Mercedes Vázquez

Advances in three-dimensional rapid prototyping of microfluidic devices for biological applications

The capability of 3D printing technologies for direct production of complex 3D structures in a single step has recently attracted an ever increasing interest within the field of microfluidics. Recently, ultrafast lasers have also allowed developing new methods for production of internal microfluidic channels within the bulk of glass and polymer materials by direct internal 3D laser writing. This review critically summarizes the latest advances in the production of microfluidic 3D structures by using 3D printing technologies and direct internal 3D laser writing fabrication methods. Current applications of these rapid prototyped microfluidic platforms in biology will be also discussed. These include imaging of cells and living organisms, electrochemical detection of viruses and neurotransmitters, and studies in drug transport and induced-release of adenosine triphosphate from erythrocytes.

Review on recent and advanced applications of monoliths and related porous polymer gels in micro-fluidic devices.

This review critically summarises recent novel and advanced achievements in the application of monolithic materials and related porous polymer gels in micro-fluidic devices appearing within the literature over the period of the last 5 years (2005-2010). The range of monolithic materials has developed rapidly over the past decade, with a diverse and highly versatile class of materials now available, with each exhibiting distinct porosities, pore sizes, and a wide variety of surface functionalities. A major advantage of these materials is their ease of preparation in micro-fluidic channels by in situ polymerisation, leading to monolithic materials being increasingly utilised for a larger variety of purposes in micro-fluidic platforms. Applications of porous polymer monoliths, silica-based monoliths and related homogeneous porous polymer gels in the preparation of separation columns, ion-permeable membranes, preconcentrators, extractors, electrospray emitters, micro-valves, electrokinetic pumps, micro-reactors and micro-mixers in micro-fluidic devices are discussed herein. Procedures used in the preparation of monolithic materials in micro-channels, as well as some practical aspects of the micro-fluidic chip fabrication are addressed. Recent analytical/bioanalytical and catalytic applications of the final micro-fluidic devices incorporating monolithic materials are also reviewed.

In vitro fibroblast and pre-osteoblastic cellular responses on laser surface modified Ti-6Al-4V.

The success of any implant, dental or orthopaedic, is driven by the interaction of implant material with the surrounding tissue. In this context, the nature of the implant surface plays a direct role in determining the long term stability as physico-chemical properties of the surface affect cellular attachment, expression of proteins, and finally osseointegration. Thus to enhance the degree of integration of the implant into the host tissue, various surface modification techniques are employed. In this work, laser surface melting of titanium alloy Ti-6Al-4V was carried out using a CO2 laser with an argon gas atmosphere. Investigations were carried out to study the influence of laser surface modification on the biocompatibility of Ti-6Al-4V alloy implant material. Surface roughness, microhardness, and phase development were recorded. Initial knowledge of these effects on biocompatibility was gained from examination of the response of fibroblast cell lines, which was followed by examination of the response of osteoblast cell lines which is relevant to the applications of this material in bone repair. Biocompatibility with these cell lines was analysed via Resazurin cell viability assay, DNA cell attachment assay, and alamarBlue metabolic activity assay. Laser treated surfaces were found to preferentially promote cell attachment, higher levels of proliferation, and enhanced bioactivity when compared to untreated control samples. These results demonstrate the tremendous potential of this laser surface melting treatment to significantly improve the biocompatibility of titanium implants in vivo.

Fast Fabrication Process of Microfluidic Devices Based on Cyclic Olefin Copolymer

A new low-cost process for fast fabrication of multilayer microfluidic devices using cyclic olefin copolymer film materials is presented. This novel process consists of the fabrication of microfluidic features by xurography, followed by multilayer lamination via cyclohexane vapor exposure. Exposure time to this solvent and compression time were optimized for bond tensile strength. A three-layer microfluidic chip capable of withstanding back pressures up to 23 MPa was fabricated in less than an hour. The suitability of this fast prototyping method for fabrication of functional UV-transparent microfluidic devices was demonstrated by development and testing of a microfluidic mixer and preparation of a polymer monolithic column within the microfluidic channel.

Laser assisted synthesis of carbon nanoparticles with controlled viscosities for printing applications

High-quality carbon nanoparticles with controlled viscosity and high aqueous stability were prepared by liquid-phase laser ablation of a graphite target in deionized water. The size distribution was found to vary from 5nm to 50nm with mean size of 18nm, in the absence of any reducing chemical reagents. Efficient generation of short chain polyynes was recorded for high laser repetition rates. Homogeneous and stable nanoparticle suspensions with viscosities ranging from 0.89 to 12mPa.s were obtained by suspending the nanoparticles in different solvent mixtures such as glycerol-water and isopropanol-water. Optical properties were investigated by absorption and photoluminescence spectroscopy. Raman spectroscopy confirmed graphitic-like structure of nanoparticles and the surface chemistry was revealed by Fourier-transform infrared spectroscopy demonstrating sufficient electrostatic stabilization to avoid particle coagulation or flocculation. This paper present an exciting alternative method to engineer carbon nanoparticles and their potential use as a ligand-free nano-ink for ink jet printing (jetting) applications.

New strategies for stationary phase integration within centrifugal microfluidic platforms for applications in sample preparation and pre-concentration

New approaches for fabrication of centrifugal microfluidic platforms (μCDs) for sample micro-extraction and pre-concentration in bioanalytical and environmental applications are presented. The integration of both octadecylsilica (C18) micro-particulate and porous carbon monolithic stationary phases was demonstrated and on-disc extractions of analytes in samples of different nature were performed. A novel strategy based on the packing of micro-particulate stationary phases using porous organic polymer monoliths as column frits was demonstrated through the in situ photo-polymerisation of monolithic frits in a specific area of the micro-channel, thereby greatly facilitating stationary phase packing within μCD platforms. An enrichment factor of 3.7 was obtained for vitamin B12 following on-disc pre-concentration on the octadecylsilica columns. UV-Vis absorbance measurements were also performed in the outlet reservoir permitting quasi-on-line analysis of the small volume fractions collected after extraction, with limits of detection (LODs) found for vitamin B12 (LOD = 43 μM) being rather similar to those found with a commercially available spectrophotometer (LOD = 37 μM). Furthermore, the first integration of carbon monoliths within microfluidic channels is reported. Carbon monoliths were fabricated as rods and cut into discs for their integration within the microfluidic network, offering a highly porous bimodal structure with low flow-through back-pressures, excellent chemical stability as well as adequate mechanical stability. The carbon monolith-based μCD platform was evaluated as a rapid semi-automated pre-concentration approach suitable for in-field use prior to in-lab HPLC quantitation of pollutants at low concentration levels. Calculated mean recoveries for phenol from tap water spiked-samples by using this on-disc pre-concentration method were 68 ± 4% (n = 4, RSD = 5%).

Nanoparticle functionalized laser patterned substrate: an innovative route towards low cost biomimetic platforms

Integration of nanotechnology and advanced manufacturing processes presents an attractive route to produce devices for adaptive biomedical device technologies. However, tailoring biological, physical, and chemical properties often leads to complex processing steps and therefore to high manufacturing cost impeding further scalability. Herein, a novel laser-based approach is introduced to manufacture low cost biocompatible polymer substrates functionalized with ultrapure nanoparticles. Laser direct writing was performed to create micron-sized patterns on 188 μm-thick cyclic olefin polymer (COP) substrates using a picosecond pulsed 1064 nm Nd:YAG laser. The Pulsed Laser Ablation in Liquids (PLAL) technique was exploited in this work to prepare colloidal solutions of ultrapure nanoparticles to impart bio-functionality onto laser patterned surfaces. Combining the laser patterns and their modification with PLAL-nanoparticles resulted in a functional and biocompatible substrate for biosensing applications. Our in vitro cell viability studies using a model cell line (human skin keratinocyte, HaCaT) suggest that these nanoparticles immobilized on the surfaces function as a biomimetic platform with the ability to interact with different biological entities (e.g. DNA, antibodies etc.).

Laser micro-engineering of functionalised cyclic olefin polymers for microfluidic applications

Direct-write laser processing has been demonstrated to be capable of both surface patterning of micro- and nanoscale structures on polymer surfaces without significant modification of the surface chemistry or optical transmission of the laser processed area. In this work, the creation of microchannels via direct-write laser processing of 188 μm thickness cyclic olefin polymers is demonstrated, along with a route towards channel functionalization. Cyclic olefin polymers (COP) are an emerging class of polymers noted for their high chemical resistance, biocompatibility and higher optical transparency when compared to other common polymers. These properties make them excellent substrates for the fabrication of microfluidic devices. This paper presents the first investigation into infrared laser processing of COP using a 1064 nm Nd:YAG laser. Scanning electron microscopy and Raman spectroscopy were utilized to investigate the morphology and composition of these laser textured surfaces. A route for functionalization of these substrates for chemical and biological speciation and separation was examined using carbon nanoparticles. The nanoparticles were produced using pulsed laser ablation in liquid (PLAL) which has been reported as a fast and adaptable method for nanoparticle production. The nanoparticles produced were using transmission electron microscopy while the coating of substrates with these CNPs was examined using SEM. These results are discussed in the context of development of a new route for achieving surfaces optimized for microfluidicbased separations and speciation.

Laser Processing of Quartz for Microfluidic Device Fabrication

This paper presents a fast fabrication process of microfluidic channels with quartz substrates. Microchannels were ablated on the surface of quartz samples with a CO2 laser. Double sided Pressure Sensitive Adhesive (PSA) was applied to bond the samples with scribed microchannels to flat glass sheets. Dimensions of the fabricated channels were characterised with optical microscopy and laser profilometry. The recorded data was modelled with a BoxBehnken experiment design using Response Surface Methodology. Characterisation included also the measurement of optical transmission through the processed glass and measurement of flow rate through the fabricated channels. With an average width of 165 µm and depth of 280µm, fabricated channels had appropriate dimensions for a range of microfluidic applications. A significant width of the laser processed channels provided 100% transmission for a wide range of the optical spectrum. These fabricated channels were also shown to not significantly retard the fluid flow rate thus making these channels applicable for integration into numerous detection systems for chemical separation applications.

Laser-assisted synthesis of ultrapure nanostructures for biological sensing applications

In the last decades, nanotechnology has converged various fields such physical, chemical and biological sciences to bring significant technological advancement. The potential of nanotechnology can be envisaged based on the fact that in the last two decades this technology has touched and revolutionized the research in the fields of electronics, computers, communications, defense, energy and medicine. Nanoparticles, in particular, are a class of nanomaterials which has drawn tremendous interest and advancement in its synthesis (chemical, physical or biological). In this work, a Pulsed laser ablation approach has been developed for the synthesis of ligand-free nanoparticles. Characterization techniques such as optical spectroscopy and Transmission Electron Microscopy (TEM) were combined with Dynamic Light Scattering (DLS) measurements. To further understand this synthesis technique, nanoparticle generation was studied as a function of height of liquid above ablation target. Additionally, systematic investigation was performed to study the effect of irradiation time on nanoparticle yield.