Determining the mechanical properties of electrospun poly-ε-caprolactone (PCL) nanofibers using AFM and a novel fiber anchoring technique

Abstract

Due to its low cost, biocompatibility and slow bioresorption, poly-ε-caprolactone (PCL) continues to be a suitable material for select biomedical engineering applications. We used a combined atomic force microscopy (AFM)/optical microscopy technique to determine key mechanical properties of individual electrospun PCL nanofibers with diameters between 440-1040nm. Compared to protein nanofibers, PCL nanofibers showed much lower adhesion, as they slipped on the substrate when mechanically manipulated. We, therefore, first developed a novel technique to anchor individual PCL nanofibers to micrometer-sized ridges on a substrate, and then mechanically tested anchored nanofibers. When held at constant strain, tensile stress relaxed with fast and slow relaxation times of 1.0±0.3s and 8.8±3.1s, respectively. The total tensile modulus was 62±26MPa, the elastic (non-relaxing) component of the tensile modulus was 53±36MPa. Individual PCL fibers could be stretched elastically (without permanent deformation) to strains of 19-23%. PCL nanofibers are rather extensible; they could be stretched to a strain of at least 98%, and a tensile strength of at least 12MPa, before they slipped off the AFM tip. PCL nanofibers that had aged for over a month at ambient conditions became stiffer and less elastic. Our technique provides accurate nanofiber mechanical data, which are needed to guide construction of scaffolds for cells and other biomedical devices.

Elastin-PLGA hybrid electrospun nanofiber scaffolds for salivary epithelial cell self-organization and polarization

“…AFM measurements were performed in dry conditions, which is different from the cells’ wet environment. While it is expected that the mechanical properties of elastin may change in wet conditions, we expect that the values of elastic modulus in wet conditions may be lower than in air for all types of electrospun scaffolds that we fabricated, as reported elsewhere [73–74]; however, the trend is expected to be conserved [73–74]. …”

Rotary jet spinning review – a potential high yield future for polymer nanofibers

“…These are however all time-consuming methods which require a high degree of precision, coupled with the fact that it remains difficult to manipulate single fibers within these test rigs. The most common methods of nanofiber tensile testing include the use of atomic force microscope (AFM) cantilevers,174-176 3-point bending testing [177][178][179] or commercial nano-tensile testing. 38,127 The AFM testing method essentially relies on the fixing of fibers to the ends of the AFM cantilever before applying a tensile load.…”

Antibacterial electrospun chitosan-polyethylene oxide nanocomposite mats containing ZIF-8 nanoparticles

“…Nowadays, electrospinning is one of the most cost-effective methods for producing nonwoven nanofibrous mats from various polymers including chitosan (CS) [7], chitosan-gelatin [8], poly(lactic-co-glycolide) [9], sodium alginate [10], poly--caprolactone [11], collagen [12] and polyurethane [13]. The nanofiber mats have important properties including small fiber size, extremely large specific surface, high porosity and low fabric weight which are favorable for drug release, absorbency, wound dressing, pharmaceuticals, cosmetics, food coating and food packaging [14].…”