The effect of surface chemistry modification of titanium alloy on signalling pathways in human osteoblasts

Evolving marine biomimetics for regenerative dentistry

New products that help make human tissue and organ regeneration more effective are in high demand and include materials, structures and substrates that drive cell-to-tissue transformations, orchestrate anatomical assembly and tissue integration with biology. Marine organisms are exemplary bioresources that have extensive possibilities in supporting and facilitating development of human tissue substitutes. Such organisms represent a deep and diverse reserve of materials, substrates and structures that can facilitate tissue reconstruction within lab-based cultures. The reason is that they possess sophisticated structures, architectures and biomaterial designs that are still difficult to replicate using synthetic processes, so far. These products offer tantalizing pre-made options that are versatile, adaptable and have many functions for current tissue engineers seeking fresh solutions to the deficiencies in existing dental biomaterials, which lack the intrinsic elements of biofunctioning, structural and mechanical design to regenerate anatomically correct dental tissues both in the culture dish and in vivo.

Bone regeneration performance of surface-treated porous titanium

The large surface area of highly porous titanium structures produced by additive manufacturing can be modified using biofunctionalizing surface treatments to improve the bone regeneration performance of these otherwise bioinert biomaterials. In this longitudinal study, we applied and compared three types of biofunctionalizing surface treatments, namely acid-alkali (AcAl), alkali-acid-heat treatment (AlAcH), and anodizing-heat treatment (AnH). The effects of treatments on apatite forming ability, cell attachment, cell proliferation, osteogenic gene expression, bone regeneration, biomechanical stability, and bone-biomaterial contact were evaluated using apatite forming ability test, cell culture assays, and animal experiments. It was found that AcAl and AnH work through completely different routes. While AcAl improved the apatite forming ability of as-manufactured (AsM) specimens, it did not have any positive effect on cell attachment, cell proliferation, and osteogenic gene expression. In contrast, AnH did not improve the apatite forming ability of AsM specimens but showed significantly better cell attachment, cell proliferation, and expression of osteogenic markers. The performance of AlAcH in terms of apatite forming ability and cell response was in between both extremes of AnH and AsM. AcAl resulted in significantly larger volumes of newly formed bone within the pores of the scaffold as compared to AnH. Interestingly, larger volumes of regenerated bone did not translate into improved biomechanical stability as AnH exhibited significantly better biomechanical stability as compared to AcAl suggesting that the beneficial effects of cell-nanotopography modulations somehow surpassed the benefits of improved apatite forming ability. In conclusion, the applied surface treatments have considerable effects on apatite forming ability, cell attachment, cell proliferation, and bone ingrowth of the studied biomaterials. The relationship between these properties and the bone-implant biomechanics is, however, not trivial.

Osteoconductive Potential of Mesoporous Titania Implant Surfaces Loaded with Magnesium: An Experimental Study in the Rabbit

BACKGROUND

Mesoporous coatings enable incorporation of functional substances and sustainedly release them at the implant site. One bioactive substance that can be incorporated in mesoporous is magnesium, which is strongly involved in bone metabolism and in osteoblast interaction.

PURPOSE

The aim of this experimental study was to evaluate the effect of incorporation of magnesium into mesoporous coatings of oral implants on early stages of osseointegration.

MATERIAL AND METHODS

Titanium implants were coated with thin films of mesoporous TiO2 having pore diameters of 6 nm and were loaded with magnesium. The implant surfaces were extensively characterized by means of interferometry, atomic force microscopy, scanning electron microscopy, and energy-dispersive spectroscopy and then placed in the tibiae of 10 rabbits. After 3 weeks of healing, osseointegration was evaluated by means of removal torque testing and histology and histomorphometry.

RESULTS

Histological and biomechanical analyses revealed no side effects and successful osseointegration of the implants. The biomechanical evaluation evidenced a significant effect of magnesium doping on strengthening the implant-bone interface.

CONCLUSIONS

A local release of magnesium from the implant surfaces enhances implant retention at the early stage of healing (3 weeks after implantation), which is highly desirable for early loading of the implant.

Kaolin-reinforced 3D MBG scaffolds with hierarchical architecture and robust mechanical strength for bone tissue engineering

Mechanically stable MBG-XK scaffolds with hierarchical porous structure and excellent biologic performance were prepared via a facile multi-template method with kaolin as reinforcing agent.

Reprogramming and carcinogenesis--parallels and distinctions

Rapid progress made in various areas of regenerative medicine in recent years occurred both at the cellular level, with the Nobel prize-winning discovery of reprogramming (generation of induced pluripotent stem (iPS) cells) and also at the biomaterial level. The use of four transcription factors, Oct3/4, Sox2, c-Myc, and Klf4 (called commonly "Yamanaka factors") for the conversion of differentiated cells, back to the pluripotent/embryonic stage, has opened virtually endless and ethically acceptable source of stem cells for medical use. Various types of stem cells are becoming increasingly popular as starting components for the development of replacement tissues, or artificial organs. Interestingly, many of the transcription factors, key to the maintenance of stemness phenotype in various cells, are also overexpressed in cancer (stem) cells, and some of them may find the use as prognostic factors. In this review, we describe various methods of iPS creation, followed by overview of factors known to interfere with the efficiency of reprogramming. Next, we discuss similarities between cancer stem cells and various stem cell types. Final paragraphs are dedicated to interaction of biomaterials with tissues, various adverse reactions generated as a result of such interactions, and measures available, that allow for mitigation of such negative effects.

In vitro evaluation of human fetal osteoblast response to magnesium loaded mesoporous TiO2 coating

This work aimed to evaluate the in vitro response of Transfected Human Foetal Osteoblast (hFOB) cultured on a magnesium-loaded mesoporous TiO2 coating. The application of mesoporous films on titanium implant surfaces has shown very promising potential to enhance osseointegration. This type of coating has the ability to act as a framework to sustain bioactive agents and different drugs. Magnesium is the element that, after calcium, is the most frequently used to dope titanium implant surfaces, since it is crucial for protein formation, growth factor expression, and aids for bone mineral deposition on implant surfaces. Mesoporous TiO2 films with an average pore-size of 6 nm were produced by the evaporation-induced self-assembly method (EISA) and deposited onto titanium discs. Magnesium loading was performed by soaking the mesoporous TiO2 discs in a magnesium chloride solution. Surface characterization was conducted by SEM, XPS, optical interferometry, and AFM. Magnesium release profile was assessed at different time points using a Magnesium Detection kit. Cell morphology and spreading were observed with SEM. The cytoskeletal organization was stained with TRITC-conjugated Phalloidin and cell viability was evaluated through a mitochondrial colorimetric (MTT) assay. Furthermore, gene expression of bone markers and cell mineralization were analyzed by real time RT-PCR and alizarin-red staining, respectively. The surface chemical analysis by XPS revealed the successful adsorption of magnesium to the mesoporous coating. The AFM measurements revealed the presence of a nanostructured surface roughness. Osteoblasts viability and adhesion as well as the gene expression were unaffected by the addition of magnesium possibly due to its rapid burst release, however, were enhanced by the 3D nanostructure of the TiO2 layer.

Cellular reactions to biodegradable magnesium alloys on human growth plate chondrocytes and osteoblasts

PURPOSE

In recent decades operative fracture treatment using elastic stable intramedullary nails (ESINs) has mainly taken precedence over conservative alternatives in children. The development of biodegradable materials that could be used for ESINs would be a further step towards treatment improvement. Due to its mechanical and elastic properties, magnesium seems to be an ideal material for biodegradable implant application. The aim of this study was therefore to investigate the cellular reaction to biodegradable magnesium implants in vitro.

METHODS

Primary human growth plate chondrocytes and MG63 osteoblasts were used for this study. Viability and metabolic activity in response to the eluate of a rapidly and a slower degrading magnesium alloy were investigated. Furthermore, changes in gene expression were assessed and live cell imaging was performed.

RESULTS

A superior performance of the slower degrading WZ21 alloy's eluate was detected regarding cell viability and metabolic activity, cell proliferation and morphology. However, the ZX50 alloy's eluate induced a favourable up-regulation of osteogenic markers in MG63 osteoblasts.

CONCLUSIONS

This study showed that magnesium alloys for use in biodegradable implant application are well tolerated in both osteoblasts and growth plate chondrocytes respectively.

Evaluation of stability changes in magnesium-incorporated titanium implants in the early healing period

The aim of the present study was to determine the bone response to magnesium (Mg) ion-incorporated titanium (Ti) implants during the early healing period. A total of 114 patients (69 men and 45 women aged between 29 and 71 years) participated in the study. Overall, one hundred thirty-three 10-mm-long fixtures were installed, composed of 65 Mg ion-incorporated fixtures in the test group (55 participants; 30 males and 25 females) and 68 resorbable blast media (RBM) surface fixtures in the control group (59 participants; 39 males and 20 females). The bone responses were evaluated by resonance frequency analysis (RFA) at the following time points after implant insertion (ie, the healing period): 0, 2, 4, 8, and 12 weeks. Each time an RFA measurement was taken, the stability changes relating to both bone quality and implant arch location (maxilla or mandible) were recorded for further analysis. The mean stabilities were lowest at week 4 of healing for both the test and control groups. Significant differences in RFA values between the 2 groups were found at week 12 of healing. The mean percentage change in implant stability quotient (ISQ) from the baseline revealed that the implant stability of the Mg ion-incorporated test group had increased (4.55%) more than the RBM surface group (2.23%) by week 12 of healing. With respect to bone quality, the mean ISQ of Mg-incorporated Ti implants only changed significantly during the 12-week period for type 4 bone. Furthermore, at weeks 4 and 12 of healing, significant differences were found between the 2 groups for type 2 and type 4 bone. A comparison of the stability patterns of mandibular and maxillary implants revealed that the overall stability was higher in the mandible; however, no significant difference was found for Mg-incorporated Ti implants. The Mg-incorporated Ti implants exhibited a slightly better bone response with respect to ISQ than did the RBM surface implants, and the percentage change in mean ISQ from the baseline was greater for the Mg-incorporated group than for the RBM surface group at the end point of this study.

Effect of Poly-L-Lysine coating on titanium osseointegration: from characterization to in vivo studies

Dental implant prostheses cannot preclude a correct and stable implant osseointegration, which is still a challenge and greatly depends on biomaterial-cell interface. Titanium (Ti) coating using polyelectrolyte poly-L-lysine (PLL) may represent an interesting and simple approach, to provide a charged surface net able to improve cell adherence. However, in vitro and in vivo effects of Ti coated with PLL have been poorly investigated. The aims of the present study are (1) to obtain and characterize, chemically and physically, Ti disks coated with PLL (TiPLL); (2) to perform in vitro studies on osteoblast cell lines' cytocompatibility and functionality (alkaline phosphatase [ALP] activity, calcium deposition, proinflammatory interleukin 6 production); (3) to obtain in vivo evidence of osseointegration, using a sheep animal model. XPS, AFM, and contact-angle analyses demonstrated that the Ti disk was successfully covered with PLL, providing higher hydrophilicity to the Ti disk. No cellular toxicity, enhanced calcium deposition, and a decreased tendency toward interleukin-6 production were observed in the osteoblast seeded onto TiPLL. In vivo experiments showed cortical bone microhardness at 3 months significantly improved in the presence of the PLL coating. PLL coating on Ti implants seemed to safely enhance calcium deposition and implant early osseointegration in animals, suggesting promising evidence to optimize the surface properties of dental implants.

Hydroxyapatite, fluor-hydroxyapatite and fluorapatite produced via the sol-gel method: bonding to titanium and scanning electron microscopy

OBJECTIVES

Hydroxyapatite (HA), fluor-hydroxyapatite (FHA) with varying levels of fluoride ion substitution and fluorapatite (FA) production has been characterised and optimised by the sol-gel method and the dissolution and biological properties of these materials were investigated. It was the objective of this study to investigate the potential bond strength and interaction of these materials with titanium.

METHODS

HA, FHA and FA were synthesised by a sol-gel method. Calcium nitrate and triethyl phosphite were used as precursors under an ethanol-water based solution. Different amounts of ammonium fluoride (NH4F) were incorporated for the preparation of the FHA and FA sol-gels. Using a spin coating technique the sol-gels were coated onto commercially pure titanium disks and crystallised at various temperatures. Using scanning electron microscopy (SEM) and elemental analysis, the surface characteristics, coating thickness and interaction of the Ti substrate and coating were investigated. The bond strengths of the coating to the Ti were investigated using an Instron Universal Load Testing Machine. Statistical analysis was performed with a two-way analysis of variance and post hoc testing with a Bonferroni correction.

RESULTS

(1) Coating speed inversely influenced the coating thickness. (2) Increasing fluoride ion substitution and heating temperature significantly increased bond strength and (3) increasing fluoride ion substitution increased the coating thickness.

SIGNIFICANCE

FHA and FA synthesised using the sol-gel technique may offer a superior alternative to coating titanium implants with HA and plasma spraying. HA, FHA and FA materials synthesised by the sol-gel method may also have a use as bone grafting materials.

Evaluating the feasibility of utilizing the small molecule phenamil as a novel biofactor for bone regenerative engineering

Osteoblast cell adhesion and differentiation on biomaterials are important achievements necessary for implants to be useful in bone regenerative engineering. Recombinant bone morphogenetic proteins (BMPs) have been shown to be important for these processes; however, there are many challenges associated with the widespread use of these proteins. A recent report demonstrated that the small molecule phenamil, a diuretic derivative, was able to induce osteoblast differentiation and mineralization in vitro via the canonical BMP signalling cascade (Park et al., 2009). In this study, the feasibility of using phenamil as a novel biofactor in conjunction with a biodegradable poly(lactide-co-glycolide acid) (PLAGA) polymeric scaffold for engineering bone tissue was evaluated. The in vitro cellular behaviour of osteoblast-like MC3T3-E1 cells cultured on PLAGA scaffolds in the presence of phenamil at 10 μM were characterized with regard to initial cell adhesion, proliferation, alkaline phosphatase (ALP) activity and matrix mineralization. The results demonstrate that phenamil supported cell proliferation, promoted ALP activity and facilitated matrix mineralization of osteoblast-like MC3T3-E1 cells. Moreover, in this study, we found that phenamil promoted integrin-mediated cell adhesion on PLAGA scaffolds. It was also shown that phenamil encapsulated within porous, microsphere PLAGA scaffolds retained its osteogenic activity upon release. Based on these findings, the small molecule phenamil has the potential to serve as a novel biofactor for the repair and regeneration of bone tissues.

Surface modification of titanium by hydrothermal treatment in Mg-containing solution and early osteoblast responses

Surface modification on titanium was carried out in order to improve its bioactivity. Pure titanium was hydrothermally treated in distilled water and 0.1 M MgCl(2) solutions at 200°C for 24 h. Surface morphology, roughness, wettability and chemical composition were characterized before and after treatment. Bovine serum albumin was used as model to study protein adsorption. MC3T3-E1 cells were cultured and initial cell attachment, morphology, proliferation were evaluated. After hydrothermal treatment, nano-sized precipitations were observed and samples showed superhydrophilicity. Magnesium (Mg) was immobilized into titanium surface by hydrothermal treatment. Protein adsorption was significantly increased on Mg-containing samples. Cell attachment was improved and cell spreading was enhanced on Mg-containing samples compared with untreated or those treated in distilled water. Increased early cellular attachment on the MgTi surface resulted in subsequent increase of number of proliferated cells. Hydrothermal treatment in MgCl(2) solution was expected to be an effective method to fabricate titanium implant with good bioactivity.

ELECTROHYDRODYNAMIC PROCESSING OF CALCIUM PHOSPHATES: COATING AND PATTERNING FOR MEDICAL IMPLANTS

Hydroxyapatite (HA)-coated metallic prostheses, which combine the osteoconductivity of HA and high strength of metallic alloys, have been increasingly the choice of joint replacement prostheses by surgeons as the general population lives longer. Surface modification of metallic implant surfaces is one of the key focal points to implantation technology. In addition to material chemistry, surface topography has been found to positively impact cellular response and is able to enhance the life time of the implant. Recently, a new technique, template-assisted electrohydrodynamic atomization (TAEA) spraying, developed using the principles of electrohydrodynamic atomization spraying, which is an electrically driven jet-based deposition method, is of considerable interest in surface topography formation. The process offers the attractive advantages of compatibility with micro-fabrication technology and versatility in pattern specification for advanced implant designs. This technology incorporates nanosized calcium phosphate to mimic the size and chemical composition of bone mineral in a micrometer-dimension pattern configuration to guide cellular responses. In vitro studies showed that both pillar and track nano Silicon-substituted HA (SiHA) patterns were able to encourage the attachment and growth of osteoblast cells, the track patterns provided the favourite surface for the initial cell attachment while a fast cell proliferation rate was found on the pillar pattern from day 1 to day 5 in comparison with that of a SiHA-coated surface. The alignment of actin cytoskeleton of osteoblast cells matched the orientation of the entire cell. The shear peel strength of the patterned interlocking nano-HA coating was found to be at least an order of magnitude higher than the conventional HA coating. Therefore, TAEA offers great potential for producing new coatings with a tailored surface topography, on both the micro- and nano-scale in a more cost effective way to enhance the performance of medical implants.

Effect of self-assembled nanofibrous silk/polycaprolactone layer on the osteoconductivity and mechanical properties of biphasic calcium phosphate scaffolds

We here present the first successful report on combining nanostructured silk and poly(ε-caprolactone) (PCL) with a ceramic scaffold to produce a composite scaffold that is highly porous (porosity ∼85%, pore size ∼500 μm, ∼100% interconnectivity), strong and non-brittle with a surface that resembles extracellular matrix (ECM). The ECM-like surface was developed by self-assembly of nanofibrous structured silk (20-80 nm diameter, similar to native collagen found in ECM) over a thin PCL layer which is coated on biphasic calcium phosphate (BCP) scaffolds. The effects of different concentrations of silk solution on the mechanical and physical properties of the scaffolds were also comprehensively examined. Our results showed that using silk only (irrespective of concentration) for the modification of ceramic scaffolds could drastically reduce the compressive strength of the modified scaffolds in aqueous media, and the modification made a limited contribution to improving scaffold toughness. Using PCL/nanostructured silk the compressive strength and modulus of the modified scaffolds reached 0.42 MPa (compared with 0.07 MPa for BCP) and ∼25 MPa (compared with 5 MPa for BCP), respectively. The failure strain of the modified scaffold increased more than 6% compared with a BCP scaffold (failure strain of less than 1%), indicating a transformation from brittle to elastic behavior. The cytocompatibility of ECM-like composite scaffolds was investigated by studying the attachment, morphology, proliferation and bone-related gene expression of primary human bone-derived cells. Cells cultured on the developed scaffolds for 7 days had significant up-regulation of cell proliferation (∼1.6-fold higher, P<0.001) and osteogenic gene expression levels (collagen type I, osteocalcin and bone sialoprotein) compared with the other groups tested.

Global gene expression profile of osteoblast-like cells grown on polyester copolymer scaffolds

One of the principal goals in tissue engineering is to produce scaffold materials that will guide cells to differentiate and regenerate functional replacement tissue at the site of injury. Poly(l-lactide-co-1,5-dioxepan-2-one) [Poly(LLA-co-DXO)], a potential scaffolding material for bone tissue engineering, has high hydrophilicity. Previous in vitro studies using human osteoblast-like cells (HOBs) demonstrated greater cytocompatibility and enhanced osteogenic differentiation when HOBs were seeded onto Poly(LLA-co-DXO) compared to Poly(l-lactide) [P(LLA)] scaffolds. The aim of the study was to identify the gene expression profiles of HOBs obtained from alveolar bone and grown on Poly(LLA-co-DXO) biodegradable polymer scaffolds compared to P(LLA) one. Illumina HumanWG-6 v3.0 Expression BeadChips were used for the gene expression analysis. Several genes were found as differentially expressed at 24 h and at 21 days. Expression of genes related to cell adhesion, cytoskeleton, antiapoptosis, proliferation, and bone mineralization was influenced by adding the monomer 1,5-dioxepan-2-one to the L-lactide. Genes related to three biological pathways involving Integrin, Notch, and Ras were found to be upregulated. For selected genes, results were confirmed by quantitative reverse transcriptase-polymerase chain reaction. Further, calcium content analysis revealed a significant enhancement of calcium deposition on both tested scaffolds. This observation was confirmed by Von Kossa and Alizarin Red S staining. Findings of this study are relevant to a better understanding of the molecular mechanisms underlying the behavior of HOBs in bone regenerative procedure.

Biomaterials and interface with bone

In this paper, some examples from the literature or from my own experience will be given to illustrate the influence of surface topography and surface chemistry at the nano- and micro-scale on the cell and tissue response.

Enhancement of surface wettability via the modification of microtextured titanium implant surfaces with polyelectrolytes

Micrometer- and submicrometer-scale surface roughness enhances osteoblast differentiation on titanium (Ti) substrates and increases bone-to-implant contact in vivo. However, the low surface wettability induced by surface roughness can retard initial interactions with the physiological environment. We examined chemical modifications of Ti surfaces [pretreated (PT), R(a) ≤ 0.3 μm; sand blasted/acid etched (SLA), R(a) ≥ 3.0 μm] in order to modify surface hydrophilicity. We designed coating layers of polyelectrolytes that did not alter the surface microstructure but increased surface ionic character, including chitosan (CHI), poly(L-glutamic acid) (PGA), and poly(L-lysine) (PLL). Ti disks were cleaned and sterilized. Surface chemical composition, roughness, wettability, and morphology of surfaces before and after polyelectrolyte coating were examined by X-ray photoelectron spectroscopy (XPS), contact mode profilometry, contact angle measurement, and scanning electron microscopy (SEM). High-resolution XPS spectra data validated the formation of polyelectrolyte layers on top of the Ti surface. The surface coverage of the polyelectrolyte adsorbed on Ti surfaces was evaluated with the pertinent SEM images and XPS peak intensity as a function of polyelectrolyte adsorption time on the Ti surface. PLL was coated in a uniform thin layer on the PT surface. CHI and PGA were coated evenly on PT, albeit in an incomplete monolayer. CHI, PGA, and PLL were coated on the SLA surface with complete coverage. The selected polyelectrolytes enhanced surface wettability without modifying surface roughness. These chemically modified surfaces on implant devices can contribute to the enhancement of osteoblast differentiation.

Osseointegration of commercial microstructured titanium implants incorporating magnesium: a histomorphometric study in rabbit cancellous bone

OBJECTIVE

Recent studies have suggested that magnesium (Mg) ions exert a beneficial effect on implant osseointegration. This study assessed the osseointegration of nanoporous titanium (Ti) surface incorporating the Mg produced by hydrothermal treatment in rabbit cancellous bone to determine whether this surface would further enhance bone healing of moderately rough-surfaced implants in cancellous bone, and compared the result with commercially available micro-arc oxidized Mg-incorporated implants.

MATERIAL AND METHODS

The Mg-incorporated Ti surfaces (RBM/Mg) were obtained by hydrothermal treatment using an alkaline Mg-containing solution on grit-blasted moderately rough (RBM) implants. Untreated RBM and recently introduced Mg-incorporated microporous Ti implants produced by micro-arc oxidation (M) were used controls in this study. The surface characteristics were evaluated by scanning electron microscopy, X-ray photoelectron spectroscopy and optical profilometry. Twenty-four threaded implants with a length of 10 mm (eight RBM implants, eight RBM/Mg implants and eight M implants) were placed in the femoral condyles of 12 New Zealand White rabbits. Histomorphometric analysis was performed 4 weeks after implantation.

RESULTS

Hydrothermally treated and untreated grit-blasted implants displayed almost identical surface morphologies and R(a) values at the micron-scale. The RBM/Mg implants exhibited morphological differences compared with the RBM implants at the nano-scale, which displayed nanoporous surface structures. The Mg-incorporated implants (RBM/Mg and M) exhibited more continuous bone apposition and a higher degree of bone-to-implant contact (BIC) than the untreated RBM implants in rabbit cancellous bone. The RBM/Mg implants displayed significantly greater BIC% than untreated RBM implants, both in terms of the all threads region and the total lateral length of implants (P<0.05), but no statistical differences were found between the RBM/Mg and M implants except BIC% values in total lateral length.

CONCLUSION

These results indicate that a nanoporous Mg-incorporated surface may be effective in enhancing the osseointegration of moderately rough grit-blasted implants by increasing the degree of bone-implant contact in areas of cancellous bone.

Osteoblasts on rod shaped hydroxyapatite nanoparticles incorporated PCL film provide an optimal osteogenic niche for stem cell differentiation

After the clinical insertion of a bone biomaterial, the surrounding osteoblasts would migrate and attach to the implant surface and foster a microenvironment that largely determines the differentiation fate of the comigrated mesenchymal stem cells. Whether the fostered microenvironment is suitable for osteogenic differentiation of mesenchymal stem cells is critical for the subsequent osseointegration. In this study, we determined (1) how the spherical or rod-shaped hydroxyapatite nanoparticles (nHA) incorporated poly(ɛ-caprolactone) (PCL) films (PCL-spherical nHA, PCL-rod nHA) interact with primary human osteoblasts (HOBs); (2) how the microenvironment rendered by their interaction affects osteogenic differentiation of adipose tissue-derived mesenchymal stem cells (ASCs). HOBs were seeded on PCL, PCL-spherical nHA, and PCL-rod nHA films, respectively. When cultured alone, the HOBs on PCL-rod nHA films showed most efficient osteoblastic differentiation compared with those on PCL or PCL-spherical nHA films. When cocultured with ASCs in an indirect coculture system, only the HOBs on PCL-rod nHA films up-regulated the gene expression of Runx2, bone sialoprotein, and osteocalcin of ASCs. Additionally, the HOBs on PCL-rod nHA films showed significant up-regulation of bone morphogenic protein 2 gene and protein expression and induced highest phosphorylated Smad1/5 protein level in ASCs. Treatment of the coculture medium with bone morphogenic protein 2 inhibitor (Noggin) largely abolished the osteogenic differentiation of the ASCs induced by the HOBs on PCL-rod nHA films. In conclusion, HOBs can not only best display their osteoblastic phenotype by culturing on PCL-rod nHA films but also render an optimal osteogenic niche for the differentiation of stem cells.

Relative influence of surface topography and surface chemistry on cell response to bone implant materials. Part 1: physico-chemical effects

Knowledge of the complexity of cell-material interactions is essential for the future of biomaterials and tissue engineering, but we are still far from achieving a clear understanding, as illustrated in this review. Many factors of the cellular or the material aspect influence these interactions and must be controlled systematically during experiments. On the material side, it is essential to illustrate surface topography by parameters describing the roughness amplitude as well as the roughness organization, and at the scales pertinent for the cell response, i.e., from the nano-scale to the micro-scale. Authors interested in this field must be careful to develop surfaces or methods systematically, allowing perfect control of the relative influences of surface topography and surface chemistry.

Assessment of the genetic risks of a metallic alloy used in medical implants

The use of artificial implants provides a palliative or permanent solution for individuals who have lost some bodily function through disease, an accident or natural wear. This functional loss can be compensated for by the use of medical devices produced from special biomaterials. Titanium alloy (Ti-6Al-4V) is a well-established primary metallic biomaterial for orthopedic implants, but the toxicity of the chemical components of this alloy has become an issue of concern. In this work, we used the MTT assay and micronucleus assay to examine the cytotoxicity and genotoxicity, respectively, of an extract obtained from this alloy. The MTT assay indicated that the mitochondrial activity and cell viability of CHO-K1 cells were unaffected by exposure to the extract. However, the micronucleus assay revealed DNA damage and an increase in micronucleus frequency at all of the concentrations tested. These results show that ions released from Ti-6Al-4V alloy can cause DNA and nuclear damage and reinforce the importance of assessing the safety of metallic medical devices constructed from biomaterials.

Effects of bioactive glass nanoparticles on the mechanical and biological behavior of composite coated scaffolds

Biphasic calcium phosphates (BCP) scaffolds are widely used for bone tissue regeneration. However, brittleness, low mechanical properties and compromised bioactivities are, at present, their major disadvantages. In this study we coated the struts of a BCP scaffold with a nanocomposite layer consisting of bioactive glass nanoparticles (nBG) and polycaprolactone (PCL) (BCP/PCL-nBG) to enhance its mechanical and biological behavior. The effect of various nBG concentrations (1-90 wt.%) on the mechanical properties and in vitro behavior of the scaffolds was comprehensively examined and compared with that for a BCP scaffold coated with PCL and hydroxyapatite nanoparticles (nHA) (BCP/PCL-nHA) and a BCP scaffold coated with only a PCL layer (BCP/PCL). Introduction of 1-90 wt.% nBG resulted in scaffolds with compressive strengths in the range 0.2-1.45 MPa and moduli in the range 19.3-49.4 MPa. This trend was also observed for BCP/PCL-nHA scaffolds, however, nBG induced even better bioactivity and a faster degradation rate. The maximum compressive strength (increased ∼14 times) and modulus (increased ∼3 times) were achieved when 30 wt.% nBG was added, compared with BCP scaffolds. Moreover, BCP/PCL-nBG scaffolds induced the differentiation of primary human bone-derived cells (HOBs), with significant up-regulation of osteogenic gene expression for Runx2, osteopontin and bone sialoprotein, compared with the other groups.

Bone-implant interface strength and osseointegration: Biodegradable magnesium alloy versus standard titanium control

Previous research on the feasibility of using biodegradable magnesium alloys for bone implant applications mainly focused on biocompatibility and corrosion resistance. However, successful clinical employment of endosseous implants is largely dependent on biological fixation and anchorage in host bone to withstand functional loading. In the present study, we therefore aimed to investigate whether bone-implant interface strength and osseointegration of a novel biodegradable magnesium alloy (Mg-Y-Nd-HRE, based on WE43) is comparable to that of a titanium control (Ti-6Al-7Nb) currently in clinical use. Biomechanical push-out testing, microfocus computed tomography and scanning electron microscopy were performed in 72 Sprague-Dawley rats 4, 12 and 24 weeks after implantation to address this question. Additionally, blood smears were obtained from each rat at sacrifice to detect potential systemic inflammatory reactions. Push-out testing revealed highly significantly greater maximum push-out force, ultimate shear strength and energy absorption to failure in magnesium alloy rods than in titanium controls after each implantation period. Microfocus computed tomography showed significantly higher bone-implant contact and bone volume per tissue volume in magnesium alloy implants as well. Direct bone-implant contact was verified by histological examination. In addition, no systemic inflammatory reactions were observed in any of the animals. We conclude that the tested biodegradable implant is superior to the titanium control with respect to both bone-implant interface strength and osseointegration. These results suggest that the investigated biodegradable magnesium alloy not only achieves enhanced bone response but also excellent interfacial strength and thus fulfils two critical requirements for bone implant applications.

Relative influence of surface topography and surface chemistry on cell response to bone implant materials. Part 2: Biological aspects

A current medical challenge is the replacement of tissue which can be thought of in terms of bone tissue engineering approaches. The key problem in bone tissue engineering lies in associating bone stem cells with material supports or scaffolds that can be implanted in a patient. Beside bone tissue engineering approaches, these types of materials are used daily in orthopaedics and dental practice as permanent or transitory implants such as ceramic bone filling materials or metallic prostheses. Consequently, it is essential to better understand how bone cells interact with materials. For several years, the current authors and others have developed in vitro studies in order to elucidate the mechanisms underlying the response of human bone cells to implant surfaces. This paper reviews the current state of knowledge and proposes future directions for research in this domain.

Statistical approach of chemistry and topography effect on human osteoblast adhesion

Our objective in this work was to determine statistically the relative influence of surface topography and surface chemistry of metallic substrates on long-term adhesion of human bone cell quantified by the adhesion power (AP). Pure titanium, titanium alloy, and stainless steel substrates were processed with electro-erosion, sandblasting, or polishing giving various morphologies and amplitudes. The surface chemistry was characterized by X-ray photoelectron spectroscopy (XPS) associated with an extensive analysis of surface topography. The statistical analysis demonstrated that the effect on AP of the material composition was not significant. More, no correlation was found between AP and the surface element concentrations determined by XPS demonstrating that the surface chemistry was not an influencing parameter for long-term adhesion. In the same way, the roughness amplitude, independently of the process, had no influence on AP, meaning that roughness amplitude is not an intrinsic parameter of long-term adhesion. On the contrary, the elaboration process alone had a significant effect on AP. For a same surface elaboration process, the number of inflexion points, or G parameter, was the most pertinent roughness parameter for describing the topography influence on long-term adhesion. Thus, more the inflexion points, more the discontinuities, higher the long-term adhesion.

Osteoblast response to magnesium ion-incorporated nanoporous titanium oxide surfaces

OBJECTIVE

This study investigated the surface characteristics and in vitro osteoconductivity of a titanium (Ti) surface incorporated with the magnesium ions (Mg) produced by hydrothermal treatment for future application as an endosseous implant surface.

MATERIAL AND METHODS

Mg-incorporated Ti oxide surfaces were produced by hydrothermal treatment using Mg-containing solution on two different microstructured surfaces--abraded minimally rough (Ma) or grit-blasted moderately rough (RBM) samples. The surface characteristics were evaluated using scanning electron microscopy, thin-film X-ray diffractometry, X-ray photoelectron spectroscopy, optical profilometry, and inductively coupled plasma atomic emission spectroscopy (ICP-AES). MC3T3-E1 pre-osteoblast cell attachment, proliferation, alkaline phosphatase (ALP) activity, and quantitative analysis of osteoblastic gene expression on Ma, RBM, Mg-incorporated Ma (Mg), and Mg-incorporated grit-blasted (RBM/Mg) Ti surfaces were evaluated.

RESULTS

Hydrothermal treatment produced an Mg-incorporated Ti oxide layer with nanoporous surface structures. Mg-incorporated surfaces showed surface morphologies and surface roughness values almost identical to those of untreated smooth or micro-rough surfaces at the micron scale. ICP-AES analysis showed Mg ions released from treated surfaces into the solution. Mg incorporation significantly increased cellular attachment (P=0 at 0.5 h, P=0.01 at 1 h) on smooth surfaces, but no differences were found on micro-rough surfaces. Mg incorporation further increased ALP activity in cells grown on both smooth and micro-rough surfaces at 7 and 14 days of culture (P=0). Real-time polymerase chain reaction analysis showed higher mRNA expressions of the osteoblast transcription factor gene (Dlx5), various integrins, and the osteoblast phenotype genes (ALP, bone sialoprotein and osteocalcin) in cells grown on micro-rough (RBM) and Mg-incorporated (Mg and RBM/Mg) surfaces than those on Ma surfaces. Mg incorporation further increased the mRNA expressions of key osteoblast genes and integrins (α1, α2, α5, and β1) in cells grown on both the smooth and the micro-rough surfaces.

CONCLUSION

These results indicate that an Mg-incorporated nanoporous Ti oxide surface produced by hydrothermal treatment may improve implant bone healing by enhancing the attachment and differentiation of osteoblastic cells.

Cell response of titanium implant with a roughened surface containing titanium hydride: an in vitro study

PURPOSE

The purpose of this study was to investigate the effect of surface chemistry of a sandblasted and acid-etched implant (with and without titanium hydride [TiH(2)]) on cell attachment, proliferation, and differentiation of preosteoblasts (MC3T3-E1).

MATERIALS AND METHODS

Sandblasted and dual acid-etched titanium discs comprised the test group, whereas sandblasted, acid-etched, and heat-treated discs comprised the control group. Both groups' discs were sent for surface characterization. MC3T3-E1 cells were cultured on these 2 groups' discs, and then cell attachment, cell proliferation, and cell differentiation were analyzed.

RESULTS

Scanning electron microscope analysis showed that the titanium discs in the 2 groups shared the same surface topography; however, x-ray diffraction examination showed that the TiH(2) diffractions only appeared in the test group. Cell attachment and cell proliferation were much better in the test group than in the control group at all time points investigated (P < .05). The expressions of alkaline phosphatase and osteocalcin were significantly higher in the test group than in the control group for both protein and transcription level at every time point (P < .05 or P < .01).

CONCLUSIONS

These results suggested that surface chemistry played a significant role in cell response to the sandblasted and acid-etched surface and the presence of TiH(2) might promote the attachment, proliferation, and differentiation of preosteoblasts.

Structure-property relationships of silk-modified mesoporous bioglass scaffolds

Porous mesopore-bioglass (MBG) scaffolds have been proposed as a new class of bone regeneration materials due to their apatite-formation and drug-delivery properties; however, the material's inherent brittleness and high degradation and surface instability are major disadvantages, which compromise its mechanical strength and cytocompatibility as a biological scaffold. Silk, on the other hand, is a native biomaterial and is well characterized with respect to biocompatibility and tensile strength. In this study we set out to investigate what effects blending silk with MBG had on the physiochemical, drug-delivery and biological properties of MBG scaffolds with a view to bone tissue engineering applications. Transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were the methods used to analyze the inner microstructure, pore size and morphology, and composition of MBG scaffolds, before and after addition of silk. The effect of silk modification on the mechanical property of MBG scaffolds was determined by testing the compressive strength of the scaffolds and also compressive strength after degradation over time. The drug-delivery potential was evaluated by the release of dexamethasone (DEX) from the scaffolds. Finally, the cytocompatibility of silk-modified scaffolds was investigated by the attachment, morphology, proliferation, differentiation and bone-relative gene expression of bone marrow stromal cells (BMSCs). The results showed that silk modification improved the uniformity and continuity of pore network of MBG scaffolds, and maintained high porosity (94%) and large-pore size (200-400 microm). There was a significant improvement in mechanical strength, mechanical stability, and control of burst release of DEX in silk-modified MBG scaffolds. Silk modification also appeared to provide a better environment for BMSC attachment, spreading, proliferation, and osteogenic differentiation on MBG scaffolds.

In vivo studies of the ceramic coated titanium alloy for enhanced osseointegration in dental applications

This paper reports the effect of the various ceramic coatings viz., hydroxyapatite (HA) and partially stabilized zirconia (PSZ) on the bond strength between the bone and implant, and cell compatibility of screw-shaped Ti-6Al-7Nb dental implants. Electrophoretic deposition technique (EPD) was used to obtain a uniform coating of one of the three types of ceramic layers (HA, PSZ and 50%HA + 50%PSZ) on the screws. Structural investigations were carried out on the prepared HA powder and the modified surfaces of the Ti-6Al-7Nb alloy using different techniques, namely X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The in vivo studies were performed by the implantation of screw-shaped uncoated and coated implants in the tibia of white New Zealand rabbits. To understand the bone-implant interface, biomechanical test was carried out after 2, 6 and 18 weeks healing periods. There was increased mechanical strength (torque value) of bone-implant interface with time, and the highest increment in the bond strength was recorded for implants coated with a 50% HA and 50% PSZ. Histological results show that the coated Ti-6Al-7Nb screws after 18 weeks of the implantation seem to be well-tolerated by the bone since no adverse tissue reaction was evident. However, there was a faster reaction of bone towards the coated implants compared to the uncoated one. The histochemical stain studies shows higher cellular activity and mature bone formation on all the samples.

Proliferation and differentiation of osteoblast-like MC3T3-E1 cells on biomimetically and electrolytically deposited calcium phosphate coatings

Biomimetic and electrolytic deposition are versatile methods to prepare calcium phosphate coatings. In this article, we compared the effects of biomimetically deposited octacalcium phosphate and carbonate apatite coatings as well as electrolytically deposited carbonate apatite coating on the proliferation and differentiation of mouse osteoblast-like MC3T3-E1 cells. It was found that MC3T3-E1 cells cultured on the biomimetically deposited carbonate apatite coating demonstrated the greatest proliferation rate and the highest differentiation potential. Cells on the biomimetically deposited octacalcium phosphate coating had lower proliferation rate before day 7, but higher after that, than those on the electrolytically deposited carbonate apatite coating. There was no difference on the expression of early differentiation markers, that is, alkaline phosphatase activity and collagen content, between biomimetically deposited octacalcium phosphate and electrolytically deposited carbonate apatite coatings. However, higher expression of late differentiation markers, that is, osteocalcin and bone sialoprotein mRNA, was found on the biomimetically deposited octacalcium phosphate coating on day 14. These results suggest that the difference in in vitro osteoblast cell performance of calcium phosphate coatings might relate to their physicochemical properties. Biomimetic carbonate apatite coating is the most favorable surface for the proliferation and differentiation of MC3T3-E1 cells.

Specific biofunctional performances of the hydroxyapatite-sodium maleate copolymer hybrid coating nanostructures evaluated by in vitro studies

The nanohybrid structures consisting of hydroxyapatite (HA) and sodium maleate-vinyl acetate copolymer (MP) deposited by Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique on Ti surfaces were investigated for specific biological qualities required in bone implantology. The data from in vitro studies demonstrated that human primary osteoblasts (OBs) firmly adhered to Ti coated with HA-MP as indicated by cytoskeleton and vinculin dynamics. OBs spread onto biomaterial surface and formed groups of cells which during their biosynthetic activity expressed OB phenotype specific markers (collagen and non-collagenous proteins) and underwent controlled proliferation.

Increased Biocompatibility and Bioactivity after Energetic PVD Surface Treatments

Ion implantation, a common technology in semiconductor processing, has been applied to biomaterials since the 1960s. Using energetic ion bombardment, a general term which includes conventional ion implantation plasma immersion ion implantation (PIII) and ion beam assisted thin film deposition, functionalization of surfaces is possible. By varying and adjusting the process parameters, several surface properties can be attuned simultaneously. Extensive research details improvements in the biocompatibility, mainly by reducing corrosion rates and increasing wear resistance after surface modification. Recently, enhanced bioactivity strongly correlated with the surface topography and less with the surface chemistry has been reported, with an increased roughness on the nanometer scale induced by self-organisation processes during ion bombardment leading to faster cellular adhesion processes.

Bone growth is enhanced by novel bioceramic coatings on Ti alloy implants

Calcium phosphate ceramics are widely used as coating materials to orthopedic implants and are found to enhance initial bony ingrowth by stimulating osseous apposition to the implant surface. In this study, two novel calcium orthophosphate materials were selected for coating onto the commonly used orthopedic implant material Ti-6Al- 4V. One was calcium alkali orthophosphate with the crystalline phase Ca10[K/Na](PO4)7 with a small addition of SiO2 (AW-Si) and the other was calcium orthophosphate composed of 70 mol % fluorapatite, Ca10(PO4)6F2 and 30 mol % CaZr4(PO4)6 (FA7Z). The coated implants were placed in cortical and cortico-cancellous bone of sheep femur for six weeks. Retrieved samples were tested for osseointegration and mechanical strength. It was found that both coatings produced enhanced bone/implant contact rate compared to the control when implanted in cortico-cancellous bone. This study demonstrates that the two coatings have the capability of encouraging bone growth, and hence the potential for being used as coating materials on Ti implants.

Orthopedic coating materials: considerations and applications

The host response to titanium and its alloys is not always favorable, as a fibrous layer may form at the skeletal tissue-device interface, causing aseptic loosening. Therefore, a great deal of current orthopedic research is focused on developing implants with improved osseointegration properties in order to increase their clinical success. Promising new studies have been reported regarding coating the currently available implants with various coating materials and techniques so as to improve the long-term stability of implants. This article will discuss various coating materials developed, their advantages and disadvantages as coating materials and their biological performance.

Spatial and temporal changes in the morphology of preosteoblastic cells seeded on microstructured tantalum surfaces

It has been widely reported that surface morphology on the micrometer scale affects cell function as well as cell shape. In this study, we have systematically compared the influence of 13 topographically micropatterned tantalum surfaces on the temporal development of morphology, including spreading, and length of preosteoblastic cells (MC3T3-E1). Cells were examined after 0.5, 1, 4, and 24 h on different Ta microstructures with vertical dimensions (heights) of 0.25 and 1.6 mum. Cell morphologies depended upon the underlying surface topography, and the length and spreading of cells varied as a function of time with regard to the two-dimensional pattern and vertical dimension of the structure. Microstructures of parallel grooves/ridges caused elongated cell growth after 1 and 4 h in comparison to a flat, nonstructured, reference surface. For microstructures consisting of pillars, cell spreading was found to depend on the distance between the pillars with one specific pillar structure exhibiting a decreased spreading combined with a radical change in morphology of the cells. Interestingly, this morphology on the particular pillar structure was associated with a markedly different distribution of the actin cytoskeleton. Our results provide a basis for further work toward topographical guiding of cell function.