Different Types Of Patches Research Articles

Application of Bovine Pericardium and Expanded Polytetrafluoroethylene Patches in Tricuspid Valvuloplasty after Cardiac Surgery.

Leaflet augmentation is often required to correct an inadequate leaflet size due to leaflet thickening, contracture and junctional fusion in patients with tricuspid valve regurgitation (TR) after left-side valve surgery (LSVS). However, the ideal material for leaflet augmentation remains controversial. This article aims to compare the medium- and long-term results of tricuspid valve repair with bovine pericardium (BP) and expanded Polytetrafluoroethylene (ePTFE) patches for the augmentation of tricuspid leaflets and to compare the durability of the two materials. From January 2015 to April 2023, a total of 69 patients with severe isolated TR underwent tricuspid valvuloplasty (TVP) by leaflets augmentation with patches in our institute. According to the different types of patches, they were divided into the BP group (n = 44) and the ePTFE group (n = 25). There were 3 perioperative deaths (4.3%), one case was due to low cardiac output syndrome in the BP group, and 2 cases were due to acute respiratory dysfunction syndrome and low cardiac output syndrome in the ePTFE group, respectively. Before discharge, the area of the TR jet on echocardiography decreased from 23.5 9.1 to 4.2 3.4 . One case in each group was found to have increased blood flow velocity at the tricuspid orifice. After discharge, one patient in each group underwent repeat TVP, in the BP group because of shortened chordae and in the ePTFE group because of calcification of the patch. During the entire follow-up period, there were 7 cases of severe TR (10.1%), 5 in the BP group and 2 in the ePTFE group, a total of 5 cases of tricuspid stenosis (7.2%), 4 in the BP group and 1 in the ePTFE group, and a total of 6 deaths (8.7%), 5 in the BP group and 1 in the ePTFE group. Transthoracic ultrasound in a patient with tricuspid stenosis suggests stiff leaflet movement and poor motion. Leaflet patch enlargement can be safely used in tricuspid valve repair, but BP patches carry a risk of reduced flexibility and stiffness of movement, and ePTFE patches carries a risk of calcification.

Landscape pattern changes in coal resource-based cities: A case study of Huainan City in China

Currently, coal resource-based cities (CRBCs) are facing challenges such as ecological destruction, resource exhaustion, and disordered urban development. By analyzing the landscape pattern, the understanding of urban land use can be clarified, and optimization strategies can be proposed for urban transformation and sustainable development. In this study, based on the interpretation of remote sensing data for three dates, the landscape pattern changes in the urban area of Huainan City, a typical coal resource-based city in Anhui Province, China were empirically investigated. The results indicate that: (1) There is a significant spatial-temporal transformation of land use, with construction land gradually replacing arable land as the dominant land use type in the region. (2) Landscape indices are helpful to reveal the characteristics of land transfer and distribution of human activities during a process. At the landscape type level, construction land, grassland, and water bodies are increasingly affected by human activities. At the landscape composition level, the number of landscape types increases, and the distribution of different types of patches becomes more balanced. In addition, to address the problems caused by the coal mining subsidence areas in Huainan city, three landscape pattern optimization strategies are proposed at both macro and micro levels. The research findings contribute to a better understanding of land use changes and their driving forces, and offer valuable alternatives for ecological environment optimization.

Coarse woody debris legacies and their dynamics in retained forest patches

Retaining trees in small patches at final harvest is a common forest conservation measure to maintain structural and biological diversity through the young forest phase. Long-term studies of coarse woody debris (CWD, breast height diameter ≥ 10 cm) changes in retention patches remain uncommon, especially in relation to different types of patches with varying tree species composition, ground moisture, size, shape, and exposure. In the present study we re-inventoried CWD three times (1–3, 5–7 and 18–20 years after harvesting) in 60 small tree retention patches (0.03–0.54 ha) of six commonly created retention patch types, in central boreal Sweden. Most retention patch types, despite being very small (<0.55 ha) and exposed, did not experience severe tree mortality and input of CWD over the two decades. Average total volumes of CWD did not change significantly over time, although volumes of downed CWD generally increased whilst standing CWD decreased. Volumes of different decay classes were dynamic over time, but all retention types supported a variety of decay stages after 18–20 years. The volume of CWD varied significantly between the six retention patch types, with buffer zones to mire having the lowest average volume of 9 m3 ha−1 and buffer zones to rocky outcrop the highest average volume of 32 m3 ha−1, when summarised over the whole study period. Very few patch-level environmental variables (except type) related to the amount of CWD in retention patches; only the retained living tree volume of patches during creation was clearly positively correlated with higher post-harvest CWD volumes. Patch characteristics such as size and shape index did not relate to the CWD volumes in retention patches, and patch exposure only related to higher CWD volumes within the first 1–3 years after harvest. Retention patches generally supported a variety of living trees, CWD volumes and qualities over time. Several retention patch types; such as free-standing coniferous and deciduous patches, rocky outcrop buffers, wet forest patches and buffers to water, supported average CWD volumes between 19–41 m3 ha−1 after 18–20 years, under remaining canopy cover. Our findings challenge the traditional management principles aimed at minimizing severe windthrow and CWD input (i.e., creating larger patches (>0.5–1 ha), choosing topographically sheltered areas, selecting specific tree species and ground conditions). However, our study was too small in scale to investigate multiple within-patch-type interacting environmental variables. Future larger-scale studies over extended time periods are needed to disentangle such interactions for the dynamics of CWD and associated biodiversity in retention patches.

Snipped Triple Band Microstrip Antenna for ISM Band and Wi-MAX Applications

The work suggests a snipped shaped patch antenna design and its analysis which will work in the microwave frequency in the low spectrum. Here the patch is introduced which is made up of denim cotton material. This type of antenna is relatively new device used for medical applications. This antenna is light in weight, compact in size, and inexpensive. This antenna resonates at 1.18 GHz, 2.45 GHz, 3.1 GHz, and 7.9 GHz to 10.6 GHz. As a result, it is used in Industrial Scientific and Medical (ISM) band and Wi-MAX applications. There are different types of patch antenna here a microstrip is used as wearable antenna. As a result, the patient’s condition can be diagnosed by using this antenna after studying the radiation pattern, return loss. Ansoft HFSS can be used to emulate them.

Two-Dimensional Structures Formed by Triblock Patchy Particles with Two Different Patches.

Two-dimensional structures formed by spherical triblock patchy particles are examined by performing Monte Carlo simulations. In the model, the triblock patchy particles have two different types of patches at the polar positions. The patch sizes are different from each other, and the attractive interaction acts only between the same types of patches. The particles translate on a flat plane and rotate three-dimensionally. When varying the two patch sizes, the pressure, and interaction energy, various structures are observed. When the difference between two patch sizes is small, kagome lattices, hexagonal structures, and two-dimensional dodecagonal quasi-crystal structures are observed. When the difference between two patch sizes is large, chain-like structures are created. With lower temperature, sparse structures such as ring-like structures form.

Multi-attention multiple instance learning

A new multi-attention based method for solving the MIL problem (MAMIL), which takes into account the neighboring patches or instances of each analyzed patch in a bag, is proposed. In the method, one of the attention modules takes into account adjacent patches or instances, several attention modules are used to get a diverse feature representation of patches, and one attention module is used to unite different feature representations to provide an accurate classification of each patch (instance) and the whole bag. Due to MAMIL, a combined representation of patches and their neighbors in the form of embeddings of a small dimensionality for simple classification is realized. Moreover, different types of patches are efficiently processed, and a diverse feature representation of patches in a bag by using several attention modules is implemented. A simple approach for explaining the classification predictions of patches is proposed. Numerical experiments with various datasets illustrate the proposed method.

Use of a non-medicated plaster in chronic lumbar back pain: a randomized controlled trial.

Background and aim:The latest technology on far infrared radiations reflects the radiations emitted by the human body and induces an antalgic and anti-inflammatory effect without active ingredients. Our primary aim was to assess pain level modifications throughout the treatment period with two different types of patches, compared to a placebo. As secondary aims, we focused on addressing patients’ quality of life and range of motion changes with each patch.Methods:We assessed 54 patients with chronic lumbar back pain treated with FIT Therapy (far infrared technology) patch. Three different types of FIT Therapy patches (F4, F3, and placebo) were used according to the different power of action and patients allocated in a randomized fashion into the 3 arms of the study. Every single patient was assessed during the study using the VAS pain scale, the Roland Morris Disability Questionnaire for quality of life, and ROM for a total of 14 days.Results:Only the F4 patch group significantly reduced pain level at T14 compared to the placebo group (p<0.05). Meanwhile, F3 showed only a non-significant decrease compared to placebo (p=0.254). In terms of lifestyle improvements, both F3 and F4 recorded a decrease on the RMDQ of 4 and 6 points, respectively.Conclusions:Currently, we still need further studies with longer follow-up to consider the FIT Therapy patches F4 a valid alternative as a “non-medicated pain relief”, but it proved to have a role in alleviating painful symptoms and improving function in chronic lumbar back pain without adverse events. (www.actabiomedica.it)

Extensive horse grazing improves grassland vegetation diversity, seed bank and forage quality of artificial embankments (Rhône River - southern France): Influence of extensive horse grazing on artificial embankments

Grazing by herds of herbivores modifies plant communities in different ways, depending on the herbivore species. Horse grazing is already known to be effective in increasing plant diversity and maintaining herbaceous vegetation, creating different types of patches and thus ensuring spatial heterogeneity. On an artificial embankment at the Donzère-Mondragon hydroelectric facility in the Rhône Valley, extensive grazing by a rustic horse (Konik-Polski) was introduced several years ago to control shrub encroachment and to enhance plant grassland diversity. Vegetation monitoring surveys over a five-year period (2014–2018) showed that horse grazing maintained patches of open and short grasslands and increased species-richness, in particular of annual species, some of which have heritage value. In contrast, overly-low grazing pressure led to the dominance of an unpalatable perennial grass (Brachypodium phoenicoides) at the expense of the annual species that significantly enhance the forage value of the most heavily grazed patches. Horse grazing also had a positive impact on the permanent seed bank of the soil, increasing its heterogeneity and the density of viable seeds. Extensive horse grazing thus appears to be a relevant management tool to preserve the diversity and the forage quality of the most open and short grasslands. Nevertheless, grazing pressure here remained too low to allow restoration of grasslands already colonised by woody species. Combining different livestock species might be a better alternative to pure horse grazing, to increase heterogeneity and diversity. Our results are discussed in relation to extensive horse grazing on artificial ecosystems, such as the embankments bordering rivers and canals.

Effect of grazing intensity and dung on herbage and soil nutrients

Dung deposited by grazing animals is a key driver affecting sward structure and nutrient cycling in pastures. We tested herbage and soil properties in three types of tall sward-height patches (&amp;gt; 10 cm): (i) patches with dung under intensive grazing; (ii) patches with dung under extensive grazing; and (iii) patches with no dung under extensive grazing. These patches were compared with grazed swards under intensive and extensive grazing. Analyses indicated no significant effect of different types of patches on plant available nutrients. Herbage nutrient concentrations from the different types of patches differed significantly. The highest concentrations of nitrogen (30.65 g/kg), phosphorus (4.51 g/kg) and potassium (22.06 g/kg) in the herbage dry matter were in the tall patches with dung presence under intensive grazing regime because of nutrients from dung utilized for sward regrowth. Regardless of dung presence, similar herbage nutrient concentrations were revealed in non-grazed tall sward-height patches in extensive grazing regime. The presence of dung did not have any effect on the plant available nutrients in any type of patches, therefore we suppose that non-utilized nutrients were probably leached, volatilised or transformed into unavailable forms and thus soil nutrient enrichment was low.

A Framework for Spatiotemporal Analysis of Gastrointestinal Spike Burst Propagation.

Gastrointestinal spike bursts are a bioelectrical phenomenon associated with motility. These events when initiated propagate a small distance and abruptly terminate activating a small area defined as a patch. Understanding normal and abnormal propagation patterns of these events may shed light on the root causes of functional motility disorders. This study develops an automated framework for spatiotemporal analysis of spike bursts. High-resolution electrical signals were obtained from the pig intestine, after which intestinal spike bursts were identified and clustered into their propagating wavefronts. Propagation velocity was estimated by fitting a polynomial surface to the activation times. The fit was able to estimate the velocity of spike burst patches covering at least six channels with an average RMSE of 0.4 s. Propagation within patches was visualized by plotting the fit as activation maps and velocity maps. Average velocities were calculated to compare the propagation characteristics of different types of patches. In the future, this framework will be extended to generate amplitude maps and spike burst duration maps. These tools can be used to analyze spike patch propagation and their relationship to motility.

长江流域景观格局与生态系统水质净化服务的关系

PDF HTML阅读 XML下载 导出引用 引用提醒 长江流域景观格局与生态系统水质净化服务的关系 DOI: 10.5846/stxb201801130100 作者: 作者单位: 中国科学院生态环境研究中心,中国科学院生态环境研究中心 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点研发计划项目（2016YFC0503401）；中国科学院科技服务网络计划项目（KFJ-STS-ZDTP-022） Relationships between landscape pattern and ecosystem water purification service in the Yangtze River Basin Author: Affiliation: Research Center for Eco-Environmental Sciences,Research Center for Eco-Environmental Sciences Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:流域景观格局通过影响生态过程，改变进入河流污染物的数量，进而对水质净化服务产生重要影响，探讨流域景观格局对水质净化服务的影响对于流域景观规划、生态系统保护和生态系统服务提升具有重要意义。以长江流域为研究区域，在分析45个子流域景观格局特征、应用InVEST模型评估流域水质净化服务基础上，探讨了两者的关系，结果表明：①景观组成上，长江流域农田和城镇面积比例分别与生态系统水质净化服务存在显著对数关系（P < 0.01），森林面积比例则与之呈极显著正相关关系（P < 0.01）；②流域景观配置上，斑块密度和景观破碎度与水质净化服务呈显著负相关（P < 0.01），而平均斑块面积和形状规律相反（P < 0.01）；③斑块类型水平上，森林平均斑块面积、灌丛/湿地平均斑块形状与生态系统水质净化服务呈显著正相关（P < 0.01），而农田平均斑块面积/边缘密度、城镇斑块密度则与之呈显著负相关（P < 0.01）；④森林主导景观的子流域，仅有景观破碎度与生态系统水质净化服务呈显著负相关，而农田主导景观的子流域，景观蔓延度、香农多样性与其分别呈正相关（P < 0.01）。研究结果可以为长江流域生态系统水质净化服务的提升提供多途径的管理信息：流域景观尺度上，增加森林面积比例、控制农田与城镇面积比例，并减少景观破碎度而增加平均斑块形状复杂性；斑块类型水平上，可增加灌丛/湿地斑块形状复杂性，减小农田边缘密度和城镇斑块密度；森林主导景观的子流域应降低景观破碎度，以农田主导景观的子流域则应该增加斑块类型丰富度和团聚程度。研究也可为其他流域水质净化服务管理提供参考。 Abstract:Landscape patterns can affect pollutant discharge into rivers by influencing ecological processes, and further affect water purification service of ecosystems in the watershed. It is of great significance for landscape planning, ecosystem protection, and ecosystem services promotion to explore the relationships between landscape patterns and ecosystem water purification service. The landscape pattern characteristics were analyzed and ecosystem water purification service was assessed by using InVEST (Integrated Valuation of Ecosystem Services and Tradeoffs) model in 45 sub-basins of the Yangtze River Basin. Then the relationships between landscape patterns and ecosystem water purification service were identified. For the landscape composition, the proportions of farmland and urban areas were logarithmically correlated with ecosystem water purification service (P < 0.01), whereas the proportion of forest area was positively correlated with it (P < 0.01). For the landscape configuration, water purification service was negatively correlated with patch density and landscape fragmentation, and positively correlated with the average patch area and shape (P < 0.01). For the patch-type, average patch area of forest/shrub and the average patch shape of shrub and wetland were positively correlated with ecosystem water purification service, while the average patch area and edge density of farmland and urban patch density were negatively correlated with water purification service (P < 0.01). Only landscape fragmentation and the ecosystem water purification service was negatively correlated in the forest-dominated sub-basin (P < 0.01). In the farmland-dominated sub-basin, ecosystem water purification services were positively correlated with landscape aggregation and Shannon diversity indexes (P < 0.01). The above results can provide management information for the promotion of ecosystem services in the Yangtze River basin. At the landscape scale of the basin, increasing the area proportion of forest, controlling the farmland and urban area proportions, reducing the landscape fragmentation, and increasing the complexity of the average patch shape would be helpful for the improvement of ecosystem water purification service. At the patch-type level, increasing the area of the shrub patch and the shape complexity of the shrub and wetland patches, and reducing the edge density of urban and the patch density of farmland would also contribute to the promotion of ecosystem water purification service. In the forest-dominated sub-basins, landscape fragmentation should be prevented, while the diversity and aggregation of different types of patches should be increased in the farmland-dominated sub-basins. The information can also provide important for the management of ecosystem water purification service in other basins. 参考文献 相似文献 引证文献

A study of tensile residual strength of composite laminates under different patch-repaired series

The tensile behavior of composite laminate structures repaired by bonding external patches was studied in the paper. Two different types of patches including wedge patches and inverted wedge patches were used and failure mechanisms, failure load and strength predictions were studied. A convenient and fast method of building 2-D finite element modeling (FEM) of laminate structure repaired was proposed and the strength of repaired laminate structures was calculated by FEM. The results showed that more than 80% tensile strength of the undamaged laminate could be recovered by bonding patch repairs. Moreover, the results indicated that the strength of inverted wedge patches repair were higher than that of wedge patches repair. FEM simulation results indicated that high stress concentration was found along the edges of invert patches and the most weakness part located in the adhesive bondline. FEM analysis results showed that the strength predicted matched well with the test strength.

Percolation in binary and ternary mixtures of patchy colloids.

We investigate percolation in binary and ternary mixtures of patchy colloidal particles theoretically and using Monte Carlo simulations. Each particle has three identical patches, with distinct species having different types of patch. Theoretically we assume tree-like clusters and calculate the bonding probabilities using Wertheim's first-order perturbation theory for association. For ternary mixtures, we find up to eight fundamentally different percolated states. The states differ in terms of the species and pairs of species that have percolated. The strongest gel is a trigel or tricontinuous gel, in which each of the three species has percolated. The weakest gel is a mixed gel in which all of the particles have percolated, but none of the species percolates by itself. The competition between entropy of mixing and internal energy of bonding determines the stability of each state. Theoretical and simulation results are in very good agreement. The only significant difference is the temperature at the percolation threshold, which is overestimated by the theory due to the absence of correlations between bonds in the theoretical description.

不同斑块类型的景观指数粒度效应响应研究——以无锡市为例

不同斑块类型的景观指数粒度效应响应研究——以无锡市为例

Visual-Patch-Attention-Aware Saliency Detection.

The human visual system (HVS) can reliably perceive salient objects in an image, but, it remains a challenge to computationally model the process of detecting salient objects without prior knowledge of the image contents. This paper proposes a visual-attention-aware model to mimic the HVS for salient-object detection. The informative and directional patches can be seen as visual stimuli, and used as neuronal cues for humans to interpret and detect salient objects. In order to simulate this process, two typical patches are extracted individually and in parallel from the intensity channel and the discriminant color channel, respectively, as the primitives. In our algorithm, an improved wavelet-based salient-patch detector is used to extract the visually informative patches. In addition, as humans are sensitive to orientation features, and as directional patches are reliable cues, we also propose a method for extracting directional patches. These two different types of patches are then combined to form the most important patches, which are called preferential patches and are considered as the visual stimuli applied to the HVS for salient-object detection. Compared with the state-of-the-art methods for salient-object detection, experimental results using publicly available datasets show that our produced algorithm is reliable and effective.

Repair of aircraft structures using composite patches bonded through induction heating

In this study, we investigated the use of composite patches to repair aluminum alloy double-lap joints. The carbon composite patches were cured using induction curing or oven curing. Joints were repaired using precured or cocured composite patches. The bond strengths of the different joints were compared. We also investigated whether the incorporation of carbon nanotubes (CNTs) in the adhesive bondline affected bond strength. We found that the induction-cured samples exhibited bond strengths similar to those of the corresponding oven-cured samples; this was true for both the baseline and the CNT-reinforced samples. Further, the samples processed using cocured patches exhibited higher bond strengths than did the corresponding samples processed using precured patches. In the case of both the precured and the cocured patch samples, the dispersion of 0.5 wt% CNTs in the adhesive bondline increased the bond strength slightly. The effect of the two different types of patches placed on top of the aluminum substrate on the rate of temperature increase by induction curing was shown experimentally, and, numerical simulations were performed to verify the experimental results. The results from this study show that the induction curing and co-curing method may be regarded as a sound and efficient method for composite patch bonding repair.

Enhanced analysis of landscape structure: Inclusion of transition zones and small-scale landscape elements

Landscape diversity is an essential component of biodiversity because it determines the diversity of habitats and species. It is necessary to adopt an adaptive and realizable landscape structure monitoring model for ecosystem management. However, the existing methods of landscape structure analysis often do not consider the transitions between different types of patch, which are dynamic and play several functional roles in landscape structure. Another component of information that has often been ignored is “small-scale landscape elements” inside patches, which leads to within-patch heterogeneity being underestimated. This paper presents a method for solving these problems by regular landscape monitoring using RapidEye remote sensing data. We incorporate the third altitude dimension in landscape structure analysis, especially for detecting certain small-scale landscape structures such as groves, tree rows, and transitions at forest boundaries. For these detailed structures a number of landscape metrics are computed under a three-dimensional perspective. The results indicate that a more realistic and more precise representation of landscape structure is obtained on the basis of the detailed spatial scale and the true surface geometries of patches. Taking transitions into account helps smooth “edge effects” between patches and leads to more realistic quantification of fragmentation.

On FEM modeling of piezoelectric actuators and sensors for thin-walled structures

Thin-walled adaptive structures render a large and important group of adaptive structures. Typical material system used for them is a composite laminate that includes piezoelectric material based sensors and actuators. The piezoelectric active elements are in the form of thin patches bonded onto or embedded into the structure. Among different types of patches, the paper considers those polarized in the thickness direction. The finite element method (FEM) imposed itself as an essential technical support for the needs of structural design. This paper gives a brief description of a developed shell type finite element for active/adaptive thin-walled structures and the element is, furthermore, used as a tool to consider the aspect of mesh distortion over the surface of actuators and sensors. The aspect is of significance for simulation of behavior of adaptive structures and implementation of control algorithms.

Shrub facilitation increases plant diversity along an arid scrubland–temperate rain forest boundary in South America

AbstractAimTheoretical models predict nurse plant facilitation enhances species richness by ameliorating stressful environmental conditions and expanding distributional ranges of stress‐intolerant species into harsh environments. We studied the role of nurse facilitation on the recruitment of perennial plants along an arid scrubland–temperate rain forest boundary to test the following predictions: (1) nurse shrub canopy increases seedling abundance and species richness along the rain forest–scrubland boundary; (2) scrubland species are less dependent on facilitative interactions than temperate rain forest species, especially at the moister, upper end of the gradient.LocationBosque Fray Jorge National Park, north‐central Chile, South America (30° 39′ S – 71° 40′ W).MethodsWe examined seedling abundance and species richness of perennial plants in the open and under different types of patches that may facilitate species recruitment (living shrubs, dead shrubs, perennial grasses and trees) along an arid scrubland–temperate rain forest boundary. To assess whether the potential role of the shrub canopy on seedling survival in the scrubland and forest differs, we designed a 2 × 2 factorial field experiment with shrub canopy (under shrub or open patch) and small mammal herbivory (access or closed) as factors. At both sides of the scrubland–forest gradient, we planted young seedlings of scrubland (Senna cumingii) and forest (Myrceugenia correifolia and Griselinia scandens) species under the four treatment combinations.ResultsNurse living shrubs increased seedling abundance and diversity. Under living shrubs, the number of recruiting species was 100% and 30% larger than in open patches of the arid scrubland and temperate rain forest patches, respectively. Seedling abundance was 60% and 300% larger under living shrubs compared to open patches of the scrubland and the temperate rain forest, respectively. Despite their low cover, dead shrubs were particularly important for recruitment of young seedlings in the scrubland. Seedlings of forest species were extremely rare. The field experiment demonstrated the importance of nurse plant facilitation for the survival of the forest species at both sides of the boundary. In contrast, scrubland species were less dependent on nurse plants than forest and intermediate forest–scrubland species.ConclusionsOur results show that facilitative interactions increase seedling abundance and species richness along an arid scrubland–temperate rain forest boundary, notably by enhancing seedling establishment of forest species. Despite increasing nurse shrub–seedling competition in the arid scrubland, shrubs have a net positive effect on plant community diversity.

DNA‐Linked Nanoparticle Building Blocks for Programmable Matter

Programmable matter is a distributed system of agents that act cooperatively to configure themselves into arbitrary shapes with arbitrary functions. Molecular self-assembled structures containing many nanoparticles are candidates for programmable matter. Programmability implies that system designers are able to control the properties of assembly products. The system should be able to assemble into arbitrary, anisotropic shapes, like an electronic circuit, with the capability of incorporating different materials at specific locations within the structure. Defects or errors should be minimized, and 3D assembly should be possible. In self-assembly, component parts, or building blocks, interact locally to produce a coherent and organized whole. At the molecular level, the interactions are determined by “patches” that react between building blocks. Frequently, the assemblies exhibit collective properties that are distinct from those of their constituent components. These properties often depend upon the shape of the structure. Thus, the difficulty of programmability is really the difficulty of controlling the shape of resulting nanostructures. The ability to program the shape of a final assembly is computationally difficult and subject to frequent errors. Nevertheless, through careful design and implementation of building blocks, desired shapes and properties might be achieved. To maximize programmability (i.e., control), there should be a large number of types of patches available. Otherwise, there is no variety of interactions to assemble complicated shapes. The placement and relative orientation of patches on the surface of the building block should be controlled. Different types of patches should be able to be placed on the same building block to diversify the shapes available. Finally, the chemistry for patch conjugation to the building block should be relatively simple and sustainable, and it should be able to be used with a variety of materials. Because of its unique molecular recognition properties, structural features, and ease of manipulation, beginning with seminal work by Seeman and Chen, DNA has been considered as a promising material to achieve programmable assembly of nanostructures. Nanoparticle (NP) building blocks with different surface functionalities for DNA linkers have been reported. DNA computing verified the programmability of DNA-based nanotechnology and, in fact, demonstrated that DNA self-assembly was computationuniversal. DNA programmability has demonstrated the ability to assemble a variety of shapes 9] and, when NPs are incorporated, to control the position of NPs in linear, 2D, and 3D assemblies, including those based upon origami techniques. 10] Nevertheless, the rational self-assembly of functional structures with arbitrary shapes in all dimensions and at all scales that can incorporate many different NPs into a variety of final geometries remains difficult to attain. Herein we present a strategy to control the number, placement, and relative orientation of DNA linkers on the surface of a colloidal NP building block to maximize its programmability and realize enhanced control over the shape and function of final self-assembled structures. Figure 1 shows a schematic illustration of the assembly sequence to produce the DNA-linked colloidal gold NP building blocks (termed nBLOCKs). A measure of control was achieved by the sequential ligand replacement approach and stiff DNA linkers, which were shorter than the persistence length of double-stranded DNA. In the assembly reaction, the electrostatic repulsions and steric hindrances of DNA molecules influence the layout of DNA on a NP. The net charge of DNA at a pH value above its isoelectric point (i.e., pH 5) is negative, so it would tend to position on a NP to minimize its mutual electrostatic repulsions, in analogy to the valence shell electron pair repulsion model, thus contributing to the molecular geometry. Also, mutual steric hindrance could be another factor to further constrain the overall geometry, particularly using small NPs. In our strategy, a Au NP is functionalized by DNA strand by strand: for example, a NP with one DNA strand is the starting material for the second DNA attachment, a NP with two DNA strands is the starting material for the third DNA attachment, etc. (Figure 1; see Figure S1 in the Supporting Information). With this constraint, the position of DNA attachment would be chosen to minimize the electrostatic and steric interactions with existing DNA on the NP, yielding the optimal arrangement of DNA on a NP with up to sixfold symmetry, that is, linear (one and two DNA strands), T-shaped (three DNA strands), square planar (four DNA strands), square pyramidal (five DNA [*] Prof. J.-W. Kim, Dr. J.-H. Kim Bio/Nano Technology Laboratory Department of Biological and Agricultural Engineering and Institute for Nanoscience and Engineering University of Arkansas, Fayetteville, AR 72701 (USA) E-mail: jwkim@uark.edu