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Purpose This study aims to obtain the mechanistic insights for the fabrication of pure copper thin wall components by selective infrared (IR) laser melting (SLM) and correlated with microstructure development, microhardness, surface morphology and phase analysis. Experimental processes for single track and selection of substrate materials have been studied using a combination of different laser powers and scanning speeds. Design/methodology/approach SLM of pure copper was performed on a YONGNIAN Laser YLMS-120 SLM machine using an Nd: YAG fiber laser operating at 1,060 nm in the NIR region. Single-track experiments and processing parameters are investigated through different combinations of laser power and scanning speed. The microstructure of the fabricated pure copper samples by SLM technique was analyzed by means of X-ray diffraction, scanning electron microscope equipped with energy disperse spectrometer, optical microscope (OM) and micro-hardness tester. Findings Steel-based substrates were found suitable for pure copper manufacturing due to sufficient heat accumulation. The width of a single track was determined by liner energy density, showing discontinuities and irregular morphologies at low laser powers and high scanning speeds. As a result of instability of the molten pool induced by Marangoni convection, cracks and cavities were observed to appear along grain boundaries in the microstructure. The top surface morphology of SLM-processed component showed a streamflow structure and irregular shapes. However, the powder particles attached to side surface, which manifest copper powders, are even more sensitive to melt pool of contour track. The crystal phase characteristics of copper components indicated increasing crystallite size of a-Cu, and the decreasing intensity of diffraction peak was attributed to the presence of defects during SLM. The maximum relative density and microhardness were 82 per cent and 61.48 HV0.2, respectively. The minimum thickness of a pure copper thin wall component was 0.2 mm. Originality/value This paper demonstrated the forming mechanism and explored feasibility of pure copper thin wall parts by SLM technology in the NIR region. The surface morphology, microstructure and crystal structure were preliminary studied with laser processing parameters. more...

A family of entangled coordination polymers, namely, [Cd(cba)(ibpi)] (1), [Cd(sdc)(ibpi)]·H2O (2), [Cd2(bpdc)2(ibpi)2] (3), [Ni2(sdc)2(ibpi)2(H2O)2]·H2O (4), [Cd2(tdc)2(ibpi)]·H2O (5), [Cd(Hbtc)(ibpi)] (6), [Co2(tdc)2(ibpi)2·H2O]·2H2O (7) and [Cd2(cdc)2(ibpi)2]·2H2O (8). [ibpi = 1-(4-(4-(1H-imidazol-1-yl)benzyloxy)phenyl)-1H-imidazole, H2cba = 4,4′-carbonyldibenzoic acid, H2sdc = 4,4′-sulfonyldibenzoic acid, H2bpdc = biphenyl-4,4′-dicarboxylic acid, H2cdc = 1,4-cyclohexanedicarboxylic acid, H2tdc = thiophene-2,5-dicarboxyl acid, and H3btc = 1,3,5-benzenetricarboxylic acid], have been synthesized and structurally characterized. Compound 1 exhibits a 2-fold parallel interpenetration of sql networks. Compound 2 presents a 3-fold parallel interpenetration of sql networks. Compound 3 features a parallel polycatenation of 3-fold interpenetrated sql networks. Compound 4 shows a unique type of inclined interpenetration of sql networks. Compound 5 displays a 3-fold interpenetration of pcu network. Compound 6 exhibits a uninodal self-catenating mab network. Compound 7 shows an 8-connected self-catenating framework of 8T10 topology with the point symbol (420·68). Compound 8 presents a unique 8-connected 8T21 self-catenating framework with the point symbol (424·64). The thermal stabilities and photochemical properties of compounds 1, 2, 3, 5, 6 and 8 have also been studied. more...

Two novel polyrotaxane-like coordination polymers, [Ni4(L)4(H2O)3(bpp)4]·3H2O (1) and [Cd4(L)4(bpp)3]·3H2O (2) (H2L = Me2Si(p-C6H4COOH)2, bpp = 1,3-bis(4-pyridyl)propane), have been synthesized and structurally characterized. Compound 1 features a 2D → 3D polyrotaxane array by the interlock of bilayer networks. Compound 2 exhibits an unusual 3D polyrotaxane-like self-threading framework. In addition, compound 2 shows an emission at 485 nm when it was excitated at 400 nm. more...

A novel metal–organic framework based on binuclear cadmium clusters has been synthesized and characterized, which represents a new kind of 8-connected uninodal network topology presently known for self-penetrating systems. more...

Based on a V-shaped multicarboxylic acid and various bisimidazole ligands, six new coordination polymers, namely, [Zn4(otba) (1,4-bix)4]·3H2O (1), [Ni4(otba)2(1,4-bix)3(H2O)2]·2H2O (2), [Zn2(H2otba)2(bib) (H2O)2] (3), [Cd2(H2otba)2(bib)]·2H2O (4), [Zn3(otba)2(bidpe)2(H2O)2] (5), [Ni2(H2otba)2(bidpe)3(H2O)2]·H2O (6) (H4otba = 3,5,3′,5′-oxytetrabenzoic acid, 1,4-bix = 1,2-bis(imidazol-1-ylmethyl)benzene, bib = 1,4-bis(imidazol-1-yl)benzene and bidpe = 4,4’-bis(imidazol-1-yl)diphenyl ether) have been hydrothermally synthesized and structurally characterized. Compound 1 displays an uncommon hexanodal 3D 4-connected network. Compound 2 features a trinodal 3D (4, 4, 6)-connected framework. Compound 3 shows an interesting polythreaded 1D→3D species. Compound 4 exhibits a binodal 3D (3, 8)-connected network. Compound 5 displays a three-fold interpenetration of trinodal (3, 3, 4)-connected network. Compound 6 shows a five-fold interpenetration of five-connected bilayer network. The luminescent properties of compounds 1, 3, 4 and 5 were also measured. more...

Two novel coordination polymers, [Cd2(cdc)2(bmis)2] (1) and [Zn6(cdc)4(OH)4(bmis)4]·2H2O·4DMF (2) (bmis = bis(4-(2′-methylimidazol-ylphenyl)sulfone, H2cdc = 1,4-cyclohexanedicarboxylic acid), have been synthesized and structurally characterized. Compound 1 features an interesting usf net presenting the alternate arrangement of the single- and triple-stranded helices. Compound 2 exhibits an unusual two-fold interpenetrating polyrotaxane motif composed of two interlocked sets of identical pcu nets. In addition, their photoluminescent properties have also been evaluated. more...

Seven new entangled coordination polymers, namely, [Zn(sdc)(bita)] (1), [Zn(1,4-ndc)(bita)] (2), [Zn2(bdc)2(bita)2] (3), [Zn2(sda)2(bita)2] (4), [Cd(odc)(bita)]·0.5H2O (5), [Cd2(bpdc)2(bita)2] (6) and [Cd3(bpdc)3(bita)2]·2DMF (7) [bita = 4,4′-bisimidazyltriphenylamine, H2sdc = 4,4′-sulfonyldibenzoic acid, 1,4-H2ndc = naphthalene-1,4-dicarboxylic acid, H2bdc = 1,4-benzenedicarboxylic acid, H2odc = 4,4′-oxybisbenzoic acid, H2sda = 4,4′-stilbenedicarboxylic acid, H2bpdc = biphenyl-4,4′-dicarboxylic acid], have been synthesized and structurally characterized. Compound 1 exhibits a 2D → 2D polycatenane of three-fold interpenetrated sql networks. Compound 2 displays a four-fold interpenetration of a dia network in a [2 + 2] mode. Compound 3 features both polyrotaxane and polycatenane composed of two interlocked sets of hcb network. Compound 4 shows three-fold interpenetration of a pcu network. Compound 5 presents unusual two-fold interpenetration of a self-penetrating framework with (42·6·83) topology. Compound 6 displays a 2D → 3D polycatenane of three-fold interpenetrated sql networks. Compound 7 exhibits an unusual self-penetrating framework with (425·63) topology. The thermal stabilities and photochemical properties of these compounds have also been studied. more...

Two novel coordination polymers, [Co(1,4-ndc)(bipe)] (1), [Cd2(bdc)2(bipe)2]·2H2O (2) (bipe = bis(4-imidazolphenoxy)ethane, H2bdc = 1,4-benzenedicarboxylic acid and 1,4-H2ndc = naphthalene-1,4-dicarboxylic acid), have been synthesized and structurally characterized. Compound 1 features a five-fold interpenetration of dia network in a [3 + 2] mode. Compound 2 shows an eight-fold interpenetration of dia network in a [4 + 4] mode. In addition, compound 2 shows an emission at 435 nm when it was excitated at 332 nm. more...

A novel coordination polymer [AgBF4(bocb)2] (1) (bocb = 1,4-bis(4-oxy-1-cyano)benzene) has been synthesized. This compound exhibits a ten-fold diamondoid framework with an unusual [5 + 5] mode of interpenetration. Its luminescent property was also investigated. more...

Based on a V-shaped bisimidazole ligand and various dicarboxylic acids, nine entangled coordination polymers, namely, [Zn(o-bdc)(bips)]·2H2O (1), [Zn2(cdc)2(bips)2]·2H2O (2), [Zn2(bpedc)2(bips)2] (3), [Zn(odc)(bips)]·H2O (4), [Zn2(sdc)2(bips)2]·5H2O (5), [Co2(sdc)2(bips)2(H2O)]·2H2O (6), [Cd2(bpdc)2(bips)2]·3H2O (7), [Cd2(2,6-ndc)2(bips)2(H2O)2]·2H2O (8) and [Cd(1,4-ndc)(bips)]·DMF·H2O (9) (bips = bis(4-imidazol-ylphenyl)sulfone, o-H2bdc = o-phenyldicarboxylic acid, H2cdc = 1,4-cyclohexanedicarboxylic acid, H2bpedc = 4,4′-stibenedicarboxylic acid, H2odc = 4,4′-oxybisbenzoic acid, H2sdc = 4,4′-sulfonyldibenzoic acid, H2bpdc = biphenyl-4,4′-dicarboxylic acid, 1,4-H2ndc = naphthalene-1,4-dicarboxylic acid, 2,6-H2ndc = naphthalene-1,4-dicarboxylic acid), have been synthesized and structurally characterized. Compound 1 exhibits a 2D → 2D polycatenane of 3-fold interpenetrated sql layers. Compound 2 shows a 2D → 3D polycatenane of 3-fold interpenetrated sql layers. Compound 3 displays a 2D → 3D polycatenane of 5-fold interpenetrated sql layers. Compound 4 exhibits a 2-fold interpenetration of CdSO4 networks. Compound 5 presents a 2D → 3D polycatenane by three-fold interpenetrated {42·63·8}2 layers. Compound 6 features an unusual 2D → 2D polycatenane framework assembled by the entanglement of sql layers containing 2-membered loops. Compound 7 exhibits a 1D → 3D polycatenane by the 3-fold interpenetration of 3-connected ribbons. Compound 8 displays a 3-fold interpenetration of SrAl2 networks. Compound 9 exhibits a 4-fold interpenetration of dia networks in a [2 + 2] mode. Their luminescence properties were also measured. more...

Five novel entangled coordination polymers, namely, [Cd(sdc)(bipm)(H2O)]·DMF (1), [Cd2(bdc)2(bipm)2(DMF)2] (2), [Cd2(ndc)2(bipm)2]·2H2O (3), [Cd(bdc)(bipm)] (4) and [Cd2(bpdc)2(bipm)2] (5) [bipm = bis(4-imidazolphenoxy)methane, H2sdc = 4,4′-sulfonyldibenzoic acid, H2bdc = 1,4-benzenedicarboxylic acid , H2bpdc = biphenyl-4,4′-dicarboxylic acid, and H2ndc = naphthalene-2,6-dicarboxylic acid], have been synthesized and structurally characterized. Compound 1 exhibits a 2-fold interpenetration of (4,4)-connected sql network. Compound 2 displays an inclined catenation of (6,3)-connected hcb network. Compound 3 features an unusual twofold interpenetrating polyrotaxane motif composed of two interlocked sets of identical pcu nets. Compounds 4 and 5 both show 3D polycatenane motifs generated by the 2D → 2D parallel → 3D parallel interpenetration of (4,4)-connected sql network. But in 4, one net is interpenetrated by five others, while in 5, unusually, one net is interpenetrated by eight others. The thermal stabilities and photochemical properties of these compounds have also been studied. more...

C34H26O6N4Ni, monoclinic, P2 1 /c, a = 11.4709(19) Å, b = 13.328(2) Å, c = 20.062(3) Å, β = 94.305(3)°, V = 3058.5(9) Å3, Z = 4, R gt (F) = 0.0393, wR ref (F 2 ) = 0.0868, T = 293 K.

Extrusion container is the most important tooling in steel hot extrusion processing. Traditional designs such as the multilayered cylinder are difficult to execute for large extrusion containers. A novel design is proposed in this article, a salient feature of which is that the container employs steel wire winding technology. The primary difficulty of applying wire winding to the design of extrusion container is that the container should be heated to 350 °C while the temperature of steel wire cannot exceed 75 °C due to accelerated creep and stress relaxation at high temperature. In addition, the prestress generated by steel wire should fulfill the requirements necessary for the container. The proposed design should meet both goals. The functional requirements including preheating, protection of steel wire from high temperature, and stress distribution are discussed, and solutions are proposed. A new method to generate prestress called thermally induced prestress is introduced and detailed. To verify the design, a proof-of-concept prototype model was fabricated and tested. Results showed that the container using the proposed design could meet the expected prestressing goals, and the temperature of the wire would not exceed the limit and can offer an alternative to conventional design methods of extrusion containers. more...

The mechanism of phase transformation and microstructure of yttria-stabilized zirconia (YSZ), prepared by selective laser melting (SLM) at a laser wavelength of 1 μm, has been investigated. Also, the effect of different working gases and heat treatment has been studied. Experimental results present that processing parameters can be optimized and determined by Liner Energy Density. X-ray diffraction analysis confirmed the absence of monoclinic phase under argon flow during SLM, with gray-color appearance due to the lack of oxygen, which impedes the transformation from tetragonal to monoclinic phase partially. Later, the color becomes white during heat treatment because samples are exposed to the air with sufficient amount of the oxygen and the diffraction peaks of monoclinic phase increased. When SLM and heat treatment was carried out in the air, the YSZ samples appeared in white-color, which indicates the presence of both monoclinic and tetragonal phase. The morphology and microstructure showed there occurred bonding phenomenons among particles, only surface partially melted between particles with weak bonding strength. The top surface morphology of air-prepared sample showed cracks, un-melting particles and cave-like pores because of uneven distribution of temperature variations. This paper also made a preliminary research and provided a feasibility method to melt zirconia ceramics completely, in which more energy input by multi-scanning in the air working gas. more...

The current research analyzes the reliability of a dissected frame of heavy equipment in terms of stress distribution, integrality, and fatigue. Through the use of the finite element analysis method, the results demonstrated that the stress field and deformation of the dissected frame were identical to those of the integral frame. Under the working condition, slight slides existed along the dissecting planes between arch beams and columns. On the other dissecting positions, there were no slides during either the working state or the pre-stressed state. The wires and frames both appeared to have limitless fatigue lives. Fatigue of the dissected frame was the same as that of the integral frame. This experiment illustrates that dissected frames can meet the requirements of integrality much better than integral frames. At the same time, local slides or detachments along dissecting planes would not expand during long-term service. more...

Although most in vitro studies indicate that transforming growth factor β3 (TGF-β3) immobilized scaffold is suitable for cartilage tissue engineering, in vivo studies of implanting immobilized scaffold for chondral defect repair are still lacking. This study is to evaluate the potentials of TGF-β3 immobilized poly-(lactic-co-glycolic acid)-gelatin/chondroitin sulfate/hyaluronic acid (PLGA-GCH) hybrid scaffold for cartilage regeneration. The scaffold was fabricated by incorporating GCH micro-sponges into PLGA frameworks and then crosslinked with TGF-β3 to mimic natural cartilaginous extra cellular matrix (ECM). In vitro study demonstrated that MSCs proliferated vigorously and produced abundant ECM on scaffold. The immunohistochemistry staining and alcian blue staining confirmed the cartilaginous ECM production. The chondrogenic differentiation of MSCs on scaffold was proved by the expression of collagen II gene in mRNA and protein level. Then MSCs/TGF-β3 immobilized scaffolds were implanted in rabbits for chondral defects repair. After eight weeks, histological observation showed that differentiated MSCs were located in lacunae within the metachromatic staining matrix and exhibited typical chondrocyte morphology. Histological grading scores also indicated the congruent cartilage was regenerated. In conclusion, the TGF-β3 immobilized PLGA-GCH hybrid scaffold has great potential in constructing the tissue-engineered cartilage. more...

Rapid prototyping (RP)-based highly porous poly(DL-lactic-co-glycolic acid)/tricalcium phosphate (PLGA/TCP(RP)) scaffolds were fabricated. PLGA/TCP constructs (PLGA/TCP(TS)) were also made via thermally induced phase separation with solvent casting and by particulate leaching approach. Both scaffolds were loaded with bovine bone protein extract (BBPE). Sixty-four New Zealand white rabbits were randomized into four groups (groups of A, B, C, and D) and unilaterally underwent posterior lumbar interlaminar fusion at L2—L4 level. Spinal fusions were systematically evaluated. In groups of A (PLGA/TCP (RP)/BBPE constructs) and C (autogenous iliac bone grafts), good bone fusions occurred in vivo. Histological analyses indicated that endochondral ossification played an essential role in initiation of bone fusions in group A, whereas in group B (PLGA/TCP(TS)/BBPE constructs), few bone fusions were observed. In group D (PLGA/TCP(RP) scaffolds alone), the scaffolds were biocompatible and biodegradable; however, no newly formed bone mass or bone fusion was found. Twelve weeks after surgery, the fusion was significantly higher in groups of A and C compared with groups B and D (p(RP)/BBPE biomaterials have potential as grafting substitutes for bone healing and spinal fusion. more...

Presently, there is a recognized and imperative need for bioartificial organs. The technological advances in transgenosis, tissue engineering, and rapid prototyping have led to the development of spatially complex tissues. An ideal artificial organ should provide nutrient transport system, mechanical stable architecture, and synergetic multicellular organization in one construct. The multinozzle rapid prototyping technique simultaneously assembles vascular systems including hierarchical multicellular structures in an automated and reproducible manner and offers an effective way for treating organ failures. In this article, a brief overview of the recent trends and outstanding challenges in organ manufacturing is provided. From the viewpoint of disciplinary crossing, integration, and development, future directions in the coming years were pointed out. more...

A poly(DL-lactic-co-glycolic acid) (PLGA) sandwich fibrinogen/ adipose stem cell (ADSC) construct was fabricated to generate smooth muscle tissue. The mechanical properties and ADSC compatibility of PLGA, poly(ethylene glycol-1,6-hexamethyl diisocyanate-caprolactone) i.e. polyurethane (PU), gelatin, alginate, and fibrin composites were evaluated for vascular smooth muscle tissue generation. Synthetic PLGA and PU combined with natural gelatin, alginate, and fibrin for strength and cell compatibility were found to be effective. A trilayer construct was designed and built with a microporous inner PLGA layer to provide nutrient, oxygen, and metabolite transfer while the outer PLGA layer with no pores prevented leakage during in vitro culture and in vivo implantation. The fibrin layer suitably accommodated ADSC growth, migration, proliferation, and differentiation inside the construct. This design has the potential for wide use in tissue engineering and complex organ construction. more...

The bumpy-ridge structure applied in the field of heavy equipment is analysed based on fracture mechanics and contact theory. At the same time, the elastic—plastic contact of the ridges is simulated using the finite element method. Having been researched, the separated bumpy-ridge structure can be seen as a special integral structure that has a through crack. It was also found that, as long as there are adequate normal forces and treated contact surfaces, this kind of separated structure has the ability to resist detachment and parallel slide. The height of the notch and radius of the contact zone are the foremost indexes affecting the application of the bumpy-ridge technique, and these parameters are influenced by several factors, such as the shape of the ridges, the curvature of the contact point, the distance between neighbouring ridges, etc. The elastic contact of the ridge can be solved completely by the use of theoretical calculation and graphical method. Through comparison with the elastic contact, some principles of the elastic—plastic contact can be obtained with a finite element analysis method. A bumpy-ridge structure has been successfully applied to a 350 MN die forging press and a 360 MN extrusion press in China. more...

Three-dimensional highly porous poly(DL-lactic-co-glycolic acid)/ tricalcium phosphate (PLGA/TCP) scaffolds were fabricated using a rapid prototyping technique (RP). The 3D rhombic lamellar PLGA/TCP carriers (20 mm × 20 mm × 3 mm) subsequently were coated with collagen type I (Col) to produce PLGA/TCP/Col composites. Both the RP-based PLGA/TCP scaffolds and the PLGA/TCP/Col composites were observed by scanning electron microscopy. Forty New Zealand white rabbits were equally randomized into 2 groups (group A and group B) and bilaterally underwent posterolateral intertransverse process arthrodesis at the L4—L5 level using the following graft materials: In group A, PLGA/TCP/Col/BMSCs-OB composites (on the right side, group A1, n = 20) and autogenous iliac bone grafts (on the left side, group A2, n = 20) were used; In group B, PLGA/TCP scaffolds plus fresh autogenous bone marrow (on the right side, group B1, n = 20) and PLGA/TCP scaffolds alone (on the left side, group B2, n = 20) were utilized. In group A1, rabbit bone marrow stromal cells (BMSCs) were isolated and cultured under the osteogenic conditions (BMSCs-OB). Structural PLGA/TCP/Col composites then were efficiently loaded with BMSCs-OB and cultured 5 days to make PLGA/TCP/ Col/BMSCs-OB biomaterials. Rabbits were sacrificed after 12-week follow-up and the spinal fusion were evaluated by a general observation, a manual palpation test, histological analyses and radiography. As a result, RP established PLGA/TCP scaffolds with appropriate biomaterial properties including satisfactory microstructure, inter-connectivity and porosity. Modifications to the structural highly porous PLGA/TCP scaffolds with Col (PLGA/TCP/Col) essentially increased the affinity of the carriers to seeding cells. In group A1, radiological evaluation revealed strong ability of new bone formation and bony fusion in the implanted sites and histological analyses showed highly cellular bone marrow between the newly formed trabecular bone was present in the fusion mass. In group A2, there was a reduced amount of newly formed bone. In group B1, only a few bony fusions were obtained. In group B2, PLGA/TCP scaffolds were biocompatible and biodegradable; whereas, no newly formed bone or bony fusion was found. Twelve weeks after surgery, spinal fusion rates in groups of A1, A2, B1, and B2 were 70.0%(14/20), 45.0%(9/20), 15.8%(3/19), and 0%(0/19), respectively. The rates of fusion were significantly higher in groups of A1 and A2 compared with groups of B1 and B2 (p0.05). Therefore, RP-based 3D PLGA/TCP/Col/BMSCs-OB biomaterial holds promise as a bone grafting substitute for spinal fusion. Our attempts may provide a novel method for biofabrication of the bionic construct. more...

Cryopreservation technology plays an important role in conserving three dimensional (3D) constructs containing cells. Besides preserving the characteristics of the construct, it can also save a lot of resources in many aspects, such as cell culture space, culture vessel, culture medium etc. Otherwise, the biological properties of the cells and the 3D geometrical configuration will disappear with the death of cells and breakage of configuration. Consequently, a cryopreservation method for the 3D construct fabricated with a controlled cell assembling technology was studied. 10% dimethylsulfoxide (DMSO) was incorporated into the adipose-derived stem cell (ADSC)/gelatin/ alginate/fibrinogen mixture before assembling. Results indicate that the 3D construct containing cells can be preserved below —80°C for more than 1 week. After the construct underwent the thawing process, cell viability and proliferation ability were regained. This technique holds potential to be used widely in tissue engineering and organ manufacturing fields. more...

The rapid prototyping and manufacturing technology (RPM), is an integration of many different disciplines. It is based on an advanced dispersed-accumulated forming principle and originated from 1980s. It generates an entity by first forming a series of layers according to the dispersed section information of the digital model, and then piling the formed layers sequentially together. It is capable of forming parts with complicated structures and non-homogeneous materials. Traditional RPM techniques are mainly used as prototypes in product invention process, such as stereolithography, three-dimensional printing, laminated object manufacturing, and fused deposition modeling. Later, with the progress of material and enabling technology, many new RPM techniques emerged out and have been already applied in the fields such as rapid tooling/moulding, direct formed usable part, nano-/micro-RPM, and biomanufacturing. This high flexible digital manufacturing method has a likely ability to become an almighty forming technology. more...

The patternless casting manufacturing (PCM) technique, which adopts a new concept of double scanning method, combines the principle of discreteness and deposition with resin-bonded sand technique. This paper is to evaluate the dimensional accuracy of sand mould on PCM. The two important factors—the liquid penetration rule in the space of particles and the shape and dimension of the agglomeration unit body, which influence the process parameters such as scanning speed, layer thickness, liquid flux on dimension accuracy, and surface qualities, were investigated systematically, thus the theoretical basis for these parameters was provided. Experiments on rapid manufacturing of sand mould were carried out, and the results of the free penetration and the constraint penetration well verified the relationship of the two factors and the process parameters. more...

A functional-region/separate-interface/single-cell-type of tissue engineering pathway was evaluated to regenerate osteochondral defects that are deep in the marrow cavity. A gradient osteochondral scaffold fabricated via a rapid prototyping technology, called multi-nozzle low-temperature deposition manufacturing, was composed of three parts with different materials and pore-structures, respectively, for bone, cartilage and a separate interface between them. The separate interface was composed of micro-pores, that were less than 5 urn and with low porosity, to reduce or to avoid the destruction of the micro-environment in vivo by preventing blood and cells and reducing the amount of oxygen and nutrients moving from the marrow cavity to the articulate marrow. The preliminary results after 6 weeks of implantation into 4 mm diameter osteochondral defects in the knee joints of rabbits showed that the defects with the scaffold/cells composition had bone-like or cartilage-like tissue filling the defects with smooth surface, while the defects with nothing (blank) showed only fibrous tissue. more...

One of the major obstacles in engineering thick and complex tissues while vascularizing tissues in vitro is to maintain cell viability during tissue growth and structural organization. Adipose-derived stromal (ADS) cells were used to establish a multicellular system through a cell-assembly technique. Attempts were made to control ADS cells differentiation into different targeted cell types according to their positions within an orderly 3D structure. Oil red 0 staining confirmed that the ADS cells in the structure differentiated into adipocytes with a spherical shape while immunostaining tests confirmed that the endothelial growth factor induced ADS cells on the walls of channels differentiated into mature endothelial cells and then organized into tubular structures throughout the engineered 3D structure. The endothelin-1 and nitric oxide release rules of the endothelial cells were coincidental with those in vivo. This study provides a new approach to engineer orderly endothelial vessel networks in vitro and has potential applications in adipose-tissue engineering. more...

A 3D poly(lactic acid-co-glycolic acid)/tricalcium phosphate (PLGA-TCP) composite scaffold, generated with the low-temperature deposition modeling rapid prototyping technique, was tested for its viability in a 3D cell cultivation in vitro. The aim was to find optimal cell culture conditions for the selected scaffold material and to monitor cell division, differentiation, and migration of selected cell types in this environment. In addition, the behavior and cell-matrix interactions of selected cell types were monitored as well as the biodegradation rate of the tested scaffold material. Chinese hamster ovary cells as well as a human cell line 293 epithelial cells were cultured on the scaffolds. A variety of different preconditioning protocols were deployed to prepare the scaffolds before seeding with the cells. Cell cultivations were conducted for 1–4 weeks and the coverage of the luminal surfaces was analyzed with light microscopy. Long cultivation periods were required to achieve partial coverage of the luminal surfaces of the scaffolds. Tissue engineering with 3D cell cultures and biomaterials represents a promising approach for organ manufacturing research. It may have potential for eventual on-demand high-throughput production of artificial tissues but the process has many challenges. The culture system in a well controlled bioreactor environment is discussed. more...

Assembling multitype cells and biomimic extracellular matrix materials in a single construct is a promising method to regenerate complex tissues/organs in vitro. A new double-nozzle assembling technique was used to fabricate a hybrid cell/hydrogel construct with a vascular-like network to perform as a mass exchange conduit. Using a digital model to mimic an anatomical liver structure, adipose-derived stromal cells (ADSC) were combined within a gelatin/alginate/fibrinogen hydrogel to form a vascular-like network and hepatocytes combined gelatin/alginate/chitosan were placed around it. The construct was stabilized in a thrombin/CaCl2/Na5P3O10 solution after assembly. The ADSC were induced to differentiate into endothelial-like cells with endothelial growth factor. The albumin secretion level of the embedded hepatocytes increased during the 2 weeks culture, while the levels of urea and alanine transaminase were decreased after an increasing profile. These preliminary results indicate that this double-nozzle assembling technique could be a powerful tool for fabricating complex constructs with special intrinsic/ extrinsic structures. This technology has the potential to be widely used in medical regeneration and drug screening. more...

A new double-layer conduit that combined an outer synthetic Polyurethane (PU) layer and inner natural collagen layer was fabricated via a double-nozzle low-temperature deposition manufacturing (DLDM) technology. The outer PU layer provided a mechanically stable tunnel against scar tissue invasion in vivo, while the inner collagen layer promoted Schwann cell adhesion, migration, and proliferation. Microporous structures were found in both the layers. A tight connection between the double layers was achieved by adjusting the distance between the two deposit nozzles and adjusting other processing parameters. Schwann cells from rat sciatic nerves were cultured in the layered PU-collagen conduits for one week; a significant enhancement in their retention and viability was seen compared to those made of pure PU. The poly(urethane-collagen) double layer conduit had better Schwann cell compatibility and so has a great potential use in clinical peripheral nerve repair. more...

Three-dimensional highly porous poly(DL-lactic-co-glycolic acid)/tricalcium phosphate (PLGA/TCP) scaffolds were synthesized via a rapid prototyping (RP) technique. Bovine bone morphogenetic protein (bBMP) was loaded into the biopolymer scaffolds (PLGA/TCP/bBMP). Both the PLGA/TCP scaffolds and the PLGA/TCP/bBMP composites were evaluated by scanning electron microscopy. Lumbar intervertebral body fusion at L2~3 and L4~5 levels were performed on 15 goats using one of the following graft materials: RP synthesized PLGA/TCP scaffolds (group A), PLGA/TCP/bBMP composites (group B), and autogenous iliac bone graft (group C). All animals were sacrificed 24 weeks after surgery and the spine fusions evaluated by manual palpation tests, histological analyses, and radiography. In group A, the histological analyses showed that the PLGA/TCP scaffolds were biocompatible and biodegradable; however, no new bone was found. In group B, highly cellular bone marrow between the new trabecular bone was present in the fusion mass. In group C, there was a lesser amount of new bone. Twenty-four weeks after surgery, the fusion rate of lumbar intervertebral body fusion in group A, B, and C was 10% (1/10), 80% (8/10), and 50% (5/10), respectively. The fusion rate was significantly higher in group B compared with groups of A and C (p more...

In this study, a two-step crosslinking method derived from commercial rapid prototyping equipment was used to fabricate a gradient hydrogel scaffold in vitro. This system contained two types of nozzles; one was double-nozzle unit, used for relatively simple gradient hydrogel scaffold composed of two nonmiscible hydrogel materials. The other was single nozzle that was used for mixing a gradient hydrogel scaffold composed of two types of hydrogel materials. Different types of scaffolds were formed by modifying the gradient in one of the relevant nozzles. To improve the extrusion controlling effect, accessorial parameters were introduced. A 3D gradient construct containing neuron cells and Schwann cells was fabricated and cultured for 7 days. This construct was helpful in designing a gradient mode to observe the relationship between different cells in vitro. This work has improved tissue-engineering techniques for later manufacturing of very complicated organ analogs. more...

Unique double layer polyurethane (PU)-collagen nerve guide conduits with desirable biocompatibility and mechanical properties were fabricated using a newly developed double-nozzle low-temperature deposition manufacturing (DLDM) technique. The inner collagen layer of the conduit had oriented nano-size filaments with micro-pores (pore size 20—100μm) that permitted nutrient infiltration, while the outer PU layer had micro-pores (pore size 15—20 μm) preventing fibrous tissue invasion. In vivo animal tests (n = 6) on bridging a 10 mm long peroneal nerve defect was conducted using rats. Single layer pure PU conduit (n = 6) was used as the positive control and the same size defect with no implantation (n = 2) as the negative control. Through walk track analysis as well as electrophysiological and histological evaluations of the regenerated nerves, the double layer PU-collagen conduit demonstrated better nerve repair than the controls. This new PU-collagen has the potential for significant clinical applications in peripheral nerve repair. more...

Using a cell assembly device developed in this laboratory, we coextruded adipose derived stem cells (ADSC) and gelatin/alginate hydrogel to form cubic 3D constructions (10 × 10 × 10 mm3) with regular distributed go-through pores. The ADSC grew, proliferated, and differentiated within these constructions. With the addition of basic fibroblast growth factor (bFGF), cells located on the scaffold walls differentiated into endothelial like cells while cells embedded in the hydrogel differentiated into adipose like cells. The integrity of the constructions remained for more than 60 days. This new technology enables us to construct 3D adipose tissue with blood vessel-like structures in vitro which is a significant enhancement in adipose tissue engineering and provides a better biomimic 3D model for studying cell—cell interaction, stem cell differentiation conditions and cell organization mechanisms. more...

Gelatin and gelatin/chitosan gels, crosslinked using glutaraldehyde, were previously developed as substrates for three-dimensional cell-assembly techniques. In this study, the biocompatibility and biodegradation of gelatin and gelatin/chitosan gels were evaluated following implantation in rat livers for periods up to 16 weeks. The two gels were characterized by different inflammatory responses and degradation rates. The gelatin/chitosan gel is more efficient in inducing fibrin formation and vascularization at the implant-host interface. The degrees of inflammatory reaction for the gelatin/chitosan gel were significantly stronger than the gelatin gel. Advanced biodegradation of the gelatin gels was observed. These data indicate that the gelatin gel has better liver tissue biocompatibility and a faster biodegraded rate than the gelatin/chitosan gel. more...

A novel 3D hybrid construct was developed for liver manufacturing by depositing biodegradable polyurethane (PU) and a naturally derived polymer gelatin simultaneously via a double nozzle rapid prototyping (RP) technique. A grid object was produced by precisely and simultaneously dispersing the PU and gelatin to form 3D constructs with interconnected macro-channels at a low temperature (-28°C). Micro-pores were formed by freeze-drying the constructs. The PU polymer provided mechanical support while gelatin provided accommodation for implant cells. The hydrophilicity of the hybrid constructs was between the pure PU and pure gelatin structures. The interconnected channels allow nutrients and oxygen to be supplied throughout the construct as well as provide space for the attachment of cells. The design and fabrication strategies, used to create complex physical objects directly from computer aided design (CAD) models, represent a promising technique for implantable bioartificial livers. It is anticipated that these PU-gelatin hybrid constructs will serve as a useful model for bioartificial liver manufacturing. more...

A precise control over the internal architecture was essential for manufacture of complex organs. To create vascular systems that mimic human livers, we designed and fabricated complex 3D objects with an intrinsic network of interconnected channels. A new elastomeric polyurethane, mainly based on polycaprolactone and poly(ethylene glycol) with excellent biocompatibility and tunable biodegradation properties, was used to fabricate these vascular systems using a low temperature deposition system based on the layer-by-layer manufacturing principle. A specific model was selected via computer aided design (CAD), solid free form fabrication processes are conducted under computer direction. Two example object patterns were produced by precision controlled dispensing of a biodegradable polyurethane into 3D multi-micro-tunnels with multi-micro-pores at a low temperature (-28°C). The design and fabrication strategies used to create physical objects directly from CAD models represent a promising route for the establishment of complex organ vascular systems. more...

Rapid prototyping (RP) technologies are a set of manufacturing processes that can produce very complex structures directly from computer-aided design models without structure-specific tools or knowledge. These technologies might eventually enable the manufacture of human livers to create functional substitutes for treating liver failure or dysfunctionality. However, the approaches used currently face many challenges, such as the complex branched vascular and bile ductular systems and the variety of cell types, matrices and regulatory factors involved in liver development. Here, we discuss the challenges and provide evidence for the usefulness of RP in overcoming them. more...

The objective of this experiment is to produce a novel scaffold composed of poly (lactic-co-glycolic acid) (PLGA)/β-tricalciumphosphate (β-TCP) skeleton covered with apatite/collagen sponge. BMSCs were used to evaluate the cell behavior on the hybrid scaffold. Cell morphology on the surfaces of PLGA/β-TCP skeleton and PLGA/β-TCP skeleton with apatite/collagen sponge composite coating was studied by scanning electron microscopy (SEM). Cell proliferation was assessed by cell number counting. Differentiated BMSCs function was monitored by measuring alkaline phosphates activity of the cells. These results demonstrated that the apatite/collagen sponge composite coating could improve cell proliferation and ALP activity of the hybrid scaffolds and increase its hydrophilicity after hybridization. The experiment suggested that the PLGA/β-TCP skeleton with apatite/collagen sponge composite coating is promising as a candidate 3D substrate for bone tissue engineering. more...

There is a need for rapid fabrication of tissue or organs with well-defined structures and functions in regenerative medicine. Two patterns of cell/matrix constructs containing hepatic cells, gelatin and fibrinogen were successfully created by automated rapid prototyping techniques and stabilized with thrombin. No apparent cell damage was found during the process. Mechanical characterization demonstrated that a 1:1 ratio gelatin/fibrin mixture had the greatest elasticity modulus and compressive strength. Microscopic and histological observations showed that hepatic cells were embedded in the gelatin/fibrinogen matrix and were proliferating. Immunostaining and biochemical analysis indicated that the embedded hepatocytes secreted albumin. Fibrin appears to be a favorable component for a gelatin based cell assembly matrix in that it is bioresorbable, easily manipulated, and supports in vitro cell functions. more...

There is currently interest in the use of tube-shaped nerve guides to induce regeneration of severed peripheral nerve axons, to assist nerve growth in the correct directions and to provide protection for the regenerating nerves. In the present paper, preliminary studies on the degradation and biocompatibility of a new elastomeric polyurethane (PU), based on polycaprolactone, polyethylene glycol and 1,6-hexamethyl diisocyanate. The PU elastomer was evaluated in vivo for the repair of a 12-mm femoral nerve gap in rabbits. Histological and scanning electron microscope observations were carried out at three days and then 4, 8, 10 and 12 weeks postoperation. Electrophysiological recording was performed six months postoperation. Myelinated axon regeneration was observed from four weeks after implantation. Polymer degradation was observed over the duration of the study. The results suggest that PU channels can be used for the regeneration of peripheral nerves and are suitable for tissue engineering. more...

This paper introduces a finite element model to simulate the distribution of the temperature field in the rapid ice prototyping process. In the simulations conducted, new elements representing the newly built layers on a part are activated in sequence to reflect the material adding process of layer-by-layer fabrication. The heat transfers occurring between the newly added layers, the built structure and the surroundings of the part are taken into account during the simulation. Calculations of parameters affecting the solidification of water are analyzed and compared with actual experimental results. The influences of the various process parameters on the solidification time of water during fabrication are studied based on the simulation results. The simulation results obtained are helpful in optimizing the process parameters and improving the quality of the RIP-fabricated ice parts. more...

Brain tissue engineering has now emerged as one of the most promising treatments for the traumatic brain injury. In this article, two groups of three-dimensional (3D) hydrogel structures composed of gelatin and gelatin/hyaluronan have been formed using our 3D cell assembly technique for in vivo study in rats, in order to investigate their effects in reparation of injury in the central nervous system (CNS). The structures were implanted into cortical defects created in rat brains, and their abilities to improve the brain tissue reconstruction were then evaluated. After 4, 8, 10, and 13 weeks of implantation, sections of brains were processed with NISSL staining for observing the immigration of host neural cells into the implanted materials and the degradation property of the materials. The results showed that simplex gelatin and gelatin/hyaluronan (20:1) with 3D structures both have good biocompatibility with brain tissue while gelatin/hyaluronan has a better contiguity with the surrounding tissue. Through our primary study, it seems that 3D gelatin/hyaluronan structures may be useful in brain tissue repair. more...

Tissue engineering is expected to construct complicated hominine organs composed of many different types of cells. One of the key points is the accurate controlling of scaffold material and porous morphology point by point. A new direct rapid prototyping process called low-temperature deposition manufacturing (LDM) was proposed to fabricate scaffolds. The new process integrated extrusion/jetting and phase separation and therefore could fabricate scaffolds with hierarchical porous structures creating a wonderful environment for the growth of new tissue. The interconnected computer-designed macropores allow cells in the new tissue to grow throughout the scaffold. Also, the parameter-controlled micropores let nutrition in and metabolic wastes out. The macrocellular morphology, microcellular morphology, porosity, and mechanical properties of the poly(alpha-hydroxy acid)-TCP composite scaffolds prepared by the proposed method are investigated. These scaffolds with high controllability would potentially play an important role in tissue engineering. LDM could also be combined with multinozzle deposition or cell deposition to exactly control materials or cells point by point. This might bring a breakthrough to the engineered fabrication of complicated organs. more...

The functional realization is the most important problem in vascular tissue engineering. The small-caliber blood vessel substitutes are prone to thrombi, which results in functional loss of blood vessels. However, this is probably due to the imperfection of endothelial layer in the substitutes. In this study, MSCs were seeded on a series of porous PLGA films with various porosity and pore size made by sodium chloride (NaCl) particulate leaching, and cell proliferation on each film was inspected. The film made of the 75% (w/w) particulate proportion and 30–50 μm pore size maximized the proliferation rate and was chosen as the scaffolds for the differentiation of MSCs into endothelial cells. The induced cells expressed endothelial cells specific Flk-1, VIII factor and CD34, possessed endothelial cells specific Weible-palade (W-P) body, and had the abilities of ingesting low density lipoprotein and secreting prostacyclin (PGI2). The results show that MSCs not only have the ideal biological compatibility with the porous PLGA films, but also have the potency of differentiating into functional endothelial cells, which should facilitate the endothelialization in vascular tissue engineering. more...

A recent US-China National Science Foundation-sponsored workshop on biomanufacturing reviewed the state-of-the-art of an array of new technologies for producing scaffolds for tissue engineering, providing precision multi-scale control of material, architecture, and cells. One broad category of such techniques has been termed solid freeform fabrication. The techniques in this category include: stereolithography, selected laser sintering, single- and multiple-nozzle deposition and fused deposition modeling, and three-dimensional printing. The precise and repetitive placement of material and cells in a three-dimensional construct at the micrometer length scale demands computer control. These novel computer-controlled scaffold production techniques, when coupled with computer-based imaging and structural modeling methods for the production of the templates for the scaffolds, define an emerging field of computer-aided tissue engineering. In formulating the questions that remain to be answered and discussing the knowledge required to further advance the field, the Workshop provided a basis for recommendations for future work. more...