Biomedical interfaces: titanium surface technology for implants and cell carriers

Improved Biocompatibility and Osseointegration of Nanostructured Calcium-Incorporated Titanium Implant Surface Treatment (XPEED®)

Surface treatment of implants facilitates osseointegration, with nanostructured surfaces exhibiting accelerated peri-implant bone regeneration. This study compared bone-to-implant contact (BIC) in implants with hydroxyapatite (HA), sand-blasted and acid-etched (SLA), and SLA with calcium (Ca)-coated (XPEED®) surfaces. Seventy-five disk-shaped grade 4 Ti specimens divided into three groups were prepared, with 16 implants per group tested in New Zealand white rabbits. Surface characterization was performed using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), digital microscopy, and a contact angle analyzer. Cell viability, proliferation, and adhesion were assessed using MC3T3-E1 cells. Apatite formation was evaluated using modified simulated body fluid (m-SBF) incubation. After 4 weeks of healing, the outcomes reviewed were BIC, bone area (BA), removal torque tests, and histomorphometric evaluation. A microstructure analysis revealed irregular pores across all groups, with the XPEED group exhibiting a nanostructured Ca-coated surface. Surface characterization showed a crystalline CaTiO3 layer on XPEED surfaces, with evenly distributed Ca penetrating the implants. All surfaces provided excellent environments for cell growth. The XPEED and SLA groups showed significantly higher cell density and viability with superior osseointegration than HA (p < 0.05); XPEED exhibited the highest absorbance values. Thus, XPEED surface treatment improved implant performance, biocompatibility, stability, and osseointegration.

Study on osteoinductive activity of biotin film by low-energy electron beam deposition

Biotin film was prepared by low-energy electron beam deposition (LEBD). The molecular structure, chemical composition and micromorphology of the biotin film were investigated by ¹HNMR, FTIR, XPS, AFM and SEM. The results showed the molecular structure of a monolayer of biotin film is fully consistent with the molecular structure of the initial biotin powders. The contact angle test showed that the biotin film exhibit good hydrophilicity. The release kinetics of biotin film was tested by UV-Vis method. It was found that the film was almost completely released in about two weeks. The cell viability of MC3T3-E1 cells on the surface of the biotin film was attaining 100.54 ± 1.7% (P < 0.05), showing excellent biocompatibility and biosafety. Titanium implant with surface of biotin film was implanted into the femoral head of rabbits as experimental group. The animals were euthanized after four weeks. Compared with the control group, mature lamellar bone formation was observed with dense trabecular bone, and the expression of Coll-I, Runx2 and BMP-2 was better. The results showed that the repair effect of bone defect in the experimental group was excellent.

Improved Biological Responses of Titanium Coating Using Laser-Aided Direct Metal Fabrication on SUS316L Stainless Steel

Direct metal fabrication (DMF) coatings have the advantage of a more uniform porous structure and superior mechanical properties compared to coatings provided by other methods. We applied pure titanium metal powders to SUS316L stainless steel using laser-aided DMF coating technology with 3D printing. The purpose of this study was to determine the efficacy of this surface modification of stainless steel. The capacity of cells to adhere to DMF-coated SUS316L stainless steel was compared with machined SUS316L stainless steel in vitro and in vivo. Morphological in vitro response to human osteoblast cell lines was evaluated using scanning electron microscopy. Separate specimens were inserted into the medulla of distal femurs of rabbits for in vivo study. The distal femurs were harvested after 3 months, and were then subjected to push-out test and histomorphometrical analyses. The DMF group exhibited a distinct surface chemical composition, showing higher peaks of titanium compared to the machined stainless steel. The surface of the DMF group had a more distinct porous structure, which showed more extensive coverage with lamellipodia from osteoblasts than the machined surface. In the in vivo test, the DMF group showed better results than the machined group in the push-out test (3.39 vs. 1.35 MPa, respectively, p = 0.001). In the histomorphometric analyses, the mean bone-to-implant contact percentage of the DMF group was about 1.5 times greater than that of the machined group (65.4 ± 7.1% vs. 41.9 ± 5.6%, respectively; p < 0.001). The porous titanium coating on SUS316L stainless steel produced using DMF with 3D printing showed better surface characteristics and biomechanical properties than the machined SUS316L.

Spatial Presentation of Tissue-Specific Extracellular Matrix Components along Electrospun Scaffolds for Tissue Engineering the Bone-Ligament Interface

The bone-ligament interface transitions from a highly organized type I collagen rich matrix to a nonmineralized fibrocartilage region and finally to a mineralized fibrocartilage region that interfaces with the bone. Therefore, engineering the bone-ligament interface requires a biomaterial substrate capable of maintaining or directing the spatially defined differentiation of multiple cell phenotypes. To date the appropriate combination of biophysical and biochemical factors that can be used to engineer such a biomaterial substrate remain unknown. Here we show that microfiber scaffolds functionalized with tissue-specific extracellular matrix (ECM) components can direct the differentiation of MSCs toward the phenotypes seen at the bone-ligament interface. Ligament-ECM (L-ECM) promoted the expression of the ligament-marker gene tenomodulin (TNMD) and higher levels of type I and III collagen expression compared to functionalization with commercially available type I collagen. Functionalization of microfiber scaffolds with cartilage-ECM (C-ECM) promoted chondrogenesis of MSCs, as evidenced by adoption of a round cell morphology and increased SRY-box 9 (SOX9) expression in the absence of exogenous growth factors. Next, we fabricated a multiphasic scaffold by controlling the spatial presentation of L-ECM and C-ECM along the length of a single electrospun microfiber construct, with the distal region of the C-ECM coated fibers additionally functionalized with an apatite layer (using simulated body fluid) to promote endochondral ossification. These ECM functionalized scaffolds promoted spatially defined differentiation of MSCs, with higher expression of TNMD observed in the region functionalized with L-ECM, and higher expression of type X collagen and osteopontin (markers of endochondral ossification) observed at the end of the scaffold functionalized with C-ECM and the apatite coating. Our results demonstrate the utility of tissue-specific ECM derived components as a cue for directing MSC differentiation when engineering complex multiphasic interfaces such as the bone-ligament enthesis.

Titanium Porous Coating Using 3D Direct Energy Deposition (DED) Printing for Cementless TKA Implants: Does It Induce Chronic Inflammation?

Because of the recent technological advances, the cementless total knee arthroplasty (TKA) implant showed satisfactory implant survival rate. Newly developed 3D printing direct energy deposition (DED) has superior resistance to abrasion as compared to traditional methods. However, there is still concern about the mechanical stability and the risk of osteolysis by the titanium (Ti) nanoparticles. Therefore, in this work, we investigated whether DED Ti-coated cobalt-chrome (CoCr) alloys induce chronic inflammation reactions through in vitro and in vivo models. We studied three types of implant surfaces (smooth, sand-blasted, and DED Ti-coated) to compare their inflammatory reaction. We conducted the in vitro effect of specimens using the cell counting kit-8 (CCK-8) assay and an inflammatory cytokine assay. Subsequently, in vivo analysis of the immune profiling, cytokine assay, and histomorphometric evaluation using C57BL/6 mice were performed. There were no significant differences in the CCK-8 assay, the cytokine assay, and the immune profiling assay. Moreover, there were no difference for semi-quantitative histomorphometry analysis at 4 and 8 weeks among the sham, smooth, and DED Ti-coated samples. These results suggest that DED Ti-coated printing technique do not induce chronic inflammation both in vitro and in vivo. It has biocompatibility for being used as a surface coating of TKA implant.

Treatments for enhancing the biocompatibility of titanium implants

Titanium surface treatment is a crucial process for achieving sufficient osseointegration of an implant into the bone. If the implant does not heal sufficiently, serious complications may occur, e.g. infection, inflammation, aseptic loosening of the implant, or the stress-shielding effect, as a result of which the implant may need to be reoperated. After a titanium graft has been implanted, several interactions are crucial in order to create a strong bone-implant connection. It is essential that cells adhere to the surface of the implant. Surface roughness has a significant influence on cell adhesion, and also on improving and accelerating osseointegration. Other highly important factors are biocompatibility and resistance to bacterial contamination. Bio-inertness of titanium is ensured by the protective film of titanium oxides that forms spontaneously on its surface. This film prevents the penetration of metal compounds, and it is well-adhesive for calcium and phosphate ions, which are necessary for the formation of the mineralized bone structure. Since the presence of the film alone is not sufficient for the biocompatibility of titanium, a suitable surface finish is required to create a firm bone-implant connection. In this review, we explain and compare the most widely-used methods for modulating the surface roughness of titanium implants in order to enhance cell adhesion on the surface of the implant, e.g. plasma spraying, sandblasting, acid etching, laser treatment, sol-gel etc., The methods are divided into three overlapping groups, according to the type of modification.

Similar inductive effects of enamel and dentin matrix derivatives on osteoblast-like cell response over SLA titanium surface

OBJECTIVES

The aim of this in vitro study was to investigate the behavior of osteoblasts on titanium discs under different concentrations of enamel matrix derivatives (EMD) and dentin matrix derivative (DMD).

MATERIALS AND METHODS

MC3T3-E1 osteoblast-like cells were cultivated on coated titanium SLA discs with EMD or DMD at 100 μg/ml, 1 mg/ml, 10 mg/ml and 30 mg/ml or left uncoated. Cell viability, proliferation, adhesion and migration were assessed respectively with MTT, BrdU, DAPI and scratch wound healing assays. Messenger ribonucleic acid of different genes related to osteoblastic differentiation was quantified by means of real-time quantitative PCR. Data were analyzed using student t-test for adhesion and migration assay and ANOVA for proliferation assay (p < 0.05).

RESULTS

BrdU incorporation was found in proliferative osteoblasts for both test solutions at all concentrations. Osteoblast migrated and covered approximately 70% of the wound area observed at time zero when exposed to EMD and DMD to all concentrations. The increase of gene expression was dependent on the concentration enhancement of EMD and DMD. Higher concentrations showed proliferation augmentation if compared to lower concentrations.

CONCLUSIONS

Roughness surface of Ti SLA can limit cell adhesion independent of the presence EMD or DMD. DMD enhances cell migration of osteoblasts on SLA titanium implants in a concentration-dependent manner.

Bioadaptive nanorod array topography of hydroxyapatite and TiO2 on Ti substrate to preosteoblast cell behaviors

Bioadaptive nanostructure coatings of hydroxyapatite (HAP) and TiO₂ on titanium (Ti) implants are essential for biomaterial-tissue osteointegration. However, there is no specific report, so far, that focuses on the different influences of the two bioadaptive coatings on preosteoblast behaviors. Herein, adhesion, proliferation, and osteogenic potential of preosteoblast on HAP and TiO₂ coatings with nanorod array topography were studied. XRD, TEM, and SAED analysis indicated that rod-like HAP nanoarray and anatase TiO₂ nanoarray coatings were fabricated successfully, and there was insignificant difference in roughness and fibronectin adsorption of the two coatings. Adhesion and proliferation of MC3T3-E1 cells on the two coatings were of no significant difference, besides a larger projected area of the cells on HAP coating. MC3T3-E1 cells cultured on the HAP coating displayed significantly higher expression of runt-related transcription factor-2 (Runx2), osteocalcin (OCN) and collagen type-1 (Col I) after culture for 21 days compared with those on TiO₂ coating, except alkaline phosphatase (ALP). This study provides beneficial suggestion for intelligent selection of biocoatings.

Polydopamine coating promotes early osteogenesis in 3D printing porous Ti6Al4V scaffolds

BACKGROUND

Titanium implants are widely used in orthopedic and dental for more than 30 years. Its stable physicochemical properties and mechanical strength are indeed appropriate for implantation. However, the Bioinertia oxidized layer and higher elastic modulus often lead to the early implantation failure.

METHODS

In this study, we proposed a simple design of porous structure to minimize the disparity between scaffold and natural bone tissue, and introduced a one-step reaction to form a polydopamine (PDA) layer on the surface of titanium for the purpose of improving osteogenesis as well. The porous scaffolds with pore size of 400 µm and porosity of 44.66% were made by additive manufacturing. The cell behavior was tested by seeding MC3T3-E1 cells on Ti6Al4V films for 15 days. The biomechanical properties were then analyzed by finite element (FE) method and the in vivo osteogenesis effect was accordingly evaluated by implanting the scaffolds for 5 weeks in rabbits.

RESULTS

According to the achieved results, it was revealed that the immersion for 40 min with dopamine could significantly improve the cell adhesion. The proposed method for design of porous structure can avoid the stress shielding effect and bone growth inside the PDA coating scaffolds, which were observed at the early stage of bone healing process.

CONCLUSIONS

It can be concluded that the proposed PDA coating method is effective in promoting early osteogenesis, as well as being easy to operate, and can be helpful in the future clinical application of titanium implants.

Titanium Powder Coating Using Metal 3D Printing: A Novel Coating Technology for Cobalt-Chromium Alloy Implants

Background

Three-dimensional (3D) printing with a direct metal fabrication (DMF) technology has been innovatively introduced in the field of surface treatment of prostheses. The purpose of this study was to determine whether such modifications on the surface of cobalt-chromium (CoCr) alloy by titanium powder coating using DMF improves the osseointegration ability of CoCr alloy.

Methods

We compared the in vitro and in vivo ability of cells to adhere to DMF-coated CoCr alloy with machining. Biological and morphological responses to human osteoblast cell lines were examined by measuring cell proliferation rate and observing expression of actin filament. For in vivo study, we inserted different specimens in each medulla of the distal femurs of rabbit. After 3 months, the distal femurs were harvested, and a push-out test and histomorphometric analyses were performed.

Results

The cell proliferation rate and cell adhesion in the DMF group were higher compared with those in the machined group. Human osteoblast cells on the DMF-coated surface were more strongly adhered and well-proliferated compared with those on the other surface. In the in vivo test, there was a significant difference in the ultimate shear strength between the DMF and machined groups (2.49 MPa vs. 0.87 MPa, respectively, p = 0.001). In the histomorphometric analysis, there was a significant difference in the mean bone-to-implant contact percentages between the DMF and machined groups (72.3 ± 6.2% vs. 47.6 ± 6.9%, respectively, p < 0.001).

Conclusion

Titanium coating of CoCr alloy with 3D metal printing provides optimal surface characteristics and a good biological surface both in vitro and in vivo.

Design and manufacture of functional catalyst-carrier structures for the bioorthogonal activation of anticancer agents

Achieving the activation of a latent prodrug via bio-orthogonal chemistry on the catalytic surface of a tailored Ti-[Pd] device.

Effect of calcium ions on peptide adsorption at the aqueous rutile titania (110) interface

How the presence of Ca²⁺ ions at the aqueous TiO₂ interface influences the binding modes of two experimentally identified titania-binding peptides, Ti-1 and Ti-2, is investigated using replica exchange with solute tempering molecular dynamics simulations. The findings are compared with available experimental data, and the results are contrasted with those obtained under NaCl solution conditions. For Ti-1, Ca²⁺ ions enhance the adsorption of the negatively charged Asp8 residue in this sequence to the negatively charged surface, via Asp–Ca²⁺–TiO₂ bridging. This appears to generate a nonlocal impact on the adsorption of Lys12 in Ti-1, which then pins the peptide to the surface via direct surface contact. For Ti-2, fewer residues were predicted to adsorb directly to the surface in CaCl₂, compared with predictions made for NaCl solution, possibly due to competition between the other peptide residues and Ca²⁺ ions to adsorb to the surface. This reduction in direct surface contact gives rise to a more extensive solvent-mediated contact for Ti-2. In general, the presence of Ca²⁺ ions resulted in a loss of conformational diversity of the surface-adsorbed conformational ensembles of these peptides, compared to counterpart data predicted for NaCl solution. The findings provide initial insights into how peptide–TiO₂ interactions might be tuned at the molecular level via modification of the salt composition of the liquid medium.

Immobilization of a carbon nanomaterial-based localized drug-release system using a bispecific material-binding peptide

Introduction

Inorganic materials are widely used in medical devices, such as artificial hearts, vessels, and joints, in stents, and as nanocarriers for drug-delivery systems. Carbon nanomaterials are of particular interest due to their biological inertness and their capability to accommodate molecules. Several attempts have been proposed, in which carbon nanomaterials are used as nanocarriers for the systemic delivery of drugs.

Materials and methods

We developed a drug-delivery system in which oxidized single-walled carbon nanohorns (oxSWNHs) were immobilized on a titanium (Ti) surface using material-binding peptides to enable localized drug delivery. For this purpose, we utilized a bispecific peptidic aptamer comprising a core sequence of a Ti-binding peptide and a SWNH-binding peptide to immobilize oxSWNHs on Ti.

Results

Scanning electron microscopy was used to confirm the presence of oxSWNHs adsorbed onto the Ti surface, and a quartz crystal microbalance was used to evaluate the binding process during oxSWNH adsorption. The oxSWNHs-ornamented Ti substrate was nontoxic to cells and released biologically active dexamethasone over a sustained period.

Conclusion

This oxSWNHs-immobilized system can be used to modify the surface of Ti in implants and be loaded with drugs that stimulate osteogenesis and bone regeneration.

Immobilization of vitronectin-binding heparan sulfates onto surfaces to support human pluripotent stem cells

Functionalizing medical devices with polypeptides to enhance their performance has become important for improved clinical success. The extracellular matrix (ECM) adhesion protein vitronectin (VN) is an effective coating, although the chemistry used to attach VN often reduces its bioactivity. In vivo, VN binds the ECM in a sequence-dependent manner with heparan sulfate (HS) glycosaminoglycans. We reasoned therefore that sequence-based affinity chromatography could be used to isolate a VN-binding HS fraction (HS9) for use as a coating material to capture VN onto implant surfaces. Binding avidity and specificity of HS9 were confirmed by enzyme-linked immunosorbent assay (ELISA) and surface plasmon resonance (SPR)-based assays. Plasma polymerization of allylamine (AA) to tissue culture-treated polystyrene (TCPS) was then used to capture and present HS9 as determined by radiolabeling and ELISA. HS9-coated TCPS avidly bound VN, and this layered surface supported the robust attachment, expansion, and maintenance of human pluripotent stem cells. Compositional analysis demonstrated that 6-O- and N-sulfation, as well as lengths greater than three disaccharide units (dp6) are critical for VN binding to HS-coated surfaces. Importantly, HS9 coating reduced the threshold concentration of VN required to create an optimally bioactive surface for pluripotent stem cells. We conclude that affinity-purified heparan sugars are able to coat materials to efficiently bind adhesive factors for biomedical applications. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1887-1896, 2018.

In vitro study on the osteogenesis enhancement effect of BMP-2 incorporated biomimetic apatite coating on titanium surfaces

To fabricate a sustained-release delivery system of bone morphogenetic protein (BMP-2) on titanium surface, explore the effect of BMP-2 concentration on the loading/release behavior of BMP-2 and evaluate the cell compatibility of the system in vitro, pure titanium specimens were immersed into supersaturated calcium phosphate solutions (SCP) containing 4 different concentrations of BMP-2: 0, 50, 100, 200 and 400 ng/mL. Biomimetic calcium phosphate coating was formed on titanium surface and BMP-2 was incorporated into the coating through co-deposition. The release profile of BMP-2 suggested that BMP-2 were delivered sustainably up to 20 days. CCK-8 and ALP assay showed that 200 group and 400 ng/mL BMP-2 group have significant effect on promoting MC3T3-E1 cell proliferation and differentiation. The BMP-2 incorporated into the hybrid coating released in a sustained manner and significantly promoted the proliferation and differentiation of MC3T3-E1 on the titanium surface.

Fibrochondrocyte Growth and Functionality on TiO₂ Nanothin Films

Disorders affecting the temporomandibular joint (TMJ) are a long-standing health concern. TMJ disorders (TMJD) are often associated with an internal disc derangement accompanied by a suite of symptoms including joint noises, jaw dysfunction, and severe pain. The severity of patient symptoms and their reoccurrence can be alleviated to some extent with conservative therapy; however, refractory cases often require surgery that has shown only limited success. Bioengineered scaffolds with cell supportive surfaces an d nanoarchitectures that mimic TMJ tissue structure may offer an alternative treatment modality. In this study, titanium dioxide (TiO₂) nanothin films, fabricated by layer-by-layer assembly, were examined as means for creating such a scaffold. The viability and growth of TMJ discal fibrochondrocytes (FCs) were assessed through MTT and DNA assays and total protein content over a 14-day experimental period. ELISA was also used to measure expression of types I and II collagen, decorin and aggrecan. Quantitative analyses demonstrated that FCs synthesized characteristic discal matrix proteins, with an increased production of type I collagen and decorin as opposed to collagen type II and aggrecan. A stimulatory effect on discal FC proliferation and extracellular matrix (ECM) expression with thicker nanofilms was also observed. The cumulative results suggest that TiO₂ nanofilms may have potential as a TMJ scaffolding material.

Preparation of a small intestinal submucosa modified polypropylene hybrid mesh via a mussel-inspired polydopamine coating for pelvic reconstruction

Pelvic organ prolapse (POP) is a serious health issue that affects many adult women. Surgical treatments for POP patients comprise a common strategy in which scaffold materials are used to reconstruct the prolapsed pelvic. However, the existing materials for pelvic reconstruction cannot meet clinical requirements in terms of biocompatibility, mechanics and immunological rejection. To address these concerns, polypropylene (PP) mesh was selected because of its strong mechanical properties. Small intestinal submucosa (SIS) was used to modify the PP mesh via a mussel-inspired polydopamine coating to enhance its biocompatibility. The scanning electron microscopy (SEM) and atomic force microscopy (AFM) results demonstrated that SIS was successfully conjugated on the surface of the PP mesh. Moreover, the cytotoxicity results indicated that the PP mesh and SIS-modified PP mesh were safe to use. Furthermore, in vivo tests demonstrated that the fibroplasia around the implanted site in the SIS-modified PP mesh group was significantly less than the fibroplasia around the PP mesh group. In addition, the immunohistochemistry staining results indicated that the expression of pro-inflammatory macrophages (M1) was substantially lower and that the expression of pro-healing macrophages (M2) was higher in the SIS-modified PP mesh group. Furthermore, ELISA detection indicated that the expression of IL-1β and IL-6 in the SIS-modified PP mesh group was reduced compared with the PP mesh group. These findings suggest that a SIS-modified polypropylene hybrid mesh via a mussel-inspired polydopamine coating is a promising approach in pelvic reconstruction.

Osteogenic stem cell selection for repair and regeneration

The first osteogenic cells to attach to a titanium (Ti) implant after placement are the multipotent stromal cells (MSCs) that circulate in the bloodstream and are recruited to the site of tissue damage. The reservoirs of these cells are heterogeneous in nature, consisting of a mixture of cells with varying differentiation abilities. In order to utilise these cells and to reduce the chance of unwanted events during regenerative therapies, the selection of a subset of cells that is truly multipotent is required. The behaviour of these cells has been shown to be altered by modifications to Ti implant surfaces, most notably rough, hydrophilic Ti. These changes in behaviour underpin the differences seen in clinical performance of these surfaces. In this study Human bone marrow derived stromal cells (hBMSCs) have been cultured on modified Ti surfaces in order to analyse these changes in cell behaviour. The results demonstrate the different effects of the surfaces and suggest that one surface selectively enriches the population with osteogenic adult ‘stem cells’ by inducing the cell death of the more differentiated cells. Combined with subsequent expansion in bioreactors before implantation, this may lead to a new source of cells for regenerative therapies.

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Different titanium surfaces elicit differing responses from bone marrow derived stromal cells.

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Hydrophilic rough titanium induces increased apoptosis and necrosis in MSCs in vitro.

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Cells selected on rough hydrophilic titanium are more osteogenic than the parent population.

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This may lead to a new source of osteogenic cells for regenerative therapies.

Surface functionalization of titanium with tetracycline loaded chitosan–gelatin nanosphere coatings via EPD: fabrication, characterization and mechanism

Tetracycline loaded chitosan–gelatin nanosphere coating has been fabricated on titanium substrate via electrophoretic deposition.

Bridging Adhesion of a Protein onto an Inorganic Surface Using Self-Assembled Dual-Functionalized Spheres

For the bridging adhesion of different classes of materials in their intact functional states, the adhesion of biomolecules onto inorganic surfaces is a necessity. A new molecular design strategy for bridging adhesion was demonstrated by the introduction of two independent recognition groups on the periphery of spherical complexes self-assembled from metal ions (M) and bidentate ligands (L). These dual-functionalized M12L24 spheres were quantitatively synthesized in one step from two ligands, bearing either a biotin for streptavidin recognition or a titania-binding aptamer, and Pd(II) ions. The selective recognition of titania surfaces was achieved by ligands with hexapeptide aptamers (Arg-Lys-Leu-Pro-Asp-Ala: minTBP-1), whose fixation ability was enhanced by the accumulation effect on the surface of the M12L24 spheres. These well-defined spherical structures can be specifically tailored to promote interactions with both titania and streptavidin simultaneously without detrimentally affecting either recognition motif. The irreversible immobilization of the spheres onto titania was revealed quantitatively by quartz crystal microbalance measurements, and the adhesion of streptavidin to the titania surface mediated by the biotin surrounding the spheres was visually demonstrated by lithographic patterning experiments.

Tuning the surface microstructure of titanate coatings on titanium implants for enhancing bioactivity of implants

Biological performance of artificial implant materials is closely related to their surface characteristics, such as microtopography, and composition. Therefore, convenient fabrication of artificial implant materials with a cell-friendly surface structure and suitable composition was of great significance for current tissue engineering. In this work, titanate materials with a nanotubular structure were successfully fabricated through a simple chemical treatment. Immersion test in a simulated body fluid and in vitro cell culture were used to evaluate the biological performance of the treated samples. The results demonstrate that the titanate layer with a nanotubular structure on Ti substrates can promote the apatite-inducing ability remarkably and greatly enhance cellular responses. This highlights the potential of such titanate biomaterials with the special nanoscale structure and effective surface composition for biomedical applications such as bone implants.

Promotion of minTBP-1-PRGDN on the attachment, proliferation and collagen I synthesis of human keratocyte on titanium

AIM

To investigate the influence of minTBP-1-PRGDN on the attachment, proliferation and collagen I synthesis of human keratocyte on titanium (Ti) surface.

METHODS

The chimeric peptide RKLPDAPRGDN (minTBP-1-PRGDN) was synthesized by connecting RKLPDA (minTBP-1) to the N-terminal of PRGDN, the influence of minTBP-1-PRGDN on the attachment, proliferation and collagen I synthesis of human keratocyte on Ti surface were tested using PRGDN and minTBP-1as controls. The keratocytes attached to the surface of Ti were either stained with FITC-labeled phalloidin and viewed with fluorescence microscope or quantified with alamar Blue method. The proliferation of keratocytes on Ti were quantified with 3-(4,5-dim- ethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide up-taking methods. The secretion of type I collagen were determined using an ELISA kit.

RESULTS

The results showed that minTBP-1-PRGDN at a concentration of 100ng/mL was the most potent peptide to enhance the attachment of human keratocytes to the surface of Ti (1.40±0.03 folds, P=0.003), to promote the proliferation (1.26±0.05 folds, P=0.014) and the synthesis of type I collagen (1.530±0.128, P=0.008). MinTBP-1 at the same concentration could only promote the attachment (1.13±0.04 folds, P=0.020) and proliferation(1.15±0.06 folds, P=0.021), while PRGDN had no significant influence (P>0.05).

CONCLUSION

Our data shows that the novel chimeric peptide minTBP-1-PRGDN could promote the attachment, proliferation and type I collagen synthesis of human keratocytes on the surface of Ti.

Grafting of cross-linked hydrogel networks to titanium surfaces

The performance of medical implants and devices is dependent on the biocompatibility of the interfacial region between tissue and the implant material. Polymeric hydrogels are attractive materials for use as biocompatible surface coatings for metal implants. In such systems, a factor that is critically important for the longevity of an implant is the formation of a robust bond between the hydrogel layer and the implant metal surface and the ability for this assembly to withstand physiological conditions. Here, we describe the grafting of cross-linked hydrogel networks to titanium surfaces using grit-blasting and subsequent chemical functionalization using a silane-based adhesion promoter. Metal surface characterization was carried out using profilometry, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) analysis. Hydrogel layers composed of poly(ethylene glycol)-dimethacrylate (PEG-DMA), poly(2-hydroxyethylmethacrylate) (PHEMA), or poly(ethylene glycol)/poly(acrylic acid) (PEG/PAA) semi-interpenetrating polymer networks (semi-IPNs) have been prepared. The mechanical properties of these hydrogel-metal assemblies have been characterized using lap-shear measurements, and the surface morphology was studied by SEM and EDX. We have shown that both high surface roughness and chemical functionalization are critical for adhesion of the hydrogel layer to the titanium substrate.

Covalent Immobilization of Collagen on Titanium through Polydopamine Coating to Improve Cellular Performances of MC3T3-E1 Cells

Surface modification of orthopedic implants is critical for improving the clinical performance of these medical devices. Herein, collagen was covalently immobilized onto a titanium implant surface via a novel adherent polydopamine coating inspired by mussel adhesive proteins. The formation and composition of the collagen coating was characterized using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Fluorescent labeled collagen was also used to examine the formation and uniformity of the collagen coating. The resultant collagen coating with a polydopamine supporting substrate demonstrated better uniformity and distribution on the titanium surface compared to a physical adsorption of collagen. The covalent immobilized collagen coating is biologically active, as evidenced by its ability to enhance MC3T3-E1 cell adhesion, support cell proliferation and promote early stage osteogenic differentiation of pre-osteoblasts. Our study suggests covalent immobilization of collagen through the polydopamine coating might be an efficient way to improve the cellular performance of implant surfaces.

Modified Titanium Surfaces Alter Osteogenic Differentiation: A Comparative Microarray-Based Analysis of Human Mesenchymal Cell Response to Commercial Titanium Surfaces

The differential effects of dual-acid etched (Osseotite), hydroxyapatite coated (HA) and sand-blasted/acid-etched (SLA) titanium surfaces on human bone marrow-derived mesenchymal cells (hMSCs) were investigated. Proliferation was significantly promoted on the SLA surfaces. 16 genes were significantly upregulated when hMSCs were cultured on the Osseotite and the HA surfaces and 15 genes on the SLA surfaces. Upregulated genes control cell differentiation, signal transduction, cell cycle regulation, angiogenesis, cell adhesion, and extracellular matrix and bone formation.

A novel silicon-based electrochemical treatment to improve osteointegration of titanium implants

BACKGROUND

Titanium and its alloy represent the most commonly used biomaterials worldwide designed for bone-contact under-load applications, which often require specific mechanical properties. In particular, a large number of different biomimetic surface treatments have been developed to speed up the osteointegration process, which facilitates a reduction in recovery time.

PURPOSE

The aim of this work is to investigate the physical-chemical, mechanical and bioactivity properties of an innovative biomimetic treatment on titanium performed using Anodic Spark Deposition (ASD) electrochemical treatment.

METHODS

The proposed ASD treatment was obtained in an electrochemical solution containing silicon, calcium, phosphorous and sodium followed by an alkali etching. Surface morphology was characterized using SEM and laser profilometry. Chemical and structural composition was assessed by EDS, ICP/OES and XRD analysis. Vickers micro hardness and static contact angle measurements were performed to assess the surface mechanical properties and wettability.

RESULTS

The proposed anodization treatment was capable of providing a chemical and morphologic modified titanium oxide layer, adherent and characterized by superhydrophilic properties. The microporous morphology was enriched by calcium, silicon, sodium and phosphorous.After incubation in Kokubo's Simulated Body Fluid (SBF) the treatment showed very high mineralization potential compared to the reference surfaces, accounting for a deposited hydroxyapatite layer as thick as 12 μm after 14 days of SBF incubation.

CONCLUSIONS

On the basis of the results obtained in this study, we believe that the novel silicon-based ASD biomimetic treatment represents a promising treatment capable of enhancing the osteointegration of titanium for dental and orthopedic applications.

Micro-nanopatterning as tool to study the role of physicochemical properties on cell-surface interactions

The current nano-biotechnologies interfacing synthetic materials and cell biology requires a better understanding of cell-surface interactions on the micro-to-nanometer scale. Cell-substrate interactions are mediated by the presence of proteins adsorbed from biological fluids to the substrate. The effect of nanotopography and surface chemistry on protein adsorption as well as the mediation effect on subsequent cellular communication with substratum is not well documented. This review discusses the role of physicochemical properties of cell-surface interactions and state-of-the-art methods currently available for micro-nanoscale surface fabrication and patterning. We also briefly discuss the current surface patterning techniques that allow the combination of a fine and independent control on nanotopography and chemistry to understand the effect of surface nanoscale substrate morphology on cell-surface interactions which has never been realized in previous reports. In addition, we discuss the influence of various chemical patterning and modulation of the nano-topography of surfaces on cell functionality and phenotype.

Impact of plasma chemistry versus titanium surface topography on osteoblast orientation

Topographical and chemical modifications of biomaterial surfaces both influence tissue physiology, but unfortunately little knowledge exists as to their combined effect. There are many indications that rough surfaces positively influence osteoblast behavior. Having determined previously that a positively charged, smooth titanium surface boosts osteoblast adhesion, we wanted to investigate the combined effects of topography and chemistry and elucidate which of these properties is dominant. Polished, machined and corundum-blasted titanium of increasing microroughness was additionally coated with plasma-polymerized allylamine (PPAAm). Collagen I was then immobilized using polyethylene glycol diacid and glutar dialdehyde. On all PPAAm-modified surfaces (i) adhesion of human MG-63 osteoblastic cells increased significantly in combination with roughness, (ii) cells resemble the underlying structure and melt with the surface, and (iii) cells overcome the restrictions of a grooved surface and spread out over a large area as indicated by actin staining. Interestingly, the cellular effects of the plasma-chemical surface modification are predominant over surface topography, especially in the initial phase. Collagen I, although it is the gold standard, does not improve surface adhesion features comparably.

Biomimetic CaP coating incorporated with parathyroid hormone improves the osseointegration of titanium implant

Parathyroid hormone (PTH) is a well-known therapeutic agent for osteoporosis treatment, however, the inconvenience of daily administration and side effect from systematic administration severely limits its application in clinic. PTH has been incorporated into a biomimetic calcium phosphate (CaP) coating via a co-precipitation method in a modified simulated body fluid. The aim of the current study is to evaluate the osseointegration response of PTH incorporated CaP coating on titanium implants. Implants with different doses of PTH were inserted into tibiae of mice and evaluated by X-ray, micro-CT, histology and back-scattered scanning electron microscopy. Improved osseointegration of the implants loaded with PTH was observed compared to CaP coating only after 28 days of implantation in mouse tibiae. Micro-CT analysis showed better bone integration around the implant incorporated with PTH. Bone area and bone contact evaluations have demonstrated that peri-implant bone regeneration is highly dependent on the dosage of PTH incorporated. The higher the PTH content, the more bone formed surrounding the implant. Therefore, our results suggest that biomimetic CaP coating could be a useful a carrier for PTH local delivery, which results in improved bone-to-implant integration.

Laser surface modification of titanium substrate for pulsed laser deposition of highly adherent hydroxyapatite

Biomedical implant devices made out of titanium and its alloys are benefited by a modified surface or a bioactive coating to enhance bone bonding ability and to function effectively in vivo for the intended period of time. In this respect hydroxyapatite coating developed through pulsed laser deposition is a promising approach. Since the success of the bioactive ceramic coated implant depends mainly on the substrate-coating strength; an attempt has been made to produce micro patterned surface structure on titanium substrate for adherent hydroxyapatite coating. A pulsed Nd-YAG laser beam (355 nm) with 10 Hz repetition rate was used for surface treatment of titanium as well as hydroxyapatite deposition. The unfocussed laser beam was used to modify the substrate surface with 500-18,000 laser pulses while keeping the polished substrate in water. Hydroxyapatite deposition was done in a vacuum deposition chamber at 400 °C with the focused laser beam under 1 × 10⁻³ mbar oxygen pressure. Deposits were analyzed to understand the physico-chemical, morphological and mechanical characteristics. The obtained substrate and coating surface morphology indicates that laser treatment method can provide controlled micro-topography. Scratch test analysis and microindentation hardness values of coating on laser treated substrate indicate higher mechanical adhesion with respect to coatings on untreated substrates.

The Otto Aufranc Award: enhanced biocompatibility of stainless steel implants by titanium coating and microarc oxidation

BACKGROUND

Stainless steel is one of the most widely used biomaterials for internal fixation devices, but is not used in cementless arthroplasty implants because a stable oxide layer essential for biocompatibility cannot be formed on the surface. We applied a Ti electron beam coating, to form oxide layer on the stainless steel surface. To form a thicker oxide layer, we used a microarc oxidation process on the surface of Ti coated stainless steel. Modification of the surface using Ti electron beam coating and microarc oxidation could improve the ability of stainless steel implants to osseointegrate.

QUESTIONS/PURPOSES

The ability of cells to adhere to grit-blasted, titanium-coated, microarc-oxidated stainless steel in vitro was compared with that of two different types of surface modifications, machined and titanium-coated, and microarc-oxidated.

METHODS

We performed energy-dispersive x-ray spectroscopy and scanning electron microscopy investigations to assess the chemical composition and structure of the stainless steel surfaces and cell morphology. The biologic responses of an osteoblastlike cell line (SaOS-2) were examined by measuring proliferation (cell proliferation assay), differentiation (alkaline phosphatase activity), and attraction ability (cell migration assay).

RESULTS

Cell proliferation, alkaline phosphatase activity, migration, and adhesion were increased in the grit-blasted, titanium-coated, microarc-oxidated group compared to the two other groups. Osteoblastlike cells on the grit-blasted, titanium-coated, microarc-oxidated surface were strongly adhered, and proliferated well compared to those on the other surfaces.

CONCLUSIONS

The surface modifications we used (grit blasting, titanium coating, microarc oxidation) enhanced the biocompatibility (proliferation and migration of osteoblastlike cells) of stainless steel.

CLINICAL RELEVANCE

This process is not unique to stainless steel; it can be applied to many metals to improve their biocompatibility, thus allowing a broad range of materials to be used for cementless implants.

Osteoblast response to titanium surfaces functionalized with extracellular matrix peptide biomimetics

OBJECTIVE

Functionalizing surfaces with specific peptides may aid osteointegration of orthopedic implants by favoring attachment of osteoprogenitor cells and promoting osteoblastic differentiation. This study addressed the hypothesis that implant surfaces functionalized with peptides targeting multiple ligands will enhance osteoblast attachment and/or differentiation. To test this hypothesis, we used titanium (Ti) surfaces coated with poly-l-lysine-grafted polyethylene glycol (PLL-g-PEG) and functionalized with two peptides found in extracellular matrix proteins, arginine-glycine-aspartic acid (RGD) and lysine-arginine-serine-arginine (KRSR), which have been shown to increase osteoblast attachment. KSSR, which does not promote osteoblast attachment, was used as a control.

MATERIALS AND METHODS

Sandblasted acid-etched titanium surfaces were coated with PLL-g-PEG functionalized with varying combinations of RGD and KRSR, as well as KSSR. Effects of these surfaces on osteoblasts were assessed by measuring cell number, alkaline phosphatase-specific activity, and levels of osteocalcin, transforming growth factor beta-1 (TGF-β1), and PGE(2).

RESULTS

RGD increased cell number, but decreased markers for osteoblast differentiation. KRSR alone had no effect on cell number, but decreased levels of TGF-β1 and PGE(2). KRSR and RGD/KRSR coatings inhibited osteoblast differentiation vs. PLL-g-PEG. KSSR decreased cell number and increased osteoblast differentiation, indicated by increased levels of osteocalcin and PGE(2).

CONCLUSIONS

The RGD and KRSR functionalized surfaces supported attachment but did not enhance osteoblast differentiation, whereas KSSR increased differentiation. RGD decreased this effect, suggesting that multifunctional peptide surfaces can be designed that improve peri-implant healing by optimizing attachment and proliferation as well as differentiation of osteoblasts, but peptide combination, dose and presentation are critical variables.

Analysis of osteoblastic gene expression in the early human mesenchymal cell response to a chemically modified implant surface: an in vitro study

OBJECTIVES

The effect of a chemical modification of the SLA surface (SLActive surface) on human bone marrow-derived mesenchymal cells (hMSCs) on; (1) adhesion, (2) proliferation and (3) early transcriptional control of osteogenic differentiation was investigated. We are based on the hypothesis that expression patterns of genes responsible for osteogenesis might be dependent on the characteristics of the implant surface.

MATERIAL AND METHODS

hMSCs were allowed to grow on smooth (SMO-control), SLA and SLActive implant surfaces (chemically modified). Cell attachment and proliferation were assessed at 3 and 24 h using a MTT dye reduction assay. At 24 h of culture, DNA microarray analysis examined alterations in early gene expression using a human osteogenesis gene array, including 109 cDNAs in quadruplicates of major regulatory genes for osteogenesis.

RESULTS

Initial attachment and proliferation were found to be significantly reduced. Nineteen genes were significantly upregulated when hMSCs were cultured on the SLA surfaces and 27 genes were significantly upregulated when hMSCs were cultured on the SLActive surfaces. Upregulated genes control cell differentiation, signal transduction, cell cycle regulation, angiogenesis, cell adhesion and extracellular matrix and bone formation.

DISCUSSION

Chemical modification decreases further cell attachment and proliferation and upregulates early osteoblastic differentiation genes. Hence, a microenvironment is created around chemically modified implants that may enhance osseointegration.

Genotoxicity and cytotoxicity of zinc oxide and titanium dioxide in HEp-2 cells

Aims: The rapidly growing industrial and medical use of nanomaterials, especially zinc oxide and titanium dioxide, has led to growing concerns about their toxicity. Accordingly, the intrinsic genotoxic and cytotoxic potential of these nanoparticles have been evaluated. Materials & methods: Using a HEp-2 cell line, cytotoxicity was tested along with mitochondrial activity and neutral red uptake assays. The genotoxic potential was determined using the Comet and the cytokinesis-blocked micronucleus assays. In addition, tyrosine phosphorylation events were investigated. Results & conclusion: We found concentration- and time-dependent cytotoxicity and an increase in DNA and cytogenetic damage with increasing nanoparticle concentrations. Mainly for zinc oxide, genotoxicity was clearly associated with an increase in tyrosine phosphorylation. Our results suggest that both types of nanoparticles can be genotoxic over a range of concentrations without being cytotoxic.

Peptide aptamers against titanium-based implants identified through phage display

Commercially pure titanium (cp-Ti) is widely used in the field of long-term clinical oral implantology owing to its ability to allow close bone-implant apposition. The optimization of its function based on artificial proteins has become a key issue in the development of improved cp-Ti implants. Here, we set out to identify peptide aptamers with preferential adsorption towards titanium-based implants through the phage display methodology. Fifteen sequences were selected in the third round of biopanning. One sequence, ATWVSPY (named TBP1), had a 40% repetition rate and exhibited the strongest binding affinity to cp-Ti disks. Ten sequences were selected in the fourth round, among which the repetition rate is 80% for TBP1 and 20% for TBP2 (GVGLPHT). The peptide aptamers against cp-Ti disks can provide an alternative method of functional coating for biomaterial surfaces.

Titanium Surface Modification Techniques for Implant Fabrication – From Microscale to the Nanoscale

This manuscript reviews about titanium surface modification techniques for its application in orthopaedic and dental implants. There are a few limitations in the long term prognosis of orthopaedic and dental implants. Poor osseointegration with bone, periimplant infection leading to implant failure and short term longevity demanding revision surgery, are to mention a few. Micro- and nanoscale modification of titanium surface using physicochemical, morphological and biochemical approaches have resulted in higher bone to implant contact ratio and improved osseointegration. With recent advances in micro, nano-fabrication techniques and multidisciplinary research studies focusing on bridging biomaterials for medical applications, TiO2 nanotubes have been extensively studied for implant applications. The need for titanium implant surface that can closely mimic the nanoscale architecture of human bone has become a priority. For such purpose, TiO2 nanotubes of different dimensions and architectural fashions at the nanoscale level are being evaluated. This manuscript discusses in brief about the in-vitro and in-vivo studies on titanium surface modification techniques. This manuscript also addresses the recent studies done on such nanotubular surfaces for the effective delivery of osteoinductive growth factors and anti bacterial/ anti inflammatory drugs to promote osseointegration and prevent peri-implant infection.