동적 장면으로부터의 다중 물체 3차원 복원 기법 및 학습 기반의 깊이 초해상도 기법

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2014. 2. 이경무.In this dissertation, a framework for reconstructing 3-dimensional shape of the multiple objects and the method for enhancing the resolution of 3-dimensional models, especially human face, are proposed. Conventional 3D reconstruction from multiple views is applicable to static scenes, in which the configuration of objects is fixed while the images are taken. In the proposed framework, the main goal is to reconstruct the 3D models of multiple objects in a more general setting where the configuration of the objects varies among views. This problem is solved by object-centered decomposition of the dynamic scenes using unsupervised co-recognition approach. Unlike conventional motion segmentation algorithms that require small motion assumption between consecutive views, co-recognition method provides reliable accurate correspondences of a same object among unordered and wide-baseline views. In order to segment each object region, the 3D sparse points obtained from the structure-from-motion are utilized. These points are relative reliable since both their geometric relation and photometric consistency are considered simultaneously to generate these 3D sparse points. The sparse points serve as automatic seed points for a seeded-segmentation algorithm, which makes the interactive segmentation work in non-interactive way. Experiments on various real challenging image sequences demonstrate the effectiveness of the proposed approach, especially in the presence of abrupt independent motions of objects. Obtaining high-density 3D model is also an important issue. Since the multi-view images used to reconstruct 3D model or the 3D imaging hardware such as the time-of-flight cameras or the laser scanners have their own natural upper limit of resolution, super-resolution method is required to increase the resolution of 3D data. This dissertation presents an algorithm to super-resolve the single human face model represented in 3D point cloud. The point cloud data is considered as an object-centered 3D data representation compared to the camera-centered depth images. While many researches are done for the super-resolution of intensity images and there exist some prior works on the depth image data, this is the first attempt to super-resolve the single set of 3D point cloud data without additional intensity or depth image observation of the object. This problem is solved by querying the previously learned database which contains corresponding high resolution 3D data associated with the low resolution data. The Markov Random Field(MRF) model is constructed on the 3D points, and the proper energy function is formulated as a multi-class labeling problem on the MRF. Experimental results show that the proposed method solves the super-resolution problem with high accuracy.Abstract i Contents ii List of Figures vii List of Tables xiii 1 Introduction 1 1.1 3D Computer Vision . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Dissertation Goal and Contribution . . . . . . . . . . . . . . . . . . . 2 1.3 Organization of Dissertation . . . . . . . . . . . . . . . . . . . . . . . 3 2 Background 7 2.1 Motion Segmentation . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2 Image Super Resolution . . . . . . . . . . . . . . . . . . . . . . . . . 9 3 Multi-Object Reconstruction from Dynamic Scenes 13 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 3.2 Related Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.3 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 3.4 Recognition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 3.4.1 Co-Recognition . . . . . . . . . . . . . . . . . . . . . . . . . . 20 3.4.2 Integration of the Sub-Results . . . . . . . . . . . . . . . . . 25 3.5 Camera Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.6 Object Boundary Renement . . . . . . . . . . . . . . . . . . . . . . 28 3.7 3D Reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 3.8 Experiments and Results . . . . . . . . . . . . . . . . . . . . . . . . . 32 3.8.1 Qualitative Results . . . . . . . . . . . . . . . . . . . . . . . . 32 3.8.2 Quantitative Results . . . . . . . . . . . . . . . . . . . . . . . 39 3.8.3 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 3.9 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 4 Super Resolution for 3D Face Reconstruction 55 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 4.2 Related Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 4.3 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 4.4 Proposed Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 4.4.1 Local Patch . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 4.4.2 Likelihood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 4.4.3 Prior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 4.5 Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 4.5.1 Training Data . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 4.5.2 Building Markov Network . . . . . . . . . . . . . . . . . . . . 75 4.5.3 Reconstructing Super-Resolved 3D Model . . . . . . . . . . . 76 4.6 Experiments and Results . . . . . . . . . . . . . . . . . . . . . . . . . 78 4.6.1 Quantitative Results . . . . . . . . . . . . . . . . . . . . . . . 78 4.6.2 Qualitative Results . . . . . . . . . . . . . . . . . . . . . . . . 81 4.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 5 Conclusion 93 5.1 Summary of Dissertation . . . . . . . . . . . . . . . . . . . . . . . . . 93 5.2 Future Works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 Bibliography 97 국문 초록 107Docto

O2 variant chip to simulate site-specific skeletogenesis from hypoxic bone marrow

The stemness of bone marrow mesenchymal stem cells (BMSCs) is maintained by hypoxia. The oxygen level increases from vessel-free cartilage to hypoxic bone marrow and, furthermore, to vascularized bone, which might direct the chondrogenesis to osteogenesis and regenerate the skeletal system. Hence, oxygen was diffused from relatively low to high levels throughout a three-dimensional chip. When we cultured BMSCs in the chip and implanted them into the rabbit defect models of low-oxygen cartilage and high-oxygen calvaria bone, (i) the low oxygen level (base) promoted stemness and chondrogenesis of BMSCs with robust antioxidative potential; (ii) the middle level (two times ≥ low) pushed BMSCs to quiescence; and (iii) the high level (four times ≥ low) promoted osteogenesis by disturbing the redox balance and stemness. Last, endochondral or intramembranous osteogenesis upon transition from low to high oxygen in vivo suggests a developmental mechanism-driven solution to promote chondrogenesis to osteogenesis in the skeletal system by regulating the oxygen environment.ope

Sprayable nanomicelle hydrogels and inflammatory bowel disease patient cell chips for development of intestinal lesion-specific therapy

All-in-one treatments represent a paradigm shift in future medicine. For example, inflammatory bowel disease (IBD) is mainly diagnosed by endoscopy, which could be applied for not only on-site monitoring but also the intestinal lesion-targeted spray of injectable hydrogels. Furthermore, molecular conjugation to the hydrogels would program both lesion-specific adhesion and drug-free therapy. This study validated this concept of all-in-one treatment by first utilizing a well-known injectable hydrogel that underwent efficient solution-to-gel transition and nanomicelle formation as a translatable component. These properties enabled spraying of the hydrogel onto the intestinal walls during endoscopy. Next, peptide conjugation to the hydrogel guided endoscopic monitoring of IBD progress upon adhesive gelation with subsequent moisturization of inflammatory lesions, specifically by nanomicelles. The peptide was designed to mimic the major component that mediates intestinal interaction with Bacillus subtilis flagellin during IBD initiation. Hence, the peptide-guided efficient adhesion of the hydrogel nanomicelles onto Toll-like receptor 5 (TLR5) as the main target of flagellin binding and Notch-1. The peptide binding potently suppressed inflammatory signaling without drug loading, where TLR5 and Notch-1 operated collaboratively through downstream actions of tumor necrosis factor-alpha. The results were produced using a human colorectal cell line, clinical IBD patient cells, gut-on-a-chip, a mouse IBD model, and pig experiments to validate the translational utility.ope

Hormone autocrination by vascularized hydrogel delivery of ovary spheroids to rescue ovarian dysfunctions

The regeneration potential of implantable organ model hydrogels is applied to treat a loss of ovarian endocrine function in women experiencing menopause and/or cancer therapy. A rat ovariectomy model is used to harvest autologous ovary cells while subsequently producing a layer-by-layer form of follicle spheroids. Implantation of a microchannel network hydrogel with cell spheroids [vascularized hydrogel with ovarian spheroids (VHOS)] into an ischemic hindlimb of ovariectomized rats significantly aids the recovery of endocrine function with hormone release, leading to full endometrium regeneration. The VHOS implantation effectively suppresses the side effects observed with synthetic hormone treatment (i.e., tissue overgrowth, hyperplasia, cancer progression, deep vein thrombosis) to the normal levels, while effectively preventing the representative aftereffects of menopause (i.e., gaining fatty weight, inducing osteoporosis). These results highlight the unprecedented therapeutic potential of an implantable VHOS against menopause and suggest that it may be used as an alternative approach to standard hormone therapy.ope

실리콘 관통 비아 전극을 이용한 개별 연결을 갖는 실리콘 기반 마이크로 프로브 전극 어레이에 대한 연구

학위논문(박사)--서울대학교 대학원 :공과대학 전기·정보공학부,2019. 8. 김용권.본 논문은 투명한 특성을 갖는 유리 기판 관통 실리콘 비아를 사용하여 개별 상호 연결을 갖는 수직 평면 외 마이크로 전극 어레이의 개발에 대한 것이다. 이러한 마이크로 프로브 전극 어레이는 뇌 조직에 삽입하여 신경 신호 측정을 위한 다양한 생물학적 응용에서 사용될 수 있다. 기존에 연구된 마이크로 프로브 전극 어레이는 불투명한 전극 구조의 삽입에 의해 원치 않는 조직 손상과 어드레싱 라인에서 발생하는 신호 손실이 문제가 된다. 이러한 문제를 해결하기 위해 저저항 실리콘 웨이퍼와 유리 재흘림 공정을 이용하여 유리 기판 관통 실리콘 비아와 마이크로 프로브 전극을 제작하는 것을 목표로 한다. 유리 재흘림 공정으로 제작되는 유리기판은 투명한 성질을 가지므로 마이크로 프로브 전극을 원하는 위치에 삽입함으로써 조직의 손상을 최소화할 수 있다. 또한, 제작되는 유리기판은 절연막으로서 우수한 특성을 가지기 때문에 실리콘 비아 전극 간의 신호 손실을 최소화할 수 있다. 유리 기판 관통 실리콘 비아 구조의 직경 및 높이는 각각 80 μm 와 250 μm가 되도록 설계되었다. 먼저 DRIE 공정을 이용하여 직경 80 μm 실리콘 기둥을 제작한 후 붕규산 유리 웨이퍼를 실리콘 웨이퍼에 접착한 후 850 °C의 온도에서 재흘림 공정을 수행하여 제작된다. 제작이 완료된 유리 기판 관통 실리콘 비아 구조의 투명도는 UV/Vis 분광 광도계를 사용하여 측정되었다. 측정 결과 가시광 영역에서 60 % 이상의 투명성을 가지는 것을 확인하였다. 제작된 싱글 실리콘 비아의 저항은 1.26 ± 0.041 Ω으로 측정되었고 교차 결합 커패시턴스는 0.23 ± 0.03 pF로 측정되었다. 마이크로 프로브의 높이는 조직에 삽입하기 위해 90 μm 이상으로 설계되었으며 마이크로 프로브 사이의 간격은 전극 간의 화학적 누화를 최소화하기 위해 210 μm로 설계되었다. 마이크로 프로브 구조는 한번의 포토 리소그래피 공정과 단일 식각 마스크를 사용하여 DRIE 와 RIE과정을 결합한 공정을 수행하여 형성된다. 마이크로 프로브의 형상은 RIE 공정 동안 실리콘 마이크로 기둥 측벽의 위치 및 첫 번째 DRIE 공정의 깊이에 따른 식각 속도의 차이에 의해 얻을 수 있다. 마이크로 프로브를 개별전극으로 제작하기 위해 네거티브 포토레지스트 (DNR-L-300)을 사용하여 마이크로 프로브 구조를 노출하고 각각 200 Å 및 2000 Å의 Cr 및 Au 전도층을 증착하였다. 리프트 오프 공정을 이용하여 전극 패터닝 후 3000 Å 의 파릴렌-C 층을 절연막으로서 전극 상에 증착하였다. 그 후, 두꺼운 포토레지스트를 이용한 마스크가 필요 없는 자기 정렬 공정을 수행하여 마이크로 프로브 말단에만 도전층을 노출 시켜 개별 마이크로 프로브 전극 공정을 완료한다. 제작이 완료된 마이크로 프로브 전극은 개별적으로 유리 기판 관통 실리콘 비아를 통해 기판의 뒷면으로 직접 연결이 되는 구조이다. 개별 연결을 갖는 마이크로 프로브 전극의 전기화학적 특성을 확인하기 위해 각각의 전극의 정상 상태 제한 전류를 측정할 수 있는 순환 전압 전류법이 수행되었다. 그리고 측정 된 정상 상태 제한 전류는 이론값과 비교되었다. 또한 16개 전극에 대한 임피던스 측정이 수행되었으며 1 kHz에서의 평균 임피던스는 0.292 ± 0.156 MΩ으로 측정되었다. 그런 다음 측정된 데이터와 임피던스 모델링 소프트웨어 (Zview, AMETEK Scientific instruments)를 사용하여 마이크로 프로브 전극의 등가 회로 분석을 수행하였다. 그후 제작된 마이크로 프로브 전극에서 1차 쥐 대뇌 피질 뉴런 세포 (DIV 7)를 배양하고 신경 신호를 성공적으로 측정하였다. 측정된 신호의 평균 신호 대 잡음비는 14.4로 측정되었다. 또한 제작된 전극을 쥐의 해마 뇌 절편 조직에 삽입하고 실험을 수행하였다. 실험 결과 제조된 마이크로 프로브 전극은 높은 투명성으로 인해 프로브 전극을 해마 조직상의 원하는 위치에 삽입함으로써 조직 손상을 최소화 하며 신호를 성공적으로 측정할 수 있었다. 결론적으로 제안된 유리기판 관통 실리콘 비아와 개별적으로 연결된 마이크로 프로브 구조는 신호 대 잡음 비가 높고 화학적 누화가 없는 신호를 측정할 수 있으며 투명도가 높은 유리 기판 관통 실리콘 비아 구조를 사용하여 원하는 위치에 프로브 전극을 삽입하여 타겟 조직의 손상을 최소화할 수 있는 것을 확인하였다. 제안된 마이크로 프로브 전극은 기존의 전극 구조의 한계를 극복할 수 있기 때문에 좀 더 다양한 바이오 응용 분야에 적합하다고 할 수 있다.This dissertation proposes a vertical out-of-plane microelectrode array (MEA) with an individual interconnect substrate, which uses a silicon through-glass via (TGV) with transparency properties. The MEA can be used for a wide variety of biological applications such as insertion in brain tissues for neural signal measurement. The problems of conventional MEAs that have been investigated in numerous studies include unwanted tissue damage caused by the insertion of an opaque microprobe electrode and the signal loss in the addressing line. To solve these problems, TGVs and microprobe electrode array were fabricated using low-resistance silicon (LRS) wafer and a glass reflow process. The MEA substrate made by the glass reflow process has high transparency, and thus, damage to the tissue can be minimized by inserting the microprobe electrode at the desired position. Furthermore, the glass substrate has excellent properties as an insulating film, thereby minimizing the signal loss between the silicon-via electrodes. The diameter and height of the TGV structure are designed to be 80 μm and 250 μm, respectively. A deep reactive ion etching process is used as a fabrication method to etch silicon pillars with a diameter of 80 μm. After bonding the borosilicate glass wafer to the silicon substrate, the glass is reflowed at a temperature of 850 °C. The transparency of the fabricated TGV structure was measured using a UV/Vis spectrophotometer. The measurement result showed a transparency of 60 % or more in the visible region. The resistance of single silicon via was measured to be 1.26 ± 0.041 Ω, and the cross-coupling capacitance was measured to be 0.23 ± 0.03 pF. The height of the microprobe was designed to be greater than 90 μm for insertion into the tissue, and the spacing between the microprobes was designed to be 210 μm to minimize chemical crosstalk between the microprobe electrodes. The microprobe structure is formed by combining the deep reactive ion etching and sulfur hexafluoride (SF6) reactive ion etching processes using one-step photolithography and a single etching mask. The shape of the microprobe structure is obtained by the difference in the etching rate depending on the position of the silicon micropillar sidewall during the reactive ion etching process and depth of the first DRIE process. To fabricate individual microprobe electrodes, a microprobe structure was exposed using a negative photoresist (DNR-L-300), and Cr and Au conductive layers of 200 Å and 2000 Å, respectively, were deposited. Following this, the electrode was patterned by a lift-off process, and a Parylene-C layer of 3000 Å was deposited on the electrode as an insulating film. Then, a self-alignment procedure was performed using a thick photoresist without a photolithography mask to expose the conductive layer only at the tip-end of the microprobe electrode. Each microprobe electrode was independently connected to the backside of the substrate through the silicon TGV. To verify the electrochemical characteristics of the microprobe electrodes with individual interconnects, the steady-state limiting current through the redox reaction was measured for each electrode by the cyclic voltammetry (CV) method. The measured steady-state peak current of the microprobe electrode was compared with the theoretical calculation. Impedance measurements were performed on 16 electrodes, and the average impedance at 1 kHz was measured as 0.292 ± 0.156 MΩ. Then, an equivalent circuit analysis was conducted using the impedance modeling software (Zview, AMTEK Scientific instruments). Following this, primary rat cortical neuron cells (DIV 7) were cultured on the fabricated microprobe electrodes and neural spike signals were successfully measured. The average signal-to-noise ratio (SNR) of the measured signal was 14.4. The fabricated electrode was then inserted into the hippocampal brain slice tissue of the rat and the experiment was conducted. Owing to the high transparency of the fabricated microprobe electrode, it was confirmed that tissue damage could be minimized by inserting the probe electrode at a desired position on the hippocampal tissue. In conclusion, the proposed structure can measure signals with high SNRs and no chemical crosstalk by connecting the TGV and microprobe structures individually and it is possible to insert electrodes at the desired positions using a TGV structure with high transparency, thus minimizing damage to the target tissue. The proposed microprobe electrode is suitable to various bio application areas as it overcomes the limitations of the conventional MEA structure.Chapter 1. Introduction 1 1.1. Background 1 1.1.1. Traditional neural probe 2 1.1.2. Silicon-based microprobes 4 1.2. Motivation and objectives 9 1.2.1. Motivation 9 1.2.2. Research objectives 10 1.3. Contents and organization 12 Chapter 2. Design of MEA with TGV structure 13 2.1. Introduction 13 2.2. Design of proposed structure 17 2.2.1. Design of combined microprobe and TGV electrode 17 2.2.2. Design of conductive microprobe 19 2.2.3. Design of TGV structure 20 Chapter 3. Fabrication of MEA structure combined with TGV structure. 22 3.1. Introduction 22 3.1.1. Basic fabrication process 23 3.2. Microprobe formation mechanism 25 3.3. Detailed fabrication process 27 3.4. Fabrication results 34 3.5. Experiments of light transmittance of fabricated MEA 42 Chapter 4. Electrochemical measurement 44 4.1. Introduction 44 4.2. Measurement methods 45 4.2.1. Impedance measurement method 45 4.3. Measurement results 49 4.3.1. Individual electrode measurement using CV experiment 49 4.3.2. Impedance measurement result 56 4.3.3. Electrochemical crosstalk 60 Chapter 5. In-vitro experiment 63 5.1. Introduction 63 5.2. Measurement of neural spike through culturing of rat cortical neuron cells 64 5.2.1. Device design and fabrication 64 5.2.2. Cell culture method 66 5.2.3. Measurement method 67 5.2.4. Measurement results and analysis 69 5.3. Measurement of neural signal in rat hippocampal brain slice tissue 72 5.3.1. Device design and fabrication 72 5.3.2. Measurement method 74 5.3.3. Measurement results and analysis 77 5.4. Future works 81 Chapter 6. Conclusion 83 Reference 85 국문초록 98 감사의 글 101Docto

이단계 리가-가공된 회로내의 교차전자빔에 의한 고출력 밀리미터서브밀리미터파 발생연구

Thesis(doctoral)--서울대학교 대학원 :물리학부,2006.Docto

Action corecognition in video pairs

학위논문(석사) --서울대학교 대학원 :전기. 컴퓨터공학부, 2009.2.Maste

Hybrid-spheroids incorporating ECM like engineered fragmented fibers potentiate stem cell function by improved cell/cell and cell/ECM interactions

Extracellular matrix (ECM) microenvironment is critical for the viability, stemness, and differentiation of stem cells. In this study, we developed hybrid-spheroids of human turbinate mesenchymal stem cells (hTMSCs) by using extracellular matrix (ECM) mimicking fragmented fibers (FFs) for improvement of the viability and functions of hTMSCs. We prepared FFs with average size of 68.26 µm by partial aminolysis of poly L-lactide (PLLA) fibrous sheet (FS), which was coated with polydopamine for improved cell adhesion. The proliferation of hTMSCs within the hybrid-spheroids mixed with fragmented fibers was significantly increased as compared to that from the cell-only group. Cells and fragmented fibers were homogenously distributed with the presence of pore like empty spaces in the structure. LOX-1 staining revealed that the hybrid-spheroids improved the cell viability, which was potentially due to enhanced transport of oxygen through void space generated by engineered ECM. Transmission electron microscopy (TEM) analysis confirmed that cells within the hybrid-spheroid formed strong cell junctions and contacts with fragmented fibers. The expression of cell junction proteins including connexin 43 and E-cadherin was significantly upregulated in hybrid-spheroids by 16.53 ± 0.04 and 28.26 ± 0.11-fold greater than that from cell-only group. Similarly, expression of integrin α2, α5, and β1 was significantly enhanced at the same group by 25.72 ± 0.13, 27.48 ± 0.49, and 592.78 ± 0.06-fold, respectively. In addition, stemness markers including Oct-4, Nanog, and Sox2 were significantly upregulated in hybrid-spheroids by 96.56 ± 0.06, 158.95 ± 0.06, and 115.46 ± 0.47-fold, respectively, relative to the cell-only group. Additionally, hTMSCs within the hybrid-spheroids showed significantly greater osteogenic differentiation under osteogenic media conditions. Taken together, our hybrid-spheroids can be an ideal approach for stem cell expansion and serve as a potential carrier for bone regeneration. Statement of significance: Cells are spatially arranged within extracellular matrix (ECM) and cell/ECM interactions are crucial for cellular functions. Here, we developed a hybrid-spheroid system incorporating engineered ECM prepared from fragmented electrospun fibers to tune stem cell functions. Conventionally prepared cell spheroids with large diameters (>200 µm) is often prone to hypoxia. In contrast, the hybrid-spheroids significantly enhanced viability and proliferation of human turbinate mesenchymal stem cells (hTMSCs) as compared to spheroid prepared from cell only. Under these conditions, the presence of fragmented fibers also improved maintenance of stemness of hTMSCs for longer time cultured in growth media and demonstrated significantly greater osteogenic differentiation under osteogenic media conditions. Thus, the hybrid-spheroids can be used as a delivery carrier for stem cell based therapy or a 3D culture model for in vitro assay.restrictio

Oxygen-dependent generation of a graded polydopamine coating on nanofibrous materials for controlling stem cell functions

Substrates modified with gradient surface chemistry are of fundamental importance for designing a new bio-interface in biomaterial research and tissue engineering. However, current gradient fabrication strategies are not easily accessible to most laboratories due to complex, expensive, and expertise-requiring procedures. In this study, we generated a gradient of polydopamine (PD) coating on a PLLA nanofiber surface using a spatially restricted supply of oxygen in the reaction solution. Analysis of the oxygen distribution revealed that oxygen availability varied along different reaction solution depths during dopamine polymerization. We then extensively investigated the effects of different parameters, such as tilting angle, reaction time, pH of the reaction solution, and concentration of dopamine, on PD gradient formation, which should be appropriately modulated for PD gradient on nanofibers. Further, culturing of human mesenchymal stem cells (hMSCs) on the PD gradient nanofiber resulted in a gradient of adhesion and spreading from high to low PD coating. However, the proliferation rate was not affected by the PD gradient, with an approximately 3-fold change after 5 days of culture. Maintenance of the stem cell density gradient on the PD gradient nanofiber resulted in controlled osteogenic differentiation, which was greater in the higher PD-coated area. Interestingly, stemness analysis showed a reverse trend relative to osteogenic differentiation of hMSCs. In summary, the spatially controlled polymerization of dopamine can be a versatile tool to generate substrates with gradient surface chemistry, which holds promise to direct stem cell behavior.restrictio

Dilation-Responsive Microshape Programing Prevents Vascular Graft Stenosis

Shape memory materials have been successfully applied to minimally invasive implantation of medical devices. However, organ-movement-specific shape programing at a microscale level has never been demonstrated despite significant unmet needs. As vein-to-artery grafting induces vein dilation and stenosis, a polymeric self-enclosable external support (SES) is designed to wrap the vascular out-wall. Its micropores are programmed to increase sizes and interconnections upon dilation. Vessel dilation promotes venous maturation, but overdilation induces stenosis by disturbed blood flow. Therefore, the unique elastic shape-fixity of SES provides a foundation to enable a stable microscale shape transition by maintaining the vein dilation. The shape transition of micropore architecture upon dilation induces beneficial inflammation, thereby regenerating vasa vasorum and directing smooth muscle cell migration toward adventitia with the consequent muscle reinforcement of veins. This game-changer approach prevents the stenosis of vein-to-artery grafting by rescuing ischemic disorders and promoting arterial properties of veins.restrictio