Tri-layered Scaffold Research Articles

Trilayer scaffold with cardiosphere‐derived cells for heart valve tissue engineering

Natural polymers collagen, glycosaminoglycans, and elastin are promising candidate materials for heart valve tissue engineering scaffolds. This work produced trilayer scaffolds that resembled the layered structures of the extracellular matrices of native heart valves. The scaffolds showed anisotropic bending moduli (in both dry and hydrated statuses) depending on the loading directions (lower in the With Curvature direction than in the Against Curvature direction), which mimicked the characteristic behavior of the native heart valves. The interactions between cardiosphere-derived cells and the scaffolds were characterized by multiphoton microscopy, and relatively similar cell distributions were observed on different layers (a cell density of 3,000-4,000 mm-3 and a migration depth of 0.3-0.4 mm). The trilayer scaffold has represented a forwarding step from the previous studies, in attempting to better replicate a native heart valve structurally, mechanically, and biologically.

Electrospun microporous gelatin–polycaprolactone blend tubular scaffold as a potential vascular biomaterial

AbstractThe work reported involved the fabrication of an electrospun tubular conduit of a gelatin and polycaprolactone (PCL) blend as an adventitia‐equivalent construct. Gelatin was included as the matrix for increased biocompatibility with the addition of PCL for durability. This is contrary to most of the literature available for biomaterials based on blends of gelatin and PCL where PCL is the major matrix. The work includes the assiduous selection of key electrospinning parameters to obtain smooth bead‐free fibres with a narrow distribution of pore size and fibre diameter. Few reports elucidate the optimization of all electrospinning parameters to fabricate tubular conduits with a focus on obtaining homogeneous pores and fibres. This stepwise investigation would be unique for the fabrication of gelatin–PCL electrospun tubular constructs. The fabricated microfibrous gelatin–PCL constructs had pores of size ca 50–100 μm reportedly conducive for cell infiltration. The measured value of surface roughness of 57.99 ± 17.4 nm is reported to be favourable for protein adhesion and cell adhesion. The elastic modulus was observed to be similar to that of the tunica adventitia of the native artery. Preliminary in vitro and in vivo biocompatibility tests suggest safe applicability as a biomaterial. Minimal cytotoxicity was observed using MTT assay. Subcutaneous implantation of the scaffold demonstrated acute inflammation which decreased by day 15. The findings of this study could enable the fabrication of smooth bead‐free microfibrous gelatin–PCL tubular construct as viable biomaterial which can be included in a bilayer or a trilayer scaffold for vascular tissue engineering. © 2019 Society of Chemical Industry

3D printing of biomimetic multi-layered GelMA/nHA scaffold for osteochondral defect repair

Currently, osteochondral defects frequently cause limited motion and impaired function of the joint, leading to serious healthcare problems, and it is still very challenging to realize the simultaneous regeneration of subchondral bone with cartilage. In the current study, we designed a tri-layered scaffold and fabricated it using the extrusion-based multi-nozzle 3D printing technology. The bioinks used for 3D printing included a 15% methacrylated gelatin (GelMA) hydrogel for cartilage on top layer, a combination of 20% GelMA and 3% nanohydroxyapatite (nHA) (20/3% GelMA/nHA) hydrogel for interfacial layer, and a 30/3% GelMA/nHA hydrogel for subchondral bone at bottom layer. The water absorption capacity, biodegradation, and mechanical properties of hydrogels and scaffolds were characterized, and in vitro assay with bone marrow mesenchymal stem cells (BMSCs) was performed to indicate the biocompatibility of scaffolds. Based on the results of in vivo repair of rabbit osteochondral defect, the neo-tissues in defects integrated better with the surrounding tissues, the joint surface of the defects was smoother, and more cartilage-specific extracellular matrix and collagen type II were observed using the tri-layered scaffolds. This study not only provides a potential manufacturing method for multi-layered scaffolds, but also is helpful for understanding the regeneration mechanism of cartilage-subchondral bone.

Repair of Articular Osteochondral Defects Using an Integrated and Biomimetic Trilayered Scaffold.

Repair of articular cartilage defects using bilayered scaffolds is problematic because tissue-engineered cartilage is prone to overgrowth toward subchondral bone, resulting in structural abnormalities of cartilage and subchondral bone. A "twice freeze-drying" technique was used to construct a dense isolation layer between the cartilage and subchondral bone layers in an integrated bilayered scaffold to prevent cartilage from excessive downgrowth. Briefly, beta-tricalcium phosphate was used for the subchondral bone layer of the scaffold, high-concentration chitosan/gelatin solution for the dense isolation layer, and low-concentration chitosan/gelatin solution for the cartilage layer. As controls, cell-free trilayered scaffolds, autologous osteochondral transplantation, and the bilayered scaffolds were used for repair of osteochondral defects. After 6 months, two of the eight goats in the bilayered scaffold group showed conspicuous cartilage downgrowth, whereas no excessive downgrowth of cartilage was observed in the trilayered scaffold group. Moreover, there was no difference in the repair efficacy between the trilayered scaffold and mosaicplasty group. The results confirmed that the trilayered scaffold effectively prevented cartilage downgrowth with better cartilage repair.

Layers of bone repair

Biomaterials The repair of osteochondral defects requires proper growth of subchondral bone, articular cartilage, and the interface between them, but current treatments have been more palliative than curative. Kang et al. developed a trilayer scaffold, with variations in the architecture and mineral environment along its depth. The bottom layer was enhanced with calcium phosphate to recruit endogenous cells, whereas the upper two layers were loaded with donor cells to support stratified cartilage formation. When implanted in vivo, these trilayer scaffolds formed osteochondral tissue with a lubricin-rich cartilage surface. Acta Biomater. 10.1016/j.actbio.2018.07.039 (2018).

Functionally graded multilayer scaffolds for in vivo osteochondral tissue engineering

Osteochondral tissue repair remains a significant challenge in orthopedic surgery. Tissue engineering of osteochondral tissue has transpired as a potential therapeutic solution as it can effectively regenerate bone, cartilage, and the bone-cartilage interface. While advancements in scaffold fabrication and stem cell engineering have made significant progress towards the engineering of composite tissues, such as osteochondral tissue, new approaches are required to improve the outcome of such strategies. Herein, we discuss the use of a single-unit trilayer scaffold with depth-varying pore architecture and mineral environment to engineer osteochondral tissues in vivo. The trilayer scaffold includes a biomineralized bottom layer mimicking the calcium phosphate (CaP)-rich bone microenvironment, a cryogel middle layer with anisotropic pore architecture, and a hydrogel top layer. The mineralized bottom layer was designed to support bone formation, while the macroporous middle layer and hydrogel top layer were designed to support cartilage tissue formation. The bottom layer was kept acellular and the top two layers were loaded with cells prior to implantation. When implanted in vivo, these trilayer scaffolds resulted in the formation of osteochondral tissue with a lubricin-rich cartilage surface. The osteochondral tissue formation was a result of continuous differentiation of the transplanted cells to form cartilage tissue and recruitment of endogenous cells through the mineralized bottom layer to form bone tissue. Our results suggest that integrating exogenous cell-based cartilage tissue engineering along with scaffold-driven in situ bone tissue engineering could be a powerful approach to engineer analogs of osteochondral tissue. In addition to offering new therapeutic opportunities, such approaches and systems could also advance our fundamental understanding of osteochondral tissue regeneration and repair. Statement of SignificanceIn this work, we describe the use of a single-unit trilayer scaffold with depth-varying pore architecture and mineral environment to engineer osteochondral tissues in vivo. The trilayer scaffold was designed to support continued differentiation of the donor cells to form cartilage tissue while supporting bone formation through recruitment of endogenous cells. When implanted in vivo, these trilayer scaffolds partially loaded with cells resulted in the formation of osteochondral tissue with a lubricin-rich cartilage surface. Approaches such as the one presented here that integrates ex vivo tissue engineering along with endogenous cell-mediated tissue engineering can have a significant impact in tissue engineering composite tissues with diverse cell populations and functionality.

Fabrication of spaced monolayers of electrospun nanofibers for three-dimensional cell infiltration and proliferation

Biophysical and biochemical properties of the extracellular matrix (ECM) are important for regulation of cell behaviors and tissue functions. In this study, we fabricated monolayers of gelatin nanofibers on both sides of a honeycomb micro-frame by electrospinning and chemical crosslinking, resulting in tri-layer patches with adjustable thickness and pore size. Fibroblast cells were cultured on this tri-layer scaffold, showing an enhanced cell proliferation. More importantly, our results showed an efficient cell infiltration into the space between the two fiber layers and 3D cell distribution suitable for cell based assays.

Spatio-temporal release of NGF and GDNF from multi-layered nanofibrous bicomponent electrospun scaffolds

Scaffolds capable of providing dual neurotrophic factor (NTF) delivery with different release kinetics, spatial delivery of NTFs at different loci and topographical guidance are promising for enhanced peripheral nerve regeneration. In this study, we have designed and fabricated multi-layered aligned-fiber scaffolds through combining emulsion electrospinning, sequential electrospinning and high-speed electrospinning (HS-ES) to modulate the release behavior of glial cell line-derived growth factor(GDNF) and nerve growth factor (NGF). GDNF and NGF were incorporated into poly(lactic-co-glycolic acid) (PLGA) fibers and poly(D,L-lactic acid) (PDLLA) fibers, respectively. Aligned fibers were obtained in each layer of multi-layered scaffolds and relatively thick tri-layered and tetra-layered scaffolds with controlled layer thickness were obtained. Their morphology, structure, properties, and the in vitro release of growth factors were examined. Dual and spatio-temporal release of GDNF and NGF with different release kinetics from multi-layered scaffolds was successfully demonstrated. High separation efficiency by PDLLA fibrous barrier layer for spatial neurotrophic factor delivery from both tri-layered scaffolds and tetra-layered scaffolds was achieved.

Rational design of bone extracellular matrix mimicking tri-layered composite nanofibers for bone tissue regeneration

Multilayer nanofibrous scaffolds are gaining great attention in biomedical fields especially as tissue regeneration materials as well as drug delivery devices. Herein, we report the unique design of a tri-layered composite nanofiber scaffold mimicking the bone ECM for bone tissue regeneration. The tri-layered membrane consists of a superficial layer of PVA-PVAc loaded with simvastatin to initiate and improve osteogenesis process via sustained release of the drug as well as the excellent bioactivity of its blended polymers. The PCL-CA-β-tcp middle layer acts as a platform for stimulating the bio mineralization process mimicking the apatite like layer which mainly start after the first week of implantation. The final PCL layer performs as the fundamental layer to keep mechanical properties of the composite mat. The as prepared scaffolds were investigated in terms of morphology characterization, physiochemical properties, biomimetic mineralization, drug release and biocompatibility. The in vitro drug release study confirms the sustained release of simvastatin from the tri-layered membrane by obeying the Korsemeyer-Peppas, Higushi model and Kopcha model. The results demonstrate that the proposed biocompatible tri-layered scaffold will be a promising future material for bone tissue regeneration application by providing higher mineralization, enhanced cell attachment and proliferation.

Developing improved tissue-engineered buccal mucosa grafts for urethral reconstruction.

We aimed to compare alternative synthetic scaffolds suitable for future implantation and to examine the use of an inhibitor of lysyl oxidase (beta-amino-propionitrile [β-APN]) to reduce contraction in these implants. Three synthetic scaffolds were compared to natural dermis as substrates for the production of tissue-engineered skin. For natural dermis, Euroskin was used to provide a cell-free cadaveric dermis. Synthetic scaffolds consisted of microfibrous poly-L-lactic acid (PLA), nanofibrous poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and a micro-/nanofibrous trilayer of PLA-PHBV-PLA. The latter were all electrospun and then all four scaffolds (three synthetic, one natural) were placed in six well plates. A culture well was formed on the scaffold using a 1 cm diameter stainless steel ring and 1.5×105 oral fibroblasts were seeded one side; after two days of culture, the ring was placed on the other side of the scaffolds and 3×105 oral keratinocytes were seeded on to the scaffolds and cultured with keratinocytes uppermost. After a further two days of culture, scaffolds were cut to 1 cm2 and raised to an air-liquid interface on stainless steel grids; some were treated with 200 μg/mL β-APN throughout the culture period (28 days). Contraction in vitro was assessed by serial digital photography of cell-seeded scaffolds and cell-free scaffolds three times a week for 28 days. All cell-seeded scaffolds were assessed for cell metabolic activity, mechanical properties, histology, and morphology by scanning electron microscopy (SEM). The mean fibre diameters and pore sizes of PLA and PHBV scaffolds were 2.4±0.77, 0.85±0.21 μm (p<0.001), and 10.8±2.3, 4.3±1.1 μm (p<0.001), respectively. Oral fibroblasts and keratinocytes were tightly adhered and grew well on both surfaces of trilayer. The ultimate tensile strength (UTS) and Young's modulus (YM) of PLA samples were significantly lower than Euroskin (p<0.001 and p<0.05, respectively); only the UTS of the trilayer samples was slightly significantly lower (p<0.05). Metabolic activity was significantly increased for cells on all scaffolds, without significant differences between them from Day 0 to Day 28. There were no adverse effects of β-APN on cell viability. With respect to contraction, cells on trilayer and PHBV monolayers did not undergo any significant contraction; however, cells on PLA monolayer and Euroskin contracted 25.3% and 56.4%, respectively, over 28 days. The addition of 200 μg/ml β-APN significantly reduced contraction of Euroskin compared with the control (p<0.01); however, β-APN did not affect PLA contraction during this culture period (p>0.05). This study shows that a trilayer micro-nano-3D porous synthetic scaffold is suitable for oral keratinocyte and fibroblast growth with good cell viability and minimal contraction. This material also has good mechanical properties and histological analyses showed its ability to mimic normal human oral mucosal morphology. Furthermore, synthetic trilayer scaffolds have advantages over biological scaffolds - there is no risk of disease transmission or immunological rejection and they appear resistant to contraction. We suggest they present a good alternative to allodermis for future use in urethral reconstruction.

Engineering poly(hydroxy butyrate-co-hydroxy valerate) based vascular scaffolds to mimic native artery

Electrospun tri-layered fibrous scaffold incorporating VEGF and Platelet Factor Concentrate (PFC) in multiple layers having different layer architectures was designed to mimic native artery. The scaffold consisted of longitudinally aligned poly(hydroxy butyrate-co-hydroxy valerate) (PHBV) and poly(vinyl alcohol) (PVA) nanofibers (inner layer), radially aligned PHBV-elastin nanofibers (middle layer) to provide the bi-directional alignment and combination of longitudinally aligned PHBV-elastin and random PHBV/PVA multiscale fibers (peripheral layer). Tubular constructs of diameter <6 mm were developed. The developed electrospun fibers were characterised by Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy and Tensile tests. Further the burst strength, compliance and stiffness index of tri-layered tubular scaffold was evaluated. SEM images of fibrous layers showed the typical longitudinal and radial alignment of fibers in the tubular construct. SEM images showed that the prepared PHBV nanofibers were in the range of 500–800 nm and PHBV microfibers were of 1–2 μm in diameter in the tri-layered electrospun membrane. PVA nanofibers were of size 200–250 nm. The tensile strength, percentage compliance and stiffness index of tri-layered membrane was in accordance with that of native small blood vessels. The developed tri-layered membrane was blood compatible, with hemolysis degree 0.85 ± 0.21% and did not activate platelets. Controlled release of VEGF and PFC was observed from the scaffold. The biocompatibility of the tri-layered scaffold was evaluated using HUVECs, SMCs and MSCs and SMCs infiltration from the outer layer was also evaluated. Specific protein expression for the HUVECs and SMCs was evaluated by flow cytometry and immunocytochemistry. HUVECs and SMCs exhibited good elongation and alignment along the direction of fibers and was found to maintain its CD31, VE-Cadherin and αSMA expression respectively. The results highlight the importance of bi-directional fiber alignment on the tri-layered electrospun scaffold as a suitable architectural prototype for vascular scaffolds to mimic the native arteries.

Chitosan-Based Trilayer Scaffold for Multitissue Periodontal Regeneration

Periodontal regeneration is still a challenge for periodontists and tissue engineers, as it requires the simultaneous restoration of different tissues—namely, cementum, gingiva, bone, and periodontal ligament (PDL). Here, we synthetized a chitosan (CH)–based trilayer porous scaffold to achieve periodontal regeneration driven by multitissue simultaneous healing. We produced 2 porous compartments for bone and gingiva regeneration by cross-linking with genipin either medium molecular weight (MMW) or low molecular weight (LMW) CH and freeze-drying the resulting scaffolds. We synthetized a third compartment for PDL regeneration by CH electrochemical deposition; this allowed us to produce highly oriented microchannels of about 450-µm diameter intended to drive PDL fiber growth toward the dental root. In vitro characterization showed rapid equilibrium water content for MMW-CH and LMW-CH compartments (equilibrium water content after 5 min >85%). The MMW-CH compartment degraded more slowly and provided significantly more resistance to compression (28% ± 1% of weight loss at 4 wk; compression modulus HA = 18 ± 6 kPa) than the LMW-CH compartment (34% ± 1%; 7.7 ± 0.8 kPa) as required to match the physiologic healing rates of bone and gingiva and their mechanical properties. More than 90% of all human primary periodontal cell populations tested on the corresponding compartment survived during cytocompatibility tests, showing active cell metabolism in the alkaline phosphatase and collagen deposition assays. In vivo tests showed high biocompatibility in wild-type mice, tissue ingrowth, and vascularization within the scaffold. Using the periodontal ectopic model in nude mice, we preseeded scaffold compartments with human gingival fibroblasts, osteoblasts, and PDL fibroblasts and found a dense mineralized matrix within the MMW-CH region, with weakly mineralized deposits at the dentin interface. Together, these results support this resorbable trilayer scaffold as a promising candidate for periodontal regeneration.

Evaluation of the effectiveness of a bMSC and BMP-2 polymeric trilayer system in cartilage repair

In this study a poly(lactide-co-glycolide) acid (PLGA) tri-layer scaffold is proposed for cartilage repair. The trilayer system consists of a base layer formed by a tablet of PLGA microspheres, a second layer composed of a microsphere suspension placed on top of the tablet, and the third layer, which constitutes an external electrospun PLGA thin polymeric membrane. Combinations of bone morphogenetic protein-2 (BMP-2) encapsulated in the microspheres of the suspension layer, and bone marrow mesenchymal stem cells (bMSC) seeded on the electrospun membrane, are evaluated by histologic analyses and immunohistochemistry in a critical size osteochondral defect in rabbits. Five experimental groups, including a control group (empty defect), a blank group (blank scaffold), a bMSC treated group, two groups treated with 2.5 μg or 8.5 μg of BMP-2 and another two groups implanted with bMSC-BMP-2 combination are evaluated. The repair area increases throughout the experimental time (24 weeks). The repair observed in the treated groups is statistically higher than in control and blank groups. However, the bMSC-BMP-2 combination does not enhance the BMP-2 response. In conclusion, BMP-2 and bMSC repaired effectively the osteochondral defect in the rabbits. The bMSC-BMP-2 combination did not produce synergism.

A new strategy for fabrication of bone scaffolds using electrospun nano-HAp/PHB fibers and protein hydrogels

Electrospinning is an effective technology for fabrication of ultrafine fibers suitable for a tissue engineering scaffold. A limiting factor of electrospun scaffolds is however their tightly packed network providing only a superficial porous structure. Alternatively, hydrogels can be used to create scaffolds with a well-interconnected porous structure; but these materials provide a poor mechanical stability and a very low bioactivity, failing to create suitable three-dimensional constructs for bone tissue engineering. In this study, we therefore developed a novel hybrid scaffold system in which an electrospun mat based on biodegradable polyhydroxybutyrate (PHB) and hydroxyapatite (HAp) was combined with a protein-based hydrogel in a single tri-layered scaffold. In the resulting construct, while the hydrogel layers provide a suitable environment for cell encapsulation, the incorporated fibers act as a strong backbone increasing the mechanical properties of the scaffold. According to the results, mechanical properties of the construct were much higher than traditional hydrogels. Moreover, bone cells inside the scaffold were highly viable, and infiltrated into the electrospun center after 14days of encapsulation. Given the high strength and the ability to encapsulate cells, the new cell-laden tri-layered scaffold was expected to enhance bone regeneration in vivo.

Tri-layered silk fibroin and poly-ɛ-caprolactone small diameter vascular grafts tested in vitro and in vivo

A silk fibroin (SF) and poly-e-caprolactone (PCL) tri-layered nano-fibrous scaffold composed of an inner, middle, and outer layer is fabricated via sequential electrospinning. The middle layer of the SF/PCL blend nano-fiber is introduced to minimize delamination of each layer of the scaffold. The inner layer is composed of SF with Spirulina maxima extract (SP), and the outer is composed of PCL. The anti-thrombic effects of SP are tested first. The structure, mechanical properties, and cytocompatibility of the scaffold are evaluated. The tri-layered nano-fiber scaffold is implanted into a rat carotid artery, and the sample after 3 weeks of implantation is evaluated histologically. The SP exerts anti-thrombic activity, and the SF with SP inhibits platelet adhesion. The tri-layered scaffold with the middle layer composed of SF/PCL blend exhibits excellent tensile strengths, burst pressure strength, and suture retention strength. The fabricated material does not induce any cytotoxicity. The cells are well spread on the scaffold. Recipient vessel maintains patency 3 weeks after implantation. The inner lumen of the scaffold reveals regenerated endothelial cells. The results indicate that the tri-layered tubular SF/PCL vascular grafts can be used in vascular tissue engineering due to their excellent mechanical properties and good tissue regeneration capability. Open image in new window

Development of a Basement Membrane Substitute Incorporated Into an Electrospun Scaffold for 3D Skin Tissue Engineering

A major challenge in the production of 3D tissue engineered skin is the recreation of the basement membrane region to promote secure attachment and yet segregation of keratinocytes from the dermal substitute impregnated with fibroblasts. We have previously shown that simple electrospun scaffolds provide fibres on which the cells attach, proliferate, and self-sort into epithelium and dermis. In a development of this in this study tri-layered scaffolds were then electrospun from poly L-lactic acid and poly hydroxybutyrate-co-hydroxyvalerate. In these a central layer of the scaffolds comprising nano-porous/nano-fibrous poly hydroxybutyrate-co-hydroxyvalerate fibres was interwoven into the bulk micro-porous poly L-lactic acid microfibers to mimic the basement membrane. Keratinocytes and fibroblasts seeded onto these scaffolds and cultured for 2 weeks showed that neither cell type was able to cross the central nano-porous barrier (shown by SEM, and fluorescence monitoring with CellTracker ™ ) while the micro-fibrous poly L-lactic acid provided a scaffold on which keratinocytes could create an epithelium and fibroblasts could create a dermal substitute depositing collagen. Although cells did not penetrate this barrier the interaction of cells was still evident-essential for epithelial development.

Tri-layered elastomeric scaffolds for engineering heart valve leaflets

Tissue engineered heart valves (TEHVs) that can grow and remodel have the potential to serve as permanent replacements of the current non-viable prosthetic valves particularly for pediatric patients. A major challenge in designing functional TEHVs is to mimic both structural and anisotropic mechanical characteristics of the native valve leaflets. To establish a more biomimetic model of TEHV, we fabricated tri-layered scaffolds by combining electrospinning and microfabrication techniques. These constructs were fabricated by assembling microfabricated poly(glycerol sebacate) (PGS) and fibrous PGS/poly(caprolactone) (PCL) electrospun sheets to develop elastic scaffolds with tunable anisotropic mechanical properties similar to the mechanical characteristics of the native heart valves. The engineered scaffolds supported the growth of valvular interstitial cells (VICs) and mesenchymal stem cells (MSCs) within the 3D structure and promoted the deposition of heart valve extracellular matrix (ECM). MSCs were also organized and aligned along the anisotropic axes of the engineered tri-layered scaffolds. In addition, the fabricated constructs opened and closed properly in an ex vivo model of porcine heart valve leaflet tissue replacement. The engineered tri-layered scaffolds have the potential for successful translation towards TEHV replacements.

Bio-mechanical Properties of Novel Bi-layer Collagen-Elastin Scaffolds for Heart Valve Tissue Engineering

Collagen and elastin are two major components of the extracellular matrix of heart valves. This work examines bi-layer scaffolds made of collagen and elastin for potential use in the tissue engineering of heart valves, by investigating the effects of the layered structure on the mechanical and biological properties. The scaffolds showed anisotropic bending moduli depending on the loading directions (lower when with curvature than against curvature), which mimicked the characteristic behaviour of the native heart valves. The interaction of cardiosphere-drived cells with the scaffolds was characterized by scanning electron microscopy and multiphoton microscopy, and an asymmetrical cell distribution was observed. The bi-layer scaffolds have represented a forwarding step to the tri-layer scaffolds that more closely resemble the native heart valves.

Fabrication and mechanical evaluation of anatomically-inspired quasilaminate hydrogel structures with layer-specific formulations.

A major tissue engineering challenge is the creation of multilaminate scaffolds with layer-specific mechanical properties representative of native tissues, such as heart valve leaflets, blood vessels, and cartilage. For this purpose, poly(ethylene glycol) diacrylate (PEGDA) hydrogels are attractive materials due to their tunable mechanical and biological properties. This study explored the fabrication of trilayer hydrogel quasilaminates. A novel sandwich method was devised to create quasilaminates with layers of varying stiffnesses. The trilayer structure was comprised of two "stiff" outer layers and one "soft" inner layer. Tensile testing of bilayer quasilaminates demonstrated that these scaffolds do not fail at the interface. Flexural testing showed that the bending modulus of acellular quasilaminates fell between the bending moduli of the "stiff" and "soft" hydrogel layers. The bending modulus and swelling of trilayer scaffolds with the same formulations were not significantly different than single layer gels of the same formulation. The encapsulation of cells and the addition of phenol red within the hydrogel layers decreased bending modulus of the trilayer scaffolds. The data presented demonstrates that this fabrication method can make quasilaminates with robust interfaces, integrating layers of different mechanical properties and biofunctionalization, and thus forming the foundation for a multilaminate scaffold that more accurately represents native tissue.

Electrospun vascular graft properties following femtosecond laser ablation

AbstractFor polymers in tissue engineering to reach their full potential, the three‐dimensional integration of cells with scaffolds must become more complex. In vascular grafts this is particularly challenging as specific physical property requirements must be met. We apply a combination of polymer processing techniques—electrospinning and femtosecond laser ablation—to produce microchannels inside the walls of electrospun tubes providing for spatially‐controlled cell seeding. To determine if such a scaffold can provide the desired physical properties, a greater understanding of the relationship between manufacturing and mechanics is needed. As the strength of these scaffolds is an important functional component, the relative properties of single, bi‐ and tri‐layer combinations produced using different solvents were compared. The effect of fiber layer thickness was also investigated. The thickness of the hexafluorisopropanol‐derived layer dominated the overall scaffold properties regardless of the nature of the other two layers. Although laser‐machined microchannels had substantial effects on single layer and some of the bilayers, in the “final” trilayer scaffold, little effect on mechanical properties was observed. The concept of “vascular wall engineering” could successfully produce trilayer composite scaffolds that maintain the targeted mechanical properties while allowing intricate, three‐dimensional cell seeding. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012