ABSTRACT
Collagen consists of three peptides twisted together through a periodic array of hydrogen bonds. Here we use this as inspiration to find design rules for programmed specific interactions for self-assembling synthetic collagenlike triple helices, starting from disordered configurations. The assembly generically nucleates defects in the triple helix, the characteristics of which can be manipulated by spatially varying the enthalpy of helix formation. Defect formation slows assembly, evoking kinetic pathologies that have been observed to mutations in the primary collagen amino acid sequence. The controlled formation and interaction between defects gives a route for hierarchical self-assembly of bundles of twisted filaments.
Subject(s)
Collagen/chemistry , Models, Chemical , Amino Acid Sequence , Models, Molecular , Nanostructures/chemistry , Peptides/chemistry , Protein Conformation, alpha-HelicalABSTRACT
Wireless neural stimulators are being developed to address problems associated with traditional lead-based implants. However, designing wireless stimulators on the sub-millimeter scale (<1 mm3) is challenging. As device size shrinks, it becomes difficult to deliver sufficient wireless power to operate the device. Here, we present a sub-millimeter, inductively powered neural stimulator consisting only of a coil to receive power, a capacitor to tune the resonant frequency of the receiver, and a diode to rectify the radio-frequency signal to produce neural excitation. By replacing any complex receiver circuitry with a simple rectifier, we have reduced the required voltage levels that are needed to operate the device from 0.5 to 1 V (e.g., for CMOS) to ~0.25-0.5 V. This reduced voltage allows the use of smaller receive antennas for power, resulting in a device volume of 0.3-0.5 mm3. The device was encapsulated in epoxy, and successfully passed accelerated lifetime tests in 80°C saline for 2 weeks. We demonstrate a basic proof-of-concept using stimulation with tens of microamps of current delivered to the sciatic nerve in rat to produce a motor response.
ABSTRACT
This paper offers a derivation of phase noise in oscillators resulting in a closed-form analytic formula that is both general and convenient to use. This model provides a transparent connection between oscillator phase noise and the fundamental device physics and noise processes. The derivation accommodates noise and nonlinearity in both the resonator and feedback circuit, and includes the effects of environmental disturbances. The analysis clearly shows the mechanism by which both resonator noise and electronics noise manifest as phase noise, and directly links the manifestation of phase noise to specific sources of noise, nonlinearity, and external disturbances. This model sets a new precedent, in that detailed knowledge of component-level performance can be used to predict oscillator phase noise without the use of empirical fitting parameters.
