Scaffold

During the resorbable-polymer-boom of the 1970s and 1980s, polycaprolactone (PCL) was used in the biomaterials field and a number of drug-delivery devices. Its popularity was soon superseded by faster resorbable polymers which had fewer perceived disadvantages associated with long term degradation (up to 3-4 years) and intracellular resorption pathways; consequently, PCL was almost forgotten for most of two decades.

The concept of tissue and cell guidance is rapidly evolving as more information regarding the effect of the microenvironment on cellular function and tissue morphogenesis become available. These disclosures have lead to a tremendous advancement in the design of a new generation of multifunctional biomaterials able to mimic the molecular regulatory characteristics and the three-dimensional architecture of the native extracellular matrix. Micro-and nano-structured scaffolds able to sequester and deliver in a highly specific manner biomolecular moieties have already been proved to be effective in bone repairing, in guiding functional angiogenesis and in controlling stem cell differentiation. Although these platforms represent a first attempt to mimic the complex temporal and spatial microenvironment presented in vivo, an increased symbiosis of material engineering, drug delivery technology and cell and molecular biology may ultimately lead to biomaterials that encode the necessary signals to guide and control developmental process in tissue-and organ-specific differentiation and morphogenesis.

The aim of this study was to evaluate the osteogenic potential and the vascularization of embroidered, tissue engineered, and cell-seeded 3D poly(3)hydroxybutyrate (PHB) scaffolds in nude rats. Collagen I (coll I)- and collagen I/chondroitin sulfate (coll I/CS)-coated PHB scaffolds were seeded with human mesenchymal stem cells (hMSCs). Proliferation and differentiation were characterized by different biochemical assays in vitro. For animal experiments, the cells were cultivated on coll I- or coll I/CS-coated scaffolds and either expanded or osteogenically differentiated. Scaffolds were piled up to create a 3D scaffold pad and implanted subcutaneously into nude rats. In vitro hMSC showed proliferation and differentiation on PHB scaffolds. Alkaline phosphatase (ALP) and calcium increased in the differentiation medium and in the presence of coll I/CS. In vivo blood vessels were found in the scaffold-stack. Histological/immunohistological analyses of explanted scaffolds showed osteogenic markers such as osteopontin, osteonectin, and coll I around the PHB fibers. Coll I/CS-coated scaffolds with expanded hMSC showed higher values of ALP and calcium than the other combinations. Embroidered PHB scaffolds, coated with extracellular matrix components, provided an adequate environment and, therefore, a template for hMSC which could be differentiated in osteogenic direction. © 2009 Wiley Periodicals, Inc. J Biomed Mater Res, 2010

Poor angiogenesis within tissue-engineered grafts has been identified as a main challenge limiting the clinical introduction of bone tissue-engineering (BTE) approaches for the repair of large bone defects. Thick BTE grafts often exhibit poor cellular viability particularly at the core, leading to graft failure and lack of integration with host tissues. Various BTE approaches have been explored for improving vascularisation in tissue-engineered constructs and are briefly discussed in this review. Recent investigations relating to co-culture systems of endothelial and osteoblast-like cells have shown evidence of BTE efficacy in increasing vascularization in thick constructs. This review provides an overview of key concepts related to bone formation and then focuses on the current state of engineered vascularized co-culture systems using bone repair as a model. It will also address key questions regarding the generation of clinically relevant vascularized bone constructs as well as potential directions and considerations for research with the objective of pursuing engineered co-culture systems in other disciplines of vascularized regenerative medicine. The final objective is to generate serious and functional long-lasting vessels for sustainable angiogenesis that will enable enhanced cellular survival within thick voluminous bone grafts, thereby aiding in bone formation and remodelling in the long term. However, more evidence about the quality of blood vessels formed and its associated functional improvement in bone formation as well as a mechanistic understanding of their interactions are necessary for designing better therapeutic strategies for translation to clinical settings. Figure 1. (A) Hierarchical structure of bone from a sub-nanostructure of collagen molecules to a nanostructure of cylindrically arranged microfibrils to lamellar layers forming the macrostructure of cortical bone (adapted from Rho et al. (1998). (B) Vascularised bone anatomy and microenvironmental influences such as biomechanical, microarchitectural and low oxygen tension factors Y. Liu et al.

Polydioxanone (PDS) is a colorless, crystalline, bioabsorbable polymer that was first developed specifically for wound closure sutures. The compatibility, degradation rate, and mechanical properties (including shape memory) of PDS are of interest when considering the design of tissue engineering scaffolds. This research presents the electrospinning of PDS to fabricate unique nanofibrous structures for a variety of biomedical applications. Electrospinning is a polymer processing technique that utilizes an electric field to form fibers from a polymer solution or melt and allows the fabrication of nanofibrous non-woven structures. Results demonstrate the ability to control the fiber diameter of PDS as a function of solution concentrations and the fiber orientation with our prototype electrospinning apparatus. The results also show dependence between the fiber orientation and the elastic modulus, peak stress, and strain to failure of PDS in a uniaxial model.

In the present work, natural coral from Brazilian reefs were studied according to their crystallography by X-ray diffraction and microstructure by Scanning Electron Microscopy (SEM/EDX). FTIR spectroscopy was also used to evaluate the chemical functionalities and major components present in the material. The SEM morphology results have shown a tri-dimensional coral structure with porous ranging from 50 to 200 µm. Aragonite was identified as the major crystalline phase through XRD analysis and FTIR spectroscopy. Strontium calcium carbonate, (Sr,Ca)CO 3 , was also identified by XRD analysis. After sintering at 900º/1h, the conversion from aragonite to CaO and calcite was observed. These results have endorsed the high potential application of natural coral materials as 3D scaffolds for biomedical application, because of calcium carbonate compounds can be converted to HA by hydrothermal and biomimetic coating processes.

Research in polymer nanofibers has undergone significant progress in the last decade. One of the main driving force for this progress is the increasing use of these polymer nanofibers for tissue engineering. Adequate porosity and surface area are widely recognized as important parameters in the design of scaffolds for tissue engineering and therefore measurement of porosity is very important. Previous methods such as mercury measurement, indirect method, the porosity measurement based on density of nanofibers do not measure the porosity of various surface layers. The goal of this study is measurement of porosity of various surface layers of scaffold. Image analysis was used for this purpose. SEM images of nanofibers mat were converted to binary images using different thresholds and porosity of scaffold was measured in various layers. On the basis of the results of our study, this method can be applied to porosity measurement of various surface layers of nanofibers mat. The results showed that porosity of various surface layers is related to the number of layers of nanofibers mat.

In this study, three-dimensional silk fibroin/chitosan (SF/CTS) composite sponges were successfully prepared with an interconnected porous structure and proper mechanical properties. Silk fibroin and chitosan have the potential to mimic a natural extra-cellular matrix (ECM). For the sponge preparation, silk fibroin from the Bombyx mori silkworm and chitosan were used, in different proportions, as composites. Sponges were prepared by means of freezing and lyophylization of corresponding composite solutions. The properties of composite sponges, such as the microstructure as well as the chemical and physical properties were studied. In the present investigation, silk fibroin, chitosan and their mixtures were characterized by attenuated total reflection Fourier transform infra-red spectroscopy (ATR-FTIR), swelling properties, thermogravimetric analysis and scanning electron microscopy (SEM). The ATR-FTIR analysis indicated a shift of band corresponding to C_O, C\N, C\O\C. Moreover, NH groups of SF and C_O and NH 2 groups of chitosan might have participated in a specific intermolecular interaction among themselves. Thermogravimetric results suggested a higher temperature of decomposition for SF/CTS sponges than sponges made of pure silk fibroin or chitosan. Scanning electron microscopy observations showed the sponges of SF/CTS with pore size from 20 to 150 μm, which is appropriate for cell growth. Biocompatibility of sponges was confirmed by in vitro test. SF/CTS sponges have sufficient mechanical integrity to resist handling during implantation and in vivo loading. Both the compressive modulus and compressive strength for the sponge decrease with the increase of silk fibroin content in the sponge. Sponges made of silk fibroin/chitosan mixtures can be interesting materials for tissue engineering as scaffold for temporary supporting the formation of new tissue and organs.

Lesson planning for student teachers is often regarded in technical terms, merely as the means to ensure effective classroom performance. This approach limits the possibilities that the process of lesson planning offers to the development of professional competence among student teachers. In particular, student teachers need to begin to develop their pedagogical content knowledge (PCK), the capacity to make pedagogical choices that are logically derived from content and contextual knowledge. This article reports on a Lesson Planning Guideline which is used to scaffold the construction of student teachers’ PCK individually by requiring them to consider the constituent parts of PCK individually and in relation to one another during the planning process. This guideline was developed in response to perceived limitations of existing guidelines used in our institution and found in texts for student teachers. Called a “Rationale for lesson design” the Guideline does not attempt to simplify the planning process, but rather enables students systematically to access the complexities inherent in effective lesson preparation. By requiring students to articulate their content knowledge and narrate their pedagogical reasoning in some detail, the Guideline enables students not only to teach with confidence but also to construct PCK.

The present paper intends to overview a wide range of natural-origin polymers with special focus on proteins and polysaccharides (the systems more inspired on the extracellular matrix) that are being used in research, or might be potentially useful as carriers systems for active biomolecules or as cell carriers with application in the tissue engineering field targeting several biological tissues. The combination of both applications into a single material has proven to be very challenging though. The paper presents also some examples of commercially available natural-origin polymers with applications in research or in clinical use in several applications. As it is recognized, this class of polymers is being widely used due to their similarities with the extracellular matrix, high chemical versatility, typically good biological performance and inherent cellular interaction and, also very significant, the cell or enzyme-controlled degradability. These biocharacteristics classify the natural-origin polymers as one of the most attractive options to be used in the tissue engineering field and drug delivery applications.

The osseointegration rate of implants is related to their composition and surface roughness. Implant roughness favors both bone anchoring and biomechanical stability. Osteoconductive calcium phosphate (Ca-P) coatings promote bone healing and apposition, leading to the rapid biological fixation of implants. It has been clearly shown in many publications that Ca-P coating accelerates bone formation around the implant. This review discusses two main routes for the manufacturing of polymer-based osteoconductive scaffolds for tissue engineering, namely the incorporation of bioceramic particles in the scaffold and the coating of a scaffold with a thin layer of apatite through a biomimetic process.

Implant stability is not only a function of strength but also depends on the fixation established with surrounding tissues [Robertson DM, Pierre L, Chahal R. Preliminary observations of bone ingrowth into porous materials. J Biomed Mater Res 1976;10:335-44]. In the past, such stability was primarily achieved using screws and bone cements. However, more recently, improved fixation can be achieved by bone tissue growing into and through a porous matrix of metal, bonding in this way the implant to the bone host. Another potentially valuable property of porous materials is their low elastic modulus. Depending on the porosity, moduli can even be tailored to match the modulus of bone closer than solid metals can, thus reducing the problems associated with stress shielding. Finally, extensive body fluid transport through the porous scaffold matrix is possible, which can trigger bone ingrowth, if substantial pore interconnectivity is established [Cameron HU, Macnab I, Pilliar RM. A porous metal system for joint replacement surgery. Int J Artif Organs 1978;1:104-9; Head WC, Bauk DJ, Emerson Jr RH. Titanium as the material of choice for cementless femoral components in total hip arthroplasty. Clin Orthop 1995;85-90].

Typical applications and research areas of polymeric biomaterials include tissue replacement, tissue augmentation, tissue support, and drug delivery. In many cases the body needs only the temporary presence of a device/biomaterial, in which instance biodegradable and certain partially biodegradable polymeric materials are better alternatives than biostable ones. Recent treatment concepts based on scaffold-based tissue engineering principles differ from standard tissue replacement and drug therapies as the engineered tissue aims not only to repair but also regenerate the target tissue. Cells have been cultured outside the body for many years; however, it has only recently become possible for scientists and engineers to grow complex three-dimensional tissue grafts to meet clinical needs. New generations of scaffolds based on synthetic and natural polymers are being developed and evaluated at a rapid pace, aimed at mimicking the structural characteristics of natural extracellular matrix. This review focuses on scaffolds made of more recently developed synthetic polymers for tissue engineering applications. Currently, the design and fabrication of biodegradable synthetic scaffolds is driven by four material categories: (i) common clinically established polymers, including polyglycolide, polylactides, polycaprolactone; (ii) novel di-and tri-block polymers; (iii) newly synthesized or studied polymeric biomaterials, such as polyorthoester, polyanhydrides, polyhydroxyalkanoate, polypyrroles, poly(ether ester amide)s, elastic shape-memory polymers; and (iv) biomimetic materials, supramolecular polymers formed by self-assembly, and matrices presenting distinctive or a variety of biochemical cues. This paper aims to review the latest developments from a scaffold material perspective, mainly pertaining to categories (ii) and (iii) listed above.

Bacterial cellulose (BC)/Chitosan (Ch) composite has been successfully prepared by immersing wet BC pellicle in Ch solution followed by freeze-drying process. The morphology of BC/Ch composite was examined by scanning electron microscope (SEM) and compared with pristine BC. SEM images show that Ch molecules can penetrate into BC forming three-dimensional multilayered scaffold. The scaffold has very well interconnected porous network structure and large aspect surface. The composite was also characterized by Fourier transform infrared spectrum, X-ray diffraction, thermogravimetric analysis and tensile test. By incorporation of Ch into BC, crystallinity tends to decrease from 82% to 61%, and the thermal stability increases from 263°C to 296°C. At the same time, the mechanical properties of BC/Ch composite are maintained at certain levels between BC and Ch. The biocompatibility of composite was preliminarily evaluated by cell adhesion studies. The cells incubated with BC/Ch scaffolds for 48 h were capable of forming cell adhesion and proliferation. It showed much better biocompatibility than pure BC. Since the prepared BC/Ch scaffolds are bioactive and suitable for cell adhesion, these scaffolds can be used for wound dressing or tissue-engineering scaffolds.

The ECM of mammalian tissues has been used as a scaffold to facilitate the repair and reconstruction of numerous tissues. Such scaffolds are prepared in many forms including sheets, powders, and hydrogels. ECM hydrogels provide advantages such as injectability, the ability to fill an irregularly shaped space, and the inherent bioactivity of native matrix. However, material properties of ECM hydrogels and the effect of these properties upon cell behavior are neither well understood nor controlled. The objective of this study was to prepare and determine the structure, mechanics, and the cell response in vitro and in vivo of ECM hydrogels prepared from decellularized porcine dermis and urinary bladder tissues. Dermal ECM hydrogels were characterized by a more dense fiber architecture and greater mechanical integrity than urinary bladder ECM hydrogels, and showed a dose dependent increase in mechanical properties with ECM concentration. In vitro, dermal ECM hydrogels supported greater C2C12 myoblast fusion, and less fibroblast infiltration and less fibroblast mediated hydrogel contraction than urinary bladder ECM hydrogels. Both hydrogels were rapidly infiltrated by host cells, primarily macrophages, when implanted in a rat abdominal wall defect. Both ECM hydrogels degraded by 35 days in vivo, but UBM hydrogels degraded more quickly, and with greater amounts of myogenesis than dermal ECM. These results show that ECM hydrogel properties can be varied and partially controlled by the scaffold tissue source, and that these properties can markedly affect cell behavior.

Alginate gels have been used in both drug delivery and cell encapsulation applications in the bead form usually produced by dripping alginate solution into a CaCl bath. The major disadvantages to these systems are that the gelation rate is hard to control; the resulting structure is not uniform; and mechanically strong and complex-shaped 3-D structures are di$cult to achieve. In this work controlled gelation rate was achieved with CaCO }GDL and CaSO }CaCO }GDL systems, and homogeneous alginate gels were formulated as sca!olds with de"ned dimensions for tissue engineering applications. Gelation rate increased with increasing total calcium content, increasing proportion of CaSO , increasing temperature and decreasing alginate concentration. Mechanical properties of the alginate gels were controlled by the compositional variables. Slower gelation systems generate more uniform and mechanically stronger gels than faster gelation systems. The compressive modulus and strength increased with alginate concentration, total calcium content, molecular weight and guluronic acid (G) content of the alginate. MC3T3-E1 osteoblastic cells were uniformly incorporated in the alginate gels and cultured in vitro. These results demonstrated how alginate gel and gel/cell systems could be formulated with controlled structure, gelation rate, and mechanical properties for tissue engineering and other biomedical applications.

Drug-eluting medical implants are actually active implants that induce healing effects, in addition to their regular task of support. This effect is achieved by controlled release of active pharmaceutical ingredients (API) into the surrounding tissue. In this chapter we focus on three types of drug-eluting devices: drug-eluting vascular stents, drug-eluting wound dressings and protein-eluting scaffolds for tissue regeneration, thus describing both internal and external implants. Each of these drug-eluting devices also presents an approach for solving the drug release issue. Most drug-eluting vascular stents are loaded with water-insoluble antiproliferative agents, and their diffusion from the device to the surrounding tissue is relatively slow. In contrast, most drug-eluting wound dressings are loaded with highly water-soluble antibacterial agents and the issue of fast release must therefore be addressed. Growth factor release from scaffolds for tissue regeneration offers a new approach of incorporating high-molecular-weight bioactive agents which are very sensitive to process conditions and preserve their activity during the preparation stage. The drug-eluting medical implants are described here in terms of matrix formats and polymers, incorporated drugs and their release profiles from the implants, and implant functioning. Basic elements, such as new composite core/shell fibers and structured films, can be used to build new antibiotic-eluting devices. As presented in this chapter, the effect of the processing parameters on the microstructure and the resulting drug release profiles, mechanical and physical properties, and other relevant properties, must be elucidated in order to achieve the desired properties. Newly developed implants and novel modifications of previously developed approaches have enhanced the tools available for creating clinically important biomedical applications.

Xenogeneic extracellular matrices (ECMs) have been shown to be effective as naturally occurring scaffolds for soft-tissue repair. As acellular tissue substitutes at the time of surgical implantation, ECMs are subjected to the mechanical forces and microenvironmental conditions representative of the anatomical location in which they are placed. Ideally such natural scaffolds would possess mechanical properties that allow for normal tissue function in and around the implant site. The ball-burst test was used to simulate biaxial forces and to determine the strength of the ECM scaffold under a relevant physiological loading condition. The ballburst test, in itself, does not quantify intrinsic mechanical properties and therefore a methodology was developed to determine the maximum stress resultant tangent modulus (MSRTM) or the maximum stress tangent modulus (MSTM), stress to failure ðs f Þ; failure stress resultant ðN f Þ, ball-burst pressure ðPÞ; and maximum elongation ðl max Þ from the raw ball-burst data obtained at a constant-rate of transverse. The analytical methodology was compared to finite element simulations and showed good correlation with the analytical solution presented. The proposed approximations were used to compute biaxial failure properties for a variety of multilaminate ECM devices with varying number of layers, disinfection and sterilization, and organ origin. r

body of work is dedicated to the members of my family who have helped me bear this burden for the many years it took to complete it: • My wife, Kathleen Rubio, whose presence in my life graces it far better than I could ever deserve and without whose faithful and unwavering support this day would never have come; • My children, Daniel Rubio, Julianna Slager and her husband Jeremy and their son Judah, Angelina Dickinson and her husband Matthew, Reuben Rubio III, Raquela Rubio, Miranda Rubio, and Alicia Rubio, for giving me cause to continuously thank God for you; • My mother, Dolores Rubio, who has literally believed in me, comforted me, celebrated with me, and prayed for and with me since day one; and • My father- and mother-in-law, Robert and Wanda Bowman, who have always accepted and supported me without question. I would include those who blessed my life for many years before entering their rest: • My father, Reuben A. Rubio the original, who for 45 years was either ahead

With nearly 30 years of progress, tissue engineering has shown promise in developing solutions for tissue repair and regeneration. Scaffolds, together with cells and growth factors, are key components of this development. Recently, an increasing number of studies have reported on the design and fabrication of scaffolding materials. In particular, inspired by the nature of bone, polymer/ceramic composite scaffolds have been studied extensively. The purpose of this paper is to review the recent progress of the naturally derived biopolymers and the methods applied to generate biomimetic biopolymer/calcium phosphate composites as well as their biomedical applications in bone tissue engineering.

New regenerative treatment strategies are being developed for intervertebral disc degeneration of which the implantation of various cell types is promising. The cell types used so far all require in vitro expansion prior to clinical use, as these cells are only limited available. Adipose-tissue is an abundant, expendable and easily accessible source of mesenchymal stem cells. The use of these cells therefore eliminates the need for in vitro expansion and subsequently one-step regenerative treatment strategies can be developed. Our group envisioned, described and evaluated such a one-step procedure for spinal fusion in the goat model. In this review, we summarize the current status of cellbased treatments for intervertebral disc degeneration and identify the additional research needed before adipose-derived mesenchymal stem cells can be evaluated in a one-step procedure for regenerative treatment of the intervertebral disc. We address the selection of stem cells from the stromal vascular fraction, the specific triggers needed for cell differentiation and potential suitable scaffolds. Although many factors need to be studied in more detail, potential application of a one-step procedure for intervertebral disc regeneration seems realistic.

More and more of our aging populations will suffer from large bone defects in the next few years. But the growth factor (GF) delivery systems (DSs) currently under investigation will help overcome the limitations of the bone grafts presently used. Some GFDSs accredited by the Food and Drug Administration (FDA) are commercially available, but they have mechanical, structural and GF retention weaknesses. New studies focus on polymers and the composition of GFs in order to mimic as closely as possible the physiological environment of healing bone. This review first summarizes the process of endochondral bone healing and the major cytokines involved. We then review the latest GFDSs, with their combinations of organic, inorganic, natural and synthetic biomaterials, the kinetics of GF release and their biological effects. We will explore new research avenues such as the use of peptides derived from bone morphogenetic proteins, including our own results, and the sequential release of bone-inducing GFs. We then review the latest mathematical models of drug delivery systems (DDSs) for several transport phenomena that may be encountered when using GFDS. The final section discusses new improvements for GFDS modeling.

Silk fibroin (SF) and elastin (EL) scaffolds were successfully produced for the first time for the treatment of burn wounds. The self-assembly properties of SF, together with the excellent chemical and mechanical stability and biocompatibility, were combined with elastin protein to produce scaffolds with the ability to mimic the extracellular matrix (ECM). Porous scaffolds were obtained by lyophilization and were further crosslinked with genipin (GE). Genipin crosslinking induces the conformational transition from random coil to b-sheet of SF chains, yielding scaffolds with smaller pore size and reduced swelling ratios, degradation and release rates. All results indicated that the composition of the scaffolds had a significant effect on their physical properties, and that can easily be tuned to obtain scaffolds suitable for biological applications. Wound healing was assessed through the use of human full-thickness skin equivalents (Epi-dermFT). Standardized burn wounds were induced by a cautery and the best re-epithelialization and the fastest wound closure was obtained in wounds treated with 50SF scaffolds; these contain the highest amount of elastin after 6 days of healing in comparison with other dressings and controls. The cytocompatibility demonstrated with human skin fibroblasts together with the healing improvement make these SF/EL scaffolds suitable for wound dressing applications.

The present study aims at the preparation of silk fibroin solution for possible applications in tissue engineering. Pure silk fibroin protein was extracted from Bombyx mori silk cocoon by degumming method using aqueous Na 2 CO 3 solution followed by solubilizing in LiBr aqueous solution. The fibroin protein solution was purified and studied for the protein content. The degumming & solubility were significantly dependent on the salt concentration, treatment temperature, and time. A salt concentration of 0.02 M Na 2 CO 3, temperature of 80°C and time more than 40 min were found to be favorable degumming conditions. The proper conditions of dissolution were found as 9.3 M LiBr, 70 °C temperature, and 3 h dissolving time. The morphology of degummed silk were investigated by SEM at different magnification. SEM revealed the absence of glue like sericine over the silk fibroin surface at optimal degumming condition. The fibroin protein content of the solution was measured by Bradford protein assay. The results indicate that the regenerated silk fibroin (RSF) can be used for fabrication of porous silk fibroin scaffolds for various tissue engineering applications.

Biologic scaffold materials composed of extracellular matrix (ECM) are routinely used for a variety of clinical applications. Despite known variations in tissue remodeling outcomes, quantitative criteria by which decellularization can be assessed were only recently described and as a result, the amount of retained cellular material varies widely among commercial products. The objective of this study was to evaluate the consequences of ineffective decellularization on the host response. Three different methods of decellularization were used to decellularize porcine small intestinal ECM (SIS-ECM). The amount of cell remnants was quantified by the amount and fragmentation of DNA within the scaffold materials. The M1/M2 phenotypic polarization profile of macrophages, activated in response to these ECM scaffolds, was assessed in vitro and in vivo using a rodent model of body wall repair. The results show that, in vitro, more aggressive decellularization is associated with a shift in macrophage phenotype predominance from M1 to M2. While this shift was not quantitatively apparent in vivo, notable differences were found in the distribution of M1 vs. M2 macrophages within the various scaffolds. A clear association between macrophage phenotype and remodeling outcome exists and effective decellularization remains an important component in the processing of ECM-based scaffolds.

The need for synthetic alternatives to conventional bone grafts is due to the limitations of current grafting materials. Our approach has been to design polymer-based graft substitutes using microsphere technology. The gel microsphere matrix and the sintered microsphere matrix were designed using the random packing of poly(lactide-co-glycolide) microspheres to create a threedimensional porous structure. The evaluation of these methods dealt with analysis of effects of matrix composition and processing. Matrices were evaluated structurally by scanning electron microscopy and porosimetry, and biomechanically by compression testing.

Fused deposition modeling, a rapid prototyping technology, was used to produce novel scaffolds with honeycomb-like pattern, fully interconnected channel network, and controllable porosity and channel size. A bioresorbable polymer poly(e-caprolactone) (PCL) was developed as a filament modeling material to produce porous scaffolds, made of layers of directionally aligned microfilaments, using this computer-controlled extrusion and deposition process. The PCL scaffolds were produced with a range of channel size 160-700 mm, filament diameter 260-370 mm and porosity 48-77%, and regular geometrical honeycomb pores, depending on the processing parameters. The scaffolds of different porosity also exhibited a pattern of compressive stress-strain behavior characteristic of porous solids under such loading. The compressive stiffness ranged from 4 to 77 MPa, yield strength from 0.4 to 3.6 MPa and yield strain from 4% to 28%. Analysis of the measured data shows a high correlation between the scaffold porosity and the compressive properties based on a power-law relationship. r

O ur laboratory has developed a number of novel synthetic scaffold materials based on fumaric acid for an assortment of tissue engineering applications. These biodegradable materials include poly(propylene fumarate) (PPF), poly(propylene fumarate-co-ethylene glycol) (P(PF-co-EG)), and oligo(poly(ethylene glycol) fumarate) (OPF), each of which can be applied as an injectable liquid and crosslinked in situ to form a polymer network. Although each fumarate-based macromer presents a unique set of physical and mechanical properties, the materials can be tailored for particular applications, ranging from cell encapsulation to gene delivery. The injectability and biodegradability of fumarate-based polymers, coupled with the ease with which they can be modified, uniquely situate fumarate-based macromers as excellent scaffolds for tissue engineering.

Steel scaffolds collapse quite often in many places with a considerable number of reported casualties, but their behaviour has not been studied to the extent of many other permanent structures. This paper investigates the effect of eccentric loads on steel scaffolding systems used in construction sites. The type of scaffold considered here is the door-shaped steel scaffold with an inner reinforced gable sub-frame. The single-side cross-brace scaffolding systems with various eccentric loads are mainly focused on two issues, namely, the unrestrained boundary and the removal of cross-braces at the access location. This study shows that regardless of the lowest layer of cross-brace in a scaffold being removed or not, the critical load of a scaffolding system under an eccentric load is the lowest, whereas that of scaffolding system under a concentric load is the maximum. If the bottom jack base of a scaffolding system in construction sites is strengthened to a fixed end, the critical load of this scaffolding system will be greatly increased. If a scaffolding system is erected more than 8 stories high, the critical load of the scaffolding system with the fixed end base can be increased to 2.4 times that with the hinged base. However, whether the cross-braces at the lowest story of a scaffolding system are removed or not, the simulated scaffolding test indicates that the critical load of a used scaffolding system under the eccentric load is the lowest and its load reduction also appears significant.

One of the main issues in orthopaedic implant design is the fabrication of scaffolds that closely mimic the biomechanical properties of the surrounding bone. This research reports on a multi-stage rapid prototyping technique that was successfully developed to produce porous titanium scaffolds with fully interconnected pore networks and reproducible porosity and pore size. The scaffolds' porous characteristics were governed by a sacrificial wax template, fabricated using a commercial 3D-printer. Powder metallurgy processes were employed to generate the titanium scaffolds by filling around the wax template with titanium slurry. In the attempt to optimise the powder metallurgy technique, variations in slurry concentration, compaction pressure and sintering temperature were investigated. By altering the wax design template, pore sizes ranging from 200 to 400 mm were achieved. Scaffolds with porosities of 66.8 AE 3.6% revealed compression strengths of 104.4 AE 22.5 MPa in the axial direction and 23.5 AE 9.6 MPa in the transverse direction demonstrating their anisotropic nature. Scaffold topography was characterised using scanning electron microscopy and microcomputed tomography. Three-dimensional reconstruction enabled the main architectural parameters such as pore size, interconnecting porosity, level of anisotropy and level of structural disorder to be determined. The titanium scaffolds were compared to their intended designs, as governed by their sacrificial wax templates. Although discrepancies in architectural parameters existed between the intended and the actual scaffolds, overall the results indicate that the porous titanium scaffolds have the properties to be potentially employed in orthopaedic applications.

In this study, double diffusion method in a physiologically relevant environment was used to prepare a biomimetic gelatin-amorphous calcium phosphate nanocomposite scaffold. The precipitated calcium phosphate within gelatin as well as produced nanocomposite scaffolds were characterized by the commonly used bulk techniques. The results showed that nanocomposite scaffolds were porous with three-dimensionally interconnected microstructure, pore size ranging from 150 to 350 lm. Porosity was about 82% and nanocrystalline precipitated minerals were dispersed evenly among gelatin fibers. A mineral containing amorphous calcium phosphate and brushite precipitate was formed within the gelatin matrix at 4 C. After incubation in SBF solution at 37 C for 5 days, the mineral phase was transformed to nanocrystalline hydroxyapatite. It should be noted that precursor phases inside a scaffold implanted into the body can result in biomimetic conversion of precursors to hydroxyapatite that is very similar to the bone mineral and has a profound level of biocompatibility. Thus, our results highlight the potential use of engineered biomimetic bone tissue scaffolds in the bone tissue repair process. V C 2012

This paper investigates the influence of geometry-dependent loads and time-dependent incremental loads on the scaffolding systems with different configurations. The loading types considered are the uniform load, geometry-dependent load and incremental load. The geometrydependent loads include the trapezoidal and triangular loads. Further, the mixed and bare scaffold systems with and without wooden posts at top are considered under the rectangle, L and U configurations on plan. It was found that the mixed scaffold system with wooden posts of typical length 1.7 m at top had a buckling resistance of only half of the bare scaffold system without wooden posts. Also, the largest deformation in the bare scaffold is found to be near the upper joint of the lowest scaffold layer and, in the mixed scaffolding system, the largest deflection occurs at the location between the bottom of the wooden post and top of the highest scaffold layer. Both systems buckle in the in-plane direction of the scaffolds. The critical load of a 3-bay 5-row 3-storey mixed scaffold system is considered under uniform load and its buckling resistance is found to be invariant under geometry-dependent loads and incremental loads. The buckling resistances of increasing the number of bays in the bare and mixed scaffold systems under the uniform load effect are much greater than choosing a particular geometrical L or U configuration.

Silk fibers have potential biomedical applications beyond their traditional use as sutures. The physical properties of silk fibers and films make it a promising candidate for tissue engineering scaffold applications, particularly where high mechanical loads or tensile forces are applied or in cases where low rates of degradation are desirable. A critical issue for biomaterial scaffolds is biocompatibility. The direct inflammatory potential of intact silk fibers as well as extracts was studied in an in vitro system. The results indicate that silk fibers are largely immunologically inert in short-and long-term culture with RAW 264.7 murine macrophage cells while insoluble fibroin particles induced significant TNF release. Soluble sericin proteins extracted from native silk fibers did not induce significant macrophage activation. While sericin did not activate macrophages by itself, it demonstrated a synergistic effect with bacterial lipopolysaccharide. The low level of inflammatory potential of silk fibers makes them promising candidates in future biomedical applications. r

The development of suitable biomimetic three-dimensional scaffolds is a fundamental requirement of tissue engineering. This paper presents the first successful attempt to obtain electrospun gelatin nanofibers cross-linked with a low toxicity agent, genipin, and able to retain the original nanofiber morphology after water exposure. The optimized procedure involves an electrospinning solution containing 30 wt.% gelatin in 60/40 acetic acid/water (v/v) and a small amount of genipin, followed by further cross-linking of the as-electrospun mats in 5% genipin solution for 7 days, rinsing in phosphate-buffered saline and then air drying at 37°C. The results of scanning electron microscopy investigations indicated that the cross-linked nanofibers were defect free and very regular and they also maintained the original morphology after exposure to water. Genipin addition to the electrospinning solution dramatically reduced the extensibility of the as-electrospun mats, which displayed further remarkable improvements in elastic modulus and stress at break after successive cross-linking up to values of about 990 and 21 MPa, respectively. The results of the preliminary in vitro tests carried out using vascular wall mesenchymal stem cells indicated good cell viability and adhesion to the gelatin scaffolds.

The collagen (semed S, acid-soluble), principally collagen type I with ca. 5% type III, was a generous gift of the Kensey Nash Nanofiber scaffolds of collagen have been fabricated via electrospinning using benign solvent systems as a replacement for 1,1,1,3,3,3 hexafluoro-2-propanol. Simple binary mixtures of phosphate-buffered saline and ethanol have been found to be highly effective for electrospinning. FTIR spectra suggest that the triple helical structure of collagen was conserved after dissolution and electrospinning. Crosslinking of the electrospun collagen scaffolds was achieved with standard methods.

Glucose diffusivity in tissue engineering membranes and scaffolds are determined. The chosen materials are saturated with either water or cell culture medium (CCM). Insignificant difference in glucose diffusivity was found when the materials are in water or CCM. Pore size distribution, porosity and tortuosity of the materials are correlated to glucose diffusivity. Tortuosity and porosity relationship are found to be non-linear and non-monotonic in nature.

A limiting factor of traditional electrospinning is that the electrospun scaffolds consist entirely of tightly packed nanofiber layers that only provide a superficial porous structure due to the sheet-like assembly process. This unavoidable characteristic hinders cell infiltration and growth throughout the nanofibrous scaffolds. Numerous strategies have been tried to overcome this challenge, including the incorporation of nanoparticles, using larger microfibers, or removing embedded salt or water-soluble fibers to increase porosity. However, these methods still produce sheet-like nanofibrous scaffolds, failing to create a porous three-dimensional scaffold with good structural integrity. Thus, we have developed a three-dimensional cotton ball-like electrospun scaffold that consists of an accumulation of nanofibers in a low density and uncompressed manner. Instead of a traditional flat-plate collector, a grounded spherical dish and an array of needle-like probes were used to create a Focused, Low density, Uncompressed nanoFiber (FLUF) mesh scaffold. Scanning electron microscopy showed that the cotton ball-like scaffold consisted of electrospun nanofibers with a similar diameter but larger pores and less-dense structure compared to the traditional electrospun scaffolds. In addition, laser confocal microscopy demonstrated an open porosity and loosely packed structure throughout the depth of the cotton ball-like scaffold, contrasting the superficially porous and tightly packed structure of the traditional electrospun scaffold. Cells seeded on the cotton ball-like scaffold infiltrated into the scaffold after 7 days of growth, compared to no penetrating growth for the traditional electrospun scaffold. Quantitative analysis showed approximately a 40% higher growth rate for cells on the cotton ball-like scaffold over a 7 day period, possibly due to the increased space for in-growth within the three-dimensional scaffolds. Overall, this method assembles a nanofibrous scaffold that is more advantageous for highly porous interconnectivity and demonstrates great potential for tackling current challenges of electrospun scaffolds.

The repair of large segmental bone defects due to trauma, inflammation and tumor surgery remains a major clinical problem. Animal models were developed to test bone repair by tissue engineering approaches, mimicking real clinical situations. Studies differed with regard to animals (dog, sheep, goat), treated bone (femur, tibia, mandible), chemistry and structure of the scaffolds. Still, an advantage in the bone formation and in the healing of the segmental defect was always observed when scaffolds were seeded with bone marrow derived stromal cells (BMSCs). In the year 1998 was performed the first implantation of a porous ceramic construct in a bone segmental defect of a patient; it was the first construct seeded with cultured autologous osteogenic cells. Since then, only few other similar cases were treated by the same approach. However, in other fields, such as oral and maxillofacial surgery, injectable cells/platelet-rich plasma composites have been used as grafting materials for maxillary sinus floor augmentation and/or onlay plasty. More recently, the reconstruction of a human mandible was also reported by means of a bone-muscle-flap in vivo prefabrication technique, where the patient served as his own bioreactor. Indeed continuous implementations test and provide new means of defects treatment and cure. However, based on results so far obtained in animal models and pilot clinical studies, one can affirm that the bone tissue engineering approaches, although successful in most cases, need further validation before a wide application in clinics. In particular, the supply of oxygen and nutrients to the cells in the inner part of the implanted scaffolds remains a major concern, requiring additional investigations. r

The text analyzes a work by a woman photographer with war background in contrast to the photography of artists that have not being included inside such a context involuntary.
Definitions of physical constraints in production of the photographic image (lenses, focus, aperture, exposure...) are used to provide technical descriptions of the image, rather than descriptive, showing how they work in the production of emotion. A set of technical differences is found in records of scaffolds, the most important being; the type of lenses and approximate distance to the scene... De-focusing and the implementation of telephoto lenses, as for example, allows bridging large distances between the author and the scene, this choice of technology can be seen as a result of fear with the immediate physical contact with a scaffold. In parallel, the implementation of wide lenses and precise, sharp, focus in the same theme can be seen as a will to face the horror of it. Spatial treatment of the author within the scene, defined via lenses and focus, are connected to different interpretations of such images,  as a close psychoanalytic or a distant political.

We applied two-photon polymerization to fabricate 3D synthetic niches arranged in complex patterns to study the effect of mechano-topological parameters on morphology, renewal and differentiation of rat mesenchymal stromal cells. Niches were formed in a photoresist with low auto-fluorescence, which enabled the clear visualization of the fluorescence emission of the markers used for biological diagnostics within the internal niche structure. The niches were structurally stable in culture up to three weeks. At three weeks of expansion in the niches, cell density increased by almost 10-fold and was 67% greater than in monolayer culture. Evidence of lineage commitment was observed in monolayer culture surrounding the structural niches, and within cell aggregates, but not inside the niches. Thus, structural niches were able not only to direct stem cell homing and colony formation, but also to guide aggregate formation, providing increased surface-to-volume ratios and space for stem cells to adhere and renew, respectively.

Decellularized vascular matrices are used as scaffolds in cardiovascular tissue engineering because they retain their natural biological composition and three-dimensional (3-D) architecture suitable for cell adhesion and proliferation. However, cell infiltration and subsequent repopulation of these scaffolds was shown to be unsatisfactory due to their dense collagen and elastic fiber networks. In an attempt to create more porous structures for cell repopulation, we selectively removed matrix components from decellularized porcine aorta to obtain two types of scaffolds, namely elastin and collagen scaffolds. Histology and scanning electron microscopy examination of the two scaffolds revealed a well-oriented porous decellularized structure that maintained natural architecture of the aorta. Quantitative DNA analysis confirmed that both scaffolds were completely decellularized. Stressstrain analysis demonstrated adequate mechanical properties for both elastin and collagen scaffolds. In vitro enzyme digestion of the scaffolds suggested that they were highly biodegradable. Furthermore, the biodegradability of collagen scaffolds could be controlled by crosslinking with carbodiimides. Cell culture studies showed that fibroblasts adhered to and proliferated on the scaffold surfaces with excellent cell viability. Fibroblasts infiltrated about 120 mm into elastin scaffolds and about 40 mm into collagen scaffolds after 4 weeks of rotary cell culture. These results indicated that our novel aortic elastin and collagen matrices have the potential to serve as scaffolds for cardiovascular tissue engineering. r