Carl Zanden - Academia.edu (original) (raw)

Papers by Carl Zanden

The verification and validation of automated vehicles (AVs) is a challenging problem. There are c... more The verification and validation of automated vehicles (AVs) is a challenging problem. There are currently no verification and validation methods that can guarantee the absence of unreasonable risk. Therefore, monitoring methods are recommended to measure the residual risk caused by the AVs in the field. This paper proposes a proactive fleet monitoring approach for AVs based on Extreme Value Theory (EVT) to reduce the accident risk during first deployment and software updates. By performing sequential statistical tests on threat metrics measured in an AV fleet, the monitor is used to quickly identify and abort operations if the AVs do not meet the required level of safety. To evaluate the proposed monitoring approach, it is studied in a fictive deployment case using two different threat metrics, one predictive and one retrospective. The evaluation showed that a significant risk reduction is achievable when using the EVT fleet monitor compared to reactive fleet monitoring. Using the predictive threat metric reduces the risk and number of accidents by aborting operations unless the deployed AVs have substantially higher MTBF than required. Comparatively, the introduced retrospective threat metric is a more balanced alternative that can reduce risk without stopping operations when the required MTBF is met. In summation, EVT fleet monitoring appears to be a promising method that can be used to reduce the risk of accidents caused by sub-performing AV driving functions by aborting operations before accidents are caused.

SAE Technical Paper Series

Automated Driving Systems (ADSs) show great potential to improve our transport systems. Safety va... more Automated Driving Systems (ADSs) show great potential to improve our transport systems. Safety validation, before market launch, is challenging due to the large number of miles required to gather enough evidence for a proven in use argumentation. Hence there is ongoing research to find more effective ways of verifying and validating the safety of ADSs. It is crucial both for the design as well as the validation to have a good understanding of the environment of the ADS. A natural way of characterizing the external conditions is by modelling and analysing data from real traffic. Towards this end, we present a framework with the primary ultimate objective to completely model and quantify the statistically relevant actions that other vehicles conduct on motorways. Two categories of fundamental actions are identified by recognising that a vehicle can only move longitudinally and laterally. The fundamental actions are defined in detail to create a set that is collectively exhaustive and mutually exclusive. All physically possible combinatorial actions that can be constructed from the fundamental actions are presented. To increase the granularity of the modelling the combinatorial actions are proposed to be analysed as sequences. Further, multi-vehicle interactions, which capture correlations between actions from multiple vehicles, are discussed. The resulting modularity of the framework allows for performing statistical analysis at an arbitrary granularity to support the design of a performant ADS as well as creating applicable validation scenarios. The use of the framework is demonstrated by automatically identifying fundamental actions in field data. Identified trajectories of two types of actions are visualised and the distributions for one parameter characterising each action type are estimated.

This thesis explores the integration of electrospun polymeric structures in two fields; fibrous s... more This thesis explores the integration of electrospun polymeric structures in two fields; fibrous scaffolds as cell culture substrates for biomedical applications and fiber carrier networks in metal matrix polymer composites as thermal interface materials in microsystems. Electrospinning has been found to carry great potential for a range of future biomedical engineering applications. To exploit possible benefits of using electrospun scaffolds further investigations of how imposed physical cues emanating from fibrous extrinsic cellular microenvironments affects cell behaviour are needed. In this thesis, electrospun polyurethane (PU) fiber architectures have been fabricated, characterized and studied as cell culture scaffolds. Previous studies have shown that differentiation of human embryonic stem cells (hESC) towards neuronal lineage can be induced from electrospun PU fibrous topographies. Following this the effects of oxygen plasma treatment as a physical surface modification on the fiber network is characterized and demonstrated to improve hESC attachment and growth. To enable in-depth analysis of cell-scaffold interactions a route through direct photolithography to integrate patterned electrospun topographies within microfluidic systems allowing formation of complex microenvironments is devised. Further, protein coated electrospun scaffolds with specific dimensions are shown to render complex astrocyte morphologies, resembling in vivo appearance, that exhibit significantly reduced stress associated protein expression. The findings indicate that the fabricated electrospun structures may provide a useful platform to complement or improve traditional in vitro culture methods. Thermal interface materials (TIMs) have been identified by the semiconductor industry as one of the major bottlenecks in heat dissipation for high power density devices. New interface material technologies with improved thermomechanical properties are required to proceed towards higher integration and packaging densities. Aiming to address these needs, this thesis presents contributions to the development of a novel composite technology formed through infiltration of a metal matrix into a carrier network of electrospun fibers. Employed as a TIM, the composite relies on heat conduction through its continuous metal phase and is shown to have promising performance compared to conventional materials with heat transfer through particle-particle contacts. To facilitate liquid phase infiltration of the matrix during fabrication, a surface confined chemical reduction based synthesis of nano particles on the fiber surface is investigated. Competitive effective thermal conductivity up to 25 W/mK is attained at bond line thickness determined by the carrier network, showing that the fabricated composite has potential to meet current and future demands in microsystems.

Tissue Engineering Part C-methods, Jun 1, 2014

Neuronal signal transduction and communication in vivo is based on highly complex and dynamic net... more 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 Huntington's, Alzheimer's, and Parkinson's 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.

Biomicrofluidics, Jun 1, 2012

Journal of Neurochemistry, Nov 26, 2013

Heparin-binding epidermal growth factor-like growth factor (HB-EGF), a vascular-derived trophic f... more 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-EGFmediated 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.

Journal of Biomedical Materials Research Part A, 2015

Due to its atomic structure with sp2 hybrid orbitals and unique electronic properties, graphene h... more 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.

Biomedical Materials, Feb 10, 2015

To investigate the potential application of graphene oxide (GO) in bone repair, this study is foc... more 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.

Nanomedicine: Nanotechnology, Biology and Medicine, Jul 1, 2014

The topographical effects from functional materials on stem cell behavior are currently of intere... more 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.

European Cells & Materials, 2011

INTRODUCTION: Cell microenvironments play a very important role in basic cell research, drug disc... more INTRODUCTION: Cell microenvironments play a very important role in basic cell research, drug discovery and tissue engineering among others. The ability to define, create and control such microenvironments is rapidly increasing due to the application of microfluidic technologies in cell research. Electrospinning of polymeric fibers is a method that has been applied for many years in tissue engineering and biosensing applications. Electrospun fibers are used as cell culture substrates as they mimic native extracellular matrix properties. We have recently developed and evaluated a device that combines microfluidic networks with electrospun fibers.

European Microelectronics and Packaging Conference, Sep 1, 2013

ABSTRACT The continuous progress in miniaturization and integration of semiconductor devices have... more ABSTRACT The continuous progress in miniaturization and integration of semiconductor devices have led to increasing heat generated from unit volume in the chip. Consequently, more efficient thermal management on chip and package level is required because the reliability of electronic equipment strongly decreasing with rising the temperature of work. To improve the heat dissipation from chip to package as well as from package to heat sink the thermal interface material (TIM) is applied. One of the most important parameter of TIMs is their thermal conductivity. Example of such high thermal conductive TIM is a composite structure based on an electrospun polyimide structure infiltrated with indium. Nevertheless the thermal conductivity of TIM is not only parameter which influence on the efficiency of thermal management. It is also important their interaction with the joined materials, because the voids or delamination between TIM and chip or substrate would dramatically increase thermal contact resistance and decrease the heat transfer efficiency. Moreover the brittle intermetallic compounds which would be formed in the interface would decrease the reliability of such joints. Therefore in this study the interface between two types of materials (silicon die and copper substrate) and the polymer nanofiber-metal TIM as well as pure indium was examined. The subject of the investigation is the stack consisted of copper substrate, TIM (or pure indium) and silicon. The interfaces between layers after aging process were analyzed experimentally by using the 3D X-Ray computed tomography, metallography and optical microscopy as well as by SEM equipped with EDS (X-ray spectroscope).

ABSTRACT Carbon nanotubes (CNTs), owing to their fabulous electrical, mechanical and thermal prop... more ABSTRACT Carbon nanotubes (CNTs), owing to their fabulous electrical, mechanical and thermal properties, are getting more and more applied into the electronics packaging technology. In this paper, applications of CNTs in electronics packaging field are reviewed, which can be divided into two parts: interconnections and thermal management solutions. Examples such as flip chip bumps, through silicon vias (TSVs), CNT based thermal interface materials (TIMs) and micro coolers are introduced, including a new CNT interconnect method, which is using indium (In) to transfer the CNT bumps from original substrates at low temperature to target substrates. The resistivity of one bump after transfer is around 6.54×10-5 Ω • m, which is one order of magnitude lower than previous results. At the end of this paper, challenges on using CNTs in electronics packaging at an engineering scale are discussed.

ABSTRACT Continued miniaturization in combination with increased performance in microelectronics ... more ABSTRACT Continued miniaturization in combination with increased performance in microelectronics has generated an urgent need for improved thermal management techniques in order to maintain reliability in systems and devices. Thermal interface materials play a key role in the development of solutions for thermal management in microelectronics. In this paper, mechanical properties of a nanotechnology enhanced thermal interface material (Nano-TIM) were studied. The material is based on Sn-Ag-Cu based alloy reinforced with nano scale fiber matrix. Tensile tests were used to investigate and compare the elastic modulus at room temperature and mechanical strength between 20 to 100°C. Scanning Electron Microscopy (SEM) analysis techniques were used to investigate the morphology of the fracture section after tensile tests as well as the internal structure of the samples. The results show that the Nano-TIM can have a significantly lower elastic modulus compared to the pure alloy phase of SnAgCu due to its fiber phase. A lower elastic modulus of the solder joint can be important since it will reduce the stress transfer across the interface. This is particular important when the joint substrates have mismatching coefficients of thermal expansion. The findings of this study thus indicate that the Nano-TIM may provide a useful alternative to improve the thermomechanical reliability compared to pure solder joints.

Journal of Materials Science: Materials in Electronics, Mar 21, 2014

With increased power density and continued miniaturization, effective thermal dissipation is of s... more With increased power density and continued miniaturization, effective thermal dissipation is of significant importance for operational lifetime and reliability of electronic system. Advanced thermal interface materials (TIMs) with excellent thermal performance need to be designed and developed. Here we report novel TIMs consisted of boron nitride (BN) nanofibers and pure indium (In) solder for heat dissipation applications. The BN nanofibers are fabricated by electrospinning process and nitridation treatment. After surface metallization by sputtering, the porous BN film is infiltrated with liquid indium by squeeze casting to form the final solid composites. The new composites show the in-plane and through-plane thermal conductivity respectively of 60 and 20 W/m K. The direction dependence thermal properties of the TIM are due to the anisotropic thermal performance of BN nanofibers in the composite. A low thermal contact resistance of 0.2 K mm 2 /W is also achieved at the interface between this new composite and copper substrate. These competent thermal properties demonstrate the great potential of the BN-In TIMs in thermal management for electronic system.

European Cells & Materials, 2011

INTRODUCTION: Electrospun polymer fibers have emerged as a promising candidate for future tissue ... more INTRODUCTION: Electrospun polymer fibers have emerged as a promising candidate for future tissue engineering and biomedical in-vivo and invitro appliances (1,2). Recent studies have argued that polyurethane in electrospun form have potential applications within the area of regenerative medicine employed for wound dressing, cell alignment, annalus fibrous tissue engineering, promoting endothelial proliferation, high performance filters and scaffolding promoting neuronal differentiation of human embryonic stem cells (1,2). Even though PU is a comparably well studied biomaterial that have been readily applied in biomedical applications, the complex surface interactions between electrospun PU fibers and cells are not well understood. Oxygen plasma surface modification (PSM) is a versatile material processing technique that has been shown to selectively modify surface properties such as wettability, adhesion and biocompatibility of polymer surfaces, and can improve surface properties for...

The verification and validation of automated vehicles (AVs) is a challenging problem. There are c... more The verification and validation of automated vehicles (AVs) is a challenging problem. There are currently no verification and validation methods that can guarantee the absence of unreasonable risk. Therefore, monitoring methods are recommended to measure the residual risk caused by the AVs in the field. This paper proposes a proactive fleet monitoring approach for AVs based on Extreme Value Theory (EVT) to reduce the accident risk during first deployment and software updates. By performing sequential statistical tests on threat metrics measured in an AV fleet, the monitor is used to quickly identify and abort operations if the AVs do not meet the required level of safety. To evaluate the proposed monitoring approach, it is studied in a fictive deployment case using two different threat metrics, one predictive and one retrospective. The evaluation showed that a significant risk reduction is achievable when using the EVT fleet monitor compared to reactive fleet monitoring. Using the predictive threat metric reduces the risk and number of accidents by aborting operations unless the deployed AVs have substantially higher MTBF than required. Comparatively, the introduced retrospective threat metric is a more balanced alternative that can reduce risk without stopping operations when the required MTBF is met. In summation, EVT fleet monitoring appears to be a promising method that can be used to reduce the risk of accidents caused by sub-performing AV driving functions by aborting operations before accidents are caused.

SAE Technical Paper Series

Automated Driving Systems (ADSs) show great potential to improve our transport systems. Safety va... more Automated Driving Systems (ADSs) show great potential to improve our transport systems. Safety validation, before market launch, is challenging due to the large number of miles required to gather enough evidence for a proven in use argumentation. Hence there is ongoing research to find more effective ways of verifying and validating the safety of ADSs. It is crucial both for the design as well as the validation to have a good understanding of the environment of the ADS. A natural way of characterizing the external conditions is by modelling and analysing data from real traffic. Towards this end, we present a framework with the primary ultimate objective to completely model and quantify the statistically relevant actions that other vehicles conduct on motorways. Two categories of fundamental actions are identified by recognising that a vehicle can only move longitudinally and laterally. The fundamental actions are defined in detail to create a set that is collectively exhaustive and mutually exclusive. All physically possible combinatorial actions that can be constructed from the fundamental actions are presented. To increase the granularity of the modelling the combinatorial actions are proposed to be analysed as sequences. Further, multi-vehicle interactions, which capture correlations between actions from multiple vehicles, are discussed. The resulting modularity of the framework allows for performing statistical analysis at an arbitrary granularity to support the design of a performant ADS as well as creating applicable validation scenarios. The use of the framework is demonstrated by automatically identifying fundamental actions in field data. Identified trajectories of two types of actions are visualised and the distributions for one parameter characterising each action type are estimated.

This thesis explores the integration of electrospun polymeric structures in two fields; fibrous s... more This thesis explores the integration of electrospun polymeric structures in two fields; fibrous scaffolds as cell culture substrates for biomedical applications and fiber carrier networks in metal matrix polymer composites as thermal interface materials in microsystems. Electrospinning has been found to carry great potential for a range of future biomedical engineering applications. To exploit possible benefits of using electrospun scaffolds further investigations of how imposed physical cues emanating from fibrous extrinsic cellular microenvironments affects cell behaviour are needed. In this thesis, electrospun polyurethane (PU) fiber architectures have been fabricated, characterized and studied as cell culture scaffolds. Previous studies have shown that differentiation of human embryonic stem cells (hESC) towards neuronal lineage can be induced from electrospun PU fibrous topographies. Following this the effects of oxygen plasma treatment as a physical surface modification on the fiber network is characterized and demonstrated to improve hESC attachment and growth. To enable in-depth analysis of cell-scaffold interactions a route through direct photolithography to integrate patterned electrospun topographies within microfluidic systems allowing formation of complex microenvironments is devised. Further, protein coated electrospun scaffolds with specific dimensions are shown to render complex astrocyte morphologies, resembling in vivo appearance, that exhibit significantly reduced stress associated protein expression. The findings indicate that the fabricated electrospun structures may provide a useful platform to complement or improve traditional in vitro culture methods. Thermal interface materials (TIMs) have been identified by the semiconductor industry as one of the major bottlenecks in heat dissipation for high power density devices. New interface material technologies with improved thermomechanical properties are required to proceed towards higher integration and packaging densities. Aiming to address these needs, this thesis presents contributions to the development of a novel composite technology formed through infiltration of a metal matrix into a carrier network of electrospun fibers. Employed as a TIM, the composite relies on heat conduction through its continuous metal phase and is shown to have promising performance compared to conventional materials with heat transfer through particle-particle contacts. To facilitate liquid phase infiltration of the matrix during fabrication, a surface confined chemical reduction based synthesis of nano particles on the fiber surface is investigated. Competitive effective thermal conductivity up to 25 W/mK is attained at bond line thickness determined by the carrier network, showing that the fabricated composite has potential to meet current and future demands in microsystems.

Tissue Engineering Part C-methods, Jun 1, 2014

Neuronal signal transduction and communication in vivo is based on highly complex and dynamic net... more 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 Huntington's, Alzheimer's, and Parkinson's 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.

Biomicrofluidics, Jun 1, 2012

Journal of Neurochemistry, Nov 26, 2013

Heparin-binding epidermal growth factor-like growth factor (HB-EGF), a vascular-derived trophic f... more 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-EGFmediated 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.

Journal of Biomedical Materials Research Part A, 2015

Due to its atomic structure with sp2 hybrid orbitals and unique electronic properties, graphene h... more 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.

Biomedical Materials, Feb 10, 2015

To investigate the potential application of graphene oxide (GO) in bone repair, this study is foc... more 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.

Nanomedicine: Nanotechnology, Biology and Medicine, Jul 1, 2014

The topographical effects from functional materials on stem cell behavior are currently of intere... more 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.

European Cells & Materials, 2011

INTRODUCTION: Cell microenvironments play a very important role in basic cell research, drug disc... more INTRODUCTION: Cell microenvironments play a very important role in basic cell research, drug discovery and tissue engineering among others. The ability to define, create and control such microenvironments is rapidly increasing due to the application of microfluidic technologies in cell research. Electrospinning of polymeric fibers is a method that has been applied for many years in tissue engineering and biosensing applications. Electrospun fibers are used as cell culture substrates as they mimic native extracellular matrix properties. We have recently developed and evaluated a device that combines microfluidic networks with electrospun fibers.

European Microelectronics and Packaging Conference, Sep 1, 2013

ABSTRACT The continuous progress in miniaturization and integration of semiconductor devices have... more ABSTRACT The continuous progress in miniaturization and integration of semiconductor devices have led to increasing heat generated from unit volume in the chip. Consequently, more efficient thermal management on chip and package level is required because the reliability of electronic equipment strongly decreasing with rising the temperature of work. To improve the heat dissipation from chip to package as well as from package to heat sink the thermal interface material (TIM) is applied. One of the most important parameter of TIMs is their thermal conductivity. Example of such high thermal conductive TIM is a composite structure based on an electrospun polyimide structure infiltrated with indium. Nevertheless the thermal conductivity of TIM is not only parameter which influence on the efficiency of thermal management. It is also important their interaction with the joined materials, because the voids or delamination between TIM and chip or substrate would dramatically increase thermal contact resistance and decrease the heat transfer efficiency. Moreover the brittle intermetallic compounds which would be formed in the interface would decrease the reliability of such joints. Therefore in this study the interface between two types of materials (silicon die and copper substrate) and the polymer nanofiber-metal TIM as well as pure indium was examined. The subject of the investigation is the stack consisted of copper substrate, TIM (or pure indium) and silicon. The interfaces between layers after aging process were analyzed experimentally by using the 3D X-Ray computed tomography, metallography and optical microscopy as well as by SEM equipped with EDS (X-ray spectroscope).

ABSTRACT Carbon nanotubes (CNTs), owing to their fabulous electrical, mechanical and thermal prop... more ABSTRACT Carbon nanotubes (CNTs), owing to their fabulous electrical, mechanical and thermal properties, are getting more and more applied into the electronics packaging technology. In this paper, applications of CNTs in electronics packaging field are reviewed, which can be divided into two parts: interconnections and thermal management solutions. Examples such as flip chip bumps, through silicon vias (TSVs), CNT based thermal interface materials (TIMs) and micro coolers are introduced, including a new CNT interconnect method, which is using indium (In) to transfer the CNT bumps from original substrates at low temperature to target substrates. The resistivity of one bump after transfer is around 6.54×10-5 Ω • m, which is one order of magnitude lower than previous results. At the end of this paper, challenges on using CNTs in electronics packaging at an engineering scale are discussed.

ABSTRACT Continued miniaturization in combination with increased performance in microelectronics ... more ABSTRACT Continued miniaturization in combination with increased performance in microelectronics has generated an urgent need for improved thermal management techniques in order to maintain reliability in systems and devices. Thermal interface materials play a key role in the development of solutions for thermal management in microelectronics. In this paper, mechanical properties of a nanotechnology enhanced thermal interface material (Nano-TIM) were studied. The material is based on Sn-Ag-Cu based alloy reinforced with nano scale fiber matrix. Tensile tests were used to investigate and compare the elastic modulus at room temperature and mechanical strength between 20 to 100°C. Scanning Electron Microscopy (SEM) analysis techniques were used to investigate the morphology of the fracture section after tensile tests as well as the internal structure of the samples. The results show that the Nano-TIM can have a significantly lower elastic modulus compared to the pure alloy phase of SnAgCu due to its fiber phase. A lower elastic modulus of the solder joint can be important since it will reduce the stress transfer across the interface. This is particular important when the joint substrates have mismatching coefficients of thermal expansion. The findings of this study thus indicate that the Nano-TIM may provide a useful alternative to improve the thermomechanical reliability compared to pure solder joints.

Journal of Materials Science: Materials in Electronics, Mar 21, 2014

With increased power density and continued miniaturization, effective thermal dissipation is of s... more With increased power density and continued miniaturization, effective thermal dissipation is of significant importance for operational lifetime and reliability of electronic system. Advanced thermal interface materials (TIMs) with excellent thermal performance need to be designed and developed. Here we report novel TIMs consisted of boron nitride (BN) nanofibers and pure indium (In) solder for heat dissipation applications. The BN nanofibers are fabricated by electrospinning process and nitridation treatment. After surface metallization by sputtering, the porous BN film is infiltrated with liquid indium by squeeze casting to form the final solid composites. The new composites show the in-plane and through-plane thermal conductivity respectively of 60 and 20 W/m K. The direction dependence thermal properties of the TIM are due to the anisotropic thermal performance of BN nanofibers in the composite. A low thermal contact resistance of 0.2 K mm 2 /W is also achieved at the interface between this new composite and copper substrate. These competent thermal properties demonstrate the great potential of the BN-In TIMs in thermal management for electronic system.

European Cells & Materials, 2011

INTRODUCTION: Electrospun polymer fibers have emerged as a promising candidate for future tissue ... more INTRODUCTION: Electrospun polymer fibers have emerged as a promising candidate for future tissue engineering and biomedical in-vivo and invitro appliances (1,2). Recent studies have argued that polyurethane in electrospun form have potential applications within the area of regenerative medicine employed for wound dressing, cell alignment, annalus fibrous tissue engineering, promoting endothelial proliferation, high performance filters and scaffolding promoting neuronal differentiation of human embryonic stem cells (1,2). Even though PU is a comparably well studied biomaterial that have been readily applied in biomedical applications, the complex surface interactions between electrospun PU fibers and cells are not well understood. Oxygen plasma surface modification (PSM) is a versatile material processing technique that has been shown to selectively modify surface properties such as wettability, adhesion and biocompatibility of polymer surfaces, and can improve surface properties for...