Nanomedicine
Jonathan P. Rothstein
Mechanical and Industrial Engineering
University of Massachusetts
Amherst, MA, USA
Introduction
•
What is nanomedicine?
• It is nanotechnology used for the treatment, diagnosis, monitoring and control of
biological systems
• It includes the delivery and targeting of pharmaceutical, therapeutic, and diagnostic
agents using nanoparticles to cancer and other cells
• It includes nanomaterial for bone, cartilage,
vascular, bladder and neural applications
•
What isn’t nanomedicine?
• Flesh eating/repairing nanorobots
Introduction – Goals of Nanomedicine
•
End goal of nanomedicine is improved diagnostics, treatment and prevention of disease
• For a great review see http://www.wtec.org/nano2/Nanotechnology_Research_Directions_to_2020/
Introduction – Goals of Nanomedicine
•
Ultimate goal is to integrate detection, diagnostics, treatment and prevention of disease
into a personalized single platform
Introduction
•
Nanotechnology holds key to a number of recent and future breakthroughs in medicine
BioMEMS for Screening and Diagnostics
•
Goal is to develop handheld diagnostic devices
for personalized medical testing and treatment
Disposable Diagnostic
BioChip
Biomedical Analysis and
Communication System
BioMEMS – Micro and Nanofluidics
Nanoparticles for Pathogen Detection
Nanoparticle Probe
Targeted RNA
Fluorophore Release
• Gold nanoparticles can be functionalized with thiolated oligonucleatides.
• Bound to the oligonucleatides are fluorophores which are quenched by their proximity
to the nanoparticle.
• When the targeted RNA (H2N2, HIV or a cancer) bindes to the oligonucleatide, the
fluorophore is released and becomes fluorescence.
• The fluorescence can be detected in a BioMEMS device.
• Challenge is developing oligonucleatides with high selectivity for the target RNA.
Nanoparticles for Targeted Detection of Cancer
Breast Cancer Cells
Healthy Cells
• As an example, nanoparticle probes were developed by Chad Mirkin at Northwestern
Univ. that target the survivin RNA sequence known to exist in a certain breast cancers.
• Experiments are done ex-vivo.
• On the left, cancer cells fluoresce.
• On the right, healthy cells show minimal fluorescence.
Nanoparticles for In-vivo Detection of Pathogens
• Fluorescence is not a viable option in-vivo, but magnetic tagging works very well.
• Harmless virus can used as a building block to produce contrast agents that can be used in
Magnetic Resonance Imaging (MRI).
• Here, magnetic metal ions are bonded to the virus as are molecules that bind to cancer cells.
• A full body MRI scan detects these contrast agents and even very small tumors throughout
the body
Nanoparticle Encapsulation for Drug Delivery
•
Nanoparticle shells can be formed around spherical droplets
•
•
A.D. Dinsmore, et al., Science 298, 1006 (2002), Y. Lin, et al., Science 299, 226 (2003)
Shells are porous at lengthscales much smaller than size of nanoparticle.
A: Scanning electron microscope of a dried
10-μm-diameter colloidosome composed of
0.9- μm-diameter polystyrene spheres.
Why Particles Adsorb to Interfaces
[Pickering (1907); Pieranski PRL 45, 569 (1980)]
I. Particle (P) away from interface:
(Oil)
P
Interfacial Area = A
surface tension
Energy = AgO/W + 4pR2gP/O
(Water)
II. Particle sitting astride the interface (half-in, half-out):
Energy = (A-pR2)gO/W + 2pR2gP/O + 2pR2gP/W
• If |gP/O – gP/W| < gO/W/2, then adsorption reduces surface energy.
Nanoparticles At Interfaces
oil-nanoparticle
suspension,
w/ droplets
• Nanoparticles can be functionalized, cross linked or
sintered to make shell permanent, strengthen shell or
change shell permeability.
water droplet:
mm
to
mm
nm
Nano-Encapsulation for Drug Delivery
Drug Concentration in Patient
• By making the holes between nanoparticles approximately the same size as the
drug you want to administer you can get a constant release rate – avoids spikes in
dosage.
Standard Diffusion Based Drug Delivery
Nano-Encapsulated Drug Delivery
Time
• Can also allow encapsulation of hydrophobic drugs which are difficult to get into
you mostly water body.
Targeted Delivery to Tumors
• Goal is to inject treatment far from tumor and
have large accumulation in tumor and minimal
accumulation in normal cells/organs.
Cancer Treatments
• Tumor penetration is a key issue for successful chemotherapy
Nanoparticle use in Cancer Treatments
• Because of their small size, nanoparticles
can pass through interstitial spaces
between necrotic and quiescent cells.
• Tumor cells typically have larger
interstitial spaces than healthy cells
• Particles collect in center bringing
therapeutics to kill the tumor from inside
out.
Making Gold Nanoparticles
HAuCl4
HS
Na BH4
S S SS
S
S
S
S
S
S
S
S
SS
S S
HS
S S SS
S
S
S
S
S
S
S
S
SS
SS
HS
S S SS
S
S
S
S
S
S
S
S
SS
SS
HS
HS
HS
• AuCl4- salts are reduced using NaBH4 in the presence of thiol capping ligands
• The core size of the particles formed can be varied from <1 nm to ~ 8 nm
• The surface functionality can be controlled through the choice of thiols
• Diffusion speed can be controlled by length of thiols
Nanoparticles as Sensors and Therapeutics
• Glutathione (GSH) provides a selective and tunable release mechanism
• Once inside cells, fluorophores and drugs selectively dissociate
Nanoparticle Success
• Both cationic and anionic particles penetrate and accumulate in tumors.
• However, only cationic particles diffuse fully throughout the tumor.
• Work of Neil Forbes and Vince Rotello at UMASS
Nanoparticle Targeting and Accumulation
• To maximize their effectiveness, the microenvironment of the tumor must
be quantified and vectors developed to specifically target the tumor.
• These treatment approaches have shown great promise in mice.
Therapeutic
Accumulation (CFU/mg)
Necrotic
Quiescent
Proliferating
1,000,000
100,000
10,000
1,000
100
10
1
0
Tumo r
Liver
Spleen
Lungs
Heart
Skin
First Successful Nanomedicine - Abraxane
Alternatives to Nanoparticles - Surfactants
•
Surfactants are composed of a hydrophilic head and a long hydrophobic tail
•
When dissolved in water above the critical micellar concentration (CMC)
surfactants can self-assemble into large aggregate
•
Spherical micelles are around 10nm in size
•
Hydrophobic drugs can be encapsulated and in their core and delivered throughout
the body or to a specific target.
Nanotechnology in Tissue Engineering – Cartilage Replacement
•
Samuel Stupp at Northwestern has
shown that nanotechnology can be use to
regenerate severed spinal cords.
•
Two polypeptides amphiphiles are used
that when mixed in an aqueous solution
self assemble into a nanotube
•
As seen on right, these nanotubes display
peptide growth factors.
•
In mice, these systems have been shown
to promote axonal outgrowth and
bridging of injured areas (bottom right).
Nanotechnology in Tissue Engineering – Cartilage Replacement
•
Because cartilage doesn’t have vasculature and cannot repair itself, accepted treatments
have been mostly mechanical in their approach.
• Joint lubricants:
• Simple and effective at short-term pain relief but do not address cause of the
problem or repair any damage.
• Debridement/lavage/microfracture:
• Small lesions are repaired by shaving or shaping contour of cartilage.
• Microfracture penetrates subchondral plate (bone) and actually causes growth of
fibrocartilage – a lesser form, not desirable.
• Total joint replacement:
• Addresses problem and generally allows full repair, but
• Very invasive procedure, native tissue removed
• Prostheses do not last a lifetime in active patients.
• Nanotechnology approach
• Regrow patient’s own cartillage in-vivo to repair damage
www.hughston.com/hha/
ACT Methods
•
A popular tissue engineering approach has been to introduce new cells, via
autologous chondrocyte transplantation/implantation (ACT/ACI).
•
Some of the earliest work by Benya and Shaffer (1982) showed it was possible to
isolate and culture chondrocytes.
• More interesting result was that when cultured in vitro, the cells differentiated
and changed their phenotype to produce a lesser quality collagen.
• Need better tissue scaffolds – nanotech.
Important to tissue engineering:
Genzyme ACT method: FDA approved 1997
Cells will differentiate purely based
on mechanical stimulus.
biomed.brown.edu
Hydrogels – Self Assembly
•
Hydrogels have applications in drug delivery and tissue engineering
•
Regenerating cartilage and other tissue requires scaffolds with similar modulus and
other mechanical properties → Need to develop stiffer, tunable hydrogels
•
We investigated Polylactide-Polyethylene Oxide-Polylactide triblock copolymers.
•
Systems are biocompatible with a hydrophobic ends (PLA) and a hydrophilic center
(PEO) which self-assembles in water and can form a gel under the right conditions
Gelation
CMC
Triblock
Copolymer
Micelle
Gel
Reinforced
Through
Addition of
Nanoparticles
Rheology of Hydrogels
•
100000
Elastic Modulus (Pa)
10000
1000
The hydrogels formed are very stiff
with elastic modulus on the order of
1-10 kPa.
•
100
10
Within range of moduli of several
human tissues including cartilage.
1
72L
58L
72R
60R
0.1
0.01
0.001
0.0001
0.01
0.1
1
10
•
100
•
Frequency (Hz)
R-Lactide
Amorphous Core
L-Lactide
Crystalline Core
Gels formed from polymers with
higher degree of polymerization
maintain a high storage modulus even
at physiological temperatures (370C).
•
In-vivo applications feasible.
Rheological response of these
polymers can be easily tuned by
varying the crystallinity or block
length of PLA or through addition of
nanoparticles.
Khaled et al. Biomaterials (2003)
Photocrosslinking Hydrogels for Cartilage Replacement
•
An alternate approach is to make
the hydrogel from polymers that
can be crosslinked after injection.
•
•
From Jennifer Elisseeff’s lab
at Johns Hopkins University.
Photo-polymerizing the hydrogel
increases its modulus, allowing
the appropriate phenotype of
cartilage to be expressed and
protecting damaged area from
wear.
Keeping Things Clean – Antimicrobial Surfaces
•
Silver is an excellent anti-microbial agent
•
Silver nanoparticles are now being added to
fibers of clothing and bandages as well as
being incorporated into surfaces in hospitals to
reduce the rate of bacterial infections
•
When co-extruded with a polymer like PLLA,
the silver is released slowly over time and has
been shown to effectively kill bacteria