Regina Lüttge

Silicon micromachined hollow microneedles for transdermal liquid transport

This paper presents a novel process for the fabrication of out-of-plane hollow microneedles in silicon. The fabrication method consists of a sequence of deep-reactive ion etching (DRIE), anisotropic wet etching and conformal thin film deposition, and allows needle shapes with different, lithography-defined tip curvature. In this study, the length of the needles varied between 150 and 350 micrometers. The widest dimension of the needle at its base was 250 /spl mu/m. Preliminary application tests of the needle arrays show that they are robust and permit skin penetration without breakage. Transdermal water loss measurements before and after microneedle skin penetration are reported. Drug delivery is increased approximately by a factor of 750 in microneedle patch applications with respect to diffusion alone. The feasibility of using the microneedle array as a blood sampler on a capillary electrophoresis chip is demonstrated.

The influence of nanoscale grooved substrates on osteoblast behavior and extracellular matrix deposition

To fight bone diseases characterized by poor bone quality like osteoporosis and osteoarthritis, as well as in reconstructive surgery, there is a need for a new generation of implantable biomaterials. It is envisioned that implant surfaces can be improved by mimicking the natural extracellular matrix of bone tissue, which is highly a organized nano-composite. In this study we aimed to get a better understanding of osteoblast response to nanometric grooved substrates varying in height, width and spacing. A throughput screening biochip was created using electron beam lithography. Subsequently, uniform large-scale nanogrooved substrates were created using laser interference lithography and reactive ion etching. Results showed that osteoblasts were responsive to nanopatterns down to 75 nm in width and 33nm in depth. SEM and TEM studies showed that an osteoblast-driven calcium phosphate (CaP) mineralization was observed to follow the surface pattern dimensions. Strikingly, aligned mineralization was found on even smaller nanopatterns of 50 nm in width and 17 nm in depth. A single cell based approach for real time PCR demonstrated that osteoblast-specific gene expression was increased on nanopatterns relative to a smooth control. The results indicate that nanogrooves can be a very promising tool to direct the bone response at the interface between an implant and the bone tissue.

Improved piercing of microneedle arrays in dermatomed human skin by an impact insertion method

An electrical applicator was designed, which can pierce short microneedles into the skin with a predefined velocity. Three different shapes of microneedles were used, namely 300 mum assembled hollow metal microneedle arrays, 300 mum solid metal microneedle arrays and 245 mum hollow silicon microneedle arrays. The latter are available as 4x4, 6x6 and 9x9 arrays. When using a velocity of 1 or 3 m/s reproducible piercing of dermatomed and full thickness human skin was evident from the appearance of blue spots on the dermal side of the skin after Trypan Blue treatment and the presence of fluorescently labeled particles in dermatomed skin. Manual piercing did not result in the appearance of blue spots. Transport studies revealed that i) piercing of microneedles with a predefined velocity into human skin resulted in a drastic enhancement of the Cascade Blue (CB, Mw 538) transport, ii) A higher piercing velocity resulted in a higher CB transport rate, iii) The CB transport rate was also dependent on the shape of the microneedles and iv) no difference in transport rate was observed between 4x4, 6x6 and 9x9 hollow silicon microneedle arrays.

Current advances in the fabrication of microneedles for transdermal delivery

The transdermal route is an excellent site for drug delivery due to the avoidance of gastric degradation and hepatic metabolism, in addition to easy accessibility. Although offering numerous attractive advantages, many available transdermal systems are not able to deliver drugs and other compounds as desired. The use of hypodermic needles, associated with phobia, pain and accidental needle-sticks has been used to overcome the delivery limitation of macromolecular compounds. The means to overcome the disadvantages of hypodermic needles has led to the development of microneedles for transdermal delivery. However, since the initial stages of microneedle fabrication, recent research has been conducted integrating various fabrication techniques for generating sophisticated microneedle devices for transdermal delivery including progress on their commercialization. A concerted effort has been made within this review to highlight the current advances of microneedles, and to provide an update of pharmaceutical research in the field of microneedle-assisted transdermal drug delivery systems.

The interaction between nanoscale surface features and mechanical loading and its effect on osteoblast-like cells behavior

Osteoblasts respond to mechanical stimulation by changing morphology, gene expression and matrix mineralization. Introducing surface topography on biomaterials, independently of mechanical loading, has been reported to give similar effects. In the current study, using a nanotextured surface, and mechanical loading, we aimed to develop a multi-factorial model in which both parameters interact. Mechanical stimulation to osteoblast-like cells was applied by longitudinal stretch in parallel direction to the nanotexture (300 nm wide and 60 nm deep grooves), with frequency of 1 Hz and stretch magnitude varying from 1% to 8%. Scanning electron microscopy showed that osteoblast-like cells subjected to mechanical loading oriented perpendicularly to the stretch direction. When cultured on nanotextured surfaces, cells aligned parallel to the texture. However, the parallel cell direction to the nanotextured surface was lost and turned to perpendicular when parallel stretch to the nanotexture, greater than 3% was applied to the cells. This phenomenon could not be achieved when a texture with micro-sized dimensions was used. Moreover, a significant synergistic effect on upregulation of fibronectin and Cfba was observed when dual stimulation was used. These findings can lead to a development of new biomimetic materials that can guide morphogenesis in tissue repair and bone remodeling.

Integrated Lithographic Molding for Microneedle-Based Devices

This paper presents a new fabrication method consisting of lithographically defining multiple layers of high aspect-ratio photoresist onto preprocessed silicon substrates and release of the polymer by the lost mold or sacrificial layer technique, coined by us as lithographic molding. The process methodology was demonstrated fabricating out-of-plane polymeric hollow microneedles. First, the fabrication of needle tips was demonstrated for polymeric microneedles with an outer diameter of 250 mum, through-hole capillaries of 75-mum diameter and a needle shaft length of 430 mum by lithographic processing of SU-8 onto simple v-grooves. Second, the technique was extended to gain more freedom in tip shape design, needle shaft length and use of filling materials. A novel combination of silicon dry and wet etching is introduced that allows highly accurate and repetitive lithographic molding of a complex shape. Both techniques consent to the lithographic integration of microfluidic back plates forming a patch-type device. These microneedle-integrated patches offer a feasible solution for medical applications that demand an easy to use point-of-care sample collector, for example, in blood diagnostics for lithium therapy. Although microchip capillary electrophoresis glass devices were addressed earlier, here, we show for the first time the complete diagnostic method based on microneedles made from SU-8.

In vitro and in vivo evaluation of the inflammatory response to nanoscale grooved substrates

The immune response to an implanted biomaterial is orchestrated by macrophages. In this study various nanogrooved patterns were created by using laser interference lithography and reactive ion etching. The created nanogrooves mimic the natural extracellular matrix environment. Macrophage cell culture demonstrated that interleukin 1β and TNF-α cytokine production were upregulated on nanogrooved substrates. In vivo subcutaneous implantation in a validated mouse cage model for 14 days demonstrated that nanogrooves enhanced and guided cell adhesion, and few multinucleated cells were formed. In agreement with the in vitro results, cytokine production was found to be nanogroove dependent, as interleukin 1β, TNF-α, TGF-β and osteopontin became upregulated. The results indicate that biomaterial surface texturing, especially at the nanometric scale, can be used to control macrophage activation to induce a wound healing response, rather than a profound inflammatory response. From the Clinical Editor: The authors investigate various nano-grooved patterns that mimic the natural extracellular matrix environment and demonstrate (both in macrophage cultures and in vivo) that interleukin 1β and TNF-α cytokine production is dependent upon surface texturing at the nanometric scale. They propose that modified surfaces may trigger macrophage activation to promote a wound healing response.

Massively parallel fabrication of repetitive nanostructures: nanolithography for nanoarrays

This topical review provides an overview of nanolithographic techniques for nanoarrays. Using patterning techniques such as lithography, normally we aim for a higher order architecture similarly to functional systems in nature. Inspired by the wealth of complexity in nature, these architectures are translated into technical devices, for example, found in integrated circuitry or other systems in which structural elements work as discrete building blocks in microdevices. Ordered artificial nanostructures (arrays of pillars, holes and wires) have shown particular properties and bring about the opportunity to modify and tune the device operation. Moreover, these nanostructures deliver new applications, for example, the nanoscale control of spin direction within a nanomagnet. Subsequently, we can look for applications where this unique property of the smallest manufactured element is repetitively used such as, for example with respect to spin, in nanopatterned magnetic media for data storage. These nanostructures are generally called nanoarrays. Most of these applications require massively parallel produced nanopatterns which can be directly realized by laser interference (areas up to 4 cm2 are easily achieved with a Lloyds mirror set-up). In this topical review we will further highlight the application of laser interference as a tool for nanofabrication, its limitations and ultimate advantages towards a variety of devices including nanostructuring for photonic crystal devices, high resolution patterned media and surface modifications of medical implants. The unique properties of nanostructured surfaces have also found applications in biomedical nanoarrays used either for diagnostic or functional assays including catalytic reactions on chip. Bio-inspired templated nanoarrays will be presented in perspective to other massively parallel nanolithography techniques currently discussed in the scientific literature.

The effect of nanometric surface texture on bone contact to titanium implants in rabbit tibia

Designing biomaterial surfaces to control the reaction of the surrounding tissue is still considered to be a primary issue, which needs to be addressed systematically. Although numerous in vitro studies have described different nano-metrically textured substrates capable to influence bone cellular response, in vivo studies validating this phenomenon have not been reported. In this study, nano-grooved silicon stamps were produced by laser interference lithography (LIL) and reactive ion etching (RIE) and were subsequently transferred onto the surface of 5 mm diameter Titanium (Ti) discs by nanoimprint lithography (NIL). Patterns with pitches of 1000 nm (500 nm ridge and groove, 150 nm depth), 300 nm (150 nm ridge and groove, 120 nm depth; as well as a 1:3 ratio of 75 nm ridge and 225 nm groove, 120 nm depth) and 150 nm (75 nm ridge and groove, 30 nm depth) were created. These samples were implanted in a rabbit tibia cortical bone. Histological evaluation and histomorphometric measurements were performed, comparing each sample to conventional grit-blasted/acid-etched (GAE) titanium controls. Results showed a significantly higher bone-to-implant contact at 4 weeks for the 300 nm (1:3) specimens, compared to GAE (p = 0.006). At 8 weeks, there was overall more bone contact compared to 4 weeks. However, no significant differences between the nano-textured samples and the GAE occurred. Further studies will need to address biomechanical testing and the use of trabecular bone models.

Microneedle-based drug and vaccine delivery via nanoporous microneedle arrays

In the literature, several types of microneedles have been extensively described. However, porous microneedle arrays only received minimal attention. Hence, only little is known about drug delivery via these microneedles. However, porous microneedle arrays may have potential for future microneedle-based drug and vaccine delivery and could be a valuable addition to the other microneedle-based drug delivery approaches. To gain more insight into porous microneedle technologies, the scientific and patent literature is reviewed, and we focus on the possibilities and constraints of porous microneedle technologies for dermal drug delivery. Furthermore, we show preliminary data with commercially available porous microneedles and describe future directions in this field of research.