Patent Publication Number: US-2021187329-A1

Title: GHz-THz ULTRASONICS AND OPTICS FOR NEUROTECHNOLOGY DEVICES, METHODS, AND APPLICATIONS

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 62/675,973, filed on May 24, 2018 and entitled “GHz-THz Ultrasonics and Optics for Neurotechnology Devices, Methods, and Applications,” the entirety of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed generally to GHz-THz ultrasonic and optic devices in neurotechnology and, more particularly, to a neuro-cognitive system for interrogating and actuating neural tissue. 
     2. Description of Related Art 
     How the brain works and how it computes is a grand challenge for humanity to solve. Understanding the mind, its structure, and function will help us explain and cure diseases, such as cancer, Alzheimer&#39;s, Parkinson&#39;s, and other neurogenerative disorders. The knowledge of how the brain works also helps understand how the brain can compute very complex tasks with excellent efficiency. Research in the last several decades has provided scientists with a good understanding of how neurons work, particularly at the levels of a single neuron or small number of neurons. With the help of MRI (magnetic resonance imaging), there is also some knowledge of brain activity over a large volume at the time scale of seconds to minutes. What is now needed is new technology to bridge the significant gap in understanding between microscopic interactions at the neuronal level and the macroscopic structures that perform complex computations. 
     Impact of neurotechnology for discovery and therapeutics is limited by two major challenges. One challenge is the failure of electrical neural interfaces over long term, and the other is the lack of technology for non-invasive, localized excitation of axons and neurons with 5-resolution for nerve activation and healing using stem cell therapies. Electrical interfaces consisting of electrodes that sample neuron generated potentials and currents are regularly used in research, some even with RF-powered and RF-data linked implantable systems have been developed. However, the neural probes do not last beyond a few weeks to a few months, as tissue buildup on the electrodes insulates the signal flow, even with capacitive readout. The tissue buildup also limits the lifetime over which the electrodes can be used to excite neurons and axons. Deep-brain passivated stimulator electrodes have to be replaced every few years with life threatening surgical procedures. 
     Recent advances in optical imaging and optogenetics has led to a revolution in being able to measure and excite neural signals using optical beams through optical windows into the brain, and is an excellent tool for scientific studies of how the brain works. However, these systems require high laser power, suffer from limitations due to phototoxicity and penetration depth, and cannot be totally packaged inside the brain. Furthermore, optogenetics requires genetic modifications of brain that could be a major barrier for translation to human treatment. Hence, measuring neural signals without electrode degradation and exciting specific neurons and axons, with a completely implantable and label-free system, remains an unsolved problem. 
     Therefore, there is a need for a device and system for interrogating and actuating neural tissue. 
     Description of the Related Art Section Disclaimer: To the extent that specific patents/publications/products are discussed above in this Description of the Related Art Section or elsewhere in this disclosure, these discussions should not be taken as an admission that the discussed patents/publications/products are prior art for patent law purposes. For example, some or all of the discussed patents/publications/products may not be sufficiently early in time, may not reflect subject matter developed early enough in time and/or may not be sufficiently enabling so as to amount to prior art for patent law purposes. To the extent that specific patents/publications/products are discussed above in this Description of the Related Art Section and/or throughout the application, the descriptions/disclosures of which are all hereby incorporated by reference into this document in their respective entirety(ies). 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention are directed to a neuro-cognitive system for interrogating and actuating neural tissue. According to one aspect, the neuro-cognitive system includes a plurality of cognitive units and the cognitive units are connected. The system also includes a substrate having at least one surface and an electrode configured to detect an electrical output from at least one of the plurality of cognitive units. The system additionally includes a CMOS chip attached to the surface of the substrate and a plurality of transducers connected to the CMOS chip. Each of the plurality of transducers is configured to emit a phased ultrasonic beam which extends from the respective transducer toward the surface of the substrate. 
     According to another aspect, the present invention is a neuro-cognitive system. The system includes a plurality of cognitive units and the cognitive units are connected. The system also includes a CMOS chip having a top surface and a bottom surface, and a plurality of transducers connected to the CMOS chip. Each of the plurality of transducers is configured to emit an ultrasonic pulse to at least a portion of the plurality of cognitive units. 
     According to yet another aspect, the present invention is a method for reading an electrical output of one or more cognitive units. The method includes the steps of: (i) providing a neuro-cognitive system having a substrate with a top surface and a bottom surface, a microfluidic cavity within the top surface, an electrode extending into the microfluidic cavity, a CMOS chip attached to the bottom surface of the substrate, and a plurality of piezoelectric GHz transducers connected to the CMOS chip; (ii) placing one or more cognitive units into the microfluidic cavity, each of the one or more cognitive units having electrically excitable cells; (iii) emitting a phased ultrasonic beam from at least one of the plurality of piezoelectric GHz transducers, wherein the phased ultrasonic beam extends from the respective piezoelectric GHz transducer toward the top surface of the substrate; and (iv) detecting, via the electrode, the electrical output of at least one of the one or more cognitive units. 
     These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One or more aspects of the present invention are particularly pointed out and distinctly claimed as examples in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a perspective view schematic representation of a neuro-cognitive system, according to an embodiment; 
         FIG. 2  is an exemplary fixed phase array; 
         FIG. 3  is a perspective view schematic representation of a neuro-cognitive system, according to an alternative embodiment; 
         FIG. 4  is a perspective view schematic representation of the neuro-cognitive system of  FIG. 3  positioned on a nerve, according to an embodiment; 
         FIG. 5  shows graphs of the wavelength in water as a function of frequency and the 3 dB loss distance for ultrasonic plane waves as a function of frequency in water; 
         FIG. 6  is a diagram of data flow from the neuro-cognitive system to a control computer to create a neural network; 
         FIG. 7  is a diagram of a GHz sonar integrated onto CMOS for sonic beam scanning with 5-10 μm resolution; 
         FIG. 8  is a diagram of expansion of a neuron membrane due to action potential and graphs of Na+ and K+ ion variation and the resulting acoustic signals; and 
         FIG. 9  is a series of diagrams showing direction strain activation, radiation force, and acoustic streaming. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Aspects of the present invention and certain features, advantages, and details thereof, are explained more fully below with reference to the non-limiting examples illustrated in the accompanying drawings. Descriptions of well-known structures are omitted so as not to unnecessarily obscure the invention in detail. It should be understood, however, that the detailed description and the specific non-limiting examples, while indicating aspects of the invention, are given by way of illustration only, and are not by way of limitation. Various substitutions, modifications, additions, and/or arrangements, within the spirit and/or scope of the underlying inventive concepts will be apparent to those skilled in the art from this disclosure. 
     Referring now to the figures, wherein like reference numerals refer to like parts throughout,  FIG. 1  shows a perspective view schematic representation of a neuro-cognitive system  10 , according to an embodiment. In the depicted embodiment, the neuro-cognitive system  10  is microscale, having the following dimensions: 1-cm×1-cm×1-mm volume. In other embodiments, the depth of the neuro-cognitive system  10  has a thickness of 10 μm to 10 mm, preferably 100 μm to 1 mm; the length and width of the neuro-cognitive system  10  is within the range of 0.1 mm to 20 mm, preferably 1 mm to 10 mm. The neuro-cognitive system  10  is a substrate  12  comprising a top surface  14  and a bottom surface  16 . In an embodiment, the substrate  12  is composed of silicon. 
     The bottom surface  16  of the substrate  12  comprises a CMOS chip  18 . In the preferred embodiment, the CMOS chip  18  has RF CMOS technology, which uses RF for external powering and communication by RF wireless interlinks. As shown in  FIG. 1 , the CMOS chip  18  includes a metallization stack  20  and one or most transistors  22 . One or more piezoelectric thin film transducers  24  are connected to the metallization stack  20  of the CMOS chip  18 . In the depicted embodiment, the transducers  24  are GHz AlN transducers. Specifically, the transducers  24  are AlN piezoelectric GHz phased transducers capable of generating GHz ultrasonic waves, which can be phased to form narrow beams. In an embodiment, the CMOS chip  18  has a thickness of ˜500-700 μm, the thickness needed to allow beamforming to take place, which is enabled by the very low loss of GHz ultrasonic waves in a silicon substrate  12 . 
     Still referring to  FIG. 1 , each transducer  24  (e.g., piezoelectric AlN transducer stack) is connected to the metallization stack  20  of the CMOS chip  18 . In the depicted embodiment, the transistors  22  of the CMOS chip  18  are attached to the bottom surface  16  of the substrate  12 . Further, in the depicted embodiment, the plurality of transducers  24  are arranged in an array  26  on the CMOS chip  18 . The CMOS integrated sonic transducer arrays  16  can be tiny, 100×100 to 1000×1000 μm transducers  16  on a chip  18 , which is due to the small ultrasonic wavelength 9 μm at 1 GHz. The intensity of the pulse scales as I=½pc(N 2 Q 2 ω 2 V 2  d 33   2 ) where N is the number of elements, Q is that quality factor of each transducer  24  (˜4-5 for low-Q operation), ω is the resonance frequency, V is the voltage and d 33  is the piezoelectric coefficient. By going to higher frequencies (ω) in the above equation, one can achieve high intensities at much lower drive voltages.  FIG. 2  demonstrates this with a fixed phase array. A set of AlN transducers formed in a Fresnel lens configuration was fabricated to focus the sonic field on the opposing side of the wafer, achieving intensities of 2000 w/cm 2 . This is sufficient to tear apart and/or ablate neurons from the surface. Much lower intensities can be used to control the effect on synaptic strengths, as described below. 
     Referring back to  FIG. 1  the transducer array  26  ultimately generates narrow, pencil-like ultrasonic beams  28 . At 1-GHz frequency, the wavelength in a silicon substrate  12  is ˜9 μm, with each pixel of an array being 4.5×4.5 μm. The ultrasonic beams  28  are emitted by the transducers  24  toward the top surface  14  of the substrate  12 . As shown in  FIG. 1 , the top surface  14  of the substrate  12  comprises a microfluidic cavity  30 . The purpose of the microfluidic cavity  30  is for growing cells. The system  10  also includes a plurality of electrodes  32 . The electrodes  32  extend through the top surface  14  of the substrate  12 . Specifically, the electrodes  32  are electrical pads extending into the microfluidic cavity  30 . The electrical pads  32  are configured to read electrical output of objects in the microfluidic cavity  30 . Objects for placement in the microfluidic cavity  30  have electrically excitable cells. 
     Still referring to  FIG. 1 , the objects in the microfluidic cavity  30  are cognitive units  100 . A cognitive unit  100  can include a neuron, group of neurons, a nerve, group of nerves, and a node in a neural network. The cognitive units  100  can be connected to form a network. Each type of cognitive unit  100  is discussed below. In the embodiment shown in  FIG. 1 , each cognitive unit  100  is a neuron or a group (i.e., plurality) of neurons. Each neuron  100  includes one or more synapses  102 . The transducer array  26  can be driven by &lt;1V CMOS compatible voltage drive to achieve significant ultrasonic intensity to affect the neurons  100 . In the depicted embodiment, the neurons  100  are scanned with the pencil-like GHz ultrasonic beam  28  from the transducer array  26  to excite the synapses  102 , read cells, and form networks in the initial neural growth stage. The neurons  100  can also be read out using two-photon imaging. 
     Turning now to  FIG. 3 , there is shown a perspective view schematic representation of a neuro-cognitive system  10 , according to an alternative embodiment. In the depicted embodiment, a GHz AlN transducer  24  is integrated onto a CMOS chip  18  for sonic beam scanning with 1-5 um resolution. The CMOS chip  18  integrated with GHz sonic beam forming capabilities can interrogate and actuate neural tissue. As shown in  FIG. 3 , there is a 10×10 AlN array  26  of transducers  24  integrated on the CMOS chip  18 . 1-5 GHz ultrasonic transducers  24  can be integrated with the CMOS chip  18  and piezoelectric thin films based on two scaling laws—(1) GHz to THz piezoelectric thin films can be integrated onto CMOS chips  18 , and (2) the electronics needed to drive and sense the transducers  24  can be miniaturized and placed in the very same CMOS chips  18 . This enables generating ultrasonic pulse packets for on-chip communications. Such pulses have been used to image fingerprints with a 20 μm resolution. Phased array operation allows less than 2 μm resolution beams with 1-volt CMOS compatible voltages. 
     Referring now to  FIG. 4 , there is shown the neuro-cognitive system  10  positioned on a cognitive unit  100 , according to an embodiment. In the depicted embodiment, the cognitive unit  100  is a human nerve  104 . The CMOS integrated sonic transducer arrays  26  can be tiny, 100×100 to 1000×1000 μm chips, and can consist of RF coils  34  to for external powering and communicate by RF wireless interlinks, as shown in  FIG. 2 . These CMOS chips  18  can be placed at different locations in tissue and be used to transmit and measure ultrasonic wave packets. In the depicted embodiment, a thin film battery  36  is wirelessly connected to the RF coil  34 , powering the CMOS chip  18 . The CMOS chip  18  is placed on or up to ˜1 cm from the skin  106  near a nerve  104 . Due to the GHz-THz ultrasonic capabilities of the transducers  24  on the CMOS chip  18 , the absorption is high at such high frequencies, making fields penetrating only a few microns to even a few nanometers at THz. However, this feature can be used to confine the effects of the ultrasound to a small region near the transducer  24 , which can be analyzed using optical imaging. 
     Thus, in both embodiments ( FIGS. 1 and 3-4 ), the neuro-cognitive system  10  is a cyborg chip because it is part electronic, due to the CMOS chip  18 , and part biological, due to the neurons  100 . The purpose of the neuro-cognitive system  10  is to interrogate and actuate neural tissue. The system  10  can be used for cell growth control, neuromodulation, and using GHz ultrasonic beam  28  to extract action potentials on the top surface  14  and program synaptic weights. The data from the optics, electrodes, and ultrasonic pickups can be used to actuate and sense in the neural network formed by the neurons  100 . With a sufficient number of ultrasonic pixels, the focal point of the beam  28  can be narrow enough to focus an effect specific section of a neuron  100  to enhance or decrease synaptic weights owing to ultrasonic radiation forces and acoustic streaming. 
     By operating at GHz frequencies, sonic beams  28  are formed with 2-5 μm focal points ˜1-2 degree beam widths that can be used to interrogate and scan a neuron  100  such that specific sites of the neuron with specific synaptic connections can be exposed ( FIG. 5 ). Furthermore, energy decay in water and tissue at GHz frequencies is very high, allowing one to confine the GHz energy to within a few neurons to 100s of microns at 100 MHz. Hence, 0.1-10 GHz ultrasonics provides a good mechanism to investigate the effects of ultrasonics on neural preparations, providing sub neuron addressing, and depth-confined effects. In some embodiments, the transducers  24  have a frequency within the range of 0.1 to 500 GHz, preferably 1 GHz to 200 GHz, or 10 GHz to 200 GHz. In some embodiment, the energy is confined to have a precise sonic energy with a frequency within the range of 0.01 GHz to 20 GHz, preferably 0.1 GHz to 10 GHz, when the emitted energy reaching the biological samples (connected cognitive units) after decay. By exposing neurons  100  to just precise sonic energy, one can custom engineer neural connectivity using conventional stimulation mechanisms. These mechanisms include radiation force, acoustic streaming, direct straining of ion-channels, and potentially heat. Short terms neuromodulation effects may lead to short term effects, while longer term exposures may lead to genetic changes for cell differentiation. 
     The system  100  in  FIG. 1  can be used to form a desired network of cells, and then adjust synaptic weights between the connections of the cell network. Further, the system in  FIG. 1  can consist of thousands to millions of neurons  100  with 100-1000 synapses  102  per neuron  100 . The multi-dimensional inputs from optics, electrical readouts from the cells, and ultrasonic readouts form a large class of inputs that can be used to learn the variables of the neural network formed by the neural volume controlled by ultrasonic waves, as shown in  FIG. 6 . The neural network is composed of a plurality of cognitive units. In the embodiment of  FIG. 6 , each cognitive unit is a node in the neural network. In  FIG. 6  (left), optical data from imaging the top, electrical data, and ultrasonically measured potentials can be used to program the neural computing by adjusting the synaptic weights, and cell differentiation using the GHz sonic beams  28 . For example, data from optical imaging is transmitted to a control computer for use in creating a neural network and programming for cells. In  FIG. 6  (right), there is a multi-level deep neural network implemented using the multiple inputs and outputs applied to the brain-on-chip system  10 , shown in  FIG. 1 . 
     In an embodiment, a back-propagation or back-propagation like algorithm is implemented to program a biological neural network. The purpose of programing the system  10  is to make the system  10  generate a desired output neural activation (at pre-established output neurons) in response to a set of input stimuli. The electrical, optical, and ultrasonic data (received from ultrasonic reflected signals scanned over the neural formed layer to the silicon surface with incident sonic waves) will be interpreted by the computer program, which will in turn establish an ultrasonic beam protocol that will modify the weights to reduce the difference between present output and desired output. 
     In an embodiment for a method for stimulating, differentiating, positioning, and reading signals from neural cells, ultrasonic and acoustics are used with optical verification. Axons and neurons  100  will be placed on a surface  14  of a chip  18  with AlN (Aluminum nitride) piezoelectric thin film transducer arrays  26  (with high frequencies in the 100-200 GHz range), as shown in  FIG. 8 . The setup enables electrical isolation from the biological sample (e.g., neurons  100 ), connected only by the ultrasonic links from one surface  14  of the chip  18  to the opposite surface  16 . This enables the surface  14  facing the tissue to be independent of electrical interfaces that age over time. The piezoelectric transducers  24  generate sonic pulses, 50-70 ns in time duration, consisting of 30-40 1.3 GHz cycles. These pulses travel to the silicon substrate  12  and return back modified by the surface  14  reflection and absorption. 
     The neurons  100  and related axons are monitored optically on the top surface  14  of the ultrasonic chips  18 , while the ultrasonic and acoustic transducers  24  will be used to scan the surface  14  from the backside (or bottom surface  16 ). To quantify neural measurements and modulation, optical imaging is used, such as optical imaging of ion channel firing using optical labels, such Ca+ specific dyes. Other optical tools known in neural imaging can be used to image both single cell layers and tissue slices of up to 100-300 μm using two photon imaging. 
     The amplitude and phase of the return ultrasonic pulses from the neurons  100  will be used to detect action potential over a long time. Physical approaches include: (a) The neuron mass density variations and rigidity of the axons wall will generate sufficient ultrasonic impedance contrast to detect the cell on the transducers  24 , as shown in  FIG. 9 . The expansion and contraction of the neurons  100  would lead to changes in the surface boundary conditions in terms of increased contact area between the cells and the sensor surface  14 , and the applied pressure onto the surface  14 . The outputs of the ultrasonic imaging of neurons  100  will provide initial results necessary to show acoustic readout of action potentials using the theory of acoustic wave propagation associated with action potentials; (b) The variation of Na+ and K+ concentrations can change between 5-50 m Mol concentrations in small confined volumes, which can occur between neurons  100  and sensor surface  14 , as shown in  FIG. 9 . In preliminary data, shown in  FIG. 9 , ultrasonic absorption due to ion concentration changes can be detected using GHz sonic pulse reflections, as suggested by similar results of sonic absorption in sea-water; (c) The acoustic signals emitted from neurons  100  as pressure waves can be used to modify surfaces or actuate thin piezoelectric thin films transducers  24  with gaps to detect kHz signals. For this the AlN transducers  24  will be formed on thin membranes that act as microphones to detect sound generated by the neuron  100 . 
     Regarding neuromodulation, one or more GHz ultrasonic pixels can be phased in a way to add coherently on the tissue side such that the intensity of the ultrasound is enough to trigger effects that lead to neuromodulation. The acoustic intensity can be written as l=pcv p   2 =pcω 2  u p  where ρ is the density of water (˜1000 kg/m 3 ), c is the speed of sound (˜1500 m/s), v p  is the peak particle velocity, which is equal to ω 2  u p   2  where ω is the angular frequency, and u p  is the peak displacement of the sonic pulse. The peak displacement of a sonic pulse excited by one of the transducers can be estimated to be d 33 V where d 33  is the piezoelectric coefficient and V is the applied voltage, which is typically in the 1 to 3 volts range for CMOS compatibility. For N transducer phased to add up coherently in water, and assuming a focal point of approximately a wavelength, we estimate the strain in water to be 
     
       
         
           
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     which is ˜60*10 −6  for 1 GHz and one AlN transducer (N=1, d 33 ˜6*10 −12 C/N). 
     Mechanically induced strain on cellular membranes have been known to induce ion channel activation at 10-50μ-strain, indicating that there should be effects of the sonic beam on membrane ion channels seen. Since this strain is at a high frequency, and the mechanisms of the ion channels are likely to be nonlinear functions of applied strain owing to configurations of protein sub-assemblies that have nonlinear properties, the AC strain field is likely to be rectified to produce observable effects. In addition to direct strain, there may also be effects of radiation force, acoustic streaming. The radiation force 
     
       
         
           
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     can be very high owing to high absorption at GHz frequencies. Related to acoustic radiation forces is acoustic streaming induced by gradients in radiation forces that can excite fluid flow vortices, which in turn can cause shear stresses. In order to quantify the effect on modulation of action potential generation, optical measurements are relied on to independently verify action potentials. Optical Ca 2+  imaging will be used to measure the neural activity timed with US pulse excitation. The neural activity modulation will be quantified by varying the sonic field and frequency and correlating electrical, ultrasonic execution to electrical excitation. We plan on using an in vitro system that will allow us to characterize neuromodulation on the cellular level and build this up to a 3D cell culture system to show that we can localize effects of ultrasonic stimulation at varying depths from the transducer, using both multi-photon Ca 2+  imaging and electrode arrays with the ability to obtain readings from several micrometers in depth. In some embodiments, the depth is within the range of 1 to 1000 micrometers. 
     Regarding cell differentiation using ultrasonic forces, ultrasonic beams  28  can induce radiation forces and acoustic streaming on the transducer surface that can apply time-averaged DC mechanical stimuli to cells. GHz ultrasonic with smaller wavelengths will enable very tightly focused beams for excitation of cells at specific location enabling identification of mechanisms. It has been shown that the mechanical forces transmitted through the cells walls can activate proteins that can affect the nucleus by mechanical adhesion and pulling forces. Stem cells can be isolated from a cell culture using this technique of isolating cells via differences in cellular mechanics. Ultrasonics modifies surface adhesion in addition to forces on cells, as many studies have shown cells collecting at nodes of standing sonic waves. Stem cells that produce neural blastomas will be exposed to ultrasonic fields and be optically imaged for differentiation. There is the possibility for differentiation of cells and also the ability to distinguish the stage of differentiation of a cell using GHz ultrasonic exposure. Therefore, the experimental design takes place in two parts. 
     The first set of experiments being whether the interaction of cells with substrate can be detected, and subsequently biomechanics, using ultrasonic stimulation. The second part of experimentation will be to determine, using this biomechanics data, whether a cell has been differentiated after exposure to ultrasound. Cellular biomechanics has been investigated for a long time by using substrate interactions, a variety of force microscopy techniques, and optical trapping. Previous studies have shown the use of ultrasonics to create acoustic tweezers that can be used to deduce cellular forces. Using a similar approach, data can obtained that quantifies cellular response to ultrasonics, and by extension cellular mechanics, using optical techniques to connect this to differentiation. Then, on longer time scale, cells can be influenced with ultrasound and deduce whether cells can be differentiated, and do so in a localized manner, creating microenvironments of differentiated cells without having to rely heavily on microfluidics, much like many other studies that show in vitro differentiation and tissue engineering with complex structures defining differentiation factor compartments. In addition to this one mechanism of ultrasonic differentiation, ultrasound has been shown to influence cellular uptake, which means that cells influenced by ultrasound, due to similar mechanisms presented in  FIG. 10 , are likely to endocytose differentiation factors with a higher probability. 
     To base the observed results on hypothesis based on physical principles, and to explain phenomenological observations, analytical and COMSOL based finite element models of the transducers and interactions with biological tissue can be developed. FEM models of ion channels embedded in membranes will be simulated in COMSOL using nonlinear material models corresponding to those of tissue like materials. The sonic fields will interact with the models to allow computational verification of strain generated, radiation force, and acoustic streaming based on the velocity fields extracted from COMSOL. The FEM results can be verified from first order analytical models of ultrasonic absorption and field distribution based on piston models of the transducer in the fluids with varying degree of random heterogeneity owing to neurons distributed within tissue. 
     All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms. 
     While various embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, embodiments may be practiced otherwise than as specifically described and claimed. Embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the scope of the present disclosure. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as, “has” and “having”), “include” (and any form of include, such as “includes” and “including”), and “contain” (any form of contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a method or device that “comprises”, “has”, “includes” or “contains” one or more steps or elements. Likewise, a step of method or an element of a device that “comprises”, “has”, “includes” or “contains” one or more features possesses those one or more features, but is not limited to possessing only those one or more features. Furthermore, a device or structure that is configured in a certain way is configured in at least that way, but may also be configured in ways that are not listed. 
     The corresponding structures, materials, acts and equivalents of all means or step plus function elements in the claims below, if any, are intended to include any structure, material or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of one or more aspects of the invention and the practical application, and to enable others of ordinary skill in the art to understand one or more aspects of the present invention for various embodiments with various modifications as are suited to the particular use contemplated.