A cell leakproof PLGA-collagen hybrid scaffold for cartilage tissue engineering

Human Acellular Collagen Matrices-Clinical Opportunities in Tissue Replacement

The field of regenerative medicine is increasingly in need of effective and biocompatible materials for tissue engineering. Human acellular dermal matrix (hADM)-derived collagen matrices stand out as a particularly promising candidate. Their ability to preserve structural integrity, coupled with exceptional biocompatibility, positions them as a viable choice for tissue replacement. However, their clinical application has been largely confined to serving as scaffolds. This study aims to expand the horizon of clinical uses for collagen sheets by exploring the diverse cutting-edge clinical demands. This review illustrates the clinical utilizations of collagen sheets beyond traditional roles, such as covering skin defects or acting solely as scaffolds. In particular, the potential of Epiflex®, a commercially available and immediately clinically usable allogeneic membrane, will be evaluated. Collagen sheets have demonstrated efficacy in bone reconstruction, where they can substitute the induced Masquelet membrane in a single-stage procedure, proving to be clinically effective and safe. The application of these membranes allow the reconstruction of substantial tissue defects, without requiring extensive plastic reconstructive surgery. Additionally, they are found to be apt for addressing osteochondritis dissecans lesions and for ligament reconstruction in the carpus. The compelling clinical examples showcased in this study affirm that the applications of human ADM extend significantly beyond its initial use for skin defect treatments. hADM has proven to be highly successful and well-tolerated in managing various etiologies of bone and soft tissue defects, enhancing patient care outcomes. In particular, the application from the shelf reduces the need for additional surgery or donor site defects.

Stepwise Proliferation and Chondrogenic Differentiation of Mesenchymal Stem Cells in Collagen Sponges under Different Microenvironments

Biomimetic microenvironments are important for controlling stem cell functions. In this study, different microenvironmental conditions were investigated for the stepwise control of proliferation and chondrogenic differentiation of human bone-marrow-derived mesenchymal stem cells (hMSCs). The hMSCs were first cultured in collagen porous sponges and then embedded with or without collagen hydrogels for continual culture under different culture conditions. The different influences of collagen sponges, collagen hydrogels, and induction factors were investigated. The collagen sponges were beneficial for cell proliferation. The collagen sponges also promoted chondrogenic differentiation during culture in chondrogenic medium, which was superior to the effect of collagen sponges embedded with hydrogels without loading of induction factors. However, collagen sponges embedded with collagen hydrogels and loaded with induction factors had the same level of promotive effect on chondrogenic differentiation as collagen sponges during in vitro culture in chondrogenic medium and showed the highest promotive effect during in vivo subcutaneous implantation. The combination of collagen sponges with collagen hydrogels and induction factors could provide a platform for cell proliferation at an early stage and subsequent chondrogenic differentiation at a late stage. The results provide useful information for the chondrogenic differentiation of stem cells and cartilage tissue engineering.

ECM scaffolds mimicking extracellular matrices of endochondral ossification for the regulation of mesenchymal stem cell differentiation

Endochondral ossification (ECO) is an important process of bone tissue development. During ECO, extracellular matrices (ECMs) are essential factors to control cell functions and induce bone regeneration. However, the exact role of ECO ECMs on stem cell differentiation remains elusive. In this study, ECM scaffolds were prepared to mimic the ECO-related ECM microenvironments and their effects on stem cell differentiation were compared. Four types of ECM scaffolds mimicking the ECMs of stem cells (SC), chondrogenic (CH), hypertrophic (HY) and osteogenic (OS) stages were prepared by controlling differentiation of human bone marrow-derived mesenchymal stem cells (MSCs) at different stages. Composition of the ECM scaffolds was dependent on the differentiation stage of MSCs. They showed different influence on osteogenic differentiation of MSCs. HY ECM scaffold had the most promotive effect on osteogenic differentiation of MSCs. CH ECM and OS ECM scaffolds showed moderate effect, while SC ECM scaffold had the lowest effect on osteogenic differentiation of MSCs. Their effects on chondrogenic or adipogenic differentiation were not significantly different. The results suggested that the engineered HY ECM scaffold had superior effect for osteogenic differentiation of MSCs. Statement of significance ECM scaffolds mimicking endochondral ossification-related ECM microenvironments are pivotal for elucidation of their roles in regulation of stem cell functions and bone tissue regeneration. This study offers a method to prepare ECM scaffolds that mimic the ECMs from cells at hypertrophic, osteogenic, chondrogenic and stem cell stages. Their composition and impacts on osteogenic differentiation of MSCs were compared. The hypertrophic ECM scaffold had the highest promotive effect on osteogenic differentiation of MSCs. The results advance our understanding about the role of ECO ECMs in regulation of stem cell functions and provide perspective for bone defect repair strategies.

PLGA–collagen–ECM hybrid scaffolds functionalized with biomimetic extracellular matrices secreted by mesenchymal stem cells during stepwise osteogenesis-co-adipogenesis

Development of an in vitro 3D model that reflects the dynamic remodeling of ECMs during simultaneous osteogenesis and adipogenesis of hMSCs.

Modeling Physiological Events in 2D vs. 3D Cell Culture

Cell culture has become an indispensable tool to help uncover fundamental biophysical and biomolecular mechanisms by which cells assemble into tissues and organs, how these tissues function, and how that function becomes disrupted in disease. Cell culture is now widely used in biomedical research, tissue engineering, regenerative medicine, and industrial practices. Although flat, two-dimensional (2D) cell culture has predominated, recent research has shifted toward culture using three-dimensional (3D) structures, and more realistic biochemical and biomechanical microenvironments. Nevertheless, in 3D cell culture, many challenges remain, including the tissue-tissue interface, the mechanical microenvironment, and the spatiotemporal distributions of oxygen, nutrients, and metabolic wastes. Here, we review 2D and 3D cell culture methods, discuss advantages and limitations of these techniques in modeling physiologically and pathologically relevant processes, and suggest directions for future research.

Attachment, Proliferation, and Morphological Properties of Human Dermal Fibroblasts on Ovine Tendon Collagen Scaffolds: A Comparative Study

INTRODUCTION

Collagen type I is widely used as a biomaterial for tissue-engineered substitutes. This study aimed to fabricate different three-dimensional (3D) scaffolds using ovine tendon collagen type I (OTC-I), and compare the attachment, proliferation and morphological features of human dermal fibroblasts (HDF) on the scaffolds.

METHODS

This study was conducted between the years 2014 to 2016 at the Tissue Engineering Centre, UKM Medical Centre. OTC-I was extracted from ovine tendon, and fabricated into 3D scaffolds in the form of sponge, hydrogel and film. A polystyrene surface coated with OTC-I was used as the 2D culture condition. Genipin was used to crosslink the OTC-I. A non-coated polystyrene surface was used as a control. The mechanical strength of OTC-I scaffolds was evaluated. Attachment, proliferation and morphological features of HDF were assessed and compared between conditions.

RESULTS

The mechanical strength of OTC-I sponge was significantly higher than that of the other scaffolds. OTC-I scaffolds and the coated surface significantly enhanced HDF attachment and proliferation compared to the control, but no differences were observed between the scaffolds and coated surface. In contrast, the morphological features of HDF including spreading, filopodia, lamellipodia and actin cytoskeletal formation differed between conditions.

CONCLUSION

OTC-I can be moulded into various scaffolds that are biocompatible and thus could be suitable as scaffolds for developing tissue substitutes for clinical applications and in vitro tissue models. However, further study is required to determine the effect of morphological properties on the functional and molecular properties of HDF.

Fabrication of Aligned Nanofiber Polymer Yarn Networks for Anisotropic Soft Tissue Scaffolds

Nanofibrous scaffolds with defined architectures and anisotropic mechanical properties are attractive for many tissue engineering and regenerative medicine applications. Here, a novel electrospinning system is developed and implemented to fabricate continuous processable uniaxially aligned nanofiber yarns (UANY). UANY were processed into fibrous tissue scaffolds with defined anisotropic material properties using various textile-forming technologies, i.e., braiding, weaving, and knitting techniques. UANY braiding dramatically increased overall stiffness and strength compared to the same number of UANY unbraided. Human adipose derived stem cells (HADSC) cultured on UANY or woven and knitted 3D scaffolds aligned along local fiber direction and were >90% viable throughout 21 days. Importantly, UANY supported biochemical induction of HADSC differentiation toward smooth muscle and osteogenic lineages. Moreover, we integrated an anisotropic woven fiber mesh within a bioactive hydrogel to mimic the complex microstructure and mechanical behavior of valve tissues. Human aortic valve interstitial cells (HAVIC) and human aortic root smooth muscle cells (HASMC) were separately encapsulated within hydrogel/woven fabric composite scaffolds for generating scaffolds with anisotropic biomechanics and valve ECM like microenvironment for heart valve tissue engineering. UANY have great potential as building blocks for generating fiber-shaped tissues or tissue microstructures with complex architectures.

Analyzing Biological Performance of 3D-Printed, Cell-Impregnated Hybrid Constructs for Cartilage Tissue Engineering

Three-dimensional (3D) bioprinting of hybrid constructs is a promising biofabrication method for cartilage tissue engineering because a synthetic polymer framework and cell-impregnated hydrogel provide structural and biological features of cartilage, respectively. During bioprinting, impregnated cells may be subjected to high temperatures (caused by the adjacent melted polymer) and process-induced mechanical forces, potentially compromising cell function. This study addresses these biofabrication issues, evaluating the heat distribution of printed polycaprolactone (PCL) strands and the rheological property and structural stability of alginate hydrogels at various temperatures and concentrations. The biocompatibility of parameters from these studies was tested by culturing 3D hybrid constructs bioprinted with primary cells from embryonic chick cartilage. During initial two-dimensional culture expansion of these primary cells, two morphologically and molecularly distinct cell populations ("rounded" and "fibroblastic") were isolated. The biological performance of each population was evaluated in 3D hybrid constructs separately. The cell viability, proliferation, and cartilage differentiation were observed at high levels in hybrid constructs of both cell populations, confirming the validity of these 3D bioprinting parameters for effective cartilage tissue engineering. Statistically significant performance variations were observed, however, between the rounded and fibroblastic cell populations. Molecular and morphological data support the notion that such performance differences may be attributed to the relative differentiation state of rounded versus fibroblastic cells (i.e., differentiated chondrocytes vs. chondroprogenitors, respectively), which is a relevant issue for cell-based tissue engineering strategies. Taken together, our study demonstrates that bioprinting 3D hybrid constructs of PCL and cell-impregnated alginate hydrogel is a promising approach for cartilage tissue engineering.

Multilayered dense collagen-silk fibroin hybrid: a platform for mesenchymal stem cell differentiation towards chondrogenic and osteogenic lineages

Type I collagen is a major structural and functional protein in connective tissues. However, collagen gels exhibit unstable geometrical properties, arising from extensive cell-mediated contraction. In an effort to stabilize collagen-based hydrogels, plastic compression was used to hybridize dense collagen (DC) with electrospun silk fibroin (SF) mats, generating multilayered DC-SF-DC constructs. Seeded mesenchymal stem cell (MSC)-mediated DC-SF-DC contraction, as well as growth and differentiation under chondrogenic and osteogenic supplements, were compared to those seeded in DC and on SF alone. The incorporation of SF within DC prevented extensive cell-mediated collagen gel contraction. The effect of the multilayered hybrid on MSC remodelling capacity was also evident at the transcription level, where the expression of matrix metalloproteinases and their inhibitor (MMP1, MMP2, MMP3, MMP13 and Timp1) by MSCs within DC-SF-DC were comparable to those on SF and significantly downregulated in comparison to DC, except for Timp1. Chondrogenic supplements stimulated extracellular matrix production within the construct, stabilizing its multilayered structure and promoting MSC chondrogenic differentiation, as indicated by the upregulation of the genes Col2a1 and Agg and the production of collagen type II. In osteogenic medium there was an upregulation in ALP and OP along with the presence of an apatitic phase, indicating MSC osteoblastic differentiation and matrix mineralization. In sum, these results have implications on the modulation of three-dimensional collagen-based gel structural stability and on the stimulation and maintenance of the MSC committed phenotype inherent to the in vitro formation of chondral tissue and bone, as well as on potential multilayered complex tissues. Copyright © 2015 John Wiley & Sons, Ltd.

Influence of different surface modification treatments on silk biotextiles for tissue engineering applications

Biotextile structures from silk fibroin have demonstrated to be particularly interesting for tissue engineering (TE) applications due to their high mechanical strength, interconnectivity, porosity, and ability to degrade under physiological conditions. In this work, we described several surface treatments of knitted silk fibroin (SF) scaffolds, namely sodium hydroxide (NaOH) solution, ultraviolet radiation exposure in an ozone atmosphere (UV/O3) and oxygen (O2) plasma treatment followed by acrylic acid (AAc), vinyl phosphonic acid (VPA), and vinyl sulfonic acid (VSA) immersion. The effect of these treatments on the mechanical properties of the textile constructs was evaluated by tensile tests in dry and hydrated states. Surface properties such as morphology, topography, wettability and elemental composition were also affected by the applied treatments. The in vitro biological behavior of L929 fibroblasts revealed that cells were able to adhere and spread both on the untreated and surface-modified textile constructs. The applied treatments had different effects on the scaffolds' surface properties, confirming that these modifications can be considered as useful techniques to modulate the surface of biomaterials according to the targeted application.

Clinical applications of naturally derived biopolymer-based scaffolds for regenerative medicine

Naturally derived polymeric biomaterials, such as collagens, silks, elastins, alginates, and fibrins are utilized in tissue engineering due to their biocompatibility, bioactivity, and tunable mechanical and degradation kinetics. The use of these natural biopolymers in biomedical applications is advantageous because they do not release cytotoxic degradation products, are often processed using environmentally-friendly aqueous-based methods, and their degradation rates within biological systems can be manipulated by modifying the starting formulation or processing conditions. For these reasons, many recent in vivo investigations and FDA-approval of new biomaterials for clinical use have utilized natural biopolymers as matrices for cell delivery and as scaffolds for cell-free support of native tissues. This review highlights biopolymer-based scaffolds used in clinical applications for the regeneration and repair of native tissues, with a focus on bone, skeletal muscle, peripheral nerve, cardiac muscle, and cornea substitutes.

Tissue-engineered lymphatic graft for the treatment of lymphedema

BACKGROUND

Lymphedema is a chronic debilitating condition and curative treatment is yet to be found. Tissue engineering approach, which combines cellular components, scaffold, and molecular signals hold great potential in the treatment of secondary lymphedema with the advent of lymphatic graft to reconstruct damaged collecting lymphatic vessel. This review highlights the ideal characteristics of lymphatic graft, the limitation and challenges faced, and the approaches in developing tissue-engineered lymphatic graft.

METHODS

Literature on tissue engineering of lymphatic system and lymphatic tissue biology was reviewed.

RESULTS

The prime challenge in the design and manufacturing of this graft is producing endothelialized conduit with intraluminal valves. Suitable scaffold material is needed to ensure stability and functionality of the construct. Endothelialization of the construct can be enhanced via biofunctionalization and nanotopography, which mimics extracellular matrix. Nanocomposite polymers with improved performance over existing biomaterials are likely to benefit the development of lymphatic graft.

CONCLUSIONS

With the in-depth understanding of tissue engineering, nanotechnology, and improved knowledge on the biology of lymphatic regeneration, the aspiration to develop successful lymphatic graft is well achievable.

Preparation of cylinder-shaped porous sponges of poly(L-lactic acid), poly(DL-lactic-co-glycolic acid), and poly(ε-caprolactone)

Design of mechanical skeletons of biodegradable synthetic polymers such as poly(L-lactic acid) (PLLA), poly(DL-lactic-co-glycolic acid) (PLGA), and poly(ε-caprolactone) (PCL) is important in the construction of the hybrid scaffolds of biodegradable synthetic polymers and naturally derived polymers such as collagen. In this study, cylinder-shaped PLLA, PLGA, and PCL sponges were prepared by the porogen leaching method using a cylinder model. The effects of polymer type, polymer fraction, cylinder height, pore size, and porosity on the mechanical properties of the cylinder-shape sponges were investigated. SEM observation showed that these cylinder-shaped sponges had evenly distributed bulk pore structures and the wall surfaces were less porous with a smaller pore size than the wall bulk pore structures. The porosity and pore size of the sponges could be controlled by the ratio and size of the porogen materials. The PLGA sponges showed superior mechanical properties than those of the PLLA and PCL sponges. Higher porosity resulted in an inferior mechanical strength. The pore size and sponge height also affected the mechanical properties. The results indicate that cylinder-shaped sponges can be tethered by choosing the appropriate polymers, size and ratio of porogen materials and dimension of sponges based on the purpose of the application.

Stem cell-based tissue engineering approaches for musculoskeletal regeneration

The field of regenerative medicine and tissue engineering is an ever evolving field that holds promise in treating numerous musculoskeletal diseases and injuries. An important impetus in the development of the field was the discovery and implementation of stem cells. The utilization of mesenchymal stem cells, and later embryonic and induced pluripotent stem cells, opens new arenas for tissue engineering and presents the potential of developing stem cell-based therapies for disease treatment. Multipotent and pluripotent stem cells can produce various lineage tissues, and allow for derivation of a tissue that may be comprised of multiple cell types. As the field grows, the combination of biomaterial scaffolds and bioreactors provides methods to create an environment for stem cells that better represent their microenvironment for new tissue formation. As technologies for the fabrication of biomaterial scaffolds advance, the ability of scaffolds to modulate stem cell behavior advances as well. The composition of scaffolds could be of natural or synthetic materials and could be tailored to enhance cell self-renewal and/or direct cell fates. In addition to biomaterial scaffolds, studies of tissue development and cellular microenvironments have determined other factors, such as growth factors and oxygen tension, that are crucial to the regulation of stem cell activity. The overarching goal of stem cell-based tissue engineering research is to precisely control differentiation of stem cells in culture. In this article, we review current developments in tissue engineering, focusing on several stem cell sources, induction factors including growth factors, oxygen tension, biomaterials, and mechanical stimulation, and the internal and external regulatory mechanisms that govern proliferation and differentiation.

New biotextiles for tissue engineering: development, characterization and in vitro cellular viability

This work proposes biodegradable textile-based structures for tissue engineering applications. We describe the use of two polymers, polybutylene succinate (PBS) proposed as a viable multifilamentand silk fibroin (SF), to produce fibre-based finely tuned porous architectures by weft knitting. PBS is here proposed as a viable extruded multifilament fibre to be processed by a textile-based technology. A comparative study was undertaken using a SF fibre with a similar linear density. The knitted constructs obtained are described in terms of their morphology, mechanical properties, swelling capability, degradation behaviour and cytotoxicity. The weft knitting technology used offers superior control over the scaffold design (e.g. size, shape, porosity and fibre alignment), manufacturing and reproducibility. The presented fibres allow the processing of a very reproducible intra-architectural scaffold geometry which is fully interconnected, thus providing a high surface area for cell attachment and tissue in-growth. The two types of polymer fibre allow the generation of constructs with distinct characteristics in terms of the surface physico-chemistry, mechanical performance and degradation capability, which has an impact on the resulting cell behaviour at the surface of the respective biotextiles. Preliminary cytotoxicity screening showed that both materials can support cell adhesion and proliferation. These results constitute a first validation of the two biotextiles as viable matrices for tissue engineering prior to the development of more complex systems. Given the processing efficacy and versatility of the knitting technology and the interesting structural and surface properties of the proposed polymer fibres it is foreseen that the developed systems could be attractive for the functional engineering of tissues such as skin, ligament, bone or cartilage.

Fiber-based tissue engineering: Progress, challenges, and opportunities

Tissue engineering aims to improve the function of diseased or damaged organs by creating biological substitutes. To fabricate a functional tissue, the engineered construct should mimic the physiological environment including its structural, topographical, and mechanical properties. Moreover, the construct should facilitate nutrients and oxygen diffusion as well as removal of metabolic waste during tissue regeneration. In the last decade, fiber-based techniques such as weaving, knitting, braiding, as well as electrospinning, and direct writing have emerged as promising platforms for making 3D tissue constructs that can address the abovementioned challenges. Here, we critically review the techniques used to form cell-free and cell-laden fibers and to assemble them into scaffolds. We compare their mechanical properties, morphological features and biological activity. We discuss current challenges and future opportunities of fiber-based tissue engineering (FBTE) for use in research and clinical practice.

Novel nanostructured biodegradable polymer matrices fabricated by phase separation techniques for tissue regeneration

Biomimetic nanostructures have a wide range of applications. In particular, biodegradable polymer nanostructures that mimic the subtleties of extracellular matrix may provide favorable cell interactions. In this study, a co-solvent system was developed to configure a thermodynamically metastable biodegradable polymer solution, from which novel nanostructured matrices subsequently formed via wet phase separation (quaternary) or a combination with thermally induced phase separation. Three-dimensional (3D) nanostructured porous matrices were further fabricated by combination with particle-leaching (100-300μm glucose). The new co-solvent system may generate matrices with reproducible nanostructures from a variety of biodegradable polymers such as poly(d,l-lactide) (PLA), poly(ε-caprolactone) (PCL) and PCL-based polyurethane. In vitro cell culture experiments were performed with mouse pre-osteoblasts (MC3T3-E1) and human bone marrow-derived mesenchymal stem cells (hBM-MSC) to evaluate the osteoinductive potential of PLA nanostructures. The results showed that nanofibrous (<100nm) membranes promoted the bone-related marker gene expression and matrix mineralization of MC3T3-E1 at 14days. Nanofibrous 3D matrices seeded with hBM-MSC without osteogenic induction supplements demonstrated a 2.5-fold increase in bone matrix deposition vs. the conventional microporous matrices after 14 and 21days. Antimicrobial nanofibers were further obtained by plasma-assisted coating of chitosan on PLA nanofibers. This study reveals a platform for fabricating novel biodegradable nanofibrous architecture, with potential in tissue regeneration.

Strategic design and fabrication of engineered scaffolds for articular cartilage repair

Damage to articular cartilage can eventually lead to osteoarthritis (OA), a debilitating, degenerative joint disease that affects millions of people around the world. The limited natural healing ability of cartilage and the limitations of currently available therapies make treatment of cartilage defects a challenging clinical issue. Hopes have been raised for the repair of articular cartilage with the help of supportive structures, called scaffolds, created through tissue engineering (TE). Over the past two decades, different designs and fabrication techniques have been investigated for developing TE scaffolds suitable for the construction of transplantable artificial cartilage tissue substitutes. Advances in fabrication technologies now enable the strategic design of scaffolds with complex, biomimetic structures and properties. In particular, scaffolds with hybrid and/or biomimetic zonal designs have recently been developed for cartilage tissue engineering applications. This paper reviews critical aspects of the design of engineered scaffolds for articular cartilage repair as well as the available advanced fabrication techniques. In addition, recent studies on the design of hybrid and zonal scaffolds for use in cartilage tissue repair are highlighted.

Improving the cell distribution in collagen-coated poly-caprolactone knittings

Adequate cellular in-growth into biomaterials is one of the fundamental requirements of scaffolds used in regenerative medicine. Type I collagen is the most commonly used material for soft tissue engineering, because it is nonimmunogenic and a highly porous network for cellular support can be produced. However, in general, adequate cell in-growth and cell seeding has been suboptimal. In this study we prepared collagen scaffolds of different collagen densities and investigated the cellular distribution. We also prepared a hybrid polymer-collagen scaffold to achieve an optimal cellular distribution as well as sufficient mechanical strength. Collagen scaffolds [ranging from 0.3% to 0.8% (w/v)] with and without a mechanically stable polymer knitting [poly-caprolactone (PCL)] were prepared. The porous structure of collagen scaffolds was characterized using scanning electron microscopy and hematoxylin-eosin staining. The mechanical strength of hybrid scaffolds (collagen with or without PCL) was determined using tensile strength analysis. Cellular in-growth and interconnectivity were evaluated using fluorescent bead distribution and human bladder smooth muscle cells and human urothelium seeding. The lower density collagen scaffolds showed remarkably deeper cellular penetration and by combining it with PCL knitting the tensile strength was enhanced. This study indicated that a hybrid scaffold prepared from 0.4% collagen strengthened with knitting achieved the best cellular distribution.

Demineralized bone particle impregnated poly(l-lactide-co-glycolide) scaffold for application in tissue-engineered intervertebral discs

Demineralized bone particle (DBP) contains powerful bioactive molecules that facilitate new bone or cartilage growth. We developed hybrid scaffolds of poly(l-lactide-co-glycolide) (PLGA) with various concentrations of DBP (DBP/PLGA), of which phenotypes on intervertebral disc (IVD) cells were investigated. The hybrid scaffold has a cylindrical donut shape with two distinct parts; the inner is for the nucleus pulposus (NP) and the outer is for annulus fibrosus (AF). Rabbit NP and AF cells were seeded into the inner and outer regions of the DBP/PLGA scaffolds separately. Disc cell viability in DBP/PLGA scaffolds was superior to pure PLGA scaffold and increased with increasing DBP concentration. In vitro- and in vivo-formed tissues were characterized by RT-PCR, Safranin-O, Masson's trichrome staining and immunohistochemi- cal staining for type-I and type-II collagen. DBP/PLGA hybrid scaffolds revealed more active expression of disc phenotypes, as characterized by protein and mRNA expression, than the PLGA control. This study provides valuable information for potential disc replacement using DBP and PLGA.

Natural and Genetically Engineered Proteins for Tissue Engineering

To overcome the limitations of traditionally used autografts, allografts and, to a lesser extent, synthetic materials, there is the need to develop a new generation of scaffolds with adequate mechanical and structural support, control of cell attachment, migration, proliferation and differentiation and with bio-resorbable features. This suite of properties would allow the body to heal itself at the same rate as implant degradation. Genetic engineering offers a route to this level of control of biomaterial systems. The possibility of expressing biological components in nature and to modify or bioengineer them further, offers a path towards multifunctional biomaterial systems. This includes opportunities to generate new protein sequences, new self-assembling peptides or fusions of different bioactive domains or protein motifs. New protein sequences with tunable properties can be generated that can be used as new biomaterials. In this review we address some of the most frequently used proteins for tissue engineering and biomedical applications and describe the techniques most commonly used to functionalize protein-based biomaterials by combining them with bioactive molecules to enhance biological performance. We also highlight the use of genetic engineering, for protein heterologous expression and the synthesis of new protein-based biopolymers, focusing the advantages of these functionalized biopolymers when compared with their counterparts extracted directly from nature and modified by techniques such as physical adsorption or chemical modification.

Development of a hybrid scaffold with synthetic biomaterials and hydrogel using solid freeform fabrication technology

Natural biomaterials such as hyaluronic acid, gelatin and collagen provide excellent environments for tissue regeneration. Furthermore, gel-state natural biomaterials are advantageous for encapsulating cells and growth factors. In cell printing technology, hydrogel which contains cells was printed directly to form three-dimensional (3D) structures for tissue or organ regeneration using various types of printers. However, maintaining the 3D shape of the printed structure, which is made only of the hydrogel, is very difficult due to its weak mechanical properties. In this study, we developed a hybrid scaffold consisting of synthetic biomaterials and natural hydrogel using a multi-head deposition system, which is useful in solid freeform fabrication technology. The hydrogel was intentionally infused into the space between the lines of a synthetic biomaterial-based scaffold. The cellular efficacy of the hybrid scaffold was validated using rat primary hepatocytes and a mouse pre-osteoblast MC3T3-E1 cell line. In addition, the collagen hydrogel, which encapsulates cells, was dispensed and the viability of the cells observed. We demonstrated superior effects of the hybrid scaffold on cell adhesion and proliferation and showed the high viability of dispensed cells.

Applications of knitted mesh fabrication techniques to scaffolds for tissue engineering and regenerative medicine

Knitting is an ancient and yet, a fresh technique. It has a history of no less than 1,000 years. The development of tissue engineering and regenerative medicine provides a new role for knitting. Several meshes knitted from synthetic or biological materials have been designed and applied, either alone, to strengthen materials for the patching of soft tissues, or in combination with other kinds of biomaterials, such as collagen and fibroin, to repair or replace damaged tissues/organs. In the latter case, studies have demonstrated that knitted mesh scaffolds (KMSs) possess excellent mechanical properties and can promote more effective tissue repair, ligament/tendon/cartilage regeneration, pipe-like-organ reconstruction, etc. In the process of tissue regeneration induced by scaffolds, an important synergic relationship emerges between the three-dimensional microstructure and the mechanical properties of scaffolds. This paper presents a comprehensive overview of the status and future prospects of knitted meshes and its KMSs for tissue engineering and regenerative medicine.

Engineering ear constructs with a composite scaffold to maintain dimensions

Engineered cartilage composed of a patient's own cells can become a feasible option for auricular reconstruction. However, distortion and shrinkage of ear-shaped constructs during scaffold degradation and neocartilage maturation in vivo have hindered the field. Scaffolds made of synthetic polymers often generate degradation products that cause an inflammatory reaction and negatively affect neocartilage formation in vivo. Porous collagen, a natural material, is a promising candidate; however, it cannot withstand the contractile forces exerted by skin and surrounding tissue during normal wound healing. We hypothesised that a permanent support in the form of a coiled wire embedded into a porous collagen scaffold will maintain the construct's size and ear-specific shape. Half-sized human adult ear-shaped fibrous collagen scaffolds with and without embedded coiled titanium wire were seeded with sheep auricular chondrocytes, cultured in vitro for up to 2 weeks, and implanted subcutaneously on the backs of nude mice. After 6 weeks, the dimensional changes in all implants with wire support were minimal (2.0% in length and 4.1% in width), whereas significant reduction in size occurred in the constructs without embedded wire (14.4% in length and 16.5% in width). No gross distortion occurred over the in vivo study period. There were no adverse effects on neocartilage formation from the embedded wire. Histologically, mature neocartilage extracellular matrix was observed throughout all implants. The amount of DNA, glycosaminoglycan, and hydroxyproline in the engineered cartilage were similar to that of native sheep ear cartilage. The embedded wire support was essential for avoiding shrinkage of the ear-shaped porous collagen constructs.