Synthetic-based blended electrospun scaffolds in tissue engineering applications

Journal of Materials Science - Electrospinning, as one of the most common methodologies in nanofibers production, involves applying high voltages to a polymeric solution that is entrapped in a...     

Surface modified electrospun nanofibrous scaffolds for nerve tissue engineering

The development of biodegradable polymeric scaffolds with surface properties that dominate interactions between the material and biological environment is of great interest in biomedical applications. In this regard, poly-ε-caprolactone (PCL) nanofibrous scaffolds were fabricated by an electrospinning process and surface modified by a simple plasma treatment process for enhancing the Schwann cell adhesion, proliferation and interactions with nanofibers necessary for nerve tissue formation. The hydrophilicity of surface modified PCL nanofibrous scaffolds (p-PCL) was evaluated by contact angle and x-ray photoelectron spectroscopy studies. Naturally derived polymers such as collagen are frequently used for the fabrication of biocomposite PCL/collagen scaffolds, though the feasibility of procuring large amounts of natural materials for clinical applications remains a concern, along with their cost and mechanical stability. The proliferation of Schwann cells on p-PCL nanofibrous scaffolds showed a 17% increase in cell proliferation compared to those on PCL/collagen nanofibrous scaffolds after 8 days of cell culture. Schwann cells were found to attach and proliferate on surface modified PCL nanofibrous scaffolds expressing bipolar elongations, retaining their normal morphology. The results of our study showed that plasma treated PCL nanofibrous scaffolds are a cost-effective material compared to PCL/collagen scaffolds, and can potentially serve as an ideal tissue engineered scaffold, especially for peripheral nerve regeneration.     

Fabrication and characterization of electrospun osteon mimicking scaffolds for bone tissue engineering

Skeletal loss and bone deficiencies are a major worldwide problem with over 600,000 procedures performed in the US alone annually, making bone one of the most transplanted tissues, second to blood only. Bone is a composite tissue composed of organic matrix, inorganic bone mineral, and water. Structurally bone is organized into two distinct types: trabecular (or cancellous) and cortical (or compact) bones. Trabecular bone is characterized by an extensive interconnected network of pores. Cortical bone is composed of tightly packed units, called osteons, oriented parallel along to the axis of the bone. While the majority of scaffolds attempt to replicate the structure of the trabecular bone, fewer attempts have been made to create scaffolds to mimic the structure of cortical bone. The aim of this study was to develop a technique to fabricate scaffolds that mimic the organization of an osteon, the structural unit of cortical bone. We successfully built a rotating stage for PGA fibers and utilized it for collecting electrospun nanofibers and creating scaffolds. Resulting scaffolds consisted of concentric layers of electrospun PLLA or gelatin/PLLA nanofibers wrapped around PGA microfiber core with diameters that ranged from 200 to 600 μm. Scaffolds were mineralized by incubation in 10× simulated body fluid, and scaffolds composed of 10%gelatin/PLLA had significantly higher amounts of calcium phosphate. The electrospun scaffolds also supported cellular attachment and proliferation of MC3T3 cells over the period of 28 days.     

Biocompatibility evaluation of protein-incorporated electrospun polyurethane-based scaffolds with smooth muscle cells for vascular tissue engineering

Nanotechnology has enabled the engineering of a variety of materials to meet the current challenges and needs in vascular tissue regeneration. In this study, four different kinds of native proteins namely collagen, gelatin, fibrinogen, and bovine serum albumin were incorporated with polyurethane (PU) and electropsun to obtain composite PU/protein nanofibers. SEM studies showed that the fiber diameters of PU/protein scaffolds ranged from 245 to 273 nm, mimicking the nanoscale dimensions of native ECM. Human aortic smooth muscle cells (SMCs) were cultured on the electrospun nanofibers, and the ability of the cells to proliferate on different scaffolds was evaluated via a cell proliferation assay. Cell proliferation on PU/Coll nanofibers was found the highest compared to other electrospun scaffolds and it was 42 % higher than the proliferation on PU/Fib nanofibers after 12 days of cell culture. The cell–biomaterial interaction studies by SEM confirmed that SMCs adhered to PU/Coll and PU/Gel nanofibers, with high cell substrate coverage, and both the scaffolds promoted cell alignment. The functionality of the cells was further demonstrated by immunocytochemical analysis, where the SMCs on PU/Coll and PU/Gel nanofibers expressed higher density of SMC proteins such as alpha smooth muscle actin and smooth muscle myosin heavy chain. Cells expressed biological markers of SMCs including aligned spindle-like morphology on both PU/Coll and PU/Gel with actin filament organizations, better than PU/Fib and PU/BSA scaffolds. Our studies demonstrate the potential of randomly oriented elastomeric composite scaffolds for engineering of vascular tissues causing cell alignment.     

Electrospinning for tissue engineering scaffolds

Tissue engineering involves fabrication of three-dimensional scaffolds to support cellular in-growth and proliferation. The goal: generation of ‘neotissues’ that the body can adapt to carry out physiological function. To achieve this generation of scaffolds having tailored, biomimetic (across multiple scales) geometries has become important. The functional complexity of electrospun scaffolds provides significant advantages over other techniques; however, improvements are required before optimal utilization in vivo becomes routine. Cells on such surfaces are sensitive to topography. Electrospinning can be altered to influence either (1) the surface topography of the fibers themselves or (2) the larger topography of the ‘web’ of spun fibers. Improved deposition efficiencies are a necessary advance needed to maintain the attractiveness of this technique. While the role of residual solvent in the electrospun polymer remains unclear, high pressure CO₂ can be used to enhance chemical functionality while maintaining polymer morphology. Electrospun pore sizes, as spun, are typically too small for cells to pass through. Post-processing of these scaffolds to improve internal proliferation is expected to yield considerable benefits as tissue engineering matures as a subdiscipline and the limits of the basic electrospinning process are more widely realized.     

Microfluidic scaffolds for tissue engineering

Most methods to culture cells in three dimensions depend on a cell-seedable biomaterial to define the global structure of the culture and the microenvironment of the cells. Efforts to tailor these scaffolds have focused on the chemical and mechanical properties of the biomaterial itself. Here, we present a strategy to control the distributions of soluble chemicals within the scaffold with convective mass transfer via microfluidic networks embedded directly within the cell-seeded biomaterial. Our presentation of this strategy includes: a lithographic technique to build functional microfluidic structures within a calcium alginate hydrogel seeded with cells; characterization of this process with respect to microstructural fidelity and cell viability; characterization of convective and diffusive mass transfer of small and large solutes within this microfluidic scaffold; and demonstration of temporal and spatial control of the distribution of non-reactive solutes and reactive solutes (that is, metabolites) within the bulk of the scaffold. This approach to control the chemical environment on a micrometre scale within a macroscopic scaffold could aid in engineering complex tissues.     

Fabrication and characterization of gold nanoparticle-doped electrospun PCL/chitosan nanofibrous scaffolds for nerve tissue engineering

In the field of nerve tissue engineering, nanofibrous scaffolds could be a promising candidate when they are incorporated with electrical cues. Unique physico-chemical properties of gold nanoparticles (AuNPs) make them an appropriate component for increasing the conductivity of scaffolds to enhance the electrical signal transfer between neural cells. The aim of this study was fabrication of AuNPs-doped nanofibrous scaffolds for peripheral nerve tissue engineering. Polycaprolactone (PCL)/chitosan mixtures with different concentrations of chitosan (0.5, 1 and 1.5) were electrospun to obtain nanofibrous scaffolds. AuNPs were synthesized by the reduction of HAuCl₄ using chitosan as a reducing/stabilizing agent. A uniform distribution of AuNPs with spherical shape was achieved throughout the PCL/chitosan matrix. The UV–Vis spectrum revealed that the amount of gold ions absorbed by nanofibrous scaffolds is in direct relationship with their chitosan content. Evaluation of electrical property showed that inclusion of AuNPs significantly enhanced the conductivity of scaffolds. Finally, after 5 days of culture, biological response of Schwann cells on the AuNPs-doped scaffolds was superior to that on as-prepared scaffolds in terms of improved cell attachment and higher proliferation. It can be concluded that the prepared AuNPs-doped scaffolds can be used to promote peripheral nerve regeneration.

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Silk fibroin-polyurethane scaffolds for tissue engineering

Silk fibroin (SF) is a highly promising protein for its surface and structural properties, associated with a good bio- and hemo-compatibility. However, its mechanical properties and architecture cannot be easily tailored to meet the requirements of specific applications. In this work, SF was used to modify the surface properties of polyurethanes (PUs), thus obtaining 2D and 3D scaffolds for tissue regeneration. PUs were chosen for their well known advantageous properties and versatility; they can be obtained either as 2D (films) or 3D (foams) substrates. Films of a medical-grade poly-carbonate-urethane were prepared by solvent casting; PU foams were purposely designed and prepared with a morphology (porosity and cell size) adequate for cell growth. PU substrates were coated with fibroin by a dipping technique. To stabilize the coating layer, a conformational change of the protein from the alpha-form (water soluble) to the beta-form (not water soluble) was induced. Novel methodology in UV spectroscopy were developed for quantitatively analyzing the SF-concentration in dilute solutions. Pure fibroin was used as standard, as an alternative to the commonly used albumin, allowing real concentration values to be obtained. SF-coatings showed good stability in physiological-like conditions. A treatment with methanol further stabilized the coating. Preliminary results with human fibroblasts indicated that SF coating promote cell adhesion and growth, suggesting that SF-modified PUs appear to be suitable scaffolds for tissue engineering applications.     

Silk fibroin-based scaffolds for tissue engineering

Silk fibroin (SF) from the Bombyx mori silkworm exhibits attractive potential applications as biomechanical materials, due to its unique mechanical and biological properties. This review outlines the structure and properties of SF, including of its biocompatibility and biodegradability. It highlights recent researches on the fabrication of various SF-based composites scaffolds that are promising for tissue engineering applications, and discusses synthetic methods of various SF-based composites scaffolds and valuable approaches for controlling cell behaviors to promote the tissue repair. The function of extracellular matrices and their interaction with cells are also reviewed here.     

Carbon nanofibers produced from modified electrospun PAN/hydroxyapatite precursors as scaffolds for bone tissue engineering

In the current study we have proposed a method to obtain a carbon/HAp bioactive nanofibrous scaffold. The modified carbon nanofibrous nonwoven' fabrics were obtained by the use of electrospinning and subsequent stabilization and carbonization processes. The modified with HAp powder nanofibrous PAN nonwovens were thermally stabilized using a multi-stage process in the temperature ranging from 100 °C to 300 °C in an oxidative environment and then carbonized at 1000 °C in argon atmosphere. The changes of properties of composite precursor membranes taking place during stabilization and carbonization processes were investigated using the methods of: DSC, TGA, FTIR, SEM, EDX, WAXD and mechanical tests. Bioactivity was determined by assessing the formation of crystalline apatite on the surface of membranes upon immersion in Simulated Body Fluid (SBF). The FTIR, SEM and WAXD investigation clearly prove that hydroxyapatite added to the electrospinning solution was present also in composites nanofibrous nonwovens after stabilization and carbonization process. It was found that due to HAp addition: the significant decrease of fibers average diameter occurs and that the average pore size for modified membranes is smaller than for the unmodified one. On the other hand it was shown that the ceramic additive protects fibers from mass reduction during the stabilization treatment. Finally a drastic increase of mineralization activity of nCF/HAp scaffolds as compared to their nCF counterparts has been proved.     

Polymer-bioceramic composites for tissue engineering scaffolds

Designing tissue engineering scaffolds with the required mechanical properties and favourable microstructure to promote cell attachment, growth and new tissue formation is one of the key challenges facing the tissue engineering field. An important class of scaffolds for bone tissue engineering is based on bioceramics and bioactive glasses, including: hydroxyapatite, bioactive glass (e.g. Bioglass^®), alumina, TiO₂ and calcium phosphates. The primary disadvantage of these materials is their low resistance to fracture under loads and their high brittleness. These drawbacks are exacerbated by the fact that optimal scaffolds must be highly porous (>90% porosity). Several approaches are being explored to enhance the structural integrity, fracture strength and toughness of bioceramic scaffolds. This paper reviews recent proposed approaches based on developing bioactive composites by introducing polymer coatings or by forming interpenetrating polymer-bioceramic microstructures which mimic the composite structure of bone. Several systems are analysed and scaffold fabrication processes, microstructure development and mechanical properties are discussed. The analysis of the literature suggests that the scaffolds reviewed here might represent the optimal solution and be the scaffolds of choice for bone regeneration strategies.     

Designing porous scaffolds for tissue engineering

Biomaterials are either modified natural or synthetic materials, with an appropriate response in the host tissue, which find application in a wide spectrum of implants and prostheses used in reconstructive medicine. The subsequent integration and longevity of the implanted device depends on the effectiveness of the associated biological repair. Hence, there has been considerable interest in the development of novel, second generation, biomaterials, which are favourably bioactive in terms of promoting the desired cellular response in vivo. Such biomaterials in a porous form can also act as cellular scaffolds and allow in vitro, as well as in vivo incorporation of the appropriate tissue cells, with potential control of the sequence of cell attachment, proliferation and the production of extra-cellular matrix. Such generic tissue engineering depends critically on the porous architecture of the biomaterial scaffold so as to allow both the cellular ingress and vascularization required to create a living tissue. The particular requirements of tissue-engineering scaffolds with respect to macro- and micro-porosity, as well as chemistry, are reviewed.     

Surface-modified 3D scaffolds for tissue engineering

The aim of this work was to use sol–gel processing to develop bioactive materials to serve as scaffolds for tissue engineering that will allow the incorporation and release of proteins to stimulate cell function and tissue growth. We obtained organofunctionalized silica with large content of amine and mercaptan groups (up to 25%). The developed method can allow the incorporation and delivery of proteins at a controlled rate. We also produced bioactive foams with binary SiO₂–CaO and ternary SiO₂–CaO–P₂O₅ compositions. In order to enhance peptide–material surface properties, the bioactive foams were modified with amine and mercaptan groups. These materials exhibit a highly interconnected macroporous network and high surface area. These textural features together with the incorporation of organic functionally groups may enable them to be used as scaffolds for the engineering of soft tissue.     

Macroporous bioactive glass-ceramic scaffolds for tissue engineering

Highly bioactive scaffolds for tissue engineering were synthesized using a glass belonging to the SiO₂-CaO-K₂O (SCK) system. The glass SCK was prepared by a traditional melting-quenching route and its bioactivity was assessed by in vitro tests in a simulated body fluid (SBF). The glass was ground and sieved to obtain powders of specific size that were subsequently mixed with polyethylene particles of two different dimensions. The powders were then uniaxially pressed to obtain a crack free green compact that was thermally treated to remove the organic component and to sinter the inorganic phase. The obtained biomaterial was characterised by means of X-ray Diffraction, SEM equipped with EDS, mercury intrusion porosimetry, density measurements, image analysis, mechanical tests and in vitro evaluations. A glass-ceramic macroporous scaffold with a homogenously distributed and highly interconnected porosity was obtained. The amount and size of the introduced porosity could be tailored using various amounts of polyethylene powders of different size.     

Alginate based scaffolds for bone tissue engineering

The design and production of scaffolds for bone tissue regeneration is yet unable to completely reproduce the native bone properties. In the present study new alginate microparticle and microfiber aggregated scaffolds were produced to be applied in this area of regenerative medicine.The scaffolds' mechanical properties were characterized by thermo mechanical assays. Their morphological characteristics were evaluated by isothermal nitrogen adsorption and scanning electron microscopy. The density of both types of scaffolds was determined by helium pycnometry and mercury intrusion porosimetry. Furthermore, scaffolds' cytotoxic profiles were evaluated in vitro by seeding human osteoblast cells in their presence.The results obtained showed that scaffolds have good mechanical and morphological properties compatible with their application as bone substitutes. Moreover, scaffold's biocompatibility was confirmed by the observation of cell adhesion and proliferation after 5 days of being seeded in their presence and by non-radioactive assays.     

Polyelectrolyte-complex nanostructured fibrous scaffolds for tissue engineering

In the current work, polyelectrolyte complex (PEC) fibrous scaffolds for tissue engineering have been synthesized and a mechanism of their formation has been investigated. The scaffolds are synthesized using polygalacturonic acid and chitosan using the freeze drying methodology. Highly interconnected pores of sizes in the range of 5–20 µm are observed in the scaffolds. The thickness of the fibers was found to be in the range of 1–2 µm. Individual fibers have a nanogranular structure as observed using AFM imaging. In these scaffolds, PEC nanoparticles assemble together at the interface of ice crystals during freeze drying process. Further investigation shows that the freezing temperature and concentration have a remarkable effect on structure of scaffolds. Biocompatibility studies show that scaffold containing chitosan, polygalacturonic acid and hydroxyapatite promotes cell adhesion and proliferation. On the other hand, cells on scaffolds fabricated without hydroxyapatite nanoparticles showed poor adhesion.     

Characterisation of vascularisation of scaffolds for tissue engineering

Abstract

Vascularisation of scaffolds is now recognised as a crucial requirement for the success of tissue engineering strategies. This review summarises the state-of-the-art in the techniques available for the in vivo assessment of vascularisation of scaffolds with focus on growth factor delivering scaffolds, microfabrication technologies and in vivo characterisation methods based on the arteriovenous loop model to create three dimensionally vascularised tissue replacements.     

壳聚糖支架在组织工程中的应用

综述了壳聚糖作为细胞生长载体在软骨组织工程，骨组织工程和皮肤组织工程等方面的应用进展，表明壳聚糖有望成为优异的组织工程支架材料。