Effect of the elongation rate on the biodegradation of oriented polycaprolactone films by a pure strain of micro-organisms isolated from an industrial compost for house-hold refuse

It has been demonstrated that unidirectional orientation of semi-crystalline polycaprolactone (PCL) films strongly affects their degradation behaviour in the presence of micro-organisms. For films of the same final thickness (300 μm), elongated using strain rates between 1.6 and 0.02 min^–1, the rate of oxygen consumption is similar for all samples during the first 200 h of degradation. After that time the rate becomes strongly dependent on the elongation conditions. After 700 h of incubation, the weight loss is 99 and 25% for samples obtained with strain rates of 1.6 and 0.02 min^–1 respectively. When compared with the non-orientated sample, the 1.6 min^–1 sample degrades faster while the others degrade more slowly. The results are discussed in terms of models proposed in the literature for oriented films.     

Effect of anaesthetic and rat strain on heart rate responses to simulated haemorrhage

AIM AND METHODS: Haemorrhage is characterized by two distinct responses, sympathoexcitation that evokes tachycardia and supports blood pressure, followed by sympathoinhibition contributing to bradycardia and hypotension. It has been shown that anaesthetics alter the response to haemorrhage and we hypothesized that rat strain may also influence the response. We investigated the effect of simulated haemorrhage on heart rate (HR) responses in three strains of conscious rats, and the effect of three common anaesthetics, by comparing HR responses under anaesthesia to the conscious response. Haemorrhage was simulated by constricting the inferior vena cava. We demonstrate differential effects of anaesthetics, including both maintenance and elimination of HR responses to haemorrhage depending on anaesthetic. RESULTS: We also show that both phases of the HR response differ in different conscious rat strains, and we have demonstrated a transient increase in HR during the decompensatory phase of haemorrhage, a novel 'second HR peak' with advanced hypotension. CONCLUSION: Both rat strain and anaesthetic influence HR responses to haemorrhage, and some anaesthetics appear less suitable than others for studies of haemodynamic responses in rats. There was evidence of an additional compensatory mechanism that operates at advanced levels of hypotension in the rat.     

Effect of strain rate on tensile properties of sheep disc anulus fibrosus.

We investigated the effect of loading rate on tensile properties of sheep bone-anulus-bone specimens in axial direction. Disc anulus Samples with adjacent bone attachments were prepared from lateral, posterior and anterior regions of sheep lumbar spinal segments. The specimens were then tested at different strain rates under non-destructive cyclic tensile loading followed by destructive tensile loading. Each specimen was prepared by embedding the bony parts in the polymethylmetacrylate (PMMA) exposing the anulus portion to support tension. The results of non-destructive cyclic tests indicated a decrease in the hysteresis energy loss as strain rate increased. In the destructive tests, no significant differences in ultimate stress, ultimate strain and strain energy density were observed at different strain rates or annulus locations. However, there was a significant increase in the modulus at linear region as strain rate increased. Two major modes of failure were observed; rupture in the anulus mid-substance and at the anulus-endplate junction. The former failure was more frequent with no clear pattern across strain rates and locations, while the latter failure at anulus-endplate junction occurred primarily at slow strain rates.     

Synthesis, mechanical properties, biocompatibility, and biodegradation of polyurethane networks from lysine polyisocyanates

Bone defects, such as compressive fractures in the vertebral bodies, are frequently treated with acrylic bone cements (e.g., PMMA). Although these biomaterials have sufficient mechanical properties for fixing the fracture, they are non-degradable and do not remodel or integrate with host tissue. In an alternative approach, biodegradable polyurethane (PUR) networks have been synthesized that are designed to integrate with host tissue and degrade to non-cytotoxic decomposition products. PUR networks have been prepared by two-component reactive liquid molding of low-viscosity quasi-prepolymers derived from lysine polyisocyanates and poly(epsilon-caprolactone-co-DL-lactide-co-glycolide) triols. The composition, thermal transitions, and mechanical properties of the biomaterials were measured. The values of Young's modulus ranged from 1.20-1.43 GPa, and the compressive yield strength varied from 82 to 111 MPa, which is comparable to the strength of PMMA bone cements. In vitro, the materials underwent controlled biodegradation to non-cytotoxic decomposition products, and supported the attachment and proliferation of MC3T3 cells. When cultured in osteogenic medium on the PUR networks, MC3T3 cells deposited mineralized extracellular matrix, as evidenced by von Kossa staining and tetracycline labeling. Considering the favorable mechanical and biological properties, as well as the low-viscosity of the reactive intermediates used to prepare the PUR networks, these biomaterials are potentially useful as injectable, biodegradable bone cements for fracture healing.     

应变率成像在胎儿房性心律失常诊断中应用的初步探讨

目的探讨应用速度向量成像（VVI）技术对胎儿房性心律失常时心肌结构力学及形变学影响的应变与应变率研究，评价胎儿心律失常时对心肌应激状态、运动传导就及功能的影像。方法对检出的77例胎儿心律失常（其中室上性心动过速（SVT）12例、65例为频发性房性早搏（PAC））进行VVI成像技术分析，检测心律失常时胎儿心肌运动速度向量变化及对应变与应变率影响，对照组80例心率正常胎儿。结果胎儿SVT12例中7例持续发作48h者治疗前心室率250—310bpm，均合并心衰及出现水肿，VVI速度向量振幅明显降低，其应变与应变率明显低于对照组（P〈0．01）；阵发一陛SVT5例VVI速度向量振幅-过性降低，心肌应变与应变率无变化；频发PAC组示早搏时速度向量振幅改变，且运动方向同步，心肌运动三维数据定量可显示旱搏及代偿间期的三维模式，应变与应变率与对照组无差异（P〉0．05）。结论VVI成像通过心律失常心肌结构力学变化解析胎儿心律失常，特别是对胎儿心动过速时的快速心率可进行实时动态分析。及应用M型扫描法确认心动周期使胎儿心肌应变与应变率分析成为可行。     

Effect of curing environment on network formation of polyurethane

The variation of the allophanate concentration with curing time was determined by an amine degradation method. It was concluded that the properties of polyurethane networks prepared with the same formulation differ considerably if crosslinking reactions are carried out under different conditions.     

Effect of composite resin biodegradation products on oral streptococcal growth

Hydrolytic degradation by-products associated with the constitutive monomers 2,2-bis [4-(2-hydroxy-3-methacryloxypropoxy) phenyl] propane (bis-GMA), bisphenol A polyethylene glycol diether dimethacrylate (bis-EMA), and triethylene glycol dimethacrylate (TEDGMA) used in dental restorative composites include bis-hydroxy-propoxyphenyl propane (bis-HPPP), ethoxylated bisphenol A (E-bisPA), methacrylic acid (MA), and triethylene glycol (TEG). These products are generated from the interaction of human salivary esterases with the composites. Recent findings have indicated that TEGDMA has the ability to modulate oral bacteria but it is unclear which components of TEGDMA are related to the observed effects. The objective of the current study was to investigate the influence of TEGDMA derived degradation products MA and TEG on the growth of three strains of oral bacteria: S. mutans strains NG8 and JH1005, and S. salivarius AT2. Bacterial growth rates were measured at 37 degrees C, and pH values of 5.5 (representative of cariogenic state) or 7.0 at concentrations of 0-50mmol/l for MA (Sigma, US) and 0-100mmol/l for TEG (Sigma, US). It was found that at pH 5.5 TEG significantly stimulated the growth of both S. mutans strains ( p<0.05 ) in the concentration range of 0.5-10.0mmol/l and stimulated the growth of S. salivarius AT2 for the entire concentration range tested (p<0.05). TEG (above 50mmol/1) did not significantly affect the doubling times of S. salivarius at pH of 7.0 and it inhibited the growth of both S. mutans strains above 50mmol/l at the same pH value. At pH 5.5 MA inhibited the growth of all three strains with increasing concentration. At neutral pH, the growth of S. mutans NG8 strain was significantly reduced by MA ( p<0.05 ) above 10mmol/l. In summary, these results indicate that TEG and MA modulate the growth rate of important oral bacteria in a concentration and pH dependent manner.     

Effect of alternative crosslinking methods on the low strain rate viscoelastic properties of bovine pericardial bioprosthetic material

Early failures of bovine pericardial heart valves have been due to leaflet perforation/tearing and calcification. Since glutaraldehyde fixation has been shown to produce marked changes in leaflet mechanics and has been linked to the development of calcification, alternative crosslinking techniques have been suggested as means to overcome these obstacles. We have examined the low strain rate viscoelastic behavior of bovine pericardium: (1) fresh; (2) chemically treated with glutaraldehyde, cyanimide, or polyglycidyl ether; or (3) physically treated by freeze-drying or heat-drying. Shrinkage temperature tests were conducted to assess intrahelical crosslinking. Polyglycidyl ether and glutaraldehyde both produced substantial crosslinking, with the shrinkage temperature rising above 80 degrees C. Mechanical changes were nearly equivalent, both showing decreased stress relaxation and increased extensibility consistent with intrahelical crosslinking and shrinkage during fixation. Cyanimide, known to crosslink pure collagen materials, showed no evidence of crosslinking intact tissue. Heat-drying, also effective in pure collagen preparations, produced an increase in UTS and tissue modulus, but otherwise left the tissue unchanged. Freeze-drying had no mechanical effect, and therefore provides an attractive means for the storage of connective tissues for later mechanical testing.     

Effect of ethanol concentration on the maximal specific growth rate and biomass composition ofYarrowia lipolytica mutant strain No. 1

the effect of ethanol concentration on the maximal specific growth rate and biomass composition ofYarrowia lipolytica No. 1 was studied during culturing in the pH-auxostat mode. Growth inhibition set in starting from a 2.64 g/liter residual concentration of ethanol. The constant of ethanol inhibition was 11.0 g/liter. Growth inhibition with ethanol was associated with changes of the fatty-acid composition of lipids and a resultant reduction of lipid unsaturation. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 121, N ^o 1, pp. 71–73, January, 1996 Presented by Yu. A. Romanov, Member of the Russian Academy of Medical Sciences     

Effect of shear rate on activation rate of factor X

The activation rates of Factor X in the intrinsic coagulation pathway and by RVV were measured in the stationary condition in a concentric cylinder device in a shear field and in a capillary flow reactor. The shear rates in the cylinder device were 70 and 140 sec⁻¹ and the range of the flow rate in the flow reactor was from 0.59 to 1.20 cm³/min. The activation rates in the intrinsic pathway decreased with the increase of the shear rate and therefore with the liquid flow rate. On the other hand, the rate of activation by RVV did not vary in the shear field.     

聚氨酯黏结剂加入催化剂对釉-瓷黏结性能的影响

背景：虽然聚氨酯黏结剂具有的较强的黏结力,但其黏结条件不符合应用于口腔黏结剂的基本条件。 目的：观察催化剂对聚氨酯黏结剂黏结性能的影响。 方法：选择20颗无龋坏青年人前磨牙或前牙制备牙釉质黏结面,铸造40个直径3 mm、高3 mm的圆柱状瓷块,分组黏固,每组5颗离体牙,10个瓷块：辛酸亚锡黏结剂组(以聚氨酯黏结剂与辛酸亚锡联合黏固)、五甲基二乙烯三胺黏结剂组(以聚氨酯黏结剂与五甲基二乙烯三胺联合黏固)、单纯聚氨酯黏结剂组、帕娜碧亚黏结剂组。 结果与结论：辛酸亚锡黏结剂组黏结强度最大,五甲基二乙烯三胺黏结剂组和单纯聚氨酯黏结剂组次之,帕娜碧亚黏结剂组最小。辛酸亚锡黏结剂组、五甲基二乙烯三胺黏结剂组、单纯聚氨酯黏结剂组黏结强度均高于帕娜碧亚黏结剂组(P < 0.05),且辛酸亚锡与五甲基二乙烯三胺的加入缩短了黏结剂凝固时间。说明催化剂可有效缩短聚氨酯黏结剂的凝固时间,提高聚氨酯黏结剂的黏结强度。     

The effects of strain rate and low-gamma irradiation on the compressive properties of UHMWPE

The effects of strain rate and low-gamma irradiation on the compressive properties of ultra-high molecular-weight polyethylene (UHMWPE) were investigated. Gamma irradiation was performed at 30 kGy in nitrogen or at 29 kGy in air without post-irradiation treatment. Quasi-static and impact compressive tests using the split-Hopkinson pressure-bar technique were performed to measure stress-strain relations up to a true strain of 8% at strain rates of between 0.0004 and 260 s(-1). For both unirradiated and gamma-irradiated UHMWPE specimens, an increase in the strain rate significantly increased the Young's modulus and the 0.5% yield stress. Gamma irradiation in air significantly increased the Young's modulus, as determined by quasi-static and impact compressive testing, and the 0.5% yield stress, as determined by impact compressive testing. The strain-rate dependence in the power-law relationship was similar to that observed for strain rates ranging from 0.02 to 0.10 s(-1) (Kurtz et al., Biomaterials 23, 2002, pp. 3681-3697).     

Effect of hydroxyapatite on the biodegradation and biomechanical stability of polyester nanocomposites for orthopaedic applications

The effect of hydroxyapatite (HAP) on the performance of nanocomposites of an unsaturated polyester, i.e., hydroxy-terminated high molecular weight poly(proplyene fumarate) (HT-PPFhm), was investigated. A thermoset nanocomposite was prepared with nanoparticles of calcined HAP (<100 nm, rod-like shape, filler content 30 wt.%), HT-PPFhm and N-vinyl pyrrolidone, dibenzoyl peroxide and N,N-dimethyl aniline. Two more nanocomposites were prepared with precipitated HAP nanoparticles (<100 nm rod-like shape) and commercially available HAP nanoparticles (<200 nm spherical shape), respectively. Calcined HAP nanoparticles resulted in very good crosslinking in the resin matrix with high crosslinking density and interfacial bonding with the polymer, owing to the rod-like shape of the nanoparticles; this gave improved biomechanical strength and modulus and also controlled degradation of the nanocomposite for scaffold formation. The tissue compatibility and osteocompatibility of the nanocomposite containing calcined HAP nanoparticles was evaluated. The tissue compatibility was studied by intramuscular implantation in a rabbit animal model for 3 months as per ISO standard 10993/6. The in vivo femoral bone repair was also carried out in the rabbit animal model as per ISO standard 10993/6. The nanocomposite containing calcined HAP nanoparticles is both biocompatible and osteocompatible.     

Effect of Qi-training on blood pressure, heart rate and respiration rate.

To examine the physiological effects of Korean traditional Qi-training, we investigated the changes in blood pressure, heart and respiratory rates before, during and after ChunDoSunBup (CDSB) Qi-training. Twelve normal healthy CDSB Qi-trainees (19-37 years old; trained for 1.3 +/- 0.2 years; 9 men and 3 women) volunteered to participate in this study. Heart rate, respiratory rate, systolic blood pressure and rate-pressure product were significantly decreased during Qi-training. From these results, we suggest that CDSB Qi-training has physiological effects that indicate stabilization of cardiovascular system.     

不同表面处理方法对纤维桩与聚氨酯黏结剂黏结强度的影响

背景：纤维桩具有良好的美学性能,其弹性模量与牙本质类似,能很好地分散应力;随着其在临床应用的日益增多,纤维桩与根管的脱黏结现象逐渐增加,为此提高纤维桩的黏结是非常有意义的。聚氨酯黏结剂是近年来发展起来的黏结材料,有研究显示其对多种材料均有很强的黏结力,但在口腔修复领域应用情况研究甚少。 目的：应用聚氨酯黏结剂比较纤维桩经4种不同表面处理的黏结强度。 方法：选取25个上颌单根管离体牙截冠后经根管预备、根管充填和桩道预备,随机分为5组,纤维桩表面在粘固前分别经喷砂处理、过氧化氢处理、硅烷偶联剂处理、HF酸处理,对照组不做处理。处理后的纤维桩用聚氨酯黏结剂粘固于根管内制作试件,将牙切成2 mm厚薄片进行微推出实验,用万能试验机测试黏结强度,对表面处理前后的玻璃纤维桩进行扫描电镜观察。 结果与结论：各组之间黏结强度为过氧化氢组>硅烷化组>喷砂组>HF酸处理组>对照组,硅烷化组和喷砂组间黏结强度差异无显著性意义(P > 0.05),其余各组间相比,差异有显著性意义(P < 0.05)。扫描电镜观察显示经表面处理后的玻璃纤维桩表面有不同程度的树脂基质溶解,有些存在玻璃纤维露出。结果证实经4种表面处理的纤维桩均能提高与聚氨酯黏结材料的黏结强度,过氧化氢处理后黏结强度最强。     

Effects of metabolic rate and ambient vapour pressure on heat strain in protective clothing

Studies have shown that variations in ambient water vapour pressure from 1.7 to 3.7 kPa have little effect on heat tolerance time at a metabolic rate above 450 W while wearing protective clothing. With lighter exercise, where tolerance times exceed 60 min, variations in vapour pressure have a significant impact on evaporative heat loss and, therefore, heat tolerance. The present study has examined whether these findings extend to conditions with more extreme variations in vapour pressure. Twelve males performed light (L, 350 W) and heavy (H, 500 W) exercise at 40°C in a dry (D, 1.1 kPa) and humid (H, 4.8 kPa) environment while wearing a semi-permeable nuclear, biological and chemical protective clothing ensemble (0.29 m²×°C⁻¹·W⁻¹ or 1.88 clo; Woodcock vapour permeability coefficient,i _m=0.33). Partitional calorimetry was used to determine the rate of heat storage ( ) with evaporative heat loss from the skin ( ) calculated from changes in dressed mass or the physical properties of the clothing and the vapour pressure gradient between the skin and the environment. Skin vapour pressure was predicted from measurements of water vapour pressure above the skin surface and in the clothing with humidity sensors coupled with thermistors. Final mean skin temperature ( _sk) was higher for the humid trials and averaged 37.4 (0.3)°C, 38.9 (0.4)°C, 37.6 (0.5)°C and 38.5 (0.4)°C for LD, LH, HD and HH, respectively. Final rectal temperature (T _re ) was higher for D with respective values for LD, LH, HD and HH of 39.0 (0.4)°C, 38.7 (0.4)°C, 38.8 (0.4)°C and 38.5 (0.4)°C. Tolerance time was significantly different among the trials and averaged 120.3 (19.3) min, 54.8 (7.3) min, 63.5 (6.9) min and 36.8 (3.1) min for LD, LH, HD and HH, respectively. was overestimated and, therefore, was underestimated when the changes in dressed mass were used to determine evaporative heat loss. When skin vapour pressure determined from the humidity sensor data was used to calculate , heat storage was significantly different among the trials and averaged 15.0 (3.0), 13.0 (1.8), 14.2 (2.6) and 12.2 (1.9) kJ·kg⁻¹ for LD, LH, HD and HH, respectively. It was concluded that while wearing the protective clothing all indices of heat strain, including tolerance time, were significantly affected by the change in ambient water vapour pressure from 1.1 to 4.8 kPa during both light and heavy exercise.     

Effect of soft-segment chemistry on polyurethane biostability during in vitro fatigue loading

The effect of soft-segment chemistry on biostability of polyurethane elastomers was studied with a diaphragm-type film specimen under conditions of static and dynamic loading. During testing, the films were exposed to an H(2)O(2)/CoCl(2) solution, which simulated the oxidative component of the in vivo environment. Films treated for up to 24 days were evaluated by IR spectroscopy and by optical and scanning electron microscopy. Biostability of a poly(ether urethane) (PEU), which is known to undergo oxidative degradation, was compared with biostability of a poly(carbonate urethane) (PCU), which is thought to be more resistant to oxidation than PEU. Materials similar to PEU and PCU, in which the polyether or polycarbonate soft segment was partially replaced with poly(dimethylsiloxane) (PDMS), were also tested with the expectation that PDMS would improve soft-segment biostability. Oxidative degradation of the polyether soft segment of PEU was manifest chemically as chain scission and cross-linking and physically as surface pitting. Biaxial fatigue accelerated chemical degradation of PEU and eventually caused brittle stress cracking. In comparison, the polycarbonate soft segment was more stable to oxidation; there was minimal chemical or physical degradation of PCU, even in biaxial fatigue. Partial substitution of the polyether soft segment with PDMS enhanced oxidative stability of PEU. Although both strategies for modifying soft-segment chemistry improved the resistance to oxidative degradation, the outstanding mechanical properties of PEU were compromised to some extent.     

变应变率下的肌肉本构方程

目的在Hill肌肉三元素模型基础上推导应变率下的肌肉本构方程。方法在Hill三元素肌肉模型的基础上,利用微分和线性拟合的方法,最终获得了骨骼肌在不同应变率下的应力-应变本构方程。结果结果表明:在应变率|e|≤1下,骨骼肌的本构方程是随应变率不断变化的;当应变率|e|>1时,骨骼肌的本构方程并不受应变率的影响。同时,在|e|≤1下,应变率对应力的影响是随着应变的增加而不断减小的。结论研究结果将有助于利用有限元方法分析骨骼肌在变应变率作用下的受力情况。     

Measurement of strain rate behaviour in complete mandibular dentures

A major cause of fracture in complete lower dentures is due to the denture falling onto a hard floor. Impact failure has never been investigated in complete dentures and in a material which is strain rate dependent, a knowledge of the maximum strain and strain rate at failure is essential if laboratory tests are to evaluate materials in a realistic manner.The work described includes brittle lacquer studies to establish the strain pattern which occurs when a denture is dropped fm a height of 1 metre. This was used to orientate strain gauges and experimental dentures were then hit by a specially constructed ram driven at known velocities by a spring, whilst the strain was recorded on a storage oscilloscope. Photographs of the stored wave form were then used to establish the results at ram velocies equal to that of a denture falling 1 metre. Maximum strains were achieved of 11 × 10³ microstrain and strain rates of 1.04 × 10³ microstrain/ms. Laboratory impact machines for testing denture base materials should therefore be designed to achieve these figures.     

Dependence of the viscoelastic response of the urinary bladder wall on strain rate

In order to relate the results of measurements on strips of urinary bladder wall to clinical measurements on the intact urinary bladder, an expression is derived for the dependence of the viscoelastic response of bladder-wall material on strain rate. This expression is based on a non-linear viscoelastic model, with elastic moduli depending exponentially on strain, in accordance with the results of previous measurements. The results of measurements performed on strips of bladder-wall material at different strain rates show good agreement with the values predicted by the above mentioned expression.