Showing papers on "Tissue engineering published in 2014"

3D Bioprinting of Vascularized, Heterogeneous Cell‐Laden Tissue Constructs

Abstract: A new bioprinting method is reported for fabricating 3D tissue constructs replete with vasculature, multiple types of cells, and extracellular matrix. These intricate, heterogeneous structures are created by precisely co-printing multiple materials, known as bioinks, in three dimensions. These 3D micro-engineered environments open new -avenues for drug screening and fundamental studies of wound healing, angiogenesis, and stem-cell niches.

Principles of tissue engineering

Abstract: Contributors. Foreword by C.A. Vacanti. Preface to the Second Edition. Preface to the First Edition. Tissue Engineering in Perspective, E. Bell. Introduction to Tissue Engineering: The History and Scope of Tissue Engineering, J.P. Vavanti and C.A. Vacanti. The Challenge of Imitating Nature, R.M. Nerem. Part I: The Basis of Growth and Differentiation: Organization of Cells into Higher Ordered Structures, C.A. Erickson. Dynamics of Cell-ECM Interactions, M.Martins-Green. Matrix Molecules and Their Ligands, B.R. Olsen. Inductive Phenomena, M. Hebrok and D. A. Melton. Morphogenesis and Tissue Engineering, A.H. Reddi. Cell Determination and Differentiation, L.W. Browder. Part II: In Vitro Control of Tissue Development: Mechanical and Chemical Determinants of Tissue Development, D.E. Inger. Animal Cell Culture, G.H. Sato and D.W. Barnes. Regulation of Cell Behavior by Matricellular Proteins, A.D. Bradshaw and E.H. Sage. Growth Factors, T.F. Deuel and N. Zhang. Tissue Engineering Bioreactors, L.E. Freed and G. Vunjak-Novakovic. Tissue Assembly in Microgravity, B.R. Unsworth and P.I. Lelkes. Part III: In Vivo Synthesis of Tissues and Organs: In Vivo Synthesis of Tissues and Organs, L.V. Yannas. Part IV: Models for Tissue Engineering: Organotypic and Histiotypic Models of Engineered Tissues, E. Bell. Quantitative Aspects of Tissue Engineering: Basic Issues in Kinetics, Transport, and Mechanics, A.J. Grodzinsky, R.D. Kamm, and Douglas A. Lauffenburger. Part V: Biomaterials in Tissue Engineering: Patterning of Cells and Their Environment, S. Takayama, R.C. Chapman, R.S. Kane, and G.M. Whitesides. Cell Interactions with Polymers, W.M. Saltzman. Matrix Effects, J.A. Hubbell. Polymer Scaffold Processing, R.C. Thomson, A.K. Shung, M.J. Yaszemski, and A.G. Mikos. Biodegradable Polymers, J.M. Pachence and J. Kohn. Part VI: Transplantation of Engineered Cells and Tissues: Approaches to Transplanting Engineered Cells and Tissues, J. Hardin-Young, J. Teumer, R.N. Ross, and N.L. Parenteau. Cryopreservation, J.O.M. Karlsson and M. Toner. Immunomodulation, D. Faustman. Immunoisolation, B.A. Zielinski and M.J. Lysaght. Engineering Challenges in Immunoisolation Device Development, E.S. Avgoustiniatos, H. Wu, and C.K. Colton. Part VII: Fetal Tissue Engineering: Fetal Tissue Engineering, D.O. Fauza. Pluripotent Stem Cells, M.J. Shamblott, B.E. Edwards, and J.D. Gearhart. Part VIII: Gene Therapy: Gene-Based Therapeutics, L.G. Fradkin, J.D. Ropp, and J.F. Warner. Part IX: Breast: Breast Reconstruction, K.Y. Lee, C.R. Halberstadt, W.D. Holder, and D.J. Mooney. Part X: Cardiovascular System: Blood Vessels, L. Xue and H.P. Greisler. Small-Diameter Vascular Grafts, S.J. Sullivan and K.G.M. Brockbank. Cardiac Prostheses, J.W. Love. Part XI: Cornea: Cornea, V. Trinkaus-Randall. Part XII: Endocrinology and Metabolism: Bioartificial Pancreas, T.G. Wang and R.P. Lanza. Parathyroid, C. Hasse, A Zielke, T. Bohrer, U. Zimmerman, and M. Rothmund. Part XIII: Gastrointestinal System: Alimentary Tract, G.M. Organ and J.P. Vacanti. Liver, H.O. Jauregui. Hepat Assist Liver Support System, C. Mullon and B.A. Solomon. Lineage Biology and Liver, A.S.L. Xu, T.L. Luntz, J.M. Macdonald, H. Kubota, E. Hsu, R.E. London, and L.M. Reid. Part XIV: Hematopoietic System: Red Blood Cell Substitutes, T.M.S. Chang. Lymphoid Cells, U. Chen. Hematopoietic Stem Cells, A. Kessinger and G. Sharp. Part XV: Kidney and Genitourinary System: Renal Replacement Devices, H.D. Humes. Genitourinary System, B.-S. Kim, D.J. Mooney, and A. Atala. Part XVI: Musculoskeletal System: Structural Tissue Engineering, C.A. Vacanti, L.J. Bonassar, and J.P. Vacanti. Bone Regeneration through Cellular Engineering, S.P. Bruder and A.I. Caplan. Articular Cartilage Injury, J.M. McPherson and R. Tubo. Tendons and Ligaments, F. Goulet, D. Rancourt, R. Cloutier, L. Germain, A.R. Poole, and F.A. Auger. Mechanosensory Mechanisms in Bone, S.C. Cowin and M.L. Moss. Myoblast Therapy, J.C. Cousins, J.E. Morgan, and T.A. Partridge. Part XVII: Nervous System: Protection and Repair of Hearing, R.A. Altschuler, Y. Raphael, J. Schacht, D.J. Anderson, and J.M. Miller. Vision Enhancement Systems, G. Dagnelie, M.S. Humayun, and R.W. Massof. Brain Implants, Lars U. Wahlberg. Nerve Regeneration, E.G. Fine, R.F. Valentini, and P. Aebischer. Transplantation Strategies for Treatment of Spinal Cord Dysfunction and Injury, J. Sagen, M.B. Bunge, and N. Kleitman. Neural Stem Cells, M.P. Vacanti. Part XVIII: Periodontal and Dental Applications: Periodontal Applications, N.A. Miller, M.C. Bene, J.P., P. Ambrosini, and G.C. Faure. Regeneration of Dentin, R.B. Rutherford. Part XIX: Skin: Wound Repair: Basic Biology to Tissue Engineering, R.A.F. Clark and A.J. Singer. Skin, N.L. Parenteau, J. Hardin-Young, and R.N. Ross. Dermal Equivalents, G.K. Naughton. Part XX: Womb: Artificial Womb, C.S. Muratore and J.M. Wilson. Part XXI: Regulatory Issues: Regulatory Considerations, K.B. Hellman, R.R. Solomon, C. Gaffey, C.N. Durfor, and J.G. Bishop. Epilogue. Index.

An Overview of Poly(lactic-co-glycolic) Acid (PLGA)-Based Biomaterials for Bone Tissue Engineering

Abstract: Poly(lactic-co-glycolic) acid (PLGA) has attracted considerable interest as a base material for biomedical applications due to its: (i) biocompatibility; (ii) tailored biodegradation rate (depending on the molecular weight and copolymer ratio); (iii) approval for clinical use in humans by the U.S. Food and Drug Administration (FDA); (iv) potential to modify surface properties to provide better interaction with biological materials; and (v) suitability for export to countries and cultures where implantation of animal-derived products is unpopular. This paper critically reviews the scientific challenge of manufacturing PLGA-based materials with suitable properties and shapes for specific biomedical applications, with special emphasis on bone tissue engineering. The analysis of the state of the art in the field reveals the presence of current innovative techniques for scaffolds and material manufacturing that are currently opening the way to prepare biomimetic PLGA substrates able to modulate cell interaction for improved substitution, restoration, or enhancement of bone tissue function.

Biomimetic porous scaffolds for bone tissue engineering

Abstract: Increased use of reconstruction procedures in orthopedics, due to trauma, tumor, deformity, degeneration and an aging population, has caused a blossom, not only in surgical advancement, but also in the development of bone implants. Traditional synthetic porous scaffolds are made of metals, polymers, ceramics or even composite biomaterials, in which the design does not consider the native structure and properties of cells and natural tissues. Thus, these synthetic scaffolds often poorly integrate with the cells and surrounding host tissue, thereby resulting in unsatisfactory surgical outcomes due to poor corrosion and wear, mechanical mismatch, unamiable surface environment, and other unfavorable properties. Musculoskeletal tissue reconstruction is the ultimate objective in orthopedic surgery. This objective can be achieved by (i) prosthesis or fixation device implantation, and (ii) tissue engineered bone scaffolds. These devices focus on the design of implants, regardless of the choice of new biomaterials. Indeed, metallic materials, e.g. 316L stainless steel, titanium alloys and cobalt chromium alloys, are predominantly used in bone surgeries, especially in the load-bearing zone of prostheses. The engineered scaffolds take biodegradability, cell biology, biomolecules and material mechanical properties into account, in which these features are ideally suited for bone tissue repair and regeneration. Therefore, the design of the scaffold is extremely important to the success of clinical outcomes in musculoskeletal surgeries. The ideal scaffolds should mimic the natural extracellular matrix (ECM) as much as possible, since the ECM found in natural tissues supports cell attachment, proliferation, and differentiation, indicating that scaffolds should consist of appropriate biochemistry and nano/micro-scale surface topographies, in order to formulate favorable binding sites to actively regulate and control cell and tissue behavior, while interacting with host cells. In addition, scaffolds should also possess a similar macro structure to what is found in natural bone. This feature may provide space for the growth of cells and new tissues, as well as for the carriers of growth factors. Another important concern is the mechanical properties of scaffolds. It has been reported that the mechanical features can significantly influence the osteointegration between implants and surrounding tissues, as well as cell behaviors. Since natural bone exhibits super-elastic biomechanical properties with a Young's modulus value in the range of 1–27 GPa, the ideal scaffolds should mimic strength, stiffness and mechanical behavior, so as to avoid possible post-operation stress shielding effects, which induce bone resorption and consequent implant failure. In addition, the rate of degradation and the by-products of biodegradable materials are also critical in the role of bone regeneration. Indeed, the mechanical integrity of a scaffold will be significantly reduced if the degradation rate is rapid, thereby resulting in a pre-matured collapse of the scaffold before the tissue is regenerated. Another concern is that the by-products upon degradation may alter the tissue microenvironment and then challenge the biocompatibility of the scaffold and the subsequent tissue repair. Therefore, these two factors should be carefully considered when designing new biomaterials for tissue regeneration. To address the aforementioned questions, an overview of the design of ideal biomimetic porous scaffolds is presented in this paper. Hence, a number of original engineering processes and techniques, including the production of a hierarchical structure on both the macro- and nano-scales, the adjustment of biomechanical properties through structural alignment and chemical components, the control of the biodegradability of the scaffold and its by-products, the change of biomimetic surface properties by altering interfacial chemistry, and micro- and nano-topographies will be discussed. In general, the concepts and techniques mentioned above provide insights into designing superior biomimetic scaffolds for bone tissue engineering.

Hydrogel bioprinted microchannel networks for vascularization of tissue engineering constructs

Abstract: Vascularization remains a critical challenge in tissue engineering. The development of vascular networks within densely populated and metabolically functional tissues facilitate transport of nutrients and removal of waste products, thus preserving cellular viability over a long period of time. Despite tremendous progress in fabricating complex tissue constructs in the past few years, approaches for controlled vascularization within hydrogel based engineered tissue constructs have remained limited. Here, we report a three dimensional (3D) micromolding technique utilizing bioprinted agarose template fibers to fabricate microchannel networks with various architectural features within photocrosslinkable hydrogel constructs. Using the proposed approach, we were able to successfully embed functional and perfusable microchannels inside methacrylated gelatin (GelMA), star poly(ethylene glycol-co-lactide) acrylate (SPELA), poly(ethylene glycol) dimethacrylate (PEGDMA) and poly(ethylene glycol) diacrylate (PEGDA) hydrogels at different concentrations. In particular, GelMA hydrogels were used as a model to demonstrate the functionality of the fabricated vascular networks in improving mass transport, cellular viability and differentiation within the cell-laden tissue constructs. In addition, successful formation of endothelial monolayers within the fabricated channels was confirmed. Overall, our proposed strategy represents an effective technique for vascularization of hydrogel constructs with useful applications in tissue engineering and organs on a chip.

The Design of Scaffolds for Use in Tissue Engineering

Abstract: Problems: Tissue engineering (TE) is one of the modern strategies to provide a functional biological tissue equivalent to restore or improve the function of human tissues that lost by disease, traumatic events, or congenital abnormalities. Some essential factors in TE are tissue type and appropriate scaffold. suitable influence on cell viability and proliferation is One of the most important characteristics of a appropriate scaffold for tissue engineering. The purpose of this research was to comparative evaluation of adipose derived stem cells (ADSCs) proliferation rate and their viability on the five different scaffolds. Experimental approach: six different scaffolds were prepared including Alginate, Poly Lactic Glycolic Acid (PLGA), Fibrin glue (FG), Inactive Platelet- Rich Plasma (IPRP), Active Platelet- Rich Plasma (APRP) and Hydroxyapatite/ β

Review collagen-based biomaterials for wound healing

Abstract: With its wide distribution in soft and hard connective tissues, collagen is the most abundant of animal proteins. In vitro, natural collagen can be formed into highly organized, three-dimensional scaffolds that are intrinsically biocompatible, biodegradable, nontoxic upon exogenous application, and endowed with high tensile strength. These attributes make collagen the material of choice for wound healing and tissue engineering applications. In this article, we review the structure and molecular interactions of collagen in vivo; the recent use of natural collagen in sponges, injectables, films and membranes, dressings, and skin grafts; and the on-going development of synthetic collagen mimetic peptides as pylons to anchor cytoactive agents in wound beds.

Natural polymers for the microencapsulation of cells

Abstract: The encapsulation of living mammalian cells within a semi-permeable hydrogel matrix is an attractive procedure for many biomedical and biotechnological applications, such as xenotransplantation, maintenance of stem cell phenotype and bioprinting of three-dimensional scaffolds for tissue engineering and regenerative medicine. In this review, we focus on naturally derived polymers that can form hydrogels under mild conditions and that are thus capable of entrapping cells within controlled volumes. Our emphasis will be on polysaccharides and proteins, including agarose, alginate, carrageenan, chitosan, gellan gum, hyaluronic acid, collagen, elastin, gelatin, fibrin and silk fibroin. We also discuss the technologies commonly employed to encapsulate cells in these hydrogels, with particular attention on microencapsulation.

Chitosan-based scaffolds for bone tissue engineering

Abstract: Bone defects requiring grafts to promote healing are frequently occurring and costly problems in health care. Chitosan, a biodegradable, naturally occurring polymer, has drawn considerable attention in recent years as a scaffolding material in tissue engineering and regenerative medicine. Chitosan is especially attractive as a bone scaffold material because it supports the attachment and proliferation of osteoblast cells as well as formation of mineralized bone matrix. In this review, we discuss the fundamentals of bone tissue engineering and the unique properties of chitosan as a scaffolding material to treat bone defects for hard tissue regeneration. We present common methods for fabrication and characterization of chitosan scaffolds, and discuss the influence of material preparation and addition of polymeric or ceramic components or biomolecules on chitosan scaffold properties such as mechanical strength, structural integrity, and functional bone regeneration. Finally, we highlight recent advances in the development of chitosan-based scaffolds with enhanced bone regeneration capability.

Advanced Platelet-Rich Fibrin: A New Concept for Cell-Based Tissue Engineering by Means of Inflammatory Cells

Abstract: Choukroun's platelet-rich fibrin (PRF) is obtained from blood without adding anticoagulants. In this study, protocols for standard platelet-rich fibrin (S-PRF) (2700 rpm, 12 minutes) and advanced p...

3D printing of composite tissue with complex shape applied to ear regeneration

Abstract: In the ear reconstruction field, tissue engineering enabling the regeneration of the ear's own tissue has been considered to be a promising technology. However, the ear is known to be difficult to regenerate using traditional methods due to its complex shape and composition. In this study, we used three-dimensional (3D) printing technology including a sacrificial layer process to regenerate both the auricular cartilage and fat tissue. The main part was printed with poly-caprolactone (PCL) and cell-laden hydrogel. At the same time, poly-ethylene-glycol (PEG) was also deposited as a sacrificial layer to support the main structure. After complete fabrication, PEG can be easily removed in aqueous solutions, and the procedure for removing PEG has no effect on the cell viability. For fabricating composite tissue, chondrocytes and adipocytes differentiated from adipose-derived stromal cells were encapsulated in hydrogel to dispense into the cartilage and fat regions, respectively, of ear-shaped structures. Finally, we fabricated the composite structure for feasibility testing, satisfying expectations for both the geometry and anatomy of the native ear. We also carried out in vitro assays for evaluating the chondrogenesis and adipogenesis of the cell-printed structure. As a result, the possibility of ear regeneration using 3D printing technology which allowed tissue formation from the separately printed chondrocytes and adipocytes was demonstrated.

Highly tunable elastomeric silk biomaterials.

Abstract: Elastomeric, fully degradable and biocompatible biomaterials are rare, with current options presenting significant limitations in terms of ease of functionalization and tunable mechanical and degradation properties. We report a new method for covalently crosslinking tyrosine residues in silk proteins, via horseradish peroxidase and hydrogen peroxide, to generate highly elastic hydrogels with tunable properties. The tunable mechanical properties, gelation kinetics and swelling properties of these new protein polymers, in addition to their ability to withstand shear strains on the order of 100%, compressive strains greater than 70% and display stiffness between 200 - 10,000 Pa, covering a significant portion of the properties of native soft tissues. Molecular weight and solvent composition allowed control of material mechanical properties over several orders of magnitude while maintaining high resilience and resistance to fatigue. Encapsulation of human bone marrow derived mesenchymal stem cells (hMSC) showed long term survival and exhibited cell-matrix interactions reflective of both silk concentration and gelation conditions. Further biocompatibility of these materials were demonstrated with in vivo evaluation. These new protein-based elastomeric and degradable hydrogels represent an exciting new biomaterials option, with a unique combination of properties, for tissue engineering and regenerative medicine.

Bone tissue engineering via nanostructured calcium phosphate biomaterials and stem cells.

Abstract: Tissue engineering is promising to meet the increasing need for bone regeneration. Nanostructured calcium phosphate (CaP) biomaterials/scaffolds are of special interest as they share chemical/crystallographic similarities to inorganic components of bone. Three applications of nano-CaP are discussed in this review: nanostructured calcium phosphate cement (CPC); nano-CaP composites; and nano-CaP coatings. The interactions between stem cells and nano-CaP are highlighted, including cell attachment, orientation/morphology, differentiation and in vivo bone regeneration. Several trends can be seen: (i) nano-CaP biomaterials support stem cell attachment/proliferation and induce osteogenic differentiation, in some cases even without osteogenic supplements; (ii) the influence of nano-CaP surface patterns on cell alignment is not prominent due to non-uniform distribution of nano-crystals; (iii) nano-CaP can achieve better bone regeneration than conventional CaP biomaterials; (iv) combining stem cells with nano-CaP accelerates bone regeneration, the effect of which can be further enhanced by growth factors; and (v) cell microencapsulation in nano-CaP scaffolds is promising for bone tissue engineering. These understandings would help researchers to further uncover the underlying mechanisms and interactions in nano-CaP stem cell constructs in vitro and in vivo, tailor nano-CaP composite construct design and stem cell type selection to enhance cell function and bone regeneration, and translate laboratory findings to clinical treatments.

Liposomes in tissue engineering and regenerative medicine

Abstract: Liposomes are vesicular structures made of lipids that are formed in aqueous solutions. Structurally, they resemble the lipid membrane of living cells. Therefore, they have been widely investigated, since the 1960s, as models to study the cell membrane, and as carriers for protection and/or delivery of bioactive agents. They have been used in different areas of research including vaccines, imaging, applications in cosmetics and tissue engineering. Tissue engineering is defined as a strategy for promoting the regeneration of tissues for the human body. This strategy may involve the coordinated application of defined cell types with structured biomaterial scaffolds to produce living structures. To create a new tissue, based on this strategy, a controlled stimulation of cultured cells is needed, through a systematic combination of bioactive agents and mechanical signals. In this review, we highlight the potential role of liposomes as a platform for the sustained and local delivery of bioactive agents for tissue engineering and regenerative medicine approaches.

The extracellular matrix: Structure, composition, age-related differences, tools for analysis and applications for tissue engineering:

Abstract: The extracellular matrix is a structural support network made up of diverse proteins, sugars and other components. It influences a wide number of cellular processes including migration, wound healing and differentiation, all of which is of particular interest to researchers in the field of tissue engineering. Understanding the composition and structure of the extracellular matrix will aid in exploring the ways the extracellular matrix can be utilised in tissue engineering applications especially as a scaffold. This review summarises the current knowledge of the composition, structure and functions of the extracellular matrix and introduces the effect of ageing on extracellular matrix remodelling and its contribution to cellular functions. Additionally, the current analytical technologies to study the extracellular matrix and extracellular matrix–related cellular processes are also reviewed.

Adipose-derived stem cells: Implications in tissue regeneration.

Abstract: Adipose-derived stem cells (ASCs) are mesenchymal stem cells (MSCs) that are obtained from abundant adipose tissue, adherent on plastic culture flasks, can be expanded in vitro, and have the capacity to differentiate into multiple cell lineages. Unlike bone marrow-derived MSCs, ASCs can be obtained from abundant adipose tissue by a minimally invasive procedure, which results in a high number of cells. Therefore, ASCs are promising for regenerating tissues and organs damaged by injury and diseases. This article reviews the implications of ASCs in tissue regeneration.

Chondrogenic differentiation of mesenchymal stem cells: challenges and unfulfilled expectations.

Abstract: Articular cartilage repair and regeneration provides a substantial challenge in Regenerative Medicine because of the high degree of morphological and mechanical complexity intrinsic to hyaline cartilage due, in part, to its extracellular matrix. Cartilage remains one of the most difficult tissues to heal; even state-of-the-art regenerative medicine technology cannot yet provide authentic cartilage resurfacing. Mesenchymal stem cells (MSCs) were once believed to be the panacea for cartilage repair and regeneration, but despite years of research, they have not fulfilled these expectations. It has been observed that MSCs have an intrinsic differentiation program reminiscent of endochondral bone formation, which they follow after exposure to specific reagents as a part of current differentiation protocols. Efforts have been made to avoid the resulting hypertrophic fate of MSCs; however, so far, none of these has recreated a fully functional articular hyaline cartilage without chondrocytes exhibiting a hypertrophic phenotype. We reviewed the current literature in an attempt to understand why MSCs have failed to regenerate articular cartilage. The challenges that must be overcome before MSC-based tissue engineering can become a front-line technology for successful articular cartilage regeneration are highlighted.

Bioprinting technology and its applications

Abstract: Summary Bioprinting technology has emerged as a powerful tool for building tissue and organ structures in the field of tissue engineering. This technology allows precise placement of cells, biomaterials and biomolecules in spatially predefined locations within confined three-dimensional (3D) structures. Various bioprinting technologies have been developed and utilized for applications in life sciences, ranging from studying cellular mechanisms to constructing tissues and organs for implantation, including heart valve, myocardial tissue, trachea and blood vessels. In this article, we introduce the general principles and limitations of the most widely used bioprinting technologies, including jetting- and extrusion-based systems. Application-based research focused on tissue regeneration is presented, as well as the current challenges that hamper clinical utility of bioprinting technology.

Bone tissue engineering scaffolding: computer-aided scaffolding techniques

Abstract: Tissue engineering is essentially a technique for imitating nature. Natural tissues consist of three components: cells, signalling systems (e.g. growth factors) and extracellular matrix (ECM). The ECM forms a scaffold for its cells. Hence, the engineered tissue construct is an artificial scaffold populated with living cells and signalling molecules. A huge effort has been invested in bone tissue engineering, in which a highly porous scaffold plays a critical role in guiding bone and vascular tissue growth and regeneration in three dimensions. In the last two decades, numerous scaffolding techniques have been developed to fabricate highly interconnective, porous scaffolds for bone tissue engineering applications. This review provides an update on the progress of foaming technology of biomaterials, with a special attention being focused on computer-aided manufacturing (Andrade et al. 2002) techniques. This article starts with a brief introduction of tissue engineering (Bone tissue engineering and scaffolds) and scaffolding materials (Biomaterials used in bone tissue engineering). After a brief reviews on conventional scaffolding techniques (Conventional scaffolding techniques), a number of CAM techniques are reviewed in great detail. For each technique, the structure and mechanical integrity of fabricated scaffolds are discussed in detail. Finally, the advantaged and disadvantage of these techniques are compared (Comparison of scaffolding techniques) and summarised (Summary).