Biodegradable honeycomb collagen scaffold for dermal tissue engineering

A Micro-Scale Non-Linear Finite Element Model to Optimize the Mechanical Behavior of Bioprinted Constructs

Extrusion-based bioprinting is an enabling biofabrication technique that is used to create heterogeneous tissue constructs according to patient-specific geometries and compositions. The optimization of bioinks as per requirements for specific tissue applications is an essential exercise in ensuring clinical translation of the bioprinting technologies. Most notably, optimum hydrogel polymer concentrations are required to ensure adequate mechanical properties of bioprinted constructs without causing significant shear stresses on cells. However, experimental iterations are often tedious for optimizing the bioink properties. In this work, a nonlinear finite element modeling approach has been undertaken to determine the effect of different bioink parameters such as composition, concentration on the range of stresses being experienced by the cells in the bioprinted construct. The stress distribution of the cells at different parts of the constructs has also been modeled. It is found that both bioink chemical compositions and concentrations can substantially alter the stress effects experienced by the cells. Concentrated regions of softer cells near pore regions were found to increase stress concentrations by almost three times compared with stress generated in cells away from the pores. The study provides a method for rapid optimization of bioinks, design of bioprinted constructs, as well as toolpath plans for fabricating constructs with homogenous properties.

Surgical implantation of human adipose derived stem cells attenuates experimentally induced hepatic fibrosis in rats

BACKGROUND

Mesenchymal stem cells (MSCs) are multipotent stromal cells and could exert hepatoprotective effects against acute liver injury, steatohepatitis, and fibrogenesis. Here, we evaluated the effects of human adipose derived stem cells (hADSCs) to attenuate experimentally induced hepatic fibrosis and early cirrhosis in rats.

METHODS

Hepatic fibrosis was induced by intraperitoneal injections of CCl₄ (0.1 ml/100 g body weight) twice a week for 8 weeks. hADSCs were isolated and cultured on polyethylene discs coated with hydroxyapatite and 2 cm diameter disc was surgically implanted on the right lateral lobe of the liver. Discs implanted without hADSCs served as control. The animals were injected again with CCl₄ once a week for another 8 weeks. All the animals were sacrificed at the end of 16th week.

RESULTS

Serial administrations of CCl₄ resulted in well developed fibrosis and early cirrhosis at 8th week which maintained until the 16th week. Animals treated with hADSC discs depicted over 50% decrease of collagen with significant increase in serum albumin and total protein levels. Immunohistochemical staining for TGF-β1, α-smooth muscle actin, and collagen type I and type III demonstrated marked decrease compared to the animals without hADSC treatment.

CONCLUSIONS

Treatment with hADSCs improved liver functions, markedly reduced hepatic fibrosis and early cirrhosis. Various pleiotropic and paracrine factors secreted from the hADSCs seem to serve as reparative functions in the attenuation of liver cirrhosis. The data demonstrated that treatment with hADSCs can be successfully used as a potent therapeutic method to prevent progression of hepatic fibrosis and related adverse events.

In Vitro Biocompatibility and Degradation Analysis of Mass-Produced Collagen Fibers

Automation and mass-production are two of the many limitations in the tissue engineering industry. Textile fabrication methods such as electrospinning are used extensively in this field because of the resemblance of the extracellular matrix to the fiber structure. However, electrospinning has many limitations, including the ability to mass-produce, automate, and reproduce products. For this reason, this study evaluates the potential use of a traditional textile method such as spinning. Apart from mass production, these methods are also easy, efficient, and cost-effective. This study uses bovine-derived collagen fibers to create yarns using the traditional ring spinning method. The collagen yarns are proven to be biocompatible. Enzymatic biodegradability was also confirmed for its potential use in vivo. The results of this study prove the safety and efficacy of the material and the fabrication method. The material encourages higher cell proliferation and migration compared to tissue culture-treated plastic plates. The process is not only simple but is also streamlined and replicable, resulting in standardized products that can be reproduced.

An organic-inorganic hybrid scaffold with honeycomb-like structures enabled by one-step self-assembly-driven electrospinning

Electrospun organic/inorganic hybrid scaffolds have been appealing in tissue regeneration owing to the integrated physicochemical and biological performances. However, the conventional electrospun scaffolds with non-woven structures usually failed to enable deep cell infiltration due to the densely stacked layers among the fibers. Herein, through self-assembly-driven electrospinning, a polyhydroxybutyrate/poly(ε-caprolactone)/58S sol-gel bioactive glass (PHB/PCL/58S) hybrid scaffold with honeycomb-like structures was prepared by manipulating the solution composition and concentration during a one-step electrospinning process. The mechanisms enabling the formation of self-assembled honeycomb-like structures were investigated through comparative studies using Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) between PHB/PCL/58S and PHB/PCL/sol-gel silica systems. The obtained honeycomb-like structure was built up from nanofibers with an average diameter of 370 nm and showed a bimodal distribution of pores: large polygonal pores up to hundreds of micrometers within the honeycomb-cells and irregular pores among the nanofibers ranging around few micrometers. The cell-materials interactions were further studied by culturing MG-63 osteoblast-like cells for 7 days. Cell viability, cell morphology and cell infiltration were comparatively investigated as well. While cells merely proliferated on the surface of non-woven structures, MG-63 cells showed extensive proliferation and deep infiltration up to 100-200 μm into the honeycomb-like structure. Moreover, the cellular spatial organization was readily regulated by the honeycomb-like pattern as well. Overall, the newly obtained hybrid scaffold may integrate the enhanced osteogenicity originating from the bioactive components, and the improved cell-material interactions brought by the honeycomb-like structure, making the new scaffold a promising candidate for tissue regeneration.

A sodium alginate-based sustained-release IPN hydrogel and its applications

Interpenetrating polymer network (IPN) hydrogels are crosslinked by two or more polymer networks, providing free volume space in the three-dimensional network structure, and providing conditions for the sustained and controlled release of drugs. The IPN hydrogels based on the natural polymer sodium alginate can form a stable porous network structure. Due to its excellent biocompatibility, the loaded drug can be sustained to the maximum extent without affecting its pharmacological effect. Sodium alginate-based IPN hydrogels have broad application prospects in the field of sustained and controlled drug release. This paper begins with an overview of the formation of alginate-based IPN hydrogels; summarizes the types of alginate-based IPN hydrogels; and discusses the pharmaceutical applications of alginate-based IPN hydrogels. We aim to give an overview of the research on IPN hydrogels based on sodium alginate in sustained and controlled drug release systems.

Synergistic Effect of Chitosan and Selenium Nanoparticles on Biodegradation and Antibacterial Properties of Collagenous Scaffolds Designed for Infected Burn Wounds

A highly porous scaffold is a desirable outcome in the field of tissue engineering. The porous structure mediates water-retaining properties that ensure good nutrient transportation as well as creates a suitable environment for cells. In this study, porous antibacterial collagenous scaffolds containing chitosan and selenium nanoparticles (SeNPs) as antibacterial agents were studied. The addition of antibacterial agents increased the application potential of the material for infected and chronic wounds. The morphology, swelling, biodegradation, and antibacterial activity of collagen-based scaffolds were characterized systematically to investigate the overall impact of the antibacterial additives. The additives visibly influenced the morphology, water‑retaining properties as well as the stability of the materials in the presence of collagenase enzymes. Even at concentrations as low as 5 ppm of SeNPs, modified polymeric scaffolds showed considerable inhibition activity towards Gram-positive bacterial strains such as Staphylococcus aureus and methicillin-resistant Staphylococcus aureus and Staphylococcus epidermidis in a dose-dependent manner.

Bone Repair with Differentiated Osteoblasts from Adipose-derived Stem Cells in Hydroxyapatite/Tricalcium Phosphate In vivo

BACKGROUND

Recently, tissue engineering has developed approaches for repair and restoration of damaged skeletal system based on different scaffolds and cells. This study evaluated the ability of differentiated osteoblasts from adipose-derived stem cells (ADSCs) seeded into hydroxyapatite/tricalcium phosphate (HA-TCP) to repair bone.

METHODS

In this study, ADSCs of 6 canines were seeded in HA-TCP and differentiated into osteoblasts in osteogenic medium in vitro and bone markers evaluated by reverse transcription polymerase chain reaction (RT-PCR). Scanning electron microscopy (SEM) was applied for detection of cells in the pores of scaffold. HA-TCP with differentiated cells as the test group and without cells as the cell-free group were implanted in separate defected sites of canine's tibia. After 8 weeks, specimens were evaluated by histological, immunohistochemical methods, and densitometry test. The data were analyzed using the SPSS 18 version software.

RESULTS

The expression of Type I collagen and osteocalcin genes in differentiated cells were indicated by RT-PCR. SEM results revealed the adhesion of cells in scaffold pores. Formation of trabecular bone confirmed by histological sections that revealed the thickness of bone trabecular was more in the test group. Production of osteopontin in extracellular matrix was indicated in both groups. Densitometry method indicated that strength in the test group was similar to cell-free group and natural bone (P > 0.05).

CONCLUSIONS

This research suggests that ADSCs-derived osteoblasts in HA-TCP could be used for bone tissue engineering and repairing.

Biomedical Applications of Interpenetrating Polymer Network System

Interpenetrating polymer network (IPN) has been regarded as one of the novel technology in recent years showing the superior performances over the conventional techniques. This system is designed for the delivery of drugs at a predetermined rate and thus helps in controlled drug delivery. Due to its enhanced biological and physical characteristics like biodegradability, biocompatibility, solubility, specificity and stability, IPN has emerged out to be one of the excellent technologies in pharmaceutical industries. This article focuses mainly on the biomedical applications of IPN along with its future applicability in pharmaceutical research. It summarizes various aspects of IPN, biomedical applications and also in-cludes the different dosage forms based on IPN.

Targeted grafting of thermoresponsive polymers from a penetrative honeycomb structure for cell sheet engineering

Responsive membranes have been used to construct smart biomaterial interfaces. We report a novel approach to fabricate honeycomb films with a pattern of thermoresponsive polymer, namely poly(N-isopropylacrylamide). The approach was based on a combination of the breath figure method and reversible addition-fragmentation chain transfer. The hybrid film had morphological and chemical patterns resulting in varied wettability and morphology at various stages, as well as high thermo-responsiveness. Enhanced cell adhesion was observed at an incubation temperature of 37 °C, which is above its lower critical solution temperature (LCST). Furthermore, cells could be harvested at temperatures below the LCST without trypsin treatment. The non-invasive characteristics give this membrane potential as a substrate for cell sheet engineering.

MicroRNAs in skin tissue engineering

35.2 million annual cases in the U.S. require clinical intervention for major skin loss. To meet this demand, the field of skin tissue engineering has grown rapidly over the past 40 years. Traditionally, skin tissue engineering relies on the "cell-scaffold-signal" approach, whereby isolated cells are formulated into a three-dimensional substrate matrix, or scaffold, and exposed to the proper molecular, physical, and/or electrical signals to encourage growth and differentiation. However, clinically available bioengineered skin equivalents (BSEs) suffer from a number of drawbacks, including time required to generate autologous BSEs, poor allogeneic BSE survival, and physical limitations such as mass transfer issues. Additionally, different types of skin wounds require different BSE designs. MicroRNA has recently emerged as a new and exciting field of RNA interference that can overcome the barriers of BSE design. MicroRNA can regulate cellular behavior, change the bioactive milieu of the skin, and be delivered to skin tissue in a number of ways. While it is still in its infancy, the use of microRNAs in skin tissue engineering offers the opportunity to both enhance and expand a field for which there is still a vast unmet clinical need. Here we give a review of skin tissue engineering, focusing on the important cellular processes, bioactive mediators, and scaffolds. We further discuss potential microRNA targets for each individual component, and we conclude with possible future applications.

Insulating and semiconducting polymeric free-standing nanomembranes with biomedical applications

Free-standing nanomembranes, which are emerging as versatile elements in biomedical applications, are evolving from being composed of insulating (bio)polymers to electroactive conducting polymers.

Type II collagen and gelatin from silvertip shark (Carcharhinus albimarginatus) cartilage: isolation, purification, physicochemical and antioxidant properties

Type II acid soluble collagen (CIIA), pepsin soluble collagen (CIIP) and type II gelatin (GII) were isolated from silvertip shark (Carcharhinus albimarginatus) cartilage and examined for their physicochemical and antioxidant properties. GII had a higher hydroxyproline content (173 mg/g) than the collagens and cartilage. CIIA, CIIP and GII were composed of two identical α1 and β chains and were characterized as type II. Amino acid analysis of CIIA, CIIP and GII indicated imino acid contents of 150, 156 and 153 amino acid residues per 1000 residues, respectively. Differing Fourier transform infrared (FTIR) spectra of CIIA, CIIP and GII were observed, which suggested that the isolation process affected the secondary structure and molecular order of collagen, particularly the triple-helical structure. The denaturation temperature of GII (32.5 °C) was higher than that of CIIA and CIIP. The antioxidant activity against 1,1-diphenyl-2-picrylhydrazyl radicals and the reducing power of CIIP was greater than that of CIIA and GII. SEM microstructure of the collagens depicted a porous, fibrillary and multi-layered structure. Accordingly, the physicochemical and antioxidant properties of type II collagens (CIIA, CIIP) and GII isolated from shark cartilage were found to be suitable for biomedical applications.

Thermoplastic polyurethane:polythiophene nanomembranes for biomedical and biotechnological applications

Nanomembranes have been prepared by spin-coating mixtures of a polythiophene (P3TMA) derivative and thermoplastic polyurethane (TPU) using 20:80, 40:60, and 60:40 TPU:P3TMA weight ratios. After structural, topographical, electrochemical, and thermal characterization, properties typically related with biomedical applications have been investigated: swelling, resistance to both hydrolytic and enzymatic degradation, biocompatibility, and adsorption of type I collagen, which is an extra cellular matrix protein that binds fibronectin favoring cell adhesion processes. The swelling ability and the hydrolytic and enzymatic degradability of TPU:P3TMA membranes increases with the concentration of P3TMA. Moreover, the degradation of the blends is considerably promoted by the presence of enzymes in the hydrolytic medium, TPU:P3TMA blends behaving as biodegradable materials. On the other hand, TPU:P3TMA nanomembranes behave as bioactive platforms stimulating cell adhesion and, especially, cell viability. Type I collagen adsorption largely depends on the substrate employed to support the nanomembrane, whereas it is practically independent of the chemical nature of the polymeric material used to fabricate the nanomembrane. However, detailed microscopy study of the morphology and topography of adsorbed collagen evidence the formation of different organizations, which range from fibrils to pseudoregular honeycomb networks depending on the composition of the nanomembrane that is in contact with the protein. Scaffolds made of electroactive TPU:P3TMA nanomembranes are potential candidates for tissue engineering biomedical applications.

Slicing, stacking and rolling: fabrication of nanostructured collagen constructs from tendon sections

A novel method for fabricating both multilayer stacked 2D and 3D tubular constructs composed of sheets of aligned collagen fibers is described. These structures are created by decellularizing native tendon and sectioning the material into thin sheets using a cryo-microtome. This fabrication method preserves the collagens natural strength as well as the fiber structure which would aid in directing aligned cell growth.

Collagen--emerging collagen based therapies hit the patient

The choice of biomaterials available for regenerative medicine continues to grow rapidly, with new materials often claiming advantages over the short-comings of those already in existence. Going back to nature, collagen is one of the most abundant proteins in mammals and its role is essential to our way of life. It can therefore be obtained from many sources including porcine, bovine, equine or human and offer a great promise as a biomimetic scaffold for regenerative medicine. Using naturally derived collagen, extracellular matrices (ECMs), as surgical materials have become established practice for a number of years. For clinical use the goal has been to preserve as much of the composition and structure of the ECM as possible without adverse effects to the recipient. This review will therefore cover in-depth both naturally and synthetically produced collagen matrices. Furthermore the production of more sophisticated three dimensional collagen scaffolds that provide cues at nano-, micro- and meso-scale for molecules, cells, proteins and bulk fluids by inducing fibrils alignments, embossing and layered configuration through the application of plastic compression technology will be discussed in details. This review will also shed light on both naturally and synthetically derived collagen products that have been available in the market for several purposes including neural repair, as cosmetic for the treatment of dermatologic defects, haemostatic agents, mucosal wound dressing and guided bone regeneration membrane. There are other several potential applications of collagen still under investigations and they are also covered in this review.

Preparation of microporous silicone rubber membrane with tunable pore size via solvent evaporation-induced phase separation

Silicone rubber membrane with ordered micropores in the surface was prepared by means of the solvent evaporation-induced phase separation. A ternary solution including liquid silicone rubber precursor, liquid paraffin, and hexane was cast to form a film with a two-phase structure after the hexane was evaporated. The micropores were generated by removing liquid paraffin phase in the cured silicone rubber film. The effects of the liquid paraffin concentration, casting temperature, initial casting solution thickness, air circulation, and addition of surfactant Span-80 on the pore structure in the membrane surface were investigated. The average pore size increases with increasing liquid paraffin concentration or the initial casting solution thickness. The formation of pore structure in the membrane surface is related to the phase separation and thus the phase separation process of the casting solution surface was in situ observed using the digital microscope. The formation mechanism of pore is attributed to a nucleation, growth, and coalescence process of liquid paraffin phase in the membrane surface.

Bioengineered matrices--part 1: attaining structural success in biologic skin substitutes

Skin defect closure after injury or disease may present significant reconstructive challenges. Traditional epidermal coverage alone in the form of skin grafts often fall short in providing stable cover to restore structure and function of the skin. Excessive wound contraction and scar formation, particularly in defects of dermis and epidermis, may create functional and aesthetic problems. Progress in our understanding of molecular biology and tissue engineering have produced major advances in skin substitute technology, particularly relating to the dynamic cellular/extracellular matrix interaction that is critical to successful incorporation of a skin substitute. However, currently available skin substitutes still exhibit a range of problems including excessive wound contraction and scar formation, poor host tissue incorporation, revascularization and, in some cases, structural deficiencies in matrix design. The design principles and structural composition of the matrix must take into account collagenous forms, inherent resistance, porosity, and hydration. The ultimate matrix should be one that promotes intrinsic regeneration by encouraging cellular incorporation and cellular/extracellular cross communication. Attention to basic structural details rather than reliance on specialized cellular or peptide additions to the mix may well produce the advances we seek in improved incorporation of bioengineered skin substitutes.

Engineering of oriented myocardium on three-dimensional micropatterned collagen-chitosan hydrogel

INTRODUCTION

Surface topography and electrical field stimulation are important guidance cues that aid the organization and contractility of cardiomyocytes in vivo. We report here on the use of these biomimetic cues in vitro to engineer an implantable contractile cardiac tissue.

METHODS

Photocrosslinkable collagen-chitosan hydrogels with microgrooves of 10 µm, 20 µm and 100 µm in width were fabricated using polydimethylsiloxane (PDMS) molds. The hydrogels were seeded with cardiomyocytes, placed into a bioreactor array with the microgrooves aligned with the electrical field lines, and stimulated with biphasic square pulses at 1 Hz and 2.5 V/cm.

RESULTS

At Day 6, cardiomyocytes were aligned in the direction of the microgrooves. When cultivated without electrical stimulation, the excitation threshold of engineered cardiac tissues using micropatterned hydrogels was significantly lower than using smooth hydrogels, thus showing the importance of cell alignment to cardiac function. The success rate of achieving beating constructs was higher with the application of electrical stimulation. In addition, formation of dense contractile cardiac organoids was observed in groups with both biomimetic cues. The cultivation of cardiomyocytes on hydrogels with 10 µm grooves yielded 100% beating tissues with or without electrical stimulation, thus suggesting a smaller groove width is necessary for cells to communicate and form proper gap junctions. However, electrical field stimulation further increased cell density and enhanced tissue morphology which may be essential for the integration of the tissue construct to the native heart tissue upon implantation.

CONCLUSIONS

The biodegradability of the hydrogel substrate allows for the rapid translation of the engineered, oriented cardiac tissue to clinical applications.

Cartilage regeneration in SCID mice using a highly organized three-dimensional alginate scaffold

Tissue engineering for cartilage regeneration provides an alternative to surgery for degenerative osteoarthritis. Recently, a highly organized three-dimensional (3D) alginate scaffold was prepared using a microfluidic device; this scaffold is effective for chondrocyte culture in vitro. The performance of this scaffold was further demonstrated; an alginate scaffold seeded with porcine chondrocytes was implanted in the dorsal subcutaneous site of SCID mice. The recipients were sacrificed at 2, 4, and 6 weeks after transplantation. The grafted implants retrieved from the subcutaneous site were analyzed with histologic examinations. Real-time PCR was used to identify the gene expression patterns of the chondrocytes. The hematoxylin and eosin staining showed that the chondrocytes survived normally in SCID mice; cartilage-like structures were formed after 4 weeks implantation. Immunohistochemical staining revealed cells secreted type II collagen, produced glycosaminoglycans (proved by alcian blue stain), and maintained the expression of S-100. On the other hand, the cells were negative for type I and type X collagen staining. PCR showed that the mRNA expressions of aggrecan and type II collagen were up-regulated at weeks two and four, while type I and type X collagen were down-regulated during the study period. In summary, this highly organized 3D alginate scaffold provided a suitable environment and maintained functional phenotypes for chondrocytes in this animal study.

A highly organized three-dimensional alginate scaffold for cartilage tissue engineering prepared by microfluidic technology

Osteoarthritis is a degenerative disease and frequently involves the knee, hip and phalangeal joints. Current treatments used in small cartilage defects including multiple drilling, abrasion arthroplasty, mosaicplasty, and autogenous chondrocyte transplantation, however, there are problems needed to be solved. The standard treatment for severe osteoarthritis is total joint arthroplasty. The disadvantages of this surgery are the possibility of implant loosening. Therefore, tissue engineering for cartilage regeneration has become a promising topic. We have developed a new method to produce a highly organized single polymer (alginate) scaffold using microfluidic device. Scanning electron microscope and confocal fluoroscope examinations showed that the scaffold has a regular interconnected porous structure in the scale of 250 μm and high porosity. The scaffold is effective in chondrocyte culture; the cell viability test (WST-1 assay), cell toxicity (lactate dehydrogenase assay), cell survival rate, extracellular matrix production (glycosaminoglycans contents), cell proliferation (DNA quantification), and gene expression (real-time PCR) all revealed good results for chondrocyte culture. The chondrocytes can maintain normal phenotypes, highly express aggrecan and type II collagen, and secrete a great deal of extracellular matrix when seeded in the alginate scaffold. This study demonstrated that a highly organized alginate scaffold can be prepared with an economical microfluidic device, and this scaffold is effective in cartilage tissue engineering.

Biomedical Applications of Biodegradable Polymers

Utilization of polymers as biomaterials has greatly impacted the advancement of modern medicine. Specifically, polymeric biomaterials that are biodegradable provide the significant advantage of being able to be broken down and removed after they have served their function. Applications are wide ranging with degradable polymers being used clinically as surgical sutures and implants. In order to fit functional demand, materials with desired physical, chemical, biological, biomechanical and degradation properties must be selected. Fortunately, a wide range of natural and synthetic degradable polymers has been investigated for biomedical applications with novel materials constantly being developed to meet new challenges. This review summarizes the most recent advances in the field over the past 4 years, specifically highlighting new and interesting discoveries in tissue engineering and drug delivery applications.

Engineered pullulan-collagen composite dermal hydrogels improve early cutaneous wound healing

New strategies for skin regeneration are needed to address the significant medical burden caused by cutaneous wounds and disease. In this study, pullulan-collagen composite hydrogel matrices were fabricated using a salt-induced phase inversion technique, resulting in a structured yet soft scaffold for skin engineering. Salt crystallization induced interconnected pore formation, and modification of collagen concentration permitted regulation of scaffold pore size. Hydrogel architecture recapitulated the reticular distribution of human dermal matrix while maintaining flexible properties essential for skin applications. In vitro, collagen hydrogel scaffolds retained their open porous architecture and viably sustained human fibroblasts and murine mesenchymal stem cells and endothelial cells. In vivo, hydrogel-treated murine excisional wounds demonstrated improved wound closure, which was associated with increased recruitment of stromal cells and formation of vascularized granulation tissue. In conclusion, salt-induced phase inversion techniques can be used to create modifiable pullulan-collagen composite dermal scaffolds that augment early wound healing. These novel biomatrices can potentially serve as a structured delivery template for cells and biomolecules in regenerative skin applications.

Epidermal differentiation governs engineered skin biomechanics

Engineered skin must be mechanically strong to facilitate surgical application and prevent damage during the early stages of engraftment. However, the evolution of structural properties during culture, the relative contributions of the epidermis and dermis, and any correlation with tissue morphogenesis are not well known. These aspects are investigated by assessing the mechanical properties of engineered skin (ES) and engineered dermis (ED) during a 21-day culture period, including correlations with cellular metabolism, cellular organization and epidermal differentiation. During culture, the epidermis differentiates and begins to cornify, as evidenced by immunostaining and surface electrical capacitance. Tensile testing reveals that the ultimate tensile strength and linear stiffness increase linearly with time for ES, but are relatively unchanged for ED. ES strength correlates significantly with epidermal differentiation (p < 0.001) and a composite strength model indicates that strength is largely determined by the epidermis. These data suggest that strategies to improve ES biomechanics should target the dermis. Additionally, time-dependant changes in average ES strength and percent elongation can be used to set upper bound limits on mechanical stimulation profiles to avoid tissue damage.

Heparin-releasing scaffold for stem cells: a differentiating device for vascular aims

Aims: Current limitations of tissue-engineered vascular grafts include timing for the scaffold preparation, cell type, cell differentiation and growth inside the construct, and thrombogenicity of the final device. To surmount these shortcomings, we developed a heparin-releasing poly-L-lactide (PLLA) scaffold using the electrospinning technique, to guide the differentiation of human mesenchymal stem cells towards the endothelial phenotype and to deliver a useful drug in the management of the postimplantation period. Materials & methods: The heparin-releasing PLLA scaffold was produced by means of the electrospinning technique in a tubular shape. The scaffold was seeded with human mesenchymal stem cells and cultured for up to 1 week. Cell viability and cytotoxicity assays were performed, and cell differentiation was evaluated by immunofluorescence with confocal microscopy, cytofluorometry and western blotting. Heparin release was assayed by Azure A method and biological effectiveness of the drug was assessed by activated clotting time measurements. Results: The scaffold exhibited a morphology favorable to cell attachment. Heparin release showed an initial burst within the first 24 h, followed by a further sustained release profile. After 48 h of culturing, the construct demonstrated adequate engraftment and viability. Increased proliferation compared with the control scaffold in bare PLLA, suggested the induction of a favorable microenvironment. A shift towards CD31 positivity and modifications in cell morphology were observed in the heparin-releasing PLLA scaffold. Conclusion: By exploiting the biological effects of heparin, we developed an ad hoc differentiating device towards the endothelial phenotype for autologous stem cell seeding and, at the same time, we were able to facilitate and optimize the management of the construct once in clinical settings.

A G-CSF functionalized scaffold for stem cells seeding: a differentiating device for cardiac purposes

Myocardial infarction and its consequences represent one of the most demanding challenges in cell therapy and regenerative medicine. Transfer of skeletal myoblasts into decompensated hearts has been performed through intramyocardial injection. However, the achievements of both cardiomyocyte differentiation and precise integration of the injected cells into the myocardial wall, in order to augment synchronized contractility and avoid potentially life-threatening alterations in the electrical conduction of the heart, still remain a major target to be pursued. Recently, granulocytes colony-stimulating factor (G-CSF) fuelled the interest of researchers for its direct effect on cardiomyocytes, inhibiting both apoptosis and remodelling in the failing heart and protecting from ventricular arrhythmias through the up-regulation of connexin 43 (Cx43). We propose a tissue engineering approach concerning the fabrication of an electrospun cardiac graft functionalized with G-CSF, in order to provide the correct signalling sequence to orientate myoblast differentiation and exert important systemic and local effects, positively modulating the infarction microenvironment. Poly-(L-lactide) electrospun scaffolds were seeded with C2C12 murine skeletal myoblast for 48 hrs. Biological assays demonstrated the induction of Cx43 expression along with morphostructural changes resulting in cell elongation and appearance of cellular junctions resembling the usual cardiomyocyte arrangement at the ultrastructural level. The possibility of fabricating extracellular matrix-mimicking scaffolds able to promote myoblast pre-commitment towards myocardiocyte lineage and mitigate the hazardous environment of the damaged myocardium represents an interesting strategy in cardiac tissue engineering.

Combining electrospinning and fused deposition modeling for the fabrication of a hybrid vascular graft

Tissue engineering of blood vessels is a promising strategy in regenerative medicine with a broad spectrum of potential applications. However, many hurdles for tissue-engineered vascular grafts, such as poor mechanical properties, thrombogenicity and cell over-growth inside the construct, need to be overcome prior to the clinical application. To surmount these shortcomings, we developed a poly-L-lactide (PLLA)/poly-epsilon-caprolactone (PCL) scaffold releasing heparin by a combination of electrospinning and fused deposition modeling technique. PLLA/heparin scaffolds were produced by electrospinning in tubular shape and then fused deposition modeling was used to armor the tube with a single coil of PCL on the outer layer to improve mechanical properties. Scaffolds were then seeded with human mesenchymal stem cells (hMSCs) and assayed in terms of morphology, mechanical tensile strength, cell viability and differentiation. This particular scaffold design allowed the generation of both a drug delivery system amenable to surmount thrombogenic issues and a microenvironment able to induce endothelial differentiation. At the same time, the PCL external coiling improved mechanical resistance of the microfibrous scaffold. By the combination of two notable techniques in biofabrication--electrospinning and FDM--and exploiting the biological effects of heparin, we developed an ad hoc differentiating device for hMSCs seeding, able to induce differentiation into vascular endothelium.

Microporous collagen spheres produced via thermally induced phase separation for tissue regeneration

Collagen is an abundant protein found in the extracellular matrix of many tissues. Due to its biocompatibility, it is a potentially ideal biomaterial for many tissue engineering applications. However, harvested collagen often requires restructuring into a three-dimensional matrix to facilitate applications such as implantation into poorly accessible tissue cavities. The aim of the current study was to produce a conformable collagen-based scaffold material capable of supporting tissue regeneration for use in wound repair applications. Microporous collagen spheres were prepared using a thermally induced phase separation (TIPS) technique and their biocompatibility was assessed. The collagen spheres were successfully cross-linked with glutaraldehyde vapour, rendering them mechanically more stable. When cultured with myofibroblasts the collagen spheres stimulated a prolonged significant increase in secretion of the angiogenic growth factor, vascular endothelial growth factor (VEGF), compared with cells alone. Control polycaprolactone (PCL) spheres failed to stimulate a similar prolonged increase in VEGF secretion. An enhanced angiogenic effect was also seen in vivo using the chick embryo chorioallantoic membrane assay, where a significant increase in the number of blood vessels converging towards collagen spheres was observed compared with control PCL spheres. The results from this study indicate that microporous collagen spheres produced using TIPS are biologically active and could offer a novel conformable scaffold for tissue regeneration in poorly accessible wounds.

Influence of telopeptides, fibrils and crosslinking on physicochemical properties of type I collagen films

Type I collagen is widely used in various different forms for research and commercial applications. Different forms of collagen may be classified according to their source, extraction method, crosslinking and resultant ultrastructure. In this study, afibrillar and reconstituted fibrillar films, derived from acid soluble and pepsin digested Type I collagen, were analysed using Lateral Force Microscopy (LFM), Fourier Transform Infra-Red Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and enzymatic stability assays to asses the influence of telopeptides, fibrils and crosslinking. LFM proved to be a useful technique to confirm an afibrillar/fibrillar ultrastructure and to elucidate fibril diameters. FTIR has proved insensitive to ultrastructural differences involving telopeptides and fibrils. DSC results showed a significant increase in T(d) for crosslinked samples (+22-28 degrees C), and demonstrated that the thermal behaviour of hydrated, afibrillar films is more akin to reconstituted fibrillar films than monomeric solutions. The enzymatic stability assay has provided new evidence to show that afibrillar films of Type I collagen can be significantly more resistant to collagenase (by up to 3.5 times), than reconstituted fibrillar films, as a direct consequence of the different spatial arrangement of collagen molecules. A novel mechanism for this phenomenon is proposed and discussed. Additionally, the presence of telopeptide regions in afibrillar tropocollagen samples has been shown to increase resistance to collagenase by greater than 3.5 times compared to counterpart afibrillar atelocollagen samples. One-factor ANOVA analysis, with Fisher's LSD post-hoc test, confirms these key findings to be of statistical significance (P < 0.05). The profound physicochemical effects of collagen ultrastructure demonstrated in this study reiterates the need for comprehensive materials disclosure and classification when using these biomaterials.