Effects of pore size in 3-D fibrous matrix on human trophoblast tissue development

Harnessing the potential of hydrogels for advanced therapeutic applications: current achievements and future directions

The applications of hydrogels have expanded significantly due to their versatile, highly tunable properties and breakthroughs in biomaterial technologies. In this review, we cover the major achievements and the potential of hydrogels in therapeutic applications, focusing primarily on two areas: emerging cell-based therapies and promising non-cell therapeutic modalities. Within the context of cell therapy, we discuss the capacity of hydrogels to overcome the existing translational challenges faced by mainstream cell therapy paradigms, provide a detailed discussion on the advantages and principal design considerations of hydrogels for boosting the efficacy of cell therapy, as well as list specific examples of their applications in different disease scenarios. We then explore the potential of hydrogels in drug delivery, physical intervention therapies, and other non-cell therapeutic areas (e.g., bioadhesives, artificial tissues, and biosensors), emphasizing their utility beyond mere delivery vehicles. Additionally, we complement our discussion on the latest progress and challenges in the clinical application of hydrogels and outline future research directions, particularly in terms of integration with advanced biomanufacturing technologies. This review aims to present a comprehensive view and critical insights into the design and selection of hydrogels for both cell therapy and non-cell therapies, tailored to meet the therapeutic requirements of diverse diseases and situations.

Additively manufactured bioceramic scaffolds based on triply periodic minimal surfaces for bone regeneration

The study focused on the effects of a triply periodic minimal surface (TPMS) scaffolds, varying in porosity, on the repair of mandibular defects in New Zealand white rabbits. Four TPMS configurations (40%, 50%, 60%, and 70% porosity) were fabricated with β-tricalcium phosphate bioceramic via additive manufacturing. Scaffold properties were assessed through scanning electron microscopy and mechanical testing. For proliferation and adhesion assays, mouse bone marrow stem cells (BMSCs) were cultured on these scaffolds. In vivo, the scaffolds were implanted into rabbit mandibular defects for 2 months. Histological staining evaluated osteogenic potential. Moreover, RNA-sequencing analysis and RT-qPCR revealed the significant involvement of angiogenesis-related factors and Hippo signaling pathway in influencing BMSCs behavior. Notably, the 70% porosity TPMS scaffold exhibited optimal compressive strength, superior cell proliferation, adhesion, and significantly enhanced osteogenesis and angiogenesis. These findings underscore the substantial potential of 70% porosity TPMS scaffolds in effectively promoting bone regeneration within mandibular defects.

3D Printing, Histological, and Radiological Analysis of Nanosilicate-Polysaccharide Composite Hydrogel as a Tissue-Equivalent Material for Complex Biological Bone Phantom

Nanosilicate-polysaccharide composite hydrogels are a well-studied class of materials in regenerative medicine that combine good 3D printability, staining, and biological properties, making them an excellent candidate material for complex bone scaffolds. The aim of this study was to develop a hydrogel suitable for 3D printing that has biological and radiological properties similar to those of the natural bone and to develop protocols for their histological and radiological analysis. We synthesized a hydrogel based on alginate, methylcellulose, and laponite, then 3D printed it into a series of complex bioscaffolds. The scaffolds were scanned with CT and CBCT scanners and exported as DICOM datasets, then cut into histological slides and stained using standard histological protocols. From the DICOM datasets, the average value of the voxels in Hounsfield Units (HU) was calculated and compared with natural trabecular bone. In the histological sections, we tested the effect of standard histological stains on the hydrogel matrix in the context of future cytological and histological analysis. The results confirmed that an alginate/methylcellulose/laponite-based composite hydrogel can be used for 3D printing of complex high fidelity three-dimensional scaffolds. This opens an avenue for the development of dynamic biological physical phantoms for bone tissue engineering and the development of new CT-based imaging algorithms for the needs of radiology and radiation therapy.

3D Printed Hierarchical Porous Poly(ε-caprolactone) Scaffolds from Pickering High Internal Phase Emulsion Templating

In the realm of biomaterials, particularly bone tissue engineering, there has been a great increase in interest in scaffolds with hierarchical porosity and customizable multifunctionality. Recently, the three-dimensional (3D) printing of biopolymer-based inks (solutions or emulsions) has gained high popularity for fabricating tissue engineering scaffolds, which optimally satisfies the desired properties and performances. Herein, therefore, we explore the fabrication of 3D printed hierarchical porous scaffolds of poly(ε-caprolactone) (PCL) using the water-in-oil (w/o) Pickering PCL high internal phase emulsions (HIPEs) as the ink in 3D printer. The Pickering PCL HIPEs stabilized using hydrophobically modified nanoclay comprised of aqueous poly(vinyl alcohol) (PVA) as the dispersed phase. Rheological measurements suggested the shear thinning behavior of Pickering HIPEs having a dispersed droplet diameter of 3-25 μm. The pore morphology resembling the natural extracellular matrix and the mechanical properties of scaffolds were customized by tuning the emulsion composition and 3D printing parameters. In vitro biomineralization and drug release studies proved the scaffolds' potential in developing the apatite-rich bioactive interphase and controlled drug delivery, respectively. During in vitro osteoblast (MG63) growth experiments for up to 7 days, good adhesion and proliferation on PCL scaffolds confirmed their cytocompatibility, assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) analysis. This study suggests that the assembly of HIPE templates and 3D printing is a promising approach to creating hierarchical porous scaffolds potentially suitable for bone tissue engineering and can be stretched to other biopolymers as well.

A bioactive compliant vascular graft modulates macrophage polarization and maintains patency with robust vascular remodeling

Conventional synthetic vascular grafts are associated with significant failure rates due to their mismatched mechanical properties with the native vessel and poor regenerative potential. Though different tissue engineering approaches have been used to improve the biocompatibility of synthetic vascular grafts, it is still crucial to develop a new generation of synthetic grafts that can match the dynamics of native vessel and direct the host response to achieve robust vascular regeneration. The size of pores within implanted biomaterials has shown significant effects on macrophage polarization, which has been further confirmed as necessary for efficient vascular formation and remodeling. Here, we developed biodegradable, autoclavable synthetic vascular grafts from a new polyurethane elastomer and tailored the grafts' interconnected pore sizes to promote macrophage populations with a pro-regenerative phenotype and improve vascular regeneration and patency rate. The synthetic vascular grafts showed similar mechanical properties to native blood vessels, encouraged macrophage populations with varying M2 to M1 phenotypic expression, and maintained patency and vascular regeneration in a one-month rat carotid interposition model and in a four-month rat aortic interposition model. This innovative bioactive synthetic vascular graft holds promise to treat clinical vascular diseases.

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Small diameter vascular grafts were fabricated from a new elastomeric polyurethane designed for vascular tissue engineering.

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The grafts combined excellent elasticity, strength, porosity, hemocompatibility, degradability, and biocompatibility.

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In vivo, grafts maintained patency for four months and supported tissue regeneration resembling the native arterial wall.

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Pore size was found to influence graft characteristics and efficacy.

A Review on Stimuli-Actuated 3D Micro/Nanostructures for Tissue Engineering and the Potential of Laser-Direct Writing via Two-Photon Polymerization for Structure Fabrication

In this review, we present the most recent and relevant research that has been done regarding the fabrication of 3D micro/nanostructures for tissue engineering applications. First, we make an overview of 3D micro/nanostructures that act as backbone constructs where the seeded cells can attach, proliferate and differentiate towards the formation of new tissue. Then, we describe the fabrication of 3D micro/nanostructures that are able to control the cellular processes leading to faster tissue regeneration, by actuation using topographical, mechanical, chemical, electric or magnetic stimuli. An in-depth analysis of the actuation of the 3D micro/nanostructures using each of the above-mentioned stimuli for controlling the behavior of the seeded cells is provided. For each type of stimulus, a particular recent application is presented and discussed, such as controlling the cell proliferation and avoiding the formation of a necrotic core (topographic stimulation), controlling the cell adhesion (nanostructuring), supporting the cell differentiation via nuclei deformation (mechanical stimulation), improving the osteogenesis (chemical and magnetic stimulation), controlled drug-delivery systems (electric stimulation) and fastening tissue formation (magnetic stimulation). The existing techniques used for the fabrication of such stimuli-actuated 3D micro/nanostructures, are briefly summarized. Special attention is dedicated to structures' fabrication using laser-assisted technologies. The performances of stimuli-actuated 3D micro/nanostructures fabricated by laser-direct writing via two-photon polymerization are particularly emphasized.

Two-color fluorescent proteins reporting survivin regulation in breast cancer cells for high throughput drug screening

Reporter gene assay is widely used for high throughput drug screening and drug action mechanism evaluation. In this study, we developed a robust dual-fluorescent reporter assay to detect drugs repressing the transcription of survivin, a cancer biomarker from the inhibitor of apoptosis family, in breast cancer cells cultured in three-dimensional (3D) microbioreactors. Survivin is overexpressed in numerous malignancies but almost silent in normal tissue cells and is considered a lead target for cancer therapy. Breast cancer MCF-7 cells were engineered to express enhanced green fluorescent protein driven by a survivin promoter and red fluorescent protein driven by a cytomegalovirus promoter as internal control to detect changes in survivin expression in cells as affected by drugs. This 3D dual-fluorescent reporter assay was validated with YM155 and doxorubicin, which were known to downregulate survivin in cancer cells, and further evaluated with two widely used anticancer compounds, cisplatin, and epigallocatechin gallate, to evaluate their effects on survivin expression. The results showed that the 3D dual-fluorescent reporter assay was robust for high throughput screening of drugs targeting survivin in breast cancer cells.

A Review of Biomaterials and Scaffold Fabrication for Organ-on-a-Chip (OOAC) Systems

Drug and chemical development along with safety tests rely on the use of numerous clinical models. This is a lengthy process where animal testing is used as a standard for pre-clinical trials. However, these models often fail to represent human physiopathology. This may lead to poor correlation with results from later human clinical trials. Organ-on-a-Chip (OOAC) systems are engineered microfluidic systems, which recapitulate the physiochemical environment of a specific organ by emulating the perfusion and shear stress cellular tissue undergoes in vivo and could replace current animal models. The success of culturing cells and cell-derived tissues within these systems is dependent on the scaffold chosen; hence, scaffolds are critical for the success of OOACs in research. A literature review was conducted looking at current OOAC systems to assess the advantages and disadvantages of different materials and manufacturing techniques used for scaffold production; and the alternatives that could be tailored from the macro tissue engineering research field.

Influence of Materials Properties on Bio-Physical Features and Effectiveness of 3D-Scaffolds for Periodontal Regeneration

Periodontal diseases are multifactorial disorders, mainly due to severe infections and inflammation which affect the tissues (i.e., gum and dental bone) that support and surround the teeth. These pathologies are characterized by bleeding gums, pain, bad breath and, in more severe forms, can lead to the detachment of gum from teeth, causing their loss. To date it is estimated that severe periodontal diseases affect around 10% of the population worldwide thus making necessary the development of effective treatments able to both reduce the infections and inflammation in injured sites and improve the regeneration of damaged tissues. In this scenario, the use of 3D scaffolds can play a pivotal role by providing an effective platform for drugs, nanosystems, growth factors, stem cells, etc., improving the effectiveness of therapies and reducing their systemic side effects. The aim of this review is to describe the recent progress in periodontal regeneration, highlighting the influence of materials' properties used to realize three-dimensional (3D)-scaffolds, their bio-physical characteristics and their ability to provide a biocompatible platform able to embed nanosystems.

Halloysite Nanoclay/Biopolymers Composite Materials in Tissue Engineering

Biocompatible materials for the fabrication of tissue substitutes are crucially important in the advancement of modern medicinal biotechnology. These materials, to serve their function, should be similar in physical, chemical, biological, and structural properties to native tissues which they are aimed to mimic. The porosity of artificial scaffolds is essential for normal nutrient transmission to cells, gas diffusion, and cell attachment and proliferation. Nanoscale inorganic additives and dopants are widely used to improve the functional properties of the polymer materials for tissue engineering. Among these inorganic dopants, halloysite nanotubes are arguably the most perspective candidates because of their biocompatibility and functional properties allowing to enhance significantly the mechanical and chemical stability of tissue engineering scaffolds. Here, this vibrant field of biotechnology for regenerative medicine is overviewed.

Microfabricated tuneable and transferable porous PDMS membranes for Organs-on-Chips

We present a novel and highly reproducible process to fabricate transferable porous PDMS membranes for PDMS-based Organs-on-Chips (OOCs) using microelectromechanical systems (MEMS) fabrication technologies. Porous PDMS membranes with pore sizes down to 2.0 μm in diameter and a wide porosity range (2-65%) can be fabricated. To overcome issues normally faced when using replica moulding and extend the applicability to most OOCs and improve their scalability and reproducibility, the process includes a sacrificial layer to easily transfer the membranes from a silicon carrier to any PDMS-based OOC. The highly reliable fabrication and transfer method does not need of manual handling to define the pore features (size, distribution), allowing very thin (<10 μm) functional membranes to be transferred at chip level with a high success rate (85%). The viability of cell culturing on the porous membranes was assessed by culturing two different cell types on transferred membranes in two different OOCs. Human umbilical endothelial cells (HUVEC) and MDA-MB-231 (MDA) cells were successfully cultured confirming the viability of cell culturing and the biocompatibility of the membranes. The results demonstrate the potential of controlling the porous membrane features to study cell mechanisms such as transmigrations, monolayer formation, and barrier function. The high control over the membrane characteristics might consequently allow to intentionally trigger or prevent certain cellular responses or mechanisms when studying human physiology and pathology using OOCs.

Thermally induced self-agglomeration 3D scaffolds with BMP-2-loaded core-shell fibers for enhanced osteogenic differentiation of rat adipose-derived stem cells

Introduction

Scaffold structure plays a vital role in cell behaviors. Compared with two-dimensional structure, 3D scaffolds can mimic natural extracellular matrix (ECM) and promote cell–cell and cell–matrix interactions. The combination of osteoconductive scaffolds and osteoinductive growth factors is considered to have synergistic effects on bone regeneration.

Materials and methods

In this study, core–shell poly(lactide-co-glycolide) (PLGA)/polycaprolactone (PCL)–BMP-2 (PP–B) fibrous scaffolds were prepared through coaxial electrospinning. Next, we fabricated 3D scaffolds based on PP–B fibers with thermally induced self-agglomeration (TISA) method and compared with conventional PLGA/PCL scaffolds in terms of scaffold morphology and BMP-2 release behaviors. Then, rat adipose-derived stem cells (rADSCs) were seeded on the scaffolds, and the effects on cell proliferation, cell morphology, and osteogenic differentiation of rADSCs were detected.

Results

The results demonstrated that 3D scaffold incorporated with BMP-2 significantly increased proliferation and osteogenic differentiation of rADSCs, followed by PP–B group.

Conclusion

Our findings indicate that scaffolds with 3D structure and osteoinductive growth factors have great potential in bone tissue engineering.

3D Biomimetic Magnetic Structures for Static Magnetic Field Stimulation of Osteogenesis

We designed, fabricated and optimized 3D biomimetic magnetic structures that stimulate the osteogenesis in static magnetic fields. The structures were fabricated by direct laser writing via two-photon polymerization of IP-L780 photopolymer and were based on ellipsoidal, hexagonal units organized in a multilayered architecture. The magnetic activity of the structures was assured by coating with a thin layer of collagen-chitosan-hydroxyapatite-magnetic nanoparticles composite. In vitro experiments using MG-63 osteoblast-like cells for 3D structures with gradients of pore size helped us to find an optimum pore size between 20-40 µm. Starting from optimized 3D structures, we evaluated both qualitatively and quantitatively the effects of static magnetic fields of up to 250 mT on cell proliferation and differentiation, by ALP (alkaline phosphatase) production, Alizarin Red and osteocalcin secretion measurements. We demonstrated that the synergic effect of 3D structure optimization and static magnetic stimulation enhances the bone regeneration by a factor greater than 2 as compared with the same structure in the absence of a magnetic field.

Polymer coated mesoporous ceramic for drug delivery in bone tissue engineering

Treatment strategy for various bone fracture and defects the researchers are focusing to develop a new carrier for delivering the drug into injured area with controlled and sustained manner using biomaterials with dynamic architecture orientation. Ceramic materials are resembled with bone compositional architecture and better bioactivity, degradability as well as antimicrobial activity made its enormous application in bone tissue engineering (BTE). Current focus in regenerative medicine were orchestration of biomaterials with the capacity of loading the drugs, growth factors, ionic components to promote better healing of bone tissue. Mesoporous type materials owed a great look towards the delivery of drugs, growth factors, etc in BTE because of its unique geometry. So the guest molecules loaded with geometrically organized ceramics would deliver onto the site of injury in controlled manner also the guiding and regulation of delivery of molecules have been controlled with the polymers response to different stimulation or biochemical factors as either scaffold or encapsulated particles for bone regeneration. Hence the review aims to describing the recent progress in bone tissue engineering using the ceramic based mesoporous materials encapsulated with polymers respond to different physiochemical stimulation for the efficient and controlled delivery of drug/growth factors for better bone healing.

Cadherin- and Rigidity-Dependent Growth of Lung Cancer Cells in a Partially Confined Microenvironment

During tumor development, cancer cells constantly confront different types of extracellular barriers. However, fundamental questions like whether tumor cells will continue to grow against confinement or away from it and what key factors govern this process remain poorly understood. To address these issues, here we examined the growth dynamics of human lung epithelial carcinoma A549 cells partially confined in micrometer-sized cylindrical pores with precisely controlled wall stiffness. It was found that, after reaching confluency, the cell monolayer enclosed by a compliant wall was able to keep growing and pushing the boundary, eventually leading to a markedly enlarged pore. In contrast, a much reduced in-plane growth and elevated strain level among cells were observed when the confining wall becomes stiff. Furthermore, under such circumstance, cells switched their growth from within the monolayer to along the out-of-plane direction, resulting in cell stacking. We showed that these observations can be well explained by a simple model taking into account the deformability of the wall and the threshold stress for inhibiting cell growth. Interestingly, cadherins were found to play an important role in the proliferation and stress buildup within the cell monolayer by aggregating at cell-cell junctions. The stiff confinement led to an elevated expression level of cadherins. Furthermore, inhibition of N-cadherin resulted in a significantly suppressed cell growth under the same confining conditions.

Design of Tissue-engineered Nanoscaffold Through Self-assembly of Peptide Amphiphile

In order to mimic in vivo topography of the native tissue created by extracellular matrix (ECM) components, which make up all soft tissues, the surface features of each biomaterial should be considered as a nanodimensional structure. In this study, an artificial ECM was designed to mimic the nanostructured topography created by ECM components in native tissue. The proliferation and differentiation of mesenchymal stem cells (MSCs) was investigated in a three dimensional (3-D) network of nanofibers formed by the self-assembly of peptide amphiphile (PA) molecules. PA was synthesized by standard solid phase chemistry that ends with the alkylation of the NH2 terminus of the peptide. The sequence of arginine-glycine-aspartic acid (RGD) was included in peptide design as well. A 3-D network of nanofibers was formed by mixing MSC suspensions in a media with dilute aqueous solution of PA. The attachment, proliferation and osteogenic differentiation of MSCs were influenced by the self-assembled PA nanofibers as the cell scaffold and the values were significantly high compared with those in the static culture (2-D tissue culture plate).

Review: unraveling the less explored flocking technology for tissue engineering scaffolds

The flocking technology is may be further exploited for fabrication of scaffolds for biomedical applications like artificial skin, extra-corporeal organs, articular cartilage etc.

Development of 3D in vitro technology for medical applications

In the past few years, biomaterials technologies together with significant efforts on developing biology have revolutionized the process of engineered materials. Three dimensional (3D) in vitro technology aims to develop set of tools that are simple, inexpensive, portable and robust that could be commercialized and used in various fields of biomedical sciences such as drug discovery, diagnostic tools, and therapeutic approaches in regenerative medicine. The proliferation of cells in the 3D scaffold needs an oxygen and nutrition supply. 3D scaffold materials should provide such an environment for cells living in close proximity. 3D scaffolds that are able to regenerate or restore tissue and/or organs have begun to revolutionize medicine and biomedical science. Scaffolds have been used to support and promote the regeneration of tissues. Different processing techniques have been developed to design and fabricate three dimensional scaffolds for tissue engineering implants. Throughout the chapters we discuss in this review, we inform the reader about the potential applications of different 3D in vitro systems that can be applied for fabricating a wider range of novel biomaterials for use in tissue engineering.

IKVAV regulates ERK1/2 and Akt signalling pathways in BMMSC population growth and proliferation

Objectives

The molecular mechanism of bone marrow mesenchymal stem cell (BMMSC) population growth and proliferation, induced by Isoleucyl‐lysyl‐valyl‐alanyl‐valine (IKVAV), was explored in this study.

Materials and methods

IKVAV peptides were synthesized by the solid‐phase method. Influence of IKVAV on BMMSC population growth and proliferation were investigated by assays of CCK‐8, flow cytometry, real‐time PCR and western blotting.

Results

IKVAV peptide was found to induce proliferation and proliferating cell nuclear antigen (PCNA) synthesis of BMMSC in a dose‐ and time‐dependent manner. Cell cycle analysis showed that the proportion of IKVAV‐treated BMMSC in S phase in was higher than controls. Western blot results suggested that mitogen‐activated protein kinase/extracellular signal‐regulated kinase (MAPK/ERK) and phosphatidylinositol 3‐kinase/protein kinase B (PI3K/Akt) signalling pathways were activated by IKVAV by enhancing phosphorylation levels of ERK1/2 and Akt in the BMMSCs. Meanwhile, phosphorylation levels of ERK1/2 and Akt were partially blocked by ERK1/2 inhibitor (PD98059) and Akt inhibitor (wortmannin), respectively.

Conclusions

Our results demonstrated that IKVAV stimulated BMMSC population growth and proliferation by activating MAPK/ERK1/2 and PI3K/Akt signalling pathways. This study is the first to reveal an enhancement effect of IKVAV peptide on BMMSC at the signal transduction level, and the outcome could provide experimental evidence for application of IKVAV‐grafted scaffolds in the field of BMMSC‐based tissue engineering.

Composite nonwovens in medical applications

This chapter reviews the role of composite nonwovens in medical applications. It covers surgical gowns, clinical wearable products, wipes, wound dressings, pads, swabs, scaffolds for tissue engineering, hernia meshes, filtration materials, and incontinence products. Commercially available, innovatively designed composite nonwovens for various medical applications are improving the quality of life of many people. Specific research needs have been highlighted to further improve the effectiveness of these products. The chapter ends with some perspectives for the use of composite nonwovens in medical applications in the future.

Engineering three-dimensional collagen-IKVAV matrix to mimic neural microenvironment

Engineering the cellular microenvironment has great potential to create a platform technology toward engineering of tissue and organs. This study aims to engineer a neural microenvironment through fabrication of three-dimensional (3D) engineered collagen matrixes mimicking in-vivo-like conditions. Collagen was chemically modified with a pentapeptide epitope consisting of isoleucine-lysine-valine-alanine-valine (IKVAV) to mimic laminin structure supports of the neural extracellular matrix (ECM). Three-dimensional collagen matrixes with and without IKVAV peptide modification were fabricated by freeze-drying technology and chemical cross-linking with glutaraldehyde. Structural information of 3D collagen matrixes indicated interconnected pores structure with an average pore size of 180 μm. Our results indicated that culture of dorsal root ganglion (DRG) cells in 3D collagen matrix was greatly influenced by 3D culture method and significantly enhanced with engineered collagen matrix conjugated with IKVAV peptide. It may be concluded that an appropriate 3D culture of neurons enables DRG to positively improve the cellular fate toward further acceleration in tissue regeneration.

Three-dimensional scaffolds for tissue engineering applications: role of porosity and pore size

Tissue engineering applications commonly encompass the use of three-dimensional (3D) scaffolds to provide a suitable microenvironment for the incorporation of cells or growth factors to regenerate damaged tissues or organs. These scaffolds serve to mimic the actual in vivo microenvironment where cells interact and behave according to the mechanical cues obtained from the surrounding 3D environment. Hence, the material properties of the scaffolds are vital in determining cellular response and fate. These 3D scaffolds are generally highly porous with interconnected pore networks to facilitate nutrient and oxygen diffusion and waste removal. This review focuses on the various fabrication techniques (e.g., conventional and rapid prototyping methods) that have been employed to fabricate 3D scaffolds of different pore sizes and porosity. The different pore size and porosity measurement methods will also be discussed. Scaffolds with graded porosity have also been studied for their ability to better represent the actual in vivo situation where cells are exposed to layers of different tissues with varying properties. In addition, the ability of pore size and porosity of scaffolds to direct cellular responses and alter the mechanical properties of scaffolds will be reviewed, followed by a look at nature's own scaffold, the extracellular matrix. Overall, the limitations of current scaffold fabrication approaches for tissue engineering applications and some novel and promising alternatives will be highlighted.

Preliminary Study of the Application of PET Knitted Fabrics in Artificial Bone Scaffold

Having good mechanical strength, biocompatibility, and workability, polyethylene terephthalate (PET) is often used as a biomaterial. In this study, PET filaments with various deniers are made into plied yarn with various coefficients of twist. The plied yarn is then made into PET knitted fabrics. Mechanical property tests are performed to determine the differences among the various PET knitted fabrics. Finally, by using cell culture, the PET knitted fabrics are analyzed and evaluated with their cell attachment.

Porous membrane substrates offer better niches to enhance the Wnt signaling and promote human embryonic stem cell growth and differentiation

Human embryonic stem cells (hESCs) require specific niches for adhesion, expansion, and lineage-specific differentiation. In this study, we showed that a membrane substrate offers better tissue niches for hESC attachment, spreading, proliferation, and differentiation. The cell doubling time was shortened from 46.3±5.7 h for hESCs grown on solid substrates to 25.6±2.6 h for those on polyester (PE) membrane substrates with pore size of 0.4 μm. In addition, we observed an increase of approximately five- to ninefold of definitive endoderm marker gene expression in hESCs differentiated on PE or polyethylene terephthalate membrane substrates. Global gene expression analysis revealed upregulated expressions of a number of extracellular matrix and cell adhesion molecules in hESCs grown on membrane substrates. Further, an enhanced nuclear translocation of β-catenin was detected in these cells. These observations suggested the augmentation of Wnt signaling in hESCs grown on membrane substrates. These results also demonstrated that a membrane substrate can offer better physicochemical cues for enhancing in vitro hESC attachment, proliferation, and differentiation.

Effect of the fiber diameter and porosity of non-woven PET fabrics on the osteogenic differentiation of mesenchymal stem cells

The proliferation and osteogenic differentiation of mesenchymal stem cells (MSCs) was investigated in three-dimensional non-woven fabrics prepared from polyethylene terephthalate (PET) fiber with different diameters. When seeded into the fabrics of cell scaffold, more MSC attached in the fabric of thicker PET fibers than that of thinner ones, irrespective of the fabric porosity. The morphology of cells attached became more spreaded with an increase in the fiber diameter of fabrics. The rate of MSC proliferation depended on the PET fiber diameter and porosity of fabrics: the bigger the fiber diameter of fabrics with higher porosity, the higher their proliferation rate. When the alkaline phosphatase (ALP) activity and osteocalcin content of MSC cultured in different types of fabrics was measured to evaluate the ostegenic differentiation, they became maximum for the non-woven fabrics with a fiber diameter of 9.0 microm, although the values of low-porous fabrics were significantly high compared with those of high porous fabrics. We concluded that the attachment, proliferation and bone differentiation of MSC was influenced by the fiber diameter and porosity of non-woven fabrics as the scaffold.

Design concepts and strategies for tissue engineering scaffolds

In the emerging field of tissue engineering and regenerative medicine, new viable and functional tissue is fabricated from living cells cultured on an artificial matrix in a simulated biological environment. It is evident that the specific requirements for the three main components, cells, scaffold materials, and the culture environment, are very different, depending on the type of cells and the organ-specific application. Identifying the variables within each of these components is a complex and challenging assignment, but there do exist general requirements for designing and fabricating tissue engineering scaffolds. Therefore, this review explores one of the three main components, namely, the key concepts, important parameters, and required characteristics related to the development and evaluation of tissue engineering scaffolds. An array of different design strategies will be discussed, which include mimicking the extra cellular matrix, responding to the need for mass transport, predicting the structural architecture, ensuring adequate initial mechanical integrity, modifying the surface chemistry and topography to provide cell signaling, and anticipating the material selection so as to predict the required rate of bioresorption. In addition, this review considers the major challenge of achieving adequate vascularization in tissue engineering constructs, without which no three-dimensional thick tissue such as the heart, liver, and kidney can remain viable.

Regulation of electrospun scaffold stiffness via coaxial core diameter

Scaffold mechanics influence cellular behavior, including migration, phenotype and viability. Scaffold stiffness is commonly modulated through cross-linking, polymer density, or bioactive coatings on stiff substrates. These approaches provide useful information about cellular response to substrate stiffness; however, they are not ideal as the processing can change substrate morphology, density or chemistry. Coaxial electrospinning was investigated as a fabrication method to produce scaffolds with tunable stiffness and strength without changing architecture or surface chemistry. Core solution concentration, solvent and feed rate were utilized to control core diameter with higher solution concentration and feed rate positively correlating with increased fiber diameter and stiffness. Coaxial scaffolds electrospun with an 8 wt./vol.% polycaprolactone (PCL)-HFP solution at 1 ml h(-1) formed scaffolds with an average core diameter of 1.1±0.2 μm and stiffness of 0.027±3.3×10(-3) N mm(-1). In contrast, fibers which were 2.6±0.1 μm in core diameter yielded scaffolds with a stiffness of 0.065±4.7×10(-3) N mm(-1). Strength and stiffness positively correlated with core diameter with no significant difference in total fiber diameter and interfiber distance observed in as-spun scaffolds. These data indicate that coaxial core diameter can be utilized to tailor mechanical properties of three-dimensional scaffolds and would provide an ideal scaffold for assessing the effect of scaffold mechanics on cell behavior.

Microplate-reader compatible perfusion microbioreactor array for modular tissue culture and cytotoxicity assays

One important application of tissue engineering is to provide novel in vitro models for cell-based assays. Perfusion microbioreactor array provides a useful tool for microscale tissue culture in parallel. However, high-throughput data generation has been a challenge. In this study, a 4 x 4 array of perfusion microbioreactors was developed for plate-reader compatible, time-series quantification of cell proliferation, and cytotoxicity assays. The device was built through multilayer soft lithography. Low-cost nonwoven polyethylene terephthalate fibrous matrices were integrated as modular tissue culture scaffolds. Human colon cancer HT-29 cells with stable expression of enhanced green fluorescent protein were cultured in the device with continuous perfusion and reached a cell density over 5 x 10(7) cells/mL. The microbioreactor array was used to test a chemotherapeutic drug 5-FU for its effect on HT-29 cells in continuous perfusion 3D culture. Compared with conventional 2D cytotoxicity assay, significant drug resistance was observed in the 3D perfusion culture.

Modeling tissue growth within nonwoven scaffolds pores

In this study we present a novel approach for predicting tissue growth within the pores of fibrous tissue engineering scaffolds. Thin nonwoven polyethylene terephthalate scaffolds were prepared to characterize tissue growth within scaffold pores, by mouse NR6 fibroblast cells. On the basis of measurements of tissue lengths at fiber crossovers and along fiber segments, mathematical models were determined during the proliferative phase of cell growth. Tissue growth at fiber crossovers decreased with increasing interfiber angle, with exponential relationships determined on day 6 and 10 of culture. Analysis of tissue growth along fiber segments determined two growth profiles, one with enhanced growth as a result of increased tissue lengths near the fiber crossover, achieved in the latter stage of culture. Derived mathematical models were used in the development of a software program to visualize predicted tissue growth within a pore. This study identifies key pore parameters that contribute toward tissue growth, and suggests models for predicting this growth, based on fibroblast cells. Such models may be used in aiding scaffold design, for optimum pore infiltration during the tissue engineering process.

Synergistic effects of electrospun PLLA fiber dimension and pattern on neonatal mouse cerebellum C17.2 stem cells

Topographical features, including fiber dimensions and pattern, are important aspects in developing fibrous scaffolds for tissue engineering. In this study aligned poly(l-lactide) (PLLA) fibers with diameters of 307+/-47, 500+/-53, 679+/-72 and 917+/-84 nm and random fibers with diameters of 327+/-40, 545+/-54, 746+/-82 and 1150+/-109 nm were obtained by optimizing the electrospinning parameters. We cultured neonatal mouse cerebellum C17.2 cells on the PLLA fibers. These neural stem cells (NSCs) exhibited significantly different growth and differentiation depending upon fiber dimension and pattern. On aligned fibers cell viability and proliferation was best on 500 nm fibers, and reduced on smaller or larger fibers. However, on random fibers cell viability and proliferation was best with the smallest (350 nm) and largest (1150 nm) diameter fibers. Polarized and elongated cells were orientated along the fiber direction on the aligned fibers, with focal contacts bridging the cell body and aligned fibers. Cells of spindle and polygonal morphologies were randomly distributed on the random fibers, with no focal contacts observed. Moreover, longer neurites were obtained on the aligned fibers than random fibers within the same diameter range. Thus, the surface topographic morphologies of fibrous scaffolds, including fiber pattern, dimensions and mesh size, play roles in regulating the viability, proliferation and neurite outgrowth of NSCs. Nevertheless, our results indicated that aligned 500 nm fiber are most promising for fine tuning the design of a nerve scaffold.

Centrifugal seeding of mammalian cells in nonwoven fibrous matrices

Three-dimensional (3D) cell cultures have many advantages over two-dimensional cultures. However, seeding cells in 3D scaffolds such as nonwoven fibrous polyethylene terephthalate (PET) matrices has been a challenge task in tissue engineering and cell culture bioprocessing. In this study, a centrifugal seeding method was investigated to improve the cell seeding efficiency in PET matrices with two different porosities (93% and 88%). Both the centrifugal force and centrifugation time were found to affect the seeding efficiency. With an appropriate centrifugation speed, a high 80-90% cell seeding efficiency was achieved and the time to reach this high seeding efficiency was less than 5 min. The seeding efficiency was similar for matrices with different porosities, although the optimal seeding time was significantly shorter for the low-porosity scaffold. Post seeding cell viability was demonstrated by culturing colon cancer cells seeded in PET matrices for over 5 days. The centrifugal seeding method developed in this work can be used to efficiently and uniformly seed small fibrous scaffolds for applications in 3D cell-based assays for high-throughput screening.

A two-stage perfusion fibrous bed bioreactor system for mass production of embryonic stem cells

BACKGROUND

Embryonic stem cells (ESCs) have unlimited proliferation potential and can differentiate into all cell and tissue types, and thus are ideal sources for cell therapy and drug screening. Current supplies of ESCs are limited by the available cell sources and inefficient culture methods that grow ESCs on surfaces coated with expensive extracellular matrix (ECM) proteins and in media containing expensive growth factors.

OBJECTIVE

To meet the demand for ESCs, it is necessary to develop an economical process for their mass production.

METHODS

We review the latest development in in vitro ESC culture and introduce a two-stage perfusion bioreactor system that uses 3-D fibrous matrices and conditioned media for production of ESCs.

RESULTS/CONCLUSION

The two-stage process can produce billions of ESCs in a small bioreactor without using ECM proteins and growth factors, and is promising for further scale-up for clinical applications.

Fiber density of electrospun gelatin scaffolds regulates morphogenesis of dermal-epidermal skin substitutes

Porous, nowoven fibrous gelatin scaffolds were prepared using electrospinning. Electrospun scaffolds with varying fiber diameter, interfiber distance, and porosity were fabricated by altering the concentration of the electrospinning solution. Solution concentration was a significant predictor of fiber diameter, interfiber distance, and porosity with higher solution concentration correlated with larger fiber diameters and interfiber distances. The potential of electrospun gelatin as a scaffolding material for dermal and epidermal tissue regeneration was also evaluated. Interfiber distances >5.5 microm allowed deeper penetration of human dermal fibroblasts into the scaffold, whereas cells in scaffolds with more densely packed fibers were able to infiltrate only into the upper regions. Scaffolds with interfiber distances </=10 microm exhibited well-stratified dermal and epidermal layers including a continuous basal keratinocyte layer. These scaffolds were shown to form a keratinized layer like in normal skin, which acts as a barrier to infection and fluid loss. Interfiber distances between 5 and 10 microm appear to yield the most favorable skin substitute in vitro, demonstrating high cell viability, optimal cell organization, and excellent barrier formation. These results demonstrate the feasibility of electrospun gelatin as a scaffold for dermal-epidermal composite skin substitutes.

Characterization of arachnoidal cells cultured on three-dimensional nonwoven PET matrix

PURPOSE

To culture physiologically functional primary arachnoidal cells on a suitable polymer substrate for an in-vitro model of the cerebrospinal fluid outflow pathway.

METHODS

Primary cultures of arachnoidal cells were prepared within 24 hours post-mortem from brain tissue obtained from human cadavers at autopsy. Arachnoidal cells were characterized using immunocytochemistry and seeded onto needle punched non-woven poly(ethylene terephthalate)(PET) scaffolds. Metabolic rate, cell growth rate in log phase, morphologic assessment, immunocytochemistry, and protein analysis were used to characterize the cultures in both 2-D and 3-D-culture. Functional outflow assessment was performed using the Lucifer Yellow (LY) permeability assay and hydraulic conductivity (Lp) determination.

RESULTS

Cells cultured on PET scaffold grew slightly slower than cells grown in 2-D-culture as measured by metabolic rate and growth rate, however, they often formed sheets that bridged between the adjacent scaffold filaments forming many junctional protein connections. LY permeability coefficients of 2-D cells were compared with cells from scaffolds, and were not significantly different (p > 0.05) for both culture conditions. Average Lp of cells from 2-D-culture and 3-D-scaffolds were compared and shown not to be significantly different.

CONCLUSION

Based on the biochemical and functional analysis, it has been shown that cells cultured on 3D-PET scaffolds retained the same properties as cells from 2D-culture plates.

LIF-immobilized nonwoven polyester fabrics for cultivation of murine embryonic stem cells

Embryonic stem (ES) cells have a great interest for tissue engineering because of their pluripotent nature and proliferative capacity. The objective of this study is to constitute a synthetic microenvironment to support the in vitro propagation of murine ES cells in an undifferentiated state. That is why we used a three-dimensional matrix, nonwoven polyester fabric (NWPF), which was formed from poly(ethylene terephthalate) (PET) fibers. NWPF discs were partially hydrolyzed, and then the carboxyl groups were coupled with leukemia inhibitory factor (LIF) in the presence of water-soluble carbodiimide. The effectiveness of immobilization process was checked with ATR-FTIR spectroscopy, fluorimetry, and cell culture studies. ES cell colony morphology, alkaline phosphatase (AP) activity, stage-specific embryonic antigen-1 (SSEA-1) immunoreactivity, and SEM analysis following a 72 - 96-h culture period upon hydrolyzed and LIF-immobilized surfaces were assessed to determine the pluripotent status of ES cells. Results revealed that LIF was active in immobilized form; undifferentiated colonies had not only a significant AP and SSEA-1 immunoreactivity, but also a higher undifferentiated colony ratio on LIF-immobilized surfaces than that of hydrolyzed surfaces. The immobilized LIF protein might be a good model to provide a feeder-free system, but the physical properties of the scaffold is more convenient for differentiation studies.