Surface roughness mediates its effects on osteoblasts via protein kinase A and phospholipase A2

Arachidonic Acid and Prostaglandin E2 Influence Human Osteoblast (MG63) Response to Titanium Surface Roughness

Prior studies have shown that implant surface roughness affects osteoblast proliferation, differentiation, matrix synthesis, and local factor production. Further, cell response is modulated by systemic factors, such as 1,25(OH)2D3 and estrogen as well as mechanical forces. Based on the fact that peri-implant bone healing occurs in a site containing elevated amounts of prostaglandin E2 (PGE2), the hypothesis of the current study is that PGE2 and arachidonic acid (AA), the substrate used by cyclooxygenase to form PGE2, influence osteoblast response to implant surface roughness. To test this hypothesis, 4 different types of commercially pure titanium (cpTi) disks with surfaces of varying roughness (smooth Ti, Ra 0.30 μm; smooth and acid etched Ti [SAE Ti], Ra 0.40 μm; rough Ti, Ra 4.3 μm; rough and acid etched Ti [RAE Ti], Ra 4.15μm) were prepared. MG63 osteoblasts were seeded onto the surfaces, cultured to confluence, and then treated for the last 24 hours of culture with AA (0, 0.1, 1, and 10 nM), PGE2 (0, 1, 10, 25, and 100 nM), or the general cyclooxygenase inhibitor indomethacin (0 or 100 nM). At harvest, the effect of treatment on cell proliferation was assessed by measuring cell number and [3H]-thymidine incorporation, and the effect on cell differentiation was determined by measuring alkaline phosphatase (ALP) specific activity. The effect of AA and PGE2 on cell number was somewhat variable but showed a general decrease on plastic and smooth surfaces and an increase on rough surfaces. In contrast, [3H]-thymidine incorporation was uniformly decreased with treatment on all surfaces. ALP demonstrated the most prominent effect of treatment. On smooth surfaces, AA and PGE2 dose-dependently increased ALP, while on rough surfaces, treatment dose-dependently decreased enzyme specific activity. Indomethacin treatment had either no effect or a slightly inhibitory effect on [3H]-thymidine incorporation on all surfaces. In contrast, indomethacin inhibited ALP on smooth surfaces and stimulated ALP on rough. Taken together, the results indicate that both AA and PGE2 influence osteoblast response by promoting osteoblast differentiation on smooth surfaces, while inhibiting it on rough surfaces. Because implants with rough surfaces are acknowledged to be superior to those with smooth surfaces, these results suggest that use of nonsterioidal anti-inflammatory drugs to block PGE2 production and reduce inflammation may be beneficial in the postoperative period after implant placement. They also indicate that manipulation of the AA metabolic pathway may offer a new therapeutic approach for modulating bone healing after implant placement. Because peri-implant healing takes place in a complex cellular environment quite different from the one used in the present study, additional work will be necessary to substantiate these possibilities.

Surface modifications of dental implants

Dental implant surface technologies have been evolving rapidly to enhance a more rapid bone formation on their surface and hold a potential to increase the predictability of expedited implant therapy. While implant outcomes have become highly predictable, there are sites and conditions that result in elevated implant loss. This paper reviews the impact of macro-retentive features which includes approaches to surface oxide modification, thread design, press-fit and sintered-bead technologies to increase predictability of outcomes. Implant designs that lead to controlled lateral compression of the bone can improve primary stability as long as the stress does not exceed the localized yield strength of the cortical bone. Some implant designs have reduced crestal bone loss by use of multiple cutting threads that are closely spaced, smoothed on the tip but designed to create a hoop-stress stability of the implant as it is completely seated in the osteotomy. Following the placement of the implant, there is a predictable sequence of bone turnover and replacement at the interface that allows the newly formed bone to adapt to microscopic roughness on the implant surface, and on some surfaces, a nanotopography (<10(-9) m scale) that has been shown to preferably influence the formation of bone. Newly emerging studies show that bone cells are exquisitely sensitive to these topographical features and will upregulate the expression of bone related genes for new bone formation when grown on these surfaces. We live in an exciting time of rapid changes in the modalities we can offer patients for tooth replacement therapy. Given this, it is our responsibility to be critical when claims are made, incorporate into our practice what is proven and worthwhile, and to continue to support and provide the best patient care possible.

Effects of topographical surface modifications of electron beam melted Ti-6Al-4V titanium on human fetal osteoblasts

The aim of the study was to assess the suitability of different Ti-6Al-4V surfaces produced by the electron beam melting (EBM) process as matrices for attachment, proliferation, and differentiation of human fetal osteoblasts (hFOB 1.19). Human osteoblasts were cultured in vitro on smooth and rough-textured Ti-6Al-4V alloy disks. By means of cell number and vitality and SEM micrographs cell attachment and proliferation were observed. The differentiation rate was examined by using quantitative real-time PCR analysis for the gene expression of alkaline phosphatase (ALP), type I collagen (Coll-I), bone sialoprotein (BSP) and osteocalcin (OC). After 3 days of incubation there was a significant higher vitality (p < 0.02) and proliferation (p < 0.02) of hFOB cells on smooth surfaces (R(a) = 0.077 microm) and compact surfaces with adherent partly molten titanium particles on the surface (R(a) </= 24.9 microm). On these samples cells spread over almost the whole surface. On porous surfaces with higher R(a) values, cell proliferation was reduced significantly. Quantitative real-time PCR analysis showed that the expression of osteogenic differentiation markers was not influenced by surface characteristics. Gene expression did not differ more than twofold for the different samples. Compact titanium samples with adherent partly molten titanium particles on the surface (R(a) </= 24.9 microm) fabricated by the EBM process turned out to be best suited for cell proliferation, while highly rough surfaces (R(a) >/= 56.9 microm) reduced proliferation of hFOB cells. Surface characteristics of titanium can easily be changed by EBM in order to further improve proliferation.

Analysis of living cells grown on different titanium surfaces by time-lapse confocal microscopy

In this study we have combined fluorescence- and reflection-confocal laser scanning microscopy for the simultaneous visualization of living cells and surface topography beneath them. To this purpose we have designed a specific flow chamber and we have tested it with osteoblasts grown on an opaque, thick support, made of smooth or sandblasted titanium. Cells were loaded with Calcein-AM or tetramethylrhodamine methyl ester (TMRM), two probes employed as indicators of cell viability/morphology and mitochondrial membrane potential, respectively. Besides the acquisition of stacks of confocal sections, the system allowed also vertical views and faithful three-dimensional reconstruction of the samples. Confocal microscope implemented with our flow chamber proved to be a promising tool for time-lapse investigation of cell-biomaterial interactions.

Oxidized NiTi surfaces enhance differentiation of osteoblast-like cells

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

Calcium Phosphate Ceramic Blasting on Titanium Surface Improve Bone Ingrowth

Surface roughness modulates the osseointegration of orthopaedic and dental titanium implants. High surface roughness is currently obtained by blasting of titanium implants with silica or aluminium abrasive particles. This process includes into the surface abrasive particles and may cause the release of cytotoxic silica or aluminium ions in the peri implant tissue. To overcome this drawback, we currently develop an innovative gridblasting process using Biphasic Calcium Phosphate (BCP) particles (RBBM Resorbable and Biocompatible Blast Media) to generate biocompatible roughened titanium surface. This work present the technique of blasting using RBBM particles to provide a roughened surface which does not release cytotoxic elements and (ii) to assess the effects of such a roughened surface for bone osteointegration in critical size rabbit defect. Our results demonstrate that resorbable biphasic calcium phosphate abrasive particles can be used to create titanium surface roughness. This grid blasting process increases surface roughness of titanium implants and offers a non cytotoxic surface for rapid and efficient osteointegration.

Inhibitory Effect of Synthetic Nano-Hydroxyapatite on Dental Caries

The objective of this study was to investigate the inhibitory effect of the synthetic nanohydroxyapatite (HA) on dental caries. The nano-HA was synthesized by using the depositing reaction of Ca (H2PO4)2. The artificial dental caries was made by using sour solution and inoculating Streptococcus mutans (S.mutans) to the Sprague-Dawley (SD) rat’s mouth respectively. After mineralization of solution of nano-HA for 10 days, the hardness of enamel was measured. The inhibitory effect of the synthetic nano-HA on dental caries was detected by gargling way to rinse the rat tooth with the solution of nano-HA in the animal test. Transmission electron microscopy (TEM) revealed that the dried HA particles were needle-like with ф5-20nm×60nm and the sintered HA particles were spherical with less than 100nm. The remineralized test indicated that the solution of nano-HA with different shapes enhanced the hardness of artificial caries and improved the remineralization of artificial caries. The animal test showed that the dried nano-HA had the inhibitory effect on dental caries. The good absorptive effect of the nano-HA on both the saliva protein and the glucans leads to the development of interventions that could reduce or modify bacterial colonization of tooth surfaces.

Remineralization Effect of the Nano-HA Toothpaste on Artificial Caries

The aim of this study is to describe the remineralization effect of the nano-HA toothpaste on artificial caries. The artificial dental caries is made using sour solution. The demineralized teeth specimen is put into five kinds of toothpaste solution respectively for 5 days and 10 days, which are: solution of containing needle like nano-HA, solution of containing spherical nano-HA, solution of general HA, fluorine sodium solution and physiological saline. The hardness of specimen is measured and the surface morphology is characterized by SEM. The remineralized test indicates that the nano-HA toothpaste can enhance the hardness of artificial caries and improve the remineralization of artificial caries. The SEM analysis shows that the cavities and defects of enamel surface are decreased and many mineral salts are sedimentated, which indicate that the nano-HA could promote remineralization for the demineralized enamel.

Surface characteristics, biocompatibility, and mechanical properties of nickel-titanium plasma-implanted with nitrogen at different implantation voltages

NiTi shape memory alloy is one of the promising orthopedic materials due to the unique shape memory effect and superelasticity. However, the large amount of Ni in the alloy may cause allergic reactions and toxic effects thereby limiting its applications. In this work, the surface of NiTi alloy was modified by nitrogen plasma immersion ion implantation (N-PIII) at various voltages. The materials were characterized by X-ray photoelectron spectroscopy (XPS). The topography and roughness before and after N-PIII were measured by atomic force microscope. The effects of the modified surfaces on nickel release and cytotoxicity were assessed by immersion tests and cell cultures. The XPS results reveal that near-surface Ni concentration is significantly reduced by PIII and the surface TiN layer suppresses nickel release and favors osteoblast proliferation, especially for samples implanted at higher voltages. The surfaces produced at higher voltages of 30 and 40 kV show better adhesion ability to osteoblasts compared to the unimplanted and 20 kV PIII samples. The effects of heating during PIII on the phase transformation behavior and cyclic deformation response of the materials were investigated by differential scanning calorimetry and three-point bending tests. Our results show that N-PIII conducted using the proper conditions improves the biocompatibility and mechanical properties of the NiTi alloy significantly.

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

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

Promising in vitro performances of a new nickel-free stainless steel

Stainless steel is a metallic alloy largely employed in orthopaedics. However, the presence in its composition of a high quantity of nickel, an agent known to trigger toxic and allergic responses, is cause for concern. In this study, we have investigated the in vitro biocompatibility of a new nickel-reduced stainless steel, namely Böhler P558, in comparison to the conventional stainless steel AISI 316L. The neutral red (NR) uptake and the amido black (AB) tests were performed on L929 fibroblasts and MG63 osteoblasts to assess the cytotoxicity, while cytogenetic effects were evaluated on CHOK1 cells by studying the frequency of Sister Chromatid Exchanges (SCE) and chromosomal aberrations. Ames test was used to detect the mutagenic activity. The expression of selected markers typical of differentiated osteoblasts, such as alkaline phosphatase activity (ALP), type I collagen (CICP) and osteocalcin (OC) production, were also monitored in MG63 cells cultured on the tested materials. Our results indicate the absence of significant cytotoxicity and genotoxicity for both test alloys. ALP, CICP and OC analyses confirmed that both materials support the expression of these phenotypic markers. Overall, these data show that this Ni-free alloy possesses good in vitro biocompatibility and could have a potential for orthopaedic applications.

Human gingival fibroblast integrin subunit expression on titanium implant surfaces

BACKGROUND

Implant surface characteristics have been shown to modify cell behavior and regulate integrin expression. Integrin expression and resultant integrin-mediated cellular activity are essential components of tissue healing and homeostasis. Although both osseous and soft tissue healing around dental implants are critical to clinical success, there is limited information available on the effect of implant surfaces on integrin expression in soft tissues. Therefore, the aim of this study was to examine integrin expression for gingival fibroblasts on titanium surfaces and the influence of titanium surface roughness on integrin expression and cell morphology.

METHODS

Human gingival fibroblasts were cultured on smooth (polished) and rough (sand-blasted acid-etched) titanium surfaces and a cell culture plastic (control) surface. To analyze integrin expression, total RNA was isolated from experimental and control cells, and levels of integrin subunit mRNA were assessed by reverse transcription-polymerase chain reaction (RT-PCR) using primers specific for the alpha2, alpha4, alpha5, alpha(v), and beta1 integrin subunits and aldolase (internal control). PCR products were analyzed by polyacrylamide gel electrophoresis (PAGE), confirmed via DNA sequencing, and quantified using computer-assisted densitometry. The expression of the integrin subunits was analyzed at the protein level using flow cytometry, as well as fluorescence and confocal laser microscopy. Cell morphology was evaluated using scanning electron microscopy (SEM).

RESULTS

Our experiments demonstrated cellular expression of the alpha2, alpha4, alpha5, alpha(v), and beta1 integrin subunits at both mRNA and protein levels on all surfaces. In addition, the alpha4 and beta1 mRNA levels were significantly increased on smooth titanium relative to plastic surfaces (P <.05) with intermediate mRNA levels found on the rough titanium surfaces. The smooth titanium surfaces exhibited a flat monolayer of cells, while rough titanium surfaces showed cells orienting themselves along surface irregularities.

CONCLUSIONS

These results demonstrate the presence of multiple integrin subunits in human gingival fibroblasts grown in contact with titanium implant surfaces and that titanium surface roughness alters cellular morphology but appears to have limited effects on integrin expression. This study provides insight into the complicated cellular and molecular events occurring at the implant surface that may be critical to optimizing the soft tissue interactions with the soft tissue-implant interface.

Effects of implant surface microtopography on osteoblast gene expression

AIM

The promotion of osteoblast attachment and differentiation has been evaluated on various implant surfaces. However, the effects of different implant surface properties on gene expression of key osteogenic factors are not fully understood.

OBJECTIVE

The objectives of this study were to evaluate how topographical effects on titanium surface alter the expression of bone-related genes and transcription factors.

METHODS

Osteoblasts were cultured on titanium disks prepared with a titanium dioxide grit blasting (TiOBlast) or grit blasted and etched with hydrofluoric acid (Osseospeed), grit blasted and etched (SLA-1), or grit blasted, etched and rinsed with N2 protection and stored in isotonic NaCl (SLA-2) commercially pure titanium implant discs. High-density cultures of human mesenchymal pre-osteoblastic cells (HEPM 1486, ATCC) were grown for 72 h and real-time PCR used for quantitative analysis of alkaline phosphatase (ALP), core-binding factor alpha1 (Cbfa1), Osterix, Type I Collagen, Osteocalcin and bone sialoprotein II gene expression.

RESULTS

Real-time PCR showed significant (P<0.001) increases in ALP gene expression in osteoblasts grown on SLA-2, relative to all other surfaces. Cbfa1/RUNX-2 gene expression was significantly (P<0.01) increased on Osseospeed and TiOBlast surface as compared with SLA-1 and SLA-2 surfaces. The expression of Osterix had a trend similar to that of Cbfa1.

CONCLUSION

In conclusion, implant surface properties may contribute to the regulation of osteoblast differentiation by influencing the level of bone-related genes and transcription factors in human mesenchymal pre-osteoblastic cells.

Peri-implant osteogenesis in health and osteoporosis

Long-term clinical success of endosseous dental implants is critically related to a wide bone-to-implant direct contact. This condition is called osseointegration and is achieved ensuring a mechanical primary stability to the implant immediately after implantation. Both primary stability and osseointegration are favoured by micro-rough implant surfaces which are obtained by different techniques from titanium implants or coating the titanium with different materials. Host bone drilled cavity is comparable to a common bone wound. In the early bone response to the implant, the first tissue which comes into contact with the implant surface is the blood clot, with particular attention to platelets and fibrin. Peri-implant tissue healing starts with an inflammatory response as the implant is inserted in the bone cavity, but an early afibrillar calcified layer comparable to the lamina limitans or incremental lines in bone is just observable at the implant surface both in vitro than in vivo conditions. Just within the first day from implantation, mesenchymal cells, pre-osteoblasts and osteoblasts adhere to the implant surface covered by the afibrillar calcified layer to produce collagen fibrils of osteoid tissue. Within few days from implantation a woven bone and then a reparative trabecular bone with bone trabeculae delimiting large marrow spaces rich in blood vessels and mesenchymal cells are present at the gap between the implant and the host bone. The peri-implant osteogenesis can proceed from the host bone to the implant surface (distant osteogenesis) and from the implant surface to the host bone (contact osteogenesis) in the so called de novo bone formation. This early bone response to the implant gradually develops into a biological fixation of the device and consists in an early deposition of a newly formed reparative bone just in direct contact with the implant surface. Nowadays, senile and post-menopausal osteoporosis are extremely diffuse in the population and have important consequences on the clinical success of endosseous dental implants. In particular the systemic methabolic and site morphological conditions are not favorable to primary stability, biological fixation and final osseointegration. An early good biological fixation may allow the shortening of time before loading the implant, favouring the clinical procedure of early or immediate implant loading. Trabecular bone in implant biological fixation is gradually substituted by a mature lamellar bone which characterizes the implant ossoeintegration. As a final consideration, the mature lamellar bone observed in osseointegrated implants is not always the same as a biological turnover occurs in the peri-implant bone up to 1mm from the implant surface, with both osteogenesis and bone reabsorption processes.

1alpha,25(OH)2D3 regulation of integrin expression is substrate dependent

Osteoblasts are attachment-dependent cells that interact with their surface through integrin-mediated mechanisms. Their differentiation is regulated by 1,25-dihydroxyvitamin D3 [1alpha,25(OH)(2)D(3)] and is affected by substrate chemistry and microtopography, suggesting that 1alpha,25(OH)(2)D(3) may regulate integrin expression in a surface-specific manner. To test this hypothesis, osteoblast-like human MG63 cells were grown on tissue culture plastic and on grit-blasted and acid-etched titanium disks with a complex microtopography to induce osteoblast differentiation. Expression of alpha(2), alpha(5), alpha(v), beta(1), and beta(3) integrins were quantified by real-time polymerase chain reaction (PCR) as a function of time in culture and treatment with 1alpha,25(OH)(2)D(3). Results were correlated with expression of osteocalcin, a marker of a differentiated osteoblast. Osteocalcin mRNA increased with time and 1alpha,25(OH)(2)D(3) treatment and these changes were greater in cultures on the titanium disks. Integrin expression varied with time in culture and this was also surface dependent. At each time point, beta(1) and alpha(2) mRNAs were greater on titanium than on plastic, whereas alpha(5) expression was reduced and alpha(v),beta(3) expression was unaffected. 1alpha,25(OH)(2)D(3) increased beta(1) mRNA on both surfaces at all time points, but it increased alpha(2) expression only in 8-d cultures. 1alpha,25(OH)(2)D(3) caused reduced alpha(5) expression only in cultures grown on plastic for 8 d, and had no effect on either alpha(v) or beta(3) expression regardless of surface. These results show that integrin expression in human osteoblast-like cells is differentially modulated by 1alpha,25(OH)(2)D(3) in a time-dependent manner that is sensitive to the surface on which the cells are grown.

In vitro biological effects of titanium rough surface obtained by calcium phosphate grid blasting

Surface roughness modulates the osseointegration of orthopaedic and dental titanium implants. High surface roughness are currently obtained by blasting of titanium implants with silica or aluminium oxide abrasive particles. This process may cause the release of cytotoxic silicium or aluminium ions in the peri-implant tissue. To generate a biocompatible roughened titanium surface, we currently develop an innovative grid-blasting process using biphasic calcium phosphate (BCP) particles. Titanium alloy (Ti6Al4V) discs were either polished, BCP grid-blasted or left as-machined. BCP grid-blasting created an average surface roughness of 1.57 +/- 0.07 microm compared to the original machined surface of 0.58 +/- 0.05 microm. X-ray photoelectron spectroscopy indicated traces of calcium and phosphorus and relatively less aluminium on the BCP grid-blasted surface than on the initial titanium specimen. Scanning electronic microscopy observations and measurement of mitochondrial activity (MTS assay) showed that osteoblastic MC3T3-E1 cells were viable in contact with the BCP grid-blasted titanium surface. In addition, our results indicate that MC3T3-E1 cells expressed ALP activity and conserved their responsiveness to bone morphogenetic protein BMP-2. The overall results clearly indicate that this calcium phosphate grid-blasting technique increases the roughness of titanium implants and provides a non-cytotoxic surface with regard to mouse osteoblasts.

A systematic review of the influence of different titanium surfaces on proliferation, differentiation and protein synthesis of osteoblast-like MG63 cells

OBJECTIVES

Titanium is the standard material for dental and orthopaedical implants. The good biocompatibility has been proven in many experimental and clinical investigations. Different titanium topographies were tested in vitro using different cell culture models. The aim of this systematic review was to evaluate and summarize the medical/dental literature to assess on which kind of titanium surface structure the osteoblast-like osteosarcoma cells MG63 show the best proliferation and differentiation rate, and the best protein synthesis.

METHODS

A systematic search was carried out using different on-line databases (PubMed, Web of Science, Cochrane Library, International Poster Journal), supplemented by handsearch in selected journals and by examination of the bibliographies of the identified articles. Inclusion and exclusion criterias were applied when considering relevant articles. Studies which met the inclusion criteria were included and data extraction was undertaken by one reviewer.

RESULTS

The search yielded 348 references. Nine articles referring to nine different studies were relevant to our question. Additionally 8 less relevant articles were identified. It was found that regularly textured surfaces of pure titanium with R(a) values (average roughness) of around 4 mum are well-accepted by MG63 cells.

CONCLUSIONS

The surfaces and culture conditions vary widely. Therefore it is still difficult to recommend one particular surface. It seems that there are no differences in cell proliferation and differentiation on surfaces treated by blasting and etching. Standardization in fabrication and size of the different test surfaces as well as homogeneity in culture times and plating densities should be aspects for future research.

Gene expression profiling of bone cells on smooth and rough titanium surfaces

Titanium (Ti) and Ti alloys are widely used as dental and orthopaedic implants, but the effects of the surface characteristics of these materials on the response of cells and target tissues is not well understood. The present study has therefore examined the effects of a rough Ti (RT) and a smooth Ti (ST) surface on human bone cells in vitro. Scanning electron microscopy showed attachment and spreading of cells on both surfaces. Expression profiling using ATLAS gene arrays showed marked differences in gene responses after 3 h of culture. A number of osteoblast genes were identified as "roughness response" genes on the basis of changes in expression on the RT compared with the ST surfaces. The surface roughness of Ti was thus found to have a profound effect on the profile of genes expressed by the bone cells, and suggests that improvements in the biological activity and possibly the clinical efficacy of these materials could be achieved by selective regulation of gene expression mediated by controlled modification of Ti surface.

Effect of the particle size on the micro and nanostructural features of a calcium phosphate cement: a kinetic analysis

The aim of this work is to investigate the possibility of controlling the final micro and nanostructural features of a calcium phosphate cement by modifying the particle size of the starting powder, and to study the effect of this parameter on the kinetics of the setting reaction. The development of calcium phosphate materials with tailored structures at the micro and nanoscale levels could allow the modulation of some specific responses in biologic phenomena such as protein adsorption and cell adhesion, which strongly depend on the nano-sized roughness of the interface. It is shown that the higher specific surface, produced by the reduction of the particle size of the powder, strongly accelerates the hydrolysis of the alpha-TCP into calcium-deficient hydroxyapatite. The higher degree of supersaturation attained in the solution favours the nucleation of smaller crystals. Thus, by increasing the specific surface of the starting powder in a factor of 5, the size of the precipitated crystals is strongly reduced, and the specific surface of the set cement increases by a factor of 2. The reduction of the particle size produces a substantial decrease of the setting time and accelerates the hardening of the cement without significantly affecting the final strength attained. The mechanical strength achieved by the cement cannot be univocally related to the degree of reaction, without considering the microstructural features.

Electrostatic spray deposition (ESD) of calcium phosphate coatings, an in vitro study with osteoblast-like cells

Electrostatic spray deposition (ESD) is a recently developed technique to deposit a calcium phosphate (CaP) coating upon substrates. With this technique, an organic solvent containing calcium and phosphate is pumped through a nozzle. Between the nozzle and substrate a high voltage is applied. As a consequence, droplets coming out the nozzle disperse into a spray, and this spray is deposited upon the substrate. When the solvent has evaporated, a coating is formed on the substrate. ESD allows for a variation in coating composition and morphology. Titanium alloy (TiAl6V4) substrates were coated with a CaP layer using two different methods; radio frequency magnetron sputtering, and ESD. These surfaces were characterized with X-ray diffraction, Fourier transform infrared spectroscopy, an universal surface tester, scanning electron microscopy, and energy dispersive spectrometry. Subsequently, bone marrow cells were isolated from rat femora and cultured 1, 4, 8, 14 and 16 days. Cell proliferation, alkaline phosphatase activity, and osteocalcin concentration were assayed. RT-PCR was done for collagen type I and osteocalcin. SEM was also performed to observe cellular behaviour during culture. Two separate runs of the experiment were performed. In the first run, osteoblast-like cells on both CaP coatings showed similar results in all assays. In the second run, proliferation and osteogenic expression had increased on ESD coatings. On basis of these results, we conclude that the novel ESD coating behaved similar to, or even better than the known RF magnetron sputter coating. Thus, ESD could be a valid addition to already existing CaP coating processes.

Patterns of gene expression in rat bone marrow stromal cells cultured on titanium alloy discs of different roughness

Rat bone marrow stromal cells were cultured on either Ra (0.14 microm) or Ra (5.8 microm) Ti6Al4V discs for 24 or 48 h. Cells on the Ra (0.14 microm) surface showed typical fibroblastic morphology, whereas cells on the Ra (5.8 microm) surface were in clusters with a more epithelial appearance. RNA was extracted from the cells at both time points, and gene expression was analyzed by using a rat gene microarray. At 24 and 48 h, a similar number of genes were both up- and down-regulated at least twofold on the Ra (5.8 microm) surface compared to the Ra (0.14 microm) surface. We analyzed the relative level of specific groups of genes related to bone and cartilage development, cell adhesion and extracellular matrix proteins, transcription factors, bone morphogenetic proteins, phospholipases, and protein kinases. Roughness did not appear to be a specific stimulator of osteogenesis because genes of both the bone and cartilage lineage were up-regulated on the Ra (5.8 microm) surface. The most prominent change among transcription factors was up-regulation of Hox 1.4 on the Ra (5.8 microm) surface. Up-regulation of phospholipase A2 and SMAD 4 indicate these genes are also involved in the response of cells to an Ra (5.8 microm) surface. Our data show surface roughness alters the expression of a large number of genes in marrow stromal cells, which are related to multiple pathways of mesenchymal cell differentiation.

Roughness response genes in osteoblasts

Titanium (Ti) and Ti alloys are widely used as dental and orthopedic implants, but the effects of the surface characteristics of these materials, including roughness, on the response of target tissues in vivo are not well understood. The present study has therefore examined the effects of a moderately rough (sand-blasted, acid-etched; SLA) Ti surface, a highly rough (plasma-sprayed; TPS) surface, and a smooth surface (SMO) on bone cells in vitro. X-ray photoelectron spectroscopy showed that these surfaces had similar surface chemistry, while scanning electron microscopy suggested that the SLA provided a transiently less biocompatible surface, with initially less well-attached cells. SLA also delayed bone cell growth compared with SMO, whereas the TPS surface elicited the greatest increase in cell numbers. In addition, expression profiling using the ATLAS gene array showed marked differences in gene responses after 3 h of incubation; this increased further after 24 h, with TPS generating the largest number of up- and down-regulated genes compared with SLA and SMO. A number of osteoblast genes were also identified as 'roughness' genes on the basis of their similar response on SLA and TPS, compared with SMO. These findings show, for the first time, that the surface roughness of Ti has a profound effect on the profile of genes expressed by bone cells and suggest that improvements in the biological activity and possibly the clinical efficacy of these materials could be achieved by selective regulation of gene expression mediated via modification of surface roughness.

Effects of implant microtopography on osteoblast cell attachment

PURPOSE

The overall aim of this project was to study osteoblast cell attachment on titanium surfaces with varying surface roughness.

MATERIALS AND METHODS

Commercially pure titanium surfaces were prepared by polishing through 600-grit sandpaper, sandblasting, or sandblasting followed by acid etching to produce surfaces of varying roughness, as determined by scanning electron microscopy and atomic force microscopy. In vitro cell attachment of MC3T3-E1 osteoblasts was performed on the prepared surfaces in both serum-containing and serum-free media conditions.

RESULTS

Cell attachment was directly related to the average surface roughness, with the highest levels of cell attachment observed on sandblasted and sandblasted-acidetched surfaces. Similar patterns of cell attachment were observed when serum-free conditions were employed.

CONCLUSIONS

Combined surface analytical and cell/molecular biological techniques are powerful tools to broaden our understanding of biological events occurring at the implant-tissue interface. Data acquired from these in vitro techniques provide a translational application to in vivo clinical models leading to the next generation of dental implants.

Biomechanical and histomorphometric investigations on two morphologically differing titanium surfaces with and without fluorohydroxyapatite coating: an experimental study in sheep tibiae

The influence of fluorohydroxyapatite (FHA) coating and surface roughness of Ti6Al4V implants on bone response was investigated. Uncoated and FHA-coated screws with lower (LR and LR+FHA; Ra: 5.7+/-0.2 microm) and higher (HR and HR+FHA; Ra: 21.8+/-0.9 microm) surface roughness, were inserted into the diaphyses of 8 sheep tibiae. Twelve weeks after implantation, extraction torque and bone-to-implant contact were evaluated. The smoothest surfaces showed an improved extraction torque and significant differences were observed between LR and HR (-24.6%, p<0.0005), LR and HR+FHA (-30.7%, p<0.0005), LR+FHA and HR (-17.4%, p<0.005), and LR+FHA and HR+FHA (-24.0%, p<0.005). The bone-to-implant contact data paralleled the biomechanical data: the smoother the surface, the greater the bone-to-implant contact. Significant (p<0.0005) decreases in bone-to-implant contact were observed between LR+FHA and HR (-24.2%), and between LR+FHA and HR+FHA (-29.2%). The current findings suggest that LR surfaces significantly improve the osteointegration rate of implanted cortical screws independently of the FHA coating.

Physiological strains induce differentiation in human osteoblasts cultured on orthopaedic biomaterial

We have developed an in vitro mechanical stretching model of osteoblastic cells cultured on metallic biomaterials in order to study the effects of mechanical strain on osteointegration of orthopaedic implants. Titanium alloy discs coated with alumina or hydroxyapatite were used as substrates. Three Dynacell devices were especially designed to apply cyclic strains on rigid biomaterials. The regimen (600 mu epsilon strains, 0.25Hz) was defined on the basis of physiological data and estimated deformation on hip stem prostheses. The performances of these apparatus were reproducible and provided controlled deformations. Human osteosarcoma cell line MG-63, human osteoblasts obtained from primary cultures and ROS 17/2.8 rat osteosarcoma cells were used as cell models. Cell behaviour was assessed in terms of growth and alkaline phosphatase (ALP) activity by in situ assays for two regimens: 15-min deformations repeated three times a day to mimic rehabilitation exercises and 24-h continuous deformations. We demonstrated that continuous deformation did not affect the growth and ALP activity of MG-63 cells, in contrast with sequential deformations which had no effect on cell number, but which stimulated ALP activity after 5 days of stretching. This sequential regimen can also modify the behaviour of human bone-derived cells resulting in increased proliferation after 5 days and stimulation of ALP activity after 15 days. ROS 17/2.8 rat osteosarcoma cells submitted to sequential deformations responded faster than other cell lines by increasing their ALP activity only after 1 day of stretching. Like MG-63 cells, proliferation of the ROS 17/2.8 rat osteosarcoma cell line was not affected by sequential deformations. This study suggests that short, repeated deformations defined to mimic rehabilitation exercises recommended after prostheses implantation are more likely to exert beneficial effects on implanted bone than continuous strains.

Osteoblasts and MG-63 osteosarcoma cells behave differently when in contact with ProRoot MTA and White MTA

AIM

To test the hypothesis that MG-63 osteosarcoma cells and primary osteoblasts react differently to ProRoot trade mark MTA (mineral trioxide aggregate) and White MTA by: (i) investigating the attachment of primary osteoblasts and MG-63 osteosarcoma cells to ProRoot trade mark MTA and White MTA; and (ii) comparing the osteogenic behaviour of both cell lines in contact with these endodontic materials.

METHODOLOGY

Primary osteoblasts were harvested from foetal rat calvaria by sequential digestion and MG-63 osteosarcoma cells were purchased. Cells were exposed to ProRoot trade mark MTA and White MTA prepared according to the manufacturer's instructions. All samples and controls were prepared in quadruplicate. After 6, 9 and 13 days exposure to MTA, the cells were fixed and prepared for SEM examination. In addition, both the cell types were grown to confluence and exposed to beta-glycerophosphate and dexamethasone to assess mineralized nodule formation as a function of osteogenic behaviour.

RESULTS

The number of cells on the surface of the culture dish and on top of the materials increased in all samples throughout the 3 time periods, except for White MTA where no primary osteoblasts were visible on top of the material by the end of 13 days. After exposing cells to differentiation medium nodules were observed in cultures of primary osteoblasts, but not of MG-63 osteosarcoma cells.

CONCLUSIONS

Under the conditions of this study, whilst primary osteoblasts initially bound to White MTA, they did not survive on the surface by the end of 13 days. Primary osteoblasts formed mineralized nodules when exposed to differentiation medium, whilst MG-63 cells did not form nodules. As MG-63 cells do not behave osteogenically by forming mineralized nodules, and primary osteoblasts are more sensitive than MG-63 osteosarcoma cells to White MTA in cell culture, primary osteoblasts are more appropriate than MG-63 cells for testing endodontic materials in cell culture.

In vitro behaviour of osteoblasts cultured on orthopaedic biomaterials with different surface roughness, uncoated and fluorohydroxyapatite-coated, relative to the in vivo osteointegration rate

The effects of two surfaces with different roughness (Low Roughness, LR: Ra: 5.6-5.9 microm; High Roughness, HR: Ra: 21.5-22.5 microm), uncoated and fluorohydroxyapatite(FHA)-coated, were investigated in MG-63 osteoblasts. At 72 hours, cells proliferated on biomaterials more slowly than in the control group (p < 0.0001), the proliferation rate was higher on FHA-coated LR than uncoated HR (p = 0.037). Collagen-I production was positively affected by the LR surface (p = 0.001) as compared to controls, while it was significantly lower (p = 0.0001) in the HR surfaces. Compared to controls, LR and HR surfaces led to enhanced production of TGF-beta1, further improved by FHA (FHA-coated LR: p = 0.007; FHA-coated HR p < 0.0001 respectively). ALP, OC, IL-6 and TNF-alpha levels were not significantly different from the controls. Results suggest that collagen-I production could be useful in predicting the in vivo osteointegration rate of biocompatible biomaterials observed in previous studies.

Poly(D,L-lactic acid)-poly(ethylene glycol)-monomethyl ether diblock copolymers control adhesion and osteoblastic differentiation of marrow stromal cells

Biodegradable polymers, such as poly(lactic acid) (PLA) and poly(lactic-coglycolic acid) (PLGA), are attractive materials for tissue engineering because of their degradative and mechanical properties, which permit scaffolds to be tailored to the individual requirements of different tissues. Although these materials support tissue development, their chemical properties offer no control of cell adhesion or function because their surfaces become immediately masked by adsorbing serum proteins when the materials come into contact with body fluids. Furthermore, adhesion proteins undergo conformational changes and a decrease in bioactivity when adsorbed to hydrophobic materials, such as PLA. To overcome these limitations, we modified the properties of PLA by synthesizing a diblock copolymer with poly(ethylene glycol) (PEG), which is known to reduce the amount of adsorbed proteins and to modify their conformation. By altering the PEG content of these diblock copolymers we were able to control the adsorption of adhesion proteins and, because cell adhesion takes place only in the presence of serum proteins, to control cell adhesion and cell shape. Marrow stromal cell differentiation to the osteoblastic phenotype was strongly improved on PEG-PLA compared with PLA, PLGA and tissue culture polystyrene and led to a 2-fold increase in alkaline phosphatase activity and mineralization.

Cytokine release by osteoblast-like cells cultured on implant discs of varying alloy compositions

OBJECTIVE

The aims of this study were (i). to assess the morphological features of osteo-blast-like, osteosarcoma cells (cell line SaOS-2) cultured on implant surfaces of varying alloys and (ii). to evaluate the biological activity of these cells, following their adhesion onto these surfaces.

MATERIALS AND METHODS

SaOS-2 cells (6 x 104) were grown on titanium discs (diameter 30 mm), each with a surface of differing composition and roughness (commercially pure titanium, titanium-aluminium-vanadium alloy, oxide-blasted titanium and Astra-Tech special treatment titanium; the alloys are directly comparable with those used to construct implants). The cells were grown for time periods of 1, 3, 5 and 7 days, the media were collected and the cells were fixed with 2.5% glutaraldehyde. The media were then assayed (using enzyme-linked immunosorbant assay) for the levels of interleukin (IL)-1, interleukin-6, interleukin-18 and osteoprotegerin (OPG) produced by the cells. The discs, with the cells fixed on them, were viewed under scanning electron microscopy (SEM, x 2.0 k) to evaluate cell morphology.

RESULTS

Following attachment, the cells changed their morphology and released local factors known to activate osteoclasts. Commercially pure titanium stimulated the cells the most and titanium-aluminium-vanadium alloy the least. All implant materials stimulated production of IL-1, IL-6, IL-18 above that produced by cells grown on Petri dishes (polystyrene). The titanium-aluminium-vanadium alloy allowed cell attachment but levels of IL-1 in this medium were significantly lower (31.5 +/- 5.2 pg/ml on same day) than cultures with pure titanium (201.8 +/- 11.5 pg/ml at day 5). The same pattern was observed with the IL-6, IL-18, and OPG with polystyrene appearing to stimulate most production of OPG. Titanium-aluminium-vanadium produced the least biological response.

In vitro investigation of titanium and hydroxyapatite dental implant surfaces using a rat bone marrow stromal cell culture system

In this study, rat bone marrow cells (RBM) were used to evaluate different titanium and hydroxyapatite dental implant surfaces. The implant surfaces investigated were: a titanium surface having a porous titanium plasma-sprayed coating (sample code Ti-TPS), a titanium surface with a deep profile structure (sample code Ti-DPS), an uncoated titanium substrate with a machined surface (sample code Ti-ma) and a machined titanium substrate with a porous hydroxyapatite plasma-sprayed coating (sample code Ti-HA). RBM cells were cultured on the disc-shaped test substrates for 14 days. The culture medium was changed daily and examined for calcium and phosphate concentrations. After 14 days specimens were examined by light microscopy, scanning electron microscopy, energy dispersive X-ray analysis and morphometry of the cell-covered substrate surface. All test substrates facilitated RBM growth of extracellular matrix formation. Ti-DPS and Ti-TPS to the highest degree, followed by Ti-ma and Ti-HA. Ti-DPS and Ti-TPS displayed the highest cell density and thus seem to be well suited for the endosseous portion of dental implants. RBM cells cultured on Ti-HA showed a delayed growth pattern. This may be related to its high phosphate ion release.

Three-dimensional reconstruction of confocal laser microscopy images to study the behaviour of osteoblastic cells grown on biomaterials

The adhesion, spreading and cytoskeletal organization of osteoblastic cells seeded onto titanium and titania/hydroxyapatite composite coating (TiO2/HA) were studied using images acquired by confocal laser scanning microscopy. The fluorescence staining technique was employed to visualize actin cytoskeletal organization of cells, 2-D images were exhaustive when the cells were seeded at low density (in the first 24 h of incubation), but they were less clear when the cells proliferated and appeared stacked. Since the shareware software were not satisfactory, a new 3-D image reconstruction was developed using ordinary software and a model was obtained directly from the optical section set, in order to achieve a more realistic and faithful vision of morphological structures and to evaluate the behaviour of bone cells grown on materials. The results showed that the cells grown on titanium conform to the irregular substrate surfaces maximizing the contact between the cell membrane and the substrate and proliferate disposing close to each other. On the contrary, the osteoblasts seeded onto TiO2/HA coating develop clusters where the cells aggregated extending processes in order to establish intercellular connections. Cell aggregation is an early and critical event leading to cell differentiation and mineralization process and could be a first signal of the tendency of TiO2/HA coating to stimulate cell differentiation.

A role for surface topography in creating and maintaining bone at titanium endosseous implants

STATEMENT OF PROBLEM

A variety of claims are made regarding the effects of surface topography on implant osseointegration. Many in vivo and in vitro experimental observations have key limitations in their interpretations.

PURPOSE

This review considers the major claims made concerning the effects of commercially pure (cp) titanium implant surface topography on osseointegration. Important findings of consensus are highlighted, and existing controversies are revealed.

MATERIAL AND METHODS

This review considers many of the research publications listed in MEDLINE and presented in biomedical research publications and textbooks.

RESULTS

Implant surface topography is not well defined in the marketplace or consistently reported among experimental studies. Many in vitro evaluations are not predictive of or correlated with in vivo outcomes. In some culture models, increased surface topography positively affects pro-osteogenic cellular activities. Animal models reveal modest increases in bone-to-implant contact and increases in the biomechanical interlock of the implant with bone for implants of increased surface topography. Existing information fails to define increased surface topography as a risk factor for peri-implant inflammation.

CONCLUSION

Increased cp titanium implant surface topography improves the bone-to-implant contact and the mechanical properties of the enhanced interface. Growing clinical evidence for increased bone-to-implant contact at altered cp titanium implants confirms the temporally limited observations made in preclinical studies. In the absence of controlled comparative clinical trials, the aggregate experimental evidence supports the use of cp titanium implants with increased surface topography.