Nano-enabled biological tissues

clusters

Guided cell aggregation. COURTESY: “Modular tissue engineering: engineering biological tissues from the
bottom up”. Soft Matter, 5, 1312 (2009).

Nano-scale biofunctional surfaces
(cell membrane) http://www.nanowerk.
com/spotlight/spotid=12717.php

Flexible electronics
embedded in contact lens

Self-organized
collagen fibrils

Formation (above) and function
(below) of contractile organoids.
Biomedical Microdevices, 9, 149–
157 (2007).

DNA/protein sensor, example
of BioNEMS device (left).

“Bioprinting” to
construct a heart
(left).

biomaterial clusters

Single molecule monitoring
and bio-functionalization

Embedded and hybrid bionic devices

Self-assembled and
bioprinted organs

~ 1 nm

10-100 nm

1-100 μm

1-100 cm

1-100 mm

Soft Matter, 6,
1092-1110 (2010)

NanoLetters, 5(6),
1107-1110 (2005)

+ 1m

NanoBiotechnology, DOI: 10.1385/Nano:1:
2:153 (2005).

things better
than humans can design them.
* can use biological materials (silks)
or structures (synapses).
Biocompatibility: materials that do not interfere with biological function.
* compliant materials used to
replace skin, connective tissues.
* non-toxic polymers used to
prevent inflammatory response
in implants.

Polylactic Acid
Coating

Cyclomarin
Source

Hydroxyapatite
(Collagen)

Parylene
(Smart Skin)

voltage macroscale artificial skin”. Nature Materials, 2010.

“Tissue-Engineered Skin Containing Mesenchymal Stem Cells Improves Burn Wounds”. Artificial Organs, 2008.

Stem cells better than synthetic polymers (latter does not allow for vascularization).
* stem cells need cues to differentiate.
* ECM matrix, “niche” important.
* biomechanical structure hard to approximate.

Skin has important biomechanical, sensory functions (pain, touch, etc).
* approximated using electronics (nanoscale sensors embedded in a complex geometry).
* applied force, should generate electrophysiological-like signal.

from electronic skin, representation is close to pressure stimulus.
* only produces one class of sensory information (pressure, mechanical).
Q: does artificial skin replicate neural coding?
* patterned responses over time (rate-coding) may be possible.
* need local spatial information (specific to an area a few sensors wide).
* need for intelligent systems control theory at micro-, nano-scale.

Electronics. J. Rogers,
Nature Materials, 9, 511 (2010)

Nanoconfinement (Buehler group, MIT):
* confine material to a layer ~ 1nm thick (e.g. silk, water).
* confinement can change material, electromechanical properties.

Bio-integrated electronics (Rogers group, UIUC):
Silk used as durable, biocompatible substrate for implants, decays in vivo:
* spider web ~ steel (Young’s modulus).
* in neural implants, bare Si on tissue causes inflammation, tissue damage, electrical interference.
* a silk outer layer can act as an insulator (electrical and biological).

compliance in a device that requires electrical functionality?
* tissues need to bend, absorb externally-applied loads, conform to complex geometries, dissipate energy.
A: Flexible electronics (flexible polymer as a substrate).

Flexible e-reader

Flexible circuit board

Nano Letters, 3(10), 1353-1355 (2003)

Sparse network
of NTs.

Nano version (Nano Letters, 3(10), 1353-1355 - 2003):
* transistors fabricated from sparse networks of nanotubes, randomly oriented.
* transfer from Si substrate to flexible polymeric substrate.

properties.
Thin-film Transistors (TFTs):
* semiconducting, dielectric layers and contacts on non-Si substrate
(e.g. LCD technology).
* in flexible electronics, substrate is a compliant material (skeleton for electronic array).

PNAS, 102(35), 12321–
12325 (2005).

PNAS, 102(35), 12321–
12325 (2005).

Create a bendable array of pressure, thermal sensors.
Integrate them into a single device (B, C – on right).

Embedded array
of pressure and
thermal sensors

Conformal network of pressure sensors

form complex geometries?

PNAS 107(2),
565 (2010)

We can use nanopatterning as a substrate for cell monolayer formation.
* cells use focal adhesions, lamellapodia to move across surfaces.
* migration, mechanical forces an important factor in self-
organization, self-maintenance.

Gratings at
nanoscale dimensions

Alignment and protrusions w.r.t
nanoscale substrate

Letters, 5(6), 1107-1110 (2005).

Improvement in electrophysiology:
IPSCs (A) and patch clamp (B).

Neuronal density similar between CNTs and control.
* increase in electrical
activity due to gene expression, ion channel changes in neuron.

CNTs functionalized, purified, deposited on
glass (pure carbon network desired).

basic approaches to building tissues:
bottom-up: molecular self-assembly (lipids, proteins), from individual components into structures (networks, micelles).
2) top-down: allow cells to aggregate upon a patterned substrate (CNTs, oriented ridges, microfabricated scaffolds).

Nature Reviews Microbiology 5,
209-218 (2007).

Tissue Engineering: the scaffold”. Chapter 9.

Electrospinning procedure:
* fiber deposited on floatable table, remains charged.
* new fiber deposited nearby, repelled by still-charged, previously deposited fibers.
* wheel stretches/aligns fibers along deposition surface.
* alignment of fibers ~ guidance, orientation of cells in tissue scaffold.

Align nanofibers using electrostatic repulsion forces
(review, see Biomedical Materials, 3, 034002 - 2008).
Contact guidance theory:
Cells tend to migrate along orientations associated with chemical, structural, mechanical properties of substrate.

see review, Progress in
Materials Science, 53, 1101–1241 (2008).

Nature Nanotechnology,
3, 8 (2008).

Filament network, in vivo. PLoS ONE,
4(6), e6015 (2009).

Hierarchical Network Topology, MD simulations. PLoS ONE, 4(6), e6015 (2009).

α-helix protein networks in cytoskeleton withstand strains of 100-1000%.
* synthetic materials catastrophically fail at much lower values.
* due to nanomechanical properties, large dissipative yield regions in proteins.

conductance incrementally modified by controlling change, demonstrates short-term potentiation (biological synapse-like).

Nano Letters, 10, 1297–1301 (2010).

Nano Letters, 10, 1297–1301 (2010).

Memristor response

Biological Neuronal
response

Learning = patterned
(time domain) analog modifications at synapse (pre-post junction).

Array of pre-neurons (rows), connect with post-neurons (columns) at junctions.
* theory matches experiment!

in patterned fashion.
* 3D printers (rapid prototypers) can produce a complex geometry (see Ferrari,
M., “BioMEMS and Biomedical Nanotechnology”, 2006).

PNAS, 105(13), 4976 (2008).

Optical
Microscopy

Atomic
Microscopy

Sub-femtoliter (nano) inkjet printing:
* microfabrication without a mask.
* amorphous Si thin-film transistors (TFTs), conventionally hard to control features smaller than 100nm.
* p- and n-channel TFTs with contacts (Ag nanoparticles) printed on a substrate.