Self-assembled elastin-like polypeptide particles

In this work, the self-assembly of a recombinant elastin-based block copolymer containing both hydrophobic and cross-linking domains from the human elastin protein was investigated. The particle formation and dynamic behavior were characterized using inverted microscopy and dynamic light scattering. The morphology and stability were evaluated using scanning and transmission electron microscopy. Above a critical temperature the molecules self-assembled into a bimodal distribution of nano- and micron-sized particles. The larger particles increased in size through coalescence. Micron-sized particle formation appeared largely reversible, although a self-assembly/disassembly hysteresis was observed. At high polyethylene glycol (PEG) concentrations particle coalescence and settling were reduced, particle stability seemed enhanced and PEG coated the particles. Particle stabilization was also achieved through covalent cross-linking using glutaraldehyde. This study laid the foundation for optimization of particle size and stability through modification of the solvent system and has shown that this family of elastin-based polypeptides holds potential for use as particulate drug carriers.     

Multivalent protein polymers with controlled chemical and physical properties

In this review, we describe our work on the design, characterization, and modification of a series of alanine-rich helical polypeptides with novel functions. Glycosylation of the polypeptides has permitted investigation of polymer architecture effects on multivalent interactions. One of the members of this polypeptide family exhibits polymorphological behavior that is easily manipulated via simple changes in solution pH and temperature. Polypeptide-based fibrils formed at acidic pH and high temperature were shown to direct the one-dimensional organization of gold nanoparticles via electrostatic interactions. As a precursor to fibrils, aggregates likely comprising alanine-rich cores form at low temperatures and acidic pH and reversibly dissociate into monomers upon deprotonation. PEGylation of these polypeptides does not alter the self-association or conformational behavior of the polypeptide, suggesting potential applications in the development of assembled delivery vehicles, as modification of the polypeptides should be a useful strategy for controlling assembly.     

Bioactive peptide amphiphile nanofiber gels enhance burn wound healing

BackgroundBurns are physically debilitating and potentially fatal injuries. The standard-of-care for burn wounds is the coverage with gauze dressings designed to minimize trauma to the regenerating epidermis and dermis during dressing changes. However, deep partial- and full-thickness burns always heal slowly when standard wound care alone is performed. We have previously reported that peptide amphiphile (PA) gels, pH-induced self-assembling nanostructured fibrous scaffolds, promote cell proliferation and have great potential in regenerative medicine for rapid repair of tissues. In this study, we hypothesized that the PA gels are capable of accelerating wound healing in burn injury.MethodsArtificially generated thermally damaged fibroblasts and human umbilical vein endothelial cells were seeded onto the various PA nanofiber gels including bioactive and nonbioactive peptide sequences. Cell proliferation was assessed at different time points, and thermally damaged fibroblasts and HUVECs manifested increased proliferation with time when cultured with various PA gels. To determine in vivo effects, burn wounds of rats were treated with the bioactive Arg-Gly-Asp-Ser (RGDS)-modified gel that showed greater cell proliferation in vitro. The wound closure was observed, and skin samples were harvested for histologic evaluation.ResultsCell proliferation using the RGDS-PA gel was significantly higher than that observed in other gels. The RGDS-PA gel significantly enhanced re-epithelialization during the burn wound healing process between days 7 and 28. Application of PA gels accelerates the recovery of deep partial-thickness burn wounds by stimulation of fibroblasts and the creation of an environment conducive to epithelial cell proliferation and wound closure.ConclusionsThis biomaterial represents a new therapeutic strategy to overcome current clinical challenges in the treatment of injuries resulting from burns.     

壳聚糖/海藻酸钠自组装微球的制备及释药性能

目的利用壳聚糖(CS)聚阳离子及海藻酸钠(ALG)聚阴离子电解质的性质,在药物微球表面自组装形成多层包覆结构的壳聚糖载药微球,并研究组装层数、温度及盐离子浓度对自组装微球释药性能的影响。方法采用乳化交联法制备CS载四环素(TC)的药物微球,并在其表面交替自组装ALG及CS。利用IR测试技术及电极电位法进行表征。结果CS交联微球未破坏CS及TC的结构,CS与ALG以静电作用相结合。CS交联微球的载药量为40.2%,自组装六层的微球载药量为32%。组装后,药物释放时间延长,初期暴释现象得到极大改善,释药速率随组装层数的增加而下降,温度较高时组装完整,盐离子浓度存在较佳点。结论温度为60℃、盐离子浓度为0.5 mol.L-1、组装层数为四层的微球释药性能较佳。     

Composite lipid polyelectrolyte capsules templated on red blood cells: fabrication and structural characterisation

Charged phospholipids and mixtures of charged phospholipids with zwitterionic lipids were adsorbed onto polyelectrolyte capsules templated on erythrocytes. The assembly was proved by means of electrophoretic mobility measurements, confocal laser scanning microscopy and flow cytometry. Freezefracture electron microscopy proved that the phospholipids assemble as bilayers or multilayers. Single particle light scattering showed that bilayers composed of anionic lipids can be intercalated between subsequent polyelectrolyte inter-layers in a regular manner. Neutral lipids can form multilayers. A pronounced decrease in capsule permeability for small polar dyes upon lipid adsorption was followed by confocal laser scanning microscopy.     

钙离子对海藻酸钠自组装行为影响的AFM研究

利用氯化钙试剂掺入海藻酸钠溶液中诱导分子链聚集形成自组装膜，研究钙离子对海藻酸钠自组装膜结构的影响。运用原子力显微镜(Atomic force microscope，AFM)对不同浓度海藻酸钠在钙离子作用下的自组装膜进行成像，并结合红外谱图分析。当海藻酸钠浓度在0．01mg／m1和0．1mg／m1时，5m／m1 Ca^2 能很好的诱导海藻酸钠自组装膜，这种自组装结构呈现出典型的“蛋盒结构”。无机小分子通过与同种大分子的表面活性基团相互作用可以诱导高分子物质的自组装，这种自组装结构是一种非平衡状态下的耗散结构，自组装结构受高分子本身的性质与浓度、加入的小分子试剂的浓度、基片的性质以及外界温度等因素的影响。     

天门冬酰胺酶聚乙二醇-透明质酸/磺丁基-β-环糊精纳米粒体外稳定性的初步研究

目的 制备含载天门冬酰胺酶(Asp)的自组装聚乙二醇-透明质酸/磺丁基-β-环糊精纳米粒(THSCD),并初步研究两者在体外的活性以及稳定性.方法 采用自组装法制备THSCD;分别从最适温度、最适pH、酸碱稳定性、热稳定性、贮存稳定性、血浆稳定性、抗胰蛋白酶水解能力、部分金属离子及有机化合物影响来考察THSCD中Asp和游离Asp的差异.结果 THSCD的最适温度为50℃,游离Asp最适温度为60℃.THSCD的最适pH为6.5,游离Asp的最适pH为7.5.THSCD的热稳定性、贮存稳定性、酸碱稳定性、血浆稳定性测定、抗胰蛋白酶水解能力和抗部分金属离子和有机化合物能力均比游离Asp好.结论 THSCD在提高了Asp在体外活性的同时,也明显地增强了游离Asp在体外的稳定性.     

生物大分子自组织坍塌行为的研究

目的　研究生物分子链的自组织坍塌过程；探讨分子序列的组分、温度和链的柔性对生物分子自组织过程的影响。方法　基于粗粒化分子动力学模拟方法，研究均匀分子链和非均匀分子链的自组织坍塌过程。结果　发现链的非均匀性会使链的平衡结构产生微观网络结构，而链的柔性在很大程度上决定了链的整体构型。在链的刚性比较小的时候，均匀链和非均匀链都倾向于演化为团状结构。链的刚性比较大的时候，分子链演化为棒状和环状结构。发现在一定范围内温度对均匀链的平衡构型影响较小，而对非均匀链的平衡构型影响较大。结论　建立的粗粒化模型对于研究生物大分子的自组织过程，以及结构和功能的关系提供了一个有力的工具和新的思路。     

Microfluidic self-assembly of live <Emphasis Type="Italic">Drosophila</Emphasis> embryos for versatile high-throughput analysis of embryonic morphogenesis

A method for assembling Drosophila embryos in a microfluidic device was developed for studies of thermal perturbation of early embryonic development. Environmental perturbation is a complimentary method to injection of membrane-impermeable macromolecules for assaying genetic function and investigating robustness in complex biochemical networks. The development of a high throughput method for perturbing embryos would facilitate the isolation and mapping of signaling pathways. We immobilize Drosophila embryos inside a microfluidic device on minimal potential-energy wells created through surface modification, and thermally perturb these embryos using binary laminar flows of warm and cold solutions. We self-assemble embryos onto oil adhesive pads with an alcohol surfactant carrier fluid (detachment: 0.1 mL/min), and when the surfactant is removed, the embryo-oil adhesion increases to ∼25 mL/min flow rates, which allows for high velocities required for sharp gradients of thermal binary flows. The microfluidic thermal profile was numerically characterized by simulation and experimentally characterized by fluorescence thermometry. The effects of thermal perturbation were observed to induce abnormal morphogenetic movements in live embryos by using time-lapse differential interference contrast (DIC) microscopy.     

Self-assembly of nano-hydroxyapatite on multi-walled carbon nanotubes

Inspired by self-assembly of nano-hydroxyapatite (nHA) on collagen associated with the 67nm periodic microstructure of collagen, we used multi-walled carbon nanotubes (MWCNTs) with approximately 40nm bamboo periodic microstructure as a template for nHA deposition to form a nHA-MWCNT composite. The assembled apatite was analyzed by transmission electron microscopy and scanning electron microscopy. Defects that were analogous to edge dislocations along the carbon nanotubes' multi-walled surfaces were the nucleation sites for nHA after these defects had been functionalized principally into carboxylic groups. Spindle-shaped units consisting of an assembly of near parallel, fibril-like nHA polycrystals were formed and oriented at a certain angle to the long axis of the carbon nanotubes, unlike nHA-collagen in which the nHA is oriented along the longitudinal axis of the collagen molecule. One possible explanation for this difference is that there are more bonds for calcium chelation (-COOH, >CO) on the collagen fibril surface than on the surface of MWCNTs. Spindle-shaped units that are detached from the MWCNT template are able to maintain the ordered parallel structure of the nHA polycrystal fibril. We have thus created a self-assembled hydroxyapatite on MWCNTs.