Microstructure Of Scaffolds Research Articles

Cell-free scaffold from jellyfish Cassiopea andromeda (Cnidaria; Scyphozoa) for skin tissue engineering.

Disruption of the continuous cutaneous membrane in the integumentary system is considered a health problem of high cost for any nation. Several attempts have been made for developing skin substitutes in order to restore injured tissue including autologous implants and the use of scaffolds based on synthetic and natural materials. Current biomaterials used for skin tissue repair include several scaffold matrices types, synthetic or natural, absorbable, degradable or non-degradable polymers, porous or dense scaffolds, and cells capsulated in hydrogels or spheroids systems so forth. These materials have advantages and disadvantages and its use will depend on the desired application. Recently, marine organisms such as jellyfish have attracted renewed interest, because both its composition and structure resemble the architecture of human dermic tissue. In this context, the present study aims to generate scaffolds from Cassiopea andromeda (C. andromeda), with application in skin tissue engineering, using a decellularization process. The obtained scaffold was studied by infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), differential scanning calorimetry analysis (DSC), and scanning electron microscopy (SEM). Crystal violet staining and DNA quantification assessed decellularization effectiveness while the biocompatibility of scaffold was determined with human dermic fibroblasts. Results indicated that the decellularization process reduce native cell population leading to 70% reduction in DNA content. In addition, SEM showed that the macro and microstructure of the collagen I-based scaffold were preserved allowing good adhesion and proliferation of human dermic fibroblasts. The C. andromeda scaffold mimics human skin and therefore represents great potential for skin tissue engineering.

Nano-pearl powder/chitosan-hyaluronic acid porous composite scaffold and preliminary study of its osteogenesis mechanism.

Bone tissue engineering using osteoinductive scaffolds has evolved into a promising approach for bone regeneration. Pearl powder has recently gained interest in bone regeneration due to their bioactive characteristics and favorable mechanical properties. In order to mimic bone tissue structurally and compositionally, chitosan-hyaluronic acid (C-HA) scaffolds containing nano-pearl powder (NPP) were fabricated in current study by using freeze-drying method. The microstructure, porosity, hydrophilia, and mechanical property of scaffolds were studied by scanning electron microscopy (SEM), mercury porosimeter, contact angles, and universal material experiment machine respectively. The crystal form of NPP, which was packed in scaffolds, was tested by X-ray diffraction (XRD), and the interaction between three constituents was studied by Fourier transformed infrared (FTIR). In the other hand, the biocompatibility, osteogenic characteristics, and osteogenic related gene expression of scaffolds were examined by cell counting kit-8 (CCK-8), alkaline phosphatase activity (ALP), RT-qPCR, and Western blotting. The results revealed that the NPP was successfully incorporated in the C-HA scaffolds. The hydrophilia and mechanical properties of scaffolds increased with NPP content, whereas the pore morphology was disturbed, especially for 25% scaffold. The scaffolds had a high porosity between 89% and 93%, and decreased slightly with the increase of NPP. Cell culture tests indicated that scaffolds with higher NPP proportion were beneficial for the proliferation and differentiation of MC3T3-E1 cells, and scaffolds with 10wt% and 25wt% nano-pearl powder were most effective. The differentiation might be promoted by upregulating the expression of Col αI, OCN, OPN and Runx2 genes. Therefore, the nano-pearl powder/chitosan-hyaluronic acid (NPP/C-HA) scaffolds may serve as a promising biomaterial for bone tissue engineering.

Aliphatic Chain Modification of Collagen Type I: Development of Elastomeric, Compliant, and Suturable Scaffolds.

Collagen type I is one of the most suitable natural biomaterials for constructing tissue-engineering scaffolds. Despite their biocompositional similarities to physiological tissues, these scaffolds lack host specific and matching mechanical properties. While it is possible to enhance their stiffness by cross-linking, it often compromises their abilities to expand or strain under minimal stress, that is, compliance (inverse of stiffness). Here, we report a simple, inexpensive, cross-linking- and elastin-free collagen-based material composition for developing elastomeric scaffolds that are highly compliant, soft yet strong, and suturable, therefore, clinically attractive. Our strategy utilizes room-temperature modification of collagen type I scaffolds with linear aliphatic chains of various lengths (C7-C18). In particular, dodecenylsuccinic anhydride (size: C12, DDSA) modified scaffolds elongated up to 400% of its initial length compared to only ∼20% for collagen-control within the applied tensile stress of 0.2 MPa without breaking. Furthermore, the suture retention strength value increased to 60 g-force from 30 g-force for collagen control. We confirmed that the C12-modified material remained structurally stable at the physiological temperature (37 °C) with a tan δ value of ∼0.3, similar to collagen control; however, tan δ increased sharply for C12-modified collagen above 42 °C, compared to 59 °C for collagen control. To understand the mechanism of hyperextensibility, we studied the morphology of the resultant material by transmission electron microscopy (TEM), which showed an altered microstructure of C12-modified collagen scaffolds. While the partially C12-modified sample had a mixture of typical collagen type I triple helix and diffused gelatinized random coil-like configuration, the fully modified samples showed thick wrinkled and entangled ribbon-like microstructures, which was different than that of thermally denatured gelatin. We further confirmed that the resultant material allowed cell growth in vitro and in vivo in a subcutaneous mouse model.

Fabrication and Characterization of Poly Lactic Acid Scaffolds by Fused Deposition Modeling for Bone Tissue Engineering

Three-dimensional porous poly-lactic acid (PLA) scaffold was fabricated using fused deposition modeling (FDM) method including 30%, 50% and 70% nominal porosity. Study of phases in initial polymeric material and printed scaffolds was done by X-ray diffraction (XRD), and no significant phase difference was observed due to the manufacturing process, and the poly-lactic acid retains its crystalline properties. The results of the mechanical properties evaluation by the compression test show that the mechanical properties of the scaffold have decreased signifcantly with increasing the porosity of scaffold. The microstructure of scaffolds were studied by scanning electron microscope (SEM), showing that the pores had a regular arrangement and their morphology changed with porosity change. The mechanical properties of the poly-lactic acid scaffolds printed using fused deposition modeling, can be adapted to the surrounding tissue, by porosity change.

Effect of sintering temperature on microstructure of TiO2 scaffold

Due to an excellent biocompatibility of titanium dioxide (TiO2), it is promising to use as scaffolds for inducing bone formation. The well-interconnected pore scaffolds were fabricated by sponge replication method in order to promote osteoblast ingrowth and vascularization. The viscosity of the slurry was adjusted by addition of calcium chloride (CaCl2) which led to more uniformity and densification. The effects of sintering temperatures on microstructure were analyzed by scanning electron microscope (SEM) and microcomputed tomography (Micro-CT). Our experiments showed that the higher sintering temperature increased the grain size and more uniformity of the scaffold. Furthermore, the struts became more rounded and microcracks were not observed which probably correlated to the higher density of scaffold. Thus, it is suggested that optimization of sintering temperatures might allow better control of grain growth and result in more microstructural uniformity.

FGF-2-Induced Human Amniotic Mesenchymal Stem Cells Seeded on a Human Acellular Amniotic Membrane Scaffold Accelerated Tendon-to-Bone Healing in a Rabbit Extra-Articular Model.

Background FGF-2 (basic fibroblast growth factor) has a positive effect on the proliferation and differentiation of many kinds of MSCs. Therefore, it represents an ideal molecule to facilitate tendon-to-bone healing. Nonetheless, no studies have investigated the application of FGF-2-induced human amniotic mesenchymal stem cells (hAMSCs) to accelerate tendon-to-bone healing in vivo. Objective The purpose of this study was to explore the effect of FGF-2 on chondrogenic differentiation of hAMSCs in vitro and the effect of FGF-2-induced hAMSCs combined with a human acellular amniotic membrane (HAAM) scaffold on tendon-to-bone healing in vivo. Methods In vitro, hAMSCs were transfected with a lentivirus carrying the FGF-2 gene, and the potential for chondrogenic differentiation of hAMSCs induced by the FGF-2 gene was assessed using immunofluorescence and toluidine blue (TB) staining. HAAM scaffold was prepared, and hematoxylin and eosin (HE) staining and scanning electron microscopy (SEM) were used to observe the microstructure of the HAAM scaffold. hAMSCs transfected with and without FGF-2 were seeded on the HAAM scaffold at a density of 3 × 105 cells/well. Immunofluorescence staining of vimentin and phalloidin staining were used to confirm cell adherence and growth on the HAAM scaffold. In vivo, the rabbit extra-articular tendon-to-bone healing model was created using the right hind limb of 40 New Zealand White rabbits. Grafts mimicking tendon-to-bone interface (TBI) injury were created and subjected to treatment with the HAAM scaffold loaded with FGF-2-induced hAMSCs, HAAM scaffold loaded with hAMSCs only, HAAM scaffold, and no special treatment. Macroscopic observation, imageological analysis, histological assessment, and biomechanical analysis were conducted to evaluate tendon-to-bone healing after 3 months. Results In vitro, cartilage-specific marker staining was positive for the FGF-2 overexpression group. The HAAM scaffold displayed a netted structure and mass extracellular matrix structure. hAMSCs or hAMSCs transfected with FGF-2 survived on the HAAM scaffold and grew well. In vivo, the group treated with HAAM scaffold loaded with FGF-2-induced hAMSCs had the narrowest bone tunnel after three months as compared with other groups. In addition, macroscopic and histological scores were higher for this group than for the other groups, along with the best mechanical strength. Conclusion hAMSCs transfected with FGF-2 combined with the HAAM scaffold could accelerate tendon-to-bone healing in a rabbit extra-articular model.

Study on antibacterial properties and cytocompatibility of EPL coated 3D printed PCL/HA composite scaffolds.

Biomaterial scaffolds play a critical role in bone tissue engineering. Moreover, 3D printing technology has enormous advantage in the manufacture of bioengineering scaffolds for patient-specific bone defect treatments. In order to provide an aseptic environment for bone regeneration, ε-poly-l-lysine (EPL), an antimicrobic cationic polypeptide, was used for surface modification of 3D printed polycaprolactone/hydroxyapatite (PCL/HA) scaffolds which were fabricated by fused deposition modeling (FDM) technology. The scaffold morphology and micro-structure were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transform infrared spectroscopy (FT-IR). The release profile surface roughness, open porosity, and mechanical properties of the scaffolds were evaluated. Cell adhesion, proliferation, differentiation potential and antibacterial properties were also examined. As a result, 3D printed PCL/HA scaffolds with interconnected pores showed a slightly rough surface and improved mechanical properties due to adding hydroxyapatite (HA) particles. After being modified by EPL, favorable biocompatibility and osteoconductivity of ε-poly-l-lysine/polycaprolactone/hydroxyapatite (EPL/PCL/HA) scaffolds were observed. Moreover, antibacterial activity of the EPL/PCL/HA scaffolds was apparent. As a consequence, the EPL/PCL/HA scaffolds had great potential for bone regeneration and prevention of infections. This would yield a patient-specific bioactive and antibacterial composite scaffold for advanced bone tissue engineering applications.

Hydroxyapatite/silk fibroin composite biomimetic scaffold for dental pulp repair

Dental pulp repair is a difficult clinical problem. In the present study, the authors aimed to mimic the extracellular matrix of dental pulp tissue structurally and compositionally. Nanofibrous silk fibroin (SF) scaffolds containing hydroxyapatite (HAp) nanoparticles were fabricated by using the freeze-drying approach. Rod-shaped HAp was successfully embedded in the composite scaffold, the diameter of which was about 100–200 nm as shown by transmission electron microscopy analysis. The three-dimensional microstructure of the composite scaffold prepared in various ratios of HAp to SF was observed by scanning electron microscopy and the pore size of the optimal scaffold was about 30–120 μm. Meanwhile, the hemocompatibility of the composite scaffolds was evaluated based on their impact on the clotting function by way of activated partial thromboplastin time, prothrombin time and thromboelastographic assays. The scaffolds possessed a low hemolysis rate of red blood cells. Furthermore, cell culture tests using dental pulp stem cells found that the scaffolds had good biocompatibility. There biomimetic HAp/SF composite scaffolds may serve as a promising biomaterial for dental pulp repair.

Effect of TiO2 doping on degradation rate, microstructure and strength of borate bioactive glass scaffolds.

A titanium-containing borate glass series based on the system (52-X) B2O3-12CaO-6P2O5-14Na2O-16ZnO-XTiO2 with X varying from 0, 5 and 15 mol% of TiO2 incorporated, identified as BRT0, BRT1 and BRT3, respectively, were used in this study. Scaffolds (pore sizes, 165-230 μm and porosity, 53.51-69.51%) were prepared using a polymer foam replication technique. BRT3 scaffolds exhibited higher compressive strength (7.16 ± 0.22 MPa) when compared to BRT0 (6.02 ± 0.47 MPa) and BRT1 (5.65 ± 0.28 MPa) scaffolds with lower, or no, TiO2 content. The solubility of the scaffolds decreased as the TiO2 content increased up to 15 mol% when samples of each scaffold were immersed in DI water and the pH of all these extracts went up from 7.0 to 8.5 in 30 days. The cumulative ion release from the scaffolds showed significant difference with respect to TiO2 content; addition of 5 mol% TiO2 at the expense of borate (B2O3) decreased the ion release remarkably. Furthermore, it was found that for all three scaffolds, cumulative ion release increased with incubation time. The results indicate that the degradation rates and compressive strengths of borate bioactive glass scaffolds could be controlled by varying the amount of TiO2 incorporated, confirming their potential as scaffolds in TKA and rTKA.

A bioinspired 3D shape olibanum-collagen-gelatin scaffolds with tunable porous microstructure for efficient neural tissue regeneration.

There are a number of procedures for regeneration of injured nerves; however, tissue engineering scaffolds seems to be a promising approach for recovery of the functionality of the injured nerves. Consequently, in this study, olibanum-collagen-gelatin scaffolds were fabricated by freeze-cast technology. For this purpose, the olibanum and collagen were extracted from natural sources. The effect of solidification gradient on microstructure and properties of scaffolds was investigated. Scanning electron microscopy micrographs showed the formation of lamellar-type microstructure in which the average pore size reduced with an increase in freezing rate. According to the results, the prepared scaffolds at lower freezing rate showed a slight reduction in mechanical strength while the swelling and biodegradation ratio were increased due to the presence of larger pores and unidirectional channels. The composition of scaffolds and oriented microstructure improved cellular interaction. In addition, scaffolds with lower freezing rate exhibited promising results in terms of adhesion, spreading, and proliferation. In brief, the synthesized scaffolds at lower solidification rate have the potential for more in vitro and in vivo analyses to regeneration of neural defects.

Engineered Fibrillar Fibronectin Networks as Three-Dimensional Tissue Scaffolds.

Extracellular matrix (ECM) proteins, and most prominently, fibronectin (Fn), are routinely used in the form of adsorbed pre-coatings in an attempt to create a cell-supporting environment in both two- and three-dimensional cell culture systems. However, these protein coatings are typically deposited in a form which is structurally and functionally distinct from the ECM-constituting fibrillar protein networks naturally deposited by cells. Here, the cell-free and scalable synthesis of freely suspended and mechanically robust three-dimensional (3D) networks of fibrillar fibronectin (fFn) supported by tessellated polymer scaffolds is reported. Hydrodynamically induced Fn fibrillogenesis at the three-phase contact line between air, an Fn solution, and a tessellated scaffold microstructure yields extended protein networks. Importantly, engineered fFn networks promote cell invasion and proliferation, enable in vitro expansion of primary cancer cells, and induce an epithelial-to-mesenchymal transition in cancer cells. Engineered fFn networks support the formation of multicellular cancer structures cells from plural effusions of cancer patients. With further work, engineered fFn networks can have a transformative impact on fundamental cell studies, precision medicine, pharmaceutical testing, and pre-clinical diagnostics.

(Invited) Electrode Engineering of Solid-Oxide Electrochemical Cells at National Energy Technology Laboratory

The National Energy Technology Laboratory (NETL) Solid Oxide Fuel Cell (SOFC) Team performs fundamental SOFC technology evaluation, enhances existing SOFC technology, and develops advanced SOFC concepts in support of the U.S. Department of Energy SOFC Program. Program targets include a reduction in performance degradation to 0.2% per 1000 hours and a system cost of $900 per kilowatt. Research and development is essential to meet these targets. Research efforts are broadly focused on an investigation of cell and stack degradation, electrode engineering, grid integration challenges, and system analysis. The research approach is targeted to specifically address SOFC program technology development goals, especially regarding reducing stack costs, increasing cell efficiency, and increasing cell reliability and robustness. The goal of these efforts is to transfer technology that facilitates commercial acceptance of SOFC technology. This is accomplished through close collaboration with SOFC commercial developers, national laboratories, and academic institutions. NETL system-level analysis has shown that a critical consideration for reducing the cost of SOFC technology is the enhancement of electrode performance and longevity through materials and microstructure engineering. Within this scope is the special consideration of cell production costs and operating temperature. Specifically, at NETL, nano-electrocatalyst infiltrations have been a successful operation by scaling up the patented technology to a commercially-relevant scale, partnering with industrial manufacturers. The effort has continued to the construction of a scaffold microstructure that is optimized for surface modification and the development of gel-derived high surface area electrodes. Electrode materials selection has been made through a computational approach that uses electronic structure and energetics in conjunction with thermodynamics and statistical physics, identifying multicomponent oxides with high oxygen reduction reaction activity and stability. Highly reliable electrical conductivity relaxation analysis confirmed the predicted electrode materials’ superior surface exchange property when compared to the state-of-the-art lanthanum strontium cobalt ferrite. The developed electrode engineering techniques have been applied for reversible solid-oxide cell operation as well as single mode solid-oxide cells to stabilize electrodes while maintaining improved performance and longevity.

Simultaneous elastic shape optimization for a domain splitting in bone tissue engineering

This paper deals with the simultaneous optimization of a subset O 0 of some domain Ω and its complement O 1 = Ω ∖ O 0 ¯ both considered as separate elastic objects subject to a set of loading scenarios. If one asks for a configuration which minimizes the maximal elastic cost functional both phases compete for space since elastic shapes usually get mechanically more stable when being enlarged. Such a problem arises in biomechanics where a bioresorbable polymer scaffold is implanted in place of lost bone tissue and in a regeneration phase, new bone tissue grows in the scaffold complement via osteogenesis. In fact, the polymer scaffold should be mechanically stable to bear loading in the early stage regeneration phase and at the same time, the new bone tissue grown in the complement of this scaffold should as well bear the loading. Here, this optimal subdomain splitting problem with appropriate elastic cost functionals is introduced and the existence of optimal two-phase configurations is established for a regularized formulation. Furthermore, based on a phase-field approximation, a finite-element discretization is derived. Numerical experiments are presented for the design of optimal periodic scaffold microstructure.

Multiscale constitutive model with progressive recruitment for nanofibrous scaffolds

Biomedical applications need tailor-made scaffolds that exhibit biomimetic mechanical properties. In this context, electrospinning has emerged as a technique with promising features for their production. However, the electrospun scaffolds mechanical behavior as a function of the microstructure and nanofiber properties is still poorly understood. Besides, multiscale constitutive modeling appears as a powerful design tool, not only able to characterize electrospun structures, but also to determine the fiber properties and scaffold microstructure that would achieve the objective response. With focus in this last aspect, we developed a multiscale constitutive model for nanofibrous structures that takes into account the material constitutive properties, scaffold microstructure, and nanofiber progressive recruitment. A statistical approach of the nanofibers tortuosity with a modified Gaussian distribution was adopted, which allowed for reproducing the scaffolds macroscopic nonlinear mechanical behavior. It was observed that such behavior arises even if the nanofibers response is considered as mechanically linear. Experimental data from pressure vs. diameter inflation tests of electrospun tubular scaffolds was used to validate the model. In addition, the influence of the microstructural parameters upon the macroscopic constitutive behavior was studied. Finally, the model parameters were adjusted to obtain a vascular graft able to reproduce the mechanical response of a target natural tissue. The current study presents a step towards understanding, characterizing, and optimizing the mechanical properties of nanofibrous biomaterials.

High strength polymer/silicon nitride composites for dental restorations

ObjectivesTo fabricate polymer-infiltrated silicon nitride composite (PISNC) and evaluate the potential of PISNC in dental application. MethodsPorous silicon nitride (Si3N4) ceramics were fabricated through gelcasting and pressureless sintering. Polymer infiltrating was carried out then and composites were obtained after curing of polymer. Flexural strength and microstructures of porous ceramic scaffolds and polymer-infiltrated composites were obtained by three-point bending and SEM, respectively. Phase distributions of polymer-infiltrated ceramics were observed by EDS. Human gingival fibroblast cells (HGFs) were used to evaluate the cytocompatibility and IL-6 release. The cell morphology were observed by SEM. The amount of released IL-6 was investigated using ELISA test system. ResultsPorosity and mechanical strength of porous ceramics ranged from 45.1 to 49.3% and 171.8–262.3MPa, respectively. The bicontinuous structure of polymer-infiltrated composites possessed them with excellent mechanical properties. Porosity and mechanical strength of polymer-infiltrated Si3N4 composites ranged from 1.94 to 2.28% and 273–385.3MPa, respectively. Additionally, the PISNC enhanced the initial adhesion and spreading activity of HGFs compared with PMMA. The PISNC showed similar IL-6 release performance with PMMA samples. SignificancesThe PISNC is a promising candidate for dental restorations and high-load medical applications.

Development of decellularized meniscus extracellular matrix and gelatin/chitosan scaffolds for meniscus tissue engineering.

Meniscus tissue engineering has provided a great potential treatment for meniscal injuries. However, few scaffolds in meniscus tissue engineering have matched the mechanical properties of native meniscus. In this study, we developed a composite scaffold using decellularized meniscus extracellular matrix (DMECM) and gelatin/chitosan (G/C) to explore a preferable ratio to enhance the elastic modulus and cytotoxicity properties of scaffolds. The microstructure, porosity, cytotoxicity, and strength of the composite scaffolds were evaluated. The micro-architectures of the samples were evaluated using scanning electron microscope (SEM). Fourier Transform Infrared analysis (FTIR) was used to confirm the chemical structure with different type composite scaffolds. The compressive elastic modulus of all the scaffolds were measured by the universal tensile testing machine DNS300. Calcein-AM (fluorescent green) and propidium iodide (fluorescent red) were used to stain live cells and dead cells. Morphology and spatial distribution of cells within scaffolds were observed by confocal laser scanning microscopy FV 1000. SEM showed that the composite scaffolds had suitable porous structure. CCK-8 and live/dead staining demonstrated that the composite scaffolds had no cytotoxicity and could promote bone marrow mesenchymal stem cells (BMSCs) proliferation. The FTIR results demonstrated the successful mixing of these two elements, and the addition of DMECM improved the elastic modulus and cytotoxicity of G/C composite scaffolds. This study developed a composite scaffold using DMECM and G/C, and demonstrated that it might be suitable for meniscal tissue engineering application.

A polymer scaffold with drug-sustained release and antibacterial activity

Total alkaloids from Semen Strychnine (TASS), as an antibacterial drug, was loaded into polyetheretherketone (PEEK)/polyglycolide acid (PGA) scaffolds fabricated via 3 D printing technology. It focused on studying microstructure, drug-release behavior, antibacterial activity and biocompatibility of scaffolds. Results indicated that TASS had a good physiochemical compatibility with polymer matrix, and a sustained release for longtime in TASS-PEEK/PGA scaffolds. Moreover, the scaffolds manifested antimicrobial activity against E. coli and S. aureus in antibacterial tests and superb biocompatibility in vitro cell culture. These suggested that TASS-PEEK/PGA scaffolds were able to efficiently sustain TASS delivery and were a promising implant for treating bacterial infection.

Numerical calculation of permeability of periodic porous materials: Application to periodic arrays of spheres and 3D scaffold microstructures

SummaryIn this paper, an efficient numerical method is proposed to calculate the anisotropic permeability in porous materials characterized by a periodic microstructure. This method is based on pore‐scale fluid dynamic simulations using a static volume of fluid method. Unlike standard solution procedures for this type of problem, we here solve an average constitutive equation over both fluid and solid domain by use of a subgrid model to accurately capture momentum transfer from the fluid to solid interface regions. Using numerical simulations on periodic arrays of spheres, we first demonstrate that, by using the subgrid interface model, more accurate results can be produced, for the velocity and pressure fields, than via more conventional approaches. We then apply numerical upscaling over the unit cell to calculate the full anisotropic permeability from the pore‐scale numerical results. The obtained permeability values for a variety of periodic arrays of spheres in different arrangements and packing orders are in good agreement with semianalytical results reported in literature. This validation allows for the permeability assessment of more complex structures such as isotropic gyroid structures, or anisotropic cases, here modeled in their simplest form, the ellipsoidal inclusion.

Exploring the Role of Manganese on the Microstructure, Mechanical Properties, Biodegradability, and Biocompatibility of Porous Iron-Based Scaffolds.

In this work, the role that manganese plays in determining the structure and performance of sintered biodegradable porous Fe-Mn alloys is described. Powder metallurgy processing was employed to produce a series of biodegradable porous Fe-xMn (x = 20, 30, and 35 wt %) alloys suitable for bone scaffold applications. Increasing manganese content increased the porosity volume in the sintered alloys and influenced the ensuing properties of the metal. The Fe-35Mn alloy possessed optimum properties for orthopedic application. X-ray diffraction analysis and magnetic characterization confirmed the predominance of the antiferromagnetic austenitic phase and ensured the magnetic resonance imaging (MRI) compatibility of this alloy. The porous Fe-35Mn alloy possessed mechanical properties (tensile strength of 144 MPa, elastic modulus of 53.3 GPa) comparable to human cortical bone. The alloy exhibited high degradation rates (0.306 mm year-1) in simulated physiological fluid, likely due to its considerable Mn content and the high surface area inherent to its porous structures, while cytotoxicity and morphometry tests using mammalian preosteoblast cells (MC3T3-E1) indicated good cell viability in the Fe-35Mn alloy.

Modeling, simulations, and optimization of smooth muscle cell tissue engineering for the production of vascular grafts.

The paper presents a transient, continuum, two-phase model of the tissue engineering in fibrous scaffolds, including transport equations for the flowing culture medium, nutrient and cell concentration with transverse and in-plane diffusion and cell migration, a novel feature of local in-plane transport across a phenomenological pore and innovative layer-by-layer cell filling approach. The model is successfully validated for the smooth muscle cell tissue engineering of a vascular graft using crosslinked, electrospun gelatin fiber scaffolds for both static and dynamic cell culture, the latter in a dynamic bioreactor with a rotating shaft on which the tubular scaffold is attached. Parametric studies evaluate the impact of the scaffold microstructure, cell dynamics, oxygen transport, and static or dynamic conditions on the rate and extent of cell proliferation and depth of oxygen accessibility. An optimized scaffold of 75% dry porosity is proposed that can be tissue engineered into a viable and still fully oxygenated graft of the tunica media of the coronary artery within 2 days in the dynamic bioreactor. Such scaffold also matches the mechanical properties of the tunica media of the human coronary artery and the suture retention strength of a saphenous vein, often used as a coronary artery graft.