Preparation of poly(glycolic acid) bonded fiber structures for cell attachment and transplantation

Production of new 3D scaffolds for bone tissue regeneration by rapid prototyping

The incidence of bone disorders, whether due to trauma or pathology, has been trending upward with the aging of the worldwide population. The currently available treatments for bone injuries are rather limited, involving mainly bone grafts and implants. A particularly promising approach for bone regeneration uses rapid prototyping (RP) technologies to produce 3D scaffolds with highly controlled structure and orientation, based on computer-aided design models or medical data. Herein, tricalcium phosphate (TCP)/alginate scaffolds were produced using RP and subsequently their physicochemical, mechanical and biological properties were characterized. The results showed that 60/40 of TCP and alginate formulation was able to match the compression and present a similar Young modulus to that of trabecular bone while presenting an adequate biocompatibility. Moreover, the biomineralization ability, roughness and macro and microporosity of scaffolds allowed cell anchoring and proliferation at their surface, as well as cell migration to its interior, processes that are fundamental for osteointegration and bone regeneration.

Mandibular Tissue Engineering: Past, Present, Future

Almost 2 decades ago, the senior author's (M.T.J.) first article was with our mentor, Dr Leonard B. Kaban, a review article titled "Distraction Osteogenesis: Past, Present, Future." In 1998, many thought it would be impossible to have a remotely activated, small, curvilinear distractor that could be placed using endoscopic techniques. Currently, a U.S. patent for a curvilinear automated device and endoscopic techniques for minimally invasive access for jaw reconstruction exist. With minimally invasive access for jaw reconstruction, the burden to decrease donor site morbidity has increased. Distraction osteogenesis (DO) is an in vivo form of tissue engineering. The DO technique eliminates a donor site, is less invasive, requires a shorter operative time than usual procedures, and can be used for multiple reconstruction applications. Tissue engineering could further reduce morbidity and cost and increase treatment availability. The purpose of the present report was to review our experience with tissue engineering of bone: the past, present, and our vision for the future. The present report serves as a tribute to our mentor and acknowledges Dr Kaban for his incessant tutelage, guidance, wisdom, and boundless vision.

Superelastic, superabsorbent and 3D nanofiber-assembled scaffold for tissue engineering

Fabrication of 3D scaffold to mimic the nanofibrous structure of the nature extracellular matrix (ECM) with appropriate mechanical properties and excellent biocompatibility, remain an important technical challenge in tissue engineering. The present study reports the strategy to fabricate a 3D nanofibrous scaffold with similar structure to collagen in ECM by combining electrospinning and freeze-drying technique. With the technique reported here, a nanofibrous structure scaffold with hydrophilic and superabsorbent properties can be readily prepared by Gelatin and Polylactic acid (PLA). In wet state the scaffold also shows a super-elastic property, which could bear a compressive strain as high as 80% and recovers its original shape afterwards. Moreover, after 6 days of culture, L-929 cells grow, proliferate and infiltrated into the scaffold. The results suggest that this 3D nanofibrous scaffold would be promising for varied field of tissue engineering application.

Development of biomimetic nanocomposites as bone extracellular matrix for human osteoblastic cells

Here, we have developed biomimetic nanocomposites containing chitosan, poly(vinyl alcohol) and nano-hydroxyapatite-zinc oxide as bone extracellular matrix for human osteoblastic cells and characterized by Fourier transform infrared spectroscopy, powder X-ray diffraction. Scanning electron microscopy images revealed interconnected macroporous structures. Moreover, in this study, the problem related to fabricating a porous composite with good mechanical strength has been resolved by incorporating 5wt% of nano-hydroxyapatite-zinc oxide into chitosan-poly(vinyl alcohol) matrix; the present composite showed high tensile strength (20.25MPa) while maintaining appreciable porosity (65.25%). These values are similar to human cancellous bone. These nanocomposites also showed superior water uptake, antimicrobial and biodegradable properties than the previously reported results. Compatibility with human blood and pH was observed, indicating nontoxicity of these materials to the human body. Moreover, proliferation of osteoblastic MG-63 cells onto the nanocomposites was also observed without having any negative effect.

Fabrication of a three-dimensional tissue model microarray using laser foaming of a gas-impregnated biodegradable polymer

A microarray containing three-dimensional (3D) tissue models is a promising substitute for the two-dimensional (2D) cell-based microarrays currently available for high throughput, tissue-based biomedical assays. A cell culture microenvironment similar to in vivo conditions could be achieved with biodegradable porous scaffolds. In this study, a laser foaming technique is developed to create an array of micro-scale 3D porous scaffolds. The effects of major process parameters and the morphology of the resulting porous structure were investigated. For comparison, cell culture studies were conducted with both foamed and unfoamed samples using T98G cells. The results show that by laser foaming gas-impregnated polylactic acid it is possible to generate an array of inverse cone shaped wells with porous walls. The size of the foamed region can be controlled with laser power and exposure time, while the pore size of the scaffold can be manipulated with the saturation pressure. T98G cells grow well in the foamed scaffolds, forming clusters that have not been observed in 2D cell cultures. Cells are more viable in the 3D scaffolds than in the 2D cell culture cases. The 3D porous microarray could be used for parallel studies of drug toxicity, guided stem cell differentiation, and DNA binding profiles.

Computer aided biomanufacturing of mechanically robust pure collagen meshes with controlled macroporosity

Reconciliation of high strength and high porosity in pure collagen based structures is a major barrier in collagen's use in load-bearing applications. The current study developed a CAD/CAM based electrocompaction method to manufacture highly porous patterned scaffolds using pure collagen. Utilization of computerized scaffold design and fabrication allows the integration of mesh-scaffolds with controlled pore size, shape and spacing. Mechanical properties of fabricated collagen meshes were investigated as a function of number of patterned layers, and with different pore geometries. The tensile stiffness, tensile strength and modulus ranges from 10-50 N cm(-1), 1-6 MPa and 5-40 MPa respectively for all the scaffold groups. These results are within the range of practical usability of different tissue engineering application such as tendon, hernia, stress urinary incontinence or thoracic wall reconstruction. Moreover, 3-fold increase in the layer number resulted in more than 5-fold increases in failure load, toughness and stiffness which suggests that by changing the number of layers and shape of the structure, mechanical properties can be modulated for the aforementioned tissue engineering application. These patterned scaffolds offer a porosity ranging from 0.8 to 1.5 mm in size, a range that is commensurate with pore sizes of repair meshes in the market. The connected macroporosity of the scaffolds facilitated cell-seeding such that cells populated the entire scaffold at the time of seeding. After 3 d of culture, cell nuclei became elongated. These results indicate that the patterned electrochemical deposition method in this study was able to develop mechanically robust, highly porous collagen scaffolds with controlled porosity which not only tries to solve one of the major tissue engineering problems at a fundamental level but also has a significant potential to be used in different tissue engineering applications.

Neural tissue regeneration in experimental brain injury model with channeled scaffolds of acrylate copolymers

The objective of the present study was to evaluate the biocompatibility and cell hosting ability of a copolymer scaffold based on ethyl acrylate (EA) and hydroxyl ethyl acrylate (HEA) in vivo after an experimental brain injury. Wistar rats were subjected to cryogenic traumatic brain injury. We evaluated the tissue response to the implanted materials after 8 weeks. The materials were implanted devoid of cells; they provoked a minimal scar response by the host tissue and permitted the invasion of neurons and glia inside them. We also found new blood vessels surrounding and inside the implant. Thus, the copolymer scaffold proves to offer a suitable environment producing a cellular network potentially useful in brain repair after brain injury.

A simple and robust method for pre-wetting poly (lactic-co-glycolic) acid microspheres

Poly (lactic-co-glycolic) acid microspheres are amenable to a number of biomedical procedures that support delivery of cells, drugs, peptides or genes. Hydrophilisation or wetting of poly (lactic-co-glycolic) acid are an important pre-requisites for attachment of cells and can be achieved via exposure to plasma oxygen or nitrogen, surface hydrolysis with NaOH or chloric acid, immersion in ethanol and water, or prolonged incubation in phosphate buffered saline or cell culture medium. The aim of this study is to develop a simple method for wetting poly (lactic-co-glycolic) acid microspheres for cell delivery applications. A one-step ethanol immersion process that involved addition of serum-supplemented medium and ethanol to PLGA microspheres over 30 min–24 h is described in the present study. This protocol presents a more efficient methodology than conventional two-step wetting procedures. Attachment of human skeletal myoblasts to poly (lactic-co-glycolic) acid microspheres was dependent on extent of wetting, changes in surface topography mediated by ethanol pre-wetting and serum protein adsorption. Ethanol, at 70% (v/v) and 100%, facilitated similar levels of wetting. Wetting with 35% (v/v) ethanol was only achieved after 24 h. Pre-wetting (over 3 h) with 70% (v/v) ethanol allowed significantly greater (p ≤ 0.01) serum protein adsorption to microspheres than wetting with 35% (v/v) ethanol. On serum protein-loaded microspheres, greater numbers of myoblasts attached to constructs wetted with 70% ethanol than those partially wetted with 35% (v/v) ethanol. Microspheres treated with 70% (v/v) ethanol presented a more rugose surface than those treated with 35% (v/v) ethanol, indicating that more efficient myoblast adhesion to the former may be at least partially attributed to differences in surface structure. We conclude that our novel protocol for pre-wetting poly (lactic-co-glycolic) acid microspheres that incorporates biochemical and structural features into this biomaterial can facilitate myoblast delivery for use in clinical settings.

Enzymatic degradation and porous morphology of poly(l-lactide) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) blends

Due to the specificity of the degradation enzymes, the porous PLLA and the porous P(3HB-co-4HB) could be acquired by selectively removal of the P(3HB-co-4HB) component and the PLLA component, respectively.

Mechanical reinforcement of diopside bone scaffolds with carbon nanotubes

Carbon nanotubes are ideal candidates for the mechanical reinforcement of ceramic due to their excellent mechanical properties, high aspect ratio and nanometer scale diameter. In this study, the effects of multi-walled carbon nanotubes (MWCNTs) on the mechanical properties of diopside (Di) scaffolds fabricated by selective laser sintering were investigated. Results showed that compressive strength and fracture toughness improved significantly with increasing MWCNTs from 0.5 to 2 wt %, and then declined with increasing MWCNTs to 5 wt %. Compressive strength and fracture toughness were enhanced by 106% and 21%, respectively. The reinforcing mechanisms were identified as crack deflection, MWCNTs crack bridging and pull-out. Further, the scaffolds exhibited good apatite-formation ability and supported adhesion and proliferation of cells in vitro.

Design of 2D chitosan scaffolds via electrochemical structuring

Chitosan (CS) is a versatile biopolymer whose morphological and chemico-physical properties can be designed for a variety of biomedical applications. Taking advantage of its electrolytic nature, cathodic polarization allows CS deposition on electrically conductive substrates, resulting in thin porous structures with tunable morphology. Here we propose an easy method to obtain CS membranes with highly oriented micro-channels for tissue engineering applications, relying on simple control of process parameters and cathodic substrate geometry.

 

Cathodic deposition was performed on two different aluminum grids in galvanostatic conditions at 6.25 mA cm⁻² from CS solution [1g L⁻¹] in acetic acid (pH 3.5). Self-standing thin scaffolds were cross linked either with genipin or epichlorohydrin, weighted, and observed by optical and electron microscopy. Swelling properties at pH 5 and pH 7.4 have been also investigated and tensile tests performed on swollen samples at room temperature. Finally, direct and indirect assays have been performed to evaluate the cytotoxicity at 24 and 72 h.

Thin scaffolds with two different oriented porosities (1000µm and 500µm) have been successfully fabricated by electrochemical techniques. Both cross-linking agents did not affected the mechanical properties and cytocompatibility of the resulting structures. Depending on the pH, these structures show interesting swelling properties that can be exploited for drug delivery systems. Moreover, thanks to the possibility of controlling the porosity and the micro-channel orientation, they should be used for the regeneration of tissues requiring a preferential cells orientation, e.g., cardiac patches or ligament regeneration.

3D PLLA/ibuprofen composite scaffolds obtained by a supercritical fluids assisted process

The emerging next generation of engineered tissues is based on the development of loaded scaffolds containing bioactive molecules in order to control the cellular function or to interact on the surrounding tissues. Indeed, implantation of engineered biomaterials might cause local inflammation because of the host's immune response; thereby, the use of anti-inflammatory agents, whether steroidal or nonsteroidal is required. One of the most important stages of tissue engineering is the design and the generation of a porous 3D structure, with high porosity, high interconnectivity and homogenous morphology. Various techniques have been reported in the literature for the fabrication of biodegradable scaffolds, but they suffer several limitations. In this study, for the first time, the possibility of generating 3D polymeric scaffolds loaded with an active compound by supercritical freeze extraction process is evaluated; this innovative process combines the advantages of the thermally induced phase separation process and of the supercritical carbon dioxide drying. Poly-L-lactid acid/ibuprofen composite scaffolds characterized by a 3D geometry, micrometric cellular structures and wrinkled pores walls have been obtained; moreover, homogeneous drug distribution and controlled release of the active principle have been assured.

Erectile function restoration after repair of resected cavernous nerves by adipose-derived stem cells combined with autologous vein graft in rats

Cavernous nerve (CN) injury is the main cause of erectile dysfunction (ED) following radical prostatectomy. The recovery of erectile function following this procedure remains challenging. Here, we investigated the ability of adipose-derived stem cells (ADSCs) combined with autologous vein graft to improve erectile function in a rat model of bilateral long CN resection. Sprague-Dawley rats (n = 36) were randomized into four groups. Group A underwent sham operation. In Groups B, C, and D, an 8-mm segment of CN was excised bilaterally. In Group B and C, a 10-mm segment of autologous saphenous vein was interposed bilaterally at the site of injury, and the two nerve stumps were inserted into the vein lumen. 50 μL ADSCs were injected into each vein in Group B, and 50 μL of phosphate-buffered saline was injected in Group C. Group D underwent no repair. Erectile function assessed after 3 months by measuring intracavernosal pressure demonstrated significant recovery in erectile function in Group B with minimal recovery in Group C or D. Immunohistochemical staining showed that the nNOS-positive area was significantly larger in Group B than in Group D. ADSCs combined with autologous vein graft treatment had beneficial effects on the smooth muscle/collagen ratio in the corpus cavernosum. This procedure, therefore, provided a means of regenerating CN tissue and restoring autonomic erectile function after long bilateral CN resection (0.8 cm) in rats.

Nano/microfibrous polymeric constructs loaded with bioactive agents and designed for tissue engineering applications: a review

Nano/microfibrous polymeric constructs present various inherent advantages, such as highly porous architecture and high surface to volume ratio, making them attractive for tissue engineering purposes. Electrospinning is the most preferred technique for the fabrication of polymeric nanofibrous assemblies that can mimic the physical functions of native extracellular matrix greatly favoring cells attachment and thus influencing their morphology and activities. Different approaches have been developed to apply polymeric microfiber fabrication techniques (e.g. wet-spinning) for the obtainment of scaffolds with a three-dimensional network of micropores suitable for effective cells migration. Progress in additive manufacturing technology has led to the development of complex scaffold's shapes and microfibrous structures with a high degree of automation, good accuracy and reproducibility. Various loading methods, such as direct blending, coaxial electrospinning and microparticles incorporation, are enabling to develop customized strategies for the biofunctionalization of nano/microfibrous scaffolds with a tailored kinetics of release of different bioactive agents, ranging from small molecules, such as antibiotics, to protein drugs, such as growth factors, and even cells. Recent activities on the combination of different processing techniques and loading methods for the obtainment of biofunctionalized polymeric constructs with a complex multiscale structure open new possibilities for the development of biomimetic scaffolds endowed with a hierarchical architecture and a sophisticated release kinetics of different bioactive agents. This review is aimed at summarizing current advances in technologies and methods for manufacturing nano/microfibrous polymeric constructs suitable as tissue engineering scaffolds, and for their combination with different bioactive agents to promote tissue regeneration and therapeutic effects.

Solvent-free Fabrication of Tissue Engineering Scaffolds with Immiscible Polymer Blends

A completely organic solvent-free fabrication method is developed for tissue engineering scaffolds by gas foaming of immiscible polylactic acid (PLA) and sucrose blends, followed by water leaching. PLA scaffolds with above 90% porosity and 25-200 μm pore size were fabricated. The pore size and porosity was controlled with process parameters including extrusion temperature and foaming process parameters. Dynamic mechanical analysis showed that the extrusion temperature could be used to control the scaffold strength. Both unfoamed and foamed scaffolds were used to culture glioblastoma (GBM) cells M059K. The results showed that the cells grew better in the foamed PLA scaffolds. The method presented in the paper is versatile and can be used to fabricate tissue engineering scaffolds without any residual organic solvents.

New development of carbonate apatite-chitosan scaffold based on lyophilization technique for bone tissue engineering

Carbonate apatite-chitosan scaffolds (CA-ChSs) were fabricated using the lyophilization technique. It was found that ChSs prepared with 200 mg chitosan powder (ChSs200) had well-structured three-dimensional architecture with high porosity and good retentive form without brittleness. In addition, it was shown that the number of osteoblast-like cells MC3T3-E1 proliferated on desalinated ChSs200 was larger than that on the non-desalinated ChSs200. CA-ChSs were fabricated by adding 100 mg carbonate apatite (CA) to 200 mg chitosan gels followed by freeze-drying (CA100ChSs200). SEM observation revealed that CA100ChSs200 had favorable three- dimensional porous structures. The number of living cells increased more rapidly on CA100ChSs200 prepared with different amounts of CA than on ChSs. ALP activity significantly increased after day 14 and reached a plateau after day 21 in ChSs200 and CA100ChSs200. It was concluded that newly developed CA100ChSs200 may be a possible scaffold material for tissue engineering.

3-D PLLA scaffolds formation by a supercritical freeze extraction assisted process

Various techniques have been reported in the literature for the fabrication of biodegradable scaffolds; but, it is very difficult to obtain in the same structure macro, micro and nanostructural characteristics. In this work we developed a supercritical freeze extraction process (SFEP) for the formation of poly(L-lactic acid) (PLLA) scaffolds, that combines the advantages of thermally induced phase separation with those of supercritical drying. We processed solutions in chloroform of two PLLA molecular weights and at different polymer concentrations ranging between 5 and 20 % w/w. Supercritical drying was performed at 35 °Cand pressures ranging between 100 and 250 bar. 3-D scaffolds characterized by high porosity (between 88 and 97.5 %), with coexisting micro and nanometric morphology were obtained. Structures generated were characterized by pores ranging between 10 and 30 μm and with a wrinkled nanostructure of about 200 nm, superimposed on the internal pore surface, that could be useful for biomedical applications. A solvent residue lower than 5 ppm was also measured.

Macroscale delivery systems for molecular and cellular payloads

Macroscale drug delivery (MDD) devices are engineered to exert spatiotemporal control over the presentation of a wide range of bioactive agents, including small molecules, proteins and cells. In contrast to systemically delivered drugs, MDD systems act as a depot of drug localized to the treatment site, which can increase drug effectiveness while reducing side effects and confer protection to labile drugs. In this Review, we highlight the key advantages of MDD systems, describe their mechanisms of spatiotemporal control and provide guidelines for the selection of carrier materials. We also discuss the combination of MDD technologies with classic medical devices to create multifunctional MDD devices that improve integration with host tissue, and the use of MDD technology in tissue-engineering strategies to direct cell behaviour. As our ever-expanding knowledge of human biology and disease provides new therapeutic targets that require precise control over their application, the importance of MDD devices in medicine is expected to increase.

Decellularized bovine intervertebral disc as a natural scaffold for xenogenic cell studies

Low back pain that is associated with disc degeneration contributes to a huge economic burden in the worldwide healthcare system. Traditional methods, such as spinal fusion, have been adopted to relieve mechanical back pain, but this is compromised by decreased spinal motion. Tissue engineering has attracted much attention, and aims to correct the changes fundamentally occurring in the discs by a combination of cell biology, molecular biology and engineering. Synthetic materials including poly(l-lactic acid) or poly(glycolic acid) and biomolecules like hyaluronic acid or collagen have been adopted in the development of disc scaffolds for studying therapeutic approaches. Nevertheless, the complex biological and mechanical environment of the intervertebral disc (IVD) makes the synthesis of an artificial IVD with biomaterials a difficult task. Thus the aim of this study was to develop a natural disc scaffold for culturing disc cells for future development of biological disc constructs. We adopted a combination of currently used decellularization techniques to decellularize bovine IVD to create a complete endplate-to-endplate IVD scaffold. By altering the chemical and physical decellularization parameters, we reported the removal of up to 70% of the endogenous cells, and were able to preserve the glycosaminoglycan content, collagen fibril architecture and mechanical properties of the discs. The reintroduction of nucleus pulposus cells into the scaffold indicated a high survival rate over 7days, with cell penetration. We have shown here that conventional methods used for decellularizing thin tissues can also be applied to large organs, such as IVD. Our findings suggest the potential of using decellularized IVD as a scaffold for IVD bioengineering and culturing of cells in the context of the IVD niche.

Selective laser sintering in biomedical engineering

Selective laser sintering (SLS) is a solid freeform fabrication technique, developed by Carl Deckard for his master's thesis at the University of Texas, patented in 1989. SLS manufacturing is a technique that produces physical models through a selective solidification of a variety of fine powders. SLS technology is getting a great amount of attention in the clinical field. In this paper the characteristics features of SLS and the materials that have been developed for are reviewed together with a discussion on the principles of the above-mentioned manufacturing technique. The applications of SLS in tissue engineering, and at-large in the biomedical field, are reviewed and discussed.

Development of a bone reconstruction technique using a solid free-form fabrication (SFF)-based drug releasing scaffold and adipose-derived stem cells

For tissue regeneration, three essential components of scaffolds, signals (biomolecules), and cells are required. Moreover, because bony defects are three-dimensional in many clinical circumstances, an exact 3D scaffold is important. Therefore, we proposed an effective reconstruction tool for cranial defects using human adipose-derived stem cells (hADSCs) and a 3D functional scaffold fabricated by solid free-form fabrication (SFF) technology that secretes biomolecules. We fabricated poly(propylene fumarate)-based 3D scaffolds with embedded microsphere-deliverable bone morphogenetic protein-2 (BMP-2) by microstereolithography. BMP-2-loaded SFF scaffolds with/without hADSCs (SFF/BMP/hADSCs scaffolds and SFF/BMP scaffolds, respectively) and BMP-2-unloaded SFF scaffolds (SFF scaffolds) were then implanted in rat crania, and in vivo bone formation was observed. Analyses of bone formation areas using micro-computed tomography (micro-CT) showed the superiority of SFF/BMP/hADSCs scaffolds. Hematoxylin and eosin stain, Masson's trichrome stain, and collagen type-I stain supported the results of the micro-CT scan. And human leukocyte antigen-ABC showed that seeded, differentiated hADSCs were well grown and changed to the bone tissue at the inside of the scaffold. Results showed that our combination of a functional 3D scaffold and hADSCs may be a useful tool for improving the reconstruction quality of severe bony defects in which thick bone is required.

Strategic design and fabrication of engineered scaffolds for articular cartilage repair

Damage to articular cartilage can eventually lead to osteoarthritis (OA), a debilitating, degenerative joint disease that affects millions of people around the world. The limited natural healing ability of cartilage and the limitations of currently available therapies make treatment of cartilage defects a challenging clinical issue. Hopes have been raised for the repair of articular cartilage with the help of supportive structures, called scaffolds, created through tissue engineering (TE). Over the past two decades, different designs and fabrication techniques have been investigated for developing TE scaffolds suitable for the construction of transplantable artificial cartilage tissue substitutes. Advances in fabrication technologies now enable the strategic design of scaffolds with complex, biomimetic structures and properties. In particular, scaffolds with hybrid and/or biomimetic zonal designs have recently been developed for cartilage tissue engineering applications. This paper reviews critical aspects of the design of engineered scaffolds for articular cartilage repair as well as the available advanced fabrication techniques. In addition, recent studies on the design of hybrid and zonal scaffolds for use in cartilage tissue repair are highlighted.

Injectable preformed scaffolds with shape-memory properties

Injectable biomaterials are increasingly being explored to minimize risks and complications associated with surgical implantation. We describe a strategy for delivery via conventional needle-syringe injection of large preformed macroporous scaffolds with well-defined properties. Injectable 3D scaffolds, in the form of elastic sponge-like matrices, were prepared by environmentally friendly cryotropic gelation of a naturally sourced polymer. Cryogels with shape-memory properties may be molded to a variety of shapes and sizes, and may be optionally loaded with therapeutic agents or cells. These scaffolds have the capability to withstand reversible deformations at over 90% strain level, and a rapid volumetric recovery allows the structurally defined scaffolds to be injected through a small-bore needle with nearly complete geometric restoration once delivered. These gels demonstrated long-term release of biomolecules in vivo. Furthermore, cryogels impregnated with bioluminescent reporter cells provided enhanced survival, higher local retention, and extended engraftment of transplanted cells at the injection site compared with a standard injection technique. These injectable scaffolds show great promise for various biomedical applications, including cell therapies.

Stiffness-controlled three-dimensional extracellular matrices for high-resolution imaging of cell behavior

Regulation of cell functions by the physical properties of the extracellular matrix (ECM) has emerged as a crucial contributor to development and disease. Two specific physical properties of the ECM, stiffness and dimensionality, each influence cell signaling and function. As these ECM physical properties are linked to other properties that also regulate cell behavior, e.g., integrin ligand density, parsing the specific contributions of ECM stiffness and dimensionality has proven difficult. Here we detail a simple protocol, which can be completed in 1-2 d, for combining three-dimensional (3D) ECM engagement with controlled underlying ECM stiffness. In these 'sandwich gels', cells are sandwiched between a 3D fibrillar ECM and an ECM-coupled polyacrylamide gel of defined compliance, allowing the study of the specific effects of ECM compliance on cell function in physiologically relevant 3D ECMs. This type of system enables high-resolution time-lapse imaging and is suitable for a wide range of cell types and molecular perturbations.

Development of a bioartificial liver employing xenogeneic hepatocytes

Liver failure is a major cause of mortality. A bioartificial liver (BAL) employing isolated hepatocytes can potentially provide temporary support for liver failure patients. We have developed a bioartificial liver by entrapping hepatocytes in collagen loaded in the luminal side of a hollow fiber bioreactor. In the first phase of development, liver-specific metabolic activities of biosynthesis, biotransformation and conjugation were demonstrated. Subsequently anhepatic rabbits were used to show that rat hepatocytes continued to function after the BAL was linked to the test animal. For scale-up studies, a canine liver failure model was developed using D-galactosamine overdose. In order to secure a sufficient number of hepatocytes for large animal treatment, a collagenase perfusion protocol was established for harvesting porcine hepatocytes at high yield and viability. An instrumented bioreactor system, which included dissolved oxygen measurement, pH control, flow rate control, an oxygenator and two hollow fiber bioreactors in series, was used for these studies. An improved survival of dogs treated with the BAL was shown over the controls. In anticipated clinical applications, it is desirable to have the liver-specific activities in the BAL as high as possible. To that end, the possibility of employing hepatocyte spheroids was explored. These self-assembled spheroids formed from monolayer culture exhibited higher liver-specific functions and remained viable longer than hepatocytes in a monolayer. To ease the surface requirement for large-scale preparation of hepatocyte spheroids, we succeeded in inducing spheroid formation in stirred tank bioreactors for both rat and porcine hepatocytes. These spheroids formed in stirred tanks were shown to be morphologically and functionally indistinguishable from those formed from a monolayer. Collagen entrapment of these spheroids resulted in sustaining their liver-specific functions at higher levels even longer than those of spheroids maintained in suspension. For use in the BAL, a mixture of spheroids and dispersed hepatocytes was used to ensure a proper degree of collagen gel contraction. This mixture of spheroids and dispersed cells entrapped in the BAL was shown to sustain the high level of liver-specific functions. The possibility of employing such a BAL for improved clinical performance warrants further investigations.

Marine algae sulfated polysaccharides for tissue engineering and drug delivery approaches

Biomedical field is constantly requesting for new biomaterials, with innovative properties. Natural polymers appear as materials of election for this goal due to their biocompatibility and biodegradability. In particular, materials found in marine environment are of great interest since the chemical and biological diversity found in this environment is almost uncountable and continuously growing with the research in deeper waters. Moreover, there is also a slower risk of these materials to pose illnesses to humans.   In particular, sulfated polysaccharides can be found in marine environment, in different algae species. These polysaccharides don't have equivalent in the terrestrial plants and resembles the chemical and biological properties of mammalian glycosaminoglycans. In this perspective, are receiving growing interest for application on health-related fields. On this review, we will focus on the biomedical applications of marine algae sulfated polymers, in particular on the development of innovative systems for tissue engineering and drug delivery approaches.

Collagen for bone tissue regeneration

In the last decades, increased knowledge about the organization, structure and properties of collagen (particularly concerning interactions between cells and collagen-based materials) has inspired scientists and engineers to design innovative collagen-based biomaterials and to develop novel tissue-engineering products. The design of resorbable collagen-based medical implants requires understanding the tissue/organ anatomy and biological function as well as the role of collagen's physicochemical properties and structure in tissue/organ regeneration. Bone is a complex tissue that plays a critical role in diverse metabolic processes mediated by calcium delivery as well as in hematopoiesis whilst maintaining skeleton strength. A wide variety of collagen-based scaffolds have been proposed for different tissue engineering applications. These scaffolds are designed to promote a biological response, such as cell interaction, and to work as artificial biomimetic extracellular matrices that guide tissue regeneration. This paper critically reviews the current understanding of the complex hierarchical structure and properties of native collagen molecules, and describes the scientific challenge of manufacturing collagen-based materials with suitable properties and shapes for specific biomedical applications, with special emphasis on bone tissue engineering. The analysis of the state of the art in the field reveals the presence of innovative techniques for scaffold and material manufacturing that are currently opening the way to the preparation of biomimetic substrates that modulate cell interaction for improved substitution, restoration, retention or enhancement of bone tissue function.

Progress of key strategies in development of electrospun scaffolds: bone tissue

There has been unprecedented development in tissue engineering (TE) over the last few years owing to its potential applications, particularly in bone reconstruction or regeneration. In this article, we illustrate several advantages and disadvantages of different approaches to the design of electrospun TE scaffolds. We also review the major benefits of electrospun fibers for three-dimensional scaffolds in hard connective TE applications and identify the key strategies that can improve the mechanical properties of scaffolds for bone TE applications. A few interesting results of recent investigations have been explained for future trends in TE scaffold research.