Microfluidics emerged during the early 1990s with channel networks in silicon or glass. Microprocessing of these materials is labor-intensive and time-consuming, it requires sophisticated equipment in a clean room, and often involves hazardous chemicals. The subsequent use of polymer greatly simplified the fabrication of microchips and led to the rapid development of the field. Polymer such as poly(dimethylsiloxane) (PDMS), has other attractive properties, such as being elastic (easy to make efficient microvalves), permeable to gases, and compatible with culturing biological cells. Despite these advantages, applications of PDMS chips are severely limited by a few drawbacks that are inherent to this material: (i) strong adsorption of molecules, particularly large biomolecules, onto its surface; (ii) absorption of nonpolar and weakly polar molecules into PDMS bulk; (iii) leaching of small molecules from PDMS bulk into solutions; and (iv) incompatibility with organic solvents. To overcome all these problems, Teflon plastics seem to be the perfect solution. They are well-known for their superior inertness to almost all chemicals and all solvents; they also show excellent resistance to molecular adsorption and molecule leaching from the polymer bulk to solutions. However, Teflon has a high chemical inertness of the surface, which is restricted the bonding temperature (>260¢XC).It is not conducive to the low-temperature packaging process. This study presents a simple and rapid process for sealing Teflon-based microfluidic chip at a temperature of 140oC which is lower than typical bonding temperature of 260oC. A simple ammonium plasma treatment is used to enhance the surface energy of Teflon substrates such that the bonding temperature can be greatly reduced. Results indicate that the ammonium plasma treated Teflon substrates can be sealed using hot press bonding at a temperature of 140oC for 20 min. The measured iv bonding strength for the Teflon-based microfluidic devices is higher than those bonded at a reported temperature of 260oC for 60 min. It shows the measured contact angle for the Teflon substrates treated with different plasmas. Results indicated that the ammonium hydroxide plasma exhibited the best wettability property and the contact angle reached the minimum value of 45o after 5 min of treatment. The ESCA analysis showed the best Defluorination by ammonium plasma. The fluorine/carbon atomic ratio degraded from 1.96 to 1.10 by 5 minutes. The measured bonding strength for the Teflon substrates bonded with different surface activation protocols. Results showed that the bonding strength was enhanced upto 93% after the plasma treatment. The plasma treatment not only enhanced the bonding strength but also reduced the bonding temperature and time. The measured surface roughness only increased 15¡Ó5 nm (Ra) after the plasma treatment, which is acceptable for most applications in microfluidic systems. Finally, the fluorescence optical architecture and cross-chip successfully detected and isolated £XX-174 fragment of DNA samples confirmed the Teflon substrate for the emerging microfluidic plastic chip. The developed method provides a simple and rapid way to fabricate Teflon-based microfluidic devices.

In this study, pH-sensitive poly(acrylamide-co-acrylic acid) hydrogels were synthesized as controlled release systems in the presence of N,N-methylene bisacrylamide as crosslinker and ammonium persulfate as initiator. A set of hydrogels were used in the form they were prepared. One set of hydrogels were prepared as porous networks by incorporating sodium chloride into the reaction medium and then leaching of it after the completion of polymerization reaction. Two sets of hydrogels were modified by argon-plasma at different discharge powers. Hydrogels were characterized by 13C-NMR, XPS, SEM, ATR-FTIR, ESR as well as equilibrium degree of swelling (EDS) and contact angle measurements. Prepared hydrogels were loaded with a model antibiotic, ciprofloxacin-HCl (CPFX), and in-vitro release of CPFX from hydrogel matrices were examined in buffer solutions of varying pH values. There are two factors determining the release rates of CPFX / one is the pH-dependent solubility of CPFX and the other is EDS of the hydrogel samples. For porous samples drug loading and release rates were higher when compared to the control samples and CPFX solubility dominated over release kinetics. Plasma treatment resulted in prolonged release rates in acidic medium.

In this study calcium carbonate (CaCO3) particles are surface modified by using plasma polymerized natural gas and effects of surface modification of CaCO3 filler on mechanical properties of CaCO3-PP composites are investigated. Different combination of plasma factors / RF power, natural gas flow rate, and plasma discharge durations, are investigated. Mechanical properties such as tensile strength and Young&rsquo / s Modulus are measured by tensile testing machine. Storage modulus and loss modulus measurements are done by DMA. Some information about structures generated by natural gas plasma surface modification is obtained by FTIR tests. The tensile fracture surfaces of prepared composites are investigated by using SEM micrographs. It is concluded that, despite some enhancement obtained in the moduli / the technique of natural gas plasma surface modification of CaCO3 particles did not introduce significant improvement in mechanical properties of composite as expected. This result may partially be attributed to selected plasma parameters (i.e., flow rate, RF power, and discharge duration).

The combined use of additive manufacturing (AM), biocompatible and biodegradable materials, cells and biomolecular signals is the most common biomanufacturing strategy applied in scaffold fabrication. AM processes offer a better control and the ability to actively design the porosity and interconnectivity of the scaffolds. When combined with clinical imaging data, these fabrication techniques can be used to produce constructs that are customised to the shape of the defect or injury. However, due to the hydrophobicity of the commonly used synthetic biopolymers, cell-seeding and proliferation efficiency are limited. Moreover, due to the tortuosity of the scaffolds, non-uniform cell distribution with rare cell adhesion in the core region also commonly exists. Additionally, the commercial available machines are not able to create multi-material and material gradient scaffolds that are required to mimic the nature of nature tissues. To overcome the above limitations, this thesis describes the development of a hybrid bio-additive manufacturing system, called plasma-assisted bioextruson system (PABS), to produce smart scaffold by combining multi-head polymer extrusion and the plasma surface modification layer by layer, in the same chamber. PABS allows not only multiple biomaterials printing with the multi-extrusion heads, but also enables in-process plasma surface modification for zonal plasma-treated scaffolds fabrication. The in-house user interface enables a high degree of scaffold design freedom as it allows users to create single or multi-material constructs with uniform pore size or pore size gradient by changing process parameters such as lay-down pattern, filament distance, feed rate and layer thickness. Water contact angle tests and in vitro biological tests confirm that the hydrophilicity of synthetic polymers is improved and cell attachment and proliferation are enhanced after the in-process plasma modification. The effect of plasma treatment is also investigated by using different plasma modification strategies and various plasma modification parameters, including the plasma deposition velocity and the distance between the plasma jet and the printed scaffolds. The biological results also show dependence between the surface modification strategies and cell proliferation. The mechanical compression results show that for a fixed plasma deposition velocity, the effect of changing the distance between the plasma head and the deposited material is not significant. However, for a fixed distance, the compressive modulus increases with the increase in the plasma deposition velocity.

PMMA is a widely used biomaterial especially in the fields of orthopedia, orthodontia and ophthalmology. When biocompatibility is considered, modification of the biomaterials&amp / #8217 / surface may be needed to optimize interactions of the biomaterial with the biological environment. After the surface modifications one of the most important changes that occur is the change in the surface free energy (SFE). SFE is an important but an obscure property of the material and evaluation methods with different assumptions exist in the literature. In this study, SFE of pristine and oxygen plasma modified PMMA films were calculated by means of numerous theoretical approaches (Zisman, Saito, Fowkes, Berthelot, Geometric and Harmonic Mean and Acid-Base) using numerous liquids and the results were compared to each other to elucidate the differences of methods. Dispersive, polar, acidic and basic components of the SFE were calculated by the use of different liquid couples and triplets with the application of Geometric and Harmonic mean methods and Acid-Base approach. The effect of SFE and the components of SFE on the cell attachment efficiencies were examined by using fibroblast cells. It was observed that with the treatment of oxygen plasma, cell attachment capability and hydrophilicity of PMMA surfaces were altered depending on the applied power and duration of the plasma.

Textiles ultrahochmolekulares Polyethylen (UHMWPE) besitzt, aufgrund seiner außerordentlich hohen Molmasse und einem kristallinen Anteil von mehr als 80 %, exzellente spezifische Reißfestigkeiten sowie sehr gute Beständigkeiten gegenüber biologischen, chemischen und physikalischen Einflüssen, wodurch es sich für den Einsatz in Schutztextilien, als textiler Träger für funktionelle Partikel, zur Faserverstärkung in Kunststoffen für hochbelastbare Bauteile und auch zur Herstellung hochwertiger, technischer Textilmembranen anbietet. Voraussetzung für diese Applikationen ist ein hohes Wechselwirkungsvermögen der Fasergrenzflächen. Im Rahmen dieser Dissertationsschrift wurden systematisch die Möglichkeiten zur Oberflächenaktivierung von textilem UHMWPE mittels Atmosphärendruckplasma (ADP) untersucht und Eigenschafts-Wirkungsbeziehungen verschiedener Einflussparameter, u. a. Plasmaleistung, Elektrodenabstand, Behandlungsintensität, aufgeklärt. Dabei lag ein besonderes Augenmerk auf den textilen Eigenheiten des Materials und der dadurch stark beeinflussten Durchdringung des Plasmas. Entsprechend wurden umfangreiche Messreihen zu chemischen und physikalischen Veränderungen der Faseroberfläche erstellt, um schließlich eine industrielle Nutzbarkeit der ADP-Behandlung ableiten zu können. Hierzu wurden auch zwei weitere Verfahren vergleichend begutachtet und in Kooperation mit dem Leibniz-Institut für Polymerforschung Dresden e.V. eine mögliche Anwendung aktivierter UMHWPE-Garne als Träger für magnetisierbare Nanopartikel betrachtet.

No description available.