Testing of skeletal implant surfaces with human fetal osteoblasts

Human Fetal Osteoblast Response on Poly(Methyl Methacrylate)/Polystyrene Demixed Thin Film Blends: Surface Chemistry Vs Topography Effects

Recent advances in materials sciences have allowed for the development and fabrication of biomaterials that are capable of providing requisite cues to instigate cells to respond in a predictable fashion. We have developed a series of poly(methyl methacrylate)/polystyrene (PMMA/PS) polymer demixed thin films with nanotopographies ranging from nanoislands to nanopits to study the response of human fetal osteoblast cells (hFOBs). When PMMA was in excess in the blend composition, a nanoisland topography dominated, whereas a nanopit topography dominated when PS was in excess. PMMA was found to segregate to the top of the nanoisland morphology with PS preferring the substrate interface. To further ascertain the effects of surface chemistry vs topography, we plasma treated the polymer demixed films using an atmospheric pressure dielectric barrier discharge reactor to alter the surface chemistry. Our results have shown that hFOBs did not have an increased short-term cellular response on pristine polymer demixed surfaces. However, increasing the hydrophilicty/wettability of the surfaces by oxygen functionalization causes an increase in the cellular response. These results indicate that topography alone is not sufficient to induce a positive cellular response, but the underlying surface chemistry is also important in regulating cell function.

Significance of nano- and microtopography for cell-surface interactions in orthopaedic implants

Cell-surface interactions play a crucial role for biomaterial application in orthopaedics. It is evident that not only the chemical composition of solid substances influence cellular adherence, migration, proliferation and differentiation but also the surface topography of a biomaterial. The progressive application of nanostructured surfaces in medicine has gained increasing interest to improve the cytocompatibility and osteointegration of orthopaedic implants. Therefore, the understanding of cell-surface interactions is of major interest for these substances. In this review, we elucidate the principle mechanisms of nano- and microscale cell-surface interactions in vitro for different cell types onto typical orthopaedic biomaterials such as titanium (Ti), cobalt-chrome-molybdenum (CoCrMo) alloys, stainless steel (SS), as well as synthetic polymers (UHMWPE, XLPE, PEEK, PLLA). In addition, effects of nano- and microscaled particles and their significance in orthopaedics were reviewed. The significance for the cytocompatibility of nanobiomaterials is discussed critically.

High-throughput gene expression analysis in bone healing around titanium implants by DNA microarray

OBJECTIVE

Bone generation occurs around titanium implants; however, its underlying mechanisms are relatively unknown. We attempt to identify gene transcripts specifically upregulated in in vivo bone healing with titanium implants using DNA microarray.

MATERIAL AND METHODS

Titanium implants were placed into rat femurs, and total RNA was extracted from the implant-associated tissue at weeks 1, 2 and 4 of healing. As a control, RNA was extracted from the tissue undergoing osteotomy healing. The RNA samples were hybridized onto oligo DNA microarray.

RESULTS

Most of the 20,000 genes tested were expressed similarly in both the implant- and osteotomy-healing groups. Eighty-six genes were upregulated (>2-fold) in the implant-healing group compared with the osteotomy-healing group in at least one time point of healing. Twelve genes were upregulated in the implant healing at week 2 and earlier, while 31 genes were upregulated at week 2 and later. Only one gene was upregulated specifically at week 1, while three genes were consistently upregulated from weeks 1 to 4. The upregulated genes included collagenous and non-collagenous extracellular matrix (ECM)-related genes, proteoglycans and bone resorption-related genes. Pathway analysis revealed the involvement of ECM and receptor interaction in implant healing.

CONCLUSIONS

This study provides evidence that a set of gene transcripts is upregulated in the implant healing over the osteotomy healing, which seems to represent the coordinated biological events of long-lasting osteogenesis and bone remodeling required for osseointegration. Further studies are needed to identify the significance and biological roles of the transcripts in osseointegration. Proven reliability and usefulness of microarray technology should encourage future approaches to develop a high-throughput molecular assessment for osseointegration capacity of new implant surfaces.

Influence of substratum surface chemistry/energy and topography on the human fetal osteoblastic cell line hFOB 1.19: Phenotypic and genotypic responses observed in vitro

Time-dependent phenotypic response of a model osteoblast cell line (hFOB 1.19, ATCC, and CRL-11372) to substrata with varying surface chemistry and topography is reviewed within the context of extant cell-adhesion theory. Cell-attachment and proliferation kinetics are compared using morphology as a leading indicator of cell phenotype. Expression of (alpha2, alpha3, alpha4, alpha5, alphav, beta1, and beta3) integrins, vinculin, as well as secretion of osteopontin (OP) and type I collagen (Col I) supplement this visual assessment of hFOB growth. It is concluded that significant cell-adhesion events-contact, attachment, spreading, and proliferation-are similar on all surfaces, independent of substratum surface chemistry/energy. However, this sequence of events is significantly delayed and attenuated on hydrophobic (poorly water-wettable) surfaces exhibiting characteristically low-attachment efficiency and long induction periods before cells engage in an exponential-growth phase. Results suggest that a 'time-cell-substratum-compatibility-superposition principle' is at work wherein similar bioadhesive outcomes can be ultimately achieved on all surface types with varying hydrophilicity, but the time required to arrive at this outcome increases with decreasing cell-substratum-compatibility. Genomic and proteomic tools offer unprecedented opportunity to directly measure changes in the cellular machinery that lead to observed cell responses to different materials. But for the purpose of measuring structure-property relationships that can guide biomaterial development, genomic/proteomic tools should be applied early in the adhesion/spreading process before cells have an opportunity to significantly remodel the cell-substratum interface, effectively erasing cause and effect relationships between cell-substratum-compatibility and substratum properties. IMPACT STATEMENT: This review quantifies relationships among cell phenotype, substratum surface chemistry/energy, topography, and cell-substratum contact time for the model osteoblast cell line hFOB 1.19, revealing that genomic/proteomic tools are most useful in the pursuit of understanding cell adhesion if applied early in the adhesion/spreading process.

Gentamicin negatively influenced osteogenic function in vitro

Local delivery of gentamicin is an accepted method of infection prophylaxis in the surgery of open fractures. However, the few reports of studies into the effect of locally applied gentamicin on osteoblasts used inadequate methods. In our study, we used the well-characterised C2C12 cell line with reproducible differentiation pathway into the osteoblast lineage. We investigated the viability, cell number, alkaline phosphatase activity, and the expression of osteogenic genes of C2C12 cells after exposure to gentamicin at concentrations of 12.5-800 microg/ml for 48 h. Exposure of C2C12 cells to gentamicin (12.5-800 mg/ml) for 48 h showed no significant changes in the cell number, but cell viability was decreased by one-third at the tested concentrations of 200-800 microg/ml. The alkaline phosphatase activity was significantly decreased by one-third to one-half at any tested concentration (12.5-800 microg/ml) of gentamicin. Any tested concentration of gentamicin up to 800 microg/ml for 48 h did not inhibit or decrease the osteogenic gene expression of osterix and alkaline phosphatase of the C2C12 cells. In conclusion, gentamicin at high concentrations as achieved by local application reduced cellular viability and alkaline phosphatase activity in vitro and therefore may be detrimental for bone healing and repair in vivo.

Dose- and time-dependent effect of bioactive gel-glass ionic-dissolution products on human fetal osteoblast-specific gene expression

Bioactive glasses dissolve upon immersion in culture medium, and release their constitutive ions into solution. There has been some evidence suggesting that these ionic-dissolution products influence osteoblast-specific processes. Here, the effect of 58S sol-gel-derived bioactive glass (60% SiO(2), 36% CaO, 4% P(2)O(5), in molar percentage) on primary osteoblasts derived from human fetal long bone explant cultures is investigated, and it is hypothesized that critical concentrations of sol-gel-dissolution products (consisting of a combination of simple inorganic ions) can enhance osteoblast phenotype in vitro by affecting the expression of a number of genes associated with the differentiation and extracellular matrix deposition processes. Cells were exposed to a range of 58S dosages continuously for a period of 4-14 days in monolayer cultures. Quantitative real-time RT-PCR analysis of a panel of osteoblast-specific markers showed a varied gene expression pattern in response to the material. The highest concentration of Ca and Si tested (96 and 50 ppm, respectively) promoted upregulation of gene expression for most markers (including alkaline phosphatase, osteocalcin, and osteopontin) at the latest time point, compared to non-58S-treated control, although this observation was not statistically significant. The same 58S concentration produced higher ALP activity levels and increased proliferation throughout the culture period, compared to lower dosages tested; however, the results generated were again not statistically significant. The data overall suggest that no significant effect can be ascribed to the ionic products of 58S bioactive gel-glass dissolution tested here and their ability to stimulate osteoblastic marker gene expression.

Effects of Different Titanium Alloys and Nanosize Surface Patterning on Adhesion, Differentiation, and Orientation of Osteoblast-Like Cells

To test nanosize surface patterning for application as implant material, a suitable titanium composition has to be found first. Therefore we investigated the effect of surface chemistry on attachment and differentiation of osteoblast-like cells on pure titanium prepared by pulsed laser deposition (TiPLD) and different Ti alloys (Ti6Al4V, TiNb30 and TiNb13Zr13). Early attachment (30 min) and alkaline phosphatase (ALP) activity (day 5) was found to be fastest and highest, respectively, in cells grown on TiPLD and Ti6Al4V. Osteoblasts seeded on TiPLD produced most osteopontin (day 10), whereas expression of this extracellular matrix protein was an order of magnitude lower on the TiNb30 surface. In contrast, expression of the corresponding receptor, CD44, was not influenced by surface chemistry. Thus, TiPLD was used for further experiments to explore the influence of surface nanostructures on osteoblast adhesion, differentiation and orientation. By laser-induced oxidation, we produced patterns of parallel Ti oxide lines with different widths (0.2-10 microm) and distances (2-20 and 1,000 microm), but a common height of only 12 nm. These structures did not influence ALP activity (days 5-9), but had a positive effect on cell alignment. Two days after plating, the majority of the focal contacts were placed on the oxide lines. The portion of larger focal adhesions bridging two lines was inversely related to the line distance (2-20 microm). In contrast, the portion of aligned cells did not depend on the line distance. On average, 43% of the cells orientated parallel towards the lines, whereas 34% orientated vertically. In the control pattern (1,000 microm line distance), cell distribution was completely at random. Because a significant surplus of the cells preferred a parallel alignment, the nanosize difference in height between Ti surface and oxide lines may be sufficient to orientate the cells by contact guiding. However, gradients in electrostatic potential and surface charge density at the Ti/Ti oxide interface may additionally influence focal contact formation and cell guidance.

Response of primary fibroblasts and osteoblasts to plasma treated polyetheretherketone (PEEK) surfaces

Polyetheretherketone (PEEK) is a synthetic polymer with suitable biomechanical and stable chemical properties, which make it attractive for use as an endoprothetic material and for ligamentous replacement. However, chemical surface inertness does not account for a good interfacial biocompatibility, and PEEK requires a surface modification prior to its application in vivo. In the course of this experimental study we analyzed the influence of plasma treatment of PEEK surfaces on the cell proliferation and differentiation of primary fibroblasts and osteoblasts. Further we examined the possibility of inducing microstructured cell growth on a surface with plasma-induced chemical micropatterning. We were able to demonstrate that the surface treatment of PEEK with a low-temperature plasma has significant effects on the proliferation of fibroblasts. Depending on the surface treatment, the proliferation rate can either be stimulated or suppressed. The behavior of the osteoblasts was examined by evaluating differentiation parameters. By detection of alkaline phosphatase, collagen I, and mineralized extracellular matrix as parameters for osteoblastic differentiation, the examined materials showed results comparable to commercially available polymer cell culture materials such as tissue culture polystyrene (TCPS). Further microstructured cell growth was produced successfully on micropatterned PEEK foils, which could be a future tool for bioartificial systems applying the methods of tissue engineering. These results show that chemically inert materials such as PEEK may be modified specifically through the methods of plasma technology in order to improve biocompatibility.

The proliferation and phenotypic expression of human osteoblasts on tantalum metal

Tantalum (Ta) is increasingly used in orthopaedics, although there is a paucity of information on the interaction of human osteoblasts with this material. We investigated the ability of Ta to support the growth and function of normal human osteoblast-like cells (NHBC). Cell responses to polished and textured Ta discs were compared with responses to other common orthopaedic metals, titanium and cobalt-chromium alloy, and tissue culture plastic. No consistent differences, that could be attributed to the different metal substrates or to the surface texture, were found in several measured parameters. Attachment of NHBC to each substrate was similar, as was cell morphology, as determined by confocal microscopy. Cell proliferation was slightly faster on plastic than on Ta at 3 days, but by 7 days neither the absolute cell numbers, nor the number of cell divisions, was different between Ta and the other substrates. No consistent, substrate-dependent differences were seen in the expression of a number of mRNA species corresponding to the pro-osteoclastic or the osteogenic activity of osteoblasts. No substrate-dependent differences were seen in the extent of in vitro mineralisation by NHBC. These results indicate that Ta is a good substrate for the attachment, growth and differentiated function of human osteoblasts.

Statistical correlation between cell adhesion and proliferation on biocompatible metallic materials

Our ambition for several years is to appreciate and quantify the long-term adhesion of cells on materials at times where the interface between cells and substrate becomes more complex, more closed to the cell/matrix/substrate interface existing in vivo. With this objective, we quantified the long-term adhesion and proliferation of human osteoblasts cultured from 24 h to 21 days on pure titanium, titanium alloy, and stainless-steel substrates presenting six different surface morphologies and two different roughness amplitude. Hence, we did proceed to the statistical correlation of cell adhesion and cell proliferation on 30 different substrates. Additionally, we described surface topography not only by the roughness amplitude but also by the roughness morphology using new specific parameters. By multiple analysis of variance, we demonstrated that nor material composition nor surface roughness amplitude did influence cell proliferation, whereas a very significant influence of the process used to produce the surface was observed meaning that the main influent factor on cell proliferation was the surface morphology. The long-term adhesion and proliferation capacity of cells were positively correlated on 23 types of substrates on 30, this positive correlation being statistically asserted on 13 types of substrates on 23. This study is the first demonstration of the existence of a statistical correlation between long-term adhesion and proliferation capacity of human bone cells on substrates with various chemical composition, surface chemistry, and surface topography.

Osteoblasts response to allogenic and xenogenic solvent dehydrated cancellous bone in vitro

The present in vitro study investigates the cellular interaction of primary human osteoblasts with human and bovine solvent dehydrated cancellous bone (SDCB) discs. These are bio-implants from solvent dehydrated, gamma-irradiated preserved human and bovine cancellous bone, pre-treated to remove all cells, genetic components and water soluble proteins. Primary human osteoblasts were harvested from cancellous chips of trauma patients undergoing osteosynthesis with bone grafting from the iliac crest. All patients provided informed consent. The present investigation tested proliferation, synthesis of phenotypic marker, and morphology of primary cultured human osteoblasts on SDCB in vitro. The total protein and collagen type 1 content could not be revealed, due to the inherent naturally occurring protein content in these two bio-implants. In conclusion, our in vitro results suggest that SDCB may be a suitable bone substitute which provides a well structured and biocompatible scaffold for ingrowing human osteoblasts.

IGF-I and TGF-beta 1 incorporated in a poly(D,L-lactide) implant coating stimulates osteoblast differentiation and collagen-1 production but reduces osteoblast proliferation in cell culture

Previous in vivo studies revealed a stimulating effect of locally applied IGF-I and TGF-beta1 released from poly(D,L-lactide)-coated titanium implants on rat and porcine fracture healing. The purpose of the present study was to evaluate the effect of IGF-I (5% w/w) and TGF-beta1 (1% w/w) and the carrier PDLLA on osteoblasts in cell culture to improve the understanding of these growth factors. The well-characterized human osteoblast cell line hFOB 1.19 was used in the study. The implants and cells were cocultured in a noncontact manner. The cells were incubated for 10 days in total, and the implants (n = 6 each group and time point) were added for 1 h, 12 h, 24 h, 2 d, 4 d, or 10 d. To analyze a possible effect of the growth factors or the coating, cell proliferation, metabolism, and differentiation were investigated. As an indicator for differentiation the production of collagen I was chosen. All experimental groups showed comparable cell vitality. No change in the pH of the medium was detectable between the analyzed groups. When the effect of the titanium implant and the PDLLA coating were compared with the control culture, no differences in proliferation, metabolic activity, and collagen I production were detectable. The osteoblasts treated with IGF-I and TGF-beta1 released from PDLLA revealed a significantly enhanced collagen I production with a decrease in proliferation and metabolic activity compared to the other groups. No significant differences in collagen I production were seen due to the incubation time points. None of the experimental groups evoked an immunological response on mouse macrophages. In conclusion, the PDLLA-carrier showed no negative effect on osteoblasts, whereas the incorporated growth factors stimulated osteoblast differentiation.