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At least 73 records · Page 4Linked to original sources

PubMed2004

Morphological evaluation of bioartificial hydrogels as potential tissue engineering scaffolds.

Poly(vinyl alcohol) hydrogels prepared by freeze-thawing procedure represent synthetic systems widely investigated as non-biodegradable scaffolds for tissue regeneration. In order to improve the biocompatibility properties of pure poly(vinyl alcohol) (PVA) hydrogels, blends of PVA with different biological macromolecules, such hyaluronic acid, dextran, and gelatin were prepared and used to produce "bioartificial hydrogels". The porosity characteristics of these hydrogels were investigated by scanning electron microscopy and mercury intrusion porosimetry. The morphology of bioartificial hydrogels was evaluated and compared with that of pure PVA hydrogels. In particular the effect exerted by each biological component on pore size and distribution was investigated. The obtained results indicate that when a natural macromolecule is added to PVA the internal structure of the material changes. A small amount of biopolymer induces the structural elements of PVA matrix to take on a well evident lamellar appearance and an apparent preferential orientation. Comparing the results of SEM and mercury intrusion porosimetry it was concluded that hydrogels containing 20% of biological component have the most regular structure and at the same time the lowest total porosity. On the contrary samples with the highest content of natural polymer (40%) show the less regular structure and the highest total porosity.

Biocompatible Materials↗

PubMed2001

Thermal compression and characterization of three-dimensional nonwoven PET matrices as tissue engineering scaffolds.

Nonwoven fibrous matrices have been widely used as scaffolds in tissue engineering, and modification of microstructure of these matrices is needed to organize cells in three-dimensional space with spatially balanced proliferation and differentiation required for functional tissue development. The method of thermal compression of nonwoven polyethylene terephthalate (PET) fabrics was developed and key parameters of temperature, pressure, and compression duration were evaluated in this study. The permanent deformation was obtained at elevated temperature under pressure and the viscoelastic compressional behaviors were observed, characterized by a distinct apparent modulus change in glass transition temperature region. A liquid extrusion method was further employed to analyze both pore size and its distribution for matrices with porosity ranging from 84 to 93%. It is also found that a more uniformly distributed pore size was resulted from thermal compression and the isotropic nature of nonwoven fabrics was preserved because of the proportional reduction of the pore by compression. The thermally compressed fabric matrices with two different pore sizes (15 and 20 microm in pore radius) were used to culture human trophoblast ED27 and NIH 3T3 cells. It was found that cells cultured in the different pore-size PET matrices had different cell spatial organization and proliferation rates. The smaller pores in the matrix allowed cells to spread better and proliferate faster, while cells in the larger pores tended to form large aggregates and had lower proliferation rate. The thermal compression technique also can be applied to other synthetic fibrous matrices including biodegradable polymers used in tissue engineering to modify the microstructure according to their viscoelastic properties.

3T3 Cells↗

PubMedDate not supplied

Synthesis, material properties, and biocompatibility of a novel self-cross-linkable poly(caprolactone fumarate) as an injectable tissue engineering scaffold.

A novel self-cross-linkable and biodegradable macromer, poly(caprolactone fumarate) (PCLF), has been developed for guided bone regeneration. This macromer is a copolymer of fumaryl chloride, which contains double bonds for in-situ cross-linking, and poly(epsilon-caprolactone), which has a flexible chain to facilitate self-cross-linkability. PCLF was characterized with Fourier transform infrared spectroscopy, 1H and 13C nuclear magnetic resonance spectroscopy, and gel permeation chromatography. Porous scaffolds were fabricated with sodium chloride particles as the porogen and a chemical initiation system. The PCLF scaffolds were characterized with scanning electron microscopy and micro-computed-tomography. The cytotoxicity and in vivo biocompatibility of PCLF were also assessed. Our results suggest that this novel copolymer, PCLF, is an injectable, self-cross-linkable, and biocompatible macromer that may be potentially used as a scaffold for tissue engineering applications.

Animals↗

PubMed2002

The use of ischaemic vessels as prostheses or tissue engineering scaffolds after cryopreservation.

OBJECTIVE: to evaluate the condition of organ donor arteries subjected to prolonged cold-ischaemia followed by cryopreservation, for their possible use as vascular grafts. MATERIALS AND METHODS: fresh specimens of human iliac artery from organ donors were used as controls. These arteries were divided into two portions, one of which was cryopreserved in an automated freezer. A further group of arteries was immersed in Wisconsin solution and kept for 4 days at 4 degrees C (cold-ischaemia). After this period, the arteries were also cut into two, and one of these portions was cryopreserved. All the cryopreserved arterial segments were stored for a month and then subjected to automated gradual thawing. The thawed specimens were evaluated by light microscopy, scanning and transmission electron microscopy, immunohistochemical analysis (MMPs, elastin, CD31, von Willebrand factor) and the in situ detection of fragmented DNA (TUNEL method). RESULTS: the most marked changes induced by cryopreservation were partial vessel deendothelialisation and morphological changes in cells of the intima that were in the process of detachment. No significant changes were observed in the medial layer, other than discrete elastic fibre fragmentation. Following cold-ischaemia, the endothelium was the most affected layer, with large denuded areas and exposure of the fibroelastic layer. Increased MMP-2 expression was also noted after cold-ischaemia. When subjected to both cold-ischaemia and cryopreservation, a large proportion of endothelial cells showed positivity for the TUNEL technique, however, no significant difference was observed between the ischaemic and the ischaemic/cryopreserved specimens. CONCLUSIONS: prolonged cold-ischaemia causes some additional damage to the arterial wall compared to cryopreservation alone. However, the structural component of the ischaemic vessel remains in a condition that is suitable for subsequent cryopreservation and use as a vessel substitute or a scaffold for tissue engineering.

Adult↗

PubMed2003

Photocrosslinked hyaluronic acid hydrogels: natural, biodegradable tissue engineering scaffolds.

Ideally, rationally designed tissue engineering scaffolds promote natural wound healing and regeneration. Therefore, we sought to synthesize a biomimetic hydrogel specifically designed to promote tissue repair and chose hyaluronic acid (HA; also called hyaluronan) as our initial material. Hyaluronic acid is a naturally occurring polymer associated with various cellular processes involved in wound healing, such as angiogenesis. Hyaluronic acid also presents unique advantages: it is easy to produce and modify, hydrophilic and nonadhesive, and naturally biodegradable. We prepared a range of glycidyl methacrylate-HA (GMHA) conjugates, which were subsequently photopolymerized to form crosslinked GMHA hydrogels. A range of hydrogel degradation rates was achieved as well as a corresponding, modest range of material properties (e.g., swelling, mesh size). Increased amounts of conjugated methacrylate groups corresponded with increased crosslink densities and decreased degradation rates and yet had an insignificant effect on human aortic endothelial cell cytocompatibility and proliferation. Rat subcutaneous implants of the GMHA hydrogels showed good biocompatibility, little inflammatory response, and similar levels of vascularization at the implant edge compared with those of fibrin positive controls. Therefore, these novel GMHA hydrogels are suitable for modification with adhesive peptide sequences (e.g., RGD) and use in a variety of wound-healing applications.

Absorbable Implants↗

PubMed2006

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.

Biocompatible Materials↗

PubMed2001

Synthesis and characterization of macroporous chitosan/calcium phosphate composite scaffolds for tissue engineering.

Chitosan scaffolds reinforced by beta-tricalcium phosphate (beta-TCP) and calcium phosphate invert glass were fabricated with a low-cost, bioclean freeze-drying technique via thermally induced phase separation. The microstructure, mechanical performance, biodegradation, and bioactivity of the scaffolds were studied. The composite scaffolds were macroporous, and the pore structures of the scaffolds with beta-TCP and the glass appeared very different. Both the compressive modulus and yield strength of the scaffolds were greatly improved, and reinforced microstructures were achieved. The bioactivity tests showed a continuous decrease in both Ca and P concentrations of a simulated body fluid (SBF) after the scaffolds with beta-TCP were immersed in the SBF for more than 20 h, which suggests that an apatite layer might be formed on the scaffolds. However, the same was not observed for the pure chitosan scaffolds or the scaffolds incorporated with the glass. This was further confirmed by micrographs from scanning electron microscopy. This study suggests that the desirable pore structure, biodegradation rate, and bioactivity of the composite scaffolds might be achieved through controlling the ratio of chitosan and calcium phosphates or beta-TCP and the glass.

Biocompatible Materials↗

PubMed2006

The effect of anisotropic architecture on cell and tissue infiltration into tissue engineering scaffolds.

A common phenomenon in tissue engineering is rapid tissue formation on the outer edge of the scaffold which restricts cell penetration and nutrient exchange to the scaffold centre, resulting in a necrotic core. To address this problem, we generated scaffolds with both random and anisotropic open porous architectures to enhance cell and subsequent tissue infiltration throughout the scaffold for applications in bone and cartilage engineering. Hydroxyapatite (HA) and poly(D,L-lactic acid) (P(DL)LA) scaffolds with random open porosity were manufactured, using modified slip-casting and by supercritical fluid processing respectively, and subsequently characterised. An array of porous aligned channels (400 microm) was incorporated into both scaffold types and cell (human osteoblast sarcoma, for HA scaffolds; ovine meniscal fibrochondrocytes, for P(DL)LA scaffolds) and tissue infiltration into these modified scaffolds was assessed in vitro (cell penetration) and in vivo (tissue infiltration; HA scaffolds only). Scaffolds were shown to have an extensive random, open porous structure with an average porosity of 85%. Enhanced cell and tissue penetration was observed both in vitro and in vivo demonstrating that scaffold design alone can influence cell and tissue infiltration into the centre of tissue engineering scaffolds.

Animals↗

PubMed2005

Plasmid delivery in vivo from porous tissue-engineering scaffolds: transgene expression and cellular transfection.

Tissue engineering scaffolds capable of sustained plasmid release can promote gene transfer locally and stimulate new tissue formation. We have investigated the scaffold design parameters that influence the extent and duration of transgene expression and have characterized the distribution of transfected cells. Porous scaffolds with encapsulated plasmid were fabricated from poly(lactide-co-glycolide) with a gas foaming procedure, with wet granulation employed to mix the components homogeneously prior to foaming. Wet granulation enhanced plasmid incorporation relative to standard procedures and also enhanced in vivo transgene expression, possibly through the increased loading and maintenance of the scaffold pore structure. The plasmid loading regulated the quantity and duration of transgene expression, with expression for 105 days achieved at the highest dosage. Expression was localized to the implantation site, though the distribution of transfected cells varied with time. Transfected cells were initially observed at the scaffold periphery (day 3), then within the pores and adjacent to the polymer (day 17), and finally throughout the scaffold interior (day 126). Delivery of a plasmid encoding VEGF increased the blood vessel density relative to control. Correlating scaffold design with gene transfer efficiency and tissue formation will facilitate application of plasmid-releasing scaffolds to multiple tissues.

Animals↗

PubMed2002

Bioreactors mediate the effectiveness of tissue engineering scaffolds.

We hypothesized that the mechanically active environment present in rotating bioreactors mediates the effectiveness of three-dimensional (3D) scaffolds for cartilage tissue engineering. Cartilaginous constructs were engineered by using bovine calf chondrocytes in conjunction with two scaffold materials (SM) (benzylated hyaluronan and polyglycolic acid); three scaffold structures (SS) (sponge, non-woven mesh, and composite woven/non-woven mesh); and two culture systems (CS) (a bioreactor system and petri dishes). Construct size, composition [cells, glycosaminoglycans (GAG), total collagen, and type-specific collagen mRNA expression and protein levels], and mechanical function (compressive modulus) were assessed, and individual and interactive effects of model system parameters (SM, SS, CS, SM*CS and SS*CS) were demonstrated. The CS affected cell seeding (higher yields of more spatially uniform cells were obtained in bioreactor-grown than dish-grown 3-day constructs) and subsequently affected chondrogenesis (higher cell numbers, wet weights, wet weight GAG fractions, and collagen type II levels were obtained in bioreactor-grown than dish-grown 1-month constructs). In bioreactors, mesh-based scaffolds yielded 1-month constructs with lower type I collagen levels and four-fold higher compressive moduli than corresponding sponge-based scaffolds. The data imply that interactions between bioreactors and 3D tissue engineering scaffolds can be utilized to improve the structure, function, and molecular properties of in vitro-generated cartilage.

Animals↗

PubMed1994

Biodegradable polymer scaffolds for tissue engineering.

Synthetic polymer scaffolds designed for cell transplantation were reproducibly made on a large scale and studied with respect to biocompatibility, structure and biodegradation rate. Polyglycolic acid (PGA) was extruded and oriented to form 13 microns diameter fibers with desired tenacity. Textile processing techniques were used to produce fibrous scaffolds with a porosity of 97% and sufficient structural integrity to maintain their dimensions when seeded with isolated cartilage cells (chondrocytes) and cultured in vitro at 37 degrees C for 8 weeks. Cartilaginous tissue consisting of glycosaminoglycan and collagen was regenerated in the shape of the original PGA scaffold. The resulting cell-polymer constructs were the largest grown in vitro to date (1 cm diameter x 0.35 cm thick). Construct mass was accurately predicted by accounting for accumulation of tissue components and scaffold degradation. The scaffold induced chondrocyte differentiation with respect to morphology and phenotype and represents a model cell culture substrate that may be useful for a variety of tissue engineering applications.

Biocompatible Materials↗

PubMed2006

Micro-CT-based screening of biomechanical and structural properties of bone tissue engineering scaffolds.

The development of successful scaffolds for bone tissue engineering requires a concurrent engineering approach that combines different research fields. In order to limit in vivo experiments and reduce trial and error research, a scaffold screening technique has been developed. In this protocol seven structural and three biomechanical properties of potential scaffold materials are quantified and compared to the desired values. The property assessment is done on computer models of the scaffolds, and these models are based on micro-CT images. As a proof of principle, three porous scaffolds were evaluated with this protocol: stainless steel, hydroxyapatite, and titanium. These examples demonstrate that the modelling technique is able to quantify important scaffold properties. Thus, a powerful technique for automated screening of bone tissue engineering scaffolds has been developed that in a later stage may be used to tailor the scaffold properties to specific requirements.

Biocompatible Materials↗

PubMed2002

Emerging design principles in biomaterials and scaffolds for tissue engineering.

Biomaterials and scaffolds play an essential role in tissue engineering by guiding new tissue growth in vivo and in vitro. While adaptation of existing surgical materials has fulfilled some needs in the field, new applications demand better control of bulk properties such as degradation and of surface properties that control cell interactions. Advances in molecular cell biology are driving the incorporation of new biological moieties into materials, and a set of design principles based on quantitative analysis of key cellular processes involved in regeneration is emerging. At the same time, new materials-processing methodologies are emerging to allow fabrication of these fragile materials into devices appropriate for delivery.

Animals↗

PubMed2006

Implantation of a new porous gelatin-siloxane hybrid into a brain lesion as a potential scaffold for tissue regeneration.

For brain tissue regeneration, any scaffold for migrated or transplanted stem cells with supportive angiogenesis is important once necrotic brain tissue has formed a cavity after injury such as cerebral ischemia. In this study, a new porous gelatin-siloxane hybrid derived from the integration of gelatin and 3-(glycidoxypropyl) trimethoxysilane was implanted as a three-dimensional scaffold into a defect of the cerebral cortex. The porous hybrid implanted into the lesion remained at the same site for 60 days, kept integrity of the brain shape, and attached well to the surrounding brain tissues. Marginal cavities of the scaffolds were occupied by newly formed tissue in the brain, where newly produced vascular endothelial, astroglial, and microglial cells were found with bromodeoxyuridine double positivity, and the numbers of those cells were dose-dependently increased with the addition of basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF). Extension of dendrites was also found from the surrounding cerebral cortex to the newly formed tissue, especially with the addition of bFGF and EGF. The present study showed that a new porous gelatin-siloxane hybrid had biocompatibility after implantation into a lesion of the central nervous system, and thus provided a potential scaffold for cell migration, angiogenesis and dendrite elongation with dose-dependent effects of additive bFGF and EGF.

Animals↗

PubMed2006

Nano-featured scaffolds for tissue engineering: a review of spinning methodologies.

Tissue engineering is a multidisciplinary field that is rapidly emerging as a promising new approach in the restoration and reconstruction of imperfect tissues. In this approach, scaffolds play a pivotal role in supporting the cells to accommodate and guide their growth into a specific tissue; therefore, designing scaffolds that are favorable to cellular growth is of great importance. Electrospinning is a straightforward, cost-effective, and versatile technique that has been applied recently for the fabrication of nano-featured scaffolds suitable for tissue engineering. By mimicking a natural extracellular matrix, it offers many advantages over conventional scaffold methodologies. This paper reviews the current state of art of designing nanostructure scaffolds by using the electrospinning technique. Furthermore, an overview of this technique and its spinning mechanism is described, with special attention to areas of interest to the readers.

Animals↗

PubMed2004

Preparation and characterization of macroporous chitosan/wollastonite composite scaffolds for tissue engineering.

Chitosan/wollastonite composite scaffolds were prepared by a thermally induced phase separation method. The microstructure, mechanical performance and in vitro bioactivity of the composite scaffolds were investigated. The composite scaffolds were macroporous and wollastonite particles were dispersed uniformly on the surface of the pore walls. Scanning electron microscope images of the composite scaffolds demonstrated that the scaffolds had interconnected pores with diameters from 60 to 200 microm. Both the pore size and structure were affected by freezing temperature. The mechanical performance of the composite scaffolds was improved compared to that of pure chitosan scaffolds. The in vitro bioactivity of the scaffolds was evaluated by soaking samples in simulated body fluid and the apatite layer was observed on the surface of the pore walls of the composite scaffolds. Our results suggest that the incorporation of wollastonite into chitosan could enhance both the mechanical strength and the in vitro bioactivity of the resultant composite. The macroporous chitosan/wollastonite scaffolds may be a potential candidate for application in tissue engineering.

Biocompatible Materials↗

PubMed2005

A modular and supramolecular approach to bioactive scaffolds for tissue engineering.

Bioactive polymeric scaffolds are a prerequisite for the ultimate formation of functional tissues. Here, we show that supramolecular polymers based on quadruple hydrogen bonding ureido-pyrimidinone (UPy) moieties are eminently suitable for producing such bioactive materials owing to their low-temperature processability, favourable degradation and biocompatible behaviour. Particularly, the reversible nature of the hydrogen bonds allows for a modular approach to gaining control over cellular behaviour and activity both in vitro and in vivo. Bioactive materials are obtained by simply mixing UPy-functionalized polymers with UPy-modified biomolecules. Low-molecular-weight bis-UPy-oligocaprolactones with cell adhesion promoting UPy-Gly-Arg-Gly-Asp-Ser (UPy-GRGDS) and the synergistic UPy-Pro-His-Ser-Arg-Asn (UPy-PHSRN) peptide sequences are synthesized and studied. The in vitro results indicate strong and specific cell binding of fibroblasts to the UPy-functionalized bioactive materials containing both UPy-peptides. An even more striking effect is seen in vivo where the formation of single giant cells at the interface between bioactive material and tissue is triggered.

3T3 Cells↗

PubMed2004

Gene delivery from polymer scaffolds for tissue engineering.

The combination of gene therapy with tissue engineering offers the potential to direct progenitor cell proliferation and differentiation into functional tissue replacements. Many approaches to engineering tissue replacements feature a polymer scaffold to create and maintain a space, support cell adhesion, and organize tissue formation. Polymer scaffolds, either natural, synthetic, or a combination of the two, have also been adapted to serve as delivery vehicles for viral and nonviral vectors, which can induce the expression of tissue inductive factors. Gene delivery is a versatile approach, capable of targeting any cellular process through localized expression of tissue inductive factors. The design and application of tissue engineering scaffolds for localized gene transfer are reviewed. Scaffolds are designed either to release the vector into the local tissue environment or maintain the vector at the polymer surface, which is regulated by the effective affinity of the vector for the polymer. Polymeric delivery can enhance gene transfer locally, promote and extend transgene expression, avoid vector distribution to distant tissues, and reduce the immune response to the vector. Scaffolds capable of controlled DNA delivery can provide a fundamental tool for directing progenitor cell function, which has applications with the engineering of numerous types of tissue. The utility of this approach will increase with the development of design parameters that correlate release and transgene expression, and with continued research into the biology of tissue formation.

Cell Culture Techniques↗