Lucy A. Bosworth

State of the art composites comprising electrospun fibres coupled with hydrogels: a review

UNLABELLED Research into scaffolds tailored for specific tissue engineering and biomaterial applications continues to develop as these structures are commonly impeded by their limitations. For example, electrospun fibres and hydrogels are commonly exploited because of their ability to mimic natural tissues; however, their clinical use remains restricted due to negligible cellular infiltration and poor mechanical properties, respectively. A small number of research groups are beginning to investigate composite scaffolds based on electrospun fibres and hydrogels in an attempt to overcome their individual shortcomings. This review paper discusses the various methodologies and approaches currently undertaken to create these novel composite structures and their intended applications. The combination of these two commonly used scaffold architectures to create synergistically superior structures is showing potential with regards to therapeutic use within the tissue engineering community. FROM THE CLINICAL EDITOR This review discusses methodologies to create novel electrospun nanofibers and hydrogels, and their intended applications. The combination of these two scaffold architectures has important future clinical applications, although their use is currently limited to the experimental tissue engineering community.

Investigation of 2D and 3D electrospun scaffolds intended for tendon repair

Two-dimensional (2D) electrospun fibre mats have been investigated as fibrous sheets intended as biomaterials scaffolds for tissue repair. It is recognised that tissues are three-dimensional (3D) structures and that optimisation of the fabrication process should include both 2D and 3D scaffolds. Understanding the relative merits of the architecture of 2D and 3D scaffolds for tendon repair is required. This study investigated three different electrospun scaffolds based on poly(ε-caprolactone) fibres intended for repair of injured tendons, referred to as; 2D random sheet, 2D aligned sheet and 3D bundles. 2D aligned fibres and 3D bundles mimicked the parallel arrangement of collagen fibres in natural tendon and 3D bundles further replicated the tertiary layer of a tendon’s hierarchical configuration. 3D bundles demonstrated greatest tensile properties, being significantly stronger and stiffer than 2D aligned and 2D random fibres. All scaffolds supported adhesion and proliferation of tendon fibroblasts. Furthermore, 2D aligned sheets and 3D bundles allowed guidance of the cells into a parallel, longitudinal arrangement, which is similar to tendon cells in the native tissue. With their superior physical properties and ability to better replicate tendon tissue, the 3D electrospun scaffolds warrant greater investigation as synthetic grafts in tendon repair.

Electrospinning for tissue regeneration

Part 1 Introduction Polymer chemistry Process control Regulatory issues. Part 2 Electrospinning for organ tissue regeneration: Blood vessel tissue regeneration Cartilage tissue regeneration Nerve tissue regeneration Muscle tissue regeneration Skin tissue regeneration Bladder tissue regeneration Renal tissue regeneration Cardiac tissue regeneration Pancreactic tissue regeneration Liver tissue regeneration Tendon tissue regeneration Bone tissue regeneration. Part 3 Electrospinning for other tissue regeneration: Interface region (tendon/bone) applications Stem cell regeneration Wound healing applications Bicomponent Electrospinning Dental restoration.

Dynamic loading of electrospun yarns guides mesenchymal stem cells towards a tendon lineage

Alternative strategies are required when autograft tissue is not sufficient or available to reconstruct damaged tendons. Electrospun fibre yarns could provide such an alternative. This study investigates the seeding of human mesenchymal stem cells (hMSC) on electrospun yarns and their response when subjected to dynamic tensile loading. Cell seeded yarns sustained 3600 cycles per day for 21 days. Loaded yarns demonstrated a thickened cell layer around the scaffold׳s exterior compared to statically cultured yarns, which would suggest an increased rate of cell proliferation and/or matrix deposition, whilst maintaining a predominant uniaxial cell orientation. Tensile properties of cell-seeded yarns increased with time compared to acellular yarns. Loaded scaffolds demonstrated an up-regulation in several key tendon genes, including collagen Type I. This study demonstrates the support of hMSCs on electrospun yarns and their differentiation towards a tendon lineage when mechanically stimulated.

Electrospun nanofibres of polycaprolactone, and their use for tendon regeneration

Inferior scar tissue formed when injured tendons heal often results in ongoing pain and site morbidity. With current treatments being ineffective, there is a clinical need for a tissue engineered approach. Electrospinning produces nanofibres with morphologies and architectures similar to the natural extra cellular matrix. Research incorporating electrospinning for tendon regeneration is limited. We report the effects of varying process parameters for fabricating electrospun polycaprolactone nanofibres, and the methods of fibre collection to achieve uniaxially aligned fibre bundles, particularly when spun into a liquid reservoir. We aim to group these bundles to develop a temporary scaffold mimicking the hierarchical tendon structure.

Travelling along the Clinical Roadmap: Developing Electrospun Scaffolds for Tendon Repair

Biopolymers, such as poly(e-caprolactone), can be easily electrospun to create fibrous scaffolds. It is also possible to control the alignment of the emitted fibres and further manipulate these scaffolds to create 3D yarn structures, which resemble part of the tendon tissue hierarchy. Material properties, such as tensile strength, can be tailored depending on the selection and combination of polymer and solvent used during electrospinning. The scaffolds have been proven to separately support the adhesion and proliferation of equine tendon fibroblasts and human mesenchymal stem cells whilst simultaneously directing cell orientation, which caused their alignment parallel to the underlying fibres. Implantation of scaffolds into the flexor digitorum profundus tendon of mice hindpaws yielded encouraging results with minimal inflammatory reaction and observation of cell infiltration into the scaffold. This research demonstrates the progression of electrospun fibres along the clinical roadmap towards becoming a future medical device for the treatment of tendon injuries.

Biocompatible three-dimensional scaffolds for tendon tissue engineering using electrospinning

This chapter first discusses the importance of applying ideal electrospinning parameters for creating fibres of micron to nanometre diameter and their applications in tissue engineering. Examples of biopolymers and structural aspects of the scaffold are considered. Particular attention is drawn to the different fibre collection techniques for creating bundles of electrospun fibres and how these could be used for regenerating tendon by mimicking the morphological and mechanical properties of the natural tissue.

Cell response to sterilized electrospun poly(ɛ-caprolactone) scaffolds to aid tendon regeneration in vivo

Abstract The functional replacement of tendon represents an unmet clinical need in situations of tendon rupture, tendon grafting, and complex tendon reconstruction, as usually there is a finite source of healthy tendon to use as donors. The microfibrous architecture of tendon is critical to the function of tendon. This study investigates the use of electrospun poly(ɛ‐caprolactone) scaffolds as potential biomaterial substitutes for tendon grafts. We assessed the performance of two electrospinning manufacturers (small‐ and large‐scale) and the effect of two sterilization techniques—gamma irradiation and ethanol submersion—on cell response to these electrospun scaffolds after their implantation into a murine tendon model. Cell infiltration and proliferation analyses were undertaken to determine the effect on cell response within the implant over a 6‐week period. Immunohistochemical analysis was performed to characterize inflammatory response and healing characteristics (proliferation, collagen deposition, myofibroblast activity, and apoptosis). Neither the sterilization techniques nor the manufacturer was observed to significantly affect the cell response to the scaffold. At each time point, cell response was similar to the autograft control. This suggests that ethanol submersion can be used for research purposes and that the scaffold can be easily reproduced by a large‐scale manufacturer. These results further imply that this electrospun scaffold may provide an alternative to autograft, thus eliminating the need for sourcing healthy tendon tissue from a secondary site.

Optimizing Attachment of Human Mesenchymal Stem Cells on Poly(ε- caprolactone) Electrospun Yarns

Research into biomaterials and tissue engineering often includes cell-based in vitro investigations, which require initial knowledge of the starting cell number. While researchers commonly reference their seeding density this does not necessarily indicate the actual number of cells that have adhered to the material in question. This is particularly the case for materials, or scaffolds, that do not cover the base of standard cell culture well plates. This study investigates the initial attachment of human mesenchymal stem cells seeded at a known number onto electrospun poly(ε-caprolactone) yarn after 4 hr in culture. Electrospun yarns were held within several different set-ups, including bioreactor vessels rotating at 9 rpm, cell culture inserts positioned in low binding well plates and polytetrafluoroethylene (PTFE) troughs placed within petri dishes. The latter two were subjected to either static conditions or positioned on a shaker plate (30 rpm). After 4 hr incubation at 37 oC, 5% CO2, the location of seeded cells was determined by cell DNA assay. Scaffolds were removed from their containers and placed in lysis buffer. The media fraction was similarly removed and centrifuged – the supernatant discarded and pellet broken up with lysis buffer. Lysis buffer was added to each receptacle, or well, and scraped to free any cells that may be present. The cell DNA assay determined the percentage of cells present within the scaffold, media and well fractions. Cell attachment was low for all experimental set-ups, with greatest attachment (30%) for yarns held within cell culture inserts and subjected to shaking motion. This study raises awareness to the actual number of cells attaching to scaffolds irrespective of the stated cell seeding density.