Micro & Nanotech : Micromachining


Photoreceptor Scaffold for In Vitro Modeling and Transplantation Therapy

Using state-of-the-art microfabrication techniques, UW–Madison researchers have developed microstructured scaffold systems that can guide the growth of photoreceptor cells and mimic polarized outer retinal tissue. The scaffolds also may be used for transplantation of organized photoreceptor tissue with or without RPE.

Transplantation of photoreceptor-seeded scaffolds may improve grafted cell retention, survival, integration and functional visual rescue as compared to simple bolus injections. By recapitulating in vivo outer retinal architecture, these uniquely fabricated scaffolds also can be used for in vitro developmental and disease studies as well as drug screening.

The microfabrication process for scaffold production is fully compatible with numerous biomaterials, including biodegradable and non-biodegradable materials, thus allowing the scaffolds to be tailored to both in vitro and in vivo applications. The scaffolds feature biocompatible support layers (e.g., PDMS film) patterned with an array of unique through-holes having a curvilinear cell receiver and cell guide channels. The structure enables photoreceptors to be grown in a polarized orientation that mimics their development in vivo.

Smoother Surfaces with Pulsed Laser Polishing

UW–Madison researchers have developed a two-regime method to reduce rough surface features using a multiple-pass PLP approach.

In the first regime, melt pools are created on the surface using energy pulses, which generate higher temperatures where the beam is focused. Thermocapillary flow pulls down asperities into the melt pools. This can cause material to push up at the edge of the pools as they resolidify. A second regime applies different energy pulses to remove and/or rearrange the upwelled material.

Atmospheric Growth of Vertically Oriented Graphene

Researchers at the University of Wisconsin – Milwaukee have developed an atmospheric pressure based deposition method to produce vertically oriented graphene nanosheets, two-dimensional ‘graphitic’ platelets standing vertically on silicon, stainless steel and copper substrates. The resulting product shows increased surface area compared to traditional horizontally oriented graphene structures. Early data shows improved performance when compared to existing materials. Early research has shown the method to be amenable to continuous production.

Wear-Resistant Nanocrystalline Diamond Coating for Micro-End Mills and Other Micro-Cutting Tools

A team of UW-Madison engineers has developed a nanocrystalline diamond coating (NCD) to strengthen and improve the performance of existing tungsten carbide-containing micro-end mills and other micro-cutting tools. To apply the coating, the team first etched cobalt from the tool surface and seeded it with diamond powder composed of particles less than 50 nanometers in size. They then deposited an NCD coating on the surface by using the hot filament chemical vapor deposition process. In tests comparing the performance of NCD-coated and uncoated micro-end mills when cutting an aluminum alloy, the inventors found the coating greatly increases wear resistance, reduces adhesion of workpiece material to the tool, significantly reduces required cutting and thrust forces, and produces a cleaner, more uniformly machined workpiece.

Micro-Electro-Discharge Machining Using Semiconductor Electrodes

UW-Madison researchers have developed micromachined silicon electrode arrays for use in micro-electro-discharge machining of various materials, including metals. An array of multiple electrodes is fabricated in a single-crystal silicon wafer by using wet or dry anisotropic etching, doped to provide electrical conductivity, and optionally metal-coated to increase both conductivity and wear resistance. The silicon electrode array is consumed during use and disposed of after a single application; however, the low cost of producing the array and its capacity to provide “cookie cutter” micromachining of many parts simultaneously makes this technology an efficient and low cost alternative to conventional, serial micro-EDM.

Micromachined Scanning Thermal Probe

UW-Madison researchers have developed a micromachined scanning thermal probe with polyimide as its structural material and an embedded thin-film thermocouple as its temperature-sensing element. Probes are micromachined using a low-temperature, multimask process that can be easily integrated into a CMOS fabrication sequence, and contain a built-in scanning tip that is exposed by a unique flip-over assembly step at the end of processing.

Micro-Electro-Discharge Machining Method and Device

UW-Madison researchers have developed a micro-EDM technology that achieves high throughput micromachining by increasing both the spatial density of electrodes and the temporal density of electrical discharges. The device is composed of a LIGA-fabricated electrode array that sits atop a lithographically patterned thin film interconnect. The array achieves spatial parallelism in machining, while a pulse generation scheme exploiting the parasitic capacitance of the interconnect allows simultaneous discharge of electrodes to provide temporal parallelism.

Micromachined Strain Sensor

A UW–Madison researcher has developed a strain sensor that may be incorporated with other micromechanical and microelectronic devices to electronically monitor residual stress in these devices and packages.