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Nanotechnology Delivers Drugs More Efficiently

Nanotechnology is holding out the promise of some great improvements in the area of drug delivery, from lotions absorbed through the skin to time-released subcutaneous medications.

One obstacle to delivering drugs into cells is that many types of nanoparticles can’t get through the membranes surrounding cells to deliver drugs. To understand why that’s so and how nano can provide a solution for breaking through cell membranes; you have to understand a bit about the nature of cells.

Cell membranes in our bodies are composed of molecules called phospholipids. One end of these phospholipids, called the head, is hydrophilic, meaning that it mixes well with water. On the other end of the cell are two tails that are hydrophobic, meaning that they don’t mix well with water.

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The hydrophilic end of the phospholipid mixes well with water because it’s polar, meaning that it’s composed of atoms that have different levels of attraction to electrons (this measurement of attraction is called electronegativity).

The hydrophobic end of the phospholipid is composed of atoms that have similar electronegativity; therefore the electrons are evenly distributed, making this end of the molecule nonpolar. Nonpolar molecules don’t mix well with water, a characteristic you’ve seen in practice if you’ve ever tried to mix water and oil.

The membrane of a cell is composed of many of these molecules in a two-layer film. In this film hydrophilic ends of the outer layer of the molecules form the outside of the membrane, and the hydrophobic tails of the molecules meet in the middle.

This structure has a couple of purposes: the hydrophilic outer layer lets the cell mix with the water-containing fluids in our bodies while the hydrophobic layer in the middle of the membrane prevents the water-containing fluids inside the cell from leaving.

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The result of this structure is that the cell membrane blocks the entry of many therapeutic drugs into the interior of the cell, motivating researchers to develop methods to deliver these drug molecules through the cell membrane.

One way to get drugs through cell membranes is to enclose drug molecules in artificially created spherical nanoparticles called liposomes. Place these molecules with the hydrophilic head and hydrophobic tails in water containing the drug molecules to be encapsulated. The hydrophilic heads line up to form an outer shell facing the water solution, while another set of hydrophilic heads form an inner shell that contains a solution of drug molecules.

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The shells of these liposomes can fuse with cell membranes. If a therapeutic drug is encased in a liposome, the liposome membrane creates an opening as it fuses with the cell membrane, and the drug inside the liposome can be delivered into the cell.

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Proteins are designed to deliver materials through cell membranes. For example, hemoglobin is a protein that picks up oxygen in your lungs and distributes it to cells throughout your body. Hemoglobin is actually capable of burrowing through cell membranes to deliver oxygen.

In a different approach to drug delivery, AbraxisBioScience is enclosing therapeutic drug molecules in an albumin protein. Nanoparticles of albumin can burrow through cancer cell membranes and deliver a drug to the interior of the cell.

Another method is a little more aggressive. This method, developed at the Georgia Institute of Technology, blasts temporary holes in the cell membrane, allowing therapeutic drug molecules to enter the cell.

In this method, researchers inject carbon nanoparticles into the fluid floating around cancer cells, and then a laser heats the fluid. This heat creates gas bubbles; when the bubbles burst, they blow a hole in the membrane of the cancer cells. Drug molecules floating in the fluid around the cancer cells can then enter the cells and destroy them.

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