Regulation of implant surface cell adhesion: characterization and quantification of S-phase primary osteoblast adhesions on biomimetic nanoscale substrates

Integration of an orthopedic prosthesis for bone repair must be associated with osseointegration and implant fixation, an ideal that can be approached via topographical modification of the implant/bone interface. It is thought that osteoblasts use cellular extensions to gather spatial information of the topographical surroundings prior to adhesion formation and cellular flattening. Focal adhesions (FAs) are dynamic structures associated with the actin cytoskeleton that form adhesion plaques of clustered integrin receptors that function in coupling the cell cytoskeleton to the extracellular matrix (ECM). FAs contain structural and signalling molecules crucial to cell adhesion and survival. To investigate the effects of ordered nanotopographies on osteoblast adhesion formation, primary human osteoblasts (HOBs) were cultured on experimental substrates possessing a defined array of nanoscale pits. Nickel shims of controlled nanopit dimension and configuration were fabricated by electron beam lithography and transferred to polycarbonate (PC) discs via injection molding. Nanopits measuring 120 nm diameter and 100 nm in depth with 300 nm center-center spacing were fabricated in three unique geometric conformations: square, hexagonal, and near-square (300 nm spaced pits in square pattern, but with +/-50 nm disorder). Immunofluorescent labeling of vinculin allowed HOB adhesion complexes to be visualized and quantified by image software. Perhipheral adhesions as well as those within the perinuclear region were observed, and adhesion length and number were seen to vary on nanopit substrates relative to smooth PC. S-phase cells on experimental substrates were identified with bromodeoxyuridine (BrdU) immunofluorescent detection, allowing adhesion quantification to be conducted on a uniform flattened population of cells within the S-phase of the cell cycle. Findings of this study demonstrate the disruptive effects of ordered nanopits on adhesion formation and the role the conformation of nanofeatures plays in modulating these effects. Highly ordered arrays of nanopits resulted in decreased adhesion formation and a reduction in adhesion length, while introducing a degree of controlled disorder present in near-square arrays, was shown to increase focal adhesion formation and size. HOBs were also shown to be affected morphologicaly by the presence and conformation of nanopits. Ordered arrays affected cellular spreading, and induced an elongated cellular phenotype, indicative of increased motility, while near-square nanopit symmetries induced HOB spreading. It is postulated that nanopits affect osteoblast-substrate adhesion by directly or indirectly affecting adhesion complex formation, a phenomenon dependent on nanopit dimension and conformation.

The effects of nanoscale pits on primary human osteoblast adhesion formation and cellular spreading

Current understanding of the mechanisms involved in ossesoinegration following implantation of a biomaterial has led to an emphasis being placed on the modification of material topography to control interface reactions. Recent studies have inferred nanoscale topography as an important mediator of cell adhesion and differentiation. Biomimetic strategies in orthopaedic research aim to exploit these influences to regulate cellular adhesion and subsequent bony tissue formation. Here experimental topographies of nanoscale pits demonstrating varying order have been fabricated by electron-beam lithography in (poly)carbonate. Osteoblast adhesion to these nanotopographies was ascertained by quantification of the relation between adhesion complex formation and total cell area. This study is specifically concerned with the effects these nanotopographies have on adhesion formation in S-phase osteoblasts as identified by BrdU incorporation. Nanopits were found to reduce cellular spreading and adhesion formation.

The interaction of human bone marrow cells with nanotopographical features in three dimensional constructs

Until now, nanotopography has been considered in 2D construct designs. This has been due to fabrication limitations with traditional lithographic processes relying on the ability to focus radiation that will expose a radiation sensitive resist (e.g. photolithography and electron beam lithography). More recently, alternative methods that offer rapid and cheap nanofabrication have been developed; such methods include polymer demixing and colloidal lithography. Polymer demixing in 2D has relied on spin casting of polymer blends-such as polystyrene and polybromostyrene in a solvent such as toluene. As the solvent evaporates, the polymers phase separate and form nanoislands. In this study, the polymer blend solution has been blown through fine tubes and allowed to demix, thus providing 3D constructs for cell biology. The ability to fabricate in tubes may be useful in many applications, for example stents, conduits, and bone repair (when considering structures such as Haversian tubes and Volkmann's canals). As proof of concept, human osteoprogenitor cells have been used to test the cell response to the nanopatterned tubes. The results show that nanofeatures of size X, diameter Y, and spacing Z decrease cell spreading, reduce cytoskeletal organization, and increase endocytotic activity within the cells.

Radiation dose reduction without compromise of image quality in cardiac angiography and intervention with the use of a flat panel detector without an antiscatter grid

OBJECTIVE

To test the hypothesis that replacing the antiscatter grid with an air gap will reduce patient radiation exposure without significant compromise of image quality.

METHODS

457 patients having either uncomplicated diagnostic studies or a single vessel angioplasty (percutaneous transluminal coronary angioplasty (PTCA)) on a flat plate system (GE Innova) were studied. For two months their total dose-area product score was recorded on standard gridded images and then for two months on images made with the grid out, with an air gap used to reduce scatter. Detector magnification was reduced one step when an air gap was used to achieve the same final image size. A sample set of studies was reviewed blind by five observers, who scored sharpness and contrast on a non-linear scale.

RESULTS

The average dose-area product was significantly reduced, both in the diagnostic group (n = 276), from a mean (SD) of 26.2 (14.7) Gy.cm2 with the grid in to 16.1 (12) Gy.cm2 with the grid out (p = 0.01), and in the PTCA group (n = 181), from 48.2 (36.2) to 37 (27.5) (p = 0.01). The mean image quality scores of the gridless cohort were not significantly different from those of the gridded cohort.

CONCLUSION

With the use of a flat plate detector, air gap gridless angiography reduces the radiation dose to the patient and, in consequence, to the operator without significantly affecting image quality. It is proposed that gridless imaging should be the default technique for adults and children and in most installations.

Morphological and microarray analysis of human fibroblasts cultured on nanocolumns produced by colloidal lithography

The environment around a cell during in vitro culture is unlikely to mimic those in vivo. Preliminary experiments with nanotopography have shown that nanoscale features can strongly influence cell morphology, adhesion, proliferation and gene regulation, but the mechanisms mediating this cell response remain unclear. In this study a well defined nanotopography, consisting of 100 nm wide and 160 nm high cylindrical columns, was used in fibroblast culture. In order to build on previously published morphological data that showed changes in cell spreading on the nanocolumns, in this study gene regulation was monitored using a 1718 gene microarray. Transmission electron microscopy, fluorescent observation of actin and Rac and area quantification have been used to re-affirm the microarray observations. The results indicate that changes in cell spreading correlate with a number of gene up- and down-regulations as will be described within the manuscript.

Cells React to Nanoscale Order and Symmetry in Their Surroundings

Mammalian cells react to microstructured surfaces, but there is little information on the reactions to nanostructured surfaces, and such as have been tested are poorly ordered or random in their structure. We now report that ordered surface arrays (orthogonal or hexagonal) of nanopits in polycaprolactone or polymethylmethacrylate have marked effects in reducing cell adhesion compared with less regular arrays or planar surfaces. The pits had diameters of 35, 75, and 120 nm, respectively, with pitch between the pits of 100, 200, and 300 nm, respectively. The cells appear to be able to distinguish between different symmetries of array. We suggest that interfacial forces may be organized by the nanostructures to affect the cells in the same way as they affect liquid crystal orientations.

Cell response to nano-islands produced by polymer demixing: a brief review

This review looks at the present literature available regarding cell response to nano-islands produced by nanotopography. Polymer demixing is a chemical method of fabricating large areas of nanotopography quickly and cheaply, making it ideal for cell testing and thus allowing it to be one of the first well-researched methods in cell engineering. The review shows that cells respond strongly to the islands (cell types observed include endothelial cells, fibroblasts, osteoblasts, leucocytes and platelets). Such changes include differences in adhesion, growth, gene expression and morphology.

Rapid fibroblast adhesion to 27nm high polymer demixed nano-topography

It is well known that many cell types react strongly to micro-topography. It is rapidly becoming clear than cells will also react to nano-topography. Polymer demixing is a rapid and low-cost chemical method of producing nano-topography. This manuscript investigates human fibroblast response to 27nm high nano-islands produced by polymer demixing. Cell spreading, cytoskeleton, focal adhesion and Rac localisation were studied. The results showed that an initial rapid adhesion and cytoskeletal formation on the islands at 4 days of culture gave way to poorly formed contacts and vimentin cytoskeleton at 30 days of culture.

Investigating the limits of filopodial sensing: a brief report using SEM to image the interaction between 10 nm high nano-topography and fibroblast filopodia

Having the ability to control cell behaviour would be of great advantage in tissue engineering. One method of gaining control over cell adhesion, proliferation, guidance and differentiation is use of topography. Whilst it has be known for some time that cells can be guided by micro-topography, it is only recently becoming clear that cells will respond strongly to nano-scale topography. The fact that cells will take cues from their micro- and nano-environment suggests that the cells are in some way 'spatially aware'. It is likely that cells probe the shape of their surroundings using filopodia, and that this initial filopodia/topography interaction may be critical to down-stream cell reactions to biomaterials, or indeed, the extracellular matrix. One intriguing question is how small a feature can cells sense? In order to investigate the limits of cell sensing, high-resolution scanning electron microscopy has been used to simultaneously view cell filopodia and 10 nm high nano-islands. Fluorescence microscopy has also been used to look at adhesion formation. The results showed distinct filopodial/nano-island interaction and changes in adhesion morphology.

Transfer for Primary Angioplasty Versus Immediate Thrombolysis in Acute Myocardial Infarction

Background— The benefit of primary percutaneous coronary intervention (PCI) over thrombolysis has been clearly demonstrated in acute myocardial infarction (AMI). However, the best therapeutic strategy for a patient with AMI presenting to acute care services without catheterization facilities remains under debate. Our objective was to gather all available information from clinical trials comparing transfer of patients experiencing AMI for angioplasty versus immediate thrombolysis.

Methods and Results— We performed a meta-analysis of all data available from published randomized trials and from presentations in scientific sessions of major cardiology congresses comparing the 2 strategies. The primary end point was the combined criteria (CC) of death/reinfarction/stroke as defined in each trial. Relative risk (RR) evaluated the treatment effect. We identified 6 clinical trials including 3750 patients. Transfer time was always <3 hours. The CC was significantly reduced by 42% (95% confidence interval [CI] 29% to 53%, P <0.001) in the group transferred for primary PCI compared with the group receiving on-site thrombolysis. When CC parameters were considered separately, reinfarction was significantly reduced by 68% (95% CI, 34% to 84%; P <0.001) and stroke by 56% (95% CI, −15% to 77%; P =0.015). There was a trend toward reduction in all-cause mortality of 19% (95% CI, −3% to 36%; P =0.08) with transfer for PCI.

Conclusion— Even when transfer to an angioplasty center is necessary, primary PCI remains superior to immediate thrombolysis. Organization of ambulance systems, prehospital management, and adequate PCI capacity appear now to be the key issues in providing reperfusion therapy for AMI.

Enhanced HAPEX topography: comparison of osteoblast response to established cement

The use of poly(methylmethacrylate) PMMA cement by Charnley in the 1960s revolutionized orthopaedic medicine. Since this time, however, little has changed. The development of bioactive composites, such as HAPEX (a composite of 40% vol hydroxyapatite (HA) in a polyethylene matrix) have potential in orthopaedic applications. The composite has been shown to allow direct bone bonding in vivo, and in vitro studies have shown preferential attachment to HA exposed on the composite surface. In vitro study has also shown that altering the topography HAPEX can enhance osteoblast response. This study uses microscopical investigation of osteoblast cytoskeleton, and biochemical measurement of proliferation (by thymidine incorporation) and phenotype (by alkaline phosphatase activity) to compare primary human osteoblast (HOB) activity on HAPEX and PMMA cement. The study shows large increases in HOB response to the new generation material compared to PMMA, the current implant standard.

Fibroblast reaction to island topography: changes in cytoskeleton and morphology with time

In order to develop next-generation tissue engineering materials, the understanding of cell responses to novel material surfaces needs to be better understood. Topography presents powerful cues for cells, and it is becoming clear that cells will react to nanometric, as well as micrometric, scale surface features. Polymer-demixing of polystyrene and polybromostyrene has been found to produce nanoscale islands of reproducible height, and is very cheap and fast compared to techniques such as electron beam lithography. This study observed temporal changes in cell morphology and actin and tubulin cytoskeleton using scanning electron and fluorescence microscopy. The results show large differences in cell response to 95 nm high islands from 5 min to 3 weeks of culture. The results also show a change in cell response from initial fast organisation of cytoskeleton in reaction to the islands, through to lack of cell spreading and low recruitment of cell numbers on the islands.

The effect of varying percentage hydroxyapatite in poly(ethylmethacrylate) bone cement on human osteoblast-like cells

Poly(ethylmethacrylate) (PEMA) bone cement has been developed, and the cements mechanical properties are improved by the incorporation of particulate fillers, such as hydroxyapatite (HA). In this in vitro study, human osteoblast-like (HOB) cells were used to examine the effect on cellular behavior of the addition of HA to PEMA using a plain PEMA control. Thymidine uptake ((3)H-TdR) and total DNA were used to assess cell growth and proliferation. Confocal laser scanning microscopy (CLSM) was used to study focal contacts and actin cytoskeletal organisation. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to assess cell morphology and cellular ultrastucture. The early time points showed preferential anchorage to the HA exposed on the cement surface, but no difference in adhesion or proliferation. These results have been attributed to increases in residual monomer with HA incorporation, as shown by proton nuclear magnetic resonance (H(1)-NMR) spectra.

Nonadhesive nanotopography: Fibroblast response to poly(n-butyl methacrylate)-poly(styrene) demixed surface features

It is becoming clear that cells do not only respond to micrometric scale topography, but may also respond to topography at the nanometric scale. Nano-fabrication methods such as electron beam lithography are, however, expensive and time consuming. Polymer demixing of poly(styrene) and poly(4-bromostyrene) has been found to produce nano-scale islands of reproducible height, and the islands have been previously shown to effect cell events such as adhesion, spreading, proliferation, and differentiation. This study uses demixed poly(styrene) and poly(n-butyl methacrylate) to produce nano-islands with closer packing and narrower widths compared with those previously studied. Observations have been made of morphological and cytoskeletal changes in human fibroblasts interacting with 10- and 50-nm-high islands. The methods used included scanning electron microscopy, fluorescent microscopy, and optical microscopy. The results indicated that the cells do not respond differently to the 10-nm islands compared with planar samples but, in contrast, the 50-nm islands are nonadhesive.

Polymer-demixed nanotopography: control of fibroblast spreading and proliferation

Cell response to nanometric scale topography is a growing field. Nanometric topography production has traditionally relied on expensive and time-consuming techniques such as electron beam lithography. This presents disadvantages to the cell biologist in regard to material availability. New research is focusing on less expensive methods of nanotopography production for in vitro cell engineering. One such method is the spontaneous demixing of polymers (in this case polystyrene and polybromostyrene) to produce nanometrically high islands. This article observes fibroblast response to nanometric islands (13, 35, and 95 nm in height) produced by polymer demixing. Changes in cell morphology, cytoskeleton, and proliferation are observed by light, fluorescence, and scanning electron microscopy. Morphological features produced by cells in response to the materials were selected, and cell shape parameters were measured with shape-recognition software. The results showed that island height could either increase or reduce cell spreading and proliferation in relation to control, with 13-nm islands producing cells with the greatest area and 95 nm islands producing cells with the lowest areas. Interaction of filopodia with the islands could been seen to increase as island size was increased.

Transfer for primary angioplasty: who and how?

Randomised trials have led to the conclusion that percutaneous coronary intervention (PCI) is the best reperfusion strategy for most patients with acute myocardial infarction (AMI). However, these trials have limited application to routine practice. Modern trials of mechanical reperfusion strategies need to take account of logistics, transfer times, and adjunctive drug treatment during transfer (facilitated PCI). Such PCI protocols need to be judged against very early thrombolysis with modern agents. This has been the thrust behind a series of recent studies addressing these "real world" issues in early AMI management

New acrylic bone cements conjugated to vitamin E: curing parameters, properties, and biocompatibility

Acrylic bone cement formulations with antioxidant character were prepared by incorporation of a methacrylic monomer derived from vitamin E (MVE). Increasing concentrations of this monomer provided decreasing peak temperature values, ranging from 62 to 36 degrees C, and increasing setting time with values between 17 and 25 min. Mechanical properties were evaluated by compression and tension tests. Compressive strength of the new formulations were superior to 70 MPa in all cases. The cement containing 25 wt % MVE, however, showed a significant decrease in tensile properties. Biocompatibility of the new formulations was studied in vitro. The analysis of the effect of leachables from cements into the media showed continued cell proliferation and cell viability with a significant increase for the cement containing 15 wt % MVE. This formulation also showed a significant increase in cellular proliferation over a period of 7 days as indicated by the Alamar Blue test. The cells were able to differentiate and express phenotypical markers in presence of all materials. A significant increase in alkaline phosphatase activity was observed on the cements prepared in presence of 15-25 wt % MVE compared with PMMA. Morphological assessment showed that the human osteoblast (HOB) cells were able to adhere, retain their morphology, and proliferate on all the cements.

In vitro reaction of endothelial cells to polymer demixed nanotopography

The introduction of topography to material surfaces has been shown to strongly affect cell behaviour, and the effects of micrometric surface morphologies have been extensively characterised. Research is now starting to investigate the reaction of cells to nanometric topography. This study used polymer demixing of polystyrene and poly(4-bromostyrene) producing nanometrically high islands, and observed endothelial cell response to the islands. Three island heights were investigated; these were 13, 35 and 95 nm. The cells were seen to be more spread on the manufactured topographies than that on flat surfaces of similar chemistry. Other morphological differences were also noted by histology, fluorescence and scanning electron microscopy, with many arcuate cells noted on the test surfaces, and cytoskeletal alignment along the arcuate features. Of the nanotopographies, the 13 nm islands were seen to give the largest response, with highly spread cell morphologies containing well-defined cytoskeleton.

In vitro adhesion and biocompatability of osteoblast-like cells to poly(methylmethacrylate) and poly(ethylmethacrylate) bone cements

A bone cement, poly(ethylmethacrylate)/n-butylmethacrylate (PEMA/nBMA) has been developed with lower exotherm and monomer leaching compared to the traditional poly(methylmethacrylate)/methylmethacrylate (PMMA/MMA) cement. This study compares the in vitro biological response to the cements using primary human osteoblast-like cells (HOB). Cell attachment was qualified by immunolocalization of vinculin and actin cytoskeleton, showing more organization on PEMA/nBMA compared to PMMA/MMA. Proliferation was assessed using tritiated thymidine incorporation, and phenotype expression determined by measuring alkaline phosphatase (ALP) activity. An increase in proliferation and ALP activity was observed on PEMA/nBMA compared to PMMA/MMA. The results confirm the biocompatability of PEMA/nBMA, and an enhanced cell attachment and expression of differentiated cell phenotype.

Initial attachment of osteoblasts to an optimised HAPEX topography

The interactions between an implant material and the surrounding tissue are of a complicated nature, and the initial attachment of cells to the surface is important in determining the implant success. HAPEX has been developed as a second-generation orthopaedic biomaterial, with both mechanical and biological characteristics that make it suitable for bone augmentation. Further optimisation of the material is being continued to increase the attachment of osteoblasts coupled with improving mechanical characteristics, so it may be used in load bearing applications. It has been previously observed that polishing followed by roughening the surface of HAPEX enhances osteoblast proliferation and phenotype. This article discusses the recruitment of primary human osteoblast cells onto the optimised surface, by examining morphology and cytoskeletal changes using scanning electron microscopy and confocal laser scanning microscopy. The results show that the cells attach in greater numbers to the optimised surface, and develop notably faster, than cells on machined HAPEX.

Osteoblast behaviour on HA/PE composite surfaces with different HA volumes

A hydroxyapatite (HA) reinforced polyethylene (PE) composite (designated HAPEX), with high mechanical specification and a bioactive HA phase, has been optimised as a bone analogue material. Manufacturing conditions and machining of the materials were carefully controlled to give a reproducible material surface roughness with minimal batch variation. The effect of surface composition was examined in vitro using primary human osteoblasts (HOB). HOBs were cultured in direct contact with the test materials containing 20% and 40% vol. HA. The results showed that 40% HA/PE enhanced cellular activity by increasing proliferation rate and differentiation compared to the 20% vol. HA composite. The cytoskeletal organisation of the cells was also examined and HOBs cultured on 40% HA/PE were flatter and had an enhanced rate of cytoskeletal organisation and an increase in focal contact points compared to the 20% HA/PE.

Increasing hydroxyapatite incorporation into poly(methylmethacrylate) cement increases osteoblast adhesion and response

Poly(methylmethacrylate) (PMMA) is the current standard for cement held prostheses. It forms a strong bond with the implant, but the bond between the cement and the bone is considered to be weak, with fibroblastic cells observed at the implant site, rather than direct bone contact, a contributing factor leading to implant failure. Incorporation of hydroxyapatite (HA) increases the biological response to the cement from tissue around the implant site, thus giving increased bone apposition. In this study, PMMA discs with 0, 4.6 and 8.8 vol%. HA were examined. Primary human osteoblast-like cells (HOBs) were used for the biological evaluation of the response to the cements in vitro. Morphology was observed using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Measurement of tritiated thymidine (3H-TdR) incorporation and alkaline phosphatase (ALP) activity were used to assess proliferation and differentiation. A synergy between increasing focal contact formation, cytoskeletal organisation, cell proliferation and expression of phenotype was observed with increasing HA volume. Preferential anchorage of HOBs to HA rather than PMMA was a prominent observation.

Initial interaction of osteoblasts with the surface of a hydroxyapatite-poly(methylmethacrylate) cement

Failure of the bone/cement interface in cemented joint prostheses is a contributor to implant loosening. The introduction of a bioactive phase, such as hydroxyapatite (HA), to cement may enhance fixation by encouraging direct bone apposition rather than encapsulation of the implant by fibrous tissue. The effect of poly(methylmethacrylate) (PMMA) bone cement (incorporating 17.5% HA wt.) on bioactivity has been investigated using primary human osteoblast-like cells (HOB). A significantly higher cell proliferation and differentiation was seen on the PMMA/HA cement compared to the PMMA cement alone, with retention of phenotype up to 21 days of culture on both materials.