Wireless chemical sensing schemes using environmentally sensitive hydrogels

In situ sensing of chemical parameters such as pH, glucose, enzymes, and other analytes is of immense importance in health care and environmental monitoring. There has been considerable research in this area using hydrogels as a chemo-mechanical transducer. Hydrogels are water-swollen polymers containing chemical groups that are sensitive to environmental stimuli. When there is a chemical change, e.g. alkali to acidic pH, hydrogel swells or shrinks. This reversible volume change can be coupled to capacitive, inductive or other sensing mechanisms. Despite many years of research, hydrogel-based sensors have not been of practical utility. This has been due to several reasons such as: 1) manipulation difficulties of hydrated gel and their integration with hard inorganic materials, 2) slow response of transducer due to diffusion limited sensing mechanism, 3) baseline and sensitivity drift, and 4) biofouling. In 2006, Ziaie\u27s group presented a wireless MEMS-based pH/glucose sensitive sensor using hydrogel. Despite successful demonstration for a proof of concept, the device had several shortcomings such as a complicated fabrication processes resulting in low yield, difficulty in snugfilling of a small cavity with hydrogel, and slow response time. The doctoral work presented here reports on several investigations undertaken to overcome the aforementioned shortcomings by developing novel, simple to fabricate, and inexpensive methods using 1) immobilized ferrogel (magnetic nanoparticles embedded in hydrogel) on top of an integrated flat coil, 2) hydrogel/polymeric magnet bilayer, and 3) microbubbles embedded hydrogel. The reversible swelling/shrinking of hydrogel results in 1) a change of inductance, which can be wirelessly monitored by standard phase 6 detection methods, 2) vertical movement of a polymeric magnet, which can be remotely detected by a giant magneto resistance (GMR) sensor, and 3) a variation of microbubble-density inside of the hydrogel, which can be evaluated using an ultrasound imaging equipment. The primary engineering contributions of this research includes design, fabrication, and characterization of the systems using pH and glucose sensitive hydrogels

Efficient Storage and Processing Of High Volume Network Monitoring Data

No Abstrac

The Stanford OpenRoads Deployment

ABSTRACT We have built and deployed OpenRoad

Characterisation and State Estimation of Magnetic Soft Continuum Robots

Minimally invasive surgery has become more popular as it leads to less bleeding, scarring, pain, and shorter recovery time. However, this has come with counter-intuitive devices and steep surgeon learning curves. Magnetically actuated Soft Continuum Robots (SCR) have the potential to replace these devices, providing high dexterity together with the ability to conform to complex environments and safe human interactions without the cognitive burden for the clinician. Despite considerable progress in the past decade in their development, several challenges still plague SCR hindering their full realisation. This thesis aims at improving magnetically actuated SCR by addressing some of these challenges, such as material characterisation and modelling, and sensing feedback and localisation. Material characterisation for SCR is essential for understanding their behaviour and designing effective modelling and simulation strategies. In this work, the material properties of commonly employed materials in magnetically actuated SCR, such as elastic modulus, hyper-elastic model parameters, and magnetic moment were determined. Additionally, the effect these parameters have on modelling and simulating these devices was investigated. Due to the nature of magnetic actuation, localisation is of utmost importance to ensure accurate control and delivery of functionality. As such, two localisation strategies for magnetically actuated SCR were developed, one capable of estimating the full 6 degrees of freedom (DOFs) pose without any prior pose information, and another capable of accurately tracking the full 6-DOFs in real-time with positional errors lower than 4~mm. These will contribute to the development of autonomous navigation and closed-loop control of magnetically actuated SCR

Tailoring electron beams with high-frequency self-assembled magnetic charged particle micro optics

Tunable electromagnets and corresponding devices, such as magnetic lenses or stigmators, are the backbone of high-energy charged particle optical instruments, such as electron microscopes, because they provide higher optical power, stability, and lower aberrations compared to their electric counterparts. However, electromagnets are typically macroscopic (super-)conducting coils, which cannot generate swiftly changing magnetic fields, require active cooling, and are structurally bulky, making them unsuitable for fast beam manipulation, multibeam instruments, and miniaturized applications. Here, we present an on-chip microsized magnetic charged particle optics realized via a self-assembling micro-origami process. These micro-electromagnets can generate alternating magnetic fields of about ±100 mT up to a hundred MHz, supplying sufficiently large optical power for a large number of charged particle optics applications. That particular includes fast spatiotemporal electron beam modulation such as electron beam deflection, focusing, and wave front shaping as required for stroboscopic imaging

Secure Incentives to Cooperate for Wireless Networks

The operating principle of certain wireless networks makes essential the cooperation between the mobile nodes. However, if each node is an autonomous selfish entity, cooperation is not guaranteed and therefore we need to use incentive techniques. In this thesis, we study cooperation in three different types of networks: WiFi networks, Wireless Mesh Networks (WMNs), and Hybrid Ad-hoc networks. Cooperation has a different goal for each of these networks, we thus propose incentive mechanisms adapted to each case. In the first chapter of this thesis, we consider WiFi networks whose wide-scale adoption is impeded by two major hurdles: the lack of a seamless roaming scheme and the variable QoS experienced by the users. We devise a reputation-based solution that (i) allows a mobile node to connect to a foreign Wireless ISP in a secure way while preserving his anonymity and (ii) encourages the WISPs to cooperate, i.e., to provide the mobile clients with a good QoS. Cooperation appears here twofold: First, the mobile clients have to collaborate in order to build and maintain the reputation system and second, the use of this reputation system encourages the WISPs to cooperate. We show, by means of simulations, that our reputation model indeed encourages the WISPs to behave correctly and we analyze the robustness of our solution against various attacks. In the second chapter of the thesis, we consider Wireless Mesh Networks (WMNs), a new and promising paradigm that uses multi-hop communications to extend WiFi networks. Indeed, by connecting only one hot spot to the Internet and by deploying several Transit Access Points (TAPs), a WISP can extend its coverage and serve a large number of clients at a very low cost. We analyze the characteristics of WMNs and deduce three fundamental network operations that need to be secured: (i) the routing protocol, (ii) the detection of corrupt TAPs and (iii) the enforcement of a proper fairness metric in WMNs. We focus on the fairness problem and propose FAME, an adaptive max-min fair resource allocation mechanism for WMNs. FAME provides a fair, collision-free capacity use of the WMN and automatically adjusts to the traffic demand fluctuations of the mobile clients. We develop the foundations of the mechanism and demonstrate its efficiency by means of simulations. We also experimentally assess the utility of our solution when TAPs are equipped with directional antennas and distinct sending and receiving interfaces in the Magnets testbed deployed in Berlin. In the third and last chapter of this thesis, we consider Hybrid Ad-hoc networks, i.e., infrastructured networks that are extended using multi-hop communications. We propose a secure set of protocols to encourage the most fundamental operation in these networks, namely packet forwarding. This solution is based on a charging and rewarding system. We use "MAC layering" to reduce the space overhead in the packets and a stream cipher encryption mechanism to provide "implicit authentication" of the nodes involved in the communication. We analyze the robustness of our protocols against rational and malicious attacks. We show that the use of our solution makes cooperation rational for selfish nodes. We also show that our protocols thwart rational attacks and detect malicious attacks

크기가 조절된 산화 그래핀 플레이크를 이용한 인간줄기세포의 세포 활성 및 분화 조절

학위논문(박사) -- 서울대학교대학원 : 공과대학 화학생물공학부, 2023. 2. 박태현.There is increasing interest in studying stem cell differentiation through cellular physical stimulation which can be translated into cell-recognized tension. It has been known that physical stimulation can direct human mesenchymal stem cell differentiation which called mechanotransduction. Recently, graphene oxide (GO), major derivative of graphene, has been synthesized as promising material which has suitable physico-chemical characteristics for stem cell lineage specification. GO can interact with integrin, the transmembrane receptor protein, through electrostatic, hydrophobic interactions. However, GO used in previous stem cell research has used GO with an irregular morphology and size. Such irregularity of GO causes diverse cellular responses according to lateral sizes of GO. In this study, we fabricated graphite mechanically with narrow size distribution by adjusting the ball-milling time. Then, size-controlled GO flakes were chemically synthesized from ball-milled graphite using modified Hummers method. Size distribution of GO were measured by hydrodynamic situations. Dose-dependent cytotoxicity of the size-controlled GO flakes on human stem cells was observed. The interaction between GO flakes and cells was analysed with electron microscopy. Also, effect of GO with osteogenic and neural differentiation of hMSCs were measured by staining and gene expression level. Also, by analyzing the shape and size of the cells through immunostaining, we confirmed that focal adhesion was key component involved in promoting stem cell differentiation and enhanced cell viability in apoptotic circumstances. We suggest that the size-controlled GO sheets would be efficient candidate for enhancement of lineage determination of human stem cells and therapeutic applications.세포 인식 장력으로 번역될 수 있는 세포 물리적 자극을 통한 줄기 세포 분화 연구에 대한 관심이 증가하고 있다. 물리적 자극은 기계적 형질도입(mechanotransduction)이라고 하는 인간 중간엽줄기세포 분화를 조절할 수 있는 것으로 알려져 있다. 최근 그래핀의 주요 유도체인 산화 그래핀이 줄기세포 계통 사양에 적합한 물리화학적 특성을 갖는 유망한 물질로 주목되고 있다. 산화 그래핀은 정전기적 소수성 상호작용을 통해 막횡단 수용체 단백질인 인테그린과 상호작용할 수 있다. 그러나 기존 줄기세포 연구에서 사용된 물질은 형태와 크기가 불규칙한 산화 그래핀을 사용하고 있다. 이러한 산화 그래핀 물성의 불규칙성은 산화 그래핀의 측면 크기에 따라 통제되기 어려운 다양한 세포 반응을 일으킨다. 이 연구에서는 볼 밀링 시간을 조정하여 좁은 크기 분포를 가진 흑연을 기계적으로 제작하였다. 그런 다음 수정된 Hummers의 방법을 사용하여 볼 밀링된 흑연에서 크기가 제어된 산화 그래핀 플레이크를 화학적으로 합성하였다. 합성된 산화 그래핀의 크기 분포는 수용액 환경에서 측정되었다. 인간 줄기 세포에서 크기 조절된 산화 그래핀 플레이크의 용량 의존적 세포독성이 관찰되었다. 산화 그래핀 플레이크와 세포 사이의 상호 작용은 전자현미경 분석되었고 인간 중간엽줄기세포의 골형성 및 신경 분화와 함께 산화 그래핀의 효과를 분석하기 위해 염색 및 유전자 발현을 측정하였다. 또한 면역염색을 통해 세포의 모양과 크기를 분석함으로써 국소적 접착이 줄기세포 분화 촉진과 세포자멸사 촉진 환경에서 세포 생존력 향상에 관여하는 핵심 요소이며 이는 세포 종류와 배양 환경에 따라 다른 크기의 산화 그래핀이 효율적임을 확인하였다. 이로서 크기 조절 산화 그래핀 플레이크가 인간 줄기 세포의 분화 계통 결정 및 치료적 응용을 위한 효율적인 후보가 될 것이라고 제안한다.Chapter 1. Research background and objectives 2 Chapter 2. Literature review 6 2.1. Human stem cells 6 2.1.1. Human mesenchymal stem cells 6 2.1.2. Human embryonic stem cells 6 2.2. Stem cell research utilizing graphene oxide 7 Chapter 3. Experimental procedures 11 3.1. Preparation of GO 11 3.1.1. Ball-milling of graphite 11 3.1.2. Preparation of GO by ball-milled graphite 11 3.2. Characterization of GO 11 3.3. Preparation of magnetic nanoparticles 12 3.4. Cultivation and differentiation of hMSCs 12 3.5. Cultivation of hESCs 13 3.6. Generation of hEBs and neural differentiation 14 3.7. Cell adhesion assay of GO 14 3.8. Cell viability assay 15 3.8.1. CCK8 assay 15 3.8.2 Fluorescence-based live and dead assay 15 3.9. qRT-PCR analysis 15 3.10. Alkaline phosphatase staining and Alizarin Red S staining 18 3.11. Immunocytochemistry 18 3.12. Western blotting 18 3.13. Statistical analysis 19 Chapter 4. Material characteristics and cellular interactions of size-controlled graphene oxide flakes 21 4.1. Introduction 21 4.2. Characterization of GO processed by ball-milling 21 4.3. Morphology and cytotoxic effect of GO attached to hMSCs 27 4.4. Conclusions 30 Chapter 5. Enhanced osteogenic differentiation of bone marrow-derived human mesenchymal stem cells using size-controlled graphene oxide flakes 31 5.1. Introduction 32 5.2. Enhancing effect of GO on osteogenic differentiation of hMSCs 35 5.3. Promotion of early cell spreading and focal adhesion complex formation of hMSCs by GO-1.7 39 5.4. Expression and localization of osteogenic marker proteins by GO-1.7 43 5.5. Proposed mechanism of osteogenic differentiation enhanced by GO 47 5.6. Conclusions 52 Chapter 6. Enhancing effect of graphene oxide flakes on stem cell viability in single-cell detachment and shear stress-caused apoptotic circumstances 53 6.1. Introduction 54 6.2. Viability of hMSCs treated with GO-1.7 in non-adhesive condition and shear stress 56 6.3. Viability of hESCs treated with size-controlled GO flakes in non-adhesive condition 60 6.4. Conclusions 62 Chapter 7. Enhanced neural differentiation of adipose-derived human mesenchymal stem cells using size-controlled graphene oxide flakes 64 7.1. Introduction 65 7.2. 3D culture of ADSCs 67 7.3. Gene expression of neural induction markers in ADSCs 69 7.4. Expression of neural induction markers in ADSCs 72 7.5. Conclusions 75 Chapter 8. Overall discussion and further suggestions 77 Appendix. Enhanced neural differentiation of 3D human embryonic stem cells via magnetic nanoparticle-based physical stimuli 80 A.1. Introduction 81 A.2. Improved neural induction of MNP-incorporated hEBs, manufactured through a concentrated magnetic force system 84 A.3. Morphological analysis of neurally induced hESCs 87 A.4. Genetical analysis of neural induction marker genes 91 A.5. Related mechanisms to accelerated neural induction of hEBs 94 A.6. Conclusions 96 Bibliography 97 국 문 초 록 109박