Nanoparticles Flashcards
Nanoparticle (definition, why it’s useful in science)
Definition:
A particle with at least one dimension <100nm
Use in science:
-Nanoparticles are of great scientific interest as they are effectively a bridge
between bulk materials and atomic or molecular structures
-On the same scale as proteins, molecules, etc that the cell is used to seeing
-In engineering nanoparticles can add different coats etc to control how they react in body
Properties of nanoparticles compared to bulk that change and examples (6)
Bulk materials have constant physical properties, but at the nano-scale, size-dependent properties occur
-Optical (ex. gold NPs are the cause of colours in stained windows)
-Electronic (ex. quantum dots)
-Magnetic (ex. superparamagnetism occurs in which individual magnetic domains arise that align in a magnetic field and collapse when taken away)
-Mechanical (ex. carbon nanotube is stronger than steel)
-Thermal
-Chemical (ex. As particle size decreases, the surface area : volume ratio increases.
-Can attach a lot more to nanoparticles.
-Surface atoms tend to have more unsatisfied bonds, with a higher surface energy. They want to achieve surface
stabilisation, therefore readily interact, adsorb & react with other atoms.
This causes them to be more reactive to certain other molecules
In body it will readily react with blood, tissue, cells, etc which may not aligned with desired outcome (specific targeting is goal)
Types of Nanoparticles
Natural : pollen,
spores (anthrax)
etc. Breathed into body and have adverse effects
Environmental : pollution & industry (ex. diesel can make carbon black and when it reacts with other chemicals in exhaust pipe will coat itself in toxins. Can interfere with testosterone production, reducing fertility)
Engineered : nanotubes &
nanowires, nanoparticles (ex. can add different coats etc to control how they react in body)
Cell uptake of NPs: importance, how, what dictates this, properties to influence/alter
Many applications of NPs rely on cells uptaking lots of NPs. Ex. in MRI, imaging is better with more NPs uptaken by cells
The process is dynamic and complicated but 3 things are involved in a cells uptake
CELL MEMBRANE
Need to understand stiffness and the specific and nonspecific interactions with membranes,
ligand-receptor affinity.
3 methods that cell uptakes particles
-Clathrin-mediated endocytosis (~120nm)
Clathrin initiates the formation of a vesicle at the cell surface which buds off and internalises the particles (major route of all cellular uptake)
-Caveolin-mediated endocytosis (~ 60 nm)
Small pits in the membrane that resemble pits
-Macropinocytosis (> 1 μm)
Cell engulfs larger volumes of extracellular fluids and particles through the actin cytoskeleton forming larger vesicles
NP CHARECTERISTICS
Influencing cell uptake:
The nano-bio interface between NP and cell govern cellular
internalisation.
The properties of NPs that affect their nano-bio interface are charge, elasticity, shape, size, surface modifications (ex. antibodies, small molecules), hydrophobicity, etc
Research: Experimental analysis and mathematical models for theoretical (simulation) analysis to predict effect of altering a property
PHYSIOCHEMICAL PROPERTIES OF SURROUNDING MEDIA
When designing the NP, should consider the properties of the blood/synovial fluid in joints, etc
pH, ionic strength,
presence of biological material
(protein, lipoids etc)
How nanoparticles may enter and exit body and what dictates this
Enter:
-Inhalation; inhaled in lungs down bronchioles into alveoli in which gas exchange occurs. Enter bloodstream (ex. pollen)
-Ingestion (ex. nail biting)
-Skin; small enough to pass transdermal membrane (ex. nicotine patch)
Exit:
Localisation depends on size
* Kidney (<5 nm). Urinated
* Lung (>100 nm). Coughed out
* Liver (20-100 nm). Metabolised into smaller
* Spleen (>20 nm). Metabolise and collect
Everyday applications of NPs
-Iridescent colours in makeup eyeshadow
-Silver NPs are toxic to bacteria so developed for better antibiotics due to rise in resistance (ex. in plasters and paint in hospital walls)
-Carbon nanotube (roll of graphite) adds strength to sports equipment
-Titanium/Zinc oxide in sunscreen
Examples of ways to engineer/design NP
NP sphere core that can vary in size, shape and material:
-Metal-based : e.g. gold or iron oxide.
-Semiconductor nanocrystal quantum dots (very fluorescent)
-Silica-based : highly biological compatibility
-Carbon-based (hollow spheres or tubes)
Coat with:
-Drug/nucleic acid (deliver treatment to cells)
-Ligand/antibody (for targeting, ex. cancer cell)
-Fluorescent dye (visualise the NP with fluorescent microscopy)/radioisotope (radiotherapy for cancer cells)
-polyethylene glycol (PEG) for biocompatibility (reduce aggregation of core) and in blood it won’t be recognised as foreign and ignored by immune cells (increase half life in bloodstream)
- Peptides/polymer to increase cell uptake
Benefits of metal based NP
Iron, nickel or cobalt core:
Can manipulate under a magnetic field (float in bloodstream but when you apply magnet and direct localisation)
Gold core:
-Easy and cheap to synthesise and get variety of shapes and sizes
-Intense colour change dependent on size (smaller is more purple)
-Easy to visualise since they absorb and scatter light via surface plasmon resonance)
-Inert
Engineered NP Applications
-Cell labelling (magnetic cell sorting) & Bioimaging (MRI)
Magnetic cell sorting:
Coat magnetite/magnemite NP in antibodies/ligands specific for cell surface receptor (ex. STRO1 for MSCs) that will label cells.
Labelled cells are separated and migrate to walls of tube when magnetic field is applied (positive selection or negative selection)
MRI: iron oxide contrast agent to obtain clearer image for more accurate diagnosis
Ex. select for the MSC and HSC in bone marrow of femur ball and socket joint obtained from hip replacement surgery
-Cell imaging
Coat gold NP (2-5 nm) with antibody for a protein on cell
Can use at low and high resolution imaging (light fluorescence and electron microscopy) to map protein
Useful in research
-Malignant Hyperthermia for targeted cancer treatment
-Targeted Drug Delivery & Gene Therapy (nuclear targeting)
How an MRI works and application of NPs here
Patient is injected with an iron oxide contrast agent to obtain clearer image for more accurate diagnosis
Scanner consists of a strong magnet (1.5-3 Tesla)
Tissues and fat are primarily water and water contains lots of protons
Protons spin with varied alignment and in a magnet field they align with it. When the magnetic field is removed they relax. The spin relaxation time (T1; longitudinal and T2; transverse) is how long it takes the protons to relax when the magnetic field is repeated turned on and off (radiofrequency current pulse)
Protons from different tissues react differently, giving different T1 and T2 values. This can generate a
picture of anatomical structures since they’ll appear different in MRI images
Contrast agents diffuse through body based on size so alter the NP size based on which tissue you want to image (ex. smaller NPs clear out slower in blood, tumours have enhanced uptake for NPs 30-200 nm and due to the large number of leaky vasculature there’s rapid accumulation)
Janus (Roman two faced god) particle:
A composite micro or nano-scale particle with multiple parts each with distinct chemical or physical properties
Ex. Half of the core is iron allowing magnetic imaging, but half is gold allowing wider range of ligands that can be fused for targeting to a cell/tissue type
Ideal NP properties to increase cell uptake
Interdiscinplinary approach is required to make smart NPs. Use of physicists, material engineers, chemists, biologists, etc generate NP with ideal core, coating of chemical and biological compounds for desired purpose
Size
40-100nm is small enough to enter via endocytosis but large enough to avoid rapid clearance by immune system
Larger particles are slower to uptake
Shape
Cells prefer spheres since it allows it to hit the cell membrane in a way to optimise ligand-receptor interaction
Spheres then cubes have fastest uptake and lowest membrane bending energies (minimises stress and strain on the membrane)
Asbestos is a long thing jagged fibre that ruptures cell membrane
Charge
Cell membranes have an overall negative charge
Positively charged NPs form electrostatic interactions so have increased cell uptake
Ligands
Use of ligands the cell responds well to
Ex. RGD encourages cell uptake (small, cheap, easy to work with, readily binds engineered material)
Ex. Transferrin is a large blood protein native to cell (so it will respond well to it) that interacts with iron so can coat iron particle with it to encourage uptake. RGD is less bulky so prefered
How engineered NPs can be used in cancer therapy, why, and how to optomise
Malignant Hyperthermia
Goal in cancer treatment is preferential killing of cancer cells without damaging healthy cells
Current treatments include:
-Chemotherapy (affects/damages liver, kidney, heart, nerves, loss of fertility)
-Radiotherapy (generic cell destruction, breathing difficulties, loss of fertility)
-Cancer drugs (high blood pressure, sickness, diarrhoea, numbness, loss of fertility)
-Surgery (painful, unsuitable for deep tissue cancers)
Cells are sensitive to high temperature and cancer cells have poor recovery (sensitive to >41°C) due to disorganised vasculature (from fast growth) causing poorer heat dissipation so it’s retained longer
Whole body, regional or localised hyperthermia used at present, however it is not very targeted to tumours so use ex. IV injection of magnetic NPs with biocompatible PEG-PCL coating
Use of NPs as nanoheaters is a targeted effective treatment with very quick onset:
-Iron NPs under a radiofrequency pulse and alternating magnetic field, generates heat energy from magnetic energy:
Neel relaxation: the movement of many particles in and out of alignment
Brownian motion: increases under magnetic field
Can induce tumour cell death from localised heating (additionally, heat induces increase in ROS which is detrimental to cell)
-Gold NPs for noninvasive photodynamic therapy
Heat is generated from exciting electrons with light causing them to oscillate, and thus forming surface plasmon resonance.
Shifting of electron clouds causes heat
Fast (secs, not mins like iron oxide)
Optomise:
-Smart NPs
Interdisciplinary approach is required to make smart NPs. Use of physicists, material engineers, chemists, biologists, etc generate NP with ideal core, coating of chemical and biological compounds for desired purpose
Here can attach chemotherapeutic (potentiate effect) or chemical that increases cancer cell’s effect to radiation, attached to NP via chemistry that has a heat induced release
-Vary gold NP size/shape can alter the hear generation capacity. Nanonachos are more effective than nanorods
How NPs can be used to study cancer
Can use NPs for
Near infrared light is effective at penetrating deep tissue to reach targeted area
Energy can be supplied via a continuous wave (wider and slower) or pulsed laser (selective and focused)
Can use near IR light with gold NPs to image and treat (photodynamic therapy) tumours in vivo
Issues with use of magnetic NPs for cancer therapies
Gold
Aggregation
Limits to NIR tissue penetration
Still in early days of research with most work in vitro so still questions to be answer (ex. is there sufficient heat generation longer term)
Iron
Takes mins to kill cells compared to gold which is secs
Why is targeted drug delivery necessary over systemic drug delivery and how to use NPs for this
Problems with systemic drug delivery that cause adverse side effects:
Biodistribution
Drug specificity
Large dose required for a high local concentration (toxicity and more expensive)
Inactivation of drug
Lower efficiency overall
Ex. only 1% of paracetamol goes to head for headache, rest is diffused in body
Magnetofection:
Inject NP coated in drug into artery supplying tissue/tumour. Apply magnetic field with an external magnet to the target site to retain the drug there
Benefits:
Fast
High transfection rate to cytoplasm (doesn’t achieve nuclear localisation)
Lower dose
How to target NPs to cell nucleus: why, how, issues
Useful in magnetofection to deliver a KO specific gene to cancer cell
Mammalian cells nuclear envelope is comprised of an inner and outer lipid bilayer to protect nuclear components. The membranes make contact at several points termed nuclear pore complexes that dictates cargo in and out of nucleus (~9nm can diffuse) and is the only known route of direct nucleocytoplasmic exchange
Microinjection but issue with cell viability (damages cells) and labour intensive (performed one cell at a time)
Electroporation in which temporary pores are shocked into cells but this has poor transfection efficiency especially for larger molecules (plasmids, etc) and can cause cell death
Receptor mediated endocytosis but this has technical requirements (correct cell targeting and optimising internalisation), can be degraded by lysosome in cell and general applicability
Cell penetrating peptides
Research by Green and Frankel showed HIV infected cells had a specific active (not degraded by endosome) protein in their nuclei passed from cell to cell; HIV-1 tat peptide
Other cell penetrating peptides have been identified to date. They cross the PM and can target the nucleus
Sequenced peptide, identified NLS and so can conjugate to our molecule
