Multifunctional nanofibrous scaffold for tissue engineering

In tissue engineering, scaffolds with multiscale functionality, especially with the ability to release locally multiple or specific bioactive molecules to targeted cell types, are highly desired in regulating appropriate cell phenotypes. In this study, poly (epsilon-caprolactone) (PCL) solutions (8% w/v) containing different amounts of bovine serum albumin (BSA) with or without collagen were electrospun into nanofibres. As verified by protein release assay and fluorescent labelling, BSA and collagen were successfully incorporated into electrospun nanofibres. The biological activity of functionalised fibres was proven in the cell culture experiments using human dermal fibroblasts. By controlling the sequential deposition and fibre alignment, 3D scaffolds with spatial distribution of collagen or BSA were assembled using fluorescently labelled nanofibres. Human dermal fibroblasts showed preferential adhesion to PCL nanofibres containing collagen than PCL alone. Taken together, multiscale scaffolds with diverse functionality and tunable distribution of biomolecules across the nanofibrous scaffold can be fabricated using electrospun nanofibres.     

Bio-functionalized PCL nanofibrous scaffolds for nerve tissue engineering

Surface properties of scaffolds such as hydrophilicity and the presence of functional groups on the surface of scaffolds play a key role in cell adhesion, proliferation and migration. Different modification methods for hydrophilicity improvement and introduction of functional groups on the surface of scaffolds have been carried out on synthetic biodegradable polymers, for tissue engineering applications. In this study, alkaline hydrolysis of poly (ε-caprolactone) (PCL) nanofibrous scaffolds was carried out for different time periods (1 h, 4 h and 12 h) to increase the hydrophilicity of the scaffolds. The formation of reactive groups resulting from alkaline hydrolysis provides opportunities for further surface functionalization of PCL nanofibrous scaffolds. Matrigel was attached covalently on the surface of an optimized 4 h hydrolyzed PCL nanofibrous scaffolds and additionally the fabrication of blended PCL/matrigel nanofibrous scaffolds was carried out. Chemical and mechanical characterization of nanofibrous scaffolds were evaluated using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, contact angle, scanning electron microscopy (SEM) and tensile measurement. In vitro cell adhesion and proliferation study was carried out after seeding nerve precursor cells (NPCs) on different scaffolds. Results of cell proliferation assay and SEM studies showed that the covalently functionalized PCL/matrigel nanofibrous scaffolds promote the proliferation and neurite outgrowth of NPCs compared to PCL and hydrolyzed PCL nanofibrous scaffolds, providing suitable substrates for nerve tissue engineering.     

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.     

Electrospun nanofibrous materials for tissue engineering and drug delivery

Abstract

The electrospinning technique, which was invented about 100 years ago, has attracted more attention in recent years due to its possible biomedical applications. Electrospun fibers with high surface area to volume ratio and structures mimicking extracellular matrix (ECM) have shown great potential in tissue engineering and drug delivery. In order to develop electrospun fibers for these applications, different biocompatible materials have been used to fabricate fibers with different structures and morphologies, such as single fibers with different composition and structures (blending and core-shell composite fibers) and fiber assemblies (fiber bundles, membranes and scaffolds). This review summarizes the electrospinning techniques which control the composition and structures of the nanofibrous materials. It also outlines possible applications of these fibrous materials in skin, blood vessels, nervous system and bone tissue engineering, as well as in drug delivery.     

Template synthesis of porous organic polymers

This review describes the possibilities of using templates to create organic polymer networks with new architectures and functionalities. Examples are given for the whole range of templates starting from functional organic molecules (molecular imprinting) to organized arrays of solid colloids (colloidal imprinting) up to micelles, microemulsions and lyotropic phases (self-organized templates), whereas classical thermodynamic techniques like addition of structural cosolvents or gelation during precipitation polymerization, are not considered. Also some examples for potential applications of the discussed porous polymer gels are presented.     

Bioactive collagen-grafted poly-L-lactic acid nanofibrous membrane for cartilage tissue engineering

Biodegradable nanofibrous membrane was prepared from poly-L-lactic acid by electrospinning and used as a scaffold for cartilage tissue engineering. Operating parameters during the electrospinning process were studied in terms of their influences on fiber diameter, membrane porosity and pore size. In order to improve cell attachment and growth, nanofibrous membrane was subject to DC-pulsed oxygen plasma treatment, followed by acrylic acid grafting and collagen coating by covalent binding of collagen to carboxylic moieties of the polyacrylic acid. The membrane was fully characterized for its physical and chemical properties. Primary chondrocyte cells seeded into the membrane proliferated well and maintain high viability within the membrane from Confocal Laser Scanning Microscopy. Cell differentiation was confirmed by secretion of glycoaminoglycan and collagen during the cultivation period. Scanning electron microscope observation of the cell-scaffold construct confirms the tight attachment of cells to nanofibers and in-growth of cells into the interior of the membrane with proper maintenance of morphology and structure of chondrocytes.     

Hierarchical porous materials for tissue engineering

Biological organisms have evolved to produce hierarchical three-dimensional structures with dimensions ranging from nanometres to metres. Replicating these complex living hierarchical structures for the purpose of repair or replacement of degenerating tissues is one of the great challenges of chemistry, physics, biology and materials science. This paper describes how the use of hierarchical porous materials in tissue engineering applications has the potential to shift treatments from tissue replacement to tissue regeneration. The criteria that a porous material must fulfil to be considered ideal for bone tissue engineering applications are listed. Bioactive glass foam scaffolds have the potential to fulfil all the criteria, as they have a hierarchical porous structure similar to that of trabecular bone, they can bond to bone and soft tissue and they release silicon and calcium ions that have been found to up-regulate seven families of genes in osteogenic cells. Their hierarchical structure can be tailored for the required rate of tissue bonding, resorption and delivery of dissolution products. This paper describes how the structure and properties of the scaffolds are being optimized with respect to cell response and that tissue culture techniques must be optimized to enable growth of new bone in vitro.     

Template assisted synthesis of europium sulfide nanotubes

We report the template assisted synthesis of europium sulfide (EuS) nanotubes. These structures were fabricated by thermolysis of a single source precursor that was infused into porous alumina membranes. TEM and STEM analysis confirmed the formation of EuS nanotubes, while X-ray diffraction and selected area electron diffraction analysis probed their crystallinity. Room temperature optical spectroscopy identified an energy-band blue-shift in the absorption spectra into the UV, compared to bulk EuS. Interestingly, no such shift was observed in the photoluminescence. We attribute these changes to quantum confinement effects on the photoexcited charge carriers within the nanotubes' walls and strain-induced lattice deformations.     

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.     

Electrospun nanofibrous biodegradable polyester coatings on Bioglass-based glass-ceramics for tissue engineering

Biodegradable polymeric nanofibrous coatings were obtained by electrospinning different polymers onto sintered 45S5 Bioglass^®-based glass-ceramic pellets. The investigated polymers were poly(3-hydroxybutyrate) (P3HB), poly(3-hydroxybutyrate-co-hydroxyvalerate) (PHBV) and a composite of poly(caprolactone) (PCL) and poly(ethylene oxide) (PEO) (PCL–PEO). The fibrous coatings morphology was evaluated by optical microscopy and scanning electron microscopy. The electrospinning process parameters were optimised to obtain reproducible coatings formed by a thin web of polymer nanofibres. In-vitro studies in simulated body fluid (SBF) were performed to investigate the bioactivity and mineralisation of the substrates by inducing the formation of hydroxyapatite (HA) on the nanofiber-coated pellets. HA crystals were detected on all samples after 7 days of immersion in SBF, however the morphology of the HA layer depended on the characteristic fibre diameter, which in turn was a function of the specific polymer-solvent system used. The bioactive and resorbable nanofibrous coatings can be used to tailor the surface topography of bioactive glass-ceramics for applications in tissue engineering scaffolds.     

Stem cell differentiation on electrospun nanofibrous substrates for vascular tissue engineering

Nanotechnology has enabled the engineering of a variety of materials to meet the current challenges and requirements in vascular tissue regeneration. In our study, poly-l-lactide (PLLA) and hybrid PLLA/collagen (PLLA/Coll) nanofibers (3:1 and 1:1) with fiber diameters of 210 to 430 nm were fabricated by electrospinning. Their morphological, chemical and mechanical characterizations were carried out using scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared (ATR-FTIR), and tensile instrument, respectively. Bone marrow derived mesenchymal stem cells (MSCs) seeded on electrospun nanofibers that are capable of differentiating into vascular cells have great potential for repair of the vascular system. We investigated the potential of MSCs for vascular cell differentiation in vitro on electrospun PLLA/Coll nanofibrous scaffolds using endothelial differentiation media. After 20 days of culture, MSC proliferation on PLLA/Coll(1:1) scaffolds was found 256% higher than the cell proliferation on PLLA scaffolds. SEM images showed that the MSC differentiated endothelial cells on PLLA/Coll scaffolds showed cobblestone morphology in comparison to the fibroblastic type of undifferentiated MSCs. The functionality of the cells in the presence of ‘endothelial induction media’, was further demonstrated from the immunocytochemical analysis, where the MSCs on PLLA/Coll (1:1) scaffolds differentiated to endothelial cells and expressed the endothelial cell specific proteins such as platelet endothelial cell adhesion molecule-1 (PECAM-1 or CD31) and Von Willebrand factor (vWF). From the results of the SEM analysis and protein expression studies, we concluded that the electrospun PLLA/Coll nanofibers could mimic the native vascular ECM environment and might be promising substrates for potential application towards vascular regeneration.     

Microporous biodegradable polyurethane membranes for tissue engineering

Microporous membranes with controlled pore size and structure were produced from biodegradable polyurethane based on aliphatic diisocyanate, poly(ε-caprolactone) diol and isosorbide chain extender using the modified phase-inversion technique. The following parameters affecting the process of membrane formation were investigated: the type of solvent, solvent–nonsolvent ratio, polymer concentration in solution, polymer solidification time, and the thickness of the polymer solution layer cast on a substrate. The experimental systems evaluated were polymer–N,N-dimethylformamide–water, polymer–N,N-dimethylacetamide–water and polymer–dimethylsulfoxide–water. From all three systems evaluated the best results were obtained for the system polymer–N,N-dimethylformamide–water. The optimal conditions for the preparation of microporous polyurethane membranes were: polymer concentration in solution 5% (w/v), the amount of nonsolvent 10% (v/v), the cast temperature 23°C, and polymer solidification time in the range of 24–48 h depending on the thickness of the cast polymer solution layer. Membranes obtained under these conditions had interconnected pores, well defined pore size and structure, good water permeability and satisfactory mechanical properties to allow for suturing. Potential applications of these membranes are skin wound cover and, in combination with autogenous chondrocytes, as an “artificial periosteum” in the treatment of articular cartilage defects. Various parts of this study were presented at the European Society for Biomaterials Meeting, Sorrento, Italy, September 11–15, 2005, and at the International Conference on Advanced Materials Design & Development (ICAMDD 2005), Goa, India, December 14–16, 2005. An experimental part of this work was carried out at the Polymer Research Department, AO Research Institute, Clavadelerstrasse 8, CH-7270 Davos, Switzerland.     

Cellular materials as porous scaffolds for tissue engineering

A major goal of tissue engineering is to synthesize or regenerate tissues and organs. Today, this is done by providing a synthetic porous scaffold, or matrix, which mimics the body's own extracellular matrix, onto which cells attach, multiply, migrate and function. Porous scaffolds are currently being developed for regeneration of skin, cartilage, bone, nerve and liver. The microstructures of many porous scaffolds ressemble that of an engineering foam. In this paper, we describe the microstructural requirements for porous scaffolds, review several processes for making them and show typical microstructures. Clinical studies have found that a collagen-based scaffold for skin regeneration reduces wound contraction during the healing process, reducing scar formation. The process of wound contraction is not well understood. Here, we describe the measurement of contraction of collagen-based scaffolds by fibroblasts in vitro using a cell force monitor.     

Characterization and in vitro evaluation of bacterial cellulose membranes functionalized with osteogenic growth peptide for bone tissue engineering

The aim of this study was to characterize the physicochemical properties of bacterial cellulose (BC) membranes functionalized with osteogenic growth peptide (OGP) and its C-terminal pentapeptide OGP[10-14], and to evaluate in vitro osteoinductive potential in early osteogenesis, besides, to evaluate cytotoxic, genotoxic and/or mutagenic effects. Peptide incorporation into the BC membranes did not change the morphology of BC nanofibers and BC crystallinity pattern. The characterization was complemented by Raman scattering, swelling ratio and mechanical tests. In vitro assays demonstrated no cytotoxic, genotoxic or mutagenic effects for any of the studied BC membranes. Culture with osteogenic cells revealed no difference in cell morphology among all the membranes tested. Cell viability/proliferation, total protein content, alkaline phosphatase activity and mineralization assays indicated that BC-OGP membranes enabled the highest development of the osteoblastic phenotype in vitro. In conclusion, the negative results of cytotoxicity, genotoxicity and mutagenicity indicated that all the membranes can be employed for medical supplies, mainly in bone tissue engineering/regeneration, due to their osteoinductive properties.     

Characterization of TEMPO-oxidized bacterial cellulose scaffolds for tissue engineering applications

Introduction of active groups on the surface of bacterial cellulose (BC) nanofibers is one of the promising routes of tailoring the performance of BC scaffolds for tissue engineering. This paper reported the introduction of aldehyde groups to BC nanofibers by 2,2,6,6-tetramethylpyperidine-1-oxy radical (TEMPO)-mediated oxidation and evaluation of the potential of the TEMPO-oxidized BC as tissue engineering scaffolds. Periodate oxidation was also conducted for comparison. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses were carried out to determine the existence of aldehyde groups on BC nanofibers and the crystallinity. In addition, properties relevant to scaffold applications such as morphology, fiber diameter, mechanical properties, and in vitro degradation were characterized. The results indicated that periodate oxidation could introduce free aldehyde to BC nanofibers and the free aldehyde groups on the TEMPO-oxidized BC tended to transfer to acetal groups. It was also found that the advantageous 3D structure of BC scaffolds remained unchanged and that no significant changes in morphology, fiber diameter, tensile structure and in vitro degradation were found after TEMPO-mediated oxidation while significant differences were observed upon periodate oxidation. The present study revealed that TEMPO-oxidation could impart BC scaffolds with new functions while did not degrade their intrinsic advantages.     

Thermal-crosslinked porous chitosan scaffolds for soft tissue engineering applications

The aim of this study was to demonstrate the feasibility of using a steam autoclave process for sterilization and simultaneously thermal-crosslinking of lyophilized chitosan scaffolds. This process is of great interest in biomaterial development due to its simplicity and low toxicity. The steam autoclave process had no significant effect on the average pore diameter (~ 70 μm) and overall porosity (> 80%) of the resultant chitosan scaffolds, while the sterilized scaffolds possessed more homogenous pore size distribution. The sterilized chitosan scaffolds exhibited an enhanced compressive modulus (109.8 kPa) and comparable equilibrium swelling ratio (23.3). The resultant chitosan scaffolds could be used directly for in vitro cell culture without extra sterilization. The data of in vitro studies demonstrated that the scaffolds facilitated cell attachment and proliferation, indicating great potential for soft tissue engineering applications.     

Nanoindentation on porous bioceramic scaffolds for bone tissue engineering

We report nanoindentation mechanical properties measurements on porous ceramic scaffolds made for tissue engineering applications. The scaffolds have been made from tricalcium phosphate (TCP), hydroxyapatite (HA) nanopowder and mixed powders of HA (50 wt%) and TCP (50 wt%) using the polyurethane sponge method, which produces open porous ceramic scaffolds through replication of a porous polymer template. The scaffolds prepared by this method have a controllable pore size and interconnected pore structure. The crystal structures and morphology of porous scaffolds were determined by X-ray diffraction (XRD) and atomic force microscopy (AFM) respectively. Nanoindentation measurements to a depth of 600 nm showed a Young's modulus value of 10.3 GPa for HA+TCP composite scaffolds and 1.5 GPa for TCP scaffolds. The hardness values were 240 MPa for HA+TCP composites and 21 MPa for TCP sample respectively. The results showed that the mechanical properties of the biodegradable scaffolds can be considerably enhanced with the addition of HA while maintaining the interconnected open pores and pore geometry desirable for bone tissue engineering.     

白色葡萄球菌辅助合成多孔阵列形貌CeO2粉体材料

二氧化铈(CeO2)是一种很重要的稀土氧化物,应用前景广泛。介绍了一种新的制备方法制备出一种具有不同微观结构形貌的CeO2颗粒。该制备方法是通过在HMT醇水反应体系中加入白色葡萄球菌,用共沉淀得到表面具有多孔阵列结构的CeO2纳米粉体材料。借助扫描电镜、透射电镜、X射线衍射、热重分析等方法,表征和分析了所得样品的形貌、晶相组成、微观结构和反应成形机理。并最终对所得样品进行甲基橙脱色实验,考察了其污水处理能力。结果表明,所得CeO2样品颗粒在10nm左右,多孔阵列的孔洞直径约为400nm。多孔阵列结构样品对甲基橙脱色结果较好,脱色率可达95%以上。