Osteoblasts response to microstructured and nanostructured polyimide film, processed by the use of silica bead microlenses.

The surface of polyimide films was modified by the use of silica microspheres as microlenses to focus radiation emitted by an excimer laser. The resultant surface had both microstructures and nanostructures. Physical and chemical characterization was performed by atomic force and Fourier transform-infrared microscopy. Laser processing resulted in surfaces that had similar roughness but different component frequencies. Chemical changes were not observed with the techniques used. The response of osteoblasts to the surface was assayed by measuring their metabolic activity and the enzyme alkaline phosphatase activity, after 24 hours of growth. Cytoskeleton and expression were both investigated. Metabolic activity was similar on treated and untreated samples. Total cell number and size were increased on microstructured polymer, where specific structures were observed (protrusions). Adhesion was noted, and the actin cytoskeleton showed normal morphology. Cells on nanostructured samples had a diffuse actin network and less mature adhesions as compared with the control. FROM THE CLINICAL EDITOR: Polyimide films with microstructure and nanostructure surface elements were studied from the standpoint of osteoblast response. Total cell number and size were increased on microstructured polymer and protrusions were also observed. Adhesion was noted and the actin cytoskeleton exhibited normal morphology. Cells on nanostructured samples had a diffuse actin network and less mature adhesions.

Investigating the colloidal stability of fluorescent silica nanoparticles under isotonic conditions for biomedical applications.

Fluorescent silica nanoparticle (NP) labels are of great interest in biomedical diagnostics, however, when used in bioassays under physiological conditions they rapidly agglomerate and precipitate from solution leading to high levels of non-specific binding. In this work, using size and zeta-potential data obtained from Dynamic and Electrophoretic Light Scattering analysis, the improvement in colloidal stability of silica NPs under physiological conditions was correlated with an increase in the concentration of three additives: (1) a protein, bovine serum albumin (BSA); (2) a neutral surfactant, Tween 20®; and (3) a charged surfactant, sodium dodecyl sulfate (SDS). The number of BSA molecules present in the NP corona at each concentration was calculated using UV-Vis spectroscopy and a bicinchoninic acid protein assay (BCA). The optimal concentration of each additive was also effective in stabilizing antibody labeled fluorescent nanoparticles (αNPs) under physiological conditions. Using a fourth additive, trehalose, the colloidal stability of αNPs after freeze-drying and long-term storage also significantly improved. Both as-prepared and freeze-dried αNPs were tested in a standard fluorescence immunoassay for the detection of human IgG. The as-prepared assay showed a higher sensitivity at low concentration and a lower limit of detection when compared to a free dye assay. Assays performed with freeze dried αNPs after 4 and 22 days also showed good reproducibility.

The effect of intraluminal contact mediated guidance signals on axonal mismatch during peripheral nerve repair.

The current microsurgical gold standard for repairing long gap nerve injuries is the autograft. Autograft provides a protective environment for repair and a natural internal architecture, which is essential for regeneration. Current clinically approved hollow nerve guidance conduits allow provision of this protective environment; however they fail to provide an essential internal architecture to the regenerating nerve. In the present study both structured and unstructured intraluminal collagen fibres are investigated to assess their ability to enhance conduit mediated nerve repair. This study presents a direct comparison of both structured and unstructured fibres in vivo. The addition of intraluminal guidance structures was shown to significantly decrease axonal dispersion within the conduit and reduced axonal mismatch of distal nerve targets (p < 0.05). The intraluminal fibres were shown to be successfully incorporated into the host regenerative process, acting as a platform for Schwann cell migration and axonal regeneration. Ultimately the fibres were able to provide a platform for nerve regeneration in a long term regeneration study (16 weeks) and facilitated increased guidance of regenerating axons towards their distal nerve targets.

Straightforward, one-step fabrication of ultrathin thermoresponsive films from commercially available pNIPAm for cell culture and recovery.

The use of thermoresponsive surfaces as platforms for cell culture and cell regeneration has been explored over the last couple of decades. Poly-N-isopropylacrylamide (pNIPAm) is a well characterized thermoresponsive polymer which has an aqueous lower critical solution temperature (LCST) in a physiologically useful range, which allows it to reversibly attract (T < 32 °C) and repel water (T > 32 °C). It is this phenomenon that is exploited in temperature-controlled cell harvesting. pNIPAm coatings are generally poorly cell compatible and a number of complex or expensive techniques have been developed in order to overcome this issue. This study seeks to design a simple one-step system whereby commercially sourced pNIPAm is used to achieve similar results. Films were deposited using the operationally simple but rheologically complex spin coating technique. Reversible temperature modulated cell adhesion was achieved using a variety of different cell lines. This system offers a simplistic and cheaper alternative to methods used elsewhere.

Effect of functionalized micropatterned PLGA on guided neurite growth.

When coaptation is not possible in the repair of nerve injuries, a bridge of biomaterial scaffold provides a structural support for neuronal cell growth and guides nerve regeneration. Poly(lactide-co-glycolide) (PLGA) scaffolds have been widely investigated for neural tissue engineering applications. In order to investigate guided neurite growth, we have fabricated micropatterns on PLGA films using laser ablation methods. The micropatterned PLGA films were coated with collagen type I or laminin peptide (PPFLMLLKGSTR) to promote axon growth. Micropatterned PLGA films provide a guidance effect on both early stage neurite outgrowth and elongation. Small (5 microm) grooves showed more statistically significant parallel neurite growth compared with larger size grooves (10 microm). Micropatterned PLGA films coated with laminin peptide showed more parallel neurite growth compared with those coated with collagen type I. Primary neurite number and total neurite length per cell decreased on micropatterned PLGA films compared with the controls. Neurites showed a preference for growth in the microgrooves rather than on the spaces. This study indicates that surface micropatterned structures with conjugated functional molecules can be used to guide neurite growth.

Comparison of cell interactions with laser machined micron- and nanoscale features in polymer.

Control of cell responses to artificial surfaces is a research goal for much of the biomaterials community. The role that the micron scale topography of a surface can play in controlling cell responses has been well documented and recent advances in nanofabrication techniques have lead to an interest in cells' responses to submicron-scale surface features. The study described here compares the relative influences that nanoscale and micron-scale features exert on cells by examining cytoskeletal organisation. Micron-scale structures were generated on the polyamide Kapton using a 193 nm ArF Excimer laser, at 400 mJ/cm2 fluence. Nanoscale features were generated on Kapton using the excimer laser with a phase mask. Osteoblasts were seeded onto surfaces for 24 h, then the cell membranes were detergent-extracted, and the cells were applied with a primary antibody to actin and a colloidal gold-conjugated secondary antibody. Samples to be examined using the confocal were mounted in glycerol, those for electron microscopy were carbon-coated. The organisation of actin was examined on micron- and nano-scale structures by scoring sections for order of branching and angles of branching to relate changes in the cytoskeleton relative to the control. Although there was a strong influence of micron-scale structures, the cytoskeleton of cells on the nanoscale structures were similar to the controls.