Fine‐tuning scaffolds for tissue regeneration: effects of formic acid processing on tissue reaction to silk fibroin

Formic acid (FA) plays a key role in the preparation of silk fibroin (SF) scaffolds from cocoons of Bombyx mori and is used for fibre distribution. In this study, we used a subcutaneous implantation model in Wistar rats to examine SF scaffolds prepared by treating the degummed cocoon with FA for either 30 or 60 min. The tissue reaction and inflammatory response to SF was assessed by qualitative histology at intervals from 3 to 180 days. Additionally, dynamic biomaterial‐induced vascularization and biomaterial degradation were quantified using a technique for analysing an image of the entire implanted biomaterial. Varying the FA treatment time led to different scaffold morphologies and resulted in two distinct peri‐implant tissue reactions. The 30 min‐treated scaffold was integrated into the surrounding tissue beginning at day 3 after implantation and vascularization increased 10‐fold from 15 to 180 days, while the scaffold was continuously degraded throughout the first 90 days. In contrast, the 60 min‐treated SF scaffold appeared as bulk for the first 90 days after implantation, after which a rapid degradation and vascularization process began. After 180 days, the tissue response was similar for both scaffolds, with eventual formation of a well vascularized connective tissue integrating the SF fibres. This study indicates that by modifying the FA treatment time, the tissue reaction to SF scaffolds can be tailored for different tissue‐engineering applications. The tunability and biocompatibility of SF make it an attractive scaffold for exploration in regenerative medicine and clinical tissue engineering. Copyright © 2010 John Wiley & Sons, Ltd.     

Design and characterization of a biodegradable double‐layer scaffold aimed at periodontal tissue‐engineering applications

The inefficacy of the currently used therapies in achieving the regeneration ad integrum of the periodontium stimulates the search for alternative approaches, such as tissue‐engineering strategies. Therefore, the core objective of this study was to develop a biodegradable double‐layer scaffold for periodontal tissue engineering. The design philosophy was based on a double‐layered construct obtained from a blend of starch and poly‐ε‐caprolactone (30:70 wt%; SPCL). A SPCL fibre mesh functionalized with silanol groups to promote osteogenesis was combined with a SPCL solvent casting membrane aiming at acting as a barrier against the migration of gingival epithelium into the periodontal defect. Each layer of the double‐layer scaffolds was characterized in terms of morphology, surface chemical composition, degradation behaviour and mechanical properties. Moreover, the behaviour of seeded/cultured canine adipose‐derived stem cells (cASCs) was assessed. In general, the developed double‐layered scaffolds demonstrated adequate degradation and mechanical behaviour for the target application. Furthermore, the biological assays revealed that both layers of the scaffold allow adhesion and proliferation of the seeded undifferentiated cASCs, and the incorporation of silanol groups into the fibre‐mesh layer enhance the expression of a typical osteogenic marker. This study allowed an innovative construct to be developed, combining a three‐dimensional (3D) scaffold with osteoconductive properties and with potential to assist periodontal regeneration, carrying new possible solutions to current clinical needs. Copyright © 2013 John Wiley & Sons, Ltd.     

Physico‐chemical characterization and biological evaluation of two fibroin materials

Silk fibroin fibres from two different sources, Bombyx mori pure‐breed silkworms and polyhybrid cross‐bred silkworm cocoons, were treated with formic acid under planar stirring conditions to prepare non‐woven nets. The treatment partially dissolved the fibres, which bound together and formed a non‐woven micrometric net with fibres coated by a thin layer of low molecular weight fibroin matrix. The starting fibres, net materials and fibroin coating layer were characterized in terms of amino acid composition, molecular weight and calorimetric properties. In vitro cell culture tests with rat fibroblasts were performed to investigate cell proliferation, morphology and spreading. Moreover, host‐rat fibroblasts were preseeded on the afore‐mentioned nets and implanted in the thorax of rats for histological analysis. In spite of the chemical differences between the two starting fibroins, the response of the said materials in vitro and in vivo were very similar. These results suggest that the outcome is likely correlated with the modification of the processing technique; that during the formation of the net, a thin gel layer of similar amino acid composition was formed on the fibroin fibres. Copyright © 2012 John Wiley & Sons, Ltd.     

A collagen‐coated sponge silk scaffold for functional meniscus regeneration

Tissue engineering is a promising solution for meniscal regeneration after meniscectomy. However, in situ reconstruction still poses a formidable challenge due to multifunctional roles of the meniscus in the knee. In this study, we fabricate a silk sponge from 9% (w/v) silk fibroin solution through freeze drying and then coat its internal space and external surface with collagen sponge. Subsequently, various characteristics of the silk‐collagen scaffold are evaluated, and cytocompatibility of the construct is assessed in vitro and subcutaneously. The efficacy of this composite scaffold for meniscal regeneration is evaluated through meniscus reconstruction in a rabbit meniscectomy model. It is found that the internally coated collagen sponge enhances the cytocompatibility of the silk sponge, and the external layer of collagen sponge significantly improves the initial frictional property. Additionally, the silk‐collagen composite group shows more tissue ingrowth and less cartilage wear than the pure silk sponge group at 3 months postimplantation in situ. These findings thus demonstrate that the composite scaffold had less damage to the joint surface than the silk alone through promoting functional meniscal regeneration after meniscectomy, which indicates its clinical potential in meniscus reconstruction.     

Core‐shell silk hydrogels with spatially tuned conformations as drug‐delivery system

Hydrogels of spatially controlled physicochemical properties are appealing platforms for tissue engineering and drug delivery. In this study, core‐shell silk fibroin (SF) hydrogels of spatially controlled conformation were developed. The core‐shell structure in the hydrogels was formed by means of soaking the preformed (enzymatically crosslinked) random coil SF hydrogels in methanol. When increasing the methanol treatment time from 1 to 10 min, the thickness of the shell layer can be tuned from about 200 to about 850 μm as measured in wet status. After lyophilization of the rehydrated core‐shell hydrogels, the shell layer displayed compact morphology and the core layer presented porous structure, when observed by scanning electron microscopy. The conformation of the hydrogels was evaluated by Fourier transform infrared spectroscopy in wet status. The results revealed that the shell layer possessed dominant β‐sheet conformation and the core layer maintained mainly random coil conformation. Enzymatic degradation data showed that the shell layers presented superior stability to the core layer. The mechanical analysis displayed that the compressive modulus of the core‐shell hydrogels ranged from about 25 kPa to about 1.1 MPa by increasing the immersion time in methanol. When incorporated with albumin, the core‐shell SF hydrogels demonstrated slower and more controllable release profiles compared with the non‐treated hydrogel. These core‐shell SF hydrogels of highly tuned properties are useful systems as drug‐delivery system and may be applied as cartilage substitute. Copyright © 2016 John Wiley & Sons, Ltd.     

Phospholipid‐induced silk fibroin hydrogels and their potential as cell carriers for tissue regeneration

Silk fibroin (SF) hydrogels can be obtained via self‐assembly, but this process takes several days or weeks, being unfeasible to produce cell carrier hydrogels. In this work, a phospholipid, namely, 1,2‐dimyristoyl‐sn‐glycero‐3‐phospho‐(1′‐rac‐glycerol) sodium salt (DMPG), was used to induce and accelerate the gelation process of SF solutions. Due to the amphipathic nature and negative charge of DMPG, electrostatic and hydrophobic interactions between the phospholipids and SF chains will occur, inducing the structural transition of SF chains to the beta sheet and consequently a rapid gel formation is observed (less than 50 min). Moreover, the gelation time can be controlled by varying the lipid concentration. To assess the potential of the hydrogels as cell carriers, several mammalian cell lines, including L929, NIH/3T3, SaOS‐2, and CaSki, were encapsulated into the hydrogel. The silk‐based hydrogels supported the normal growth of fibroblasts, corroborating their cytocompatibility. Interestingly, an inhibition in the growth of cancer‐derived cell lines was observed. Therefore, DMPG‐induced SF hydrogels can be successfully used as a 3D platform for in situ cell encapsulation, opening promising opportunities in biomedical applications, such as in cell therapies and tissue regeneration.     

Biocompatibility of two model elastin‐like recombinamer‐based hydrogels formed through physical or chemical cross‐linking for various applications in tissue engineering and regenerative medicine

Biocompatibility studies, especially innate immunity induction, in vitro and in vivo cytotoxicity, and fibrosis, are often lacking for many novel biomaterials including recombinant protein‐based ones, such as elastin‐like recombinamers (ELRs), and has not been extensively explored in the scientific literature, in contrast to traditional biomaterials. Herein, we present the results from a set of experiments designed to elucidate the preliminary biocompatibility of 2 types of ELRs that are able to form extracellular matrix‐like hydrogels through either physical or chemical cross‐linking both of which are intended for different applications in tissue engineering and regenerative medicine. Initially, we present in vitro cytocompatibility results obtained upon culturing human umbilical vein endothelial cells on ELR substrates, showing optimal proliferation up to 9 days. Regarding in vivo cytocompatibility, luciferase‐expressing hMSCs were viable for at least 4 weeks in terms of bioluminescence emission when embedded in ELR hydrogels and injected subcutaneously into immunosuppressed mice. Furthermore, both types of ELR‐based hydrogels were injected subcutaneously in immunocompetent mice and serum TNFα, IL‐1β, IL‐4, IL‐6, and IL‐10 concentrations were measured by enzyme‐linked immunosorbent assay, confirming the lack of inflammatory response, as also observed upon macroscopic and histological evaluation. All these findings suggest that both types of ELRs possess broad biocompatibility, thus making them very promising for tissue engineering and regenerative medicine‐related applications.     

Airway tissue engineering

Introduction: Prosthetic replacements, autologous tissue transfer and allografts have so far failed to offer functional solutions for the treatment of long circumferential tracheal defects and loss of a functioning larynx. Interest has therefore turned increasingly to the field of tissue-engineering which applies the principles and methods of bioengineering, material science, cell transplantation and life sciences in an effort to develop in vitro biological substitutes able to restore, maintain or improve tissue and organ function.

Areas covered: This article gives an overview of the tissue-engineering approach to airway replacement and will describe the encouraging results obtained so far in tracheal regeneration. The recent advances in the field of tissue-engineering have provided a new attractive approach towards the concept of functional substitutes and may represent an alternative to the shortage of suitable grafts for reconstructive airway surgery. We summarize fundamental questions, as well as future directions in airway tissue engineering.

Expert opinion: The replacement of active movement, as would be necessary to replace an entire larynx introduces another order of magnitude of complexity, although progress in this area is starting to bear fruit. In addition, the stem cell field is advancing rapidly, opening new avenues for this type of therapy.     

多孔素蛋白支架修复兔下颌骨临界性骨缺损

背景：丝素蛋白具有良好的生物相容性和可降解性。目的：观察多孔丝素蛋白支架原位修复兔下颌骨临界性骨缺损效果。方法：建立免双侧下颌骨临界性骨缺损模型,随机选取一侧缺损植入多孔丝素蛋白支架作为实验组,另一侧缺损不作处理作为对照组。结果与结论：①大体标本：术后12周,实验组骨缺损腔表面完全被新生骨覆盖,材料无脱出;对照组骨缺损腔内充满肉芽组织,骨不连。②×射线骨密度测定：术后2,6,12周,两组骨密度均随着时间延长逐渐增高,组内不同时间点间差异有显著性意义（P〈0．05）,且同期实验组高于对照组（P〈0．05）。③组织病理切片苏木精伊红染色：术后12周,实验组岛状新生骨及骨小梁明显增多,而且粗大而致密,材料内部明显疏松,部分区域塌陷;对照组宿主骨边缘可见散在分布的新生骨组织,但并无粗大骨小梁形成。④骨形态发生蛋白2免疫组织化学染色：术后2,6,12周,两组骨形态发生蛋白2阳性细胞数均随着时间延长逐渐增多,组内不同时间点间差异有显著性意义（P〈0.05）,且同期实验组多于对照组（P〈0．05）。表明多孔丝素蛋白支架用于原位组织工程修复骨缺损具有一定可行性。     

Airway tissue engineering: an update

Introduction: Prosthetic materials, autologous tissues, cryopreserved homografts and allogeneic tissues have thus far proven unsuccessful in providing long-term functional solutions to extensive upper airway disease and damage. Research is therefore focusing on the rapidly expanding fields of regenerative medicine and tissue engineering in order to provide stem cell-based constructs for airway reconstruction, substitution and/or regeneration.

Areas covered: Advances in stem cell technology, biomaterials and growth factor interactions have been instrumental in guiding optimization of tissue-engineered airways, leading to several first-in-man studies investigating stem cell-based tissue-engineered tracheal transplants in patients. Here, we summarize current progress, outstanding research questions, as well as future directions within the field.

Expert opinion: The complex immune interaction between the transplant and host in vivo is only beginning to be untangled. Recent progress in our understanding of stem cell biology, decellularization techniques, biomaterials and transplantation immunobiology offers the prospect of transplanting airways without the need for lifelong immunosuppression. In addition, progress in airway revascularization, reinnervation and ever-increasingly sophisticated bioreactor design is opening up new avenues for the construction of a tissue-engineered larynx. Finally, 3D printing is a novel technique with the potential to render microscopic control over how cells are incorporated and grown onto the tissue-engineered airway.     

Gelatin‐ and hydroxyapatite‐based cryogels for bone tissue engineering: synthesis,characterization, in vitro and in vivo biocompatibility

The aim of this study was the synthesis and characterization of gelatin‐ and hydroxyapatite (osteoconductive component of bone)‐based cryogels for tissue‐engineering applications. Preliminary in vitro and in vivo biocompatibility tests were conducted. Gelatin‐ and hydroxyapatite‐based cryogels of varying concentrations were synthesized using glutaraldehyde as the crosslinking agent. Chemical structure, pore morphology, pore size distribution, mechanical properties, swelling characteristics and degradation profiles of the synthesized cryogels were demonstrated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), mercury porosimetry, a mechanical test device, swelling ratio tests and weight loss measurements, respectively. In vitro cell viability and in vivo biocompatility tests were performed in order to show the performance of the cryogels in the biological environment. Changing the concentrations of gelatin, hydroxyapatite and crosslinker changed the chemical structure, pore size and pore size distribution of the cryogels, which in turn resulted in the ultimate behaviour (mechanical properties, swelling ratio, degradation profile). In vitro cell culture tests showed the viability of the cells. The cryogels did not show any cytotoxic effects on the cells. Clinical outcomes and the gross pathological results demonstrated that there was no necrosis noted in the abdominal and thoracic regions at the end of implantation and the implanted cryogel was found to be non‐irritant and non‐toxic at 12 weeks of implantation. Copyright © 2013 John Wiley & Sons, Ltd.     

Development of decellularized scaffolds for stem cell‐driven tissue engineering

Organ transplantation is an effective treatment for chronic organ dysfunctioning conditions. However, a dearth of available donor organs for transplantation leads to the death of numerous patients waiting for a suitable organ donor. The potential of decellularized scaffolds, derived from native tissues or organs in the form of scaffolds has been evolved as a promising approach in tissue‐regenerative medicine for translating functional organ replacements. In recent years, donor organs, such as heart, liver, lung and kidneys, have been reported to provide acellular extracellular matrix (ECM)‐based scaffolds through the process called ‘decellularization’ and proved to show the potential of recellularization with selected cell populations, particularly with stem cells. In fact, decellularized stem cell matrix (DSCM) has also emerged as a potent biological scaffold for controlling stem cell fate and function during tissue organization. Despite the proven potential of decellularized scaffolds in tissue engineering, the molecular mechanism responsible for stem cell interactions with decellularized scaffolds is still unclear. Stem cells interact with, and respond to, various signals/cues emanating from their ECM. The ability to harness the regenerative potential of stem cells via decellularized ECM‐based scaffolds has promising implications for tissue‐regenerative medicine. Keeping these points in view, this article reviews the current status of decellularized scaffolds for stem cells, with particular focus on: (a) concept and various methods of decellularization; (b) interaction of stem cells with decellularized scaffolds; (c) current recellularization strategies, with associated challenges; and (iv) applications of the decellularized scaffolds in stem cell‐driven tissue engineering and regenerative medicine. Copyright © 2015 John Wiley & Sons, Ltd.     

A systematic review on cell‐seeded tissue engineering of penile corpora

Tissue engineering of corporal tissue is a new development in otherwise untreatable erectile dysfunction and in urethral reconstructions to treat hypospadias or severe urethral stricture disease. Multiple complications can arise with the current treatments, whereas engineered tissue, if well vascularized and existing of autologous cells, may lead to better results. The aim of this review was to provide an overview of literature on cell‐seeded‐based tissue engineering of corporal penile tissue. A literature search was performed following the PRISMA guidelines. Papers describing cell‐seeded tissue engineering of corporal tissue were included. Studies using different techniques, such as intracavernous injection were excluded. Fifteen articles were included in the review. Twelve of these studies described engineering of the corpus cavernosum in animal models. Two articles were found on engineering of animal corpus spongiosum and one article on engineering of the human glans. Both synthetic scaffolds and biological scaffolds were used. The advantage of a biological, acellular scaffold was that the native, complex architecture of corporal tissue was maintained. Most studies used endothelial and smooth muscle cells from corporal origin, but stem cells were also investigated. Furthermore, dynamic culturing achieved an improved cell content and functionality. This review has summarized the developments in tissue engineering of corpus cavernosum and spongiosum tissue. Functional tissue has been developed in animal studies with the use of seeded cells on scaffolds. This knowledge will form a basis for the development of tissue engineering of corporal tissue for clinical applications.     

Polysaccharide‐based materials for cartilage tissue engineering applications

Tissue engineering was proposed approximately 15 years ago as an alternative and innovative way to address tissue regeneration problems. During the development of this field, researchers have proposed a variety of ways of looking into the regeneration and engineering of tissues, using different types of materials coupled with a wide range of cells and bioactive agents. This trilogy is commonly considered the basis of a tissue‐engineering strategy, meaning by this the use of a support material, cells and bioactive agents. Different researchers have been adding to these basic approaches other parameters able to improve the functionality of the tissue‐engineered construct, such as specific mechanical environments and conditioned gaseous atmospheres, among others. Nowadays, tissue‐engineering principles have been applied, with different degrees of success, to almost every tissue lacking efficient regeneration ability and the knowledge and intellectual property produced since then has experienced an immense growth. Materials for regenerating tissues, namely cartilage, have also been continuously increasing and most of the theoretical requirements for a tissue engineering support have been addressed by a single material or a mixture of materials. Due to their intrinsic features, polysaccharides are interesting for cartilage tissue‐engineering approaches and as a result their exploitation for this purpose has been increasing. The present paper intends to provide an overview of some of the most relevant polysaccharides used in cartilage tissue‐engineering research. Copyright © 2010 John Wiley & Sons, Ltd.     

Characterizing human decellularized crystalline lens capsules as a scaffold for corneal endothelial tissue engineering

The idea of transplanting a sheet of laboratory‐grown corneal endothelium dates back to 1978; however, the ideal scaffold is still lacking. We hypothesized that human crystalline lens capsules (LCs) could qualify as a scaffold and aimed to characterize the properties of this material for endothelial tissue engineering. LCs were isolated from donor eyes, stored at ?80 °C, and decellularized with water and trypsin‐EDTA. The decellularization was investigated by nuclear staining and counting and the capsule thickness was determined by optical coherence tomography and compared with Descemet's membrane (DM). Transparency was examined by spectrometry, and collagenase degradation was performed to evaluate its resistance to degradation. Cell‐scaffold interaction was assessed by measuring focal adhesions surface area on LC and plastic. Finally, primary corneal endothelial cells were grown on LCs to validate the phenotype. Trypsin‐EDTA decellularized most effectively, removing 99% of cells. The mean LC thickness was 35.76 ± 0.43 μm, whereas DM measured 25.93 ± 0.26 μm (p < .0001). Light transmission was 90% for both LC and DM. On a collagenase challenge, LC and amniotic membrane were digested after 13 hr, whereas DM was digested after 17 hr. The surface area of focal adhesions for cells grown on coated LCs was at least double that compared with other conditions, whereas tight junctions, ion pumps, and hexagonal morphology were well maintained when endothelial cells were cultured on LCs. In conclusion, LCs demonstrate excellent scaffolding properties for tissue engineering and sustain the cell phenotype and can be considered a suitable substrate for ocular tissue engineering or as a template for future scaffolds.     

Genipin‐crosslinked gelatin–silk fibroin hydrogels for modulating the behaviour of pluripotent cells

Different hydrogel materials have been prepared to investigate the effects of culture substrate on the behaviour of pluripotent cells. In particular, genipin‐crosslinked gelatin–silk fibroin hydrogels of different compositions have been prepared, physically characterized and used as substrates for the culture of pluripotent cells. Pluripotent cells cultured on hydrogels remained viable and proliferated. Gelatin and silk fibroin promoted the proliferation of cells in the short and long term, respectively. Moreover, cells cultured on genipin‐crosslinked gelatin–silk fibroin blended hydrogels were induced to an epithelial ectodermal differentiation fate, instead of the neural ectodermal fate obtained by culturing on tissue culture plates. This work confirms that specific culture substrates can be used to modulate the behaviour of pluripotent cells and that our genipin‐crosslinked gelatin–silk fibroin blended hydrogels can induce pluripotent cells differentiation to an epithelial ectodermal fate. Copyright © 2014 John Wiley & Sons, Ltd.     

Hybrid scaffolds based on PLGA and silk for bone tissue engineering

Porous silk scaffolds, which are considered to be natural polymers, cannot be used alone because they have a long degradation rate, which makes it difficult for them to be replaced by the surrounding tissue. Scaffolds composed of synthetic polymers, such as PLGA, have a short degradation rate, lack hydrophilicity and their release of toxic by‐products makes them difficult to use. The present investigations aimed to study hybrid scaffolds fabricated from PLGA, silk and hydroxyapatite nanoparticles (Hap NPs) for optimized bone tissue engineering. The results from variable‐pressure field emission scanning electron microscopy (VP–FE–SEM), equipped with EDS, confirmed that the fabricated scaffolds had a porous architecture, and the location of each component present in the scaffolds was examined. Contact angle measurements confirmed that the introduction of silk and HAp NPs helped to change the hydrophobic nature of PLGA to hydrophilic, which is the main constraint for PLGA used as a biomaterial. Thermo‐gravimetric analysis (TGA) and FT–IR spectroscopy confirmed thermal decomposition and different vibrations caused in functional groups of compounds used to fabricate the scaffolds, which reflected improvement in their mechanical properties. After culturing osteoblasts for 1, 7 and 14 days in the presence of scaffolds, their viability was checked by MTT assay. The fluorescent microscopy results revealed that the introduction of silk and HAp NPs had a favourable impact on the infiltration of osteoblasts. In vivo experiments were conducted by implanting scaffolds in rat calvariae for 4 weeks. Histological examinations and micro‐CT scans from these experiments revealed beneficial attributes offered by silk fibroin and HAp NPs to PLGA‐based scaffolds for bone induction. Copyright © 2015 John Wiley & Sons, Ltd.     

Electrospun silk fibroin‐based neural scaffold for bridging a long sciatic nerve gap in dogs

Silk fibroin (SF)‐derived silkworms represent a type of highly biocompatible biomaterial for tissue engineering. We have previously investigated biocompatibility of SF with neural cells isolated from the central nervous system or peripheral nerve system in vitro, and also developed a SF‐based nerve graft conduit or tissue‐engineered nerve grafts by introducing bone marrow mesenchymal stem cells, as support cells, into SF‐based scaffold and evaluated the outcomes of peripheral nerve repair in a rat model. As an extension of the previous study, the electrospun technique was performed here to fabricate SF‐based neural scaffold inserted with silk fibres for bridging a 30‐mm‐long sciatic nerve gap in dogs. Assessments including functional, histological and morphometrical analyses were applied 12 months after surgery. All the results indicated that the SF‐based neural scaffold group achieved satisfactory regenerative outcomes, which were close to those achieved by autologous nerve grafts as the golden‐standard for peripheral nerve repair. Overall, our results raise a potential possibility for the translation of SF‐based electrospun neural scaffolds as an alternative to nerve autografts into the clinic.     

Advances in tissue engineering through stem cell‐based co‐culture

Stem cells are the future in tissue engineering and regeneration. In a co‐culture, stem cells not only provide a target cell source with multipotent differentiation capacity, but can also act as assisting cells that promote tissue homeostasis, metabolism, growth and repair. Their incorporation into co‐culture systems seems to be important in the creation of complex tissues or organs. In this review, critical aspects of stem cell use in co‐culture systems are discussed. Direct and indirect co‐culture methodologies used in tissue engineering are described, along with various characteristics of cellular interactions in these systems. Direct cell–cell contact, cell–extracellular matrix interaction and signalling via soluble factors are presented. The advantages of stem cell co‐culture strategies and their applications in tissue engineering and regenerative medicine are portrayed through specific examples for several tissues, including orthopaedic soft tissues, bone, heart, vasculature, lung, kidney, liver and nerve. A concise review of the progress and the lessons learned are provided, with a focus on recent developments and their implications. It is hoped that knowledge developed from one tissue can be translated to other tissues. Finally, we address challenges in tissue engineering and regenerative medicine that can potentially be overcome via employing strategies for stem cell co‐culture use. Copyright © 2014 John Wiley & Sons, Ltd.     

Environmental cues to guide stem cell fate decision for tissue engineering applications

The human body contains a variety of stem cells capable of both repeated self-renewal and production of specialised, differentiated progeny. Critical to the implementation of these cells in tissue engineering strategies is a thorough understanding of which external signals in the stem cell microenvironment provide cues to control their fate decision in terms of proliferation or differentiation into a desired, specific phenotype. These signals must then be incorporated into tissue regeneration approaches for regulated exposure to stem cells. The precise spatial and temporal presentation of factors directing stem cell behaviour is extremely important during embryogenesis, development and natural healing events, and it is possible that this level of control will be vital to the success of many regenerative therapies. This review covers existing tissue engineering approaches to guide the differentiation of three disparate stem cell populations: mesenchymal, neural and endothelial. These progenitor cells will be of central importance in many future connective, neural and vascular tissue regeneration technologies.