 %, Fe – 0.3 %, N – 0.015 %, Ti-bal. (wt. pct.)]. Nanostructuring involved SPD processing by equal-channel angular pressing followed by thermo-mechanical treatment (TMT) using forging and drawing to produce 7 mm diameter bars with a 3 m length. This processing resulted in a large reduction in grain size, from the 25 lm equiaxed grain structure of the initial titanium rods to 150 nm after combined SPD and TMT processing, as shown in Figure 1. The selected area electron diffraction pattern, Figure 1(c), further suggests that the ultra fine grains contained predominantly high-angle non-equilibrium grain boundaries with increased grain-to-grain internal stresses. A similar structure for CP Ti can be produced in small discs using other SPD methods, for example – high pressure torsion (HPT) as studied in detail. In the present work it was essential to produce homogeneous ultrafine-grained structure throughout a three-meter length rod to enable the pilot production of implants and provide sufficient material for thorough testing of the mechanical and bio-medical properties of the nanostructured titanium. Table 1 illustrates mechanical property benefits attainable by nanostructuring of CP titanium, for example, the strength of the nanostructured titanium is nearly twice that of conventional CP titanium. Notably this improvement has been achieved without the drastic ductility reductions (to below C O M M U N IC A IO N S

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Nanostructured titanium for biomedical applications

Nanostructured titanium (nTi) with essential enhanced strength and fatigue characteristics is an advanced material for dental implant applications. Nano Ti is commercially pure titanium, that was nanostructured by a special technique of severe plastic deformation. It is bio inert, does not contain even potentially toxic or allergenetic additives and has significantly higher specific strength properties than any other titanium applied in dental implants. Cylindrical threaded screw implants Nanoimplant® sized 2.4 mm in diameter and 12 mm in length were made from nTi. It is the first application of nTi dental implant in the world reported. Recently more than 250 successful clinical applications dealing with surgery on the front teeth were carried out. No complications were noticed during the early postoperative period and early loading. Laboratory cytocompatibility tests undertaken so far on mice fibroblast cells have indicated that nanocrystalline Ti surface has a significantly better property for cell colonisation and healing of tissue consequently.

Nanostructured SPD Processed Titanium for Medical Implants

Nanostructured commercially pure titanium (CP Ti) has become technologically and commercially interesting because of its enhanced mechanical and functional properties. The superior strength of nanostructured CP Ti provides an opportunity to reduce the size of biomedical implants so miniaturized implants can bear the same mechanical load as their conventional counterparts. Improved biocompatibility and bioactivity of nanostructured CP Ti allow the minimization of the postsurgery rehabilitation period of patients. This chapter gives an overview on the application of nanostructured CP Ti in two types of implants: small-diameter dental implants and maxillofacial mini-implants. For these medical applications, > 9000 nanostructured items have been placed with no reported cases of failure. Attention is also paid to the commercially viable processing routes for manufacturing of nanostructured CP Ti, its superior mechanical properties and functional performance, and the future prospective uses of this unique material in biomedical engineering.

Nanostructured commercially pure titanium for development of miniaturized biomedical implants

Titanium offers excellent biocompatibility and extraordinary mechanical properties. As a result, it is used as a material for dental implants. Implants infected by peri-implantitis can be cleaned for successful re-osseointegration. Optimal surface properties, such as roughness and wettability, have a significant impact on cell adhesion. The aim of this study was to evaluate the adhesion and proliferation of osteoblasts on the surface of repeatedly cleaned nanostructured titanium samples. Human osteoblast-like cells MG-63 were seeded on nanostructured titanium specimens manufactured from rods produced by the equal channel angular pressing. For surface characterization, roughness and wettability were measured. Cell adhesion after 2 h as well as cell proliferation after 48 h from plating was assessed. We have found that this repeated cleaning of titanium surface reduced cell adhesion as well as proliferation. These events depend on interplay of surface properties, such as wettability, roughness and topography. It is difficult to distinguish which factors are responsible for these events and further investigations will be required. However, even after the several rounds of repeated cleaning, there was a certain rate of adhesion and proliferation recorded. Therefore the attempts to save failing implants by using in situ cleaning are promising.

Ludek Dluhoš

Papers

Nanostructured titanium for biomedical applications

Nanostructured SPD Processed Titanium for Medical Implants

Nanostructured commercially pure titanium for development of miniaturized biomedical implants

Repeated Exposure of Nanostructured Titanium to Osteoblasts with Respect to Peri-Implantitis.

Bulk nanostructured metals for advanced medical implants and devices