Richard Sherlock

Effect of functionalized micropatterned PLGA on guided neurite growth

When coaptation is not possible in the repair of nerve injuries, a bridge of biomaterial scaffold provides a structural support for neuronal cell growth and guides nerve regeneration. Poly(lactide-co-glycolide) (PLGA) scaffolds have been widely investigated for neural tissue engineering applications. In order to investigate guided neurite growth, we have fabricated micropatterns on PLGA films using laser ablation methods. The micropatterned PLGA films were coated with collagen type I or laminin peptide (PPFLMLLKGSTR) to promote axon growth. Micropatterned PLGA films provide a guidance effect on both early stage neurite outgrowth and elongation. Small (5 microm) grooves showed more statistically significant parallel neurite growth compared with larger size grooves (10 microm). Micropatterned PLGA films coated with laminin peptide showed more parallel neurite growth compared with those coated with collagen type I. Primary neurite number and total neurite length per cell decreased on micropatterned PLGA films compared with the controls. Neurites showed a preference for growth in the microgrooves rather than on the spaces. This study indicates that surface micropatterned structures with conjugated functional molecules can be used to guide neurite growth.

Osteoblasts response to microstructured and nanostructured polyimide film, processed by the use of silica bead microlenses

UNLABELLED The surface of polyimide films was modified by the use of silica microspheres as microlenses to focus radiation emitted by an excimer laser. The resultant surface had both microstructures and nanostructures. Physical and chemical characterization was performed by atomic force and Fourier transform-infrared microscopy. Laser processing resulted in surfaces that had similar roughness but different component frequencies. Chemical changes were not observed with the techniques used. The response of osteoblasts to the surface was assayed by measuring their metabolic activity and the enzyme alkaline phosphatase activity, after 24 hours of growth. Cytoskeleton and expression were both investigated. Metabolic activity was similar on treated and untreated samples. Total cell number and size were increased on microstructured polymer, where specific structures were observed (protrusions). Adhesion was noted, and the actin cytoskeleton showed normal morphology. Cells on nanostructured samples had a diffuse actin network and less mature adhesions as compared with the control. FROM THE CLINICAL EDITOR Polyimide films with microstructure and nanostructure surface elements were studied from the standpoint of osteoblast response. Total cell number and size were increased on microstructured polymer and protrusions were also observed. Adhesion was noted and the actin cytoskeleton exhibited normal morphology. Cells on nanostructured samples had a diffuse actin network and less mature adhesions.

Fabrication of a reusable microlens array for laser-based structuring

A microlens array optic was fabricated for laser surface microstructuring of polymer surfaces. The optic contains a hexagonal close-packed monolayer of SiO 2 microspheres, held together by an adhesive substance and supported on fused silica glass. The array is placed in direct contact with the target substrate and is exposed to UV light at a wavelength of 193 nm. During this exposure, the SiO 2 spheres act as microlenses, which focus the incoming laser light, but also enhance the optical near-field intensity underneath each microsphere. A large number of identical structures are produced simultaneously using this type of direct laser ablation, which leads to a highly efficient process. The ablated holes are approximately 1.8 μm in diameter, with a pitch of 8.4 μm and a depth of 80 nm. This microlens array has many advantages over other types of array, including the fact that it is inexpensive and easy to fabricate. An important feature is that it can transmit light at a wavelength less than 300 nm, which makes it suitable for laser surface patterning.

TEM investigation of laser-induced periodic surface structures on polymer surfaces

Laser Induced Periodic Surface Structures (LIPSS) may have numerous applications, ranging from biomaterial applications to LCDs, microelectronic fabrication and photonics. However, in order to control the development of these structures for their particular application, it is necessary to understand how they are generated. We report our work on investigating the melting that occurs during LIPSS formation. LIPSS were generated on three polymer surfaces - polyethylene terephthalate (PET), amorphous polycarbonate (APC) and oriented crystalline polycarbonate (OPC) - which were irradiated with a polarized ArF excimer laser (193 nm) beam with fluences between 3 and 5 mJ/cm2. The structures were imaged using a Transmission Electron Microscope (TEM), which facilitated investigation of changes in the polymer structures and consequently the depth of the melt zone that accompanies LIPSS generation. We also present theoretical calculations of the temperature-depth profile due to the interaction of the low fluence 193 nm laser beam with the polymer surfaces and compare these calculations with our experimental results.

Laser-based workstation for the manufacture of fused biconical tapered coupler devices

Fused biconic tapered (FBT) couplers are essential components in todays telecommunications networks where they are used for a number of different applications. The manufacturing process consists of aligning two adjacent fibres from which the buffer has been stripped, and subsequently heating and stretching them, creating an input taper, output taper either side of the fused coupling region. It is the coupling region where energy transfer between cores is possible; this gives the device its main characteristics, and the basic geometry can be used to create a range of devices such as 3 dB splitters, tap couplers, WDMs, etc. Low losses for these devices are achievable if made with reference to the adiabatic approximation. In this paper we report the development of a laser-based rig for the manufacture of couplers in which a CO2 laser replaces the gas torch typically used as a heat source in modern manufacturing processes. In addition to the use of a laser source, we describe the integration of advanced optical techniques and feedback mechanisms to improve the workstations reliability and flexibility. These characteristics should be advantageous for efficient manufacture of standard devices and novel devices for niche applications.

Cell growth on surface-modified medical polymers

Cellular reactions to implantable medical devices are dominated by the surface properties of materials from which the device is constructed. Consequently, in recent times much effort has been expended on modifying material surface properties to control bioactivity. We examine the effect of exposing surfaces to ultra-violet (UV) light from excimer lasers (λ = 193nm) in a room air environment. Working below the threshold of ablation, samples of nylon-12 and PET were treated. Physical and chemical studies of the surfaces following treatment demonstrated an increase in sample hydrophilicity, though no significant increases in roughness were recorded. Spectroscopic analyses revealed increased oxygen content in the surface layers while there were no chemical alterations in the bulk material. The assessment of in vitro interactions concerning the polymer samples and 3T3 fibroblast cells was conducted using cell counting, viability assays and a confocal microscopic analysis of cytoskeletal fluorescent staining. Results from cell counting and the viability tests confirmed that, subsequent to treatment, there was an increase in cell population on the surface, while improved spreading and activity was observed by confocal microscopy.

Rapid prototyping process based on the use of an intelligent pinhole mask and 193 nm excimer laser used to fabricate polymer microfluidic devices

Laser use for rapid prototyping of microfluidic devices has proven useful but can have certain drawbacks including variations in channel width, depth and shape when producing complex geometries. We describe our work on an advanced rapid laser prototyping technique, based on the use of an “intelligent pinhole” and 193 nm excimer laser. The pinhole, a dynamic mask, consists of four individually programmable blades and is controlled through a LabVIEW user interface. Each blade has the capability to be positioned with sub-micron repeatability with a response time on the order of 5 ms. Synchronization with the excimer laser software allows the fabrication of more complex microchannel layouts that are not possible with fixed mask techniques. Using the programmability of the pinhole we can eliminate some of the undesirable effects associated with scanning laser ablation, such as ramps leading into and out of microchannels and banking or undercutting effects at microchannel junctions and corners. The paper will demonstrate beam re-configuration techniques which allow the creation of zero lead-ins to microchannels and show the system’s potential to rapidly generate varying design iterations by fabricating a working microfluidic device and testing its application.Laser use for rapid prototyping of microfluidic devices has proven useful but can have certain drawbacks including variations in channel width, depth and shape when producing complex geometries. We describe our work on an advanced rapid laser prototyping technique, based on the use of an “intelligent pinhole” and 193 nm excimer laser. The pinhole, a dynamic mask, consists of four individually programmable blades and is controlled through a LabVIEW user interface. Each blade has the capability to be positioned with sub-micron repeatability with a response time on the order of 5 ms. Synchronization with the excimer laser software allows the fabrication of more complex microchannel layouts that are not possible with fixed mask techniques. Using the programmability of the pinhole we can eliminate some of the undesirable effects associated with scanning laser ablation, such as ramps leading into and out of microchannels and banking or undercutting effects at microchannel junctions and corners. The paper will d...

Excimer laser and lamp-based techniques applied to the nanostructuring of biomaterials

Bone-bonding implants include some of the commonest biomaterials currently used. The useful lifetimes of these materials are limited in part by the capacity of the material to support an intimate bond with the tissue in which they are implanted. A number of materials currently used have either good mechanical properties but poor biological responses, or have the ability to form suitable bonds with bone but lack the requisite strength, wear resistance, etc. In particular, polymeric materials have generally been shown to be inert with respect to bone. We report on our work on developing methods to surface treat polymers to encourage colonisation by bone, either for clinical implantation or in vitro tissue engineering applications. Polymers were treated by one of two methods; either 1) using an excimer laser to machine arrays of grooves in the surface; the periodicity of the grooves was varied from a few hundred nanometers to 10 μm; or 2) using an excimer lamp to affect the chemistry of the surface layer by breaking surface bonds and incorporating atmospheric oxygen. Surface structures of samples treated by method 1 were examined using Scanning Electron Microscopy (SEM), White Light Intereferometry and Atomic Force Microscopy (AFM) and surfaces of samples treated by method 2 were examined by using contact angle measurements which indicated a higher surface energy. The difference in cellular response to the control surfaces and modified surfaces was investigated. In conclusion, these methods provide viable means for altering polymers and may generate improved polymers for bone-bonding applications.