Nikolaj Gadegaard

Nanoscale surfaces for the long-term maintenance of mesenchymal stem cell phenotype and multipotency

There is currently an unmet need for the supply of autologous, patient-specific stem cells for regenerative therapies in the clinic. Mesenchymal stem cell differentiation can be driven by the material/cell interface suggesting a unique strategy to manipulate stem cells in the absence of complex soluble chemistries or cellular reprogramming. However, so far the derivation and identification of surfaces that allow retention of multipotency of this key regenerative cell type have remained elusive. Adult stem cells spontaneously differentiate in culture, resulting in a rapid diminution of the multipotent cell population and their regenerative capacity. Here we identify a nanostructured surface that retains stem-cell phenotype and maintains stem-cell growth over eight weeks. Furthermore, the study implicates a role for small RNAs in repressing key cell signalling and metabolomic pathways, demonstrating the potential of surfaces as non-invasive tools with which to address the stem cell niche.

Ultrasensitive detection and characterization of biomolecules using superchiral fields.

The spectroscopic analysis of large biomolecules is important in applications such as biomedical diagnostics and pathogen detection, and spectroscopic techniques can detect such molecules at the nanogram level or lower. However, spectroscopic techniques have not been able to probe the structure of large biomolecules with similar levels of sensitivity. Here, we show that superchiral electromagnetic fields, generated by the optical excitation of plasmonic planar chiral metamaterials, are highly sensitive probes of chiral supramolecular structure. The differences in the effective refractive indices of chiral samples exposed to left- and right-handed superchiral fields are found to be up to 10(6) times greater than those observed in optical polarimetry measurements, thus allowing picogram quantities of adsorbed molecules to be characterized. The largest differences are observed for biomolecules that have chiral planar sheets, such as proteins with high β-sheet content, which suggests that this approach could form the basis for assaying technologies capable of detecting amyloid diseases and certain types of viruses.

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.

Rapid fibroblast adhesion to 27 nm 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.

Design and fabrication of memory devices based on nanoscale polyoxometalate clusters

Flash memory devices—that is, non-volatile computer storage media that can be electrically erased and reprogrammed—are vital for portable electronics, but the scaling down of metal–oxide–semiconductor (MOS) flash memory to sizes of below ten nanometres per data cell presents challenges. Molecules have been proposed to replace MOS flash memory, but they suffer from low electrical conductivity, high resistance, low device yield, and finite thermal stability, limiting their integration into current MOS technologies. Although great advances have been made in the pursuit of molecule-based flash memory, there are a number of significant barriers to the realization of devices using conventional MOS technologies. Here we show that core–shell polyoxometalate (POM) molecules can act as candidate storage nodes for MOS flash memory. Realistic, industry-standard device simulations validate our approach at the nanometre scale, where the device performance is determined mainly by the number of molecules in the storage media and not by their position. To exploit the nature of the core–shell POM clusters, we show, at both the molecular and device level, that embedding [(Se(iv)O3)2]4− as an oxidizable dopant in the cluster core allows the oxidation of the molecule to a [Se(v)2O6]2− moiety containing a {Se(v)–Se(v)} bond (where curly brackets indicate a moiety, not a molecule) and reveals a new 5+ oxidation state for selenium. This new oxidation state can be observed at the device level, resulting in a new type of memory, which we call ‘write-once-erase’. Taken together, these results show that POMs have the potential to be used as a realistic nanoscale flash memory. Also, the configuration of the doped POM core may lead to new types of electrical behaviour. This work suggests a route to the practical integration of configurable molecules in MOS technologies as the lithographic scales approach the molecular limit.

Micropatterned surfaces with covalently grafted unsymmetrical polyoxometalate-hybrid clusters lead to selective cell adhesion.

Mn-Anderson based polyoxometalate clusters with different terminal groups have been patterned successfully onto self-assembled monolayer (SAM) using microcontact printing. Studies of the interactions between the designed SAMs and human fibroblast (hTERT-BJ1) cells have been reported, and it was observed that cells attach and spread efficiently for monolayer presenting a terminal aromatic pyrene platform with a polyoxometalate Mn-Anderson cluster as linker, demonstrating the crucial role played by the polyoxometalate metal oxide cluster as an intermediary in cell adhesion to the surface.

Nanotopographical stimulation of mechanotransduction and changes in interphase centromere positioning

We apply a recently developed method for controlling the spreading of cultured cells using electron beam lithography (EBL) to create polymethylmethacrylate (PMMA) substrata with repeating nanostructures. There are indications that the reduced cell spreading on these substrata, compared with planar PMMA, results from a reduced adhesivity since there are fewer adhesive structures and fewer of their associated stress fibres. The reduced cell spreading also results in a reduced nuclear area and a closer spacing of centrosomes within the nucleus, suggesting that the tension applied to the nucleus is reduced as would be expected from the reduction in stress fibres. In order to obtain further evidence for this, we have used specific inhibitors of components of the cytoskeleton and have found effects comparable with those induced by the new substrata. We have also obtained evidence that these subtrata result in downregulation of gene expression which suggests that this may be due to the changed tension on the nucleus: an intriguing possibility that merits further investigation. J. Cell. Biochem. 100: 326–338, 2007.

Design of Hydrophobic Polyoxometalate Hybrid Assemblies Beyond Surfactant Encapsulation

Grafting of C-6, C-16 and C-18 alkyl chains onto the hydrophilic Mn-Anderson clusters (compounds 2-4) has been achieved. Exchange of the tetrabutyl ammonium (TBA) with dimethyldioctadecyl ammonium (DMDOA) results in the formation of new polyoxometalate (POM) assemblies (compounds 5-6), in which the POM cores are covalently functionalized by hydrophilic alkyl-chains and enclosed by surfactant of DMDOABr. As a result, we have been able to design and synthesize POM-containing hydrophobic materials beyond surfactant encapsulation. In solid state, scanning electron and transmission electron microscopy (SEM and TEM) studies of the TBA salts of compounds 3 and 4 show highly ordered, uniform, reproducible assemblies with unique segmented rodlike morphology. SEM and TEM studies of the DMDOA salts of compounds 5 and 6 show that they form spherical and sea urchin 3D objects in different solvent systems. In solution, the physical properties of compound 5 and 6 (combination of surfactant-encapsulated cluster (SEC) and surface-grafted cluster (SGC)) show a liquid-to-gel phase transition in pure chloroform below 0 degrees C, which are much lower than other reported SECs. By utilizing light scattering measurements, the nanoparticle size for compounds 5 and 6 were measured at 5 degrees C and 30 degrees C, respectively. Other physical properties including differential scanning calorimetry have been reported.

Induced chirality through electromagnetic coupling between chiral molecular layers and plasmonic nanostructures.

We report a new approach for creating chiral plasmonic nanomaterials. A previously unconsidered, far-field mechanism is utilized which enables chirality to be conveyed from a surrounding chiral molecular material to a plasmonic resonance of an achiral metallic nanostructure. Our observations break a currently held preconception that optical properties of plasmonic particles can most effectively be manipulated by molecular materials through near-field effects. We show that far-field electromagnetic coupling between a localized plasmon of a nonchiral nanostructure and a surrounding chiral molecular layer can induce plasmonic chirality much more effectively (by a factor of 10(3)) than previously reported near-field phenomena. We gain insight into the mechanism by comparing our experimental results to a simple electromagnetic model which incorporates a plasmonic object coupled with a chiral molecular medium. Our work offers a new direction for the creation of hybrid molecular plasmonic nanomaterials that display significant chiroptical properties in the visible spectral region.

Cell signaling arising from nanotopography: implications for nanomedical devices

This review discusses the roles in signaling to cells by nanochemical, nanostructural (nanotopography) and mechanical means, as well as recent work and trends in nanobioscience that are relevant to therapeutic applications. It is suggested that the mechanical results may often integrate the other two types of signal. Although the field is still in an almost embryonic but rapidly developing state, it is possible to envisage potential medical devices. Nanoparticle-based therapies are recognized as having some appreciable hazards, while those based on extended nanofeatured surfaces probably have fewer risks.