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You know those sponges that little kids use to finger
paint? That's what a new drug delivery system developed by bioengineers
at Harvard and Caltech looks like. The gel-based sponges can be molded into
any shape (including stars and hearts) and injected into the body to deliver
drugs or serve as a support structure for the surrounding tissue.
Medical sponges. Image
Credit: Sidi Bencherif
The sponges are made primarily of alginate, a gel made
from algae. Alginate is a salt of alginic acid which is extracted from marine
kelp. It is commonly used in foam, cloth, and gauze for absorbent surgical
dressings. Soluble alginates, such as those of sodium, potassium, or magnesium,
form a viscous sol that is changed into a gel by a chemical reaction with
compounds such as calcium sulfate. Previously, alginate in the gel state has
been used to take dental impressions, but scientists have created a new
sponge-like gel with a freezing process called cryogelation. Pure ice crystals
form as the water in the alginate solution starts to freeze. This makes the
surrounding gel more concentrated as it sets. Later on, the ice crystals melt,
leaving behind a network of pores. The cryogelation process has been calibrated
so that a strong and extremely compressible gel is formed.
The gel-based sponge can be molded into any shape and
compressed to a fraction of its size. This means that the sponge can be
delivered via injection with a small-bore needle. Once injected, the sponge
resumes its original shape and can deliver the drug before safely degrading in
the body.
The potential applications for this discovery are vast.
The 3D structure could be used to influence the surrounding cells and promote
tissue formation. If a tissue has been lost or is deficient, the sponge could
provide bulking for the area, as well as the transplant of stem cells or immune
cells for immotherapy. The sponge can hold large and small proteins for gradual
release as the biocompatible matric starts to break down. The new sponge can flow
to and fill in whatever space is available. The children sponges - see the confusion? Image Credit: Mega Brands
"Furthermore, the ability of these materials to reassume
specific, pre-defined shapes after injection is likely to be useful in
applications such as tissue patches where one desires a patch of a specific
size and shape, and when one desires to fill a large defect site with multiple
smaller objects. These could pack in such a manner to leave voids that enhance
diffusional transport to and from the objects and the host, and promote
vascularization around each object." says Bencherif, lead author and
postdoctoral research associate at SEAA at the Wyss Institute of Harvard. Image Credit: Sidi
Bencherif
The next step for this discovery is to perfect the
degradation rate of the scaffold so that it breaks down at the same rate at
which newly grown tissue replaces it. Harvard is filing the paperwork so this
might be something we all see in the OR very soon.
Resources
Injectable
sponge delivers drugs, cells, and structure
Injectable
Sponges Can Expand Inside The Body To Deliver Drugs
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