Carl Zandén

Bioactive 3D cell culture system minimizes cellular stress and maintains the in vivo-like morphological complexity of astroglial cells

We tested the hypothesis that astrocytes grown in a suitable three‐dimensional (3D) cell culture system exhibit morphological and biochemical features of in vivo astrocytes that are otherwise lost upon transfer from the in vivo to a two‐dimensional (2D) culture environment. First, we report development of a novel bioactively coated nanofiber‐based 3D culture system (Bioactive3D) that supports cultures of primary mouse astrocytes. Second, we show that Bioactive3D culture system maintains the in vivo‐like morphological complexity of cultured cells, allows movement of astrocyte filopodia in a way that resembles the in vivo situation, and also minimizes the cellular stress, an inherent feature of standard 2D cell culture systems. Third, we demonstrate that the expression of gap junctions is reduced in astrocytes cultured in a 3D system that supports well‐organized cell–cell communication, in contrast to the enforced planar tiling of cells in a standard 2D system. Finally, we show that astrocytes cultured in the Bioactive3D system do not show the undesired baseline activation but are fully responsive to activation‐inducing stimuli. Thus, astrocytes cultured in the Bioactive3D appear to more closely resemble astrocytes in vivo and represent a superior in vitro system for assessing (patho)physiological and pharmacological responses of these cells and potentially also in co‐cultures of astrocytes and other cell types.

Stem cell responses to plasma surface modified electrospun polyurethane scaffolds

UNLABELLED The topographical effects from functional materials on stem cell behavior are currently of interest in tissue engineering and regenerative medicine. Here we investigate the influence of argon, oxygen, and hydrogen plasma surface modification of electrospun polyurethane fibers on human embryonic stem cell (hESC) and rat postnatal neural stem cell (NSC) responses. The plasma gases were found to induce three combinations of fiber surface functionalities and roughness textures. On randomly oriented fibers, plasma treatments lead to substantially increased hESC attachment and proliferation as compared to native fibers. Argon plasma was found to induce the most optimal combination of surface functionality and roughness for cell expansion. Contact guided migration of cells and alignment of cell processes were observed on aligned fibers. Neuronal differentiation around 5% was found for all samples and was not significantly affected by the induced variations of surface functional group distribution or individual fiber topography. FROM THE CLINICAL EDITOR In this study the influence of argon, oxygen, and hydrogen plasma surface modification of electrospun polyurethane fibers on human embryonic stem cell and rat postnatal neural stem cell (NSC) responses is studied with the goal of clarifying the potential effects of functional materials on stem cell behavior, a topic of substantial interest in tissue engineering and regenerative medicine.

The promising application of graphene oxide as coating materials in orthopedic implants: preparation, characterization and cell behavior

To investigate the potential application of graphene oxide (GO) in bone repair, this study is focused on the preparation, characterization and cell behavior of graphene oxide coatings on quartz substrata. GO coatings were prepared on the substrata using a modified dip-coating procedure. Atomic force microscopy (AFM), scanning electron microscopy (SEM) and Raman spectroscopy results demonstrated that the as-prepared coatings in this study were homogeneous and had an average thickness of ~67 nm. The rapid formation of a hydroxyapatite (HA) layer in the simulated body fluid (SBF) on GO coated substrata at day 14, as proved by SEM and x-ray diffraction (XRD), strongly indicated the bioactivity of coated substrata. In addition, MC3T3-E1 cells were cultured on the coated substrata to evaluate cellular activities. Compared with the non-coated substrata and tissue culture plates, no significant difference was observed on the coated substrata in terms of cytotoxicity, viability, proliferation and apoptosis. However, interestingly, higher levels of alkaline phosphatase (ALP) activity and osteocalcin (OC) secretion were observed on the coated substrata, indicating that GO coatings enhanced cell differentiation compared with non-coated substrata and tissue culture plates. This study suggests that GO coatings had excellent biocompatibility and more importantly promoted MC3T3-E1 cell differentiation and might be a good candidate as a coating material for orthopedic implants.

HB-EGF affects astrocyte morphology, proliferation, differentiation, and the expression of intermediate filament proteins

Heparin‐binding epidermal growth factor‐like growth factor (HB‐EGF), a vascular‐derived trophic factor, belongs to the epidermal growth factor (EGF) family of neuroprotective, hypoxia‐inducible proteins released by astrocytes in CNS injuries. It was suggested that HB–EGF can replace fetal calf serum (FCS) in astrocyte cultures. We previously demonstrated that in contrast to standard 2D cell culture systems, Bioactive3D culture system, when used with FCS, minimizes the baseline activation of astrocytes and preserves their complex morphology. Here, we show that HB‐EGF induced EGF receptor (EGFR) activation by Y1068 phosphorylation, Mapk/Erk pathway activation, and led to an increase in cell proliferation, more prominent in Bioactive3D than in 2D cultures. HB‐EGF changed morphology of 2D and Bioactive3D cultured astrocytes toward a radial glia‐like phenotype and induced the expression of intermediate filament and progenitor cell marker protein nestin. Glial fibrillary acidic protein (GFAP) and vimentin protein expression was unaffected. RT‐qPCR analysis demonstrated that HB‐EGF affected the expression of Notch signaling pathway genes, implying a role for the Notch signaling in HB‐EGF‐mediated astrocyte response. HB‐EGF can be used as a FCS replacement for astrocyte expansion and in vitro experimentation both in 2D and Bioactive3D culture systems; however, caution should be exercised since it appears to induce partial de‐differentiation of astrocytes.

A method to integrate patterned electrospun fibers with microfluidic systems to generate complex microenvironments for cell culture applications

The properties of a cells microenvironment are one of the main driving forces in cellular fate processes and phenotype expression invivo. The ability to create controlled cell microenvironments invitro becomes increasingly important for studying or controlling phenotype expression in tissue engineering and drug discovery applications. This includes the capability to modify material surface properties within well-defined liquid environments in cell culture systems. One successful approach to mimic extra cellular matrix is with porous electrospun polymer fiber scaffolds, while microfluidic networks have been shown to efficiently generate spatially and temporally defined liquid microenvironments. Here, a method to integrate electrospun fibers with microfluidic networks was developed in order to form complex cell microenvironments with the capability to vary relevant parameters. Spatially defined regions of electrospun fibers of both aligned and random orientation were patterned on glass substrates that were irreversibly bonded to microfluidic networks produced in poly-dimethyl-siloxane. Concentration gradients obtained in the fiber containing channels were characterized experimentally and compared with values obtained by computational fluid dynamic simulations. Velocity and shear stress profiles, as well as vortex formation, were calculated to evaluate the influence of fiber pads on fluidic properties. The suitability of the system to support cell attachment and growth was demonstrated with a fibroblast cell line. The potential of the platform was further verified by a functional investigation of neural stem cell alignment in response to orientation of electrospun fibers versus a microfluidic generated chemoattractant gradient of stromal cell-derived factor 1 alpha. The described method is a competitive strategy to create complex microenvironments invitro that allow detailed studies on the interplay of topography, substrate surface properties, and soluble microenvironment on cellular fate processes.

A Novel Method for Three-Dimensional Culture of Central Nervous System Neurons

Neuronal signal transduction and communication in vivo is based on highly complex and dynamic networks among neurons expanding in a three-dimensional (3D) manner. Studies of cell-cell communication, synaptogenesis, and neural network plasticity constitute major research areas for understanding the involvement of neurons in neurodegenerative diseases, such as Huntingtons, Alzheimers, and Parkinsons disease, and in regenerative neural plasticity responses in situations, such as neurotrauma or stroke. Various cell culture systems constitute important experimental platforms to study neuronal functions in health and disease. A major downside of the existing cell culture systems is that the alienating planar cell environment leads to aberrant cell-cell contacts and network formation and increased reactivity of cell culture-contaminating glial cells. To mimic a suitable 3D environment for the growth and investigation of neuronal networks in vitro has posed an insurmountable challenge. Here, we report the development of a novel electrospun, polyurethane nanofiber-based 3D cell culture system for the in vitro support of neuronal networks, in which neurons can grow freely in all directions and form network structures more complex than any culture system has so far been able to support. In this 3D system, neurons extend processes from their cell bodies as a function of the nanofiber diameter. The nanofiber scaffold also minimizes the reactive state of contaminating glial cells.

A carbon fiber solder matrix composite for thermal management of microelectronic devices

A carbon fiber based tin–silver–copper alloy matrix composite (CF-TIM) was developed via electrospinning of a mesophase pitch with polyimide and carbonization at 1000 °C, followed by sputter coating with titanium and gold, and alloy infiltration. The carbonized fibers, in film form, showed a thermal conductivity of ∼4 W m−1 K−1 and the CF-TIM showed an anisotropic thermal conductivity of 41 ± 2 W m−1 K−1 in-plane and 20 ± 3 W m−1 K−1 through-plane. The thermal contact resistance of the CF-TIM was estimated to be below 1 K mm2 W−1. The CF-TIM showed no reduction in effective through-plane thermal conductivity after 1000 temperature cycles, which indicates the potential use of CF-TIM in thermal management applications.

Thermal characterization of power devices using graphene-based film

Due to its atomic structure with sp2 hybrid orbitals and unique electronic properties, graphene has an extraordinarily high thermal conductivity which has been reported to be up to 5000 W/mK. As a consequence, the use of graphene-based materials for thermal management has been subject to substantial attention during recent years in both academia and industry. In this paper, the development of a new type of graphene-based thin film for heat dissipation in power devices is presented. The surface of the developed graphene based film is primarily composed of functionalized graphene oxide, that can be bonded chemically to the device surface and thus minimize the interface thermal resistance caused by surface roughness. A very high in-plane thermal conductivity with a maximum value of 1600 W/mK was detected by laser flash machine regarding to the graphene-based films. To investigate the structure of the graphene-based films, scanning electron microscopy (SEM) and raman spectroscopy were carried out. Finally, LED demonstrators were built to illustrate the thermal performance of graphene-based film and the functional layers. IR camera recorded a 5°C lower temperature of a LED demonstrator with SHT G1000 as the binding layer instead of a commercial thermal conductive adhesive.

Fabrication and characterization of a metal matrix polymer fibre composite for thermal interface material applications

Dealing with increasing power densities in high performance micro- and power -electronics applications is continuously becoming more challenging. Many applications today need thermal interface materials (TIMs) that can offer significantly higher performance than what is currently available. One of the main challenges for TIMs is to combine material properties that result in the thermo-mechanical characteristics required. Solder TIMs can provide excellent thermal transport, but high stiffness, causing lack of sufficient thermal-mechanical decoupling, limits their applicability. To mitigate these issues we pursue the development of a composite metal matrix based TIM technology concept with potential to combine high thermal conductivity with low joint stiffness. In this work we optimize the fabrication of an indium matrix polyimide fibre composite and investigate its thermal performance as an interface material. The fabricated composite is shown to have high effective thermal conductivity (up to 22 W/mK) and result in low contact resistance (<;1 Kmm<;sup>2<;/sup>/W).

Shape of red blood cells in contact with artificial surfaces

The phenomenon of physical contact between red blood cells and artificial surfaces is considered. A fully three-dimensional mathematical model of a bilayer membrane in contact with an artificial surface is presented. Numerical results for the different geometries and adhesion intensities are found to be in agreement with experimentally observed geometries obtained by means of digital holographic microscopy.