High-fidelity replication of thermoplastic microneedles with open microfluidic channels

Development of microneedles for unskilled and painless collection of blood or drug delivery addresses the quality of healthcare through early intervention at point-of-care.Microneedles with submicron to millimeter features have been fabricated from materials such as metals,silicon,and polymers by subtractive machining or etching.However,to date,large-scale manufacture of hollow microneedles has been limited by the cost and complexity of microfabrication techniques.This paper reports a novel manufacturing method that may overcome the complexity of hollow microneedle fabrication.Prototype microneedles with open microfluidic channels are fabricated by laser stereolithography.Thermoplastic replicas are manufactured from these templates by soft-embossing with high fidelity at submicron resolution.The manufacturing advantages are(a)direct printing from computeraided design(CAD)drawing without the constraints imposed by subtractive machining or etching processes,(b)high-fidelity replication of prototype geometries with multiple reuses of elastomeric molds,(c)shorter manufacturing time compared to three-dimensional stereolithography,and(d)integration of microneedles with open-channel microfluidics.Future work will address development of open-channel microfluidics for drug delivery,fluid sampling and analysis.

High-resolution two-photon polymerization:the most versatile technique for the fabrication of microneedle arrays

Microneedle patches have received much interest in the last two decades as drug/vaccine delivery or fluid sampling systems for diagnostic and monitoring purposes.Microneedles are manufactured using a variety of additive and subtractive micromanufacturing techniques.In the last decade,much attention has been paid to using additive manufacturing techniques in both research and industry,such as 3D printing,fused deposition modeling,inkjet printing,and two-photon polymerization(2PP),with 2PP being the most flexible method for the fabrication of microneedle arrays.2PP is one of the most versatile and precise additive manufacturing processes,which enables the fabrication of arbitrary three-dimensional(3D)prototypes directly from computer-aided-design(CAD)models with a resolution down to 100 nm.Due to its unprecedented flexibility and high spatial resolution,the use of this technology has been widespread for the fabrication of bio-microdevices and bio-nanodevices such as microneedles and microfluidic devices.This is a pioneering transformative technology that facilitates the fabrication of complex miniaturized structures that cannot be fabricated with established multistep manufacturing methods such as injection molding,photolithography,and etching.Thus,microstructures are designed according to structural and fluid dynamics considerations rather than the manufacturing constraints imposed by methods such as machining or etching processes.This article presents the fundamentals of 2PP and the recent development of microneedle array fabrication through 2PP as a precise and unique method for the manufacture of microstructures,which may overcome the shortcomings of conventional manufacturing processes.