A permeability measurement system for tissue engineering scaffolds

A three-dimensional fractal permeability model for granular porous media incorporating pore roughness.

The spatial distribution of subsurface parameters such as permeability are increasingly relevant for regional to global climate, land surface, and hydrologic models that are integrating groundwater dynamics and interactions. Despite the large fraction of unconsolidated sediments on Earth's surface with a wide range of permeability values, current global, high‐resolution permeability maps distinguish solely fine‐grained and coarse‐grained unconsolidated sediments. Representative permeability values are derived for a wide variety of unconsolidated sediments and applied to a new global map of unconsolidated sediments to produce the first geologically constrained, two‐layer global map of shallower and deeper permeability. The new mean logarithmic permeability of the Earth's surface is −12.7 ± 1.7 m2 being 1 order of magnitude higher than that derived from previous maps, which is consistent with the dominance of the coarser sediments. The new data set will benefit a variety of scientific applications including the next generation of climate, land surface, and hydrology models at regional to global scales.

Characterization of mass transfer properties was achieved in the longitudinal, radial, and tangential directions for four Australian hardwood species: spotted gum, blackbutt, jarrah, and messmate. Measurement of mass transfer properties for these species was necessary to complement current vacuum drying modeling research. Water-vapour diffusivity was determined in steady state using a specific vapometer. Permeability was determined using a specialized device developed to measure over a wide range of permeability values. Permeability values of some species and material directions were extremely low and undetectable by the mass flow meter device. Hence, a custom system based on volume evolution was conceived to determine very low, previously unpublished, wood permeability values. Mass diffusivity and permeability were lowest for spotted gum and highest for messmate. Except for messmate in the radial direction, the four species measured were less permeable in all directions than the lowest published figures, demonstrating the high impermeability of Australian hardwoods and partly accounting for their relatively slow drying rates. Permeability, water-vapour diffusivity, and associated anisotropic ratio data obtained for messmate were extreme or did not follow typical trends and is consequently the most difficult of the four woods to dry in terms of collapse and checking degradation.

In this study, we have extended and applied the diffuse source upscaling methodology to sandstone and carbonate pore network models in order to evaluate their effective transmissibility and permeability. The proposed method allows us to find transmissibility values for sub-volumes of the pore network during the transition from transient to pseudo steady state flow. The pore network models utilize a lattice grid construction, consisting of nodes and bonds that connect the nodes. The Eikonal equation is solved on the lattice using Dijkstra's method to obtain the diffusive time of flight, which is then used to model the transition from transient to pseudo steady state flow. The solution uses the concept of a transient drainage volume, which increases with time as pressure propagates into the nodes of the pore network. The diffuse source upscaling approach allows us to calculate the transmissibility of the drainage volume as it increases with time. The calculated results can be compared to the analytical results, where the sample is assumed to be internally homogeneous. A synthetic model was created to illustrate how the calculated lattice model and the analytic reference results compare for a homogeneous model. The comparison of the carbonate analytical and calculated results showed that there exists a high degree of internal heterogeneity while the more homogeneous sandstone model showed a close agreement with the synthetic model. For both samples, the late time pseudo steady state permeability showed a good correspondence with other permeability evaluations. The diffuse source method has more directional information available than the steady state method. Hence, the new method of analysis can be viewed as an extension of pseudo steady state concepts of permeability to transient flow, with increased spatial resolution corresponding to the transient drainage volume. Instead of obtaining only the steady state transmissibility from a pore network model, the diffuse source approach provides us with the ability to better characterize the internal heterogeneity of a model and to explain the wide range of permeability values obtained by other approaches.

Drainage and Imbibition CO2/Brine Relative Permeability Curves at in Situ Conditions for Sandstone Formations in Western Canada

PurposeThis paper details the derivation of the mathematical formulae of a novel system for designing and fabricating tissue engineering (TE) scaffolds.Design/methodology/approachThis work combines the unique capability of rapid prototyping (RP) techniques with computer‐aided design (CAD) and imaging software to design and fabricate customised scaffolds that are not only consistent in microstructure but also readily reproducible. The prototype system, called the computer‐aided system for tissue scaffolds (CASTS), has a parametric library of design units which can be assembled into scaffold structures through an in‐house algorithm. An additional module, the slicing routine, has also been added to improve the functionality of the system. To validate the system, scaffolds designed were fabricated using a powder‐based RP technique called selective laser sintering (SLS).FindingsIt is shown that the CASTS can be used to exploit CAD and medical imaging techniques together with RP systems to produce viable scaffolds that can be customised for various applications to suit the needs of individual patients.Research limitations/implicationsFurther research is being done to examine the internal microstructure of the scaffolds and to determine the mechanical properties, as well as to study the inter‐relationship between cell proliferation and the pore shapes of the scaffolds.Originality/valueThe crucial role of scaffolds in TE has long been recognised. Successful TE scaffolds should have controllable characteristics such as pore size, porosity, and surface area to volume ratio as well as interconnectivity within the scaffolds. Much work has been carried out to produce such TE scaffolds with varying degrees of success. One major drawback is that the resultant TE scaffolds are not readily reproducible. The potential of CASTS lies in its ability to design and fabricate scaffolds with varying properties through the use of different unit cells and biomaterials to suit different applications.

Bioreactors are widely used in tissue engineering as a way to distribute nutrients within porous materials and provide physical stimulus required by many tissues. However, the fluid dynamics within the large porous structure are not well understood. In this study, we explored the effect of reactor geometry by using rectangular and circular reactors with three different inlet and outlet patterns. Geometries were simulated with and without the porous structure using the computational fluid dynamics software Comsol Multiphysics 3.4 and/or ANSYS CFX 11 respectively. Residence time distribution analysis using a step change of a tracer within the reactor revealed non-ideal fluid distribution characteristics within the reactors. The Brinkman equation was used to model the permeability characteristics with in the chitosan porous structure. Pore size was varied from 10 to 200 microm and the number of pores per unit area was varied from 15 to 1,500 pores/mm(2). Effect of cellular growth and tissue remodeling on flow distribution was also assessed by changing the pore size (85-10 microm) while keeping the number of pores per unit area constant. These results showed significant increase in pressure with reduction in pore size, which could limit the fluid flow and nutrient transport. However, measured pressure drop was marginally higher than the simulation results. Maximum shear stress was similar in both reactors and ranged approximately 0.2-0.3 dynes/cm(2). The simulations were validated experimentally using both a rectangular and circular bioreactor, constructed in-house. Porous structures for the experiments were formed using 0.5% chitosan solution freeze-dried at -80 degrees C, and the pressure drop across the reactor was monitored.

As the tissue engineering scaffolds, the pore structure and condensed structure of silk fibroin scaffolds should be adjusted and controlled. In this study, Antheraea pernyi/Bombyx mori (A. p/B. m) silk fibroin blend scaffolds were prepared by freeze-drying. The influence of blend ratios on the pore structure and condensed structure of the scaffolds was investigated. The results showed that the average pore diameter of the blend scaffolds changed from 56 to 326 μm. Due to the difference of properties and the macromolecules aggregation status of two silk fibroin solutions, the pore diameter, content of α-helix and crystallinity of the scaffolds decreased with the increasing of the proportion of B. m silk fibroin. By adjusting the blend ratios, the pore structure and condensed structure of A. p/B. m silk fibroin blend scaffolds could be controlled.

Arc welding is still the dominant welding process in industry and a major challenge in this context is robotisation and automation, which require sensor based adaptive control. Therefore, the present paper describes the application of neural network technology for gas metal arc welding control. A system based on a multilayer feed forward network has been developed for modelling and online adjustment of welding parameters appropriate to guarantee a certain degree of quality in the field of butt joint welding with full penetration when the gap varies during the welding process. It has been shown that operating in an open loop, the developed system can tackle gap variations relevant to many welding situations. However, to improve robustness to uncertainties, disturbances, etc. a closed loop control system based on a 'single neuron self-learning proportional, sum, and differential' control algorithm, which compensates for non-monitorial changes in welding conditions by feeding back information on the realised front bead geometry, has also been developed and tested. The Levenberg–Marquardt algorithm for non-linear least squares has been used with a back propagation algorithm for training the neural networks, and a Bayesian regularisation technique has been successfully applied for minimising the risk of inexpedient overtraining.

Porous scaffolds for dermal tissue engineering were fabricated by freeze-drying a mixture of chitosan and gelatin (CG) solutions. Different crosslinking agents including glutaraldehyde, 1-(3-dimethylaminopropyl)-3-ethyl-carbodimide hydrochloride (EDC), and genipin were used to crosslink the scaffolds and improve their biostability. The porous structure and mechanical properties were determined for the scaffolds. The proliferation of human fibroblasts in the scaffolds was analyzed. It was found that EDC crosslinked scaffolds had the greatest amount of cells after four days. EDC crosslinked CG scaffolds had tensile modulus in a dry state and compressive modulus in a wet state similar to commercial collagen wound dressing. They also showed appropriate pore size, high water absorption, and good dimensional stability during cell culture. When human fibroblasts were seeded on acellular porcine dermis (APD), acellular human dermis (AHD), and CG scaffolds for 3D cell culture, they were well-distributed in the centre of the CG scaffolds but stayed only on the superficial layer of APD or AHD after seven days. A gelatin-based bioglue was applied to the CG scaffolds where the keratinocytes were seeded to mimic epidermal structure. After 14 days, the bioglue degraded and keratinocytes grew to form monolayers on the scaffolds. This study showed that CG scaffolds crosslinked by EDC and seeded with human fibroblasts could serve as dermal constructs, while the bioglue coating seeded with keratinocytes could serve as an epidermal construct. Such a combination could help regenerate skin with integrated dermal and epidermal layers and a have potential use in tissue-engineered skin.

In this work, the fabrication and in vitro degradation of porous fumarate-based/alumoxane nanocomposites were evaluated for their potential as bone tissue engineering scaffolds. The biodegradable polymer poly (propylene fumarate)/propylene fumarate-diacrylate (PPF/PF-DA), a macrocomposite composed of PPF/PF-DA and boehmite microparticles, and a nanocomposite composed of PPF/PF-DA and surface-modified alumoxane nanoparticles were used to fabricate porous scaffolds by photo-crosslinking and salt-leaching. Scaffolds then underwent 12 weeks of in vitro degradation in phosphate buffered saline at 37 degrees C. The presence of boehmite microparticles and alumoxane nanoparticles in the polymer inhibited scaffold shrinkage during crosslinking. Furthermore, the incorporation of alumoxane nanoparticles into the polymer limited salt-leaching, perhaps due to tighter crosslinking within the nanocomposite. Analysis of crosslinking revealed that the acrylate and overall double bond conversions in the nanocomposite were higher than in the PPF/PF-DA polymer alone, though these differences were not significant. During 12 weeks of in vitro degradation, the nanocomposite lost 5.3% +/- 2.4% of its mass but maintained its compressive mechanical properties and porous architecture. The addition of alumoxane nanoparticles into the fumarate-based polymer did not significantly affect the degradation of the nanocomposite compared with the other materials in terms of mass loss, compressive properties, and porous structure. These results demonstrate the feasibility of fabricating degradable nanocomposite scaffolds for bone tissue engineering by photo-crosslinking and salt-leaching mixtures of fumarate-based polymers, alumoxane nanoparticles, and salt microparticles.

Cartilage is a tissue with limited repair capacity and also sparse population of cells entrapped within a dense extracellular matrix, therefore, delivery of the cells to site of damaged cartilage can improve its healing potential. Synthetic biomaterials such as poly (d,l-lactide-co-glycolide) (PLGA) have been used as both preformed or injectable scaffolds in tissue engineering in order to carry and keep cells in the site of injury with minimal side effects. The injectable biocompatible polymeric scaffolds can reach to effected area via minimally invasive injection without need to open the joint, less painful approach and also having possibility to fill complicated shape defects. In this study, it was hypothesized that PLGA solved in n-methyl pyrrolidine (NMP) may act as a proper carrier for cell delivery to the site of the damage and also supports their growth. The results of in vitro assays including both live/dead (AO/PI) and MTT showed the majority of the cells were remained alive between 3 up to 21 days, respectively. The amount of resealed GAG from the mesenchymal stem cells (MSCs) which were in contact with both PLGA and alginate constructs (used as control) indicated that for day 7 MSCs in contact with alginate secreted more GAG (3.45 ± 0.453 µg/mL for alginate and 2.36 ± 0.422 µg/mL for PLGA matrices), but at longer times (21 days) cells in contact with PLGA elicited more GAG (6.26 ± 0.968 µg/mL for alginate and 8.47 ± 0.871 µg/mL for the PLGA matrices). Sol–gel systems comprising PLGA, NMP, and cells as well as alginate/cells were subcutaneously injected into four nude mice (each mouse had three injection sites). PLGA/NMP was solidify immediately and formed an interconnecting 3-D porous structure that allowed body fluid to penetrate through them. In vivo evaluation showed that PLGA/NMP scaffolds could support injected cells as a fibrocartilage tissue was formed after 6 months of injection. We found that PLGA/NMP system might be a proper minimally invasive therapeutics option for cartilage repair.

Tissue engineering (TE) is a modern approach to improve or restore tissues that has been diseased or damaged by combining the factors in growth signaling and appropriate cells to form compatible biomaterial scaffold. Bone repair has been a major global health challenge in recent decades. Bone transplantation is widely used as an effective clinical treatment for this purpose. However, there are several serious issues with transplantation, including a shortage of autologous bone, immune rejection, the risk of virus transmission with allogeneic bone, and postoperative complications. In recent years, scaffolds for bone tissue engineering have emerged as a promising alternative for bone repair. These scaffolds have porous structures that mimic the extracellular matrix, which can enhance the migration, proliferation, and differentiation of osteoblasts. This process accelerates the repair of bone defects.The usage of bioactive materials has become important tool in tissue engineering and regenerative medicine application as they are to mimic tissues mechanically, chemically, and physically. Polymeric scaffold provides numerous advantageous for tissue engineering since the physicochemical properties such as porosity, pore size, solubility and biocompatibility can be controlled. Therefore, research works were carried out to explore the potential of various materials in producing bone scaffolds in tissue engineering technology. As for both newcomers and experts, this review paper will help them to find information on various types of biomaterials in imparting or enhancing their biological properties such as biocompatibility, bacterial inhibition, tissue regeneration and cell growth, bio inertness, bioactive and resorbability for bone scaffold tissue engineering application.

ABSTRACTPoly(caprolactone‐co‐glycolide)‐co‐poly(ethylene gylcol) copolymers (PCEG) with various composition were synthesized by copolymerization of GA, CL, and PEG. PCEG microspheres were fabricated by oil‐in‐water (o/w) emulsion and solvent‐evaporation technique. Effect of chemical composition on hydrophilicity, crystallinity, and degradation of the PCEG was investigated. It was demonstrated that morphology structure of the microspheres was greatly influenced by chemical composition and hydrophilicity of the PCEG polymer. PCEG microspheres could change from a smooth structure to a regular porous structure and an irregular structure. Moreover, the pore size of them increased with increment of PEG content and length. Cell attachment and growth on the PCEG microspheres were evaluated by using mouse NIH 3T3 fibroblasts as model cells in vitro. The result showed that the PCEG microspheres with large porous structure were more favorable for cell attachment and growth. Thus the PCEG microspheres with rapid degradation rate and large porous structure possess potential use as injectable scaffolds in tissue engineering. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 132, 42861.

The structures of scaffolds for tissue engineering have significant effects on the seeding, migration, and proliferation of the tissue cells. Fibrous scaffolds consisting of microfibers or nanofibers have attracted increasing attention and applications in tissue engineering because of their high porosity and surface area and their ability to direct cell growth and alignment. However, water-soluble and hydrophilic polymeric microfibers and nanofibers lose their fibrous morphology in aqueous conditions such as body fluid and culture media. Cross-linking has been proven an effective method for stabilizing fibrous structure and improving mechanical properties of the fibrous scaffolds. In this article, we will review the current technologies for fabricating cross-linked fibrous scaffolds by the combination of electrospinning and different cross-linking methods including chemical, physical and photo-cross-linking. Their effects on solvent resistance, biocompatibility, mechanical properties, and cell viability will be discussed. Chemical cross-linking with nontoxic cross-linkers such as genipin and the reactive electrospinning with in-situ photo-cross-linking are promising new technologies to fabricate novel nanofibrous scaffolds with enhanced solvent resistance and mechanical strength as well as tunable biodegradation property. Keywords: Electrospinning, nanofibers, chemical cross-linking agent, physical cross-linking, photo-cross-linking, solvent resistance, biocompatibility, mechanical properties, hydrophilic, biochemistry.