Nitinol surface roughness modulates in vitro cell response: a comparison between fibroblasts and osteoblasts

A novel injectable hydrogel containing polyetheretherketone for bone regeneration in the craniofacial region

Polyetheretherketone (PEEK) is an organic material introduced as an alternative for titanium implants. Injectable hydrogels are the most promising approach for bone regeneration in the oral cavity to fill the defects with irregular shapes and contours conservatively. In the current study, injectable Aldehyde-cellulose nanocrystalline/silk fibroin (ADCNCs/SF) hydrogels containing PEEK were synthesized, and their bone regeneration capacity was evaluated. Structure, intermolecular interaction, and the reaction between the components were assessed in hydrogel structure. The cytocompatibility of the fabricated scaffolds was evaluated on human dental pulp stem cells (hDPSCs). Moreover, the osteoinduction capacity of ADCNCs/SF/PEEK hydrogels on hDPSCs was evaluated using Real-time PCR, Western blot, Alizarin red staining and ALP activity. Bone formation in critical-size defects in rats' cranial was assessed histologically and radiographically. The results confirmed the successful fabrication of the hydrogel and its osteogenic induction ability on hDPSCs. Furthermore, in in vivo phase, bone formation was significantly higher in ADCNCs/SF/PEEK group. Hence, the enhanced bone regeneration in response to PEEK-loaded hydrogels suggested its potential for regenerating bone loss in the craniofacial region, explicitly surrounding the dental implants.

Plasma Electrolytic Polishing of Nitinol: Investigation of Functional Properties

A novel, environmentally friendly, fast, and flexible polishing process for Nitinol parts is presented in this study. Nitinol samples with both superelastic and shape memory properties at room temperature were investigated. The chemical contamination and surface roughness of superelastic Nitinol plates were examined before and after plasma electrolytic polishing. The shift in phase transformation temperature and tensile strength before and after the polishing process were analysed using Nitinol wire with shape memory properties. The obtained experimental results were compared to the data obtained on reference samples examined in the as-received condition. It was found that plasma electrolytic polishing, when the right process parameters are applied, is capable of delivering Nitinol parts with extremely high surface quality. Moreover, it was experimentally proven that plasma electrolytic polishing does not have a negative impact on functionality or mechanical properties of polished parts.

Advances in Laser Additive Manufacturing of Ti-Nb Alloys: From Nanostructured Powders to Bulk Objects

The additive manufacturing of low elastic modulus alloys that have a certain level of porosity for biomedical needs is a growing area of research. Here, we show the results of manufacturing of porous and dense samples by a laser powder bed fusion (LPBF) of Ti-Nb alloy, using two distinctive fusion strategies. The nanostructured Ti-Nb alloy powders were produced by mechanical alloying and have a nanostructured state with nanosized grains up to 90 nm. The manufactured porous samples have pronounced open porosity and advanced roughness, contrary to dense samples with a relatively smooth surface profile. The structure of both types of samples after LPBF is formed by uniaxial grains having micro- and nanosized features. The inner structure of the porous samples is comprised of an open interconnected system of pores. The volume fraction of isolated porosity is 2 vol. % and the total porosity is 20 vol. %. Cell viability was assessed in vitro for 3 and 7 days using the MG63 cell line. With longer culture periods, cells showed an increased cell density over the entire surface of a porous Ti-Nb sample. Both types of samples are not cytotoxic and could be used for further in vivo studies.

Osseointegration of Antimicrobial Acrylic Bone Cements Modified with Graphene Oxide and Chitosan

Acrylic bone cement (ABC) is one of the most used materials in orthopedic surgery, mainly for the fixation of orthopedic implants to the bone. However, ABCs usually present lack of biological activity and osseointegration capacity that leads to loosening of the prosthesis. This work reports the effect of introducing graphene oxide (GO) and chitosan (CS), separately or together, in the ABC formulation on setting performance, mechanical behavior, and biological properties. Introduction of both CS and GO to the ABC decreased the maximum temperature by 21% and increased the antibacterial activity against Escherichia coli by 87%, while introduction of only CS decreased bending strength by 32%. The results of cell viability and cell adhesion tests showed in vitro biocompatibility. The in vivo response was investigated using both subdermal and bone parietal implantations in Wistar rats. Modified ABCs showed absence of immune response, as confirmed by a normal inflammatory response in Wistar rat subdermal implantation. The results of the parietal bone implantation showed that the addition of CS and GO together allowed a near total healing bone–cement interface, as observed in the micrographic analysis. The overall results support the great potential of the modified ABCs for application in orthopedic surgery mainly in those cases where osseointegration is required.

Experimental implantoplasty outcomes correlate with fibroblast growth in vitro

BACKGROUND

Implantoplasty is an option in peri-implantitis treatment, but little is known about the effect on the soft tissue. The aim of the study was to characterize surface roughness following experimental implantoplasty and to examine its effect on human fibroblast growth and secretion of selected proteins.

METHODS

Titanium grade IV coins were mechanically treated with six different rotating bur sequences; diamond burs or carbide burs alone, or followed by either Arkansas stone bur or silicone burs. Machined and rough-surface sandblasted, acid-etched (SLA) coins were used as control. The surface topography was characterized by scanning electron microscope and profilometer. Human gingival fibroblasts from two donors were cultured on the coins to quantify the effect on cell morphology, growth, and protein secretion by confocal microscopy and multiplex immunoassay.

RESULTS

All surface roughness parameters were lower for the surfaces treated with experimental implantoplasty than for the SLA surface, and the sequence of carbide burs followed by silicone burs rendered the least rough surface of the test groups. The implantoplasty procedures changed the elemental composition of the titanium surface. High surface roughness showed a weak to moderate negative correlation to fibroblast growth, but induced a higher secretion of VEGF, IL-6 and MCP-3 to the cell medium compared to the least rough surfaces of the test groups. At day 30 fibronectin levels were higher in the SLA group.

CONCLUSIONS

The surface roughness following implantoplasty demonstrated a weak to moderate negative correlation with the growth of fibroblasts. The addition of Arkansas stone and silicon burs to the experimental implantoplasty bur protocol rendered an initial increase in fibroblast growth. Implantoplasty altered the elemental composition of the titanium surface, and had an effect on the fibroblast cytokine secretion and fibronectin levels.

Cell Behavior on 3D Ti-6Al-4 V Scaffolds with Different Porosities

Porous titanium (Ti) and its alloys fabricated by additive manufacturing (AM) techniques have attractive potential for dental and bone defect repair fields. Understanding the relationship between cells and the surface of the as-built three-dimensional (3D) scaffold interactions is not only necessary for tissue engineering but also promising for improving the fabrication process in the manufacture of artificial implants by AM technology. In this study, we have aimed to investigate the cell behavior including adhesion and proliferation of fibroblasts (L929) on Ti-6Al-4 V scaffolds fabricated by the electron beam melting method. The porosities of Ti-6Al-4 V scaffolds are 0% (compact), 60%, and 70%, respectively. Different cell behaviors have been observed from all of the specimens after 4 and 8 days of cell incubation. The present result indicates that, besides the surface roughness, the surface topography of specimens should also be taken into consideration to investigate the interaction between implants and cells. Therefore, this study would provide several possibilities for improving the osteointegration functions of the manufactured porous metallic implants in orthopedic and dental applications.

Influence of macroporosity on NIH/3T3 adhesion, proliferation, and osteogenic differentiation of MC3T3-E1 over bio-functionalized highly porous titanium implant material

Highly porous Ti implant materials are being used in order to overcome the stress shielding effect on orthopedic implants. However, the lack of bioactivity on Ti surfaces is still a major concern regarding the osseointegration process. It is known that the rapid recruitment of osteoblasts in bone defects is an essential prerequisite for efficient bone repair. Conventionally, osteoblast recruitment to bone defects and subsequent bone repair has been achieved using growth factors. Thus, in this study highly porous Ti samples were processed by powder metallurgy using space holder technique followed by the bio-functionalization through microarc oxidation using a Ca- and P-rich electrolyte. The biological response in terms of early cell response, namely, adhesion, spreading, viability, and proliferation of the novel biofunctionalized highly porous Ti was carried out with NIH/3T3 fibroblasts and MC3T3-E1 preosteoblasts in terms of viability, adhesion, proliferation, and alkaline phosphatase activity. Results showed that bio-functionalization did not affect the cell viability. However, bio-functionalized highly porous Ti (22% porosity) enhanced the cell proliferation and activity. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 73-85, 2019.

Biocompatibility and Inflammatory Potential of Titanium Alloys Cultivated with Human Osteoblasts, Fibroblasts and Macrophages

The biomaterials used to maintain or replace functions in the human body consist mainly of metals, ceramics or polymers. In orthopedic surgery, metallic materials, especially titanium and its alloys, are the most common, due to their excellent mechanical properties, corrosion resistance, and biocompatibility. Aside from the established Ti6Al4V alloy, shape memory materials such as nickel-titanium (NiTi) have risen in importance, but are also discussed because of the adverse effects of nickel ions. These might be reduced by specific surface modifications. In the present in vitro study, the osteoblastic cell line MG-63 as well as primary human osteoblasts, fibroblasts, and macrophages were cultured on titanium alloys (forged Ti6Al4V, additive manufactured Ti6Al4V, NiTi, and Diamond-Like-Carbon (DLC)-coated NiTi) to verify their specific biocompatibility and inflammatory potential. Additive manufactured Ti6Al4V and NiTi revealed the highest levels of metabolic cell activity. DLC-coated NiTi appeared as a suitable surface for cell growth, showing the highest collagen production. None of the implant materials caused a strong inflammatory response. In general, no distinct cell-specific response could be observed for the materials and surface coating used. In summary, all tested titanium alloys seem to be biologically appropriate for application in orthopedic surgery.

Influence of different grained powders and pellets made of Niobium and Ti-42Nb on human cell viability

Nowadays, biomaterials can be used to maintain or replace several functions of the human body if necessary. Titanium and its alloys, i.e. Ti6Al4V are the most common materials (70 to 80%) used for structural orthopedic implants due to their unique combination of good mechanical properties, corrosion resistance and biocompatibility. Addition of β-stabilizers, e.g. niobium, can improve the mechanical properties of such titanium alloys further, simultaneously offering excellent biocompatibility. In this in vitro study, human osteoblasts and fibroblasts were cultured on different niobium specimens (Nb Amperit, Nb Ampertec), Nb sheets and Ti-42Nb (sintered and 3D-printed by selective laser melting, SLM) and compared with forged Ti6Al4V specimens. Furthermore, human osteoblasts were incubated with particulates of the Nb and Ti-42Nb specimens in three concentrations over four and seven days to imitate influence of wear debris. Thereby, the specimens with the roughest surfaces, i.e. Ti-42Nb and Nb Ampertec, revealed excellent and similar results for both cell types concerning cell viability and collagen synthesis superior to forged Ti6Al4V. Examinations with particulate debris disclosed a dose-dependent influence of all powders with Nb Ampertec showing the highest decrease of cell viability and collagen synthesis. Furthermore, interleukin synthesis was only slightly increased for all powders. In summary, Nb Ampertec (sintered Nb) and Ti-42Nb materials seem to be promising alternatives for medical applications compared to common materials like forged or melted Ti6Al4V.

Differences in cytocompatibility, dynamics of the oxide layers' formation, and nickel release between superelastic and thermo-activated nickel-titanium archwires

Superelastic (SE) and thermo-activated (TA) nickel-titanium (NiTi) archwires are used in everyday orthodontic practice, based on their acceptable biocompatibility and well-defined shape memory properties. However, the differences in their surface microstructure and cytotoxicity have not been clearly defined, and the standard cytotoxicity tests are too robust to detect small differences in the cytotoxicity of these alloys, all of which can lead to unexpected adverse reactions in some patients. Therefore, we tested the hypothesis that the differences in manufacture and microstructure of commercially available SE and TA archwires may influence their biocompatibility. The archwires were studied as-received and after conditioning for 24 h or 35 days in a cell culture medium under static conditions. All of the tested archwires, including their conditioned medium (CM), were non-cytotoxic for L929 cells, but Rematitan SE (both as received and conditioned) induced the apoptosis of rat thymocytes in a direct contact. In contrast, TruFlex SE and Equire TA increased the proliferation of thymocytes. The cytotoxic effect of Rematitan SE correlated with the higher release of Ni ions in CM, higher concentration of surface Ni and an increased oxygen layer thickness after the conditioning. In conclusion, the apoptosis assay on rat thymocytes, in contrast to the less sensitive standard assay on L929 cells, revealed that Rematitan SE was less cytocompatible compared to other archwires and the effect was most probably associated with a higher exposition of the cells to Ni on the surface of the archwire, due to the formation of unstable oxide layer.

Review and the state of the art: Sol-gel and melt quenched bioactive glasses for tissue engineering

Biomaterial development is currently the most active research area in the field of biomedical engineering. The bioglasses possess immense potential for being the ideal biomaterials due to their high adaptiveness to the biological environment as well as tunable properties. Bioglasses like 45S5 has shown great clinical success over the past 10 years. The bioglasses like 45S5 were prepared using melt-quenching techniques but recently porous bioactive glasses have been derived through sol-gel process. The synthesis route exhibits marked effect on the specific surface area, as well as degradability of the material. This article is an attempt to provide state of the art of the sol-gel and melt quenched bioactive bioglasses for tissue regeneration. Fabrication routes for bioglasses suitable for bone tissue engineering are highlighted and the effect of these fabrication techniques on the porosity, pore-volume, mechanical properties, cytocompatibilty and especially apatite layer formation on the surface of bioglasses is analyzed in detail. Drug delivery capability of bioglasses is addressed shortly along with the bioactivity of mesoporous glasses. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1248-1275, 2016.

Differentiation, apoptosis, and GM-CSF receptor expression of human gingival fibroblasts on a titanium surface treated by a dual acid-etched procedure

OBJECTIVES

Analysis of the effects of titanium surface properties on the biological behavior of human gingival fibroblasts (HGFs).

MATERIALS AND METHODS

HGFs were in vitro cultured on a titanium surface modified by a dual acid-etched procedure and on a control machined surface. Cell adhesion, proliferation, apoptosis, production of certain extracellular matrix (ECM) proteins, and expression of granulocyte macrophage-colony stimulating factor receptor (GM-CSFR) were investigated using in each experiment a total of 18 samples for each titanium surface.

RESULTS

Cell attachment at 3 h of culture was statistically significantly higher on the etched surface. HGF growth increased on both surfaces during the entire experimental period and at day 14 of culture cell proliferation was statistically significantly higher on the treated surface than on the control. No statistically significant differences in percentage of apoptosis events were observed between the surfaces. ECM protein production increased progressively over time on both surfaces. A statistically significant deposition was observed at day 7 and 14 for collagen I and only at day 14 for fibronectin and tenascin, when compared to the baseline. GM-CSFR registered a positive expression on both surfaces, statistically significant at day 14 on the etched surface in comparison with the machined one.

CONCLUSIONS

Data showed that titanium surface microtopography modulates in vitro cell response and phenotypical expression of HGFs. The etched surface promoted a higher cell proliferation and differentiation improving the biological behavior of HGFs.

CLINICAL RELEVANCE

Results suggest a possible beneficial effect of surface etching modification on peri-implant biological integration and soft tissue healing which is critical for the formation of a biological seal around the neck of dental implants.

A mild process to design silk scaffolds with reduced β-sheet structure and various topographies at the nanometer scale

Three-dimensional (3-D) porous silk scaffolds with good biocompatibility and minimal immunogenicity show promise in a range of tissue regeneration applications. However, the challenge remains to effectively fabricate their microstructures and mechanical properties to satisfy the specific requirements of different tissues. In this study, silk scaffolds were fabricated to form an extracellular matrix (ECM) mimetic nanofibrous architecture using a mild process. A slowly increasing concentration process was applied to regulate silk self-assembly into nanofibers in aqueous solution. Then glycerol was blended with the nanofiber solution and induced silk crystallization in the lyophilization process, endowing freeze-dried scaffolds with water stability. The glycerol was leached from the scaffolds, leaving a similar porous structure at the micrometer scale but different topographies at the nanoscale. Compared to previous salt-leached and methanol-annealed scaffolds, the present scaffolds showed lower β-sheet content, softer mechanical property and improved cell growth and differentiation behaviors, suggesting their promising future as platforms for controlling stem cell fate and soft tissue regeneration.

Effect of coupling asynchronous acoustoelectric effects on the corrosion behavior, microhardness and biocompatibility of biomedical titanium alloy strips

The coupling asynchronous acoustoelectric effects (CAAE) of the high-energy electropulsing treatment (EPT) technique and ultrasonic surface strengthening modification (USSM) are innovatively combined in improving the surface microhardness, corrosion behavior and biocompatibility of the pre-deformed titanium alloy strips. Experimental results show that EPT and USSM processes facilitate the surface grain refining and USSM brings in the micro-dimples on the materials surface, which is attributed to the atoms diffusion acceleration under EPT and severe surface plastic deformation under USSM. These microstructure changes can not only enhance the corrosion resistance in the acidic simulated body fluids and fluoridated acidic artificial saliva but also improve the biocompatibility of the titanium alloy strip materials. Moreover, the surface microhardness of the titanium alloy strips is enhanced to improve the wear resistance. Therefore, CAAE processing is a high-efficiency and energy-saving method for obtaining biomedical titanium alloys with superior anti-corrosion performance, microhardness and biocompatibility, which can be widely applied in dental implants and artificial joint.

Growth and surface characterization of TiNbZr thin films deposited by magnetron sputtering for biomedical applications

Low modulus of elasticity and the presence of non-toxic elements are important criteria for the development of materials for implant applications. Low modulus Ti alloys can be developed by designing β-Ti alloys containing non-toxic alloying elements such as Nb and Zr. Actually, most of the metallic implants are produced with stainless steel (SS) because it has adequate bulk properties to be used as biomaterials for orthopedic or dental implants and is less expensive than Ti and its alloys, but it is less biocompatible than them. The coating of this SS implants with Ti alloy thin films may be one alternative to improve the biomaterial properties at a relatively low cost. Sputtering is a physical deposition technique that allows the formation of nanostructured thin films. Nanostructured surfaces are interesting when it comes to the bone/implant interface due to the fact that both the surface and the bone have nanoscale particle sizes and similar mechanical properties. TiNbZr thin films were deposited on both Si(111) and stainless steel (SS) substrates. The TiNbZr/Si(111) film was used as a model system, while the TiNbZr/SS film might improve the biocompatibility and extend the life time of stainless steel implants. The morphology, chemical composition, Young's modulus, and hardness of the films were analyzed by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), and nanoindentation.

Surface modification of porous polycaprolactone/biphasic calcium phosphate scaffolds for bone regeneration in rat calvaria defect

In this study, polycaprolactone scaffolds fabricated by a salt-leaching process were loaded with biphasic calcium phosphate successfully to improve the osteoconductivity in bone regeneration. The surface of polycaprolactone/biphasic calcium phosphate scaffolds was aminolyzed by 1,6-hexamethylenediamine to introduce amino groups onto the surface, which was verified qualitatively by ninhyrin staining. Collagen was further immobilized on the aminolyzed porous polycaprolactone via N-ethyl-N'-(3-dimethylaminopropy) carbodiimide hydrochloride/hydroxy-2,5-dioxopyrolidine-3-sulfonic acid sodium cross-linking. The pore size of polycaprolactone/biphasic calcium phosphate-collagen scaffolds was 200-300 µm, which was suitable for bone in-growth. The X-ray photoelectron spectroscopy confirmed the coupling of collagen immobilized on the surface of polycaprolactone/biphasic calcium phosphate. In vitro results demonstrated that the spreading and viability of MC3T3-E1 cells were remarkably improved in the polycaprolactone/biphasic calcium phosphate-collagen scaffolds. The in vivo study was carried out by implanting the porous polycaprolactone, polycaprolactone/biphasic calcium phosphate, and polycaprolactone/biphasic calcium phosphate-collagen to the skulls of rats. Although the addition of biphasic calcium phosphate particles in the polycaprolactone scaffolds does not have a strong effect on the new bone formation, the immobilization of collagen on the polycaprolactone/biphasic calcium phosphate scaffolds significantly improved the bone regeneration even though the implantation time was short, 6 weeks. The present results provide more evidence that functionalizing polycaprolactone with biphasic calcium phosphate and collagen may be a feasible way to improve the osteoconduction in bone regeneration.

Effect of laser treatment on the attachment and viability of mesenchymal stem cell responses on shape memory NiTi alloy

The objectives of this study were to investigate the effect of laser-induced surface features on the morphology, attachment and viability of mesenchymal stem cells (MSCs) at different periods of time, and to evaluate the biocompatibility of different zones: laser-melted zone (MZ), heat-affected zone (HAZ) and base metal (BM) in laser-treated NiTi alloy. The surface morphology and composition were studied by scanning electron microscope (SEM) and X-ray photoemission spectroscopy (XPS), respectively. The cell morphology was examined by SEM while the cell counting and viability measurements were done by hemocytometer and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay. The results indicated that the laser-induced surface features, such as surface roughening, presence of anisotropic dendritic pattern and complete surface Ni oxidation were beneficial to improve the biocompatibility of NiTi as evidenced by the highest cell attachment (4 days of culture) and viability (7 days of culture) found in the MZ. The biocompatibility of the MZ was the best, followed by the BM with the HAZ being the worst. The defective and porous oxide layer as well as the coarse grained structure might attribute to the inferior cell attachment (4 days of culture) and viability (7 days of culture) on the HAZ compared with the BM which has similar surface morphology.

Synthesis and characterization of hybrid micro/nano-structured NiTi surfaces by a combination of etching and anodizing

The purpose of this study was to generate hybrid micro/nano-structures on biomedical nickel-titanium alloy (NiTi). To achieve this, NiTi surfaces were firstly electrochemically etched and then anodized in fluoride-containing electrolyte. With the etching process, the NiTi surface was micro-roughened through the formation of micropits uniformly distributed over the entire surface. Following the subsequent anodizing process, self-organized nanotube structures enriched in TiO2 could be superimposed on the etched surface under specific conditions. Furthermore, the anodizing treatment significantly reduced water contact angles and increased the surface free energy compared to the surfaces prior to anodizing. The results of this study show for the first time that it is possible to create hybrid micro/nano-structures on biomedical NiTi alloys by combining electrochemical etching and anodizing under controlled conditions. These novel structures are expected to significantly enhance the surface biofunctionality of the material when compared to conventional implant devices with either micro- or nano-structured surfaces.

Surface hydride on titanium by cathodic polarization promotes human gingival fibroblast growth

Connective tissue seal to dental abutment is crucial for peri-implant health. Several efforts have been made previously to optimize abutment surfaces, but no consensus has been reached regarding the optimal surface architecture and/or composition for soft tissue seal. Here, we report on experiments using cathodic polarization in organic acids to optimize titanium (Ti) surfaces for use as abutments. The three main factors affecting surface topography and chemistry were electrolyte composition, current density, and polarization time. Under identical conditions, oxalic acid created rougher surfaces than tartaric acid and acetic acid, and acetic acid produced more surface hydride. Surface hydride amount was suggested to first increase and then decrease with current density from 1 mA/cm(2) to 15 mA/cm(2) . The complexity of the surface topography and hydride production both increased with polarization time. Proliferation rate of human gingival fibroblasts (HGFs) was positively correlated with surface hydride content, suggesting the positive effect of surface hydride on connective tissue growth around dental abutment. Changes in surface topography and hydrophilicity did not significantly influence HGF growth.

PIIID-formed (Ti, O)/Ti, (Ti, N)/Ti and (Ti, O, N)/Ti coatings on NiTi shape memory alloy for medical applications

(Ti, O)/Ti, (Ti, N)/Ti and (Ti, O, N)/Ti composite coatings were fabricated on NiTi shape memory alloy via plasma immersion ion implantation and deposition (PIIID). Surface morphology of samples was investigated using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Cross-sectional morphology indicated that the PIIID-formed coatings were dense and uniform. X-ray diffraction (XRD) was used to characterize the phase composition of samples. X-ray photoelectron spectroscopy (XPS) results showed that the surface of coated NiTi SMA samples was Ni-free. Nanoindentation measurements and pin-on-disc tests were carried out to evaluate mechanical properties and wear resistance of coated NiTi SMA, respectively. For the in vitro biological assessment of the composite coatings in terms of cell morphology and cell viability, osteoblast-like SaOS-2 cells and breast cancer MCF-7 cells were cultured on NiTi SMA samples, respectively. SaOS-2 cells attached and spread better on coated NiTi SMA. Viability of MCF-7 cells showed that the PIIID-formed composite coatings were noncytotoxic and coated samples were more biocompatible than uncoated samples.

Cytotoxicity of Ni from Surface-Treated Porous Nitinol (PNT) on Osteoblast Cells

The leaching of nickel from the surface of porous Nitinol (PNT) is mainly dependent on its surface characteristics, which can be controlled by appropriate surface treatments. In this investigation, PNT was subjected to two surface treatments, namely, water-boiling and dry-heating passivations. Phosphate buffer saline (PBS) solutions obtained from cyclic potentiodynamic polarization tests on PNT were employed to assess the cytotoxicity of Ni contained therein on osteoblast cells by Sulforhodamine B (SRB) assay. In addition, similar concentrations of Ni were added exogenously to cell culture media to determine cytotoxic effects on osteoblast cells. The morphologies of the untreated and the surface-treated PNTs were examined using SEM and AFM. Furthermore, growth of human osteoblast cells was observed on the PNT surfaces.

An Investigation into the Effect of Surface Roughness of Stainless Steel on Human Umbilical Vein Endothelial Cell Gene Expression

The surface properties of vascular devices dictate the initial postimplantation reactions that occur and thus the efficacy of the implantation procedure. Over the last number of years, a number of different stent designs have emerged and stents are generally polished to a mirror finish during the manufacturing procedure. This study sought to investigate the effect of stainless steel surface roughness on endothelial cell gene expression using an appropriate cell culture in vitro assay system. Stainless steel discs were roughened by shot blasting or polished by mechanical polishing. The surface roughness of the treated and untreated discs was determined by atomic force microscopy (AFM). Cells were seeded on collagen type 1 gels and left to attach for 24 h. Stainless steel discs of varying roughness were then placed in contact with the cells and incubated for 24 h. RNA extractions and quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR) was then performed to determine the expression levels of candidate genes in the treated cells compared to suitable control cells. E-selectin and vascular cellular adhesion molecule (VCAM-1) were found to be significantly up-regulated in cells incubated with polished and roughened samples, indicating endothelial cell activation and inflammation. This study indicates that the surface roughness of stainless steel is an important surface property in the development of vascular stents.

Structure and properties of strontium-doped phosphate-based glasses

Owing to similarity in both ionic size and polarity, strontium (Sr2+) is known to behave in a comparable way to calcium (Ca2+), and its role in bone metabolism has been well documented as both anti-resorptive and bone forming. In this study, novel quaternary strontium-doped phosphate-based glasses, containing 1, 3 and 5 mol% SrO, were synthesized and characterized. (31)P magic angle spinning (MAS) nuclear magnetic resonance results showed that, as the Sr2+ content is increased in the glasses, there is a slight increase in disproportionation of Q2 phosphorus environments into Q(1) and Q3 environments. Moreover, shortening and strengthening of the phosphorus to bridging oxygen distance occurred as obtained from FTIR. The general broadening of the spectral features with Sr2+ content is most probably due to the increased variation of the phosphate-cation bonding interactions caused by the introduction of the third cation. This increased disorder may be the cause of the increased degradation of the Sr-containing glasses relative to the Sr-free glass. As confirmed from elemental analysis, all Sr-containing glasses showed higher Na2O than expected and this also could be accounted for by the higher degradation of these glasses compared with Sr-free glasses. Measurements of surface free energy (SFE) showed that incorporation of strontium had no effect on SFE, and samples had relatively higher fractional polarity, which is not expected to promote high cell activity. From viability studies, however, the incorporation of Sr2+ showed better cellular response than Sr(2+)-free glasses, but still lower than the positive control. This unfavourable cellular response could be due to the high degradation nature of these glasses and not due to the presence of Sr2+.

Biological behaviour of an endothelial cell line (HPMEC) on vascular prostheses grafted with hydroxypropylgamma-cyclodextrine (HPgamma-CD) and hydroxypropylbeta-cyclodextrine (HPbeta-CD)

The cytocompatibility of cyclodextrins (CDs) grafting on vascular polyester (PET) prostheses for further loading with biomolecules was investigated in this study. Viability tests demonstrated no toxicity of HP-CDs and PolyHP-CDs at 4,000 mg/l with survival rates of 80 to 96%. Proliferation tests using the human pulmonary microvascular endothelial cell line (HPMEC-ST1) revealed an excellent biocompatibility for Melinex (Film form of PET). For Polythese and Polymaille, a good proliferation rate was observed at 3 days (60-80%) but decreased at 6 days (56-73%). For all CD-grafted samples, low proliferation rates were observed after 6 days (35-38%). Vitality tests revealed excellent functional capacities of HPMEC cells after 3 and 6 days for all samples. Adhesion kinetics tests showed a similar adhesion of HPMEC cells on control and Melinex. A low adhesion was observed on Polythese and especially on Polymaille compared to control. After CD grafting, the cell adhesion was decreased. The woven or knitted architecture and CD grafting were the most likely causes of this weak adhesion. The adhesion kinetic test was confirmed by SEM observations and immunocytochemistry. The low proliferation of HPMEC on virgin prostheses and especially on grafted prostheses was not due to a cytotoxic effect, but to the physical surface characteristics of the prostheses.

Critical overview of Nitinol surfaces and their modifications for medical applications

Nitinol, a group of nearly equiatomic shape memory and superelastic NiTi alloys, is being extensively explored for medical applications. Release of Ni in the human body, a potential problem with Nitinol implant devices, has stimulated a great deal of research on its surface modifications and coatings. In order to use any of the developed surfaces in implant designs, it is important to understand whether they really have advantages over bare Nitinol. This paper overviews the current situation, discusses the advantages and disadvantages of new surfaces as well as the limitations of the studies performed. It presents a comprehensive analysis of surface topography, chemistry, corrosion behavior, nickel release and biological responses to Nitinol surfaces modified mechanically or using such methods as etching in acids and alkaline solutions, electropolishing, heat and ion beam treatments, boiling in water and autoclaving, conventional and ion plasma implantations, laser melting and bioactive coating deposition. The analysis demonstrates that the presently developed surfaces vary in thickness from a few nanometers to micrometers, and that they can effectively prevent Ni release if the surface integrity is maintained under strain and if no Ni-enriched sub-layers are present. Whether it is appropriate to use various low temperature pre-treatment protocols (< or = 160 degrees C) developed originally for pure titanium for Nitinol surface modifications and coatings is also discussed. The importance of selection of original Nitinol surfaces with regard to the performance of coatings and comparative performance of controls in the studies is emphasized. Considering the obvious advantages of bare Nitinol surfaces for superelastic implants, details of their preparation are also outlined.

Oxidized NiTi surfaces enhance differentiation of osteoblast-like cells

A new oxidation treatment (OT) on NiTi shape memory alloys was developed in a previous work. This OT treatment significantly decreases Ni ion release into the exterior medium, and therefore is thought to be beneficial for NiTi cytocompatibility. As to confirm this expectation, the in vitro response of MG63 osteoblast-like cells cultured on untreated and oxidized NiTi surfaces was studied. An adhesion test at 1, 4, and 8 h of incubation was performed. Statistical differences were evidenced at 1 h of adhesion depending on the surface treatment and chemical composition of the substrate. However, at larger times of study, there were no statistically significant differences between untreated and oxidized surfaces. The proliferation test (until 9 days) showed that untreated and oxidized NiTi surfaces are not cytotoxic for MG63 cells. The differences of adhesion at short times did not affect the proliferation of MG63 cells. However, after 48 h of stimulation with ascorbic acid and dexamethasone, the MG63 cells cultured on oxidized surfaces showed higher alkaline phosphatase activity and osteocalcin levels. The improvement of osteoblast differentiation due to OT treatment could accelerate bone formation, and, therefore, could allow earlier loading of NiTi devices used in dental and orthopedic applications.

Systematic study of osteoblast and fibroblast response to roughness by means of surface-morphology gradients

The surface roughness of a medical implant is of great importance since the surface is in direct contact with the host tissue (e.g. bone, fibrous tissue). The response of cells to roughness is different depending on the cell type. However, the influence of roughness on cell behavior has only rarely been systematically studied. We have developed a surface-modification process to produce roughness gradients that cover a wide range of roughness values on one substratum. Such gradients allow for systematic investigations of roughness on cell behavior. Gradients were fabricated using a two-step roughening and smoothening process, involving sandblasting and a subsequent chemical polishing step. In order to produce a set of identical surfaces we applied a replica technique. Cell experiments were carried out with rat calvarial osteoblasts (RCO) and human gingival fibroblasts (HGF). RCOs showed a significantly increased proliferation rate with increasing surface roughness. The footprint of osteoblasts varied in size at different positions on the gradient, remaining small on the rough end of the gradient and increasing considerably as the roughness decreased. HGF showed the opposite proliferation behavior, proliferation decreasing with increasing roughness. The fibroblast morphology was found to be similar to that seen for osteoblasts.

Cytotoxicity of polyethyleneimine (PEI), precursor base layer of polyelectrolyte multilayer films

Polyethyleneimine (PEI) is a synthetic polymer commonly used as precursor base layer in polyelectrolyte multilayer films. However, the biological properties of this cationic macromolecule are poorly understood. The aim of this experimental investigation was to evaluate in vitro the biocompatibility of PEI towards two different human cell lines. The experimental investigation was undertaken on pure titanium (Ti) and nickel-titanium (NiTi) alloy samples with an average surface roughness of Ra=0.3microm. A biological study was undertaken at day 0 (2h after seeding), day 2, day 4 and day 7 to observe the cellular response of fibroblasts and osteoblasts cell lines in terms of morphology, adhesion (as observed by scanning electron microscopy), and viability (Mosmann's test). The results showed that PEI can be successfully deposited onto Ti or NiTi alloy, but generates a detrimental cellular response on both substrates as illustrated by a decrease of both fibroblast and osteoblast adhesion and proliferation over a 7-day culture period. These results suggest that PEI is potentially cytotoxic and may not be biocompatible enough in clinical applications using high molecular weight. As a consequence, polyelectrolyte multilayer films, which are promising in prosthesis and implantology fields, could not be coated with PEI at a high molecular weight. A lower molecular weight should be considered or a more biocompatible molecular base as precursor layer of polyelectrolyte multilayer films would be better to use for a good human bio-integration.

New oxidation treatment of NiTi shape memory alloys to obtain Ni-free surfaces and to improve biocompatibility

Various oxidation treatments were applied to nearly equiatomic NiTi alloys so as to form a Ni-free protective oxide on the surface. Sample surfaces were analyzed by X-ray Photoelectron Spectroscopy, and NiTi transformation temperatures were determined by differential scanning calorimetry (DSC) before and after the surface treatment. An ion release experiment was carried out up to one month of immersion in SBF for both oxidized and untreated surfaces. The results show that oxidation treatment in a low-oxygen pressure atmosphere leads to a high surface Ti/Ni ratio, a very low Ni surface concentration and a thick oxide layer. This oxidation treatment does not significantly affect the shape memory properties of the alloy. Moreover, the oxide formed significantly decreases Ni release into exterior medium comparing with untreated surfaces. As a consequence, this new oxidation treatment could be of great interest for biomedical applications, as it could minimize sensitization and allergies and improve biocompatibility and corrosion resistance of NiTi shape memory alloys.