Laboratory of Polymers & Biomaterials

Methods  for nanofibers producing are known from about century. However, only about 20 years ago appeared appropriate analytical methods, allowing for the precise study of theis structure and morphology. Materials with nanometer scale offer many new opportunities to support the tissues and organs regeneration. The main advantage of nanofibers is their similarity to the extracellular matrix of collagen, whereby the cells treat them as their native environment. 

               Increasing number of publications about nanofibers in the years 1999-2012

Source: www.nafigate.com/en/section/portal/app/theme/detail/30-a-dramatic-rise-of-interest-in-nanofibers-has-been-confirmed

Methods 

Methods of producing nanofibers include: 

- drawing, 

- template synthesis, 

- phase separation,

- molecular self-assembly, 

- electrospininng. 

In drawing sodium citrate is used. Pipette with a diameter of several micrometers is immersed in a drop of a solution of sodium citrate in chlorine- gold acetic close contact surface. Drawing the fiber occurs when removing the pipette from the solution at a suitable speed (about 10-4 m / s). Then the nanofibers is deposited onto a suitable surface by contacting it with the end of the pipette. For one drop of these steps are repeated several times, because the nanofibers have a small volume. The drawing is required nanofibers of high viscosity material, since it can be subjected to large deformations without losing consistency.

Types of nanofibres 

Changing different parameters of electrospinning process like polymer concentration, humidity, evaporation rate or by selecting polymer with different molecular weight we can create fibres with different morphology. We can distinguish many types of nanofibres:  porous, flattened ,  ribbon like, branched, helical or hollow.  

                                                                     Porous nanofibres

Source: Nishath Khan,  ,,Applications of Electrospun Nanofibres in the Biomedical Field. A Review'', Surg Vol 5, No 2 (2012) 

Porous nanofibres can be produced in high humidity conditions during the electrospinning nanofibers. The pore size ranges from several tens nm to 1 micron, and depends on the type of polymer and solvent, as well as process conditions

                                                                    Ribbon like nanofibres

Source: Aravind Dasari, Berta Herrero, ,,Nano-manufacturing multifunctional ultrathin fibres'', Multifunctional Nanocomposites Group of IMDEA-Materials

The way how morphology of the flatted or ribbon like nanofibers appear can be explained by evaporating the solvent during the electrospinning process. Flat shaped fibers can be achieved using a solution of polyvinyl alcohol (PVA) with high molecular weight and increased concentration of polymer in solution. Evaporation of water solvent decreases with increasing viscosity of the solution. Wet fibers become flatten during impact with the collector.

                                                                        Branched nanofibres

Source: http://cheed.nus.edu.sg/stf/cheleejy/Gallery.html

Branched nanofibres can be obtained by the detachment of the small stream from the surface of the main stream. This happens when there is an imbalance between the forces of surface tension, electrical and which leads to instability of the shape of the stream. This instability can be reduced as a result of tearing or rupture of the original jet stream into two smaller ones.

Hollow fibres can be obtained using a sequence of processes of chemical and electro deposition from vapor deposition (CVD) and oriented coaxial spinning. When fibers are produced by electrospinning constituting the core, and then when CVD is applied to the core layer. The inner core is removed by annealing. Hollow nanofibers can be obtained in a single stage process using a coaxial spinning direction.

Characteristic 

The basic characteristics of the nanofibers is their morphology (fiber diameter) and mechanical properties. The nanofibers may be characterized using SEM (morphology, fiber diameter, chemical composition - EDS detector), AFM, TEM or nanoCT. In order to investigate the mechanical properties by standard methods we can use static tensile test. The deformation of nonwoven in the direction transverse to the rotation and the collector is investigated by this method.  One of the most important properties for medical application is surface contact angle which also usually is characterised.  Hydrophilicity of the material  influence on the cell repopulation of its surface. Of course also materials structure should be studied. For this reasone DSC, XRD or spectroscopy like FT-IR can be used. 

Materials 

For medical application mainly polymer fibres are used. From this group of materials, both, synthetic and natural polymers are used. Natural polymers used for this applications are hyauronic acid, collagen, gelatin, chitosan, elastin, wheat protein or silk. From this polymers one of the best  studied is collagen and gelatin. Collagen is compatible with number of cell types and create a suitable enviroment for cell growth.  The same like collagen, hyauronic acid,, is natural component of ECM (Extracellular Matrix). To synthetic polymer group used for nanofibres includes PLA, PET, PCL or PLGA.  

Funcionalisation 

Applications in Tissue Engineering 

Nanofibres can be succesfuly use in muscoleskeletal tissue engineering. Attempts are made to regenerate bone tissue, cartilage, ligament or skeletal muscle. In case of bone tissue it is the most important to recreate 3D structure and approperiate physical and mechanical properties like mechanical strenght, pore size, porosity and hardness.  Cartilage is more problematic then bone tissue because of its specific contruction. Morover nanofibres can be used to build structures for skin or blood vessels regeneration. nanofibres also can be used as a drug delivery system to improve the terapeutic efficiency and safty of drugs. 

Literature: 

1. Ramakrishna S., Fujihara K., Teo W. E., Lim T.C., Ma Z.,  ,,An Introduction to Electrospinning and Nanofibres'', World Scientific, 

2. www.zasoby.open.agh.edu.pl/~11sashot/strona.php?t=pm&h=nw&v=

3. www.aksolotl.org/index.php/prezentacje/98-nanowlokna-nowa-nadzieja-medycyny-regeneracyjnej