自就位个性化钛网连接体的优化设计

目的 对3D打印自就位钛网主体与两端定位翼的连接处进行优化,包括定位翼厚度、宽度以及连接处构型。分析优化改进前后仿真模型的结构性能,最终获得最优设计的新型自就位钛网。 方法 基于 SolidWorks 软件,构建自就位钛网仿真模型,优化、改进尺寸参数。 采用仿真软件 ANSYS Workbench 对连接处厚度和宽度进行多目标 优化设计。 并在连接处设计间断连接构型,获得优化后的自就位钛网。 结果 当对新型自就位钛网嵴顶外表面施加 40 N 载荷,连接处最大应变未超过钛网的断裂应变,且应力与变形皆在可接受范围内。 当对一侧定位翼的游离端施加 10 N 的 45°弯折力时,连接处最大应变超过了钛网的断裂应变,且裂纹集中于连接线处。 虚拟模型的仿真结果与力学性能验证试验的结果基本一致。 结论 通过优化自就位个性化钛网连接体的尺寸以及构型,实现手术中摆放、按压个性化钛网时,连接体不发生折断和较大位移。 术后对定位翼游离端简单弯折,即可实现连接体沿连接线整齐断裂分离,并且断面光滑平整。 本研究对自就位个性化钛网连接处尺寸及构型进行的优化取得了较为理想的临床效果。     

Reprocessable Polymer Networks Designed with Hydroxyurethane Dynamic Cross‐links: Effect of Backbone Structure on Network Morphology,Phase Segregation,and Property Recovery

Polybutadiene (PB), poly(tetramethylene oxide) (PTMO), and polydimethylsiloxane (PDMS) networks are synthesized using relatively low wt% of dynamic hydroxyurethane cross‐links, and recovery of cross‐link density, network morphology, and properties are investigated as a function of reprocessing. PB and PTMO networks exhibit full recovery of rubbery plateau modulus, and thus cross‐link density, and tensile properties after multiple melt‐state recycling steps. PDMS networks exhibit a small loss in rubbery plateau modulus with reprocessing. Small‐angle X‐ray scattering reveals nanophase separation in PB and PDMS networks. Although PTMO networks are not nanophase separated, cold crystallization is observed, with crystallinity increasing after reprocessing because of chain alignment. This work establishes the effective use of hydroxyurethane cross‐links toward full property recovery in different networks and provides insights on the design of reprocessable networks with distinctive morphology and sustainability.     

Auto‐ and cross‐reactivity to thioredoxin allergens in allergic bronchopulmonary aspergillosis

Background: Thioredoxins are cross‐reactive allergens involved in the pathogenesis of atopic eczema and asthma. Cross‐reactivity to human thioredoxin can contribute to the exacerbation of severe atopic diseases. Methods: Human thioredoxin, Asp f28 and Asp f29, two thioredoxins of Aspergillus fumigatus, and thioredoxin of Malassezia sympodialis were cloned and produced as recombinant proteins. Allergenicity and cross‐reactivity to thioredoxins in allergic bronchopulmonary aspergillosis patients were assessed by enzyme‐linked immunosorbent assay (ELISA), inhibition ELISA, immunoblot analysis, proliferation assays and skin tests. Molecular homology modelling was used to identify conserved, surface‐exposed amino acids potentially involved in immunoglobulin E (IgE)‐binding. Results: All thioredoxins, including the human enzyme, bind IgE from patients with allergic bronchopulmonary aspergillosis and induce allergen‐specific proliferation in peripheral blood mononuclear cells and positive skin reactions in thioredoxin‐sensitized patients. Inhibition experiments showed that the thioredoxins are cross‐reactive indicating humoral immune responses based on molecular mimicry. To identify structural surface elements involved in cross‐reactivity, the three‐dimensional structures were modelled based on solved thioredoxin structures. Analysis of the molecular surfaces combined with sequence alignments allowed identification of conserved solvent exposed amino acids distantly located in the linear sequences which cluster to patches of continuous surface areas. The size of the surface areas conserved between human and fungal thioredoxins correlates well with the inhibitory potential of the molecules in inhibition ELISA indicating that the shared amino acids are involved in IgE‐binding. Conclusions: Conserved, solvent exposed residues shared between different thioredoxins cluster to continuous surface regions potentially forming cross‐reactive conformational B‐cell epitopes responsible for IgE‐mediated cross‐reactivity and autoreactivity.     

A Computational Approach to Understand Phenotypic Structure and Constitutive Mechanics Relationships of Single Cells

The goal of this study is to construct a representative 3D finite element model (FEM) of individual cells based on their sub-cellular structures that predicts cell mechanical behavior. The FEM simulations replicate atomic force microscopy (AFM) nanoindentation experiments on live vascular smooth muscle cells. Individual cells are characterized mechanically with AFM and then imaged in 3D using a spinning disc confocal microscope. Using these images, geometries for the FEM are automatically generated via image segmentation and linear programming algorithms. The geometries consist of independent structures representing the nucleus, actin stress fiber network, and cytoplasm. These are imported into commercial software for mesh refinement and analysis. The FEM presented here is capable of predicting AFM results well for 500 nm indentations. The FEM results are relatively insensitive to both the exact number and diameter of fibers used. Despite the localized nature of AFM nanoindentation, the model predicts that stresses are distributed in an anisotropic manner throughout the cell body via the actin stress fibers. This pattern of stress distribution is likely a result of the geometric arrangement of the actin network.     

Influence of Chemical Interactions on the Macroscopic Spreading of a Maleic Anhydride Copolymer Melt

We report on wetting experiments of a maleic anhydride copolymer melt on smooth horizontal silicon wafers which were either cleaned or coated with a crosslinked network of a poly(aminosiloxane). The surface properties of the solid substrates have been controlled using contact angle and zeta potential measurements, FT‐IR attenuated total reflection (ATR) spectroscopy, and atomic force microscopy. Compared to the bare silicon wafer surface, which had a surface free energy of 61 mJ·m^–2 and a weakly acidic surface character due to silanol groups, the poly(aminosiloxane) layer is characterized by basic amino groups at the outermost surface (pH_IEP > 9) and a lower surface free energy (γ_sv = 47 mJ·m^–2). The results of the wetting experiments indicate clearly that macroscopic spreading of the maleic anhydride copolymer melt can be influenced by strong interactions at the solid–liquid interface near the triple line. As could be shown by FT‐IR microscopy and spectroscopic ellipsometry, an interfacial chemical reaction takes place between the amino groups available on the solid poly‐(aminosiloxane) surface and the anhydride groups of the copolymer melt to form imide structures at the solid–liquid interface during wetting. Due to this interfacial chemical reaction, the spreading process of the maleic anhydride copolymer melt was slowed down and the contact angle was time‐dependent indicating a non‐equilibrium system. It is also remarkable that lower contact angles were obtained after a certain time of contact compared to the non‐reactive system, though the surface free energy of the solid substrate was lower in the reactive system. We assume that the increase of the spreading force at a given spreading speed is due to the release of the free energy during the interfacial reaction, indicating that the chemical reaction is an additional driving force within the spreading process.     

Characterization of Polydimethylsiloxane (PDMS) Properties for Biomedical Micro/Nanosystems

Polydimethylsiloxane (PDMS Sylgard 184, Dow Corning Corporation) pre-polymer was combined with increasing amounts of cross-linker (5.7, 10.0, 14.3, 21.4, and 42.9 wt.%) and designated PDMS1, PDMS2, PDMS3, PDMS4, and PDMS5, respectively. These materials were processed by spin coating and subjected to common micro-fabrication, micro-machining, and biomedical processes: chemical immersion, oxygen plasma treatment, sterilization, and exposure to tissue culture media. The PDMS formulations were analyzed by gravimetry, goniometry, tensile testing, nano-indentation, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Spin coating of PDMS was formulation dependent with film thickness ranging from 308 microm on PDMS1 to 171 microm on PDMS5 at 200 revolutions per minute (rpm). Ultimate tensile stress (UTS) increased from 3.9 MPa (PDMS1) to 10.8 MPa (PDMS3), and then decreased down to 4.0 MPa (PDMS5). Autoclave sterilization (AS) increased the storage modulus (sigma) and UTS in all formulations, with the highest increase in UTS exhibited by PDMS5 (218%). PDMS surface hydrophilicity and micro-textures were generally unaffected when exposed to the different chemicals, except for micro-texture changes after immersion in potassium hydroxide and buffered hydrofluoric, nitric, sulfuric, and hydrofluoric acids; and minimal changes in contact angle after immersion in hexane, hydrochloric acid, photoresist developer, and toluene. Oxygen plasma treatment decreased the contact angle of PDMS2 from 109 degrees to 60 degrees. Exposure to tissue culture media resulted in increased PDMS surface element concentrations of nitrogen and oxygen.     

ABA type block copolymers of poly(monobutyl itaconate) and poly(monocyclohexyl itaconate) with poly(dimethylsiloxane): Synthesis and characterization

Monoesters of itaconic acid (monobutyl itaconate and monocyclohexyl itaconate) were synthesized and used as monomers. Poly(monobutyl itaconate) (PMBI) and poly(monocyclohexyl itaconate) (PMCHI) were prepared by free radical polymerization of these monomers using tert‐butyl hydroperoxide as initiator. Subsequently, ABA type block copolymers where the A block is PMBI or PMCHI and the B block is poly(dimethyl siloxane) (PDMS) were synthesized by free radical polymerization using a macroinitiator (diperoxycarbamate) containing PDMS units. The structural formulae of the products were confirmed by spectral analysis. The molecular weights of the products are not high. Therefore the mechanical and physical properties are rather poor. However, porous structures of copolymers are observed by means of SEM.     

Phylogenetic patterns and correlation of key structures for jumping: bone crests and cross‐sectional areas of muscles in Leptodactylus (Anura,Leptodactylidae)

Anurans are characterized by their saltatory mode of locomotion, which is associated with a specific morphology. The coordinated action of the muscles and bones of the pelvic girdle is key to the transmission of the force of the hindlimbs to the axial skeleton during jumping. Two features are critical for optimal locomotory performance: the cross‐sectional area of muscle and the bone crest attachment sites. The first character is a proxy of the force exerted by the muscle, whereas the crests are muscle attachments sites related to muscle force. The provisory relationship between these features has previously been identified and bone crest size can be used to infer the magnitude and, therefore, muscle force in fossils records. In this work, we explore the correlation between the cross‐sectional area of essential muscles to the jumping mechanism (longissimus dorsi, extensor iliotibialis B, tenuissimus, puboischiofemoralis internus B, coccygeo‐sacralis and coccygeo‐iliacus) and the bone crests where these muscles are inserted (dorsal tubercle, dorsal crest and urostylar crest) in species of the genus Leptodactylus. This genus, along with other leptodactylids, exhibits a diversity of locomotor modes, including jumping, hopping, swimming and burrowing. We therefore analyzed the morphometric variation in the two features, cross‐sectional area and bone crest area, expecting a correlation with different locomotor types. Our results showed: (i) a correlation between the urostylar crest and the cross‐sectional area of the related muscles; (ii) that the bone crest surface area of urostyle and ilium and the cross‐sectional area of the corresponding muscles can be utilized to infer locomotor faculties in leptodactylid frogs; and (iii) that the evolution of both characters demonstrates a general tendency from lower values in leptodactylid ancestors to higher values in the Leptodactylus genus. The results attest to the importance of the comparison of current ecological and phylogenetic analogues as they allow us to infer functionality and behavior in fossil and extant groups based on skeletal evidence. Phylogenetic patterns in character evolution and their correlation with locomotory types could imply that functional restrictions are also inherited in leptodactylid.     

Influence of micro-well biomimetic topography on intestinal epithelial Caco-2 cell phenotype

A microfabrication approach was utilized to create topographic analogs of intestinal crypts on a polymer substrate. It was hypothesized that biomimetic crypt-like micro-architecture may induce changes in small intestinal cell (i.e. Caco-2 cell) phenotype. A test pattern of micro-well features with similar dimensions (50, 100, and 500 μm diameter, 50 μm spacing, 120 μm in depth) to the crypt structures found in native basal lamina was produced in the surface of a poly(dimethylsiloxane) (PDMS) substrate. PDMS surfaces were coated with fibronectin, seeded with intestinal-epithelial-cell-like Caco-2 cells, and cultured up to fourteen days. The cells were able to crawl along the steep side walls and migrated from the bottom to the top of the well structures, completely covering the surface by 4–5 days in culture. The topography of the PDMS substrates influenced cell spreading after seeding; cells spread faster and in a more uniform fashion on flat surfaces than on those with micro-well structures, where cell protrusions extending to micro-well side walls was evident. Substrate topography also affected cell metabolic activity and differentiation; cells had higher mitochondrial activity but lower alkaline phosphatase activity at early time points in culture (2–3 days post-seeding) when seeded on micro-well patterned PDMS substrates compared to flat substrates. These results emphasize the importance of topographical design properties of a scaffolds used for tissue engineered intestine.     

Oxidation and degradation of polypropylene transvaginal mesh

Polypropylene (PP) transvaginal mesh (TVM) repair for stress urinary incontinence (SUI) has shown promising short-term objective cure rates. However, life-altering complications have been associated with the placement of PP mesh for SUI repair. PP degradation as a result of the foreign body reaction (FBR) has been proposed as a contributing factor to mesh complications. We hypothesized that PP oxidizes under in vitro conditions simulating the FBR, resulting in degradation of the PP. Three PP mid-urethral slings from two commercial manufacturers were evaluated. Test specimens (n = 6) were incubated in oxidative medium for up to 5 weeks. Oxidation was assessed by Fourier Transform Infrared Spectroscopy (FTIR), and degradation was evaluated by scanning electron microscopy (SEM). FTIR spectra of the slings revealed evidence of carbonyl and hydroxyl peaks after 5 weeks of incubation time, providing evidence of oxidation of PP. SEM images at 5 weeks showed evidence of surface degradation, including pitting and flaking. Thus, oxidation and degradation of PP pelvic mesh were evidenced by chemical and physical changes under simulated in vivo conditions. To assess changes in PP surface chemistry in vivo, fibers were recovered from PP mesh explanted from a single patient without formalin fixation, untreated (n = 5) or scraped (n = 5) to remove tissue, and analyzed by X-ray photoelectron spectroscopy. Mechanical scraping removed adherent tissue, revealing an underlying layer of oxidized PP. These findings underscore the need for further research into the relative contribution of oxidative degradation to complications associated with PP-based TVM devices in larger cohorts of patients.     

Tuning Structures of Mesogen‐Jacketed Liquid Crystalline Polymers and Their Rod–Coil Diblock Copolymers by Varying Chain Rigidity

Two mesogen‐jacketed liquid crystalline (LC) polymers with different rigid side‐chain cores, poly[2,5‐bis(tert‐butoxylcarbonyl)styrene] (PM1) and poly[2,5‐bis(4‐tert‐butoxylcarbonyl phenyl)styrene] (PM3), as well as their corresponding block copolymers (BCPs), poly(dimethylsiloxane)‐b‐PM1 (PDMS‐b‐PM1) and PDMS‐b‐PM3, are synthesized and characterized. The LC phase structures of the homopolymers and the microphase‐separated structures of the BCPs can be controlled by changing the rigidity of the polymer chains with the different rigid side‐chain cores used. The LC phase structure of PM1 homopolymer is dependent on its molecular weight (MW). On the other hand, PM3 is always amorphous below thermal decomposition temperature regardless of its MW, owing to much higher rigidity of PM3 compared with that of PM1. Although both BCPs can self‐assemble into lamellae (LAM) and hexagonally packed cylinders (HEX) with varying compositions, PDMS‐b‐PM3 can form the HEX structure at a smaller weight fraction of the PM3 block because PDMS‐b‐PM3 possesses a larger geometric asymmetric factor compared with PDMS‐b‐PM1. For PDMS‐b‐PM1 with a large enough MW, it can form hierarchically ordered nanostructures, including the LAM or HEX nanostructure of the BCP and the columnar nematic phase of the PM1 block.     

Porous Poly(styrene‐co‐divinylbenzene) Neutral Monolith: From Design and Characterization to Reversed‐Phase Capillary Electrochromatography Applications

Macroporous cross‐linked organic polymers, based on styrene and divinylbenzene (PS‐DVB), are prepared as monolithic stationary phases for capillary electrochromatographic applications. The synthetic strategy, which relies on the semi‐interpenetrating polymer network (semi‐IPN) approach, is performed through UV‐initiated free radical copolymerization of the comonomers in the presence of poly(?‐caprolactone) (PCL) within the confines of fused silica capillaries. The characterization of PS‐DVB monoliths is carried out at the different stages of the synthesis using a combination of experimental techniques, thus providing information on the chemical and porous structures. All experimental results evidence the sole role of the PCL oligomer as a porogen.     

High-grade optical polydimethylsiloxane for microfluidic applications

Commercially available polydimethylsiloxane (PDMS) elastomers, such as Sylgard 184® are widely used in soft lithography and for microfluidic applications. These PDMS elastomers contain fillers to enhance their mechanical stability. The reinforcing fillers, often sub-micrometer small SiO₂ particles, tend to aggregate, swell with water, and thereby become cognoscible in a way that can strongly interfere with the visualization of micro-scale events taking place next to PDMS structures. As PDMS microfluidics are often used for studying cells and micro-/nanoparticles and for creating/handling nanodroplets, it has become highly desirable to employ a PDMS having high optical quality and that allows microscopy observation without artifacts. Here, we present a PDMS formulation that is free of fillers and has sufficiently low viscosity to perform a filtration step of the mixed prepolymers before curing. By molding a bi-layer microfluidic network (MFN), composed of a thin filler-free PDMS layer and a thicker Sylgard 184® backing layer, PDMS MFNs featuring both high optical quality and mechanical stability, can be fabricated.     

<Emphasis Type="Italic">In situ</Emphasis> micropatterning technique by cell crushing for co-cultures inside microfluidic biochips

To perform dynamic cell co-culture on micropatterned areas, we have developed a new type of “on chip and in situ” micropatterning technique. The microchip is composed of a 200 μm thick PDMS (polydimethylsiloxane) chamber at the top of which are located 100 μm thick microstamps. The PDMS chamber is bonded to a glass slide. After sterilization and cell adhesion processes, a controlled force is applied on the top of the PDMS chamber. Mechanically, the microstamps come into contact of the cells. Due to the applied force, the cells located under the microstamps are crushed. Then, a microfluidic perfusion is applied to rinse the microchip and remove the detached cells. To demonstrate the potential of this technique, it was applied successfully to mouse fibroblasts (Swiss 3T3) and liver hepatocarcinoma (HepG2/C3a) cell lines. Micropatterned areas were arrays of octagons of 150, 300 and 500 μm mean diameter. The force was applied during 30 to 60s depending on the cell types. After cell crushing, when perfusion was applied, the cells could successfully grow over the patterned areas. Cultures were successfully performed during 72 h of perfusion. In addition, monolayers of HepG2/C3a were micropatterned and then co cultured with mouse fibroblasts. Numerical simulations have demonstrated that the presence of the microstamps at the top of the PDMS chamber create non uniform flow and shear stress applied on the cells. Once fabricated, the main advantage of this technique is the possibility to use the same microchip several times for cell micropatterning and microfluidic co-cultures. This protocol avoids complex and numerous microfabrication steps that are usually required for micropatterning and microfluidic cell culture in the same time.     

Differential strain patterns of the human gastrocnemius aponeurosis and free tendon,in vivo

Aim: The mechanical characteristics of the human free tendon and aponeurosis, in vivo, remains largely unknown. The present study evaluated the longitudinal displacement of the separate free Achilles tendon and distal (deep) aponeurosis of the medial gastrocnemius muscle during voluntary isometric contraction. Methods: Ultrasonography‐obtained displacement of the free tendon and tendon–aponeurosis complex, electromyography of the gastrocnemius, soleus, and dorsiflexor muscles, and joint angular rotation were recorded during isometric plantarflexion (n = 5). Tendon cross‐sectional area, moment arm and segment lengths (L_o) were measured using magnetic resonance imaging. Tendon force was calculated from joint moments and tendon moment arm, and stress was obtained by dividing force by cross‐sectional area. The difference between the free tendon and tendon–aponeurosis complex deformation yielded separate distal aponeurosis deformation. Longitudinal aponeurosis and tendon strain were obtained from the deformations normalized to segment lengths. Results: At a common tendon force of 2641 ± 306 N, the respective deformation and L_o were 5.85 ± 0.85 and 74 ± 0.8 mm for the free tendon and 2.12 ± 0.64 and 145 ± 1.3 mm for the distal aponeurosis, P < 0.05. Longitudinal strain was 8.0 ± 1.2% for the tendon and 1.4 ± 0.4% for the aponeurosis, P < 0.01. Stiffness and stored energy was 759 ± 132 N mm^?1 and 6.14 ± 1.89 J, respectively, for the free tendon. Cross‐sectional area of the Achilles tendon was 73 ± 4 mm², yielding a stress of 36.5 ± 4.6 MPa and Young's modulus of 788 ± 181 MPa. Conclusion: The free Achilles tendon demonstrates greater strain compared with that of the distal (deep) aponeurosis during voluntary isometric contraction, which suggests that separate functional roles may exist during in vivo force transmission.     

Enhanced Thermal Ageing Stability of Mechanophore in Polyurethane Network by Introducing Polyhedral Oligomeric Silsesquioxanes (POSS)

Spiropyran (SP) shows excellent ability in light‐ or force‐triggered color and fluorescence generation. However, it has the fatal weakness of poor antithermal bleaching properties in polymers, especially when exposed to severe environments, which will shorten the life of mechanical responsive materials. Here, a strategy is reported to protect SP through incorporation of multifunctional polyhedral oligomeric silsesquioxanes (POSS) as cross‐linkers into a polyurethane network. The introduction of POSS not only improves the mechanical strength of the elastomer, but also enhances the thermal stability of the mechanophore, showing much more sensitive force‐responsive and photoresponsive properties, especially after thermal annealing. POSS contributes to the construction of a 3D network and hinders the mobility of the hard domains of molecular chains, thus enhancing the thermal stability of the mechanophore in the network. The strategy can not only extend the life of the stimuli‐responsive materials, but also promote the application temperature of the mechanically responsive polymers.     

A lithographically-patterned, elastic multi-electrode array for surface stimulation of the spinal cord

A new, scalable process for microfabrication of a silicone-based, elastic multi-electrode array (MEA) is presented. The device is constructed by spinning poly(dimethylsiloxane) (PDMS) silicone elastomer onto a glass slide, depositing and patterning gold to construct wires and electrodes, spinning on a second PDMS layer, and then micropatterning the second PDMS layer to expose electrode contacts. The micropatterning of PDMS involves a custom reactive ion etch (RIE) process that preserves the underlying gold thin film. Once completed, the device can be removed from the glass slide for conformal interfacing with neural tissue. Prototype MEAs feature electrodes smaller than those known to be reported on silicone substrate (60 microm diameter exposed electrode area) and were capable of selectively stimulating the surface of the in vitro isolated spinal cord of the juvenile rat. Stretchable serpentine traces were also incorporated into the functional PDMS-based MEA, and their implementation and testing is described.     

PDMS‐Modified Polyurethane Films with Low Water Contact Angle Hysteresis

Summary: Polyurethane (PU) films with low water contact angle hysteresis (CAH) were prepared by employing less than 0.2 wt.‐% of mono‐ or bihydroxyl‐functionalized polydimethylsiloxane (PDMS) of 60–70 DMS repeat units. A Si content of as low as 0.03 wt.‐% was sufficient to lead to a CAH of 20°. The curing temperature demonstrated strong effects on the wetting behavior of the PDMS‐modified PU films: a relatively low curing temperature (40 °C) resulted in stronger surface segregation of PDMS than higher curing temperatures, giving rise to high water receding CAs and thus low CAH. It was found from angle‐resolved X‐ray photoelectron spectroscopy analysis that the surface silicon content was greater when cured at a lower temperature. The surface of PDMS‐modified PU films was very smooth from AFM observations, but the Si content had strong effects on the surface phase contrast. The chain length of 60–70 DMS repeating units for both mono‐ and bifunctional PDMS appeared to be long enough to prevent the surface reorganization during the CA measurements.

Schematic, simplified illustration of PDMS chains at the surface of PU films modified by PDMS₆₀? OH and PDMS₇₀? (OH)₂.     

Tailored Synthesis and Fundamental Characterization of Organic‐Inorganic Hybrid Gels by Means of a Hydrosilylation Reaction

Summary: Organic‐inorganic hybrid gels have been synthesized from siloxane, 1,3,5,7‐tetramethylcyclotetrasiloxane (TMCTS), tetrakis(dimethylsilyloxy)silane (TDSS) or silsesquioxane, 1,3,5,7,9,11,13,15‐octakis(dimethylsilyloxy)pentacyclo‐[9,5,1,1,1,1]octasilsesquioxane (POSS), as crosslinking reagents and α,ω‐nonconjugated dienes, 1,5‐hexadiene (HD), 1,7‐octadiene (OD) and 1,9‐decadiene (DD), using a hydrosilylation reaction with a Pt catalyst. The network structures of the resulting gels were investigated by means of a novel scanning microscopic light scattering system. The structures of the crosslinking reagent and the length of the α,ω‐non‐conjugated dienes strongly affected the formation and network structures of the resulting gels. The critical gel concentration decreased when the molecular length of the non‐conjugated diene used was increased. The structures and Si? H group numbers of the crosslinking reagents affected the critical gel concentration, and its values decreased in the following order: TDSS > TMCTS > POSS. The mesh size distribution in the network structure was quantitatively characterized using the light scattering system and almost presupposed sizes with quite narrow size distributions were attained in the gels from TMCTS‐HD, OD systems and TDSS‐OD systems. On the other hand, the gels derived from POSS or DD showed larger mesh sizes than expected.

     

Comparison of arterial wall mechanics using ring and cylindrical segments

Thin rings and intact cylindrical segments of canine carotid and iliac arteries were used to determine wall mechanics. Measurements of force and length were obtained from the ring segments, whereas measurements of pressure and diameter were obtained from the cylindrical segments under conditions of active (147 mM K+) and passive smooth muscle (Ca2+ free and 2 mM ethyleneglycolbis (beta-aminoethylether)-N,N'-tetraacetic acid). These measurements were normalized to values of segment stress and strain. Under passive conditions stress-strain relations for the rings appeared to be stiffer than those obtained using cylindrical segments. Pressure-diameter curves computed using force-length data from the rings were shifted to higher values of diameter compared with values from the intact segments at all pressure levels. Passive mechanics derived from measurements on ring segments yielded poor estimates of mechanics derived from intact segments. Despite this finding, values of active force development from the two sample geometries were similar. No statistically significant differences were found in values of maximum force development expressed in terms of sample cross-sectional area. Some differences in values of active force development at low values of muscle length were found. The latter were probably related to the differences in passive mechanics and the procedure used to normalize muscle length. Reasonable values of active force development can be obtained from ring segments.