Inflowmation Chronicles, Spring 2009 Issue 1001

Polymer What is solution Electrospinning? Jet The electrospinning process uses high voltage to create an electric field between a droplet of polymer solution at the tip of a needle and a collector plate (see Figure 1&2). One electrode Syringe Pump Pipette of the voltage source is placed into the solu- tion and the other is connected to the collector. This creates an electrostatic force. As the volt- Taylor age is increased, the electric field intensifies cone High Voltage causing a force to build up on the pendant drop Supply Collector Screen of polymer solution at the tip of the needle. This (Rotating or Stationary) force acts in a direction opposing the surface tension of the drop. The increasing electro- Figure 1: Basic Electrospinning Setup: Experimental setup. static force causes the drop to elongate form- understand the process by which these fibers ingrowth has been reported in electrospun ing a conical shape known as a Taylor cone. scaffolds. Previous findings have shown that When the electrostatic force overcomes the are produced. the scaffold can function as a sieve, keeping surface tension of the drop, a charged, contin- cells on the scaffold surface, and that cell uous jet of solution is ejected from the cone. Tailoring Fiber Diameter in migration into the scaffold does not occur in The jet of solution accelerates towards the Electrospun Poly (e-Caprolactone) time. Because fiber diameter is directly related collector, whipping and bending wildly. As the to the pore size of an electrospun scaffold, the solution moves away from the needle and Scaffolds for Optimal Cellular objective of this study was to systematically toward the collector, the jet rapidly thins Infiltration in Cardiovascular evaluate how cell delivery can be optimized by and dries as the Tissue Engineering tailoring the fiber diameter of electrospun solvent evapo- Product highlighted: poly(e-caprolactone) (PCL) scaffolds. Five rates. On the KDS Model 100 syringe pump groups of electrospun PCL scaffolds with surface of the increasing average fiber diameters (3.4–12.1 grounded collec- mm) were seeded with human venous myofi- tor, a nonwoven KDS Model 100 broblasts. Cell distribution was analyzed after 3 mat of randomly syringe pump days of culture. Cell penetration increased oriented solid proportionally with increasing fiber diameter. nanofibers is Unobstructed delivery of cells was observed deposited. Some exclusively in the scaffold with the largest fiber important applica- diameter (12.1 mm). This scaffold was subse- tions for these quently evaluated in a 4-week TE experiment nanofibers in- Figure 2: Resulting and compared with a poly(glycolic acid)- clude, but are not nanofibers. poly(4-hydroxybutyrate) scaffold, a standard limited to, catalytic scaffold used successfully in cardiovascular substrates, photonics, filtration, protective tissue engineering applications. The PCL con- clothing, cell scaffolding, drug delivery and structs showed homogeneous tissue formation wound healing. Different applications may Key features for this application: and sufficient matrix deposition. In conclusion, require the fibers to possess different proper- • High precision and accuracy fiber diameter is a crucial parameter to allow ties. For instance, one application might require • Smooth flow for homogeneous cell delivery in electrospun the nanofibers to be hydrophobic or scaffolds. The optimal electrospun scaffold hydrophilic; another may need the fiber to be Despite the attractive features of nanofibrous geometry, however, is not generic and should biodegradable or biocompatible. It will, there- scaffolds for cell attachment in tissue-engi- be adjusted to cell size. fore, be extremely important to completely neering (TE) applications, impeded cell

84 October Hill Rd Holliston, MA 01746 phone 508.429.6809 • fax 508.893.0160 • email [email protected] www.kdscientific.com Inflowmation Chronicles, Spring 2009 Issue 1001 Introduction Scaffold design in tissue engineering (TE) plays Unislide an Important role in modulating tissue growth and development. Various scaffold fabrication techniques, including rapid prototyping, solvent casting, salt leaching, and electrospinning, are used to construct a broad range of scaffold Needle geometries.Using electrospinning, highly porous, nonwoven, three-dimensional fiber structures can be made, of which the fiber diameter can range from nano- to micro- scale. The basis of this technique is to produce Metering Pump thin fibers by electrically charging a polymer Power Supply solution flowing through a needle. The geome- Collector Plate try of the collector determines the gross shape of the fiber mesh; this can be adapted to suit its purpose (e.g., blood vessel or heart valve geometry). The morphology of fibers can be controlled with various parameters in the elec- trospinning process, such as solution proper- ties (e.g., viscosity, conductivity, polymer molecular weight), controlled variables (e.g., flow rate, electric field strength), and ambient Vertical Electrospinning Setup (A) sions of natural extracellular matrix (ECM). were produced by varying the spinning Although this resemblance may apply to parameters: flow rate (Q), the applied voltage the fiber thickness and the porosity of the (V), and the concentration of the polymer solu- nanofibrous scaffold, the spatial characteris- tion. The thickness of all electrospun sheets tics of ECM were not attained. In fact, the pore was approximately 1 mm. size of the scaffold was smaller with decreas- In summary, successful delivery of cells ing fiber diameter and can be as small as 100 during seeding on an electrospun scaffold (B) nm. Such small pore sizes may interfere with strongly depends on the fiber diameter, and cellular infiltration in the scaffold, thus undoing hence pore size, of the electrospun mesh. the advantages of nanofibrous scaffolds for Despite the attractive features of nanofibrous use in TE. However, this featuremay be benefi- structures for cell attachment, the data pre- cial when the nanofiber mesh is used as a sented here encourage a shift from nano- to membrane, separating cell types, yet allowing microfiber meshes for use in TE. Because cell communication through interconnected pores. size varies over a broad range, the optimal electrospun scaffold structure is not generic Histological images of toluidine blue stained slides of poly(e-caprolactone) (PCL) group E and should be adapted to the dimensions of the (A) and poly glycolic acid coated with poly Materials and Methods cells to be used. (4-hydroxybutyrate) (PGA-P4HB) (B). Homo- geneous tissue throughout the whole PCL Electrospinning scaffold was observed in the PCL construct, The custom-built electrospinning set-up Reference: whereas in the PGA-P4HB constuct, the TISSUE ENGINEERING: Part A tissue structure was more compact at the existed of a highvoltage power supply, an edges. Scale bar indicates 1mm. infusion pump (Kd Scientific, USA), a 10-mL Volume 15, Number 2, 2009 plastic syringe (Terumo, Belgium), a stainless ª Mary Ann Liebert, Inc. parameters (e.g., temperature, humidity). One steel blunt needle (inner diameter 0.6 mm), and DOI: 10.1089=ten.tea.2007.0294 advantage of electrospun scaffolds is that their a stagnant grounded collector. The syringe Angelique Balguid, Ph.D.,1,2 Anita Mol, Ph.D.,1 fiber structure, particularly when in nanoscale, was horizontally fixed in the infusion pump. The Mieke H. van Marion, M.Sc.,1 Ruud A. Bank, is associated with high surface-to-volume polymer solution was led through a plastic tube Ph.D.,3 Carlijn V.C. Bouten, Ph.D.,1 and Frank ratios, providing a large area for cell attach- to the needle, which was vertically fixed 15cm P.T. Baaijens, Ph.D.1 ment. Furthermore, the physical form of the above the collector. The polymer solution was nanofibrillar matrices provides high porosity electrostatically drawn from the tip of the and high spatial interconnectivity. It was pos- needle using high voltage between the needle tulated that the use of nanofibrous structures and the collector. Five sheet-like scaffolds would bear a close resemblance to the dimen- (groups A to E) with increasing fiber diameters

84 October Hill Rd Holliston, MA 01746 phone 508.429.6809 • fax 508.893.0160 • email [email protected] www.kdscientific.com