Polydimethylsiloxane (PDMS) modulates CD38 expression, absorbs retinoic acid and may perturb retinoid signalling

Polydimethylsiloxane (PDMS) is the most commonly used material in the manufacture of customized cell culture devices. While there is concern that uncured PDMS oligomers may leach into culture medium and/or hydrophobic molecules may be absorbed into PDMS structures, there is no consensus on how or if PDMS influences cell behaviour. We observed that human umbilical cord blood (CB)-derived CD34+ cells expanded in standard culture medium on PDMS exhibit reduced CD38 surface expression, relative to cells cultured on tissue culture polystyrene (TCP). All-trans retinoic acid (ATRA) induces CD38 expression, and we reasoned that this hydrophobic molecule might be absorbed by PDMS. Through a series of experiments we demonstrated that ATRA-mediated CD38 expression was attenuated when cultures were maintained on PDMS. Medium pre-incubated on PDMS for extended durations resulted in a time-dependant reduction of ATRA in the medium and increasingly attenuated CD38 expression. This indicated a time-dependent absorption of ATRA into the PDMS. To better understand how PDMS might generally influence cell behaviour, Ingenuity Pathway Analysis (IPA) was used to identify potential upstream regulators. This analysis was performed for differentially expressed genes in primary cells including CD34+ haematopoietic progenitor cells, mesenchymal stromal cells (MSC), and keratinocytes, and cell lines including prostate cancer epithelial cells (LNCaP), breast cancer epithelial cells (MCF-7), and myeloid leukaemia cells (KG1a). IPA predicted that the most likely common upstream regulator of perturbed pathways was ATRA. We demonstrate here that ATRA is absorbed by PDMS in a time-dependent manner and results in the concomitant reduced expression of CD38 on the cell surface of CB-derived CD34+ cells.

The Nonlinear Phenomena Of Thin Polydimethylsiloxane (Pdms) Films In Electrowetting

Electrowetting (EW) is an effective way to manipulate small volume liquid in micro- and nano-devices, for it can improve its wettability. Since the late 1990s, electrowetting-on-dielectric (EWOD) has been used widely in bio-MEMS, lab-on-a-chip, etc. Polydimethlsiloxane (PDMS) is extensively utilized as base materials in the fabrication of biomedical micro- and nano-devices. The properties of thin PDMS films used as dielectric layer in EW are studied in this paper. The experimental results show that the thin PDMS films exhibit good properties in EWOD. As to PDMS films with different thicknesses, a threshold voltage and a hysteresis were observed in the EIWOD experiments.

Non-linear mechanical behavior of the elastomer polydimethylsiloxane (PDMS) used in the manufacture of microfluidic devices

Polydimethylsiloxane (PDMS) is the elastomer of choice to create a variety of microfluidic devices by soft lithography techniques (eg., [1], [2], [3], [4]). Accurate and reliable design, manufacture, and operation of microfluidic devices made from PDMS, require a detailed characterization of the deformation and failure behavior of the material. This paper discusses progress in a recently-initiated research project towards this goal. We have conducted large-deformation tension and compression experiments on traditional macroscale specimens, as well as microscale tension experiments on thin-film (≈ 50µm thickness) specimens of PDMS with varying ratios of monomer:curing agent (5:1, 10:1, 20:1). We find that the stress-stretch response of these materials shows significant variability, even for nominally identically prepared specimens. A non-linear, large-deformation rubber-elasticity model [5], [6] is applied to represent the behavior of PDMS. The constitutive model has been implemented in a finite-element program [7] to aid the design of microfluidic devices made from this material. As a first attempt towards the goal of estimating the non-linear material parameters for PDMS from indentation experiments, we have conducted micro-indentation experiments using a spherical indenter-tip, and carried out corresponding numerical simulations to verify how well the numerically-predicted P(load-h(depth of indentation) curves compare with the corresponding experimental measurements. The results are encouraging, and show the possibility of estimating the material parameters for PDMS from relatively simple micro-indentation experiments, and corresponding numerical simulations.

Magnetite-doped polydimethylsiloxane (PDMS) for phosphopeptide enrichment

Reversible phosphorylation plays a key role in numerous biological processes. Mass spectrometry-based approaches are commonly used to analyze protein phosphorylation, but such analysis is challenging, largely due to the low phosphorylation stoichiometry. Hence, a number of phosphopeptide enrichment strategies have been developed, including metal oxide affinity chromatography (MOAC). Here, we describe a new material for performing MOAC that employs a magnetite-doped polydimethylsiloxane (PDMS), that is suitable for the creation of microwell array and microfluidic systems to enable low volume, high throughput analysis. Incubation time and sample loading were explored and optimized and demonstrate that the embedded magnetite is able to enrich phosphopeptides. This substrate-based approach is rapid, straightforward and suitable for simultaneously performing multiple, low volume enrichments. © the Partner Organisations 2014.

Ultraviolet photodetection of flexible ZnO nanowire sheets in polydimethylsiloxane polymer

ZnO nanowires are normally exposed to an oxygen atmosphere to achieve high performance in UV photodetection. In this work we present results on a UV photodetector fabricated using a flexible ZnO nanowire sheet embedded in polydimethylsiloxane (PDMS), a gas-permeable polymer, showing reproducible UV photoresponse and enhanced photoconduction. PDMS coating results in a reduced response speed compared to that of a ZnO nanowire film in air. The rising speed is slightly reduced, while the decay time is prolonged by about a factor of four. We conclude that oxygen molecules diffusing in PDMS are responsible for the UV photoresponse

Colored polydimethylsiloxane micropillar arrays for high throughput measurements of forces applied by genetic model organisms

Measuring forces applied by multi-cellular organisms is valuable in investigating biomechanics of their locomotion. Several technologies have been developed to measure such forces, for example, strain gauges, micro-machined sensors, and calibrated cantilevers. We introduce an innovative combination of techniques as a high throughput screening tool to assess forces applied by multiple genetic model organisms. First, we fabricated colored Polydimethylsiloxane (PDMS) micropillars where the color enhances contrast making it easier to detect and track pillar displacement driven by the organism. Second, we developed a semiautomated graphical user interface to analyze the images for pillar displacement, thus reducing the analysis time for each animal to minutes. The addition of color reduced the Young's modulus of PDMS. Therefore, the dye-PDMS composite was characterized using Yeoh's hyperelastic model and the pillars were calibrated using a silicon based force sensor. We used our device to measure forces exerted by wild type and mutant Caenorhabditis elegans moving on an agarose surface. Wild type C. elegans exert an average force of similar to 1 mu N on an individual pillar and a total average force of similar to 7.68 mu N. We show that the middle of C. elegans exerts more force than its extremities. We find that C. elegans mutants with defective body wall muscles apply significantly lower force on individual pillars, while mutants defective in sensing externally applied mechanical forces still apply the same average force per pillar compared to wild type animals. Average forces applied per pillar are independent of the length, diameter, or cuticle stiffness of the animal. We also used the device to measure, for the first time, forces applied by Drosophila melanogaster larvae. Peristaltic waves occurred at 0.4Hz applying an average force of similar to 1.58 mu N on a single pillar. Our colored microfluidic device along with its displacement tracking software allows us to measure forces applied by multiple model organisms that crawl or slither to travel through their environment. (C) 2015 AIP Publishing LLC.

Influence Of Different Amount Of Au On The Wetting Behavior Of Pdms Membrane

Polydimethylsiloxane (PDMS) has been widely used as a base material for bio-MEMS/NEMS devices. It is difficult for PDMS to transfer and spread aqueous solution as a kind of highly hydrophobic material. Therefore, surface modification is necessary for PDMS to make it hydrophilic. In this paper, a method of hydrophilization of PDMS surface is proposed. Gold is sputtered to the PDMS substrate by sputter coater in different average thicknesses. Relationship between the average thickness of gold on the PDMS substrate and the contact angle of the surface was studied. It was found that even gold of average thickness less than 1 nm can result in about 25 degrees change of contact angle. AFM is also used to get topographic information of PDMS surface coated with gold. Three cases are classified with different amount of Au: (1) Heterogeneous zone; (2) Transition zone; (3) Film zone. For heterogeneous zone, a simple model about heterogeneous phase wetting is put forward to interpret this phenomenon.

一种PDMS薄膜型微阀的制备与性能分析

通过厚胶光刻工艺在硅片上制备SU 8胶模板,利用该模板制备了高分子聚合物PDMS(Polydimethylsiloxane,聚二甲基硅氧烷)微流道和薄膜结构。通过对不同结构的两层PDMS的不可逆粘接得到一种简单的阀结构,在外加气源压力作用下薄膜产生变形实现对微流道的控制。实验测量了微阀的控制气源压力与被控制液体流量之间的关系,说明膜阀的开闭性能良好。根据弹性薄膜的变形理论,对影响微阀性能的参数进行了分析,并提出了几种可行的用于薄膜微阀控制的方法。

聚二甲基硅氧烷（PDMS）表面液滴动力学的实验研究

液滴是自然界中普遍存在的一种物质形态。非连续微流体（液滴）是近年来微流体技术重要发展方向之一。对液滴的产生、启动、移动、合并、分离和碰撞过程的研究对于航天、微纳系统、电子显示、计算机冷却、喷墨、生物医学等学科领域有着重要的应用价值。液滴属于软物质，其力学性质介于流体和固体之间，其类固体（solid-like）行为来自于曲率产生的Laplace压力和表面张力的约束。对液滴动力学行为的研究有着重要的学术价值。 本文的主要工作是针对生物微电子机械系统（Bio-MEMS）以及柔性微纳电子加工中常用的材料聚二甲基硅氧烷（Polydimethylsiloxane，PDMS）为基底的液滴动力学实验研究。 液滴是一个理想的微反应器，许多实验可以集成在一个液滴或多个液滴内完成。液滴本身的动力学特性对于实验的完成效率和质量有着重要的影响。液滴的微操控技术包括多相流法、电润湿法、热毛细管法、介电泳法等。液滴的动力学特性受到基底的影响非常大，包括基频、振动模态、运动过程等均随基底的润湿性、弹性模量的变化而有所变化。 在Bio-MEMS以及柔性微纳电子加工当中，PDMS扮演着越来越重要的角色，尤其是PDMS的润湿性和电润湿特性。目前的PDMS在Bio-MEMS当中主要是用于制备各种微流道。常见的问题主要是一方面PDMS是疏水材料，影响流体的输运。另一方面是液体在这种低Reynolds数情况下不易混合，反应效率低。本文提出了在PDMS表面溅射纳米厚度的金来减小PDMS表观接触角的方法。这种方式在特定喷金量的情况下可以在PDMS表面产生多层次的压应力波纹。这种压应力波纹对于柔性微纳电子加工，以及微流道中加速流体混合有着非常重要的作用。 电润湿是另一种可以使PDMS亲水化的方法。实验证明，PDMS具有较好的电润湿性质。此外电润湿也是目前操纵液滴的主要方式。目前一个常见的问题是电击穿现象阻碍了驱动电压的低压化，且低Reynolds数情况下液滴的混合效率偏低。此外电极还会由于少量电解的发生导致腐蚀及对液体样品的污染。本文提出了接触式的电润湿，在电极逐渐触碰液滴的过程中，液滴发生百Hz的失稳振动，稳定后接触角减小。这种电润湿模式可以有效的提高临界击穿电压，避免液滴被腐蚀后的电极污染，同时可以加快液滴的混合效率。其失稳特征时间在10 ms量级，这恰是所用液滴特征尺度在1 mm左右的电润湿器件的最快响应时间。并采用液滴振动的理论估算了液滴的失稳时间，同时还考虑了基底润湿性对液滴振动过程的影响。 液滴的启动是电润湿操控液滴过程中的重要环节。通常的液滴启动都是在非连续基底上依靠逻辑电路产生的电势变化来驱动液滴。无论是逻辑电路的设计还是驱动装置的加工都非常复杂。本文首次实现了在超疏水生物样品荷叶上的液滴启动，启动速度为数十毫米/秒，启动时间为10 ms量级。并利用PDMS成功的仿制了荷叶结构实现了超疏水的PDMS表面，荷叶同仿荷叶的PDMS超疏水表面具有相近的润湿性。 在数字微流体操控液滴的过程中，液滴的合并涉及液滴的碰撞，而且MEMS系统当中利用液滴撞击进行冷却的实验已经有所开展。同时理解液滴碰撞还对许多领域包括生物、化学、喷墨、大气物理等有着非常重要的作用。本文实验研究了Weber数和毛细数对液滴碰撞过程的影响，通过改变Weber数和毛细数得到了四种不同的响应模式。

RELATIONSHIP BETWEEN CRYSTALLIZATION OF THE PDMS BLOCK AND MORPHOLOGY OF POLY(BUTADIENE-B-DIMETHYLSILOXANE)

Studies using transmission electron microscopy, differential scanning calorimetry, and X-ray diffraction showed correlations between the crystallization behavior of the polydimethylsiloxane (PDMS) block and the morphology of the block copolymer poly (butadiene-b-dimethylsiloxane) (PB-PDMS). When the PDMS component existed as spheres dispersed in a PB matrix, the crystallization rate of the PDMS block was lower than when the PDMS phase existed in rod or cylinder form.

Concurrent recordings of bladder afferents from multiple nerves using a microfabricated PDMS microchannel electrode array

In this paper we present a compliant neural interface designed to record bladder afferent activity. We developed the implant's microfabrication process using multiple layers of silicone rubber and thin metal so that a gold microelectrode array is embedded within four parallel polydimethylsiloxane (PDMS) microchannels (5 mm long, 100 μm wide, 100 μm deep). Electrode impedance at 1 kHz was optimized using a reactive ion etching (RIE) step, which increased the porosity of the electrode surface. The electrodes did not deteriorate after a 3 month immersion in phosphate buffered saline (PBS) at 37 °C. Due to the unique microscopic topography of the metal film on PDMS, the electrodes are extremely compliant and can withstand handling during implantation (twisting and bending) without electrical failure. The device was transplanted acutely to anaesthetized rats, and strands of the dorsal branch of roots L6 and S1 were surgically teased and inserted in three microchannels under saline immersion to allow for simultaneous in vivo recordings in an acute setting. We utilized a tripole electrode configuration to maintain background noise low and improve the signal to noise ratio. The device could distinguish two types of afferent nerve activity related to increasing bladder filling and contraction. To our knowledge, this is the first report of multichannel recordings of bladder afferent activity.

Polydimethylsiloxane/polypyrrole stir bar sorptive extraction and liquid chromatography (SBSE/LC-UV) analysis of antidepressants in plasma samples

A new polymeric coating consisting of a dual-phase, polydimethylsiloxane (PDMS) and polypyrrole (PPY) was developed for the stir bar sorptive extraction (SBSE) of antidepressants (mirtazapine, citalopram, paroxetine, duloxetine, fluoxetine and sertraline) from plasma samples, followed by liquid chromatography analysis (SBSE/LC-UV). The extractions were based on both adsorption (PPY) and sorption (PDMS) mechanisms. SBSE variables, such as extraction time, temperature, pH of the matrix, and desorption time were optimized, in order to achieve suitable analytical sensitivity in a short time period. The PDMS/PPY coated stir bar showed high extraction efficiency (sensitivity and selectivity) toward the target analytes. The quantification limits (LOQ) of the SBSE/LC-UV method ranged from 20 ng mL(-1) to 50 ng mL(-1), and the linear range was from LOQ to 500 ng mL(-1), with a determination coefficient higher than 0.99. The inter-day precision of the SBSE/LC-UV method presented a variation coefficient lower than 15%. The efficiency of the SBSE/LC-UV method was proved by analysis of plasma samples from elderly depressed patients. (C) 2008 Elsevier B.V. All rights reserved.

TiO2/PDMS nanocomposites for use on self-cleaning surfaces

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Synthesis of PDMS-metal oxide hybrid nanocomposites using an in situ sol-gel route

Organic-inorganic hybrid nanocomposites are widely studied and applied in broad areas because of their ability to combine the flexibility, low density of the organic materials with the hardness, strength, thermal stability, good optical and electronic properties of the inorganic materials. Polydimethylsiloxane (PDMS) due to its excellent elasticity, transparency, and biocompatibility has been extensively employed as the organic host matrix for nanocomposites. For the inorganic component, titanium dioxide and barium titanate are broadly explored as they possess outstanding physical, optical and electronic properties. In our experiment, PDMS-TiO2 and PDMS-BaTiO3 hybrid nanocomposites were fabricated based on in-situ sol-gel technique. By changing the amount of metal precursors, transparent and homogeneous PDMS-TiO2 and PDMS-BaTiO3 hybrid films with various compositions were obtained. Two structural models of these two types of hybrids were stated and verified by the results of characterization. The structures of the hybrid films were examined by a conjunction of FTIR and FTRaman. The morphologies of the cross-sectional areas of the films were characterized by FESEM. An Ellipsometer and an automatic capacitance meter were utilized to evaluate the refractive index and dielectric constant of these composites respectively. A simultaneous DSC/TGA instrument was applied to measure the thermal properties. For PDMS-TiO2 hybrids, the higher the ratio of titanium precursor added, the higher the refractive index and the dielectric constant of the composites are. The highest values achieved of refractive index and dielectric constant were 1.74 and 15.5 respectively for sample PDMS-TiO2 (1-6). However, when the ratio of titanium precursor to PDMS was as high as 20 to 1, phase separation occurred as evidenced by SEM images, refractive index and dielectric constant decreased. For PDMS-BaTiO3 hybrids, with the increase of barium and titanium precursors in the system, the refractive index and dielectric constant of the composites increased. The highest value was attained in sample PDMS-BaTiO3 (1-6) with a refractive index of 1.6 and a dielectric constant of 12.2. However, phase separation appeared in SEM images for sample PDMS-BaTiO3 (1-8), the refractive index and dielectric constant reduced to lower values. Different compositions of PDMS-TiO2 and PDMS-BaTiO3 hybrid films were annealed at 60 °C and 100 °C, the influences on the refractive index, dielectric constant, and thermal properties were investigated.

The use of polydimethylsiloxane for injection laryngoplasty

BACKGROUND: Injuries of the recurrent laryngeal nerve with consecutive vocal cord paralysis is a typical complication in chest, esophageal, thyroideal, and neck surgery. Glottic insufficiency secondary to such a lesion can be treated by endolaryngeal vocal cord augmentation (injection laryngoplasty). Many different substances have been used, often showing complications or disadvantages. This study reports on the use of injectable polydimethylsiloxane (PDMS), with special regard to the long-term results. METHODS: In this prospective study, 21 patients with unilateral vocal cord paralysis underwent injection laryngoplasty using PDMS at a volume of 0.5-1.0 ml. Preoperatively, 6 weeks and 12 months after the injection the following parameters concerning patients' voice were evaluated: Glottic closure by videolaryngostroboscopy, maximum phonation time, voice range, voice dynamic, jitter, shimmer, noise-to-harmonic-ratio, and roughness, breathiness, and hoarseness (RBH). In addition, patients were asked to give their own evaluation of how satisfied they felt with their voice and of the handicaps it caused them. RESULTS: Postoperatively an improvement was evident in all the parameters that were investigated, and this significant improvement was still in evidence for most of the parameters more than one year after the injection. In our study no complications were observed more than one year after injection. CONCLUSION: PDMS is a safe substance for injection laryngoplasty in unilateral vocal cord paresis. Objective and subjective parameters confirm its effectiveness. It is suitable for obtaining satisfying results in the reestablishment of the patient's voice and communication ability.