Increased Stiffness Downregulates Focal Adhesion Kinase Expression in Pancreatic Cancer Cells Cultured in 3D Self-Assembling Peptide Scaffolds.

The focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that participates in integrin-mediated signal transduction and contributes to different biological processes, such as cell migration, survival, proliferation and angiogenesis. Moreover, FAK can be activated by autophosphorylation at position Y397 and trigger different signaling pathways in response to increased extracellular matrix stiffness. In addition, FAK is overexpressed and/or hyperactivated in many epithelial cancers, and its expression correlates with tumor malignancy and invasion potential. One of the characteristics of solid tumors is an over deposition of ECM components, which generates a stiff microenvironment that promotes, among other features, sustained cell proliferation and survival. Researchers are, therefore, increasingly developing cell culture models to mimic the increased stiffness associated with these kinds of tumors. In the present work, we have developed a new 3D in vitro model to study the effect of matrix stiffness in pancreatic ductal adenocarcinoma (PDAC) cells as this kind of tumor is characterized by a desmoplastic stroma and an increased stiffness compared to its normal counterpart. For that, we have used a synthetic self-assembling peptide nanofiber matrix, RAD16-I, which does not suffer a significant degradation in vitro, thus allowing to maintain the same local stiffness along culture time. We show that increased matrix stiffness in synthetic 3D RAD16-I gels, but not in collagen type I scaffolds, promotes FAK downregulation at a protein level in all the cell lines analyzed. Moreover, even though it has classically been described that stiff 3D matrices promote an increase in pFAKY397/FAK proteins, we found that this ratio in soft and stiff RAD16-I gels is cell-type-dependent. This study highlights how cell response to increased matrix stiffness greatly depends on the nature of the matrix used for 3D culture.

ß-Sheet to Random Coil Transition in Self-Assembling Peptide Scaffolds Promotes Proteolytic Degradation.

One of the most desirable properties that biomaterials designed for tissue engineering or drug delivery applications should fulfill is biodegradation and resorption without toxicity. Therefore, there is an increasing interest in the development of biomaterials able to be enzymatically degraded once implanted at the injury site or once delivered to the target organ. In this paper, we demonstrate the protease sensitivity of self-assembling amphiphilic peptides, in particular, RAD16-I (AcN-RADARADARADARADA-CONH2), which contains four potential cleavage sites for trypsin. We detected that when subjected to thermal denaturation, the peptide secondary structure suffers a transition from ß-sheet to random coil. We also used Matrix-Assisted Laser Desorption/Ionization-Time-Of-Flight (MALDI-TOF) to detect the proteolytic breakdown products of samples subjected to incubation with trypsin as well as atomic force microscopy (AFM) to visualize the effect of the degradation on the nanofiber scaffold. Interestingly, thermally treated samples had a higher extent of degradation than non-denatured samples, suggesting that the transition from ß-sheet to random coil leaves the cleavage sites accessible and susceptible to protease degradation. These results indicate that the self-assembling peptide can be reduced to short peptide sequences and, subsequently, degraded to single amino acids, constituting a group of naturally biodegradable materials optimal for their application in tissue engineering and regenerative medicine.

Erlotinib Promotes Ligand-Induced EGFR Degradation in 3D but Not 2D Cultures of Pancreatic Ductal Adenocarcinoma Cells.

The epithelial growth factor receptor (EGFR) is a tyrosine kinase receptor that participates in many biological processes such as cell proliferation. In addition, EGFR is overexpressed in many epithelial cancers and therefore is a target for cancer therapy. Moreover, EGFR responds to lots of stimuli by internalizing into endosomes from where it can be recycled to the membrane or further sorted into lysosomes where it undergoes degradation. Two-dimensional cell cultures have been classically used to study EGFR trafficking mechanisms in cancer cells. However, it has been widely demonstrated that in 2D cultures cells are exposed to a non-physiological environment as compared to 3D cultures that provide the normal cellular conformation, matrix dimensionality and stiffness, as well as molecular gradients. Therefore, the microenvironment of solid tumors is better recreated in 3D culture models, and this is why they are becoming a more physiological alternative to study cancer physiology. Here, we develop a new model of EGFR internalization and degradation upon erlotinib treatment in pancreatic ductal adenocarcinoma (PDAC) cells cultured in a 3D self-assembling peptide scaffold. In this work, we show that treatment with the tyrosine kinase inhibitor erlotinib promotes EGFR degradation in 3D cultures of PDAC cell lines but not in 2D cultures. We also show that this receptor degradation does not occur in normal fibroblast cells, regardless of culture dimensionality. In conclusion, we demonstrate not only that erlotinib has a distinct effect on tumor and normal cells but also that pancreatic ductal adenocarcinoma cells respond differently to drug treatment when cultured in a 3D microenvironment. This study highlights the importance of culture systems that can more accurately mimic the in vivo tumor physiology.

Syndecans and Pancreatic Ductal Adenocarcinoma.

Pancreatic Ductal Adenocarcinoma (PDAC) is a fatal disease with poor prognosis because patients rarely express symptoms in initial stages, which prevents early detection and diagnosis. Syndecans, a subfamily of proteoglycans, are involved in many physiological processes including cell proliferation, adhesion, and migration. Syndecans are physiologically found in many cell types and their interactions with other macromolecules enhance many pathways. In particular, extracellular matrix components, growth factors, and integrins collect the majority of syndecans associations acting as biochemical, physical, and mechanical transducers. Syndecans are transmembrane glycoproteins, but occasionally their extracellular domain can be released from the cell surface by the action of matrix metalloproteinases, converting them into soluble molecules that are capable of binding distant molecules such as extracellular matrix (ECM) components, growth factor receptors, and integrins from other cells. In this review, we explore the role of syndecans in tumorigenesis as well as their potential as therapeutic targets. Finally, this work reviews the contribution of syndecan-1 and syndecan-2 in PDAC progression and illustrates its potential to be targeted in future treatments for this devastating disease.

Culture and Differentiation of Human Hair Follicle Dermal Papilla Cells in a Soft 3D Self-Assembling Peptide Scaffold.

Hair follicle dermal papilla cells (HFDPC) are a specialized cell population located in the bulge of the hair follicle with unique characteristics such as aggregative behavior and the ability to induce new hair follicle formation. However, when expanded in conventional 2D monolayer culture, their hair inductive potency is rapidly lost. Different 3D culture techniques, including cell spheroid formation, have been described to restore, at least partially, their original phenotype, and therefore, their hair inductive ability once transplanted into a recipient skin. Moreover, hair follicle dermal papilla cells have been shown to differentiate into all mesenchymal lineages, but their differentiation potential has only been tested in 2D cultures. In the present work, we have cultured HFDPC in the 3D self-assembling peptide scaffold RAD16-I to test two different tissue engineering scenarios: restoration of HFDPC original phenotype after cell expansion and osteogenic and adipogenic differentiation. Experimental results showed that the 3D environment provided by RAD16-I allowed the restoration of HFDPC signature markers such as alkaline phosphatase, versican and corin. Moreover, RAD16-I supported, in the presence of chemical inductors, three-dimensional osteogenic and adipogenic differentiation. Altogether, this study suggests a potential 3D culture platform based on RAD16-I suitable for the culture, original phenotype recovery and differentiation of HFDPC.

Elastomeric cardiopatch scaffold for myocardial repair and ventricular support.

OBJECTIVES: Prevention of postischaemic ventricular dilatation progressing towards pathological remodelling is necessary to decrease ventricular wall deterioration. Myocardial tissue engineering may play a therapeutic role due to its capacity to replace the extracellular matrix, thereby creating niches for cell homing. In this experimental animal study, a biomimetic cardiopatch was created with elastomeric scaffolds and nanotechnologies. METHODS: In an experimental animal study in 18 sheep, a cardiopatch was created with adipose tissue-derived progenitor cells seeded into an engineered bioimplant consisting of 3-dimensional bioabsorbable polycaprolactone scaffolds filled with a peptide hydrogel (PuraMatrix™). This patch was then transplanted to cover infarcted myocardium. Non-absorbable poly(ethyl) acrylate polymer scaffolds were used as controls. RESULTS: Fifteen sheep were followed with ultrasound scans at 6 months, including echocardiography scans, tissue Doppler and spectral flow analysis and speckle-tracking imaging, which showed a reduction in longitudinal left ventricular deformation in the cardiopatch-treated group. Magnetic resonance imaging (late gadolinium enhancement) showed reduction of infarct size relative to left ventricular mass in the cardiopatch group versus the controls. Histopathological analysis at 6 months showed that the cardiopatch was fully anchored and integrated to the infarct area with minimal fibrosis interface, thereby promoting angiogenesis and migration of adipose tissue-derived progenitor cells to surrounding tissues. CONCLUSIONS: This study shows the feasibility and effectiveness of a cardiopatch grafted onto myocardial infarction scars in an experimental animal model. This treatment decreased fibrosis, limited infarct scar expansion and reduced postischaemic ventricular deformity. A capillary network developed between our scaffold and the heart. The elastomeric cardiopatch seems to have a positive impact on ventricular remodelling and performance in patients with heart failure.

Culturing Mammalian Cells in Three-dimensional Peptide Scaffolds.

A useful technique for culturing cells in a self-assembling nanofiber three-dimensional (3D) scaffold is described. This culture system recreates an environment that closely mimics the structural features of non-polarized tissue. Furthermore, the particular intrinsic nanofiber structure of the scaffold makes it transparent to visual light, which allows for easy visualization of the sample under microscopy. This advantage was largely used to study cell migration, organization, proliferation, and differentiation and thus any development of their particular cellular function by staining with specific dyes or probes. Furthermore, in this work, we describe the good performance of this system to easily study the redifferentiation of expanded human articular chondrocytes into cartilaginous tissue. Cells were encapsulated into self-assembling peptide scaffolds and cultured under specific conditions to promote chondrogenesis. Three-dimensional cultures showed good viability during the 4 weeks of the experiment. As expected, samples cultured with chondrogenic inducers (compared to non-induced controls) stained strongly positive for toluidine blue (which stains glycosaminoglycans (GAGs) that are highly present in cartilage extracellular matrix) and expressed specific molecular markers, including collagen type I, II and X, according to Western Blot analysis. This protocol is easy to perform and can be used at research laboratories, industries and for educational purposes in laboratory courses.

Development of a 3D Co-Culture System as a Cancer Model Using a Self-Assembling Peptide Scaffold.

Cancer research has traditionally relied on two-dimensional (2D) cell culture, focusing mainly on cancer cells and their abnormal genetics. However, over the past decade, tumors have been accepted as complex tissues rather than a homogenous mass of proliferating cells. Consequently, cancer cells' behavior can only be deciphered considering the contribution of the cells existing in the tumor stroma as well as its complex microenvironment. Since the tumor microenvironment plays a critical role in tumorigenesis, it is widely accepted that culturing cells in three-dimensional (3D) scaffolds, which mimic the extracellular matrix, represents a more realistic scenario. In the present work, an in vitro 3D co-culture system based on the self-assembling peptide scaffold RAD16-I (SAPS RAD16-I) was developed as a cancer model. For that, PANC-1 cells were injected into a RAD16-I peptide scaffold containing fibroblasts, resulting in a 3D system where cancer cells were localized in a defined area within a stromal cells matrix. With this system, we were able to study the effect of three well-known pharmaceutical drugs (Gemcitabine, 5-Fluorouracil (5-FU), and 4-Methylumbelliferone (4-MU)) in a 3D context in terms of cell proliferation and survival. Moreover, we have demonstrated that the anti-cancer effect of the tested compounds can be qualitatively and quantitatively evaluated on the developed 3D co-culture system. Experimental results showed that Gemcitabine and 5-FU prevented PANC-1 cell proliferation but had a high cytotoxic effect on fibroblasts as well. 4-MU had a subtle effect on PANC-1 cells but caused high cell death on fibroblasts.

Use of RGD-Functionalized Sandwich Cultures to Promote Redifferentiation of Human Pancreatic Beta Cells After In Vitro Expansion.

Islet transplantation has provided proof of concept that cell therapy can restore normoglycemia in patients with diabetes. However, limited availability of islet tissue severely restricts the clinical use of the treatment. Thus, there is an urgent need to develop new strategies to generate an abundant source of insulin-producing cells that could be used to treat diabetes. A potential approach is the in vitro expansion of pancreatic beta cells obtained from cadaveric organ donors. However, when human beta cells are expanded in vitro, they dedifferentiate and lose the expression of insulin, probably as a consequence of pancreatic islet dissociation into single cells. We have studied whether reestablishment of cell-cell and cell-matrix relationships with a biomimetic synthetic scaffold could induce redifferentiation of expanded dedifferentiated beta cells. Cells isolated from human islet preparations were expanded in monolayer cultures and allowed to reaggregate into islet-like cell clusters (ICCs). Afterward, ICCs were embedded between two thin layers of the noninstructive self-assembling peptide (SAP), RAD16-I or RAD16-I functionalized with the integrin-binding motif RGD (RAD16-I/RGD) (R: arginine, G: glycine, D: aspartic acid), which was expected to promote cell-extracellular matrix interactions. ICCs cultured with RAD16-I were viable, maintained their cluster conformation, and increased in size by aggregation of ICCs, suggesting a self-organizing process. ICCs cultured in RAD16-I/RGD showed enhanced cell adhesion to RAD16-I matrix and reexpression of the beta cell-specific genes, Ins, Pdx1, Nkx6.1, and MafA. Redifferentiation was caused solely by bioactive cues introduced to the RAD16-I peptide since no differentiation factors were added to the culture medium. The results indicate that RGD-functionalized SAP in sandwich conformation is a promising three-dimensional platform to induce redifferentiation toward a beta cell phenotype and to generate insulin-expressing cells that could be used in diabetes therapy.

Chondroitin Sulfate- and Decorin-Based Self-Assembling Scaffolds for Cartilage Tissue Engineering.

Cartilage injury and degenerative tissue progression remain poorly understood by the medical community. Therefore, various tissue engineering strategies aim to recover areas of damaged cartilage by using non-traditional approaches. To this end, the use of biomimetic scaffolds for recreating the complex in vivo cartilage microenvironment has become of increasing interest in the field. In the present study, we report the development of two novel biomaterials for cartilage tissue engineering (CTE) with bioactive motifs, aiming to emulate the native cartilage extracellular matrix (ECM). We employed a simple mixture of the self-assembling peptide RAD16-I with either Chondroitin Sulfate (CS) or Decorin molecules, taking advantage of the versatility of RAD16-I. After evaluating the structural stability of the bi-component scaffolds at a physiological pH, we characterized these materials using two different in vitro assessments: re-differentiation of human articular chondrocytes (AC) and induction of human adipose derived stem cells (ADSC) to a chondrogenic commitment. Interestingly, differences in cellular morphology and viability were observed between cell types and culture conditions (control and chondrogenic). In addition, both cell types underwent a chondrogenic commitment under inductive media conditions, and this did not occur under control conditions. Remarkably, the synthesis of important ECM constituents of mature cartilage, such as type II collagen and proteoglycans, was confirmed by gene and protein expression analyses and toluidine blue staining. Furthermore, the viscoelastic behavior of ADSC constructs after 4 weeks of culture was more similar to that of native articular cartilage than to that of AC constructs. Altogether, this comparative study between two cell types demonstrates the versatility of our novel biomaterials and suggests a potential 3D culture system suitable for promoting chondrogenic differentiation.

Heparin-based self-assembling peptide scaffold reestablish chondrogenic phenotype of expanded de-differentiated human chondrocytes.

The use of chondrocytes in cell-based therapies for cartilage lesions are limited by quantity and, therefore, require an in vitro expansion. As monolayer culture leads to de-differentiation, different culture techniques are currently under development to recover chondrocyte phenotype after cell expansion. In the present work, we studied the capacity of the bimolecular heparin-based self-assembling peptide scaffold (RAD16-I) as a three-dimensional (3D) culture system to foster reestablishment of chondrogenic phenotype of de-differentiated human Articular Chondrocytes (AC). The culture was performed in a serum-free medium under control and chondrogenic induction and good viability results were observed after 4 weeks of culture in both conditions. Cells changed their morphology to a more elongated shape and established a cellular network that induced the condensation of the constructs in the case of chondrogenic medium, leading to a compacted structure with improved mechanical properties. Specific extracellular matrix (ECM) proteins of mature cartilage, such as collagen type II and aggrecan were up-regulated under chondrogenic medium and significantly enhanced with the presence of heparin in the scaffold. 3D constructs became highly stained with toluidine blue dye after 4 weeks of culture, indicating the presence of synthetized proteoglycans (PGs) by the cells. Interestingly, the full viscoelastic behavior was closely related to that found in chicken native cartilage. Altogether, the results suggest that the 3D culture model described can help de-differentiated human chondrocytes to recover its cartilage phenotype. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1694-1706, 2016.

Three-Dimensional Cultures of Human Subcutaneous Adipose Tissue-Derived Progenitor Cells Based on RAD16-I Self-Assembling Peptide.

The prolonged ischemia after myocardial infarction leads to a high degree of cardiomyocyte death, which leads to a reduction of normal heart function. Valuable lessons can be learnt from human myocardium and stem cell biology that would help scientists to develop new, effective, safe, and affordable regenerative therapies. In vivo models are of high interest, but their high complexity limits the possibility to analyze specific factors. In vitro models permit analyzing specific factors of tissue physiology or pathophysiology providing accurate approaches that may guide the creation of three-dimensional (3D) engineered cell aggregates. These systems provide a simplistic way to examine individual factors as compared to animal models, and better mimic the reality than 2D models. In this sense, the objective of this work is to better understand the behavior of a human mesenchymal stem cell-like cell line (subcutaneous adipose tissue-derived progenitor cells [subATDPCs], susceptible to be used in cell therapies) when they are embedded in the 3D environment provided by RAD16-I self-assembling peptide (SAP). Specifically, we study the effect in subATDPCs viability, morphology, proliferation, and protein and gene expression of matrix composition (i.e., RGD motif and heparin polysaccharide modifications) in RAD16-I matrix under different media conditions. Results demonstrated that the 3D environment provided by RAD16-I SAP is able to maintain subATDPCs in this new milieu and at the same time its cardiac commitment. Additionally, it has been observed that chemical induction can induce upregulation of cardiac markers, such as TBX5, MEF2C, ACTN1, and GJA1. Therefore, we propose this 3D model as a promising platform to analyze the effect of specific cues that can help improve cell performance for future cell therapy.

Dedifferentiated Human Articular Chondrocytes Redifferentiate to a Cartilage-Like Tissue Phenotype in a Poly(ε-Caprolactone)/Self-Assembling Peptide Composite Scaffold.

Adult articular cartilage has a limited capacity for growth and regeneration and, with injury, new cellular or biomaterial-based therapeutic platforms are required to promote repair. Tissue engineering aims to produce cartilage-like tissues that recreate the complex mechanical and biological properties found in vivo. In this study, a unique composite scaffold was developed by infiltrating a three-dimensional (3D) woven microfiber poly (ε-caprolactone) (PCL) scaffold with the RAD16-I self-assembling nanofibers to obtain multi-scale functional and biomimetic tissue-engineered constructs. The scaffold was seeded with expanded dedifferentiated human articular chondrocytes and cultured for four weeks in control and chondrogenic growth conditions. The composite constructs were compared to control constructs obtained by culturing cells with 3D woven PCL scaffolds or RAD16-I independently. High viability and homogeneous cell distribution were observed in all three scaffolds used during the term of the culture. Moreover, gene and protein expression profiles revealed that chondrogenic markers were favored in the presence of RAD16-I peptide (PCL/RAD composite or alone) under chondrogenic induction conditions. Further, constructs displayed positive staining for toluidine blue, indicating the presence of synthesized proteoglycans. Finally, mechanical testing showed that constructs containing the PCL scaffold maintained the initial shape and viscoelastic behavior throughout the culture period, while constructs with RAD16-I scaffold alone contracted during culture time into a stiffer and compacted structure. Altogether, these results suggest that this new composite scaffold provides important mechanical requirements for a cartilage replacement, while providing a biomimetic microenvironment to re-establish the chondrogenic phenotype of human expanded articular chondrocytes.

Chondrogenic potential of human dermal fibroblasts in a contractile, soft, self-assembling, peptide hydrogel.

The present paper describes a simple approach to obtain three-dimensional (3D) cartilage constructs using human normal dermal fibroblasts (hNDFs) cultured in a self-assembling peptide nanofibre scaffold. During the first days of culture, the 3D constructs underwent morphological changes consisting of a substantial contraction process that ended in a small compact structure. During this process the system became sensitive to induction with standard chondrogenic medium, evidenced by the expression of specific markers of mature cartilage. First, it was detected that the samples become highly stained with toluidine blue dye over time (40-50 days), indicating that the system produced significantly high amounts of glycosaminoglycans. By quantitative PCR, it was confirmed that the system significantly upregulated the expression of the proteoglycan aggrecan, a good indicator of cartilage commitment. Moreover, collagen type II was upregulated at protein level, confirming that the system differentiated to a chondrocyte-like construct. Additionally, during the first days of culture in control medium analysed hNDFs proliferation capacity in this 3D system was analysed. This platform could be used in the future to obtain an autologous source of cells from a simple patient skin biopsy, which could be easily translated into a low-cost and effective regenerative therapy.

Cardiac differentiation potential of human induced pluripotent stem cells in a 3D self-assembling peptide scaffold.

In the past decade, various strategies for cardiac reparative medicine involving stem cells from multiple sources have been investigated. However, the intra-cardiac implantation of cells with contractile ability may seriously disrupt the cardiac syncytium and de-synchronize cardiac rhythm. For this reason, bioactive cardiac implants, consisting of stem cells embedded in biomaterials that act like band aids, have been exploited to repair the cardiac wall after myocardial infarction. For such bioactive implants to function properly after transplantation, the choice of biomaterial is equally important as the selection of the stem cell source. While adult stem cells have shown promising results, they have various disadvantages including low proliferative potential in vitro, which make their successful usage in human transplants difficult. As a first step towards the development of a bioactive cardiac patch, we investigate here the cardiac differentiation properties of human induced pluripotent stem cells (hiPSCs) when cultured with and without ascorbic acid (AA) and when embedded in RAD16-I, a biomaterial commonly used to develop cardiac implants. In adherent cultures and in the absence of RAD16-I, AA promotes the cardiac differentiation of hiPSCs by enhancing the expression of specific cardiac genes and proteins and by increasing the number of contracting clusters. In turn, embedding in peptide hydrogel based on RAD16-I interferes with the normal cardiac differentiation progression. Embedded hiPSCs up-regulate genes associated with early cardiogenesis by up to 105 times independently of the presence of AA. However, neither connexin 43 nor troponin I proteins, which are related with mature cardiomyocytes, were detected and no contraction was noted in the constructs. Future experiments will need to focus on characterizing the mature cardiac phenotype of these cells when implanted into infarcted myocardia and assess their regenerative potential in vivo.

Bimolecular based heparin and self-assembling hydrogel for tissue engineering applications.

One major goal of tissue engineering is to develop new biomaterials that are similar structurally and functionally to the extracellular matrix (ECM) to mimic natural cell environments. Recently, different types of biomaterials have been developed for tissue engineering applications. Among them, self-assembling peptides are attractive candidates to create artificial cellular niches, because their nanoscale network and biomechanical properties are similar to those of the natural ECM. Here, we describe the development of a new biomaterial for tissue engineering composed by a simple combination of the self-assembling peptide RAD16-I and heparin sodium salt. As a consequence of the presence of heparin moieties the material acquired enhances the capacity of specific binding and release of growth factors (GFs) with heparin binding affinity such as VEGF165. Promising results were obtained in the vascular tissue engineering area, where the new composite material supported the development of tubular-like structures within a three dimensional (3D) culture model. Moreover, the new scaffold enhances the cell survival and chondrogenic commitment of adipose-derived stem cells (ADSC). Interestingly, the expression of specific markers of mature cartilage tissue including collagen type II was confirmed by western blot and real-time PCR. Furthermore, positive staining for proteoglycans (PGs) indicated the synthesis of cartilage tissue ECM components. Finally, the constructs did not mineralize and exhibited mechanical properties of a tissue undergoing chondrogenesis. Altogether, these results suggest that the new composite is a promising "easy to prepare" material for different reparative and regenerative applications.

Bioengineering 3D environments for cancer models.

Tumor development is a dynamic process where cancer cells differentiate, proliferate and migrate interacting among each other and with the surrounding matrix in a three-dimensional (3D) context. Interestingly, the process follows patterns similar to those involved in early tissue formation by accessing specific genetic programs to grow and disseminate. Thus, the complex biological mechanisms driving tumor progression cannot easily be recreated in the laboratory. Yet, essential tumor stages, including epithelial-mesenchymal transition (EMT), tumor-induced angiogenesis and metastasis, urgently need more realistic models in order to unravel the underlying molecular and cellular mechanisms that govern them. The latest implementation of successful 3D models is having a positive impact on the fight against cancer by obtaining more predictive systems for pre-clinical research, therapeutic drug screening, and early cancer diagnosis. In this review we explore the latest advances and challenges in tumor tissue engineering, by accessing knowledge and tools from cancer biology, material science and bioengineering.

Engineered 3D bioimplants using elastomeric scaffold, self-assembling peptide hydrogel, and adipose tissue-derived progenitor cells for cardiac regeneration.

Contractile restoration of myocardial scars remains a challenge with important clinical implications. Here, a combination of porous elastomeric membrane, peptide hydrogel, and subcutaneous adipose tissue-derived progenitor cells (subATDPCs) was designed and evaluated as a bioimplant for cardiac regeneration in a mouse model of myocardial infarction. SubATDPCs were doubly transduced with lentiviral vectors to express bioluminescent-fluorescent reporters driven by constitutively active, cardiac tissue-specific promoters. Cells were seeded into an engineered bioimplant consisting of a scaffold (polycaprolactone methacryloyloxyethyl ester) filled with a peptide hydrogel (PuraMatrix™), and transplanted to cover injured myocardium. Bioluminescence and fluorescence quantifications showed de novo and progressive increases in promoter expression in bioactive implant-treated animals. The bioactive implant was well adapted to the heart, and fully functional vessels traversed the myocardium-bioactive implant interface. Treatment translated into a detectable positive effect on cardiac function, as revealed by echocardiography. Thus, this novel implant is a promising construct for supporting myocardial regeneration.

Online monitoring of myocardial bioprosthesis for cardiac repair.

BACKGROUND/OBJECTIVES: The aim of this study was to develop a myocardial bioprosthesis for cardiac repair with an integrated online monitoring system. Myocardial infarction (MI) causes irreversible myocyte loss and scar formation. Tissue engineering to reduce myocardial scar size has been tested with variable success, yet scar formation and modulation by an engineered graft is incompletely characterized. METHODS: Decellularized human pericardium was embedded using self-assembling peptide RAD16-I with or without GFP-labeled mediastinal adipose tissue-derived progenitor cells (MATPCs). Resulting bioprostheses were implanted over the ischemic myocardium in the swine model of MI (n=8 treated and n=5 control animals). For in vivo electrical impedance spectroscopy (EIS) monitoring, two electrodes were anchored to construct edges, covered by NanoGold particles and connected to an impedance-based implantable device. Histological evaluation was performed to identify and characterize GFP cells on post mortem myocardial sections. RESULTS: Pluripotency, cardiomyogenic and endothelial potential and migratory capacity of porcine-derived MATPCs were demonstrated in vitro. Decellularization protocol efficiency, biodegradability, as well as in vitro biocompatibility after recellularization were also verified. One month after myocardial bioprosthesis implantation, morphometry revealed a 36% reduction in infarct area, Ki67(+)-GFP(+)-MATPCs were found at infarct core and border zones, and bioprosthesis vascularization was confirmed by presence of Griffonia simplicifolia lectin I (GSLI) B4 isolectin(+)-GFP(+)-MATPCs. Electrical impedance measurement at low and high frequencies (10 kHz-100 kHz) allowed online monitoring of scar maturation. CONCLUSIONS: With clinical translation as ultimate goal, this myocardial bioprosthesis holds promise to be a viable candidate for human cardiac repair.

Matrix dimensions, stiffness, and structural properties modulate spontaneous chondrogenic commitment of mouse embryonic fibroblasts.

Experimental models for cartilage and bone development have been studied in order to understand the biomechanical and biological parameters that regulate skeletal tissue formation. We have previously described that when mouse embryonic fibroblasts (MEFs) were cultured in a three-dimensional (3D)-soft self-assembling peptide nanofiber, the system engaged in a spontaneous process of cartilage-like formation evidenced by the expression of Sox9, Collagen type II, and proteoglycans. In the present work, we studied the influence that matrix mechanical properties have in modulating lineage commitment in an in vitro model of chondrogenesis. This effect was observed only when MEFs were cultured at low elastic modulus values (∼ 0.1 kPa). Interestingly, under these conditions, the system expressed the chondrogenic inductor BMP4 and its antagonist Noggin. On the other hand, at higher elastic modulus values (∼ 5 kPa), the system expressed Noggin but not BMP4, and did not engage in chondrogenesis, which suggest that the balance between bone morphogenetic protein/Noggin could be implicated in the chondrogenic process. Finally, no evidence of hypertrophy was detected under the conditions tested (by assessing expression of Collagen type X and Runx2) unless we challenged the system by co-culturing it with endothelial cells. Importantly, under these new conditions, the system underwent spontaneous matrix calcium mineralization. These results suggest that the 3D-system described here is sensitive to respond to environmental changes such as biomechanical and biological cues.