Injectable and Biodegradable Nanohybrid Polymers with Simultaneously Enhanced Stiffness and Toughness for Bone Repair

A series of novel injectable and photo‐crosslinkable poly(propylene fumarate) (PPF)‐co‐polyhedral oligomeric silsesquioxane (POSS) copolymers are synthesized via two‐step polycondensation to improve both stiffness and toughness and to promote biological performance of bone tissue engineering scaffolds. The viscoelastic behavior of uncrosslinked PPF‐co‐POSS and the thermal, mechanical, and surface characteristics of photo‐crosslinked PPF‐co‐POSS are investigated as well as the degradation behavior and microscopic POSS domain structures at various weight compositions of POSS (?_POSS). Tensile and compressive moduli and facture toughness are enhanced for crosslinked PPF‐co‐POSS when POSS nanocages are well distributed and their crystallinity is completely confined in the networks. Decreases in these mechanical properties are observed at higher ?_POSS because of decreased crosslinking density and larger POSS aggregates. The mechanical properties are correlated with in vitro mouse pre‐osteoblastic MC3T3‐E1 cell functions including cell attachment, spreading, proliferation, differentiation, and gene expression, which all maximize at ?_POSS of 10%.     

The Interplay of Modulus,Strength, and Ductility in Adhesive Design Using Biomimetic Polymer Chemistry

High‐performance adhesives require mechanical properties tuned to demands of the surroundings. A mismatch in stiffness between substrate and adhesive leads to stress concentrations and fracture when the bonding is subjected to mechanical load. Balancing material strength versus ductility, as well as considering the relationship between adhesive modulus and substrate modulus, creates stronger joints. However, a detailed understanding of how these properties interplay is lacking. Here, a biomimetic terpolymer is altered systematically to identify regions of optimal bonding. Mechanical properties of these terpolymers are tailored by controlling the amount of a methyl methacrylate stiff monomer versus a similar monomer containing flexible poly(ethylene glycol) chains. Dopamine methacrylamide, the cross‐linking monomer, is a catechol moiety analogous to 3,4‐dihydroxyphenylalanine, a key component in the adhesive proteins of marine mussels. Bulk adhesion of this family of terpolymers is tested on metal and plastic substrates. Incorporating higher amounts of poly(ethylene glycol) into the terpolymer introduces flexibility and ductility. By taking a systematic approach to polymer design, the region in which material strength and ductility are balanced in relation to the substrate modulus is found, thereby yielding the most robust joints.     

Strong,Tailored, Biocompatible Shape‐Memory Polymer Networks

Shape‐memory polymers are a class of smart materials that have recently been used in intelligent biomedical devices and industrial applications for their ability to change shape under a predetermined stimulus. In this study, photopolymerized thermoset shape‐memory networks with tailored thermomechanics are evaluated to link polymer structure to recovery behavior. Methyl methacrylate (MMA) and poly(ethylene glycol) dimethacrylate (PEGDMA) are copolymerized to create networks with independently adjusted glass transition temperatures (T_g) and rubbery modulus values ranging from 56 to 92 °C and 9.3 to 23.0 MPa, respectively. Free‐strain recovery under isothermal and transient temperature conditions is highly influenced by the T_g of the networks, while the rubbery moduli of the networks has a negligible effect on this response. The magnitude of stress generation of fixed‐strain recovery correlates with network rubbery moduli, while fixed‐strain recovery under isothermal conditions shows a complex evolution for varying T_g. The results are intended to help aid in future shape‐memory device design and the MMA‐co‐PEGDMA network is presented as a possible high strength shape‐memory biomaterial.     

Biofunctional Polyelectrolyte Multilayers and Microcapsules: Control of Non‐Specific and Bio‐Specific Protein Adsorption

Layers of the polyelectrolytes poly(allylamine hydrochloride) (PAH, polycationic) and poly(styrene sulfonate) (PSS, polyanionic) are consecutively adsorbed on flat silicon oxide surfaces, forming stable, ultrathin multilayer films. Subsequently, a final monolayer of the polycationic copolymer poly(L ‐lysine)‐graft‐poly(ethylene glycol) (PLL‐g‐PEG) is adsorbed onto the PSS‐terminated multilayer in order to impart protein resistance to the surface. The growth of each of the polyelectrolyte layers and the protein resistance of the resulting [PAH/PPS]_n(PLL‐g‐PEG) multilayer (n = 1–4) are followed quantitatively ex situ using X‐ray photoelectron spectroscopy and in situ using real‐time optical‐waveguide lightmode spectroscopy. In a second approach, the same type of [PAH/PSS]_n(PLL‐g‐PEG) multilayer coatings are successfully formed on the surface of colloidal particles in order to produce surface‐functionalized, hollow microcapsules after dissolution of the core materials (melamine formaldehyde (MF) and poly(lactic acid) (PLA; colloid diameters: 1.2–20 μm). Microelectrophoresis and confocal laser scanning microscopy are used to study multilayer formation on the colloids and protein resistance of the final capsule. The quality of the PLL‐g‐PEG layer on the microcapsules depends on both the type of core material and the dissolution protocols used. The greatest protein resistance is achieved using PLA cores and coating the polyelectrolyte microcapsules with PLL‐g‐PEG after dissolution of the cores. Protein adsorption from full serum on [PAH/PPS]_n(PLL‐g‐PEG) multilayers (on both flat substrates and microcapsules) decreases by three orders of magnitude in comparison to the standard [PAH/PPS]_n layer. Finally, biofunctional capsules of the type [PAH/PPS]_n(PLL‐g‐PEG/PEG‐biotin) (top copolymer layer with a fraction of the PEG chains end‐functionalized with biotin) are produced which allow for specific recognition and immobilization of controlled amounts of streptavidin at the surface of the capsules. Biofunctional multilayer films and capsules are believed to have a potential for future applications as novel platforms for biotechnological applications such as biosensors and carriers for targeted drug delivery.     

Protein Biophosphors: Biodegradable,Multifunctional, Protein‐Based Hydrogel for White Emission,Sensing, and pH Detection

A highly efficient, multifunctional, bioderived white‐emitting hydrogel (biophosphor) consisting of crosslinked bovine serum albumin and three fluorescent dyes, Coumarin 460, fluorescein, and 5(6)‐carboxy‐x‐rhodamine, is reported here. White emission is obtained upon excitation of the biophosphor at 365 nm with appropriate mole ratios of the above dyes. The CIE 1931 chromaticity coordinates of white emission with 365 nm excitation are (0.36, 0.37), and the correlated color temperature is 5300 K. Multifunctional nature of the biophosphor is also demonstrated. A UV‐light‐emitting‐diode (361 nm) coated with this biophosphor, for example, indicates white emission (CIE 0.28, 0.31) with a half‐life of 106 (±5) h. The white emission is also highly sensitive to pH over a broad range (pH 1–11). Incorporation of glucose oxidase and peroxidase in the biophosphor allows for the detection of glucose over a physiologically relevant range of 1.8–288 mg dL^?1. This is a unique, advanced biophosphor with LED and sensing applications, and it is the first example of a multifunctional, proteinaceous white emitter.     

Microscopic Morphology of Polyfluorene–Poly(ethylene oxide) Block Copolymers: Influence of the Block Ratio

In this paper, we describe the synthesis and characterization of poly(9,9′‐dioctylfluorene)–poly(ethylene oxide) (PF‐PEO) block copolymers with different block ratio and molecular architectures (diblock or triblock copolymers). Tapping‐mode atomic force microscopy is used to investigate the relationship between the molecular structure and the microscopic morphology of thin deposits. Copolymers with a low average volume ratio of PEO (f_EO from 0.1 to 0.3) exhibit a well‐defined organization into nanoribbons. A model of chain packing is proposed; these structures arise from the interplay of π–π interactions between conjugated PF segments and the interactions of PEO with the mica substrate surface. For copolymers with higher average volume ratio of PEO (f_EO > 0.4), the organized structures disappear and lead to untextured aggregates, probably because long‐range, regular π–π stacking of the segments can no longer take place. We also observe that the nature of the solvent from which deposits are grown and the substrate polarity have a strong impact on the microscopic morphology.     

Supercritical CO2: A Clean and Low Temperature Approach to Blending PDLLA and PEG

The unique combination of the gas like viscosity and liquid like density of supercritical CO₂ (scCO₂) is exploited to blend poly(D,L‐lactic acid) (P_DLLA) and poly(ethylene glycol) (PEG) at near ambient temperatures. This novel process lowers the polymer blend viscosity and also permits incorporation of thermally and solvent labile protein based drugs. A series of blends are prepared with agitation in scCO₂. Differential scanning calorimetry (DSC) data shows that miscible blends can be produced at moderate temperatures. A surprising region of miscibility is revealed between 8 and 25%w/w PEG. The properties of this miscible region are probed with high pressure parallel plate rheological studies, showing that the viscosity in scCO₂ is directly related to the miscibility. Using the particles from gas saturated solutions (PGSS) method, microparticles of these P_DLLA/PEG blends are produced using scCO₂ and it is determined that the yields obtained are proportional to the miscibility of the polymers. Thus scCO₂ provides a unique route to low temperature, solvent free processing that accesses a window of miscibility that has not previously been observed. Finally, DSC analyses of these sprayed microparticles confirm the presence of the same high miscibility region observed in the bulk samples prepared under supercritical conditions.     

Mosaic,Single‐Crystal CaCO3 Thin Films Fabricated on Modified Polymer Templates

Mosaic, single‐crystal CaCO₃ thin films have been prepared on modified poly(ethylene terephthalate) (PET) templates. Surface modification of PET through the introduction of carboxylic acid groups (COOH‐PET), and the subsequent physical and chemical adsorption of poly(allylamine hydrochloride) (PAH) at pH 8 (PAH8‐PET) and pH 11 (PAH11‐PET), afford template surfaces that influenced the phase transition of an amorphous CaCO₃ (ACC) films during crystallization in air. Macroscopic ACC thin films are prepared on modified PET films in the presence of poly(acrylic acid). Polycrystalline, spherulitic vaterite (CaCO₃) films are observed to form on native PET and PAH11‐PET, while mosaic, single‐crystal calcitic (CaCO₃) films form on COOH‐PET and PAH8‐PET templates. These results confirm that single‐crystal CaCO₃ growth patterns are dependent on the surface characteristics of the PET template. We infer therefore, that the nucleation and growth of ceramic films on polymeric templates can be controlled by chemical modification of the polymeric template surface, and by the subsequent attachment of ionic polyelectrolytes.     

A Gel‐Based Model of Selective Cell Motility: Implications for Cell Sorting,Diagnostics, and Screening

The ability to precisely control cell‐loaded material systems is essential for in vitro testing of novel therapeutics poised to advance to clinic. In this report, unique patterns of cell migration are devised into an in vitro gel‐in‐gel model for the purpose of obtaining cell response data to potentially therapeutic chemical agonists. The model consists of co‐cultures in a cell‐loaded microgel invading an acellular “sorting” gel. Material properties including biophysical and chemical compositions of the sorting gel are carefully controlled to guide a desired cell‐specific behavior, leading to massive tumor cell invasion by amoeboid migration mechanisms. Optical transparency enables straightforward and high‐throughput measurements of outgrowth response in the presence of either chemical and photoradiation therapy. Important dosing and drug sensitivity information are obtained with the gel‐in‐gel model using no more than a light microscope, without further need for arduous genomic or proteomic screening of the tissue samples.     

Phase Segregation in Thin Films of Conjugated Polyrotaxane– Poly(ethylene oxide) Blends: A Scanning Force Microscopy Study

Scanning force microscopy (SFM) is used to study the surface morphology of spin‐coated thin films of the ion‐transport polymer poly(ethylene oxide) (PEO) blended with either cyclodextrin (CD)‐threaded conjugated polyrotaxanes based on poly(4,4′‐diphenylene‐vinylene) (PDV), β‐CD–PDV, or their uninsulated PDV analogues. Both the polyrotaxanes and their blends with PEO are of interest as active materials in light‐emitting devices. The SFM analysis of the blended films supported on mica and on indium tin oxide (ITO) reveals in both cases a morphology that reflects the substrate topography on the (sub‐)micrometer scale and is characterized by an absence of the surface structure that is usually associated with phase segregation. This observation confirms a good miscibility of the two hydrophilic components, when deposited by using spin‐coating, as suggested by the luminescence data on devices and thin films. Clear evidence of phase segregation is instead found when blending PEO with a new organic‐soluble conjugated polymer such as a silylated poly(fluorene)‐alt‐poly(para‐phenylene) based polyrotaxane (THS–β‐CD–PF–PPP). The results obtained are relevant to the understanding of the factors influencing the interfacial and the intermolecular interactions with a view to optimizing the performance of light‐emitting diodes, and light‐emitting electrochemical cells based on supramolecularly engineered organic polymers.     

The interplay of electronic structure,molecular orientation and charge transport in organic semiconductors: Poly(thiophene) and poly(bithiophene)

Ultrathin films of poly(thiophene) (PT) and poly(bithiophene) (PBT) were prepared by electrochemical route using ionic liquid (BFEE) as medium and electrolyte. Distinct morphologies and electrical properties were observed in these materials. To evaluate its response in photovoltaics, these films were used as active layer in bilayer geometry solar cells with the electron acceptor molecule C₆₀. The best performance was observed for PT films. In order to probe the differences in molecular dynamics and structural order, ultrafast electron dynamics in the low-femtosecond regime was evaluated by resonant Auger spectroscopy using the core–hole clock method at the sulfur K absorption edge. Electron delocalization times for the different polymeric films were derived as a function of the excitation energy. Photoabsorption measurements were conducted and molecular orientation derived. These results corroborated with the morphology found for these films and thus the performance of PT and PBT in the devices, and with the proposed conduction mechanism.     

Cover Picture: Toward Large‐Scale Alignment of Electrohydrodynamic Patterning of Thin Polymer Films (Adv. Funct. Mater. 15/2006)

By integrating lithography and self‐assembly via electrohydrodynamic instabilities, Russel and co‐workers are able to guide initially flat polymer films to evolve into periodic arrays of pillars over regions much greater in extent than their natural domain sizes, as detailed on p. 1992. Novel structures that involve a combination of linear ridges and pillars are also produced, mainly as as result of the dynamic merging among preformed pillars. To pattern thin polymer films via electrohydrodynamic instabilities, we design and utilize two different kinds of mask patterns to guide pillars into alignment over regions much greater in extent than their natural domain sizes. First, narrow protruding ridges that intersect to form regular patterns on the mask trigger the growth of pillars beneath. Later, square and triangular packings of pillars develop in the regions enclosed by those ridges, preserving the registry from one domain to the next over a much larger area than within individual domains in unpatterned portions of the mask. Second, small square protrusions that are prealigned into a large regular array on the mask guide the formation of square packings of pillars in domains that conform to the mask, forming a large array of pillars. Novel structures involving a combination of linear ridges and pillars are also produced mainly due to the dynamic merging among preformed pillars. Finally, we find vertex symmetry of the mask pattern is necessary for generating and preserving ordered patterns on the polymer film.     

Enhancement of Modulus,Strength, and Toughness in Poly(methyl methacrylate)‐Based Composites by the Incorporation of Poly(methyl methacrylate)‐Functionalized Nanotubes

Poly(methyl methacrylate) (PMMA)‐functionalized multiwalled carbon nanotubes are prepared by in situ polymerization. Infrared absorbance studies reveal covalent bonding between polymer strands and the nanotubes. These treated nanotubes are blended with pure PMMA in solution before drop‐casting to form composite films. Increases in Young's modulus, breaking strength, ultimate tensile strength, and toughness of ×1.9, ×4.7, ×4.6, and ×13.7, respectively, are observed on the addition of less than 0.5 wt % of nanotubes. Effective reinforcement is only observed up to a nanotube content of approximately 0.1 vol %. Above this volume fraction, all mechanical parameters tend to fall off, probably due to nanotube aggregation. In addition, scanning electron microscopy (SEM) studies of composite fracture surfaces show a polymer layer coating the nanotubes after film breakage. The fact that the polymer and not the interface fails suggests that functionalization results in an extremely high polymer/nanotube interfacial shear strength.     

Microtribological and Nanomechanical Properties of Switchable Y‐Shaped Amphiphilic Polymer Brushes

We have characterized the morphology and nanomechanical properties of surface‐grafted nanoscale layers consisting of Y‐shaped binary molecules with one polystyrene (PS) arm and one poly(acrylic acid) (PAA) arm. We examined these amphiphilic brushes in fluids (in‐situ visualization), and measured their microtribological characteristics as a function of chemical composition. Atomic force microscopy (AFM)‐based nanomechanical testing has shown that nanoscale reorganization greatly influences the adhesion and elastic properties of the nanoscale brush layer. In water, a bimodal distribution of the elastic modulus, arising from the mixed chemical composition of the topmost layer, is observed. In contrast, the top layer is completely dominated by PS in toluene. As a result of this reorganization, the Y‐shaped‐brush layer exhibits a dramatic variation in the friction and wear properties after exposure to different solvents. Unexpectedly, the tribological properties are enhanced for the hydrophilic and polar, PAA‐dominated, surface, which shows a lower friction coefficient and higher wear stability, despite higher adhesion and heterogeneous surface composition. We suggest that this unusual behavior is caused by the combination of the presence of a thicker water layer on the PAA‐enriched surface that acts as a boundary lubricant and the glassy state of the PAA chains.     

Autonomic Self‐Healing of PEDOT:PSS Achieved Via Polyethylene Glycol Addition

Self‐healing electronic materials are of primary interest for bioelectronics and sustainable electronics. In this work, autonomic self‐healing of films obtained from mixtures of the conducting polymer poly(3,4‐ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS) and polyethylene glycol (PEG) is reported. The presence of PEG in PEDOT:PSS films decreases the elastic modulus and increases the elongation at break, thus leading to a softer material with enhanced self‐healing characteristics. In situ imaging of the cutting/healing process shows that the healing mechanism is likely due to flowing back of the material to the damaged area right after the cutting.     

能量收集通信系统中发送功率与传输速率的在线控制算法

该文针对发送端由能量收集(EH)设备供电的无线通信系统,研究在能量收集和信道状态先验信息未知的条件下,以最大化实际可达传输速率为目标的发送功率、调制方式和信道编码码率的联合优化问题。基于Lyapunov优化框架,将能量使用的长期约束转换为能量虚队列的稳定性要求,将能量使用约束下的长期时间平均实际可达传输速率最大化问题转化为单时隙的、仅依赖于当前信道状态和电池状态的“漂移加惩罚”项上界的最小化问题。优化问题通过一个高效的数值方法求解。另外还给出了基于滑动窗口的K-means聚类方法的“漂移加惩罚”中权重和电池电量虚队列偏移量两个参数的自适应调整算法。在不同能量到达随机模型下与对比算法进行了性能的仿真对比,结果表明,该文所提算法在各种能量到达模型下都能获得更高的长期平均实际可达传输速率。另外,通过与参数固定为最优情况下算法性能的对比,证明参数自适应调整算法正确、有效。     

A Scalable and High Capacity All-Optical Packet Switch: Design,Analysis, and Control

In this paper, a modular and scalable all-optical packet switch (AOPS) is proposed. The range of its capacity can be easily scaled from gigabit per second to multi-terabits per second. Due to its broadcast-and-select property, the proposed AOPS is capable of performing a multicast function. By taking the advantage of wavelength division multiplexing (WDM), this architecture can provide the best network performance using a limited number of optical fiber delay lines as buffers. To perform the header replacement function, a novel all-optical header replacement unit (HRU) is introduced to be integrated with the switching function. The proposed HRU is shared by all the inputs which provides cost advantages. In addition, we present a generic control scheme for the proposed AOPS. To implement the function of the AOPS, two possible approaches, based on the design of wavelength conversion pools (WCPs), are presented and their cascadability performances are compared. Our simulations show that the proposed AOPS with an arrayed waveguide grating (AWG) based WCP provides better cascadability performance than the one with a star coupler based WCP. We conclude that, based on the status of current optical and electronic technologies, the proposed architecture is feasible to be implemented, and can be a good candidate for future packet switching solutions.     

Injectable Hydrogels from Triblock Copolymers of Vitamin E‐Functionalized Polycarbonate and Poly(ethylene glycol) for Subcutaneous Delivery of Antibodies for Cancer Therapy

In this study, ‘ABA’‐type triblock copolymers of vitamin E‐functionalized polycarbonate and poly(ethylene glycol) , i.e., VitE_m‐PEG‐VitE_m, with extremely short hydrophobic block VitE_m, are synthesized and employed to form physically cross‐linked injectable hydrogels for local and sustained delivery of Herceptin. The hydrogels are formed at low concentrations (4–8 wt%). By varying polymer composition and concentration, the rheological behavior, porosity, and drug release properties of hydrogels are readily tunable. The in vitro antitumor specificity and efficacy of Herceptin in hydrogel and solution are investigated by MTT assay against normal and human breast cancer cell lines with different HER2 expression levels. The results demonstrate that the Herceptin‐loaded hydrogel is specific towards HER2‐overexpressing cancer cells and cytotoxic action is comparable to that of the Herceptin solution. The biocompatibility and biodegradability of hydrogel are evaluated in mice with subcutaneous injection by histological examination. It is observed that the hydrogel does not evoke a chronic inflammatory response and degrades within 6 weeks post administration. Biodistribution and anti‐tumor efficacy studies performed in BT474 tumor‐bearing mice show that single subcutaneous injection of Herceptin‐loaded hydrogel at a site close to the tumor enhances the retention of the antibody within the tumor. This leads to superior anti‐tumor efficacy as compared to intravenous (i.v.) and subcutaneous (s.c.) delivery of Herceptin in solution. The tumor size shrank by 77% at Day 28. When the hydrogel is injected at a distal location away from the tumor site, anti‐tumor efficacy is similar to that of weekly i.v. injections of Herceptin solution over 4 weeks, with the number of injections reduced from 4 to 1. These findings suggest that this hydrogel has great potential for use in subcutaneous and sustained delivery of antibodies to increase therapeutic efficacy and/or improve patient compliance.