小口径医用聚氨酯人造血管径向顺应性研究

目的 比较小口径医用聚氨酯人造血管在干法制作与湿法制作方法下的微观形态和径向顺应 性,探讨管径大小、管壁厚度对血管顺应性的影响,分析接枝血管中不同部位的顺应性差别。 方法 通过在玻璃棒模具上复合均匀厚度的聚氨酯膜,制作出小口径聚氨酯人造血管。在自 行搭建的顺应性测试回路装置中测试得到压力与直径的关系,依据ISO7198国际标准计算 出人造血管的径向顺应性。结果 干法制作的聚氨酯人造血管表面与截面均很致密,湿法制 作的聚氨酯人造血管的截面呈微孔结构;随着人造血管管径的增大,顺应性逐渐增大;随着 管壁厚度的增加,顺应性逐渐减小;人造血管的接口处的径向顺应性波动较中间处大;湿法 制作的人造血管顺应性要优于干法制作的人造血管顺应性。结论：医用聚氨酯制作的小口径 人造血管具有良好的径向顺应性,是很有前景的小口径血管代用品材料;影响顺应性不匹配 的因素有很多,还需做进一步的研究。     

磁声电导率检测系统设计及其线性扫频理论验证

临床研究证实病灶组织的早期诊断能显著降低患癌风险,由于磁声电成像具有高分辨率和高对比度优势,因而有望成为一种新的检测方法。本文采用模块化设计思维,设计并实现了一款低成本、数字化磁声电导率检测系统,并提出线性调频连续波激励洛伦兹力电阻抗检测理论,通过0.5%NaCl均匀仿体实验,清晰获得与实际物理尺寸一致的均匀仿体电导率曲线,验证了线性扫频理论应用在本系统是准确且可行的。同时,1 000μs线性扫频时宽所获得分辨率优于500μs和1 500μs,提示线性扫频时宽是影响电导率分辨率的重要因素。通过对不同浓度NaCl均匀仿体的实验,得到了相同结论,证明了本系统的可重复测量性。     

一种血管张应力体外加载装置的实验研究

目的研制一种血管张应力体外加载装置,研究弹性基底(硅胶片)上的张应力、张应变分布。方法基于基底形变加载技术,研制一种接近人体血液动力学环境的血管张应力体外加载装置。利用装置中的摄像机拍摄硅胶片拉伸前后硅胶片网格点的图像并转化为数字图像,使用Matlab软件对网格点的位置特征进行计算,从而得到硅胶片的应变分布。利用万能材料试验机对硅胶片进行实验和计算得到硅胶片的力学参数,根据力学参数建立有限元模型,并对硅胶片的张应力、张应变分布进行模拟计算。将实验结果和模拟结果进行比较。结果有限元结果和实验结果基本一致,张应力、张应变的最大值均出现在加载点处,中间区域应力、应变较为均匀。硅胶片中间60%面积区域可视为均匀应变场。结论研究结果可为后期血管壁内皮细胞的动态培养以及细胞力学研究提供实验技术。     

出口边界条件和壁厚对冠状动脉壁面剪切力和冯米塞斯应力的影响

探讨基于个体化患者计算机断层血管造影(CTA)影像的冠状动脉流固耦合(FSI)数值分析中,不同出口边界条件和血管壁模型对时间平均壁面剪切力(TAWSS)和冯米塞斯应力(VMS)的影响。根据患者CTA影像重建右冠状动脉(RCA)管腔流域三维几何;将管腔流域表面向外扩张0.5 mm,形成均匀厚度血管壁;运用类似虚拟去除斑块的方法建立不均匀厚度血管壁模型。FSI分析时,分别给予zero和impedance两种出口边界条件;获得从舒张末期开始心动周期主要时间点TAWSS和VMS的分布,比较不同模型结果的差异。结果表明, 两种出口边界条件下,TAWSS空间分布基本一致,且血管狭窄段均高于其他部位;zero条件下峰值VMS出现在压强最大时刻点0.42 s,而impedance条件下峰值VMS出现在入口血流速度最大时刻点0.64 s,并且达到前者的20倍。同是impedance出口边界条件时,TAWSS分布基本一致,没有显著性差异;两种血管壁模型中,VMS的分布一致,血管狭窄段比其他部位低,但是不均匀厚度血管壁模型中局部位置VMS绝对值高于均匀壁厚血管壁模型。医学影像技术的发展可以提供更高精度的冠脉结构以及出入口速度和压强边界条件,不但对研究血流动力学以及结构力学因素与心血管疾病的关系具有重要意义,也可以更好的服务于患者个体化诊断与治疗。     

体外血管内皮细胞培养装置中弹性基底的应力研究

目的对一种体外血管内皮细胞动态培养装置中弹性基底的应力情况进行研究,使装置更接近人体血流动力学环境,实验并观察不同张应力情况下平行平板流动腔中弹性基底切应力的变化。方法采用一系列静态拉伸试验拟合动态拉伸的情况,即将两种不同厚度硅胶片置于装置中,从0%开始,分别以每次间隔10%拉伸率做静态拉伸(0%、10%、20%、30%),并在保持其拉伸率不变的情况下,计算硅胶片拉伸后的腔体高度。通过计算切应力得到不同拉伸率下的切应力曲线,分析比较切应力随硅胶片厚度变化的规律。结果实验结果与理论分析基本一致。当拉伸率为30%时,0.5 mm厚度硅胶片随拉伸率的变化(腔体高度的变化),对平行平板流动腔中切应力会产生一定影响,平均和最大切应力分别减小10.1%和10.4%。结论计算平行平板流动腔中切应力必须考虑引入张应力后弹性基底厚度变化所引起的影响因素。研究结果可为体外血管内皮细胞的培养以及设计研制新型平行平板流动腔提供实验技术。     

电流注入式磁声耦合成像技术仿真研究

目的:电流注入式磁声耦合成像技术是一种新型的生物组织电特性工程成像方法,具有高分辨率和高对比度的优点。探讨电流注入式磁声耦合成像的工作原理,为成像系统实验平台的设计提供理论参考,为真实生物组织电导率的成像奠定基础。方法:结合电场、磁场、超声耦合理论,运用有限元建模分析软件COMSOL Multiphysics建立电导率仿体模型,并进行电磁场分析,获得电导率仿体的电流密度分布。利用数学工具Matlab获得磁声成像声场分布,进而重建仿体模型声源。结果:从电磁场分析结果获知电导率的分布反映了仿体模型的结构形状,电流场为一无旋场,重建的声源图像精确地反映了仿体模型电导率的分布,与仿体模型的层析结构形状、尺寸高度一致。结论:电流注入式磁声成像为组织电阻抗分布的重建提供了一种新的方法,该进一步研究磁声耦合成像的理论与实验打下了基础。     

呼吸时相和模体位置对4D-CT图像均匀性的影响

目的:通过分析Catphan模体CTP486模块的四维CT（4D-CT）图像,研究呼吸时相和模体位置对4D-CT图像均匀性的影响。方法:使用西门子Sensation Open CT模拟机和瓦里安RPM系统,获取Catphan 504模体CTP486模块的4D-CT图像。对3种模体位置情形进行研究。情形A:模体悬空放置;情形T:模体下有一个碳纤维CT平板床;情形B+T:模体下有一个碳纤维固定底板和一个CT平板床。每种情形重复3次测量。使用DoseLab放疗验证软件分析4D-CT图像,得到图像均匀性值（U）。对每一套4D-CT重建10个呼吸时相（0%, 10%,[ ?], 90%）的CT图像序列。对U值进行统计分析和比较研究。结果:4D-CT所有CT序列的U值均小于5 HU。每种情形得到30个U值数据,情形A、情形T和情形B+T 3种情形U值分别为（1.44±0.79）、（1.91±0.91）和（1.99±0.77） HU。统计U值对应的4个边缘感兴趣区（ROI）出现的次数和比例,情形T中ROI 22（9点钟方向）出现13次（占比43.33%）,情形B+T中ROI 23（12点钟方向）出现13次（占比43.33%）。结论:本研究中4D-CT的图像均匀性满足使用要求,不同呼吸时相4D-CT的图像均匀性值不同,模体摆放位置对4D-CT的图像均匀性有一定影响,碳纤维CT平板床和固定底板的存在使4D-CT 的图像均匀性变差。     

新型可回收血管支架的设计与有限元分析

目的针对药物洗脱支架植入后引起的早期再狭窄问题,对镍钛合金血管支架进行结构上的可回收设计和生物力学分析。方法建立可回收血管支架及其回收系统的几何模型,其中支架回收部为圆台形网状结构,由4个对称分布的回收筋组成;分析支架在压握过程中的最大主应变分布、压握及自膨胀均匀性等,并对支架的回收过程进行仿真实验。结果当支架被压握至最小尺寸时,其最大应变为3.7%,不均匀性指数为0.62%;当支架自膨胀结束时,其不均匀性指数为1.31%;当1/2支架被回收进外鞘管时,最大应变为1.52%;而支架在回收过程中并未发生断裂或"卡顿"情况。结论支架应变在其安全范围之内,且支架的压握及自膨胀过程较均匀,能够被安全、顺利地回收进外鞘管中。研究结果可以为可回收血管支架的结构设计、生物力学分析和临床应用提供重要参考依据。     

不同厚度垫底材料对龋齿充填后应力分布的影响

目的采用有限元方法对比分析不同厚度垫底材料对充填后牙体应力分布的影响。方法选用正常形态下颌第1磨牙,基于MicroCT扫描建立Ⅰ类洞充填的三维有限元模型,选择Vitrebond和Dycal作为垫底材料,分别考虑4种不同的厚度(0.5、1.0、1.5和2.0mm),施加250N的咬合力,对各模型中牙体、充填体和垫底材料的最大/最小主应力进行比较。结果 Dycal垫底,厚度为2.0mm,牙体的最大主应力峰值超过其抗拉强度,垫底材料的最大/最小主应力峰值分别超过其抗拉和抗压强度;垫底厚度为1.5mm和2.0mm,充填体的最大主应力峰值接近其抗拉强度的90%。Vitrebond垫底时,各材料的最大主应力峰值也都在1.5mm或2.0mm时达到极值。结论从防止充填后牙体折裂的角度,建议临床上采用较薄的垫底层厚度,取0.5～1.0mm。     

传声媒质对双界面回波法测量精度的影响

目的 双界面回波法（dual-boundary echo comparison,DBEC）是一种有望实现血液超声衰减系数（ultrasonic attenuation coefficient,USAC）无损测量的新方法.使用该方法需要预先测试探头的校正系数,该值反映了声束形状.若将在水中获得的校正系数应用到非水媒质中会带来测量误差,本文通过实验研究这种误差的范围、影响因素以及减小误差的方法.方法 制作折射率与人体组织相当的仿组织超声模块,将其插入声通路中取代一部分水的声程,测量此时的校正系数并与水中所测得的数据进行比较.利用DBEC法对仿组织模块插入前后蓖麻油的USAC进行测量并比较结果.结果 探头通频带内,校正系数误差和蓖麻油USAC的测试误差均在7%以内,但校正系数误差与仿组织模块厚度的关系很复杂.结论 实验结果提示应在仿组织材料中预先测试探头的校正系数,以避免体内测量时DBEC法产生误差.     

Reduced foreign body response at nitric oxide-releasing subcutaneous implants

The tissue response to nitric oxide (NO)-releasing subcutaneous implants is presented. Model implants were created by coating silicone elastomer with diazeniumdiolate-modified xerogel polymers capable of releasing NO. The host tissue response to such implants was evaluated at 1, 3, and 6 weeks and compared to that of uncoated silicone elastomer blanks and xerogel-coated controls incapable of releasing NO. Delivery of NO (approximately 1.35 micromol/cm2 of implant surface area) reduced foreign body collagen capsule ("scar tissue") thickness by >50% compared to uncoated silicone elastomer after 3 weeks. The chronic inflammatory response at the tissue/implant interface was also reduced by >30% at NO-releasing implants after 3 and 6 weeks. Additionally, CD-31 immunohistochemical staining revealed approximately 77% more blood vessels in proximity to NO-releasing implants after 1 week compared to controls. These findings suggest that conferring NO release to subcutaneous implants may promote effective device integration into healthy vascularized tissue, diminish foreign body capsule formation, and improve the performance of indwelling medical devices that require constant mass transport of analytes (e.g., implantable sensors).     

Investigating the functionality of diamond-like carbon films on an artificial heart diaphragm

In this study, the authors used diamond-like carbon film to coat the ellipsoidal diaphragm (polyurethane elastomer) of artificial hearts. The purpose of such coatings is to prevent the penetration of hydraulic silicone oil and blood through the diaphragm. To attach diamond-like carbon film uniformly on the diaphragm, the authors developed a special electrode. In estimating the uniformity of the diamond-like carbon film, the thickness was measured using a scanning electron microscope, and the characteristics of the diamond-like carbon film was investigated using infrared spectroscopy, Ar-laser Raman spectrophotometer, and x-ray photoelectron spectrometer. Also, to estimate the penetration of silicone oil through the diaphragm, in vitro testing was operated by alternating the pressure of silicone oil for 20 days. The authors were able to successfully attach uniform deposition of diamond-like carbon film on the ellipsoidal diaphragm. In this in vitro test, diamond-like carbon film was proven to have good stability. The amount of silicone oil penetration was improved by one-third using the diamond-like carbon film coating compared with an uncoated diaphragm. It is expected that through the use of the diamond-like carbon film, the dynamic compatibility of an artificial heart diaphragm will increase.     

In vivo measurement of blood vessel wall thickness.

To understand the mechanical properties of arteries and vascular grafts, it is crucial that the wall thickness in these vessels be known. Unfortunately, all availble methods for measuring this parameter require the removal of the vessel, which precludes the study of such vessels as a function of time. A new radiographic technique for measuring the wall thickness of arteries and vascular grafts in vivo, utilizing contrast materials injected into the vessel lumen and applied to the outer surface of the vessel, is described. Radiographs are obtained with a portable X-ray machine and analyzed using a calibrated microscope. The technique has been successfully applied to the in vivo measurement of wall thickness in canine arteries, veins, and experimental vascular grafts. It is concluded that the method provides better than 95% accuracy in a variety of vessels and that it can be used to study changes in vascular grafts after their implantation into the arterial circulation.     

Inhibition of implant-associated infections via nitric oxide release

The in vivo antibacterial activity of nitric oxide (NO)-releasing xerogel coatings was evaluated against an aggressive subcutaneous Staphylococcus aureus infection in a rat model. The NO-releasing implants were created by coating a medical-grade silicone elastomer with a sol-gel-derived (xerogel) film capable of storing NO. Four of the bare or xerogel-coated silicone materials were subcutaneously implanted into male rats. Ten rats were administered 10 microl of a 10(8) cfuml(-1)S. aureus colony directly into the subcutaneous pocket with the implant prior to wound closure. Infection was quantitatively and qualitatively evaluated after 8d of implantation with microbiological and histological methods, respectively. A 82% reduction in the number of infected implants was achieved with the NO-releasing coating. Histology revealed that the capsule formation around infected bare silicone rubber controls was immunoactive and that a biofilm may have formed. Capsule formation in response to NO-releasing implants had greater vascularity in comparison with uninoculated or untreated controls. These results suggest that NO-releasing coatings may dramatically reduce the incidence of biomaterial-associated infection.     

Comparison between transmittance and reflectance measurements in glucose determination using near infrared spectroscopy

Glucose determination based on near-IR spectroscopy is investigated for reflectance and transmittance measurement. A wavelength range is 1100 to 2500 nm, which includes both the combination and overtone bands of glucose absorption. Intralipid solutions are used as samples, where glucose concentrations vary between 0 and 1000 mg/dl. Sample thickness for reflectance is 10 cm and 1- and 2-mm-thick samples are used for transmission. Partial least-squares regression (PLSR) analyses are performed to predict glucose concentrations. The standard errors of calibration are comparable between reflectance and 2-mm-thick transmittance. The reflectance method is inferior to the transmittance method in terms of the standard errors of prediction. Loading vector analysis for reflectance does not show glucose absorption features. Reflected light may not have enough information of glucose since a major portion of detected light has a short optical path length. In addition, prediction becomes more dependent on medium scattering rather than glucose, compared with transmission measurement. Loading vectors obtained from a PLSR transmittance analysis have glucose absorption profiles. The 1-mm-thick samples give better results than the 2-mm-thick samples for both calibration and prediction models. The transmittance setup is recommended for noninvasive glucose monitoring.     

The vascularization of artificial skin grafts in rats: its modification by protamine

Artificial skin is a recent development in the clinical care of the severely burned patient. Its manufacture involves the covalent bonding of collagen and polysaccharide, followed by the coating of one surface with a thin layer of silicone rubber. Neovascularization and its modification in artificial skin were studied. Experimental artificial skin was grafted onto rats and examined for vascular growth in the graft at 7 days. This was revealed by latex-perfused vascular casts which were processed for histological study. An area including the graft bed and graft matrix was viewed and examined for latex-filled vessels. Thirty-seven percent of the total vessels, identified by residual latex, had grown into the graft. When artificial skin was treated with protamine at 10 mg/ml buffered saline solution before grafting, only 6% of the total perfused blood vessels were found in the graft matrix. The remainder was found in the graft bed. Moreover, increases in the numbers of perfused blood vessels and vessel diameters were observed in the graft bed at the interface below the graft pretreated with protamine. Protamine inhibited vessel growth into the matrix, but promoted an increased number of dilated blood vessels in the surrounding graft bed. These dilated vessels were related to an altered vessel architecture.     

Transmittance of a bioceramic dental restorative material based on calcium aluminate

This article investigates the transmittance of a new ceramic filling material as a function of time, thickness, wavelength, and addition of pigments. In the hardened state the ceramic material is composed of hydrates, calcium aluminate, and glass fillers. The radiopacity of the investigated material is also measured. The results of the transmittance are compared to a commercial glass ionomer cement (Fuji II) and resin composite (Tetric Ceram). The transmittance increased with time from low values after 1 h to values close to the glass ionomer cements after 1 week. The resin composite had almost twice the transmittance as the calcium aluminate material and the glass ionomer cement. The amount of light passing through the material was dependent on both the sample thickness and the wavelength. Samples of 0.5-mm thickness transmitted almost twice as much as 1-mm-thick samples. Regarding the wavelength, blue light was scattered very effectively (low transmittance), whereas red light was not (high transmittance). Addition of pigments lowered the transmittance. The radiopacity was slightly higher than that of enamel.     

Stretch-mediated responses of osteoblast-like cells cultured on titanium-coated substrates in vitro

Cyclic stretching experiments on osteoblast-like cells have proven to be a useful tool in understanding the underlying mechanisms of load transduction at the bone-implant surface. However, most experimental setups use silicone rubber substrates, which are atypical for orthopedic and dental implant materials. Therefore, we investigated the responses of osteoblast-like cells to loading on titanium (Ti)-coated versus plain silicone substrates. Ti-coated substrates were made by a radio-frequency magnetron sputtering process, and characterized using Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy, and contact-angle measurements. Osteoblast-like cells cultured from rat bone marrow were seeded on both types of substrates and stretched for 1 h continuously. Subsequently, cell proliferation, alkaline phosphatase activity, and calcium content were measured for up to 24 days after seeding. In addition light-, scanning electron-, and confocal laser scanning micrographs were made. The results showed that our Ti coating had a thickness of 50 nm and contained Ti/oxygen as 1:1. However, further characterization proved that the silicone material had a tendency to resurface through the coating. Osteoblast-like cells proliferated faster on the Ti-coated substrates, but differentiation was slower compared with the silicone substrates. It was concluded that that there was a definitive influence of the substrate material in mechanical stress models. Therefore, extrapolation of results obtained using silicone substrates cannot be translated directly toward the situation of metallic implant materials.     

Poly-vinyl alcohol hydrogel vascular models for in vitro aneurysm simulations: the key to low friction surfaces.

PURPOSE: To develop a vessel model with poly-vinyl alcohol hydrogel (PVA-H) with low surface friction for in vitro simulations of vascular pathologies. MATERIALS AND METHODS: Simulations of variable vascular pathologies were based on human vessel casts reproduced in wax. Constructions of vascular models were then obtained by lost wax techniques. As materials, liquid silicon or PVA in organic solvents were used. After solidification, the wax was drained by heating. Comparison of PVA-H with silicone models included evaluation of surface characteristics (friction coefficient), of visibility (transparence and compatibility with medical imaging techniques), and of stiffness (pulsatility of vascular lumen). Both model types were integrated in a circulation circuit allowing for flow simulations and testing with endovascular medical devices. RESULTS AND CONCLUSION: Both model types were transparent and compatible with current medical imaging methods. PVA-H models exhibited much lower friction characteristics. PVA-H stiffness was closer to soft tissue when compared to silicone, allowing for pulsations during flow simulations.     

In vitro evaluation of in situ gels as short term vitreous substitutes

Dysfunction of the vitreous humor, present in the posterior cavity of the eye, leads to its detachment from the retina and vision loss. In this study, biopolymers were evaluated as in situ gels for short term vitreous substitution. Biophysical characterization revealed that the viscosity of the vitreous was >4000 cP at a shear rate of 0.15/s and it formed a gel with elastic modulus G' greater than the viscous modulus G'. Biopolymers of gellan and hyaluronic acid (8:2 w/w, 1% concentration) were low viscosity liquids at 37 degrees C and gelation was triggered both by the addition of 0.18 mM CaCl(2) as well as ocular temperature, thus making them feasible as in situ gels. Gelation was confirmed by viscoelastic moduli where G' was greater than G', similar to the vitreous and unlike that of silicone oil, a common vitreous substitute. The gels had a viscosity >5000 cP at a shear rate of 0.512/s, excellent light transmittance and absence of syneresis. Contact angle studies with water and simulated ocular fluids showed that gellan hyaluronic acid gels had similar wetting properties to that of vitreous with contact angles of 27 degrees +/- 1 degrees , 36.7 degrees +/- 1.6 degrees , and 33.7 degrees +/- 0.5 degrees for water, simulated tear fluid, and simulated aqueous humor, respectively. The results of this study suggest that biopolymers of gellan and hylauronic acid are suitable as in situ gels, have biophysical properties similar to that of the vitreous, and may be promising as alternatives to silicone oil as short-term vitreous substitutes.