Electrospinning is a simple, versatile and powerful process to manufacture nano- and microfibrous 3D structures. The electrospinning process was first described by Charles Vernon Boys in 1897 and patented by John Francis Cooley in the early 1900s.1 However, it only gained a lot of tempo in the early 1990s. Since then, many natural and synthetic polymers were electrospun and have found applications in fields like energy, air filtration systems, waste water, textile and membrane production and biomedical research.
During electrospinning a polymeric solution is pumped through a tube to the spinneret. Such a spinneret can be e.g. a small nozzle connected to a high voltage supply. Due to the applied electric field, the droplet at the end of the nozzle is deformed via the uniaxial stretching into the so called “Taylor’s cone”. When the electrostatic force surpasses the surface tension, the solution forms a jet, ‘flying’ from the nozzle to the grounded collector. This charged jet follows a chaotic path and the solvent evaporates during this travel, which results in the deposition of solid fibers on a collector plate or a rotating mandrel. Since the shape of the collector directly reassembles the final 3D scaffold structure, the choice of collector is related to the desired scaffold application.
The electrospinning process is governed by a number of variables which can be divided into solution properties and process parameters. Viscosity, polymer concentration, conductivity, surface tension, molecular weight and dielectric constant are among the solution properties. Distance between the needle tip and collector, applied voltage, flow rate, collector geometry and rotation speed are the general process parameters.
This basic simplicity of the required equipment in addition to the great flexibility in the process due to the various adjustable parameters, has led to a large number of publications and patents. A lot of work has been performed in biomedical research areas, such as tissue engineering applications, skin, tendon, osteochondral regeneration, cardiovascular and nerve repair application as well as in improvement of dental devices. Despite the large numbers of publications and patents released, less than 10 electrospun medical products are available on the market.
The challenges in controlling all these parameters independently were limiting the development of medical devices. In particular the changes in temperature and relative humidity between the seasons and during the day, lead to inconsistencies within one batch as well as between batches.
During the last few years, these reproducibility issues have led to an effort in studying the effect of humidity and temperature on the process, and also in constructing environmentally controlled electrospinning equipment by IME Technologies. This machine showed how important tightly controlled environment conditions are, in order to stabilize the process and to obtain reproducible scaffold morphologies.2
The possibility to maintain stable environmental conditions drastically improves the reproducibility of the electrospinning process, hence it is to be expected that much more electrospun medical devices will reach the market.