Prototype: A Product Development Blog

Nearly 40% of all war injuries are eye injuries, yet these injuries are often considered secondary to life-threatening wounds. Ophthalmologic treatment can be delayed by as much as three days. There is a need to develop solutions that can be administered immediately in the field to delay corneal damage until the patient reaches a hospital where surgery is available.

The Corneal Wound Repair Program at Mercy R&D is grant funded by the Department of Defense to develop front-line use products that can save damaged corneas and preserve eyesight after blasts and chemical injuries. During this polymer series, Dr. Kumar Vedantham, a research scientist with Mercy R&D, will discuss the different polymer systems, why polymer size does matter and the method of electrospinning for polymer fabrication as they relate to corneal wound repair research.

Mercy R&D is using electrospinning technology to synthesize a wide range of polymer fibers impregnated inside contact lenses for delivery of drugs to eye injuries suffered in the battlefield. This is a unique approach, as previously no efforts have combined the drug delivery capabilities of polymer fibers with a contact lens. We have successfully fabricated 15 different kinds of electrospun nano/micron size biocompatible polymer fibers inside contact lens material for treating injured corneas. This effort by Mercy R&D will potentially lead to development of next generation contact lenses that house polymer fibers which can help treat a wide range of eye disorders by delivering specific therapeutic agents.

A useful “matrix based” paradigm for drug delivery:

Of all the shapes, a polymer in fiber-like shape is an interesting approach that has gained recognition due to its ease of production and biological significance. Fibers in nanometer range mimic in size and form collagen fibrils within the extracellular matrix. Cells have been shown to interact favorably with fibers as small as 5 nm with documented cellular adhesion, proliferation and migration.

Currently polymeric fibers can be produced by three techniques:

1. Electrospinning
2. Self-assembly
3. Phase separation

Of these, electrospinning is the most widely studied technique and also seems to exhibit the most promising results for tissue engineering and drug delivery applications. Self-assembly and phase separation methods have disadvantages, requiring more time and a complicated processing system. Electrospinning is a simple one-step, top-down process for fabricating nanofibers, and the co-processing of polymer mixtures and chemical cross-linking can be carried out, which provides a variety of pathways for controlling the chemical composition of the nanofibers.

Unique features of electrospinning

Additionally, electrospinning seems to be the only method that can be further developed for mass production of continuous nanofibers from various polymers.

Polymer nanofibers possess unique characteristics, such as:

• Extraordinary high surface area per unit mass (for example, nanofibers with ~100 nm diameter have a specific surface of ~1000m2/g)
• Remarkably high porosity
• Excellent structural mechanical properties
• High axial strength combined with extreme flexibility,
• Low basis weight
• Cost effectiveness

How electorspinning technology works

Polymeric micro or nano sized fibers can be produced by applying an electric potential to a polymeric solution. The solution is held at the tip of a capillary tube by virtue of its surface tension. The electrical potential applied provides a charge to the polymer solution. Mutual charge repulsion in the polymer solution induces a force that is directly opposite to the surface tension of the polymer solution. An increase in the electrical potential initially leads to the elongation of the hemispherical surface of the solution at the tip of the capillary tube, to form a conical shape known as the Taylor cone. A further increase causes the electric potential to reach a critical value, at which it overcomes the surface tension forces to cause the formation of a jet that is ejected from the tip of the Taylor cone. The charged jet undergoes instabilities and gradually thins in air primarily due to elongation and solvent evaporation. The charged jet eventually forms randomly oriented nanofibers that can be collected on a stationary or rotating grounded metallic collector. (DO NOT TRY THIS AT HOME)

Kumar Vedantham received his Doctorate in Industrial and Physical Pharmacy from Purdue University in 2009. He joined Mercy R&D in February 2011 and has experience in drug delivery from polymer systems and associated pharmacokinetic studies. His research interest involves working on the interface of biomaterials and drug delivery for controlled release applications.