Fabrication of all-transparent polymer-based and encapsulated nanofluidic devices using nano-indentation lithography

In this paper,we describe a novel and simple process for the fabrication of all-transparent and encapsulated polymeric nanofluidic devices using nano-indentation lithography.First,a nanomechanical probe is used to‘scratch’nanoscale channels on polymethylmethacrylate(PMMA)substrates with sufficiently high hardness.Next,polydimethylsiloxane(PDMS)is used twice to duplicate the nanochannels onto PDMS substrates from the‘nano-scratched’PMMA substrates.A number of experiments are conducted to explore the relationships between the nano-indentation parameters and the nanochannel dimensions and to control the aspect ratio of the fabricated nanochannels.In addition,traditional photolithography combined with soft lithography is employed to fabricate microchannels on another PDMS‘cap’substrate.After manually aligning the substrates,all uncovered channels on two separate PDMS substrates are bonded to achieve a sealed and transparent nanofluidic device,which makes the dimensional transition from microscale to nanoscale feasible.The smallest dimensions of the achievable nanochannels that we have demonstrated thus far are of~20 nm depth and~800 nm width,with lengths extendable beyond 100μm.Fluid flow experiments are performed to verify the reliability of the device.Two types of colloidal solution are used to visualize the fluid flow through the nanochannels,that is,ethanol is mixed with gold colloid or fluorescent dye(fluorescein isothiocyanate),and the flow rate and filling time of liquid in the nanochannels are estimated based on time-lapsed image data.The simplicity of the fabrication process,bio-compatibility of the polymer substrates,and optical transparency of the nanochannels for flow visualization are key characteristics of this approach that will be very useful for nanofluidic and biomolecular research applications in the future.

Rapid nanomolding of nanotopography on flexible substrates to control muscle cell growth with enhanced maturation

In vivo,multiple biophysical cues provided by highly ordered connective tissues of the extracellular matrix regulate skeletal muscle cells to align in parallel with one another.However,in routine in vitro cell culture environments,these key factors are often missing,which leads to changes in cell behavior.Here,we present a simple strategy for using optical media discs with nanogrooves and other polymer-based substrates nanomolded from the discs to directly culture muscle cells to study their response to the effect of biophysical cues such as nanotopography and substrate stiffness.We extend the range of study of biophysical cues for myoblasts by showing that they can sense ripple sizes as small as a 100 nm width and a 20 nm depth for myotube alignment,which has not been reported previously.The results revealed that nanotopography and substrate stiffness regulated myoblast proliferation and morphology independently,with nanotopographical cues showing a higher effect.These biophysical cues also worked synergistically,and their individual effects on cells were additive;i.e.,by comparing cells grown on different polymerbased substrates(with and without nanogrooves),the cell proliferation rate could be reduced by as much as~29%,and the elongation rate could be increased as much as~116%.Moreover,during myogenesis,muscle cells actively responded to nanotopography and consistently showed increases in fusion and maturation indices of~28%and~21%,respectively.Finally,under electrical stimulation,the contraction amplitude of well-aligned myotubes was found to be almost 3 times greater than that for the cells on a smooth surface,regardless of the substrate stiffness.