Composite scaffolds for the engineering of hollow organs and tissues

Several types of synthetic and naturally derived biomaterials have been used for augmenting hollow organs and tissues. However, each has desirable traits which were exclusive of the other. We fabricated a composite scaffold and tested its potential for the engineering of hollow organs in a bladder tissue model. The composite scaffolds were configured to accommodate a large number of cells on one side and were designed to serve as a barrier on the opposite side. The scaffolds were fabricated by bonding a collagen matrix to PGA polymers with threaded collagen fiber stitches. Urothelial and bladder smooth muscle cells were seeded on the composite scaffolds, and implanted in mice for up to 4 weeks and analyzed. Both cell types readily attached and proliferated on the scaffolds and formed bladder tissue-like structures in vivo. These structures consisted of a luminal urothelial layer, a collagen rich compartment and a peripheral smooth muscle layer. Biomechanical studies demonstrated that the tissues were readily elastic while maintaining their pre-configured structures. This study demonstrates that a composite scaffold can be fabricated with two completely different polymer systems for the engineering of hollow organs. The composite scaffolds are biocompatible, possess adequate physical and structural characteristics for bladder tissue engineering, and are able to form tissues in vivo. This scaffold system may be useful in patients requiring hollow organ replacement.     

A Decellularization Methodology for the Production of a Natural Acellular Intestinal Matrix

Successful tissue engineering involves the combination of scaffolds with appropriate cells in vitro or in vivo. Scaffolds may be synthetic, naturally-derived or derived from tissues/organs. The latter are obtained using a technique called decellularization. Decellularization may involve a combination of physical, chemical, and enzymatic methods. The goal of this technique is to remove all cellular traces whilst maintaining the macro- and micro-architecture of the original tissue.Intestinal tissue engineering has thus far used relatively simple scaffolds that do not replicate the complex architecture of the native organ. The focus of this paper is to describe an efficient decellularization technique for rat small intestine. The isolation of the small intestine so as to ensure the maintenance of a vascular connection is described. The combination of chemical and enzymatic solutions to remove the cells whilst preserving the villus-crypt axis in the luminal aspect of the scaffold is also set out. Finally, assessment of produced scaffolds for appropriate characteristics is discussed.     

Complete recombinant silk-elastinlike protein-based tissue scaffold

Due to their improved biocompatibility and specificity over synthetic materials, protein-based biomaterials, either derived from natural sources or genetically engineered, have been widely fabricated into nanofibrous scaffolds for tissue engineering applications. However, their inferior mechanical properties often require the reinforcement of protein-based tissue scaffolds using synthetic polymers. In this study, we report the electrospinning of a completely recombinant silk-elastinlike protein-based tissue scaffold with excellent mechanical properties and biocompatibility. In particular, SELP-47K containing tandemly repeated polypeptide sequences derived from native silk and elastin was electrospun into nanofibrous scaffolds, and stabilized via chemical vapor treatment and mechanical preconditioning. When fully hydrated in 1× PBS at 37 °C, mechanically preconditioned SELP-47K scaffolds displayed elastic moduli of 3.4-13.2 MPa, ultimate tensile strengths of 5.7-13.5 MPa, deformabilities of 100-130% strain, and resilience of 80.6-86.9%, closely matching or exceeding those of protein-synthetic blend polymeric scaffolds. Additionally, SELP-47K nanofibrous scaffolds promoted cell attachment and growth, demonstrating their in vitro biocompatibility.     

Epithelial machines of morphogenesis and their potential application in organ assembly and tissue engineering

Sheets of embryonic epithelial cells coordinate their efforts to create diverse tissue structures such as pits, grooves, tubes, and capsules that lead to organ formation. Such cells can use a number of cell behaviors including contractility, proliferation, and directed movement to create these structures. By contrast, tissue engineers and researchers in regenerative medicine seeking to produce organs for repair or replacement therapy can combine cells with synthetic polymeric scaffolds. Tissue engineers try to achieve these goals by shaping scaffold geometry in such a way that cells embedded within these scaffold self-assemble to form a tissue, for instance aligning to synthetic fibers, and assembling native extracellular matrix to form the desired tissue-like structure. Although self-assembly is a dominant process that guides tissue assembly both within the embryo and within artificial tissue constructs, we know little about these critical processes. Here, we compare and contrast strategies of tissue assembly used by embryos to those used by engineers during epithelial morphogenesis and highlight opportunities for future applications of developmental biology in the field of tissue engineering.     

计算机辅助骨组织工程技术的研究进展

计算机辅助骨组织工程作为一种新的研究领域可以帮助进行复杂的个性化支架的建模,设计和制造,使支架材料达到理想的物理,化学和生物学性能。本文从骨组织工程支架材料的设计路线出发,综述了计算机辅助技术在骨组织工程支架材料上面的应用,并着重探讨了计算机辅助组织建模、骨组织工程支架的设计和快速成型制造技术的最新进展。     

Effects of three-dimensional scaffolds on cell organization and tissue development

Tissue engineering scaffolds play a critical role in regulating the reconstructed human tissue development. Various types of scaffolds have been developed in recent years, including fibrous matrix and foam-like scaffolds. The design of scaffold materials has been investigated extensively. However, the design of physical structure of the scaffold, especially fibrous matrices, has not received much attention. This paper compares the different characteristics of fibrous and foam-like scaffolds, and reviews regulatory roles of important scaffold properties, including surface geometry, scaffold configuration, pore structure, mechanical property and bioactivity. Tissue regeneration, cell organization, proliferation and differentiation under different microstructures were evaluated. The importance of proper scaffold selection and design is further discussed with the examples of bone tissue engineering and stem cell tissue engineering. This review addresses the importance of scaffold microstructure and provides insights in designing appropriate scaffold structure for different applications of tissue engineering.     

Stem cells: their source,potency and use in regenerative therapies with focus on adipose-derived stem cells – a review

Stem cells can be defined as units of biological organization that are responsible for the development and the regeneration of organ and tissue systems. They are able to renew their populations and to differentiate into multiple cell lineages. Therefore, these cells have great potential in advanced tissue engineering and cell therapies. When seeded on synthetic or nature-derived scaffolds in vitro, stem cells can be differentiated towards the desired phenotype by an appropriate composition, by an appropriate architecture, and by appropriate physicochemical and mechanical properties of the scaffolds, particularly if the scaffold properties are combined with a suitable composition of cell culture media, and with suitable mechanical, electrical or magnetic stimulation. For cell therapy, stem cells can be injected directly into damaged tissues and organs in vivo. Since the regenerative effect of stem cells is based mainly on the autocrine production of growth factors, immunomodulators and other bioactive molecules stored in extracellular vesicles, these structures can be isolated and used instead of cells for a novel therapeutic approach called “stem cell-based cell-free therapy”. There are four main sources of stem cells, i.e. embryonic tissues, fetal tissues, adult tissues and differentiated somatic cells after they have been genetically reprogrammed, which are referred to as induced pluripotent stem cells (iPSCs). Although adult stem cells have lower potency than the other three stem cell types, i.e. they are capable of differentiating into only a limited quantity of specific cell types, these cells are able to overcome the ethical and legal issues accompanying the application of embryonic and fetal stem cells and the mutational effects associated with iPSCs. Moreover, adult stem cells can be used in autogenous form. These cells are present in practically all tissues in the organism. However, adipose tissue seems to be the most advantageous tissue from which to isolate them, because of its abundancy, its subcutaneous location, and the need for less invasive techniques. Adipose tissue-derived stem cells (ASCs) are therefore considered highly promising in present-day regenerative medicine.     

Nanomaterial scaffolds for stem cell proliferation and differentiation in tissue engineering

Tissue engineering is a clinically driven field and has emerged as a potential alternative to organ transplantation. The cornerstone of successful tissue engineering rests upon two essential elements: cells and scaffolds. Recently, it was found that stem cells have unique capabilities of self-renewal and multilineage differentiation to serve as a versatile cell source, while nanomaterials have lately emerged as promising candidates in producing scaffolds able to better mimic the nanostructure in natural extracellular matrix and to efficiently replace defective tissues. This article, therefore, reviews the key developments in tissue engineering, where the combination of stem cells and nanomaterial scaffolds has been utilized over the past several years. We consider the high potential, as well as the main issues related to the application of stem cells and nanomaterial scaffolds for a range of tissues including bone, cartilage, nerve, liver, eye etc. Promising in vitro results such as efficient attachment, proliferation and differentiation of stem cells have been compiled in a series of examples involving different nanomaterials. Furthermore, the merits of the marriage of stem cells and nanomaterial scaffolds are also demonstrated in vivo, providing early successes to support subsequent clinical investigations. This progress simultaneously drives mechanistic research into the mechanotransduction process responsible for the observations in order to optimize the process further. Current understanding is chiefly reported to involve the interaction of stem cells and the anchoring nanomaterial scaffolds by activating various signaling pathways. Substrate surface characteristics and scaffold bulk properties are also reported to influence not only short term stem cell adhesion, spreading and proliferation, but also longer term lineage differentiation, functionalization and viability. It is expected that the combination of stem cells and nanomaterials will develop into an important tool in tissue engineering for the innovative treatment of many diseases.     

Modeling material-degradation-induced elastic property of tissue engineering scaffolds

The mechanical properties of tissue engineering scaffolds play a critical role in the success of repairing damaged tissues/organs. Determining the mechanical properties has proven to be a challenging task as these properties are not constant but depend upon time as the scaffold degrades. In this study, the modeling of the time-dependent mechanical properties of a scaffold is performed based on the concept of finite element model updating. This modeling approach contains three steps: (1) development of a finite element model for the effective mechanical properties of the scaffold, (2) parametrizing the finite element model by selecting parameters associated with the scaffold microstructure and/or material properties, which vary with scaffold degradation, and (3) identifying selected parameters as functions of time based on measurements from the tests on the scaffold mechanical properties as they degrade. To validate the developed model, scaffolds were made from the biocompatible polymer polycaprolactone (PCL) mixed with hydroxylapatite (HA) nanoparticles and their mechanical properties were examined in terms of the Young modulus. Based on the bulk degradation exhibited by the PCL/HA scaffold, the molecular weight was selected for model updating. With the identified molecular weight, the finite element model developed was effective for predicting the time-dependent mechanical properties of PCL/HA scaffolds during degradation.     

Apple Derived Cellulose Scaffolds for 3D Mammalian Cell Culture

There are numerous approaches for producing natural and synthetic 3D scaffolds that support the proliferation of mammalian cells. 3D scaffolds better represent the natural cellular microenvironment and have many potential applications in vitro and in vivo. Here, we demonstrate that 3D cellulose scaffolds produced by decellularizing apple hypanthium tissue can be employed for in vitro 3D culture of NIH3T3 fibroblasts, mouse C2C12 muscle myoblasts and human HeLa epithelial cells. We show that these cells can adhere, invade and proliferate in the cellulose scaffolds. In addition, biochemical functionalization or chemical cross-linking can be employed to control the surface biochemistry and/or mechanical properties of the scaffold. The cells retain high viability even after 12 continuous weeks of culture and can achieve cell densities comparable with other natural and synthetic scaffold materials. Apple derived cellulose scaffolds are easily produced, inexpensive and originate from a renewable source. Taken together, these results demonstrate that naturally derived cellulose scaffolds offer a complementary approach to existing techniques for the in vitro culture of mammalian cells in a 3D environment.     

Tissue engineering of the anterior cruciate ligament using a braid-twist scaffold design

The anterior cruciate ligament (ACL) is the most commonly injured intra-articular ligament of the knee. The insufficient vascularization of this tissue prevents it from healing completely after extreme tearing or rupture, creating a need for ACL grafts for reconstruction. The limitations of existing grafts have motivated the investigation of tissue-engineered ACL grafts. A successful tissue-engineered graft must possess mechanical properties similar to the ACL; to date no commercially available synthetic graft has achieved this. To accomplish this goal we have combined the techniques of polymer fiber braiding and twisting to design a novel poly L-lactic acid (PLLA) braid-twist scaffold for ACL tissue engineering. The scaffold is designed to accurately mimic the biomechanical profile and mechanical properties of the ACL. In this study, braid-twist scaffolds were constructed and compared to braided scaffolds and twisted fiber scaffolds. The addition of fiber twisting to the braided scaffold resulted in a significant increase in the ultimate tensile strength, an increase in ultimate strain, and an increase in the length of the toe region in these constructs over scaffolds that were braided. Based on the findings of this study, the braid-twist scaffold studied was found to be a promising construct for tissue engineering of the ACL.     

Evaluation of biological protein-based collagen scaffolds in cartilage and musculoskeletal tissue engineering--a systematic review of the literature

The term tissue engineering is the technology that combines cells, engineering and biological/synthetic material in order to repair, replace or regenerate biological tissues such as bone, muscle, tendons and cartilage. The major human applications of tissue engineering are: skin, bone, cartilage, corneas, blood vessels, left mainstem bronchus and urinary structures. In this systematic review several criteria were identified as the most desirable characteristics of an ideal scaffold. These state that an ideal scaffolds needs to be biodegradable, possess mechanical strength, be highly porous, biocompatible, non-cytotoxic, non antigentic, stuitable for cell attachment, proliferation and differentiation, flexible and elastic, three dimensional, osteoconductive and support the transport of nutrients and metabolic waste. Subsequently, studies reporting on the various advantages and disadvantages of using collagen based scaffolds in musculoskeletal and cartilage tissue engineering were identified. The purpose of this review is to 1) provide a list of ideal characteristics of a scaffold as identified in the literature 2) identify different types of biological protein-based collagen scaffolds used in musculoskeletal and cartilage tissue engineering 3) assess how many of the criteria each scaffold type meets 4) weigh different scaffolds against each other according to their relative properties and shortcomings. The rationale behind this approach is that the ideal scaffold material has not yet been identified. Hence, this review will define how many of the identified ideal characteristics are fulfilled by natural collagen-based scaffolds and address the shortcomings of its use as found in the literature.     

PCL-Based Composite Scaffold Matrices for Tissue Engineering Applications

Biomaterial-based scaffolds are important cues in tissue engineering (TE) applications. Recent advances in TE have led to the development of suitable scaffold architecture for various tissue defects. In this narrative review on polycaprolactone (PCL), we have discussed in detail about the synthesis of PCL, various properties and most recent advances of using PCL and PCL blended with either natural or synthetic polymers and ceramic materials for TE applications. Further, various forms of PCL scaffolds such as porous, films and fibrous have been discussed along with the stem cells and their sources employed in various tissue repair strategies. Overall, the present review affords an insight into the properties and applications of PCL in various tissue engineering applications.     

Tissue engineering for clinical applications

Tissue engineering is increasingly being recognized as a beneficial means for lessening the global disease burden. One strategy of tissue engineering is to replace lost tissues or organs with polymeric scaffolds that contain specialized populations of living cells, with the goal of regenerating tissues to restore normal function. Typical constructs for tissue engineering employ biocompatible and degradable polymers, along with organ-specific and tissue-specific cells. Once implanted, the construct guides the growth and development of new tissues; the polymer scaffold degrades away to be replaced by healthy functioning tissue. The ideal biomaterial for tissue engineering not only defends against disease and supports weakened tissues or organs, it also provides the elements required for healing and repair, stimulates the body's intrinsic immunological and regenerative capacities, and seamlessly interacts with the living body. Tissue engineering has been investigated for virtually every organ system in the human body. This review describes the potential of tissue engineering to alleviate disease, as well as the latest advances in tissue regeneration. The discussion focuses on three specific clinical applications of tissue engineering: cardiac tissue regeneration for treatment of heart failure; nerve regeneration for treatment of stroke; and lung regeneration for treatment of chronic obstructive pulmonary disease.     

New materials for tissue engineering: towards greater control over the biological response

One goal of tissue engineering is to replace lost or compromised tissue function, and an approach to this is to control the interplay between materials (scaffolds), cells and growth factors to create environments that promote the regeneration of functional tissues and organs. An increased understanding of the chemical signals that direct cell differentiation, migration and proliferation, advances in scaffold design and peptide engineering that allow this signaling to be recapitulated and the development of new materials, such as DNA-based and stimuli-sensitive polymers, have recently given engineers enhanced control over the chemical properties of a material and cell fate. Additionally, the immune system, which is often overlooked, has been shown to play a beneficial role in tissue repair, and future endeavors in material design will potentially expand to include immunomodulation.     

Electrospun Poly(L-lactide)/Poly(ε-caprolactone) Blend Nanofibrous Scaffold: Characterization and Biocompatibility with Human Adipose-Derived Stem Cells

The essence of tissue engineering is the fabrication of autologous cells or induced stem cells in naturally derived or synthetic scaffolds to form specific tissues. Polymer is thought as an appealing source of cell-seeded scaffold owing to the diversity of its physicochemical property and can be electrospun into nano-size to mimic natural structure. Poly (L-lactic acid) (PLLA) and poly (ε-caprolactone) (PCL) are both excellent aliphatic polyester with almost “opposite” characteristics. The controlling combination of PLLA and PCL provides varying properties and makes diverse applications. Compared with the copolymers of the same components, PLLA/PCL blend demonstrates its potential in regenerative medicine as a simple, efficient and scalable alternative. In this study, we electrospun PLLA/PCL blends of different weight ratios into nanofibrous scaffolds (NFS) and their properties were detected including morphology, porosity, degradation, ATR-FTIR analysis, stress-stain assay, and inflammatory reaction. To explore the biocompatibility of the NFS we synthesized, human adipose-derived stem cells (hASCs) were used to evaluate proliferation, attachment, viability and multi-lineage differentiation. In conclusion, the electrospun PLLA/PCL blend nanofibrous scaffold with the indicated weight ratios all supported hASCs well. However, the NFS of 1/1 weight ratio showed better properties and cellular responses in all assessments, implying it a biocompatible scaffold for tissue engineering.     

Three-dimensional scaffold containing EGF incorporated biodegradable polymeric nanoparticles for stem cell based tissue engineering applications

Stem cell-based tissue engineering holds much hope for the development of multifunctional tissues to replace diseased organs. The attachment and survival of stem cells on a three-dimensional (3D) scaffold must be enhanced for faster progression of stem cell based tissue engineering. This study evaluate the stability of mesenchymal stem cells (MSCs) in 3D porous scaffolds composed of a collagen and chitosan blend impregnated with epidermal growth factor incorporated chitosan nanoparticles (EGF-CNP). The EGF-CNP scaffolds were characterized by transmission electron microscopy, which revealed that the nanoparticles were round in shape and 20 ∼ 50 nm in size. The scaffolds were prepared by freeze drying. A Fourier-transform infrared spectrum study revealed that the linkage between collagen and chitosan was through an ionic interaction. Thermal analysis and degradation studies showed that the scaffold could be used in tissue engineering application. MSCs proliferated well in the EGF-CNP impregnated scaffold. A scanning electron microscope study showed anchored and elongated MSCs on the EGF-CNP impregnated scaffold. A 3D biodegradable collagen chitosan scaffold impregnated with EGF-CNP is a promising transportable candidate for MSC-based tissue engineering, and this scaffold could be used as an in vitro model for subsequent clinical applications.     

Application of inkjet printing to tissue engineering

Recent advances in organ printing technology for applications relating to medical interventions and organ replacement are described. Organ printing refers to the placement of various cell types into a soft scaffold fabricated according to a computer-aided design template using a single device. Computer aided scaffold topology design has recently gained attention as a viable option to achieve function and mass transport requirements within tissue engineering scaffolds. An exciting advance pioneered in our laboratory is that of simultaneous printing of cells and biomaterials, which allows precise placement of cells and proteins within 3-D hydrogel structures. This advance raises the possibility of spatially controlling not only the scaffold structure, but also the type of tissue that can be grown within the scaffold and the thickness of the tissue as capillaries and vessels could be constructed within the scaffolds. Here we summarize recent advances in printing cells and materials using the same device.     

Advanced cell therapies with and without scaffolds

Tissue engineering and regenerative medicine aim to produce tissue substitutes to restore lost functions of tissues and organs. This includes cell therapies, induction of tissue/organ regeneration by biologically active molecules, or transplantation of in vitro grown tissues. This review article discusses advanced cell therapies that make use of scaffolds and scaffold-free approaches. The first part of this article covers the basic characteristics of scaffolds, including characteristics of scaffold material, fabrication and surface functionalization, and their applications in the construction of hard (bone and cartilage) and soft (nerve, skin, blood vessel, heart muscle) tissue substitutes. In addition, cell sources as well as bioreactive agents, such as growth factors, that guide cell functions are presented. The second part in turn, examines scaffold-free applications, with a focus on the recently discovered cell sheet engineering. This article serves as a good reference for all applications of advanced cell therapies and as well as advantages and limitations of scaffold-based and scaffold-free strategies.     

Biocompatibility of hydrogel-based scaffolds for tissue engineering applications

Recently, understanding of the extracellular matrix (ECM) has expanded rapidly due to the accessibility of cellular and molecular techniques and the growing potential and value for hydrogels in tissue engineering. The fabrication of hydrogel-based cellular scaffolds for the generation of bioengineered tissues has been based on knowledge of the composition and structure of ECM. Attempts at recreating ECM have used either naturally-derived ECM components or synthetic polymers with structural integrity derived from hydrogels. Due to their increasing use, their biocompatibility has been questioned since the use of these biomaterials needs to be effective and safe. It is not surprising then that the evaluation of biocompatibility of these types of biomaterials for regenerative and tissue engineering applications has been expanded from being primarily investigated in a laboratory setting to being applied in the multi-billion dollar medicinal industry. This review will aid in the improvement of design of non-invasive, smart hydrogels that can be utilized for tissue engineering and other biomedical applications. In this review, the biocompatibility of hydrogels and design criteria for fabricating effective scaffolds are examined. Examples of natural and synthetic hydrogels, their biocompatibility and use in tissue engineering are discussed. The merits and clinical complications of hydrogel scaffold use are also reviewed. The article concludes with a future outlook of the field of biocompatibility within the context of hydrogel-based scaffolds.