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• Humans are exposed to nanoparticles - Some are unintentionally produced (air pollution) whereas some are engineered for different uses.
• Airborne particles – exhaust fumes from traffic and industrial.

  Air pollution.

  Exposure to tobacco smoke nanoparticles.
• The smaller the nanoparticle the deeper it penetrates into the organs (lung.)
• The 2 major clearance mechanisms of nanoparticles are from the alveoli and trachobronchial

  Alveoli – phagocytosis by macrophages.

  Tracheobronchial – muscociliary escalator.
• Translocation of nanoparticles across major protective barriers depend on the size and surface properties of the particles.
• Particles less than 34nm in size can cross barriers like lung epithelium as its surface is not positively charged. Due to the circulation, they can travel to many parts of the body.

  Very small particles can be cleared from the body through urine by the kidneys.
• Peripheral organ function can be damaged due to absorbed nanoparticles as they can cross natural barriers including the blood brain barrier.
• Polymer micro/nanosphere transit across intestinal wall can also occur.
• Small nanoparticles are taken up by endocytosis. Microscale particles are taken up by phagocytes (macrophages)
• When nanoparticles enter the body they can cause asbestos.

  They can also cause lung cancer. Both asbestos and lung cancer have a long lag time between exposure and onset of disease.
• Many nanoparticle reactions are chronic inflammation. However it can also cause problems in the lungs, GI tract, brain, heart and can be transported around the circulatory system affecting other vital organs.
• Nanoparticles shows incrreased uptake and reactions with biological tissue. These can alter biological functions.
• Surface to volume ration contributes to particle toxicity. Many small particles together have a larger surface area than one large particle with the same mass.

  Nanoparticles react more strongly to the biomolecular interactions as it occurs at the particle surface.

  Hydrophobicity – the more hydrophobic a particle is the stronger the immune response induction.

  Nanoparticle toxicity is very difficult to access due to the nanoparticle corona.
• Nanomedicine – the ability of a particle to interact with biological molecules and overcome natural protective barriers for medical applications.
• Nanoparticles in medicine is used for drug delivery.
• There are different drug carrier systems.

  Nanoparticles for drug delivery are formed from self assembly of amphiphilic building blocks which can carry drugs and show certain molecules on their surface.
• There are 2 types of drug targetting. Passive and active drug targetting.

  Passive – accumulation in target tissue

  Active – specific recognition and uptake by malignant cells.
• Passive targetting – can cross endothelium. The endothelial cells that line the blood vessel in tumors are more permeable to nanoparticles compared to healthy tissue

  Nanocarriers are designed of appropriate size to exploit the Enhanced permeation and retention(EPR) effect.
• Active targeting – cells of interest – the attachment of specific ligands to the surface of drug carriers. These help to recognize and bind to pathological cells and allow uptake of the drug carrier.
• Controlled degradability of drugs – the drug is released over a period of time in a controlled manner. The degradation rate depends on the size and porosity of the particle.