Bridged Silsesquioxanes with Organic Domains Self-Assembled as Functionalized Molecular Channels

A bridged silsesquioxane was obtained from a precursor synthesized by the reaction of glycidoxypropyl(trimethoxysilane) (2 mol) with cyclohexylamine (1 mol). The polycondensation in the presence of formic acid produced a hybrid material exhibiting a short-range order based on elongated organic channels accommodating the pendant cyclohexyl fragments, bounded by inorganic domains. The presence of functional groups in the organic channels (tertiary amine, ether, hydroxyl), can be used to retain small organic molecules capable of forming hydrogen bonds. Aspirin was used as a probe to illustrate this possibility.

     

Mesoscale networks and corresponding transitions from self-assembly of block copolymers

A series of cubic network phases was obtained from the self-assembly of a single-composition lamellae (L)-forming block copolymer (BCP) polystyrene-block-polydimethylsiloxane (PS-b-PDMS) through solution casting using a PS-selective solvent. An unusual network phase in diblock copolymers, double-primitive phase (DP) with space group of Im3¯m, can be observed. With the reduction of solvent evaporation rate for solution casting, a double-diamond phase (DD) with space group of Pn3¯m can be formed. By taking advantage of thermal annealing, order–order transitions from the DP and DD phases to a double-gyroid phase (DG) with space group of Ia3¯d can be identified. The order–order transitions from DP (hexapod network) to DD (tetrapod network), and finally to DG (trigonal planar network) are attributed to the reduction of the degree of packing frustration within the junction (node), different from the predicted Bonnet transformation from DD to DG, and finally to DP based on enthalpic consideration only. This discovery suggests a new methodology to acquire various network phases from a simple diblock system by kinetically controlling self-assembling process.

From constituted molecules to polymers, finally ordered hierarchical superstructures, self-assembled solids cover a vast area of nanostructures where the characters of building blocks direct the progress of self-assembly (1, 2). In nature, fascinating periodic network structures and morphologies from different species are appealing in nanoscience and nanotechnology due to their superior properties, especially for photonic crystal structures (3–7). For gyroid, trigonal planar network with chirality demonstrates its potential as chiropitc metamaterial (8–10). Beyond the splendid colors, networks either in macroscale or mesoscale mechanically strengthen their skeletons and protect those fragile but vital organs from impact (11, 12). Inspired by nature, biomimicking materials with mesoscale network may exceed the limitation of the intrinsic properties (13). The topology of networks could further improve their adaptability, allowing extreme deformation for energy dissipation (14). Moreover, network materials from hybridization of self-assembled block copolymers (BCPs) have been exploited to the design of mesoscale quantum metamaterials (15, 16). With the desire to acquire network textures for biomimicking nanomaterials, BCPs with immiscible constituted segments covalently joined together give the accessibility to the formation of nanonetwork morphologies via balancing enthalpic penalty from the repulsive interaction of constituted blocks and entropic penalty from the stretching of polymer chains (17–21). By taking advantage of precise synthesis procedures, it is feasible to obtain the aimed network phases from the self-assembly of BCPs such as Fddd (O⁷⁰) (22–24), gyroid (Q²¹⁴, Q²³⁰) (20, 21, 25–27), and diamond (Q²²⁴, Q²²⁷) (28–31) experimentally and theoretically. On the basis of theoretical prediction, the junction points (nodes) in the network phases could be coordinated with three, four, or six neighbors in three-dimensional space, resulting in the enhancement of packing frustration (31). Topologically, all these phases match the coordination number to neighbors (n = 3, 4, 6), showing no special case of quasicrystal. Accordingly, an order–order transition from double-diamond phase (DD, tetrapod) to double-gyroid phase (DG, trigonal planar network) has been observed (29). Yet, there is no DP phase being found in simple diblock systems except for liquid crystals (32, 33) or organic–inorganic nanocomposites from the mixtures of BCP with inorganic precursors (34, 35). Searching the rare occurrence of network phases and the corresponding phase transitions among phases will be essential to the demands for application by considering the deliberate structuring effects on aimed properties but the approaches remain challenging (8, 36–40). For instance, viewing the narrow window for network morphologies in diblock copolymer phase diagram, it demands harsh requirements for syntheses (2, 41). Recently, by taking advantage of using selective solvent for solution casting, it is feasible to acquire DG phase and even inverted DG phase from the self-assembly of lamellae (L)-forming polystyrene-block-polydimethylsiloxane (PS-b-PDMS) (42). Apart from that, a triclinic DG phase was recently discovered from the PS-b-PDMS which is commonly believed nonexisting in the conventional phase diagram (43). As a result, the phase diagram of BCPs with high interaction parameter is worthy of study for searching the metastable phases with unique network textures (44). Herein, we aim to acquire network phases from a simple diblock system by kinetically controlling the transformation mechanisms of self-assembly. As exemplified by using the PS-b-PDMS for solution casting, with the use of a PS-selective solvent (chloroform), a DP phase and a DD phase could be formed through controlled self-assembly, giving unique network phases simply from solution casting. Moreover, a DG phase can be also acquired from phase transformation. Consequently, a series of network phases with hexapod, tetrapod, and trigonal planar building units could be successfully obtained by using a single-composition L-forming PS-b-PDMS for self-assembly. The corresponding order–order transitions among these network phases examined by temperature-resolved in situ small-angle X-ray scattering (SAXS) combining with electron tomography results provide insights of network phase formation and the corresponding phase transformation mechanisms in the self-assembly of BCPs.     

Individual error correction drives responsive self-assembly of army ant scaffolds

An inherent strength of evolved collective systems is their ability to rapidly adapt to dynamic environmental conditions, offering resilience in the face of disruption. This is thought to arise when individual sensory inputs are filtered through local interactions, producing an adaptive response at the group level. To understand how simple rules encoded at the individual level can lead to the emergence of robust group-level (or distributed) control, we examined structures we call “scaffolds,” self-assembled by Eciton burchellii army ants on inclined surfaces that aid travel during foraging and migration. We conducted field experiments with wild E. burchellii colonies, manipulating the slope over which ants traversed, to examine the formation of scaffolds and their effects on foraging traffic. Our results show that scaffolds regularly form on inclined surfaces and that they reduce losses of foragers and prey, by reducing slipping and/or falling of ants, thus facilitating traffic flow. We describe the relative effects of environmental geometry and traffic on their growth and present a theoretical model to examine how the individual behaviors underlying scaffold formation drive group-level effects. Our model describes scaffold growth as a control response at the collective level that can emerge from individual error correction, requiring no complex communication among ants. We show that this model captures the dynamics observed in our experiments and is able to predict the growth—and final size—of scaffolds, and we show how the analytical solution allows for estimation of these dynamics.

Complex infrastructures of all kinds, whether technological, social, or biological, demand one thing above all else to function effectively: the property of resilience in the face of disruption. In this context, we consider a resilient system to be one “that returns to or exceeds its predisturbance level of performance following a perturbation,” as defined by Middleton and Latty in ref. 1. Understanding how resilience can be achieved in systems with many interacting components has emerged as a common goal across the disciplines of biology, engineering, and ecology (1, 2), and thus, it is important to identify and examine specific cases of infrastructural resilience in nature. Such examples abound among the social insects, in which difficult coordination problems are often solved through distributed control mechanisms relying on individual sensing and local interactions mediated by simple rules, without the need for complex communication (3, 4). Just as human societies rely on the organized flow of materials and information to function effectively, from the scale of the city to global trade networks (5–8), for many social insects, colony survival often depends on the effective coordination of foraging traffic to transport resources through the environment (9–11). These networks must be able to maintain their functionality when confronted with disruption and self-heal or otherwise rapidly respond to unpredictable conditions.To achieve resilience, biological systems at many scales, including these social insect infrastructures, utilize various mechanisms of feedback control. In a recent example, a core regulatory feedback mechanism common to many social insects was identified—the so-called common stomach—which achieves resilience through a saturation process that relies on negative feedback through integral control (12). Both positive and negative feedback have long been known to underlie self-organizing processes like the formation of ant foraging trails and collective decision making (13–15), and negative feedback has been shown to play a particularly important role among social insects in maintaining flexibility when environmental conditions change (16–18). Understanding how feedback control operates in distributed systems, like ant colonies, to facilitate resilience remains an important challenge, with implications across disciplines.The army ant Eciton burchellii, with large colonies of more than 500,000 workers and a distinctive nomadic life cycle (19), presents an ideal model for studying resilience and distributed control in natural systems. E. burchellii is considered a top predator in the neotropical forest leaf litter community (20) and a canonical example of self-organization among social insects (21). Unlike most ants that maintain a fixed nest location, colonies alternate every few weeks between a stationary and a nomadic phase, during which the entire colony moves nightly to a new temporary nest site, known as a bivouac (22, 23). Most workers spend the day foraging in massive swarm raids that start at dawn, combing the forest floor to flush out a diverse array of arthropod prey from the leaf litter (24, 25). At the front of the raid, fleeing prey items are attacked en masse, with those caught dismantled for transport along a branching trail network that can stretch for over 100 m back to the bivouac (26). Raids must be conducted at a rapid pace to maintain the high rates of prey delivery needed to support the ravenous appetite of the developing brood (27). This evolutionary pressure has led to a number of morphological and behavioral adaptations, including the spontaneous formation of traffic lanes that increase the efficiency of foraging trails (10), some of the highest running speeds among all ants (28), and a specialized porter caste morphology to facilitate the transport of bulky prey items, carried under the body (29).This suite of adaptations includes the remarkable capacity for self-assembly, by which ants can join together to create temporary structures that modify the environment (27, 30, 31). Various examples of self-assembly have been observed in other social insects (32, 33), and these structures have been described as intermediate-level parts of insect societies—adaptive units that function at a level between individual and colony (34). For E. burchellii and the closely related Eciton hamatum, self-assembled structures serve two primary functions: for shelter, in the case of the bivouac, and to facilitate the flow of traffic during raids and emigrations, with structures like plugs (27) and bridges (30, 31) that emerge along the trail network as needed. Our previous work on Eciton bridges has shown how these structures are robust to perturbations and responsive to traffic and environmental geometry, changing size and location to create shortcuts that benefit the colony.Here we reveal another type of self-assemblage in E. burchellii which we call “scaffolds,” given their function as temporary support structures. These structures have not been previously studied experimentally or clearly defined, although they have been described based on observations in previous literature without consistent terminology (35, 36). Scaffolds often form when the foraging trail crosses a sloped surface from which ants may slip and/or fall, such as a rock face, tree root, or even the wall of a building (as shown in SI Appendix, Movie S1). To form a scaffold, individual ants stop and grip the underlying surface with their tarsi, remaining stationary as traffic continues to pass. Scaffolds can be sparse, consisting of only a few dispersed ants, or extremely dense, with many ants overlapping one another in a continuous cluster (Fig. 1 and SI Appendix, Movie S2). To ascertain how scaffolds form and under what conditions, and to assess their effects on foraging traffic, we conducted field experiments with wild colonies of E. burchellii, using an apparatus that allowed for manipulation of the slope over which ants traversed (Fig. 1). We observed and quantified the growth of scaffold structures and measured traffic variables to assess their influence on scaffold formation.Open in a separate windowFig. 1.Overview of experimental apparatus and video analysis procedure. (A) Photo of apparatus setup in the field during an experiment, with platform set to 90°. (B) Diagram of 3D-printed apparatus assembly, with removable spacer to adjust platform angle shown in red. (C) Frames extracted from video of experiment with platform set to 90°, at experiment start (Left), after 120 s (Middle), and after 300 s (Right). (D) Diagram of image subtraction algorithm for video analysis. Moving ants are shown in gray, with stationary ants shown in black (indicating scaffold area over time) and the final scaffold area shown in red. (E) Dimensions of adjustable platform overlaid on photo of experiment in progress, with platform set to 80° (removable spacer to adjust angle visible at bottom left of platform).Our experimental results show that scaffolds repeatedly and predictably form on inclined surfaces, and we describe the relative influences of environmental and traffic variables on their growth. Informed by these observations, we propose a theoretical model that describes scaffold growth as a control response at the group level that emerges through a simple process of error correction at the individual level. Our model describes a hypothetical mechanism underlying scaffold formation that links individual-level sensing of disruption to the adaptive collective response of scaffold formation. Comparing the model predictions with our experimental observations, we show that the model captures well the observed dynamics of scaffold growth, and we derive an analytical solution that allows for straightforward prediction of these dynamics.     

Rational design of self-assembly pathways for complex multicomponent structures

The field of complex self-assembly is moving toward the design of multiparticle structures consisting of thousands of distinct building blocks. To exploit the potential benefits of structures with such “addressable complexity,” we need to understand the factors that optimize the yield and the kinetics of self-assembly. Here we use a simple theoretical method to explain the key features responsible for the unexpected success of DNA-brick experiments, which are currently the only demonstration of reliable self-assembly with such a large number of components. Simulations confirm that our theory accurately predicts the narrow temperature window in which error-free assembly can occur. Even more strikingly, our theory predicts that correct assembly of the complete structure may require a time-dependent experimental protocol. Furthermore, we predict that low coordination numbers result in nonclassical nucleation behavior, which we find to be essential for achieving optimal nucleation kinetics under mild growth conditions. We also show that, rather surprisingly, the use of heterogeneous bond energies improves the nucleation kinetics and in fact appears to be necessary for assembling certain intricate 3D structures. This observation makes it possible to sculpt nucleation pathways by tuning the distribution of interaction strengths. These insights not only suggest how to improve the design of structures based on DNA bricks, but also point the way toward the creation of a much wider class of chemical or colloidal structures with addressable complexity.Recent experiments with short pieces of single-stranded DNA (1, 2) have shown that it is possible to assemble well-defined molecular superstructures from a single solution with more than merely a handful of distinct building blocks. These experiments use complementary DNA sequences to encode an addressable structure (3) in which each distinct single-stranded “brick” belongs in a specific location within the target assembly. A remarkable feature of these experiments is that even without careful control of the subunit stoichiometry or optimization of the DNA sequences, a large number of 2- and 3D designed structures with thousands of subunits assemble reliably (1, 2, 4, 5). The success of this approach is astounding given the many ways in which the assembly of an addressable structure could potentially go wrong (6–8).Any attempt to optimize the assembly yield or to create even more complex structures should be based on a better understanding of the mechanism by which DNA bricks manage to self-assemble robustly. The existence of a sizable nucleation barrier, as originally proposed in refs. 1, 2, would remedy two possible sources of error that were previously thought to limit the successful assembly of multicomponent nanostructures: the depletion of free monomers and the uncontrolled aggregation of partially formed structures. Slowing the rate of nucleation would suppress competition among multiple nucleation sites for available monomers and give the complete structure a chance to assemble before encountering other partial structures. Recent simulations of a simplified model of a 3D addressable structure have provided evidence of a free-energy barrier for nucleation (9), suggesting that the ability to control this barrier should enable the assembly of a wide range of complex nanostructures. We therefore need to be able to predict how such a barrier depends on the design of the target structure and on the choice of DNA sequences. Until now, however, there have been no reliable techniques to predict the existence, let alone the magnitude, of a nucleation barrier for self-assembly in a mixture of complementary DNA bricks.Here we show that the assembly of 3D DNA-brick nanostructures is indeed a nucleated process, but only in a narrow range of temperatures. The nucleation barrier in these systems is determined entirely by the topology of the designed interactions that stabilize the target structure. Controllable nucleation is therefore a general feature of addressable structures that can be tuned through the rational choice of designed interactions. We find that the reliable self-assembly of 3D DNA bricks is a direct consequence of their unusual nucleation behavior, which is not accounted for by existing theories that work for classical examples of self-assembly, such as crystal nucleation. We are thus able to provide a rational basis for the rather unconventional protocol used in the recent DNA-brick experiments by showing that they exploit a narrow window of opportunity where robust multicomponent self-assembly can take place.     

Tunable assembly of amyloid-forming peptides into nanosheets as a retrovirus carrier

Using and engineering amyloid as nanomaterials are blossoming trends in bionanotechnology. Here, we show our discovery of an amyloid structure, termed “amyloid-like nanosheet,” formed by a key amyloid-forming segment of Alzheimer’s Aβ. Combining multiple biophysical and computational approaches, we proposed a structural model for the nanosheet that is formed by stacking the amyloid fibril spines perpendicular to the fibril axis. We further used the nanosheet for laboratorial retroviral transduction enhancement and directly visualized the presence of virus on the nanosheet surface by electron microscopy. Furthermore, based on our structural model, we designed nanosheet-forming peptides with different functionalities, elucidating the potential of rational design for amyloid-based materials with novel architecture and function.Numerous proteins and polypeptides have been found to self-assemble into amyloid fibrils under certain conditions (1). They are associated not only with dozens of devastating diseases including Alzheimer’s and Parkinson’s diseases (2) but are integral to many biological processes such as hormone storage, signal transduction, and cell surface adhesion (3–5). Separate from the context of their parent proteins, synthesized peptide segments can self-assemble into amyloid-like fibrils in vitro as well (6, 7). Fibrils formed by diverse proteins and peptides all share a common cross-β structure, composed of interdigitated β-sheets termed “the zipper-like fibril spine” (8, 9). The self-assembly process is a consequence of backbone hydrogen bonding for the single β-sheet layer formation and side-chain interaction (e.g., hydrophobic interaction, π-stacking, and van der Waals) for pairing β-sheet layers together (10). Their highly repetitive and ordered architecture, in particular for the short peptide fibrils, exhibits favorable properties including high thermal stability and stiffness, biocompatibility, controllable self-assembly, surface patterning and integration of functionality, and inexpensive production by chemical synthesis (11–13). These exceptional properties promote the exploitation of amyloid fibril as an emerging class of bionanomaterials (14).Several studies have demonstrated that natural amyloidogenic and designed amphiphilic peptides are capable of self-assembling into nanostructures with topographies including fibril, film, nanotube, hydrogel, and liquid crystals (15–21), and these nanostructures have been used for nanowires, biosensors, 3D culturing, environmental carbon capture, retroviral gene transfer, light harvesting, and catalysis (22–26). Amyloid fibrils were also hybridized with other nanomaterials such as graphene and DNA origami in hopes of creating new properties and functions (27–29). In this study, we expand the amyloid material field’s scope by the finding, structure characterization, and functionalization of a previously unidentified architecture—the amyloid-like nanosheet. We showed that KLVFFAK, a key amyloid-forming heptapeptide of the Italian familial form of Alzheimer’s Aβ (30), self-assembles into a 2D nanosheet with a width of over 200 nm, far larger than typical fibrils (10–20 nm) (Fig. 1). We characterized the molecular structure of the nanosheet with both biophysical and computational approaches. The unique structural architecture of the nanosheet enables us to use it as a highly effective enhancer for retroviral transduction and to directly observe virus condensation on the nanosheet. Based on our structural model, we further designed two series of artificial peptides. One highlights the potential of the nanosheet as a robust platform for integrating different functionalities, and the other sheds light on the de novo design of amyloid-like nanosheets.Open in a separate windowFig. 1.Characterization of the KLVFFAK nanosheet. (A) KLVFFAK is the key amyloid-forming segment of the Italian familial form of Aβ. Its chemical formation is shown in β-strand, and its length is ∼2.2 nm estimated from its structural model (SI Appendix, Materials and Methods). (B) AFM image (Lower) and section analysis (Upper) of the KLVFFAK nanosheet on mica. The thickness of the KLVFFAK nanosheet is about the length of the KLVFFAK β-strand, indicating an upright alignment of the peptide strands forming the nanosheet. (C) TEM images of the KLVFFAK nanosheet and a typical amyloid fibril of peptide VQIVYK (Inset). (D) Optical image (Upper) of the Congo red-stained nanosheet. It shows green birefringence when viewed between crossed polarizers (Lower). (E) X-ray diffraction image of nanosheet showing a cross-β diffraction pattern characteristically seen in fibrils (2). (F) FTIR profile indicating that the nanosheet is composed of antiparallel β-sheets.     

Nanoparticle self-assembly at the interface of liquid crystal droplets

Nanoparticles adsorbed at the interface of nematic liquid crystals are known to form ordered structures whose morphology depends on the orientation of the underlying nematic field. The origin of such structures is believed to result from an interplay between the liquid crystal orientation at the particles’ surface, the orientation at the liquid crystal’s air interface, and the bulk elasticity of the underlying liquid crystal. In this work, we consider nanoparticle assembly at the interface of nematic droplets. We present a systematic study of the free energy of nanoparticle-laden droplets in terms of experiments and a Landau–de Gennes formalism. The results of that study indicate that, even for conditions under which particles interact only weakly at flat interfaces, particles aggregate at the poles of bipolar droplets and assemble into robust, quantized arrangements that can be mapped onto hexagonal lattices. The contributions of elasticity and interfacial energy corresponding to different arrangements are used to explain the resulting morphologies, and the predictions of the model are shown to be consistent with experimental observations. The findings presented here suggest that particle-laden liquid crystal droplets could provide a unique and versatile route toward building blocks for hierarchical materials assembly.A growing body of theoretical and experimental work has sought to direct the assembly of molecules and nanoparticles at interfaces by exploiting the elastic forces that arise in liquid crystals (LCs) (1–5). Nematic LCs possess orientational order along a unit vector, the so-called nematic director. They also exhibit defects—regions of low order whose morphology and position depends on a delicate balance between elastic, enthalpic, and interfacial contributions to the free energy. The orientation of nematic LCs and any corresponding defects can be perturbed by introducing particles. The symmetry and structure of the director field around a particle also depends on the interaction between the LC and the particle, often referred to as anchoring. Particles with perpendicular (homeotropic) anchoring induce either dipolar or quadrupolar symmetry in the LC, leading to formation of point defects or Saturn-ring defects, respectively (6). Particles with planar anchoring induce quadrupolar symmetry, which is accompanied by two surface defects, generally referred to as boojums (6). Distortions of the nematic field cost elastic energy and therefore give rise to anisotropic, long-range interactions between particles. Indeed, particles in nematic LCs aggregate and “bind,” thereby minimizing the volume of defects and the large free energy that is associated with their elastic strain. Equilibrium particle arrangements in nematic LCs depend strongly on the topology of the underlying defects. Homeotropic particles with point, dipolar defects form chains along the nematic director, whereas quadrupolar, Saturn-ring defects form kinked chains that are perpendicular to the nematic director (7). Particles with planar anchoring form chains whose main axis forms a 30° angle with the nematic director (8). Recent work has also shown that particles can be trapped in topological defects (9, 10) and in chiral defects (11, 12). Particles localized at a planar LC interface also exhibit LC-induced interactions. For the particular case of perpendicular anchoring, it has been shown that particles aggregate into ordered structures whose morphology can be controlled by addition of surfactants (13). Recently, a robust mechanism has been reported to direct assembly of homeotropic particles trapped at the LC interface into reconfigurable structures by controlling surface anchoring and bulk defect structure (14).This work considers the aggregation of nanoparticles at LC droplet interfaces. Past studies from our own groups have shown that LCs confined in small droplets can be used to induce formation of intriguing surfactant nanophases at their interfaces (15). Experiments and simulations have also shown that the defects that arise in LC droplets can be used to localize individual nanoparticles or pairs of nanoparticles with considerable precision (16, 17). More generally, droplets offer an effective, yet simple means for confining LCs, thereby controlling the balance of interfacial and elastic contributions to the free energy and the response of LCs to external cues (18, 19). Depending on surface anchoring, LC droplets can exhibit two primary morphologies (20). Homeotropic anchoring leads to radial LC droplets, with a single ring or point defect in the center, whereas planar anchoring leads to bipolar droplets having two surface point (or boojum) defects. The localization of particles at boojums reduces the splay elastic free energy significantly. Remarkably, the trapping of particles into the boojums is independent of the type of anchoring of LC at the particle surfaces (16). A recent study examined the self-assembly of homeotropic particles at the surface of a bipolar droplet and observed formation of star-like patterns (21). Dipole–dipole interactions between particles led to formation of linear chains along the longitudinal orientation of the director field that, upon finding the boojums, organized into stars.Our focus is to examine and understand the behavior of planar particles located at the surface of micrometer-sized bipolar droplets. We restrict our attention to degenerate planar anchoring and planar droplets because such conditions are much more permissive than homeotropic anchoring, and it is therefore difficult to anticipate the types of arrangements that may arise on the basis of symmetry arguments. By examining the structures and LC morphologies that arise as a function of particle number, we are able to provide a systematic view of nanoparticle assembly in such systems. Our past experiments have shown that a single polystyrene (PS) particle with planar anchoring and radius of 0.5 µm adsorbed at the surface of a bipolar 5CB droplet diffuses into a boojum defect (16). Here, we show that when more particles are adsorbed at the droplet surface, they migrate to the poles and assemble into arrangements that can be mapped into hexagonal arrays around the boojum. The predictions of our theoretical calculations are shown to be consistent with experimental observations (22).     

从蛋白质自组装的角度探析甘草附子配伍减毒机制

甘草与附子配伍有减毒增效的作用。该研究从中药汤剂甘草和附子混煎过程中蛋白质自组装的现象入手,以甘草蛋白和附子主要毒性物质——乌头碱为研究对象,探析甘草附子配伍减毒机制。研究发现经分离纯化后的甘草蛋白在p H 5时可通过自组装形成粒径为(206.2±2.02)nm的稳定颗粒,且可与乌头碱形成平均粒径为(238.20±1.23)nm的甘草蛋白-乌头碱稳定颗粒。通过小鼠急性毒性实验发现注射乌头碱单体的小鼠全部死亡,而注射相同乌头碱含量的甘草蛋白-乌头碱颗粒的小鼠全部存活。对甘草蛋白-乌头碱胶体颗粒的稳定性的调查显示,该胶体颗粒在室温下较稳定,具有成为候选药物载体的可能性。综上所述,甘草蛋白可通过与乌头碱自组装而达到减毒效果。     

不同细胞接种密度体外构建“自组装”工程化软骨的实验研究

[目的]探究以人骨髓间充质干细胞(humanbonemarrowmesenchymalstemcells,hMSCs)为种子细胞体外构建“自组装”工程化软骨对应的合理细胞接种密度.[方法]体外分离与培养hMSCs.用含100ng/ml生长分化因子5(growthdifferentiationfactor5,GDF-5)的软骨诱导液(chondrogenicmedium,CM)定向诱导培养第3代hMSCs,诱导3周后重悬细胞,分别以A组2.5×106/ml,B组5×106/ml,C组1x107/ml,D组2×107/ml四种细胞密度接种于2％琼脂糖包被的24孔板,每组设5个复孔.自组装培养3周后,对标本进行大体观察、组织学及免疫组化检测并进行生化分析,比较不同组标本的软骨生物学特性的差异.[结果]“自组装”培养3周后,各组都形成了软骨样组织团块,团块直径与湿重随细胞接种密度而增加.Bem评分结果显示C、D两组明显高于A、B两组(P＜0.05),且C组与D组间差异无统计学意义,Ⅱ型胶原免疫组化染色检测到C组与D组细胞外基质内有较强的阳性信号弥漫分布,蛋白多糖(GAG)含量C、D两组亦明显高于A、B两组(P＜0.05),且C组与D组间差异无统计学意义.[结论]在一定细胞接种密度范围内,“自组装”工程化软骨的生物学特性呈密度依赖性增加.以1×107/ml接种时,可以获得具有良好生物学特性的“自组装”工程化软骨.