Materials For Tissue Engineering Applications Research Articles

Role of solvent-mediated carbodiimide cross-linking in fabrication of electrospun gelatin nanofibrous membranes as ophthalmic biomaterials

Due to their ability to mimic the structure of extracellular matrix, electrospun gelatin nanofibers are promising cell scaffolding materials for tissue engineering applications. However, the hydrophilic gelatin molecules usually need stabilization before use in aqueous physiological environment. Considering that biomaterials cross-linked via film immersion technique may have a more homogeneous cross-linked structure than vapor phase cross-linking, this work aims to investigate the chemical modification of electrospun gelatin nanofibrous membranes by liquid phase carbodiimide in the presence of ethanol/water co-solvents with varying ethanol concentrations ranging from 80 to 99.5vol%. The results of characterization showed that increasing water content in the binary reaction solvent system increases the extent of cross-linking of gelatin nanofibers, but simultaneously promotes the effect of biopolymer swelling and distortion in fiber mat structure. As compared to non-cross-linked counterparts, carbodiimide treated gelatin nanofibrous mats exhibited better thermal and biological stability where the shrinkage temperature and resistance to enzymatic degradation varied in response to ethanol/water solvent composition-mediated generation of cross-links. Irrespective of their cross-linking density, all studied membrane samples did not induce any responses in ocular epithelial cell cultures derived from cornea, lens, and retina. Unlike many other cross-linking agents and/or methods (e.g., excessive vapor phase cross-linking) that may pose a risk of toxicity, our study demonstrated that these nanofibrous materials are well tolerated by anterior segment tissues. These findings also indicate the safety of using ethanol/water co-solvents for chemical cross-linking of gelatin to engineer nanofibrous materials with negligible biological effects. In summary, the present results suggest the importance of solvent-mediated carbodiimide cross-linking in modulating structure–property relationship without compromising in vitro and in vivo biocompatibility of electrospun gelatin nanofibers for future ophthalmic applications.

Effect of mass concentration on bioactivity and cell viability of calcined silica aerogel synthesized from rice husk ash as silica source

The biocompatibility of calcined silica aerogel (900 °C) synthesized from rice husk ash via sol–gel ambient-pressure drying technique was studied. The silica aerogel was characterized by Fourier transform infrared spectroscopy, X-ray diffraction and field emission-scanning electron microscopy. The structure of silica aerogel remains intact but is deficient in silanol groups after calcination. The bioactivity of the silica aerogel was tested by immersion in simulated body fluid for 7 days with various mass concentrations (0.08–0.8 wt%). The results from Fourier transform infrared, X-ray diffraction, field emission-scanning electron microscopy and phosphorous analyses confirm that the silica aerogel could facilitate the nucleation of apatite. The silica aerogel was simultaneously resorbed and the broken Si–O–Si bonds were replaced with new apatite bonds. The optimal mass concentration was 0.16 wt%. At a higher mass concentration (0.8 wt%), silica aerogel tends to form polymeric interactions with tris-hydroxymethyl-aminomethane, a chemical compound in simulated body fluid. In the in vitro cell viability assay of the calcined silica aerogel against human dermal fibroblast cells, the cell viability increased with the increase of silica aerogel mass concentration. This early evidence shows that the calcined silica aerogel synthesized from rice husk ash via the sol–gel ambient-pressure drying technique can be considered as a potential alternative material for tissue engineering applications.

Development of a novel glucosamine/silk fibroin–chitosan blend porous scaffold for cartilage tissue engineering applications

Silk fibroin–chitosan blend is reported to be an attractive scaffold material for tissue engineering applications. In our earlier study, we developed a scaffold having an optimal silk fibroin–chitosan blend ratio of 80:20 and proved its potentiality for cartilage tissue engineering applications. Glucosamine is one of the major structural components of cartilage tissue. The present work investigates the effect of glucosamine components on the physicochemical and biocompatibility properties of this scaffold. To this end, varied amounts of glucosamine were added to silk fibroin–chitosan blend with the aim of improving various scaffold properties. The addition of glucosamine components did not show any significant change in physicochemical properties of silk fibroin–chitosan blend scaffolds. The composite scaffold showed an open pore structure with desired pore size and porosity. However, cell culture study using human mesenchymal stem cells derived from umbilical cord blood revealed an overall increase in cell supportive properties of glucosamine-added scaffolds. Cell viability, cell proliferation and glycosaminoglycan assays confirmed enhanced cell viability and proliferation of mesenchymal stem cells. Thus, this study demonstrated the beneficial effect of glucosamine on improving the cell supportive property of silk fibroin–chitosan blend scaffolds making it more potential for cartilage tissue regeneration. To the best of our knowledge, this is the first report on the study of glucosamine-added silk fibroin–chitosan blend porous scaffolds seeded with mesenchymal stem cells derived from umbilical cord blood.

Fabrication and characterization of Ag doped hydroxyapatite-polyvinyl alcohol composite nanofibers and its in vitro biological evaluations for bone tissue engineering applications

Electrospinning is one of the promising techniques to fabricate the nanofiber based scaffold for bone regeneration applications. In this study, firstly sol–gel method was employed to synthesize 5 % of Ag doped hydroxyapatite and also 10 wt% of polyvinyl alcohol solution was prepared for the electrospun process. For the first time, we have successfully fabricated the composite nanofibers in the combination of various concentration of Ag doped hydroxyapatite such as 1, 2, 3, and 5 wt% with polyvinyl alcohol solution. The developed Ag doped hydroxyapatite-polyvinyl alcohol composites were further characterized by Fourier transform infrared spectroscopy and powder-X-ray diffraction analysis to examine the characteristic functional groups and phase composition of Ag doped hydroxyapatite embedded into polyvinyl alcohol matrix. The uniform distribution of Ag doped hydroxyapatite in polyvinyl alcohol polymer with nanofiber diameter of 188–242 nm range was confirmed by high resolution transmission electron microscope and dynamic light scattering analysis, also the chemical/elemental composition was observed by scanning electron microscopy-energy dispersive spectroscopy analysis. The antibacterial activity was evaluated for the fabricated Ag doped hydroxyapatite polyvinyl alcohol composite nanofibers by using Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) pathogens and the results demonstrated that E. coli exhibits excellent zone of inhibition than S. aureus due to its lesser cell wall thickness. The hemocompatibility study proves that the developed composite nanofibers are blood compatible and showed the hemolytic ratio of less than 5 %. In addition to this, in vitro bioactivity assessment was carried out for 7 days by immersing in simulated body fluid solution to generate the dense apatite layer on their surfaces which was further examined by X-ray diffraction and scanning electron microscopy-energy dispersive spectroscopy analysis. Hence, these electrospun fabricated Ag doped hydroxyapatite-polyvinyl alcohol composite nanofibers will acts as a potential scaffold material for tissue engineering applications. Graphical abstract of electrospun fabrication of Ag@HAP-PVA composite nanofibers and its in vitro biological evaluations.

Chitin and Chitosan: Structure, Properties and Applications in Biomedical Engineering

Chitin and its deacetylated derivative chitosan are natural polymers composed of randomly distributed β-(1-4)-linked d-glucosamine (deacetylated unit) and N-acetyl-d-glucosamine (acetylated unit). Biopolymers like chitin and chitosan exhibit diverse properties that open up a wide-ranging of applications in various sectors especially in biomedical science. The latest advances in the biomedical research are important emerging trends that hold a great promise in wound-healing management products. Chitin and chitosan are considered as useful biocompatible materials to be used in a medical device to treat, augment or replace any tissue, organ, or function of the body. A body of recent studies suggests that chitosan and its derivatives are promising candidates for supporting materials in tissue engineering applications. This review article is mainly focused on the contemporary research on chitin and chitosan towards their applications in numerous biomedical fields namely tissue engineering, artificial kidney, skin, bone, cartilage, liver, nerve, tendon, wound-healing, burn treatment and some other useful purposes.

Regenerated cellulose/wool blend enhanced biomimetic hydroxyapatite mineralization

The current article investigates the effect of bioactive cellulose/wool blend on calcium phosphate biomimetic mineralization. Regenerated cellulose/wool blend was prepared by dissolution-regeneration of neat cellulose and natural wool in 1-butyl-3-methyl imidazolium chloride [Bmim][Cl], as a solvent for the two polymers. Crystalline hydroxyapatite nanofibers with a uniform size, shape and dimension were formed after immersing the bioactive blend in simulated body fluid. The cytotoxicity of cellulose/wool/hydroxyapatite was studied using animal fibroblast baby hamster kidney cells (BHK-21) and the result displayed good cytocompatability. This research work presents a green processing method for the development of novel cellulose/wool/hydroxyapatite hybrid materials for tissue engineering applications.

Interphase Induced Dynamic Self‐Stiffening in Graphene‐Based Polydimethylsiloxane Nanocomposites

The ability to rearrange microstructures and self-stiffen in response to dynamic external mechanical stimuli is critical for biological tissues to adapt to the environment. While for most synthetic materials, subjecting to repeated mechanical stress lower than their yield point would lead to structural failure. Here, it is reported that the graphene-based polydimethylsiloxane (PDMS) nanocomposite, a chemically and physically cross-linked system, exhibits an increase in the storage modulus under low-frequency, low-amplitude dynamic compressive loading. Cross-linking density statistics and molecular dynamics calculations show that the dynamic self-stiffening could be attributed to the increase in physical cross-linking density, resulted from the re-alignment and re-orientation of polymer chains along the surface of nano-fillers that constitute an interphase. Consequently, the interfacial interaction between PDMS-nano-fillers and the mobility of polymer chain, which depend on the degree of chemical cross-linking and temperature, are important factors defining the observed performance of self-stiffening. The understanding of the dynamic self-stiffening mechanism lays the ground for the future development of adaptive structural materials and bio-compatible, load-bearing materials for tissue engineering applications.

Type I collagen and its daughter peptides for targeting mucosal healing in ulcerative colitis: A new treatment strategy

Ulcerative colitis, particularly the chronic persistent form is characterized by the presence of active inflammation and extensive areas of ulceration in the colonic mucosa. The existing treatment protocol aims at only reducing intestinal inflammation, rather than targeting mucosal ulceration. In this study, type I collagen and its daughter peptides called collagen hydrolysate, highly popular reconstructive materials for tissue engineering applications, are hypothesized as healing matrices to target the recuperation of internal mucosal ulceration. The clinical assessments on day 10 of dextran sodium sulfate induced colitis in mice model revealed that both the collagen (1.56±0.29) and collagen hydrolysate treatments (1.33±0.33) showed a significant reduction in the rectal bleeding compared to the reference mesalamine treatment (2.50±0.33) and untreated negative control (2.40±0.40). VEGF, a potent angiogenic growth factor, over expressed during UC was down-regulated by collagen hydrolysate (1.06±0.25) and collagen (1.76±0.45) to a greater extent than by mesalamine (2.59±0.51) and untreated control (4.17±0.15). The down-regulation of proinflammatory cytokines such as TNF-α, IL-1β, and IL-6 also follows the same pattern. Histological observations were in accordance with the clinical indicators. Both collagen and collagen hydrolysate treatments showed significant reduction in mucosal damage score and facilitated faster regeneration of damaged mucosa.

Investigating processing techniques for bovine gelatin electrospun scaffolds for bone tissue regeneration.

Tissue engineering has emerged as a promising solution to tissue regeneration in the case of significant bone loss due to disease or injury. The ability to promote cellular attachment, migration, and differentiation into tissue is dependent on the scaffold's surface properties and composition. Bovine gelatin is a natural polymer commonly used as a scaffolding material for tissue engineering applications. Nonetheless, due to the hydrophilic behavior of gelatin, cross-linking and additives are necessary to maintain the scaffold's structure and overall strength in vivo. In this article, we discuss various processing techniques to determine the optimal electrospinning, cross-linking, sintering, and mineralization parameters necessary to yield a porous, mechanically enhanced scaffold. The scaffolds were evaluated quantitatively using compressive mechanical testing, and qualitatively using scanning electron microscopy (SEM). Mechanical data concluded the use of biocompatible microbial transglutaminase (mTG) as a cross-linking agent, led to increased compressive strength. SEM images confirmed the presence of individual gelatin and polymeric nanofibers woven into one scaffold. Sintering before leaching the scaffold yielded structured pores throughout the three-dimensional scaffold when compared to the scaffolds that were leached prior to sintering. The results presented in this article will provide novel information about processing techniques that can be utilized to develop a hybrid synthetic and biological based biomimetic mineralized scaffold for trabecular bone tissue regeneration. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1131-1140, 2017.

Rheological and Mechanical Behavior of Silk Fibroin Reinforced Waterborne Polyurethane.

Waterborne polyurethane (WPU) is a versatile and environment-friendly material with growing applications in both industry and academia. Silk fibroin (SF) is an attractive material known for its structural, biological and hemocompatible properties. The SF reinforced waterborne polyurethane (WPU) is a promising scaffold material for tissue engineering applications. In this work, we report synthesis and characterization of a novel nanocomposite using SF reinforced WPU. The rheological behaviors of WPU and WPU-SF dispersions with different solid contents were investigated with steady shear and dynamic oscillatory tests to evaluate the formation of the cross-linked gel structure. The average particle size and the zeta potential of WPU-SF dispersions with different SF content were examined at 25 °C to investigate the interaction between SF and WPU. FTIR, SEM, TEM and tensile testing were performed to study the effects of SF content on the structural morphology and mechanical properties of the resultant composite films. Experimental results revealed formation of gel network in the WPU dispersions at solid contents more than 17 wt %. The conjugate reaction between the WPU and SF as well as the hydrogen bond between them helped in dispersing the SF powder into the WPU matrix as small aggregates. Addition of SF to the WPU also improved the Young’s modulus from 0.30 to 3.91 MPa, tensile strength from 0.56 to 8.94 MPa, and elongation at break from 1067% to 2480%, as SF was increased up to 5 wt %. Thus, significant strengthening and toughening can be achieved by introducing SF powder into the WPU formulations.

Inverse high internal phase emulsion polymerization (i-HIPE) of GMMA, HEMA and GDMA for the preparation of superporous hydrogels as a tissue engineering scaffold.

A series of novel superporous hydrogels for regenerative medicine were prepared by oil-in-water (o/w) or inverse high internal phase emulsion (i-HIPE) copolymerization of glycerol monomethacrylate (GMMA), 2-hydroxy ethyl methacrylate (HEMA) and glycerol dimethacrylate (GDMA) as a cross-linker using a non toxic solvent and a redox initiator system at the physiological temperature (37 °C). The monomer GMMA was synthesized from glycidyl methacrylate (GMA) by an alternative facile method using Amberlyst-15. The described i-HIPEs showed a significantly wider stability window. The polyHIPE hydrogels were characterized by FTIR, BET method for surface area, mercury porosimetry, SEM, DSC, TGA, XRD, compressive strain and strain recovery. The swelling ratio of the hydrogels and their degradation in 0.007 M NaOH and lipase B (Candida antarctica) solutions were determined gravimetrically and the rate of degradation was explained in terms of the molecular structure of the hydrogels. The morphological studies showed that the pore diameter varied between 20 and 30 μm and the pore throats (interconnecting windows) diameter was in the range of 4-8 μm. The described polyHIPE hydrogels were found to have an open cell morphology and interconnected pore architecture, which are important characteristics for scaffold applications. The initial cytotoxicity study performed according to ISO-10993-5 indicated cytocompatibility (97% cell viability) and the subsequent cell seeding and proliferation study exhibited 55-88% cell viability (increased monotonously from GHG-1 to GHG-5), which could be attributed to modulation of the physical and chemical properties of the hydrogels. The described super porous hydrogels are considered as potential candidates for scaffold materials in tissue engineering applications.

3D printing of polymeric microspheres for tissue engineering scaffolds

Event Abstract Back to Event 3D printing of polymeric microspheres for tissue engineering scaffolds Stefan Lohfeld1, 2, Jeannie R. Salash3, Michael S. Detamore2 and Peter E. Mchugh1 1 National University of Ireland, Mechanical and Biomedical Engineering, Ireland 2 University of Kansas, Department of Chemical and Petroleum Engineering, United States 3 University of Kansas, Bioengineering Graduate Program, United States Microspheres have tremendous potential as a scaffold material for tissue engineering applications due to their capability of encapsulation and controlled release of factors that assist tissue regeneration in the desired fashion. Gradient scaffolds consisting of multiple types of microspheres can release different factors at different sites of the scaffold. Current microsphere scaffold production methods, however, cannot address the need for internal architectures to meet specific requirements in different scaffold regions, e.g., for mechanical properties or porosity. We combined 3D printing and microspheres to create scaffolds with defined internal architectures and tailored placing of materials, intended for bone/cartilage interfaces. Poly(lactic-co-glycolic acid) microspheres were mixed with agarose and hyaluronic acid hydrogel to create a highly viscous suspension. The compounds were sintered with subcritical CO2 to investigate the influence of the fluid phase on the sintering capability. It was shown that despite the second phase, CO2 can access the microspheres to sinter them and form a mechanically stable construct that withstands significant forces (Fig. 1). A syringe extruder was built and attached to a RepRap 3D printer to print scaffold structures with the compounds (Fig. 2). The material dried quickly and allowed to make scaffolds structures where no support of short struts is necessary. The hydrogel compounds were cured with UV light prior to sintering to add stability to the green body. Research was performed on optimisation of the entire manufacturing process regarding printing smaller diameter struts, and influence of the microsphere size, ideal subcritical CO2 sintering parameters, swelling and distortion due to sintering, mechanical properties of the scaffolds, and cell culturing on the scaffolds. This first demonstration of direct 3D printing of microsphere based scaffolds adds a high degree of freedom for the fabrication of such scaffolds. By design of unit cells within a scaffold it allows local definitions for mechanical properties and porosity, the microsphere technology allows controlled release of encapsulated factors to enhance tissue growth, and the printing process with multiple printing heads allows focal placement of various phases to account for different needs of tissue to create, scaffolds that serve the growth of both cartilage and subchondral bone, as it is needed for tissue engineered joint replacements. This project has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no. PIOF-GA-2013-622414, and from the Kansas Bioscience Authority Rising Star Award Keywords: Tissue Engineering, Rapid prototyping, 3D scaffold Conference: 10th World Biomaterials Congress, Montréal, Canada, 17 May - 22 May, 2016. Presentation Type: Poster Topic: Layer-by-layer deposition techniques Citation: Lohfeld S, Salash JR, Detamore MS and Mchugh PE (2016). 3D printing of polymeric microspheres for tissue engineering scaffolds. Front. Bioeng. Biotechnol. Conference Abstract: 10th World Biomaterials Congress. doi: 10.3389/conf.FBIOE.2016.01.00226 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 28 Mar 2016; Published Online: 30 Mar 2016. Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Stefan Lohfeld Jeannie R Salash Michael S Detamore Peter E Mchugh Google Stefan Lohfeld Jeannie R Salash Michael S Detamore Peter E Mchugh Google Scholar Stefan Lohfeld Jeannie R Salash Michael S Detamore Peter E Mchugh PubMed Stefan Lohfeld Jeannie R Salash Michael S Detamore Peter E Mchugh Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

The effect of glycation and cyclic loading on the material properties of isolated arterial elastin

Event Abstract Back to Event The effect of glycation and cyclic loading on the material properties of isolated arterial elastin Joseph B. Washington1 and L D Timmie Topoleski1 1 UMBC, Mechanical Engineering, United States Introduction: Elastin is a stable protein capable of enduring over a billion cycles under normal hemostatic conditions, and is an attractive material for tissue engineering applications[1][2]. Elastin stores strain energy, allowing arteries to expand and recover as blood is pumped from the heart. Glycation, where glucose molecules react with a protein or lipid, is associated with arterial aging and increased stiffness. During cyclic loading of materials, mechanical properties such as stiffness and maximum stress may change, thus altering the biomechanical integrity of a tissue engineering scaffold. This study examined the effects of glycation and extended cyclic loading on mechanical properties of isolated arterial elastin. Methods: Porcine aortas were obtained from a local abattoir. Adherent tissue was removed and “dog-bone” shaped samples were cut with a custom die. Isolated elastin specimens were prepared using the method of Lu et al[2]. Specimens were placed in 5M glucose solution for 0 (control), 1, 15, or 30 days. Samples were cyclically loaded in tension using a custom-built material testing system[3], under displacement control at 1 Hz to a maximum displacement of 3mm. All tests were performed in PBS solution at 37°C. Samples were loaded for 25k, 50k, or 100k cycles and then monotonically tested in tension to failure at a strain rate of 0.05mm/sec. Stress (σ = load/initial cross-sectional area) and stretch ratio (λ = current length/initial length) were calculated, and a linear model was used to determine the stiffness (M) and maximum stress (σmax) for each sample. Results: Two-way ANOVA failed to show a significant difference (p < 0.05) in σmax between treatment time or number of cycles (Fig. 1). Tukey’s pairwise test revealed a significant difference between 0 and 100k cycles. There was a gradual increase in M in each treatment time (Fig. 2). Two-way ANOVA showed significant differences between treatment times (p = 0.002), but not for number of cycles. Discussion: Glycation leads to the creation of advanced glycation endproducts (AGEs), which form irreversible covalent crosslinks with proteins. AGE crosslinks accumulate over several weeks[4], but the maximum glycation treatment time in this study was 30 days. There may not have been time to form enough crosslinks to cause a detectable change in mechanical behavior. Future research should include longer treatment times. Within each treatment group, the stiffness decreased with increasing number of cycles, possibly due to accumulated elastin fiber damage. Longer treatment times may have increased AGE-elastin crosslinking, which may have counteracted any damage accumulation in the elastin before 50k cycles. However, breakdown of the crosslinks between 50k and 100k cycles may explain why differences were detected at 100k cycles. Conclusions: For less than 100k cycles, glycation had an effect on the stiffness of isolated elastin, but not on the maximum stress. Extended cyclic loading may amplify the effects of subtle initial damage such that it can be detected though changes in material properties. UMBC Graduate Meyerhoff Program; GAANN Fellowship, US Department of Education

Development of Synthetic and Natural Materials for Tissue Engineering Applications Using Adipose Stem Cells.

Adipose stem cells have prominent implications in tissue regeneration due to their abundance and relative ease of harvest from adipose tissue and their abilities to differentiate into mature cells of various tissue lineages and secrete various growth cytokines. Development of tissue engineering techniques in combination with various carrier scaffolds and adipose stem cells offers great potential in overcoming the existing limitations constraining classical approaches used in plastic and reconstructive surgery. However, as most tissue engineering techniques are new and highly experimental, there are still many practical challenges that must be overcome before laboratory research can lead to large-scale clinical applications. Tissue engineering is currently a growing field of medical research; in this review, we will discuss the progress in research on biomaterials and scaffolds for tissue engineering applications using adipose stem cells.

Recombinant Resilin-Based Bioelastomers for Regenerative Medicine Applications.

The outstanding elasticity, excellent resilience at high-frequency, and hydrophilic capacity of natural resilin have motivated investigations of recombinant resilin-based biomaterials as a new class of bio-elastomers in the engineering of mechanically active tissues. Accordingly, here the comprehensive characterization of modular resilin-like polypeptide (RLP) hydrogels is presented and their suitability as a novel biomaterial for in vivo applications is introduced. Oscillatory rheology confirmed that a full suite of the RLPs can be rapidly cross-linked upon addition of the tris(hydroxymethyl phosphine) cross-linker, achieving similar in situ shear storage moduli (20 k ± 3.5 Pa) across various material compositions. Uniaxial stress relaxation tensile testing of hydrated RLP hydrogels under cyclic loading and unloading showed negligible stress reduction and hysteresis, superior reversible extensibility, and high resilience with Young's moduli of 30 ± 7.4 kPa. RLP hydrogels containing MMP-sensitive domains are susceptible to enzymatic degradation by matrix metalloproteinase-1 (MMP-1). Cell culture studies revealed that RLP-based hydrogels supported the attachment and spreading (2D) of human mesenchymal stem cells and did not activate cultured macrophages. Subcutaneous transplantation of RLP hydrogels in a rat model, which to our knowledge is the first such reported in vivo analysis of RLP-based hydrogels, illustrated that these materials do not elicit a significant inflammatory response, suggesting their potential as materials for tissue engineering applications with targets of mechanically demanding tissues such as vocal fold and cardiovascular tissues.

Physical and Electrochemical Properties of PEDOT:PSS as a Tool for Controlling Cell Growth.

PSS), are prepared using two different techniques, spin coating and electrochemical polymerization, and their oxidation state is subsequently changed electrochemically with the application of an external bias. The electrochemical properties of these different types of PSS are studied through cyclic voltammetry and spectrophotometry to assess the effectiveness of the oxidation process and its stability over time. Their surface physical properties and their dependence on the redox state of PSS are investigated using atomic force microscopy (AFM), water contact angle goniometry and sheet resistance measurements. Finally, human glioblastoma multiforme cells (T98G) and primary human dermal fibroblasts (hDF) are cultured on PSS films with different oxidation states, finding that the effect of the substrate on the cell growth rate is strongly cell-dependent: T98G growth is enhanced by the reduced samples, while hDF growth is more effective only on the oxidized substrates that show a strong chemical interaction with the cell culture medium.

Preparation of polymeric foams with a pore size gradient via Thermally Induced Phase Separation (TIPS)

Foams with a pore size gradient are promising materials for tissue engineering applications where a complex architecture involving morphological variations in space must be mimicked, e.g. in bone tissue repair. In this paper, a technique to obtain a porous scaffold with a pore size gradient is presented. The preparation procedure is based on Thermally Induced Phase Separation (TIPS), by imposing a different thermal history on the two sides of a polymeric solution. In this way, a gradient in thermal history is produced, which will generate a pore size monotonously varying along scaffold thickness. By controlling some parameters easy to manipulate, such as demixing temperature and/or residence time in the miscibility gap region, the pore size range can be easily tuned.

Review: Polymeric-Based 3D Printing for Tissue Engineering.

Three-dimensional (3D) printing, also referred to as additive manufacturing, is a technology that allows for customized fabrication through computer-aided design. 3D printing has many advantages in the fabrication of tissue engineering scaffolds, including fast fabrication, high precision, and customized production. Suitable scaffolds can be designed and custom-made based on medical images such as those obtained from computed tomography. Many 3D printing methods have been employed for tissue engineering. There are advantages and limitations for each method. Future areas of interest and progress are the development of new 3D printing platforms, scaffold design software, and materials for tissue engineering applications.

Microstructural parameter-based modeling for transport properties of collagen matrices.

Recent advances in modulating collagen building blocks enable the design and control of the microstructure and functional properties of collagen matrices for tissue engineering and regenerative medicine. However, this is typically achieved by iterative experimentations and that process can be substantially shortened by computational predictions. Computational efforts to correlate the microstructure of fibrous and/or nonfibrous scaffolds to their functionality such as mechanical or transport properties have been reported, but the predictability is still significantly limited due to the intrinsic complexity of fibrous/nonfibrous networks. In this study, a new computational method is developed to predict two transport properties, permeability and diffusivity, based on a microstructural parameter, the specific number of interfibril branching points (or branching points). This method consists of the reconstruction of a three-dimensional (3D) fibrous matrix structure based on branching points and the computation of fluid velocity and solute displacement to predict permeability and diffusivity. The computational results are compared with experimental measurements of collagen gels. The computed permeability was slightly lower than the measured experimental values, but diffusivity agreed well. The results are further discussed by comparing them with empirical correlations in the literature for the implication for predictive engineering of collagen matrices for tissue engineering applications.

Enzymatic Degradation of Films, Particles, and Nonwoven Meshes Made of a Recombinant Spider Silk Protein.

The performance of biomaterials in vivo is largely influenced by their stability and the rate and extent to which they degrade. Materials for tissue engineering applications, for example, have to be mechanically stable to support cell adhesion and proliferation without collapsing. On the other hand they need to be replaced gradually by native extracellular matrix and have to be (slowly) biodegradable. Therefore, it is of critical importance to be able to tune the degradation behavior of a biomaterial. Recombinantly produced spider silk proteins have been shown to be versatile biopolymers for medical applications. They can be processed into a variety of morphologies, and by chemical or genetic modification the properties can be adjusted to specific demands. Furthermore, in vivo experiments confirmed the lack of immunological reactions toward certain spider silks. In this study the degradation behavior of the recombinant spider silk protein eADF4(C16) in solution as well as processed into particles, films and nonwoven meshes was analyzed, and the impact of cross-linking of the scaffolds was assessed thereon. In addition to two bacterial proteolytic model enzymes, protease type XIV from Streptomyces griseus (PXIV) and collagenase type IA from Clostridium histolyticum (CHC) used in all experiments, several recombinant human matrix metalloproteinases (MMPs) and one elastase were used in studying degradation of soluble eADF4(C16). For soluble eADF4(C16) all degradation kinetics were similar. In case of eADF4(C16) scaffolds significant differences were observable between PXIV and CHC. All scaffolds were more stable toward proteolytic degradation in the presence of CHC than in the presence of PXIV. Further, particles were degraded significantly faster than films, and nonwoven meshes showed the highest proteolytic stability. Chemical cross-linking of the scaffolds led to a decrease in both degradation rate and extent.