Composite Scaffolds for Bone Tissue Engineering

Extrusion-based bioprinting (EBB) is a rapidly growing technology that has made substantial progress during the last decade. It has great versatility in printing various biologics, including cells, tissues, tissue constructs, organ modules and microfluidic devices, in applications from basic research and pharmaceutics to clinics. Despite the great benefits and flexibility in printing a wide range of bioinks, including tissue spheroids, tissue strands, cell pellets, decellularized matrix components, micro-carriers and cellladen hydrogels, the technology currently faces several limitations and challenges. These include impediments to organ fabrication, the limited resolution of printed features, the need for advanced bioprinting solutions to transition the technology bench to bedside, the necessity of new bioink development for rapid, safe and sustainable delivery of cells in a biomimetically organized microenvironment, and regulatory concerns to transform the technology into a product. This paper, presenting a first-time comprehensive review of EBB, discusses the current advancements in EBB technology and highlights future directions to transform the technology to generate viable end products for tissue engineering and regenerative medicine.

Since most starting materials for tissue engineering are in powder form, using powder-based additive manufacturing methods is attractive and practical. The principal point of employing additive manufacturing (AM) systems is to fabricate parts with arbitrary geometrical complexity with relatively minimal tooling cost and time. Selective laser sintering (SLS) and inkjet 3D printing (3DP) are two powerful and versatile AM techniques which are applicable to powderbased material systems. Hence, the latest state of knowledge available on the use of AM powderbased techniques in tissue engineering and their effect on mechanical and biological properties of fabricated tissues and scaffolds must be updated. Determining the effective setup of parameters, developing improved biocompatible/bioactive materials, and improving the mechanical/ biological properties of laser sintered and 3D printed tissues are the three main concerns which have been investigated in this article.

In the present study, we have fabricated a ternary composite nanofibrous scaffold from PCL/gelatin/ chitosan, by electrospinning technique, using a solvent system-chloroform/methanol for polycaprolactone (PCL) and acetic acid for gelatin and chitosan, for tissue engineering applications. Field emission scanning electron microscopy (FE-SEM) was used to investigate the fiber morphology of the scaffold and it was found that the fiber morphology was influenced by the concentrations of PCL, gelatin, and chitosan in polymer solution during electrospinning. X-ray diffraction, Fourier transform infrared, and thermogravimetric (TG) analysis results showed some interactions among the molecules of PCL, gelatin, and chitosan within the scaffold. In-vitro cell culture studies were done by seeding L929 mouse fibroblasts on fabricated composite scaffold, which confirmed the cell viability, high cell proliferation rate, and cell adhesion on composite scaffold as indicated by MTT assay, DNA quantification, and FE-SEM analysis of cell-scaffold construct. Thus, the ternary composite scaffold made from the combination of PCL (synthetic polymer), gelatin, and chitosan (natural polymer) may find potential application in tissue engineering.

Since most starting materials for tissue engineering are in powder form, using powder-based additive manufacturing methods is attractive and practical. The principal point of employing additive manufacturing (AM) systems is to fabricate parts with arbitrary geometrical complexity with relatively minimal tooling cost and time. Selective laser sintering (SLS) and inkjet 3D printing (3DP) are two powerful and versatile AM techniques which are applicable to powder-based material systems. Hence, the latest state of knowledge available on the use of AM powder-based techniques in tissue engineering and their effect on mechanical and biological properties of fabricated tissues and scaffolds must be updated. Determining the effective setup of parameters, developing improved biocompatible/bioactive materials, and improving the mechanical/biological properties of laser sintered and 3D printed tissues are the three main concerns which have been investigated in this article.

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Tissue engineering is a newly emerging biomedical technology, which aids and increases the repair and regeneration of deficient and injured tissues. It employs the principles from the fields of materials science, cell biology, transplantation, and engineering in an effort to treat or replace damaged tissues. Tissue engineering and development of complex tissues or organs, such as heart, muscle, kidney, liver, and lung, are still a distant milestone in twenty-first century. Generally, there are four main challenges in tissue engineering which need optimization. These include biomaterials, cell sources, vascularization of engineered tissues, and design of drug delivery systems. Biomaterials and cell sources should be specific for the engineering of each tissue or organ. On the other hand, angiogenesis is required not only for the treatment of a variety of ischemic conditions, but it is also a critical component of virtually all tissue-engineering strategies. Therefore, controlling the dose, location, and duration of releasing angiogenic factors via polymeric delivery systems, in order to ultimately better mimic the stem cell niche through scaffolds, will dictate the utility of a variety of biomaterials in tissue regeneration. This review focuses on the use of polymeric vehicles that are made of synthetic and/or natural biomaterials as scaffolds for three-dimensional cell cultures and for locally delivering the inductive growth factors in various formats to provide a method of controlled, localized delivery for the desired time frame and for vascularized tissue-engineering therapies.

Magnetic nanocomposite scaffolds based on poly(e-caprolactone) and poly(ethylene glycol) were fabricated by 3D fibre deposition modelling (FDM) and stere-olithography techniques. In addition, hybrid coaxial and bilayer magnetic scaffolds were produced by combining such techniques. The aim of the current research was to analyse some structural and functional features of 3D magnetic scaffolds obtained by the 3D fibre deposition technique and by stereolithography as well as features of multimaterial scaffolds in the form of coaxial and bilayer structures obtained by the proper integration of such methods. The compressive mechanical behaviour of these scaffolds was investigated in a wet environment at 37 °C, and the morphological features were analysed through scanning electron microscopy (SEM) and X-ray micro-computed tomography. The capability of a magnetic scaffold to absorb magnetic nanoparticles (MNPs) in water solution was also assessed. confocal laser scanning microscopy was used to assess the in vitro biological behaviour of human mes-enchymal stem cells (hMSCs) seeded on 3D structures. Results showed that a wide range of mechanical properties, covering those spanning hard and soft tissues, can be obtained by 3D FDM and stereolithography techniques. 3D virtual reconstruction and SEM showed the precision with which the scaffolds were fabricated, and a good-quality interface between poly(e-caprolactone) and poly(ethylene glycol) based scaffolds was observed for bilayer and coaxial scaffolds. Magnetised scaffolds are capable of absorbing water solution of MNPs, and a preliminary information on cell adhesion and spreading of hMSCs was obtained without the application of an external magnetic field.

In this study, a novel scaffold fabrication method was developed by combining microwave irradiation
and gas foaming. Chitosan superporous hydrogels (SPHs) and chitosan–hydroxyapatite (HA) superporous
hydrogel composites (SPHCs) were prepared by using this method in the presence of crosslinking
agent, glyoxal, and a gas-blowing agent, NaHCO3. In order to examine the effect of HA on composite
structure and cellular behaviour, two types of HA particles, i.e. spherical beads in 45–80mm diameter
and powder form, were used. While rapid heating with microwave irradiation enhances gas blowing,
pH increment, which is accelerated by NaHCO3 decomposition, provides better crosslinking. Thus,
interconnected and well-established macroporous hydrogels/hydrogel composites were produced
easily and rapidly (~1min). Cell culture studies, which were carried out under static and dynamic
conditions with MC3T3-E1 pre-osteoblastic cells, indicated that chitosan–HA bead SPHCs supported
cellular proliferation and osteoblastic differentiation better than chitosan SPHs and chitosan–HA
powder SPHCs. In conclusion, simultaneous gas foaming and microwave crosslinking can be evaluated
for the preparation of composite scaffolds which have superior properties for bone tissue engineering.

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Kemikte oluşan kusurları onarmak için kemik hücrelerini taklit eden, kemiklerin yerini alabilecek yapay kemik ikame malzemelerin arayışı geçmişten günümüze büyük bir araştırma konusu olmuştur. Kemik doku mühendisliği uygulamalarındaki gelişmeler, bu alana olan ilgi ve yeni polimerlerin ortaya çıkması sayesinde giderek artmaktadır. Uygulamalarda kullanılacak malzeme biyouyumlu, biyobozunabilir, toksik olmayan, iyi mekanik özellikler sergileyen bir yapıya sahip olmalı ve apetit oluşumunu sağlayarak kemik rejenerasyonunu desteklemelidir. Tüm bu özellikleri sağlayabilecek kemik ikame malzemesinin bulunabilmesi için bu konu hakkında birçok çalışma yapılmıştır. Bu çalışmalarda en sık kullanılan malzemelerden biri polilaktik asit (PLA) olmuştur. PLA, yenilebilir malzemelerden elde edilebilen, laktik asit türevi bir polimerdir. Biyouyumlu ve biyobozunabilir olan, toksik veya kanserojen olmayan, metabolizma yoluyla kolayca atılabilen bir yapıya sahiptir. Bu özelliklere ek olarak, üretiminde düşük enerji kullanılması ve yenilenebilir olması diğer polimerlere kıyasla PLA’yı çok güçlü bir malzeme haline getirmiştir. PLA, kemik doku mühendisliği uygulamaları için gereken özelliklerin neredeyse tamamını karşılamaktadır, fakat tedavilerde kullanılması için gerekli olan bazı özelliklerde yetersiz kalabilmektedir. Bunun üzerine, PLA bazlı kompozit malzemeler ile ilgili çalışmalar yapılmış ve birçok başarılı sonuç elde edilmiştir. Yapılan çalışmalarla; PLA’nın biyoaktivitesi, mekanik ve kemik rejenerasyonunu arttıracak özellikleri, PLA’nın farklı malzemeler ile bir araya getirilmesi ile geliştirilmektedir.

To develop osteogenic building blocks for modular bone tissue engineering applications, influence of gelatin as cell adhesive molecule and nano-hydroxyapatite (nHA) as osteoconductive component was examined on algi-nate-based hydrogel properties and microencapsulated osteoblast-like cell behavior by using factorial experimental design technique. nHA and alginate showed a statistically significant impact on swelling reduction, and improvement of stability and mechanical strength of hydrogels, respectively. Gelatin influence, however, was in a reverse manner. nHA played imperative roles in promoting microencapsulated osteoblastic cell proliferation and function due to its bioactivity and mechanical strength improvement of hydrogels to the modulus range of mineralized bone tissue in vivo. The results and their statistical analysis also revealed the importance of interaction effect of gelatin and nHA. Proliferation and osteogenic function of the cells fluctuated with increasing gelatin concentration of microcapsules in the presence of nHA, demonstrating that hydrogel properties should be balanced to provide an efficient 3D osteoconductive microcapsule. Alginate (1%)-gelatin (2.5%)-nHA (0.5%) microcapsule with compressive modulus of 0.19 MPa ± 0.02, swelling ratio of 52% ± 8 (24 h) and degradation rate of 12% ± 4 (96 h) revealed a maximum performance for the cell proliferation and function, indicating a potential microcapsule composition to prepare building blocks for modular bone tissue engineering.

The design of scaffolds with optimal biomechanical properties for load-bearing applications is an important topic of research. Most studies have addressed this problem by focusing on the material composition and not on the coupled effect between the material composition and the scaffold architecture. Polymer–bioglass scaffolds have been investigated due to the excellent bioactivity properties of bioglass, which release ions that activate osteogenesis. However, material preparation methods usually require the use of organic solvents that induce surface modifications on the bioglass particles, compromising the adhesion with the polymeric material thus compromising mechanical properties. In this paper, we used a simple melt blending approach to produce polycaprolactone/bioglass pellets to construct scaffolds with pore size gradient. The results show that the addition of bioglass particles improved the mechanical properties of the scaffolds and, due to the selected architecture, all scaffolds presented mechanical properties in the cortical bone region. Moreover, the addition of bioglass indicated a positive long-term effect on the biological performance of the scaffolds. The pore size gradient also induced a cell spreading gradient.

Growth factors (GFs) are major biochemical cues for tissue regeneration. Herein, a novel dual GF delivery system is designed composed of poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) and alginate microcapsules (MCs) via an electrodropping method. While bone morphogenetic protein (BMP)-2 is encapsulated in the PLGA NPs, vascular endothelial growth factor (VEGF) is included in the alginate MCs, where BMP-2-loaded PLGA NPs are entrapped together in the fabrication process. The initial loading efficiencies of BMP-2 and VEGF are 78% ± 3.6% and 43% ± 1.7%, respectively. When our dual GF-loaded MCs are assessed for in vitro osteogenesis of umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs) on 2D and 3D environment, MCs contribute to much better UCB-MSCs osteogenesis as confirmed by von Kossa staining, immunofluorescence (osteocalcin, collagen 1), calcium content measurement, and osteogenic markers expression. In addition, when dual GF-encapsulated MCs are combined with collagen and then applied to 8 mm diameter rat calvarial defect model, the positive effects on vascularized bone regeneration are much more pronounced; micro computed tomography (CT) and histology analyses exhibit 82.3% bone healing coupled with 12.6% vessel occupied area. Put together, current study indicates a synergistic effect of BMP-2/VEGF and highlights the great potential of dual GF delivery modality (PLGA NPs-in-MC) for regeneration of vascularized bone.

Electrospinning is useful for fabricating nanofibrous structure with different composition and morphologies. It offers great advantages through its geometrical structure and biomimetic property, which can provide a suitable environmental site for cell growth. The fiber diameter is entangled by the concentration of PCL with some adjustment of parameters during electrospinning process. PCL with lower concentration had bead structure while higher concentration had smooth fiber. The incorporation of nanoparticle hydroxyapatite (nHA) into poly( -caprolactone) fiber was studied. The fiber diameter of PCL was increased with the addition of nHA. Composition of fiber at lower concentrations of PCL and nHA into the polymer produced fiber with a homogenous distribution of nHA in PCL fiber with less agglomeration. The immersion of PCL/nHA fiber in simulated body fluid (SBF) had bonelike apatite layer on its surface while PCL showed no results. PCL/nHA showed high water uptake and had improved wettability compared to PCL alone, suggesting that PCL/nHA fibers were more hydrophilic than PCL fiber.

Collagen glycosaminoglycan (CG) scaffolds have been clinically approved as an application for skin regeneration. The goal of this study has been to examine whether a CG scaffold is a suitable biomaterial for generating human bone tissue. Specifically, we have asked the following questions: (1) can the scaffold support human osteoblast growth and differentiation and (2) how might recombinant human transforming growth factor-beta (TGF-β1) enhance long-term in vitro bone formation? We show human osteoblast attachment, infiltration and uniform distribution throughout the construct, reaching the centre within 14 days of seeding. We have identified the fully differentiated osteoblast phenotype categorised by the temporal expression of alkaline phosphatase, collagen type 1, osteonectin, bone sialo protein, biglycan and osteocalcin. Mineralised bone formation has been identified at 35 days post-seeding by using von Kossa and Alizarin S Red staining. Both gene expression and mineral staining suggest the benefit of introducing an initial high treatment of TGF-β1 (10 ng/ml) followed by a low continuous treatment (0.2 ng/ml) to enhance human osteogenesis on the scaffold. Osteogenesis coincides with a reduction in scaffold size and shape (up to 70% that of original). A notable finding is core degradation at the centre of the tissue-engineered construct after 49 days of culture. This is not observed at earlier time points. Therefore, a maximum of 35 days in culture is appropriate for in vitro studies of these scaffolds. We conclude that the CG scaffold shows excellent potential as a biomaterial for human bone tissue engineering.

Chronic wounds are difficult to heal due to several forms of infections. This issue can be addressed through the utilization of advanced approaches such as regenerative medicine and tissue engineering. One possible strategy could be the modification of bacterial cellulose (BC) structure to increase the current efforts of building scaffolds for tissue engineering. The current study was aimed to make structural comparative analysis of paraffin-altered BC and synthesis of its composite with alginate. Porous BC was produced through the addition of paraffin particles. Thereafter, a three dimensional scaffold of porous BC with alginate (BC/AL) was fabricated through the blending of BC and AL solutions. The paraffin particles were incorporated in the process of culturing Acetobacter xylinum for BC pellicle formation. Structural features of porous BC and BC/AL scaffold paralleled with original BC were investigated by the scanning electron microscope (SEM). SEM analysis revealed that porous BC possessed large surface (micro-scale pores) while the BC/AL scaffolds demonstrated a well-connected porous network. The purity and chemical structure of surfactants (Span 80 and OP-10) treated BC/AL scaffold was determined by Fourier transform infrared spectrum (FTIR) which confirmed the presence of any impurity in the form of paraffin in the 3D network of scaffold. Average water absorption analysis showed that pristine BC, porous BC, and BC/AL scaffold possessed 99.62%, 97.61%, and 96.94% water, respectively. Mechanical characteristics analysis of pristine BC, porous BC, Al, and BC/AL showed that these were conserved at certain levels between BC and AL. The MTT assay using RPMI 1640 medium (Hyclone, USA) supplemented with 10% fetal bovine serum (Gibco, USA) were used for human fetal hepatocyte L-02 cell line (Tongji Hospital, Wuhan, China) culture. Cells were incubated at 37 o C, 5% CO2 and humid atmosphere. The scaffold developed in the current study can serve as possible material for the treatment of burns and chronic wounds treatment.

Research into artificial bone scaffolds has increased substantially over the past decade as current solutions have significant limitations. Inspired by mineral hydroxyapatite (HAP) in natural bone, this study developed a facile in situ HAP coating on cellulose nanocrystals (CNCs) matrix followed by a crosslinking reaction. By changing the amount of CNCs added to a simulated body fluid (SBF), HAP content in the nanocomposite could be controlled between 0 and 40.1%, with a HAP coating thickness of ∼10 nm. Moreover, CNCs/HAP was crosslinked with poly(methyl vinyl ether-alt-maleic acid) (PMVEMA) and polyethylene glycol (PEG) to enhance its water stability and mechanical properties. FTIR and NMR analysis revealed that crosslinking happened via an esterification reaction between CNCs, HAP, PMVEMA, and PEG. Compression strength of the scaffolds showed a result as high as 41.8 MPa, almost 20 times of scaffold prepared by just mixing CNCs and HAP. Further investigations revealed that this scaffold was highly porous (as high as 91.0%) and lightweight (with a density between 60-70 mg/cm 3 ). Interestingly, this composite showed good biocompatibility as it can stabilize BSA protein, suggesting a promising material as a bone scaffold.

Issues of safety are very crucial with biomaterials and medical devices. Sixteen male New Zealand White rabbits equally into four groups: Group A, rabbits had part of their radial bone (2 cm, mid shaft) and left empty as a control. Group B, rabbits were implanted with scaffold 5211. Group C, rabbits were implanted with scaffold 5211GTA+Alginate. Group D, rabbits were implanted with 5211PLA. All scaffolds were prepared by freeze-drying method. Blood samples were collected at day 0 and 1 st , 2 nd , 3 rd , 4 th and 8 th week after implantation. The blood examination included complete hemogram and certain serum biochemical parameters. The results showed that there was no significant difference (P>0.05) among each treatment group in comparison with control group (day 0). However, red blood cells, hemoglobin, packed cell volume, mean corpuscular hemoglobin concentration, monocyte, plasma protein, inorganic phosphate, sodium, chloride and urea were significantly increased (P<0.05) among treatment groups at week 8. An abnormal architecture of viscera was observed in all animals, thus indicating a form of toxicity related to the degrading scaffold materials. The severity of histopathological lesions in viscera was not coated polymers dependent nor development materials. In conclusion, implantation of 5211 scaffold with or without coated framework has a significant impact on histopathological and certain hematological and biochemical parameters.

OPEN ACCESS  Bioactive glass scaffolds are used in bone and tissue biomedical implants, and there is great interest in their fabrication by additive manufacturing/3D printing techniques, such as robocasting. Scaffolds need to be macroporous with voids ≥100 um to allow cell growth and vascularization, biocompatible and bioactive, with mechanical properties matching the host tissue (cancellous bone for bone implants), and able to dissolve/resorb over time. Most bioactive glasses are based on silica to form the glass network, with calcium and phosphorous content for new bone growth, and a glass modifier such as sodium, the best known being 45S5 Bioglass®. 45S5 scaffolds were first robocast in 2013 from melt-quenched glass powder. Sol-gel-synthesized bioactive glasses have potential advantages over melt-produced glasses (e.g., greater porosity and bioactivity), but until recently were never robocast as scaffolds, due to inherent problems, until 2019 when high-silica-content sol-gel bioactive glasses (HSSGG) were robocast for the first time. In this review, we look at the sintering, porosity, bioactivity, biocompatibility, and mechanical properties of robocast sol-gel bioactive glass scaffolds and compare them to the reported results for robocast melt-quench-synthesized 45S5 Bioglass ® scaffolds. The discussion includes formulation of the printing paste/ink and the effects of variations in scaffold morphology and inorganic additives/dopants.

In the past few years, researchers have focused on the development of three-dimensional (3D) advanced scaffolds and multifunctional hydrogel-based materials. As reported in literature, 3D polymer-based composite scaffolds for tissue engineering have been manufactured through conventional and advanced manufacturing techniques, and different injectable materials and hydrogel-based systems have been proposed and studied. The aim of the current research was to define an approach in the development of multifunctional tools spanning from 3D hierarchical scaffolds for soft tissue engineering to advanced hydrogel-based devices for in situ cell or drug release. The mechanical/rheological behaviour as well as the structural/functional features of the designed devices were discussed and analyzed.

FREE DOWNLOAD FOR 50 DAYS AT: https://authors.elsevier.com/a/1YRYV3PCJl7r8W    This article reports the first robocasting of a sol–gel based glass ceramic scaffold. Sol–gel bioactive glass powders usually exhibit high volume fractions of meso– and micro–porosities, bad for colloidal processing as this adsorbs significant portion of the dispersing medium, affecting dispersion and flow. We circumvent these practical difficulties, to achieve pastes with particle size distributions, high solids loading and appropriate rheological properties for extrusion through fine nozzles for robocasting. Scaffolds with different macro-pore sizes (300–500 μm) with solid loadings up to 40 vol.% were robocast. The sintered (800 °C, 2 h) scaffolds exhibited compressive strength of 2.5–4.8 MPa, formed hydroxyapatite after 72 h in SBF, and had no cytotoxicity and a considerable MG63 cells viability rate. These features make the scaffolds promising candidates for tissue engineering applications and worthy for further in vivo investigations.

In the past few years, researchers have focused on the development of three-dimensional (3D) advanced scaffolds and multifunctional hydrogel-based materials. As reported in literature, 3D polymer-based composite scaffolds for tissue engineering have been manufactured through conventional and advanced manufacturing techniques, and different injectable materials and hydrogel-based systems have been proposed and studied. The aim of the current research was to define an approach in the development of multifunctional tools spanning from 3D hierarchical scaffolds for soft tissue engineering to advanced hydrogel-based devices for in situ cell or drug release. The mechanical/rheological behaviour as well as the structural/functional features of the designed devices were discussed and analyzed.

Electrospinning is useful for fabricating nanofibrous structure with different composition and morphologies. It offers great advantages through its geometrical structure and biomimetic property, which can provide a suitable environmental site for cell growth. The fiber diameter is entangled by the concentration of PCL with some adjustment of parameters during electrospinning process. PCL with lower concentration had bead structure while higher concentration had smooth fiber. The incorporation of nanoparticle hydroxyapatite (nHA) into poly( -caprolactone) fiber was studied. The fiber diameter of PCL was increased with the addition of nHA. Composition of fiber at lower concentrations of PCL and nHA into the polymer produced fiber with a homogenous distribution of nHA in PCL fiber with less agglomeration. The immersion of PCL/nHA fiber in simulated body fluid (SBF) had bonelike apatite layer on its surface while PCL showed no results. PCL/nHA showed high water uptake and had improved wettability compared to PCL alone, suggesting that PCL/nHA fibers were more hydrophilic than PCL fiber.

Since most starting materials for tissue engineering are in powder form, using powder-based additive manufacturing methods is attractive and practical. The principal point of employing additive manufacturing (AM) systems is to fabricate parts with arbitrary geometrical complexity with relatively minimal tooling cost and time. Selective laser sintering (SLS) and inkjet 3D printing (3DP) are two powerful and versatile AM techniques which are applicable to powderbased material systems. Hence, the latest state of knowledge available on the use of AM powderbased techniques in tissue engineering and their effect on mechanical and biological properties of fabricated tissues and scaffolds must be updated. Determining the effective setup of parameters, developing improved biocompatible/bioactive materials, and improving the mechanical/ biological properties of laser sintered and 3D printed tissues are the three main concerns which have been investigated in this article.

The development, fabrication, and characterization 1 of a novel miniature MEMS anemometer-nanoscale thermal 2 anemometry probe (NSTAP) for measuring velocity fluctuations 3 in turbulent flows are described. The sensor consists of a 4 freestanding 30 or 60 × 1 × 0.1 µm platinum filament with 5 electrically conductive pads and a silicon structure. A novel 6 deep reactive ion etching lag-based process for fabricating a 7 3-D silicon support structure is described together with other 8 microfabrication steps. The sensors behave similarly to conven-9 tional hot-wire anemometers, with an order of magnitude with 10 better spatial and temporal resolution. Batch fabrication allows 11 a relatively low-cost high-yield process, which together with its 12 superior frequency response and size, make it an attractive ther-13 mal anemometry sensor for velocity measurements in turbulent 14 flows. [2013-0313] 15 Index Terms-Microelectromechanical devices, anemometers, 16 velocity measurement. 17 I. INTRODUCTION 18 M EASURING turbulent velocity fluctuations continues 19 to be one of the great challenges to scientists and 20 engineers who study turbulence. Turbulent flows are composed 21 of recurrent, sometimes coherent flow structures or eddying 22 motions, that exhibit a range of length scales spanning several 23 orders of magnitude, all interacting with one another [1]. 24 To characterize turbulence fully, it is necessary to measure 25 the velocity fluctuations at all scales, including the smallest 26 eddies. In many flows, the smallest eddies can be of order 27 of micrometers, so there is a pressing need for probes that 28 can measure velocity fluctuations with sufficiently small spa-29 tial resolution and sufficiently high frequency response. The 30 widest range of length scales among turbulent eddies is found 31 in so-called high Reynolds number flows, which include flows 32 over large vehicles, inside industrial piping systems, and in the 33 earth's atmosphere. The Reynolds number is determined by the 34 relative size of the inertial forces to the viscous forces acting 35 on the flow, but it can also be interpreted as the ratio of the 36 Manuscript I E E E P r o o f 2 IEEE JOURNAL OF MICROELECTROMECHANICAL SYSTEMS the smallest of the available wires, with diameter of 0.625 μm, 84 but with the restriction of /d > 200 the smallest wire lengths 85 were limited to 125 μm. 86 Integrated circuit fabrication and MEMS fabrication tech-87 niques have introduced new possibilities for developing 88 anemometry sensors with considerably reduced physical sizes. 89 Lofdahl et al. [11] developed single and dual component 90 velocity sensors, which gave results that compared well to con-91 ventional hot-wire probes, and Ebefors et al. [12] introduced 92 micro-joints for fabricating 3D poly-silicon hot-wires. Unfor-93 tunately, the largest dimensions of the sensing elements of 94 these probes offered only a slight improvement in spatial res-95 olution compared to conventional techniques. Jiang et al. [13] 96 used MEMS fabrication techniques to manufacture a poly-97 silicon thermal anemometry probe with a geometry simi-98 lar to conventional hot-wires. These probes were a great 99 improvement in terms of spatial dimensions, with the smallest 100 having a length of 10 μm, but end-conduction was again an 101 important limitation. This was also a problem for the multi-102 component hot-wire probes fabricated by Chen [14], with 103 sensor dimensions 50 × 6 × 2.7 μm. Moreover, these sensors 104 were not suitable for conventional turbulence measurements, 105 being fixed at one wall-normal location. Wang et al. [15] had 106 a different approach, using a micro-cantilever structure for 107 measuring air flow, but these sensors were even larger than 108 conventional hot-wire anemometers. 109 At Princeton, we have been working for a number 110 of years to develop a Nano-Scale Thermal Anemometry 111 Probe (NSTAP) that will have improved spatial and tem-112 poral resolution for small-scale turbulence measurements. 113 NSTAP is a measurement device similar to conventional 114 hot-wire anemometer, having an order of magnitude smaller 115 sensing element compared to current commercial hot-wire 116 anemometers, and it is manufactured using MEMS fabrication 117 techniques. 118 The first successful effort to fabricate an NSTAP sensor was 119 reported by Bailey et al. [16]. The probe consisted of a plat-120 inum film supported on a silicon structure, with a free-standing 121 filament (the sensor) measuring about 60 × 2 × 0.1 μm 122

The biphasic calcium phosphate (BCP) concept was introduced to overcome disadvantages of single phase biomaterials. In this study, we prepared BCP from nano HA and β-TCP that were synthesized via a solid state reaction. Three different ratios of pure BCP and collagen-based BCP scaffolds (%HA/%β-TCP; 30/70, 40/60 and 50/50) were produced using a polymeric sponge method. Physical and mechanical properties of all materials and scaffolds were
investigated. XRD pattern proved the purity of each HA, β-TCP and BCP. SEM showed overall distribution of macropores (80-200 μm) with appropriate interconnected porosities. Total porosity of pure BCP (93% ± 2) was found to be higher than collagen-based BCP (85%± 3). It was observed that dimensional shrinkage of larger scaffold (39% ± 4) is lower than smaller one (42% ± 5) and scaffolds with higher HA (50%) ratio experienced greater shrinkage than those with higher β-TCP (70%) ratio (45% ±3 and 36% ±1 respectively). Mechanical properties of both groups tend to be very low and collagen coating had no influence on mechanical behavior. Further studies may improve the physical properties of these composite BCP.

Hybrid silk scaffolds combining knitted silk fibers and silk sponge have been recently developed for use as ligament-alone grafts. Incorporating an osteoinductive phase into the ends of a ligament scaffold may potentially generate an integrated “bone–ligament–bone” graft and improve graft osteointegration with host bone. To explore the possible application of hydroxyapatite (HA) coating in the fabrication of osteoinductive ends of silk-based scaffold, HA was coated on the hybrid silk scaffold and the effects to the bone-related cells were evaluated. HA could be coated in a uniform and controlled manner on the silk sponge, using an alternate soaking technology, with the amount deposited being dependent on the number of soaking cycles. HA coating also progressively reduced the hydrophobicity of silk surface (decreasing water contact angle from 87° to 42–76°, after 1–3 soaking cycles), making the HA-coated silk scaffold less favorable for initial cell attachments; but the attached cells showed viability and sustained proliferation on the HA-coated scaffold. As demonstrated by real-time polymerase chain reaction and alkaline phosphatase assay, the osteoinductivity of HA-coated silk scaffolds resulted in the osteogenic differentiation of bone marrow mesenchymal stem cells, and the osteoconductivity of HA-coated silk scaffolds supported osteoblasts growth and maintained the properties of mature osteoblasts. These properties of HA-coating demonstrated its possible application in fabricating osteoinductive ends of the silk-based ligament graft to potentially enhance graft-to-host bone integration. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2013.

Magnetic nanocomposite scaffolds based on poly(ε-caprolactone) and poly(ethylene glycol) were fabricated by 3D fibre deposition modelling (FDM) and stereolithography techniques. In addition, hybrid coaxial and bilayer magnetic scaffolds were produced by combining such techniques. The aim of the current research was to analyse some structural and functional features of 3D magnetic scaffolds obtained by the 3D fibre deposition technique and by stereolithography as well as features of multimaterial scaffolds in the form of coaxial and bilayer structures obtained by the proper integration of such methods. The compressive mechanical behaviour of these scaffolds was investigated in a wet environment at 37 °C, and the morphological features were analysed through scanning electron microscopy (SEM) and X-ray micro-computed tomography. The capability of a magnetic scaffold to absorb magnetic nanoparticles (MNPs) in water solution was also assessed. confocal laser scanning microscopy was used ...

The healing of load-bearing segmental defects in long bones is a challenge due to the complex nature of the weight that affects the bone part and due to bending, shearing, axial, and torsional forces. An innovative porous 3D scaffolds implant of CaCO aragonite nanocomposite derived from cockle shell was advanced for substitute bone solely for load-bearing cases. The biomechanical characteristics of such materials were designed to withstand cortical bone strength. In promoting bone growth to the implant material, an ideal surface permeability was formed by means of freeze drying and by adding copolymers to the materials. The properties of coating and copolymers supplement were also assessed for bone-implant connection resolutions. To examine the properties of the material in advanced biological system, an experimental trial in an animal model was carried out. Critical sized defect of bone was created in rabbit&#39;s radial bone to assess the material for a load-bearing application wi...

Research into artificial bone scaffolds has increased substantially over the past decade as current solutions have significant limitations. Inspired by mineral hydroxyapatite (HAP) in natural bone, this study developed a facile in situ HAP coating on cellulose nanocrystals (CNCs) matrix followed by a crosslinking reaction. By changing the amount of CNCs added to a simulated body fluid (SBF), HAP content in the nanocomposite could be controlled between 0 and 40.1%, with a HAP coating thickness of ∼10 nm. Moreover, CNCs/HAP was crosslinked with poly(methyl vinyl ether-alt-maleic acid) (PMVEMA) and polyethylene glycol (PEG) to enhance its water stability and mechanical properties. FTIR and NMR analysis revealed that crosslinking happened via an esterification reaction between CNCs, HAP, PMVEMA, and PEG. Compression strength of the scaffolds showed a result as high as 41.8 MPa, almost 20 times of scaffold prepared by just mixing CNCs and HAP. Further investigations revealed that this scaffold was highly porous (as high as 91.0%) and lightweight (with a density between 60-70 mg/cm 3 ). Interestingly, this composite showed good biocompatibility as it can stabilize BSA protein, suggesting a promising material as a bone scaffold.

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Perusahaan scaffolding di Tuban, Distributor scaffolding di Tuban, Tempat Beli scaffolding Tuban, Jual scaffolding Tuban, Tempat Jual scaffolding Tuban, jual beli scaffolding Tuban, penjual scaffolding di Tuban, Supplier scaffolding Projek Sipil Tuban, Scaffolding Tuban, Pusat scaffolding Tuban, Agen scaffolding Tuban, Beli scaffolding Tuban

Anda sedang mencari Scaffolding Baru / Bekas untuk kebutuhan project Anda? Baik Untuk keperluan di project Sipil maupun MIGAS.

Silahkan Hubungi kami untuk berkonsultasi dan kami akan membantu sesuai dengan kebutuhan yang Anda inginkan.

Kami menyediakan Scaffolding Bersertifikat, Terbaik untuk Keamanan dan Kelancaran Usaha ANDA. Sehingga anda tidak perlu ragu lagi untuk langsung menggunakannya di project anda.

Kami telah berpengalaman melayani klien baik onshore maupun offshore, dan mengirimkannya ke seluruh wilayah Indonesia. Harga bersaing, sepadan dengan kualitas dan pengiriman Scaffolding yang tepat waktu adalah komitmen kami.

Untuk inquiry silahkan Hubungi kontak kami dibawah ini, dan mohon disampaikan apa spesifikasi yang anda inginkan.

HUBUNGI
HP/WA: 0811-776-598 (Tsel)

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Fabrication of an ideal scaffold having proper composition, physical structure and able to have sustained release of growth factors still is challenging for bone tissue engineering. Current study aimed to design an appropriate three-dimensional (3-D) scaffold with suitable physical characteristics, including proper compressive strength, degradation rate, porosity, and able to sustained release of bone morphogenetic protein-2 (BMP2), for bone tissue engineering. A highly porous 3-D β-tricalcium phosphate (β-TCP) scaffolds, inside of which two perpendicular canals were created, was fabricated using foam-casting technique. Then, scaffolds were coated with gelatin layer. Next, BMP2-loaded chitosan (CS) nanoparticles were dispersed into collagen hydrogel and filled into the scaffold canals. Physical characteristics of fabricated constructs were evaluated. Moreover, the capability of given construct for bone regeneration has been evaluated in vitro in interaction with human buccal fat pad-derived stem cells (hBFPSCs). The results showed that gelatin-coated TCP scaffold with rhBMP2 delivery system not only could act as a mechanically and biologically compatible framework, but also act as an osteoinductive graft by sustained delivering of rhBMP2 in a therapeutic window for differentiation of hBFPSCs towards the osteoblast lineage. The proposed scaffold model can be suggested for delivering of cells and other growth factors such as vascular endothelial growth factor (VEGF), alone or in combination, for future investigations.

For over 20 years, nanostructured porous silicon (nanoPS) has found a vast number of applications in the broad fields of photonics and optoelectronics, triggered by the discovery of its photoluminescent behavior in 1990. Besides, its biocompatibility, biodegradability, and bioresorbability make porous silicon (PSi) an appealing biomaterial. These properties are largely a consequence of its particular susceptibility to oxidation, leading to the formation of silicon oxide, which is readily dissolved by body fluids. This paper reviews the evolution of the applications of PSi and nanoPS from photonics through biophotonics, to their use as cell scaffolds, whether as an implantable substitute biomaterial, mainly for bony and ophthalmological tissues, or as an in vitro cell conditioning support, especially for pluripotent cells. For any of these applications, PSi/nanoPS can be used directly after synthesis from Si wafers, upon appropriate surface modification processes, or as a composite biomaterial. Unedited studies of fluorescently active PSi structures for cell culture are brought to evidence the margin for new developments.

Silicate-based bioceramics have been found to possess excellent apatite-forming ability, and they can stimulate cell proliferation and osteogenic differentiation. In this study, bredigite (Ca7MgSi4O16) nanoparticles were synthesized and incorporated into a hydroxyapatite (HA)-based matrix to produce composite nanoparticles with improved bioactivity and biocompatibility. HA/bredigite nanoparticles containing 25% and 50% bredigite were synthesized by using the sol–gel method. X-ray diffraction, transmission electron microscopy, scanning electron microscopy, energy-dispersive x-ray spectroscopy, and Fourier transform infrared techniques were used to study the phase structure, morphology, and structural properties of prepared nanoparticles. Results indicated that HA/bredigite nanoparticles with an average particle size of less than 50 nm and homogeneous distribution of bredigite were successfully synthesized. Obtained results also revealed that the presence of bredigite led to a small increase in HA lattice parameters and to a decrease in the agglomeration of composite nanoparticles. The in vitro bioactivity studies performed in the simulated body fluid showed that composite nanoparticles had higher apatite-forming ability than pure HA. The results of a cell proliferation assay revealed that the proliferation of mesenchymal stem cells in the extract of HA/bredigite was significantly higher than those in the extract of the initial HA and control group after 72 h. As the properties of HA/bredigite nanoparticles were highly improved, compared with pure HA, it is concluded that these composite nanoparticles could potentially be good candidates for use as effective bioactive materials in bone regeneration applications.