Ablation of polymers and biological tissue by ultraviolet lasers

A mini-review on gene delivery technique using nanoparticles-mediated photoporation induced by nanosecond pulsed laser

Nanosecond pulsed laser induced photoporation has gained increasing attention from scholars as an effective method for delivering the membrane-impermeable extracellular materials into living cells. Compared with femtosecond laser, nanosecond laser has the advantage of high throughput and low costs. It also has a higher delivery efficiency than continuous wave laser. Here, we provide an extensive overview of current status of nanosecond pulsed laser induced photoporation, covering the photoporation mechanism as well as various factors that impact the delivery efficiency of photoporation. Additionally, we discuss various techniques for achieving photoporation, such as direct photoporation, nanoparticles-mediated photoporation and plasmonic substrates mediated photoporation. Among these techniques, nanoparticles-mediated photoporation is the most promising approach for potential clinical application. Studies have already been reported to safely destruct the vitreous opacities in vivo by nanosecond laser induced vapor nanobubble. Finally, we discuss the potential of nanosecond laser induced phototoporation for future clinical applications, particularly in the areas of skin and ophthalmic pathologies. We hope this review can inspire scientists to further improve nanosecond laser induced photoporation and facilitate its eventual clinical application.

Using Excimer Laser for Manufacturing Stimuli Responsive Membranes

A 248 nm KrF excimer laser can be used to manufacture temperature and pH-responsive polymer-based membranes for controlled transport applications. This is done by a two-step approach. In the first step, well-defined/shaped and orderly pores are created on commercially available polymer films by ablation by using an excimer laser. The same laser is used subsequently for energetic grafting and polymerization of a responsive hydrogel polymer inside the pores fabricated during the first step. Thus, these smart membranes allow controllable solute transport. In this paper, determination of appropriate laser parameters and grafting solution characteristics are illustrated to obtain the desired membrane performance. Fabrication of membranes with 600 nm to 25 μm pore sizes by using the laser through different metal mesh templates is discussed first. Laser fluence and the number of pulses need to be optimized to obtain the desired pore size. Mesh size and film thickness primarily control the pore sizes. Typically, pore size increases with increasing fluence and the number of pulses. Larger pores can be created by using higher fluence at a given laser energy. The vertical cross-section of the pores turns out to be inherently tapered due to the ablative action of the laser beam. The pores created by laser ablation can be grafted with PNIPAM hydrogel by using the same laser to perform a bottom-up grafting-from type pulsed laser polymerization (PLP) in order to achieve the desired transport function controlled by temperature. For this purpose, a set of laser frequencies and pulse numbers need to be determined to obtain the desired hydrogel grafting density and the extent of cross-linking, which ultimately provide controlled transport by smart gating. In other words, on-demand switchable solute release rates can be achieved by controlling the cross-linking level of the microporous PNIPAM network. The PLP process is extremely fast (few seconds) and provides higher water permeability above the lower critical solution temperature (LCST) of the hydrogel. Experiments have shown high mechanical integrity for these pore-filled membranes, which can sustain pressures up to 0.31 MPa. The monomer (NIPAM) and cross-linker (mBAAm) concentrations in the grafting solution need to be optimized in order to control the network growth inside the support membrane pores. The cross-linker concentration typically has a stronger effect on the temperature responsiveness. The pulsed laser polymerization process described can be extended to different unsaturated monomers, which can be polymerized by the free radical process. For example, poly(acrylic acid) can be the grafted to provide pH responsiveness to membranes. As for the effects of thickness, a decreasing trend is observed in the permeability coefficient with increasing thickness. Furthermore, the film thickness has little or no effect on PLP kinetics. The experimental results have shown that membranes manufactured by excimer laser are excellent choices for applications where flow uniformity is the prime requirement, as they possess uniform pore sizes and distribution.

A New Insight into High-Aspect-Ratio Channel Drilling in Translucent Dielectrics with a KrF Laser for Waveguide Applications

A new insight into capillary channel formation with a high aspect ratio in the translucent matter by nanosecond UV laser pulses is discussed based on our experiments on KrF laser multi-pulse drilling of polymethyl methacrylate and K8 silica glass. The proposed mechanism includes self-consistent laser beam filamentation along a small UV light penetration depth caused by a local refraction index increase due to material densification by both UV and ablation pressure, followed by filamentation-assisted ablation. A similar mechanism was shown to be realized in highly transparent media, i.e., KU-1 glass with a multiphoton absorption switched on instead of linear absorption. Waveguide laser beam propagation in long capillary channels was considered for direct electron acceleration by high-power laser pulses and nonlinear compression of excimer laser pulses into the picosecond range.

Experimental Analysis of Laser Micromachining of Microchannels in Common Microfluidic Substrates

Laser micromachining technique offers a promising alternative method for rapid production of microfluidic devices. However, the effect of process parameters on the channel geometry and quality of channels on common microfluidic substrates has not been fully understood yet. In this research, we studied the effect of laser system parameters on the microchannel characteristics of Polydimethylsiloxane (PDMS), polymethyl methacrylate (PMMA), and microscope glass substrate—three most widely used materials for microchannels. We also conducted a cell adhesion experiment using normal human dermal fibroblasts on laser-machined microchannels on these substrates. A commercial CO₂ laser system consisting of a 45W laser tube, circulating water loop within the laser tube and air cooling of the substrate was used for machining microchannels in PDMS, PMMA and glass. Four laser system parameters—speed, power, focal distance, and number of passes were varied to fabricate straight microchannels. The channel characteristics such as depth, width, and shape were measured using a scanning electron microscope (SEM) and a 3D profilometer. The results show that higher speed produces lower depth while higher laser power produces deeper channels regardless of the substrate materials. Unfocused laser machining produces wider but shallower channels. For the same speed and power, PDMS channels were the widest while PMMA channels were the deepest. Results also showed that the profiles of microchannels can be controlled by increasing the number of passes. With an increased number of passes, both glass and PDMS produced uniform, wider, and more circular channels; in contrast, PMMA channels were sharper at the bottom and skewed. In rapid cell adhesion experiments, PDMS and glass microchannels performed better than PMMA microchannels. This study can serve as a quick reference in material-specific laser-based microchannel fabrications.

Suturable elastomeric tubular grafts with patterned porosity for rapid vascularization of 3D constructs

Vascularization is considered to be one of the key challenges in engineering functional 3D tissues. Engineering suturable vascular grafts containing pores with diameter of several tens of microns in tissue engineered constructs may provide an instantaneous blood perfusion through the grafts improving cell infiltration and thus, allowing rapid vascularization and vascular branching. The aim of this work was to develop suturable tubular scaffolds to be integrated in biofabricated constructs, enabling the direct connection of the biofabricated construct with the host blood stream, providing an immediate blood flow inside the construct. Here, tubular grafts with customizable shapes (tubes, Y-shape capillaries) and controlled diameter ranging from several hundreds of microns to few mm are fabricated based on poly(glycerol sebacate) (PGS) / poly(vinyl alcohol) (PVA) electrospun scaffolds. Furthermore, a network of pore channels of diameter in the order of 100 µm was machined by laser femtosecond ablation in the tube wall. Both non-machined and laser machined tubular scaffolds elongated more than 100% of their original size have shown suture retention, being 5.85 and 3.96 N/mm2 respectively. To demonstrate the potential of application, the laser machined porous grafts were embedded in gelatin methacryloyl (GelMA) hydrogels, resulting in elastomeric porous tubular graft/GelMA 3D constructs. These constructs were then co-seeded with osteoblast-like cells (MG-63) at the external side of the graft and endothelial cells (HUVEC) inside, forming a bone osteon model. The laser machined pore network allowed an immediate endothelial cell flow towards the osteoblasts enabling the osteoblasts and endothelial cells to interact and form 3D structures. This rapid vascularization approach could be applied, not only for bone tissue regeneration, but also for a variety of tissues and organs.

Deep-ultraviolet laser ablation electrospray ionization mass spectrometry

A 193-nm wavelength deep ultraviolet laser was used for ambient laser ablation electrospray ionization mass spectrometry of biological samples. A pulsed ArF excimer laser was used to ablate solid samples, and the resulting plume of the desorbed material merged with charged electrospray droplets to form ions that were detected with a quadrupole time-of-flight mass spectrometer. Solutions containing peptide and protein standards up to 66-kDa molecular weight were deposited on a metal target, dried, and analyzed. No fragmentation was observed from peptides and proteins as well as from the more easily fragmented vitamin B12 molecule. The mass spectra contained peaks from multiply charged ions that were identical to conventional electrospray. Deep UV laser ablation of tissue allowed detection of lipids from untreated tissue. The mechanism of ionization is postulated to involve absorption of laser energy by a fraction of the analyte molecules that act as a sacrificial matrix or by residual water in the sample.

Effect of Process Parameters and Material Properties on Laser Micromachining of Microchannels

Laser micromachining has emerged as a promising technique for mass production of microfluidic devices. However, control and optimization of process parameters, and design of substrate materials are still ongoing challenges for the widespread application of laser micromachining. This article reports a systematic study on the effect of laser system parameters and thermo-physical properties of substrate materials on laser micromachining. Three dimensional transient heat conduction equation with a Gaussian laser heat source was solved using finite element based Multiphysics software COMSOL 5.2a. Large heat convection coefficients were used to consider the rapid phase transition of the material during the laser treatment. The depth of the laser cut was measured by removing material at a pre-set temperature. The grid independent analysis was performed for ensuring the accuracy of the model. The results show that laser power and scanning speed have a strong effect on the channel depth, while the level of focus of the laser beam contributes in determining both the depth and width of the channel. Higher thermal conductivity results deeper in cuts, in contrast the higher specific heat produces shallower channels for a given condition. These findings can help in designing and optimizing process parameters for laser micromachining of microfluidic devices.

Comparative Study of Different Techniques for the Sterilization of Poly-L-lactide Electrospun Microfibers: Effectiveness vs. Material Degradation

Electrospinning of biopolymeric scaffolds is a new and effective approach for creating replacement tissues to repair defects and/or damaged tissues with direct clinical application. However, many hurdles and technical concerns regarding biological issues, such as cell retention and the ability to grow, still need to be overcome to gain full access to the clinical arena. Interaction with the host human tissues, immunogenicity, pathogen transmission as well as production costs, technical expertise, and good manufacturing and laboratory practice requirements call for careful consideration when aiming at the production of a material that is available off-the-shelf, to be used immediately in operative settings. The issue of sterilization is one of the most important steps for the clinical application of these scaffolds. Nevertheless, relatively few studies have been performed to systematically investigate how sterilization treatments may affect the properties of electrospun polymers for tissue engineering. This paper presents the results of a comparative study of different sterilization techniques applied to an electrospun poly-L-lactide scaffold: soaking in absolute ethanol, dry oven and autoclave treatments, UV irradiation, and hydrogen peroxide gas plasma treatment. Morphological and chemical characterization was coupled with microbiological sterility assay to validate the examined sterilization techniques in terms of effectiveness and modifications to the scaffold.

The results of this study reveal that UV irradiation and hydrogen peroxide gas plasma are the most effective sterilization techniques, as they ensure sterility of the electrospun scaffolds without affecting their chemical and morphological features.

Light in diagnosis, therapy and surgery

Light and optical techniques have made profound impacts on modern medicine, with numerous lasers and optical devices being currently used in clinical practice to assess health and treat disease. Recent advances in biomedical optics have enabled increasingly sophisticated technologies — in particular those that integrate photonics with nanotechnology, biomaterials and genetic engineering. In this Review, we revisit the fundamentals of light–matter interactions, describe the applications of light in imaging, diagnosis, therapy and surgery, overview their clinical use, and discuss the promise of emerging light-based technologies.

Laser Writing Block Copolymer Self-Assembly on Graphene Light-Absorbing Layer

Recent advance of high-power laser processing allows for rapid, continuous, area-selective material fabrication, typically represented by laser crystallization of silicon or oxides for display applications. Two-dimensional materials such as graphene exhibit remarkable physical properties and are under intensive development for the manufacture of flexible devices. Here we demonstrate an area-selective ultrafast nanofabrication method using low intensity infrared or visible laser irradiation to direct the self-assembly of block copolymer films into highly ordered manufacturing-relevant architectures at the scale below 12 nm. The fundamental principles underlying this light-induced nanofabrication mechanism include the self-assembly of block copolymers to proceed across the disorder-order transition under large thermal gradients, and the use of chemically modified graphene films as a flexible and conformal light-absorbing layers for transparent, nonplanar, and mechanically flexible surfaces.

Resin-dentin bonding interface after photochemical surface treatment

OBJECTIVE

The aim of this study is to elucidate the structure of the resin-dentin interface formed by photochemical dentin treatment using an argon fluoride (ArF) excimer laser.

BACKGROUND DATA

The ArF excimer laser processes material by photochemical reaction without generating heat, while also providing surface conditioning that enhances material adhesion. In the case of bonding between resin and dentin, we demonstrated in a previous study that laser etching using an ArF excimer laser produced bonding strength comparable to that of the traditional bonding process; however, conditions of the bonding interface have not been fully investigated.

METHODS

A dentin surface was irradiated in air with an ArF excimer laser followed by bonding treatment. Cross sections were observed under light microscope, transmission electron microscope (TEM), and scanning electron microscope, then analyzed using an energy dispersive X-ray spectroscope (EDS): EDS line profiles of the elements C, O, Si, Cl, P, and Ca at the resin-dentin interface were obtained.

RESULTS

The density of C in resin decreased as it approached the interface, reaching its lowest level within the dentin at a depth of 2 μm from the resin-dentin interface on EDS. There was no hybrid layer observed at the interface on TEM. Therefore, it was suggested that the resin monomer infiltrated into the microspaces produced on the dentin surface by laser abrasion.

CONCLUSIONS

The monomer infiltration without hybrid layer is thought to be the adhesion mechanism after laser etching. Therefore, the photochemical processes at the bonding interface achieved using the ArF excimer laser has great potential to be developed into a new bonding system in dentistry.

Destruction of cancer cells by laser-induced shock waves: recent developments in experimental treatments and multiscale computer simulations

In this emerging area article we review recent progress in the mechanical destruction of cancer cells using laser-induced shock waves. The pure mechanical damaging and destruction of cancer cells associated with this technique possibly opens up a new route to tumor treatments and the corresponding therapies. At the same time progress in multiscale simulation techniques makes it possible to simulate mechanical properties of soft biological matter such as membranes, cytoskeletal networks and even whole cells and tissue. In this way an interdisciplinary approach to understanding key mechanisms in shock wave interactions with biological matter has become accessible. Mechanical properties of biological materials are also critical for many physiological processes and cover length scales ranging from the atomistic to the macroscopic scale. We argue that the latest developments and progress in experimentation enable the investigation of the shock wave interaction with cancer cells on multiple time- and length-scales. In this way the integrated use of experiment and simulation can address key challenges in this field. The exploration of the biological effects of laser-generated shock waves on a fundamental level constitutes an emerging multidisciplinary research area combining scientific methods from the areas of physics, biology, medicine and computer science.

Optimised laser microdissection of the human ocular surface epithelial regions for microarray studies

Background

The most important challenge of performing insitu transcriptional profiling of the human ocular surface epithelial regions is obtaining samples in sufficient amounts, without contamination from adjacent tissue, as the region of interest is microscopic and closely apposed to other tissues regions. We have effectively collected ocular surface (OS) epithelial tissue samples from the Limbal Epithelial Crypt (LEC), limbus, cornea and conjunctiva of post-mortem cadaver eyes with laser microdissection (LMD) technique for gene expression studies with spotted oligonucleotide microarrays and Gene 1.0 ST arrays.

Methods

Human donor eyes (4 pairs for spotted oligonucleotide microarrays, 3 pairs for Gene 1.0 ST arrays) consented for research were included in this study with due ethical approval of the Nottingham Research Ethics Committee. Eye retrieval was performed within 36 hours of post-mortem period. The dissected corneoscleral buttons were immersed in OCT media and frozen in liquid nitrogen and stored at −80°C till further use. Microscopic tissue sections of interest were taken on PALM slides and stained with Toluidine Blue for laser microdissection with PALM microbeam systems. Optimisation of the laser microdissection technique was crucial for efficient and cost effective sample collection.

Results

The starting concentration of RNA as stipulated by the protocol of microarray platforms was taken as the cut-off concentration of RNA samples in our studies. The area of LMD tissue processed for spotted oligonucleotide microarray study ranged from 86,253 μm² in LEC to 392,887 μm² in LEC stroma. The RNA concentration of the LMD samples ranged from 22 to 92 pg/μl. The recommended starting concentration of the RNA samples used for Gene 1.0 ST arrays was 6 ng/5 μl. To achieve the desired RNA concentration the area of ocular surface epithelial tissue sample processed for the Gene 1.0 ST array experiments was approximately 100,0000 μm² to 130,0000 μm². RNA concentration of these samples ranged from 10.88 ng/12 μl to 25.8 ng/12 μl, with the RNA integrity numbers (RIN) for these samples from 3.3 to 7.9. RNA samples with RIN values below 2, that had failed to amplify satisfactorily were discarded.

Conclusions

The optimised protocol for sample collection and laser microdissection improved the RNA yield of the insitu ocular surface epithelial regions for effective microarray studies on spotted oligonucleotide and affymetrix platforms.

Infra-red laser ablative micromachining of parylene-C on SiO2 substrates for rapid prototyping, high yield, human neuronal cell patterning

Cell patterning commonly employs photolithographic methods for the micro fabrication of structures on silicon chips. These require expensive photo-mask development and complex photolithographic processing. Laser based patterning of cells has been studied in vitro and laser ablation of polymers is an active area of research promising high aspect ratios. This paper disseminates how 800 nm femtosecond infrared (IR) laser radiation can be successfully used to perform laser ablative micromachining of parylene-C on SiO2 substrates for the patterning of human hNT astrocytes (derived from the human teratocarcinoma cell line (hNT)) whilst 248 nm nanosecond ultra-violet laser radiation produces photo-oxidization of the parylene-C and destroys cell patterning. In this work, we report the laser ablation methods used and the ablation characteristics of parylene-C for IR pulse fluences. Results follow that support the validity of using IR laser ablative micromachining for patterning human hNT astrocytes cells. We disseminate the variation in yield of patterned hNT astrocytes on parylene-C with laser pulse spacing, pulse number, pulse fluence and parylene-C strip width. The findings demonstrate how laser ablative micromachining of parylene-C on SiO2 substrates can offer an accessible alternative for rapid prototyping, high yield cell patterning with broad application to multi-electrode arrays, cellular micro-arrays and microfluidics.

Chitosan Gel Systems as Novel Host Materials for Optical Limiters

Two chitosan gel systems, chitosan/acetic anhydride and chitosan/glutaraldehyde, were studied as host materials for optical limiters. Both gels are transparent and have a very high laser damage threshold. The chitosan/acetic anhydride gel has a damage threshold > 540 J/cm2 while the chitosan/glutaraldehyde gel, which is slightly yellow in color, has a damage threshold > 600 J/cm2 (measurements made with 6.8 ns laser pulses at 532 nm). Different chromophore dopants, including porphyrin and CuPc, were tested. The optical limiting behavior of the guest/host gel systems was similar to their corresponding solution systems. The morphological structure of the gel systems was studied and the gelation process is discussed. Our current research explores the effect of gel morphology on the optical limiting properties of the chromophores and studies the relation between chromophores, cross-linking agents and the host materials. We have also investigated the relationship between optical properties and chemical structure of the gel/chromophore systems in order to optimize the optical behavior.

Novel Cell and Tissue Acquisition System (CTAS): microdissection of live and frozen brain tissues

We developed a novel, highly accurate, capillary based vacuum-assisted microdissection device CTAS - Cell and Tissue Acquisition System, for efficient isolation of enriched cell populations from live and freshly frozen tissues, which can be successfully used in a variety of molecular studies, including genomics and proteomics. Specific diameter of the disposable capillary unit (DCU) and precisely regulated short vacuum impulse ensure collection of the desired tissue regions and even individual cells. We demonstrated that CTAS is capable of dissecting specific regions of live and frozen mouse and rat brain tissues at the cellular resolution with high accuracy. CTAS based microdissection avoids potentially harmful physical treatment of tissues such as chemical treatment, laser irradiation, excessive heat or mechanical cell damage, thus preserving primary functions and activities of the dissected cells and tissues. High quality DNA, RNA, and protein can be isolated from CTAS-dissected samples, which are suitable for sequencing, microarray, 2D gel-based proteomic analyses, and Western blotting. We also demonstrated that CTAS can be used to isolate cells from native living tissues for subsequent recultivation of primary cultures without affecting cellular viability, making it a simple and cost-effective alternative for laser-assisted microdissection.

Can ultrasound enable efficient intracellular uptake of molecules? A retrospective literature review and analysis

Most applications of therapeutic ultrasound (US) for intracellular delivery of drugs, proteins, DNA/RNA and other compounds would benefit from efficient uptake of these molecules into large numbers of cells without killing cells in the process. In this study we tested the hypothesis that efficient intracellular uptake of molecules can be achieved with high cell viability after US exposure in vitro. A search of the literature for studies with quantitative data on uptake and viability yielded 26 published papers containing 898 experimental data points. Analysis of these studies showed that just 7.7% of the data points corresponded to relatively efficient uptake (>50% of cells exhibiting uptake). Closer examination of the data showed that use of Definity US contrast agent (as opposed to Optison) and elevated sonication temperature at 37°C (as opposed to room temperature) were associated with high uptake, which we further validated through independent experiments carried out in this study. Although these factors contributed to high uptake, almost all data with efficient uptake were from studies that had not accounted for lysed cells when determining cell viability. Based on retrospective analysis of the data, we showed that not accounting for lysed cells can dramatically increase the calculated uptake efficiency. We further argue that if all the data considered in this study were re-analyzed to account for lysed cells, there would be essentially no data with efficient uptake. We therefore conclude that the literature does not support the hypothesis that efficient intracellular uptake of molecules can be achieved with high cell viability after US exposure in vitro, which poses a challenge to future applications of US that require efficient intracellular delivery.

Effects of ArF excimer laser irradiation of dentin on the tensile bonding strength to composite resin

OBJECTIVE

The purpose of the study was to evaluate the effects of argon fluoride (ArF) excimer laser irradiation on the tensile bonding strength (TBS) of dentin to composite resin.

BACKGROUND DATA

Dental lasers use a photothermal process, which potentially entails risk of tissue damage caused by heat affecting the bond strength of resins. The ArF excimer laser functions by a photochemical process in which the energy of photons directly cuts covalent bonds in molecules without generating heat.

METHODS

Twenty extracted human molars were sectioned perpendicularly to the tooth axis to expose a flat dentin surface. The surfaces were treated with various combinations of ArF excimer laser irradiation, primer treatment, and bonding treatment. After composite resin was built up on the treated dentin surface, specimens with a 1×1 mm bonding interface were prepared and subjected to TBS tests. Treated dentin surfaces were also observed using transmission electron microscopy (TEM).

RESULTS

Specimens that underwent laser irradiation followed by bonding treatment had a TBS that did not differ significantly from that of specimens that received conventional treatment, with or without priming. TEM observations showed sectioned and dispersed collagen matrix in the hybrid layer after laser irradiation, priming, and bonding, but no hybrid layer after laser irradiation and bonding at the treated dentin surface.

CONCLUSIONS

The TBS of conditioning with ArF excimer laser irradiation was identical to that with conventional treatment when bonding was used. The bonding mechanism with the ArF irradiation differed from that of conventional bonding depending upon dentin hybridization.

Laser inactivation protein patterning of cell culture microenvironments

Protein micropatterned substrates have emerged as important tools for studying how cells interact with their environment, as well as allowing useful experimental control over, for example, cell shape and cell position on a surface. Here we present a new approach for protein micropatterning in which a focused laser is used to locally inactivate proteins on a protein-coated substrate. By translating the laser relative to the substrate, protein patterns of essentially arbitrary shape can be produced. This approach has a number of useful features. To begin, it is a maskless writing approach. Thus new patterns can be designed and implemented quickly. Laser inactivation can also be performed on a number of different substrate materials, ranging from glass to polydimethylsiloxane. Further, the inactivation is dose dependent, thus complex gradients and other non-uniform distributions of proteins can be produced. Because the focus of the laser can be changed quickly, laser-based patterning can also be applied to substrates with complex topographies or enclosed surfaces--as long as an optical path is available. To demonstrate this capability, protein patterns were made on the inside of small quartz capillary tubes. Patterned substrates produced using laser inactivation constrain cell shape in predictable ways, and we show that these substrates are compatible with a number of different eukaryotic cell lines.

Near-ultraviolet removal rates for subgingival dental calculus at different irradiation angles

The laser ablation rate of subgingival dental calculus irradiated at a 400-nm-wavelength, 7.4-mJ pulse energy, and 85- and 20-deg irradiation angles is measured using laser triangulation. Three-dimensional images taken before and after irradiation create a removal map with 6-μm axial resolution. Fifteen human teeth with subgingival calculus are irradiated in vitro under a cooling water spray with an ∼300-μm-diam, tenth-order super-gaussian beam. The average subgingival calculus removal rates for irradiation at 85 and 20 deg are 11.1±3.6 and 11.5±5.9 μm∕pulse, respectively, for depth removal and 4.5±1.7×10(5) and 4.8±2.3×10(5) μm(3)∕pulse, respectively, for volume removal. The ablation rate is constant at each irradiation site but varies between sites because of the large differences in the physical and optical properties of calculus. Comparison of the average depth- and volume-removal rates does not reveal any dependence on the irradiation angle and is likely due to the surface topology of subgingival calculus samples that overshadows any expected angular dependence.

In situ collagen polymerization of layered cell-seeded electrospun scaffolds for bone tissue engineering applications

Electrospun scaffolds have been studied extensively for their potential use in bone tissue engineering applications. However, inherent issues with the electrospinning approach limit the thickness of these scaffolds and constrain their use for repair of critical-sized bone defects. One method to increase overall scaffold thickness is to bond multiple electrospun scaffolds together with a biocompatible gel. The objective of this study was to determine whether multiple human adipose-derived stem cell (hASC-seeded electrospun, nanofibrous scaffolds could be layered via in situ collagen assembly and whether the addition of laser-ablated micron-sized pores within the electrospun scaffold layers was beneficial to the bonding process. Pores were created by a laser ablation technique. We hypothesized that the addition of micron-sized pores within the electrospun scaffolds would encourage collagen integration between scaffold layers, and promote osteogenic differentiation of hASCs seeded within the layered electrospun scaffolds. To evaluate the benefit of assembled scaffolds with and without engineered pores, hASCs were seeded on individual electrospun scaffolds, hASC-seeded scaffolds were bonded with type I collagen, and the assembled ∼3-mm-thick constructs were cultured for 3 weeks to examine their potential as bone tissue engineering scaffolds. Assembled electrospun scaffolds/collagen gel constructs using electrospun scaffolds with pores resulted in enhanced hASC viability, proliferation, and mineralization of the scaffolds after 3 weeks in vitro compared to constructs using electrospun scaffolds without pores. Scanning electron microscopy and histological examination revealed that the assembled constructs that included laser-ablated electrospun scaffolds were able to maintain a contracted structure and were not delaminated, unlike assembled constructs containing nonablated electrospun scaffolds. This is the first study to show that the introduction of engineered pores in electrospun scaffolds assists with multilayered scaffold integration, resulting in thick constructs potentially suitable for use as scaffolds for bone tissue engineering or repair of critical bone defects.

Laser direct writing of micro- and nano-scale medical devices

Laser-based direct writing of materials has undergone significant development in recent years. The ability to modify a variety of materials at small length scales and using short production times provides laser direct writing with unique capabilities for fabrication of medical devices. In many laser-based rapid prototyping methods, microscale and submicroscale structuring of materials is controlled by computer-generated models. Various laser-based direct write methods, including selective laser sintering/melting, laser machining, matrix-assisted pulsed-laser evaporation direct write, stereolithography and two-photon polymerization, are described. Their use in fabrication of microstructured and nanostructured medical devices is discussed. Laser direct writing may be used for processing a wide variety of advanced medical devices, including patient-specific prostheses, drug delivery devices, biosensors, stents and tissue-engineering scaffolds.

Gene expression analysis of neural cells and tissues using DNA microarrays

DNA microarrays pose specific challenges to those studying the central and peripheral nervous systems. Probably the most important involve difficulty in obtaining appropriate tissue for study, as well as the problems posed by cellular heterogeneity. This unit describes advances in the available technologies and provides protocols for cDNA microarray hybridization, including the use of PCR amplicons. Protocols are also provided for the two major methods for limiting cellular heterogeneity by study of RNA from single cell populations in high-throughput microarray studies, laser capture microdissection (LCM), and automated fluorescent cell sorting (FACS-array).

In-vivo optical imaging of hsp70 expression to assess collateral tissue damage associated with infrared laser ablation of skin

Laser surgical ablation is achieved by selecting laser parameters that remove confined volumes of target tissue and cause minimal collateral damage. Previous studies have measured the effects of wavelength on ablation, but neglected to measure the cellular impact of ablation on cells outside the lethal zone. In this study, we use optical imaging in addition to conventional assessment techniques to evaluate lethal and sublethal collateral damage after ablative surgery with a free-electron laser (FEL). Heat shock protein (HSP) expression is used as a sensitive quantitative marker of sublethal damage in a transgenic mouse strain, with the hsp70 promoter driving luciferase and green fluorescent protein (GFP) expression (hsp70A1-L2G). To examine the wavelength dependence in the mid-IR, laser surgery is conducted on the hsp70A1-L2G mouse using wavelengths targeting water (OH stretch mode, 2.94 microm), protein (amide-II band, 6.45 microm), and both water and protein (amide-I band, 6.10 microm). For all wavelengths tested, the magnitude of hsp70 expression is dose-dependent and maximal 5 to 12 h after surgery. Tissues treated at 6.45 microm have approximately 4x higher hsp70 expression than 6.10 microm. Histology shows that under comparable fluences, tissue injury at the 2.94-microm wavelength was 2x and 3x deeper than 6.45 and 6.10 microm, respectively. The 6.10-microm wavelength generates the least amount of epidermal hyperplasia. Taken together, this data suggests that the 6.10-microm wavelength is a superior wavelength for laser ablation of skin.

Laser-mediated microdissection for analysis of gene expression in synovial tissue

In experimental rheumatology, transcriptomics is one of the most important methods for investigating the pathogenesis of diseases. The biological material of most studies on rheumatoid arthritis has been bulk rheumatoid synovial tissues, but they are not suitable because they consist of several kinds of cells or structures. Laser-mediated microdissection (LMM) is a useful tool for isolating particular cells from tissue specimen to assess the functions of each cell. The LMM system employs a combination of a microscope and a laser-beam generator to cut out target areas on cryosections. Tissue compartments or even a single viable cell can be isolated using a non-focused laser beam without direct contact to avoid contamination, and this process is called laser pressure catapulting. An ultraviolet-A laser enables target cells to be procured without any influence on the surrounding. This technique has already been used in several studies in rheumatology, and its validity has been confirmed. Combined with other new techniques such as real-time quantitative polymerase chain reaction or microarray analysis, LMM is becoming more important in the analysis of gene expression in rheumatology.