Jenny Malmström

Large area protein patterning reveals nanoscale control of focal adhesion development.

Focal adhesion development in cells adherent to surface bound fibronectin presented as 200, 500, or 1000 nm diameter circular patches or as homogeneous controls is studied by fluorescence and scanning electron microscopy. Fundamental cellular processes such as adhesion, spreading, focal adhesion and stress fiber formation are shown to be dependent on the spatial distribution of ligands at this scale. Large area samples enable the study of whole cell populations and opens for new potential applications.

The nanoscale geometrical maturation of focal adhesions controls stem cell differentiation and mechanotransduction.

We show that the nanoscale adhesion geometry controls the spreading and differentiation of epidermal stem cells. We find that cells respond to such hard nanopatterns similarly to their behavior on soft hydrogels. Cellular responses were seen to stem from local changes in diffusion dynamics of the adapter protein vinculin and associated impaired mechanotransduction rather than impaired recruitment of proteins involved in focal adhesion formation.

Focal Complex Maturation and Bridging on 200 nm Vitronectin but Not Fibronectin Patches Reveal Different Mechanisms of Focal Adhesion Formation

The effects of protein type and pattern size on cell adhesion, spreading, and focal adhesion development are studied. Fibronectin and vitronectin patterns from 0.1 to 3 μm produced by colloidal lithography reveal important differences in how cells adhere to and bridge focal adhesions across protein nanopatterns versus micropatterns. Vinculin and zyxin in focal adhesions but not integrins are seen to bridge ligand gaps. Differences in protein mechanical properties are implicated as important factors in focal adhesion development.

Intrinsically Conducting Polymer Nanowires for Biosensing

Nanomaterials are commonly exploited to increase the sensitivity of sensors. Conductive polymers are emerging as promising sensing materials as they are easy to functionalize with the appropriate sensing probes, and also act as signal transducers. By constraining the material into one dimensional nanowires, extraordinary sensitivity is achieved. This review deals with the fabrication of these electrically conductive polymer nanowire (ECPNW) sensors and their use for detecting nucleic acid sequences, proteins and pathogens.

Conductive surfaces with dynamic switching in response to temperature and salt

This work demonstrates polymer brushes grafted from conductive polymer films which display dynamic surface switching dependent on salt, temperature and electrode potential. The electroactivity presented by the conductive polymer and the responsiveness of the grafted brushes leads to an interface with multiple control parameters. Here, we demonstrate this concept by grafting of uncharged brushes of poly(ethylene glycol)methyl ether methacrylates from conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT), and observe a temperature- and salt-induced switch of brush conformation, and their effect on the electrochemistry of the material. The switching conditions can be tailored by copolymerizing monomers with different numbers of ethylene glycol units. In addition, these surfaces exhibit antifouling properties, leading to potential applications such as electrically-addressable biointerfaces.

Graft Copolymers with Conducting Polymer Backbones: A Versatile Route to Functional Materials.

Graft copolymers with a conducting polymer backbone are a promising class of materials for diverse applications including, but not limited to, organic electronics, stimuli-responsive surfaces, sensors, and biomedical devices. These materials take advantage of the unique electrochemical and optoelectronic properties of conducting polymers, complemented by chemical and/or physical properties of the grafted sidechains. In this Personal Account, we discuss our work in designing functional surfaces based on graft copolymers with a conducting polymer backbone, in the context of broader developments in the field. We review the synthetic approaches available for the rational design of conducting-polymer-based graft copolymers, and examine the types of functional surfaces and soluble materials that may be engineered using these techniques.

Polymer electronic composites that heal by solvent vapour

Recent advances in organic electronic devices have reached new milestones in performance and function, and they are used in applications ranging from displays to sensory devices. However, they still present limitations in mechanical flexibility and electrical durability following the damage caused during their lifetime. Herein, we present a simple route to prepare conducting polymer composites that can address some of these issues through solvent vapour-induced healing of cracks formed within conducting polymer composites. Conducting polymer composites were prepared by solution blending of poly(3-hexylthiophene) (P3HT) and poly(dimethylsiloxane) (PDMS)-containing urea segmented copolymer. The bicomponent composites with various weight fractions of neutral P3HT were used to demonstrate their electroactivity whereas the electrical conductivity, mechanical and solvent vapour-induced self-healing studies were carried out with composites with various weight fractions of FeCl3-doped P3HT. A mechanically bisected free-standing film with 30 wt% of doped P3HT was observed to be readily healed through exposure to solvent vapour at room temperature, with a mechanical healing efficiency of 55 ± 24% and restoration of electrical conductivity up to 82 ± 1%.

Gold sputtered Blu-Ray disks as novel and cost effective sensors for surface enhanced Raman spectroscopy

Surface Enhanced Raman spectroscopy (SERS) offers sensitive and non-invasive detection of a variety of compounds as well as unparalleled information for establishing the molecular identity of both inorganic and organic compounds, not only in biological fluids but in all other aqueous and non-aqueous media. The localized hotspots produced through SERS at the solution/nanostructure interface of clustered gold or silver nano-particles enables detection levels of parts per trillion. Recent developments in advanced fabrication methods have enabled the manufacture of SERS substrates with repeatable surface nanostructures which provide reproducible quantitative analysis, historically a weakness of the SERS technique. In this paper we describe the novel use of gold sputtered Blu-Ray surfaces as SERS substrates. Blu-Ray disks provide ideal surfaces of SERS substrates with their repeatable and regular nano-gratings. We show that the unique surface features and composition of the recording surface enables the formation of gold nano-islands with nanogaps, simply through gold sputtering, and relate this to a 600 fold signal increase of the melamine Raman signal in aqueous solutions and detection to 68 ppb. Melamine is a triazine compound and appears not only as environmental contaminant in environmental groundwater but also as an adulterant in foods due to its high nitrogen content. We have shown significant SERS signal enhancements for spectra of melamine using gold-sputtered Blu-Ray disk surfaces, with reproducibility of 12%. Blu-Ray disks have a unique combination of design, surface features and composition of the recording surface which makes them ideal for preparation of SERS substrates by gold sputter-coating.

Modulation of cell adhesion to conductive polymers

Our work on conductive polymer (CP) systems grafted with stimuli-responsive polymer brushes is motivated by the prospect of precisely controlling cellular behaviour by tailored smart interfaces. Here, the effects on cell adhesion by applying a potential to poly(3,4-ethylenedioxythiophene) (PEDOT) during both protein coating and cell culture is investigated. The results highlight the importance of pre-adsorbing fibronectin in this case, especially for the reduced polymer which binds protein strongly. The effects of changing the surface chemistry of the PEDOT electrode by grafting of brushes by atom transfer radical polymerisation (ATRP) is also investigated. Specifically, the composition of the salt-sensitive poly(oligo(ethylene glycol methyl ether methacrylate))-based brushes was tailored to control the level of cell adhesion to the interface. The composition, and also the length of the grafted brushes was seen to be important to the cell adhesion. It is also demonstrated how PEDOT films grafted with a protein and cell rejecting brush can be converted to a cell adhesive state by attaching an integrin ligand to the brush to mediate cell adhesion.

Conducting electrospun fibres with polyanionic grafts as highly selective, label-free, electrochemical biosensor with a low detection limit for non-Hodgkin lymphoma gene.

A highly selective, label-free sensor for the non-Hodgkin lymphoma gene, with an aM detection limit, utilizing electrochemical impedance spectroscopy (EIS) is presented. The sensor consists of a conducting electrospun fibre mat, surface-grafted with poly(acrylic acid) (PAA) brushes and a conducting polymer sensing element with covalently attached oligonucleotide probes. The sensor was fabricated from electrospun NBR rubber, embedded with poly(3,4-ethylenedioxythiophene) (PEDOT), followed by grafting poly(acrylic acid) brushes and then electrochemically polymerizing a conducting polymer monomer with ssDNA probe sequence pre-attached. The resulting non-Hodgkin lymphoma gene sensor showed a detection limit of 1aM (1 × 10-18mol/L), more than 400 folds lower compared to a thin-film analogue. The sensor presented extraordinary selectivity, with only 1%, 2.7% and 4.6% of the signal recorded for the fully non-complimentary, T-A and G-C base mismatch oligonucleotide sequences, respectively. We suggest that such greatly enhanced selectivity is due to the presence of negatively charged carboxylic acid moieties from PAA grafts that electrostatically repel the non-complementary and mismatch DNA sequences, overcoming the non-specific binding.