Neural tissue engineering: adrenal chromaffin cell attachment and viability on chitosan scaffolds

Bioactive chitosan biguanidine-based injectable hydrogels as a novel BMP-2 and VEGF carrier for osteogenesis of dental pulp stem cells

Nowadays, vascularization and mineralization of bone defects is the main bottleneck in the bone regeneration field that is needed to be overcome and developed. Here, we prepared novel in-situ formed injectable hydrogels based on chitosan biguanidine and carboxymethylcellulose loaded with vascular endothelial growth factor (VEGF) and recombinant Bone morphogenetic protein 2 (BMP-2) and studied its influence on osteoblastic differentiation of dental pulp stem cells (DPSCs). The sequential release behavior of the VEGF and BMP-2 from hydrogels adjusted with the pattern of normal human bone growth. MTT assay exhibited that these hydrogels were non-toxic and significantly increased DPSCs proliferation. The Real-time PCR and Western blot analysis on CG11/BMP2-VEGF showed significantly higher gene and protein expression of ALP, COL1α1, and OCN. These results were confirmed by mineralization assay by Alizarin Red staining and Alkaline phosphatase enzyme activity. Based on these evaluations, these hydrogel holds potential as an injectable bone tissue engineering platform.

Untapped potentials of hazardous nanoarchitectural biopolymers

The First Industrial Revolution began when manual labour transitioned to machines. Fossil fuels and steam eventually replaced wood and water as an energy source used predominantly for the mechanized production of textiles and iron. The emergence of the required numerous enormous factories gave rise to smoke pollution due to the immense growth in coal consumption. The manufactured gas industry produced highly toxic effluent that was released into sewers and rivers polluting the water. Many pieces of legislation were introduced to overcome this issue, but with varying degrees of effectiveness. Alongside our growth in world population, the problems that we had with waste remained, but together with our increase in number the waste produced has also increased additionally. The immense volume of waste materials generated from human activity and the potentially detrimental effects on the environment and on public health have awakened in ourselves a critical need to embrace current scientific methods for the safe disposal of wastes. We are informed daily that our food waste must be better utilized to ensure enough food is available to feed the world's growing population in a sustainable way (Thyberg and Tonjes, 2016). Some things are easy, like waste food and cellulose products can be turned into compost, but how do we recycle sheep's wool? Or shrimp shells? Despite the fact that both these substances are hazardous, and have caused environmental and economic impact from being incinerated; but we anticipate that those substances may have the potential to convert into added value applications.We have been working in this area for over 15 years, working towards managing them and seeking their added value applications. We take the biological products, process (reconstitute) and engineer them into added value products such as functional and nanostructure materials including edible films, foams and composites including medical devices useful in the human body. Anything that we can ingest, should not cause an immune response in the human system. Natural biomacromolecules display the inherent ability to perform very specific chemical, mechanical or structural roles. Specifically, protein- and polysaccharide-based biomaterials have come to light as the most promising candidates for many biomedical applications due their biomimetic and nanostructured arrangements, their multi-functional features, and their capability to function as matrices that are capable of facilitating cell-cell and cell-matrix interactions.

Soft Materials by Design: Unconventional Polymer Networks Give Extreme Properties

Hydrogels are polymer networks infiltrated with water. Many biological hydrogels in animal bodies such as muscles, heart valves, cartilages, and tendons possess extreme mechanical properties including being extremely tough, strong, resilient, adhesive, and fatigue-resistant. These mechanical properties are also critical for hydrogels' diverse applications ranging from drug delivery, tissue engineering, medical implants, wound dressings, and contact lenses to sensors, actuators, electronic devices, optical devices, batteries, water harvesters, and soft robots. Whereas numerous hydrogels have been developed over the last few decades, a set of general principles that can rationally guide the design of hydrogels using different materials and fabrication methods for various applications remain a central need in the field of soft materials. This review is aimed at synergistically reporting: (i) general design principles for hydrogels to achieve extreme mechanical and physical properties, (ii) implementation strategies for the design principles using unconventional polymer networks, and (iii) future directions for the orthogonal design of hydrogels to achieve multiple combined mechanical, physical, chemical, and biological properties. Because these design principles and implementation strategies are based on generic polymer networks, they are also applicable to other soft materials including elastomers and organogels. Overall, the review will not only provide comprehensive and systematic guidelines on the rational design of soft materials, but also provoke interdisciplinary discussions on a fundamental question: why does nature select soft materials with unconventional polymer networks to constitute the major parts of animal bodies?

Osteogenic and antiseptic nanocoating by in situ chitosan regulated electrochemical deposition for promoting osseointegration

Ti and titanium alloy have been extensively utilized in the areas of orthopedics and other related fields, however, limited abilities in antibiosis, ossification and vascularization restrict the application of these materials in clinical. In this research, pulse electrochemical deposition was used as a method to make chitosan regulate Ag⁺ and Ca²⁺ in situ, achieving ions' dual regulations and coprecipitation of HA nanoparticles (HA-NPs) and Ag nanoparticles (Ag-NPs) on the surface of Ti. The spherical nanoparticles with even distribution were fabricated by optimizing deposition potential and the concentration of Ag⁺. The physical stabilities of coatings were significantly improved by the chelation among CS, Ag⁺ and Ca²⁺ reducing the release rate of Ag⁺, Ca²⁺. The coatings also exhibited noticeable abilities in anti-bacteria. Bone marrow mesenchymal stem cells (BMSCs) displayed adhesion, proliferation and differentiation abilities on the surface of coatings, at the same time the composite coatings revealed promising capability in inducing BMSCs differentiation to osteoblast, which is proved by the results of fluorescent dye. Similar results also can be found in investigations about vascular endothelial cells, desirable adhesion between cells and materials and proliferation are able to prove that this kind of materials has outstanding biocompatibility with VECs cells. The animal experiments indicated that the composite coatings were biocompatible with smooth muscle, myocardium and lung with slightly negative impacts on liver and kidney. According to the results of alizarin red staining, the calcified nodules were dyed red, which reveal that this material can promote bone formation. Electrochemical method was utilized in this research to successfully construct multifunctional composite coatings, such as antibiosis, osteogenesis and angiogenesis, on the surface of Ti.

Impact of Three-Dimentional Culture Systems on Hepatic Differentiation of Puripotent Stem Cells and Beyond

Generation of functional hepatocytes from human pluripotent stem cells (hPSCs) is a vital tool to produce large amounts of human hepatocytes, which hold a great promise for biomedical and regenerative medicine applications. Despite a tremendous progress in developing the differentiation protocols recapitulating the developmental signalling and stages, these resulting hepatocytes from hPSCs yet achieve maturation and functionality comparable to those primary hepatocytes. The absence of 3D milieu in the culture and differentiation of these hepatocytes may account for this, at least partly, thus developing an optimal 3D culture could be a step forward to achieve this aim. Hence, review focuses on current development of 3D culture systems for hepatic differentiation and maturation and the future perspectives of its application.

Chitosan-based hydrogels: From preparation to biomedical applications

The advances in the field of biomaterials have led to several studies on alternative biocompatible devices and to their development focusing on their properties, benefits, limitations, and utilization of alternative resources. Due to their advantages like biocompatibility, biodegradability, and low cost, polysaccharides have been widely used in the development of hydrogels. Among the polysaccharides studied on hydrogels preparation, chitosan (pure or combined with natural/synthetic polymers) have been widely investigated for use in biomedical field. In view of potential applications of chitosan-based hydrogels, this review focuses on the most recent progress made with respect to preparation, properties, and their salient accomplishments for drug delivery and tissue engineering.

Functional Hyper-Crosslinkers

Crosslinking is an essential architecture for polymers to improve mechanical and thermal properties and to form three-dimensional (3D) structures. Although conventional synthetic crosslinkers usually only serve as bridges between different polymeric chains, biological crosslinkers are multifunctional. Recently, crosslinkers with active functionality after polymerization are promising a new dimension of molecular design for generating smart materials as they may exhibit dramatic changes in structures and properties in response to external stimuli. This concept article introduces several different designs of hyper-crosslinkers (i.e., multifunctional crosslinkers that provide three or more sites for generating networks) and their applications in tailoring stimuli-responsive and self-healing soft materials. Particularly, the polymeric materials that contain functional hyper-crosslinkers are exhibiting anti-intuitive redox or thermal-pH responses. The goal of this article is to illustrate the concept that functional hyper-crosslinkers not only improve the physical and chemical performance of the polymers, but more importantly, may introduce new architectures and functionalities for soft materials.

Viability and Functionality of Bovine Chromaffin Cells Encapsulated into Alginate-PLL Microcapsules with a Liquefied Inner Core

Implantation of adrenal medullary bovine chromaffin cells (BCC), which synthesize and secrete a combination of pain-reducing neuroactive compounds including catecholamines and opioid peptides, has been proposed for the treatment of intractable cancer pain. Macro- or microencapsulation of such cells within semi-permeable membranes is expected to protect the transplant from the host's immune system. In the present study, we report the viability and functionality of BCC encapsulated into microcapsules of alginate-poly-L-lysine (PLL) with a liquefied inner core. The experiment was carried out during 44 days. Empty microcapsules were characterized in terms of morphology, permeability, and mechanical resistance. At the same time, the viability and functionality of both encapsulated and nonencapsulated BCC were evaluated in vitro. We obtained viable BCC with excellent functionality: immunocytochemical analysis revealed robust survival of chromaffin cells 30 days after isolation and microencapsulation. HPLC assay showed that encapsulated BCC released catecholamines basally during the time course study. Taken together, these results demonstrate that viable BCC can be successfully encapsulated into alginate-PLL microcapsules with a liquefied inner core.

Polymers for Induction of Revascularization in the Rat Fascial Flap: Application of Vascular Endothelial Growth Factor and Pancreatic Islet Cells

One of the major obstacles in transplanting avascular tissue or metabolically active cells for ischemic diseases is the loss of transplanted cells due to lack of oxygen and nutrients in the early posttransplantation period. Biodegradable polymeric tissue engineering scaffolds and hydrogels have a potential to incorporate cells or cellular organoids such as islets of Langerhans and growth factors. In this study, we tested the efficiency of two types of polymeric materials to carry recombinant human vascular endothelial growth factor (rhVEGF) or pancreatic tumor cell lines, namely Ins-1 and AR42J, for the induction of new vessels. Chitosan hydrogel fibers with micropores were prepared and molded into a cylinder construct (5 mm φ 8 mm height). Macroporous PLGA scaffolds with a pore size of 250–400 μm were prepared and cut into cylinders (6 mm φ 3 mm height). Both chitosan and PLGA constructs were loaded with rhVEGF (3 μg) or seeded with the cell lines (5 × 105 cells and 3 × 105 cells/construct, respectively, for AR42J and INS-1 cells), and transplanted into the fascial flaps of Wistar rats. At distinct time points up to 4 weeks postimplantation, polymers were explanted, fixed, and vessel density was counted on sections stained with anti-Factor-VIII antibody. Additionally, the kinetics of rhVEGF release from PLGA microspheres (φ of 50–80 μm) was determined using VEGF Elisa. Endogenous VEGF release from pancreatic rat cell lines was also determined. Light microscopy study was performed on H&E-stained paraffin sections of the islet-polymer samples. The vascular density of rhVEGF-loaded chitosan constructs was increased fourfold 2 weeks after subcutaneous transplantation compared with rhVEGF-unloaded controls (465 ± 144 vs. 104 ± 80 vessels per mm2, p < 0.05). Protein leakage occurred, but was not observed after 2 weeks. Higher insulin content was detected in rat islet grafts transplanted following VEGF application. More than 50% of total rhVEGF was released on the first day of in vitro culture of PLGA microspheres. rhVEGF secretion had another, but smaller, peak on the third day followed by a constant release. By comparison, endogeneous VEGF secretion of pancreatic tumor cells was measured within a 3-day culture period. Biodegradable polymer scaffolds and hydrogels may have potential use as solid supports to induce angiogenesis for pancreatic cell transplantation.

Polysaccharide matrices used in 3D in vitro cell culture systems

Polysaccharides comprise a diverse class of polymeric materials with a history of proven biocompatibility and continual use as biomaterials. Recent focus on new matrices appropriate for three-dimensional (3D) cell culture offers new opportunities to apply polysaccharides as extracellular matrix mimics. However, chemical and structural bases for specific cell-polysaccharide interactions essential for their utility as 3-D cell matrices are not well defined. This review describes how these naturally sourced biomaterials satisfy several key properties for current 3D cell culture needs and can also be synthetically modified or blended with additional components to tailor their cell engagement properties. Beyond their benign interactions with many cell types in cultures, their economical and high quality sourcing, optical clarity for ex situ analytical interrogation and in situ gelation represent important properties of these polymers for 3D cell culture applications. Continued diversification of their versatile glycan chemistry, new bio-synthetic sourcing strategies and elucidation of new cell-specific properties are attractive to expand the polysaccharide polymer utility for cell culture needs. Many 3D cell culture priorities are addressed with the portfolio of polysaccharide materials available and under development. This review provides a critical analysis of their properties, capabilities and challenges in 3D cell culture applications.

Biocompatibility of Poly(ε-caprolactone) Scaffold Modified by Chitosan—The Fibroblasts Proliferation in vitro

In this study, the surface of poly("-caprolactone) (PCL) scaffold was modified by chitosan (CS) in order to enhance its cell affinity and biocompatibility. It is demonstrated by scanning electronic microscopy (SEM) that when 0.5-2.0 wt% chitosan solutions are used to modify the PCL scaffold, the amount of adhesion of the fibroblasts on the chitosan-modified PCL scaffolds dramatically increase when compared to the control after 7 days cell culture. The results indicate that the chitosan-modified PCL scaffolds are more favorable for cell proliferation by improving the scaffold biocompatibility. The improvement may be helpful for the extensive applications of PCL scaffold in heart valve and blood vessel tissue engineering.

Injectable Hydrogels for Cardiac Tissue Repair after Myocardial Infarction

Cardiac tissue damage due to myocardial infarction (MI) is one of the leading causes of mortality worldwide. The available treatments of MI include pharmaceutical therapy, medical device implants, and organ transplants, all of which have severe limitations including high invasiveness, scarcity of donor organs, thrombosis or stenosis of devices, immune rejection, and prolonged hospitalization time. Injectable hydrogels have emerged as a promising solution for in situ cardiac tissue repair in infarcted hearts after MI. In this review, an overview of various natural and synthetic hydrogels for potential application as injectable hydrogels in cardiac tissue repair and regeneration is presented. The review starts with brief discussions about the pathology of MI, its current clinical treatments and their limitations, and the emergence of injectable hydrogels as a potential solution for post MI cardiac regeneration. It then summarizes various hydrogels, their compositions, structures and properties for potential application in post MI cardiac repair, and recent advancements in the application of injectable hydrogels in treatment of MI. Finally, the current challenges associated with the clinical application of injectable hydrogels to MI and their potential solutions are discussed to help guide the future research on injectable hydrogels for translational therapeutic applications in regeneration of cardiac tissue after MI.

Micro- and nanofabrication of chitosan structures for regenerative engineering

Repair and regeneration of human tissues and organs using biomaterials, cells and/or growth factors is the ultimate goal of tissue engineers. One of the grand challenges in this field is to closely mimic the structures and properties of native tissues. Regenerative engineering-the convergence of tissue engineering with advanced materials science, stem cell science, and developmental biology-represents the next valuable tool to overcome the challenges. This article reviews the recent progress in developing advanced chitosan structures using various fabrication techniques. These chitosan structures, together with stem cells and functional biomolecules, may provide a robust platform to gain insight into cell-biomaterial interactions and may function as excellent artificial extracellular matrices to regenerate complex human tissues and biological systems.

Effect of Synthesis Temperature on the Crystallization and Growth of In Situ Prepared Nanohydroxyapatite in Chitosan Matrix

Hydroxyapatite nanoparticles (nHA) have been used in different biomedical applications where certain particle size distribution and morphology are required. Chitosan/hydroxyapatite (CS/HA) nanocomposites were prepared using in situ coprecipitation technique and the effect of the reaction temperature on the crystallization and particle growth of the prepared nanohydroxyapatite particles was investigated. The composites were prepared at different synthesis temperatures (−10, 37, and 60°C). XRD, FTIR, thermal analysis, TEM and SEM techniques were used to characterize the prepared specimens. It was found that the increase in processing temperature had a great affect on particle size and crystal structure of nHA. The low temperature (−10°C) showed inhabitation of the HA growth in c-direction and low crystallinity which was confirmed using XRD and electron diffraction pattern of TEM. Molar ratio of the bone-like apatite layer (Ca/P) for the nanocomposite prepared at 60°C was higher was higher than the composites prepared at lower temperatures (37 and −10°C).

Microfluidic fabrication of cell adhesive chitosan microtubes

Chitosan has been used as a scaffolding material in tissue engineering due to its mechanical properties and biocompatibility. With increased appreciation of the effect of micro- and nanoscale environments on cellular behavior, there is increased emphasis on generating microfabricated chitosan structures. Here we employed a microfluidic coaxial flow-focusing system to generate cell adhesive chitosan microtubes of controlled sizes by modifying the flow rates of a chitosan pre-polymer solution and phosphate buffered saline (PBS). The microtubes were extruded from a glass capillary with a 300 μm inner diameter. After ionic crosslinking with sodium tripolyphosphate (TPP), fabricated microtubes had inner and outer diameter ranges of 70-150 μm and 120-185 μm. Computational simulation validated the controlled size of microtubes and cell attachment. To enhance cell adhesiveness on the microtubes, we mixed gelatin with the chitosan pre-polymer solution. During the fabrication of microtubes, fibroblasts suspended in core PBS flow adhered to the inner surface of chitosan-gelatin microtubes. To achieve physiological pH values, we adjusted pH values of chiotsan pre-polymer solution and TPP. In particular, we were able to improve cell viability to 92 % with pH values of 5.8 and 7.4 for chitosan and TPP solution respectively. Cell culturing for three days showed that the addition of the gelatin enhanced cell spreading and proliferation inside the chitosan-gelatin microtubes. The microfluidic fabrication method for ionically crosslinked chitosan microtubes at physiological pH can be compatible with a variety of cells and used as a versatile platform for microengineered tissue engineering.

CAD-CAM-generated hydroxyapatite scaffold to replace the mandibular condyle in sheep: preliminary results

In this study, rapid CAD-CAM prototyping of pure hydroxyapatite to replace temporomandibular joint condyles was tested in sheep. Three adult animals were implanted with CAD-CAM-designed porous hydroxyapatite scaffolds as condyle substitutes. The desired scaffold shape was achieved by subtractive automated milling machining (block reduction). Custom-made surgical guides were created by direct metal laser sintering and were used to export the virtual planning of the bone cut lines into the surgical environment. Using the same technique, fixation plates were created and applied to the scaffold pre-operatively to firmly secure the condyles to the bone and to assure primary stability of the hydroxyapatite scaffolds during masticatory function. Four months post-surgery, the sheep were sacrificed. The hydroxyapatite scaffolds were explanted, and histological specimens were prepared. Different histological tissues penetrating the scaffold macropores, the sequence of bone remodeling, new apposition of bone and/or cartilage as a consequence of the different functional anatomic role, and osseointegration at the interface between the scaffold and bone were documented. This animal model was found to be appropriate for testing CAD-CAM customization and the biomechanical properties of porous, pure hydroxyapatite scaffolds used as joint prostheses.

In VitroandIn VivoDegradation of Oxidized Acetyl- and Ethyl-Cellulose Sponges

The objective of this study was to assess the in vitro and in vivo degradation properties of macroporous sponges composed of oxidized acetyl-cellulose (AC; 45.000 Mw) and ethyl-cellulose (EC; 50.000 Mw). The sponges were constructed by solvent-casting and particulate-leaching technique using a polymer concentration of 2.5 and 5.0% (w:v), and periodate oxidation. The resulting sponges were: AC2.5, AC5.0, EC2.5 and EC5.0. While AC sponges exhibited a gradual degradation overtime, EC sponges had a very slow in vitro mass loss. In general, sponges made up of 2.5% (w:v) polymer content degraded faster than the ones with 5.0% (w:v). The sponges degraded faster at pH 5.0, compared to pH 6.0 and 7.4 conditions. About 60%, 44% and 31% of dry mass loss was determined for AC2.5 sponges after 60 weeks at pH 5.0, pH 6.0 and pH 7.4 conditions, respectively; thus, ca. 21%, 13% and 12% of dry mass loss from EC2.5 sponges was observed at the same pH conditions, in the same order. The in vivo degradation studies were performed on Wistar rats (n = 24) for a duration of 60 weeks. In general, all sponge implants were well-tolerated by the subjects. While granulation tissue or fibrotic capsule was not formed around the sponges, neovascularization was observed. AC and EC sponges demonstrated an in vivo degradation behavior quite similar to that observed for the in vitro study conducted at pH 5.0 conditions. Histomorphometric analysis revealed that the in vivo degradation of AC2.5 and EC2.5 after 60 weeks was about 47% and 18%, respectively. The results indicate that oxidized acetyl cellulose may be considered as a partially degradable scaffold material for tissue engineering applications.

Biodegradation of Chitosan-Tripolyphosphate Beads:In VitroandIn VivoStudies

In this study, chitosan [(1 --> 4) linked 2-amino-2-deoxy-beta-D-glucopyranose] beads were prepared by interacting this polycation (> 90% deacetylated) with the tripolyphosphate (TPP) polyanion. The resulting chitosan-TPP beads (C) were modified either by coating with sodium alginate (CA) or by cross-linking with glutaraldehyde (CGA). The in vitro degradation of C beads was found to be faster than its CA and CGA counterparts. C beads degraded faster at pH 6.5, compared to pH 7.4 conditions. At pH 7.4, about 41%, 37% and 10% of dry mass loss after 12 months was determined for C, CA and CGA, respectively. At pH 6.5, the dry mass loss of CA and CGA after the same period of time was found to be 73% and 37%, respectively. However, C beads completely degraded at pH 6.5 after 8 months of in vitro incubation. The in vivo biodegradation experiments were performed on Wistar rats (n = 24) for a duration of 6 months. No sign of fibrotic capsule formation was observed around any of the implanted beads at 2 and 6 months post-transplantation. At 2 months, the in vivo-degradation was slow-going and the beads in all groups were intact; CGA beads had more tissue reaction than C and CA beads at this time point. While the C beads had almost completely degraded after 6 months, the biodegradation process in CA and CGA beads was progressing. Histomorphometric analysis revealed that the in vivo biodegradation was in the order of C (approximately 85%) > CA (approximately 50%) > CGA (approximately 25%) after 6 months. Neovascularization was observed at the vicinity of the bead implants close to major blood vessels, both at 2 and 6 months time-points.

Treatment of spinal cord injury by transplantation of cells via cerebrospinal fluid

It is very important to probe into the axonal regeneration and functional recovery of central nervous system (CNS) after implantation of cells into cerebrospinal fluid (CSF) for spinal cord injury (SCI). Transplantation of cells via CSF poses great potentials for SCI in clinic. Studies on administration of cells via CSF indicate that the method is safe and convenient. The method is more suitable to treating multiple lesions of the CNS since it does not produce open lesions. However, there are disputes over its promotion effects on axonal regeneration and functional recovery of spinal cord after injury; and some questions, such as the mechanisms of functional recovery of spinal cord, the proper time window of cell transplantation, and cell types of transplantation, still need to be handled. This review summarized the method of cell transplantation via CSF for treatment of SCI.

Hydrogels for tissue engineering and delivery of tissue-inducing substances

This manuscript presents hydrogels (HGs) from a tissue engineering perspective being especially written for those who are approaching this field by offering a concise but inclusive review of hydrogel synthesis, properties, characterization methods, and applications.

Encapsulation and osteoinduction of human periodontal ligament fibroblasts in chitosan–hydroxyapatite microspheres

Periodontal ligament cells play a crucial role in the regeneration of periodontal tissues and an undifferentiated mesenchymal cell subset is thought to exist within this population. The aim of this study was to assess the osteogenic differentiation potential of human periodontal ligament fibroblasts (hPDLFs) in three dimensional (3D)-osteogenic culture environment following encapsulation in chitosan-hydroxyapatite (C/HA) microspheres with the size range of 350-450 microm. Human PDLF cultures were established and three experimental groups were formed: (i) two-dimensional (2D)-culture as single cell monolayer, (ii) 3D-static culture of C/HA encapsulated hPDLFs, and (iii) 3D-dynamic culture of C/HA encapsulated hPDLFs in a rotating wall vessel bioreactor. The cells were cultured in standard culture medium supplemented with beta-glycerophosphate, dexamethasone, and ascorbic acid. After 21 days, immunohistochemistry was performed using antibodies against osteonectin, osteopontin, bone-sialoprotein, and osteocalcin as osteogenic differentiation markers. Phase-contrast and scanning electron microscopy observations were used for histological and morphological evaluation. The combined effects of osteoinductive medium and HA-containing composite microsphere material on encapsulated hPDLFs resulted in the transformation of a considerable portion of the cells into osteoblastic lineage at the end of the experiments. Results demonstrate the ability of hPDLFs to undergo osteogenic differentiation upon induction in vitro, both under 2D and 3D culture conditions. C/HA microspheres in microgravity bioreactor may serve as a suitable 3D environment to support the osteogenic differentiation of human PDLFs, in vitro.

Polylysine-functionalised thermoresponsive chitosan hydrogel for neural tissue engineering

Foetal mouse cortical cells were cultured on 2D films and within 3D thermally responsive chitosan/glycerophosphate salt (GP) hydrogels. The biocompatibility of chitosan/GP 2D films was assessed in terms of cell number and neurites per cell. Osmolarity of the hydrogel was a critical factor in promoting cell survival with isotonic GP concentrations providing optimal conditions. To improve cell adhesion and neurite outgrowth, poly-D-lysine (PDL) was immobilised onto chitosan via azidoaniline photocoupling. Increase in PDL concentrations did not alter cell survival in 2D cultures but neurite outgrowth was significantly inhibited. Neurons exhibited a star-like morphology typical of 2D culture systems. The effects of PDL attachment on cell number, cell morphology and neurite outgrowth were more distinct in 3D culture conditions. Neurones exhibited larger cell bodies and sent out single neurites within the macroporous gel. Immobilised PDL improved cell survival up to an optimum concentration of 0.1%, however, further increases resulted in drops in cell number and neurite outgrowth. This was attributed to a higher cell interaction with PDL within a 3D hydrogel compared to the corresponding 2D surface. The results show that thermally responsive chitosan/GP hydrogels provide a suitable 3D scaffolding environment for neural tissue engineering.

Blending chitosan with polycaprolactone: effects on physicochemical and antibacterial properties

Chitosan is a well sought-after polysaccharide in biomedical applications and has been blended with various macromolecules to mitigate undesirable properties. However, the effects of blending on the unique antibacterial activity of chitosan as well as changes in fatigue and degradation properties are not well understood. The aim of this work was to evaluate the anti-bacterial properties and changes in physicochemical properties of chitosan upon blending with synthetic polyester poly(epsilon-caprolactone) (PCL). Chitosan and PCL were homogeneously dissolved in varying mass ratios in a unique 77% acetic acid in water mixture and processed into uniform membranes. When subjected to uniaxial cyclical loading in wet conditions, these membranes sustained 10 cycles of predetermined loads up to 1 MPa without break. Chitosan was anti-adhesive to Gram-positive Streptococcus mutans and Gram-negative Actinobacillus actinomycetemcomitans bacteria. Presence of PCL compromised the antibacterial property of chitosan. Four-week degradation studies in PBS/lysozyme at 37 degrees C showed initial weight loss due to chitosan after which no significant changes were observed. Molecular interactions between chitosan and PCL were investigated using Fourier transform infrared spectroscopy (FTIR) which showed no chemical bond formations in the prepared blends. Investigation by wide-angle X-ray diffraction (WAXD) indicated that the crystal structure of individual polymers was unchanged in the blends. Dynamic mechanical and thermal analysis (DMTA) indicated that the crystallinity of PCL was suppressed and its storage modulus increased with the addition of chitosan. Analysis of surface topography by atomic force microscopy (AFM) showed a significant increase in roughness of all blends relative to chitosan. Observed differences in biological and anti-bacterial properties of blends could be primarily attributed to surface topographical changes.

Inflammatory response on injection of chitosan/GP to the brain

Chitosan is a well-known biomaterial that, with the addition of glycerophosphate salt (GP), gels at physiological temperatures and therefore is useful for tissue engineering purposes. This study examines the procedure of injecting chitosan/ GP to the brain in order to form a gel track. The gel system and surgical technique were successful in this endeavour; however, on examining the inflammatory response to the material it was found that the chitosan/GP was wholly engulfed by macrophages within 7 days. This was determined by staining for both the gel and the macrophages, an important technique for localising injected material. The chitosan/GP-containing macrophages formed a neat tract at the lesion site, but after 45 days no chitosan/GP was found. It was concluded that, although chitosan/GP is present after implantation, it is not available for direct scaffolding in the brain.

Localized Angiogenesis Induced by Human Vascular Endothelial Growth Factor-Activated PLGA Sponge

The objective of this study was to assess the in vitro release kinetics and the in vivo angiogenic effect of human vascular endothelial growth factor (VEGF)-activated poly(DL-lactide-co-glycolide) (PLGA) sponge. The highly porous sponges (each 3 x 4 x 4 mm(3)) were activated by soaking in a VEGF solution (2.5 or 5.0 microg) and then freeze-drying. In vitro release in PBS was investigated by a competitive enzyme immunoassay for up to 3 weeks. The burst-type initial release within the first 3 days followed a more controlled one lasting for >2 weeks. The angiogenic potential of the VEGF sponge was evaluated by subcutaneous implantation into the epigastric groin fascia of Wistar rats. Histomorphometry and SEM confirmed the formation of new capillaries infiltrating the sponge pores starting from the first week and the drastic anostomosis at weeks 2 and 3. However, the rats implanted with control sponges or receiving VEGF injection exhibited much lower or no angiogenic response, respectively. TEM revealed the neo-vessels had a single endothelial layer surrounded by the matrix inoculated with the rat circulation. The results indicate that VEGF-activated PLGA sponge can be considered as a tool to establish neovascularized subcutaneous transplantation sites for tissue-engineering applications.

Effects of hydroxyapatite in 3-D chitosan–gelatin polymer network on human mesenchymal stem cell construct development

Human mesenchymal stem cells (hMSCs) have great potential in bone tissue engineering, and hydroxyapatite (HA), a natural component of human hard tissues, is believed to support hMSC growth and osteogenic differentiation. In this study, two types of biomimetic composite materials, chitosan-gelatin (CG) and hydroxyapatite/chitosan-gelatin (HCG), were fabricated and compared to examine the effects of HA on hMSC adhesion and 3-D construct development. The 2-D membranes were prepared to examine the influence of HA on adhesion efficiency of hMSCs, while 3-D porous scaffolds were produced to investigate the effects of HA on material adsorption properties and 3-D hMSC construct development. HA was found to promote protein and calcium ion adsorption of the 3-D porous scaffolds in the complete tissue culture media. HMSCs exhibited higher initial cell adhesion efficiency to 2-D HCG membranes, and maintained higher proliferation rates in the 3-D porous HCG than CG scaffolds with 3.3 times higher final DNA amount in HCG scaffolds over a 35-day period. Colony forming unit-fibroblast (CFU-F) assays showed that higher percentages of cells maintained their progenicity in the 3-D porous HCG scaffolds over the 35-day culture period. Differentiation assays indicated that the multi-lineage differentiation potential of the hMSCs was preserved in both 3-D porous scaffolds. However, higher alkaline phosphate activity was detected in the 3-D porous HCG scaffolds upon osteogenic induction indicating improved osteogenic differentiation potential. The results demonstrate that enhanced protein and calcium ion adsorption properties of HA in the CG polymer network improve initial cell adhesion and long-term growth, favor osteogenic differentiation upon induction, as well as maintain the progenicity of the 3-D hMSC constructs.

Porcine chromaffin cells, culture, and transplant for antinociceptive effects in rodents and primates

It has been shown that xenografts and allografts of spinally transplanted adrenal chromaffin cells produce antinociception in animals and pain relief in patients with cancer pain. As there is a very limited availability of human adrenal tissue to serve as allografts, the clinical need for xenogeneic chromaffin cells as transplants is obvious. Bovine adrenal glands as a steady source of chromaffin cells have been extensively studied. There is however concern about the possible infection in humans with retrovirus following transplantation. The purpose of this study is to use the pig as a preferred donor animal species for xenotransplantation into rat and monkey. As pigs have been cloned, this opens the door to gene-targeted technologies and allows for genetic modifications, which possibly could improve the efficacy and safety of chromaffin cell transplantation. Porcine chromaffin cells were isolated from adrenal glands of 6-8-month-old pigs. After culturing cells for 1 week in a medium containing serum, the release of met-enkephalin and norepinephrine from the cells was detected by high-performance liquid chromatography and radioimmunoassay with nicotine stimulation, lasting approximately 3 weeks. Transplantation of these cells into the subarachnoid space of rats produced antinociceptive effects on Adelta and C fiber-mediated responses lasting 2-3 weeks. Similar findings were observed in studies with macaque monkeys. Compared with the same number of bovine chromaffin cells, porcine chromaffin cells showed a more robust and longer antinociceptive effect, and could be a better source of cells for human transplantation.

Tissue engineering of cartilage with the use of chitosan-gelatin complex scaffolds

Chitosan has been shown to be a promising scaffold for various applications in tissue engineering. In this study, a chitosan-gelatin complex was fabricated as a scaffold by a freezing and lyophilizing technique. Chitosan's structure and characteristics are similar to those of glycosaminoglycan (GAG) and its analogs, and possesses various biological activities, whereas gelatin can serve as a substrate for cell adhesion, differentiation, and proliferation. With the use of autologous chondrocytes isolated from pig's auricular cartilage and seeded onto the chitosan-gelatin scaffold, elastic cartilages have been successfully engineered at the porcine abdomen subcutaneous tissue. After 16 weeks of implantation, the engineered elastic cartilages have acquired not only normal histological and biochemical, but also mechanical properties. The tissue sections of the engineered elastic cartilages showed that the chondrocytes were enclosed in the lacuna, similar to that of native cartilage. The presence of elastic fibers in the engineered cartilages was also demonstrated by Vehoeff's staining, and immunohistochemical staining confirmed the presence of type II collagen in the engineered cartilages. Quantitatively, the GAG in the engineered cartilages reached 90% of the concentration in native auricular cartilage. Furthermore, biomechanical analysis demonstrated that the extrinsic stiffness of the engineered cartilages reached 85% of the level in native auricular cartilage when it was harvested at 16 weeks. Thus, this study demonstrated that the chitosan-gelatin complex may serve as a suitable scaffold for cartilage tissue engineering.

Functional and Morphological Characteristics of Bovine Adrenal Chromaffin Cells on Macroporous Poly(D,L-lactide-co-glycolide) Scaffolds

Adrenal chromaffin cells (ACCs) secrete several neuroactive substances that are effective in influencing pain sensitivity in the central nervous system as well as enhancing the recovery of the intrinsic nigrostriatal dopaminergic system in patients with Parkinson's disease. ACC transplantation may be upregulated by the use of three-dimensional (3-D) scaffolds. In this study, we determined whether biodegradable poly(D,L-lactic-coglycolic acid) (PLGA) (85:15) sponges could be used as support for chromaffin cells. ACCs were isolated from bovine adrenal glands by standard perfusion (95% purity) followed by additional purification (>99.5% purity). ACC (approximately 5 x 10(5) cells) suspension in collagen (type I) was seeded on prewetted sponges and cultured in DMEM-F12 (1:1) medium (5% fetal bovine serum). The catecholamine and enkephalin levels of the samples were measured by high-performance liquid chromatography and radioimmunoassay. Cell morphology was examined by transmission electron microscopy. Morphological evidence showed prolonged viability of chromaffin cells on scaffolds having pores of 250-400 microm. Cell counts and scanning electron microscopy demonstrated that the majority of seeded cells were located within the scaffold. Chromaffin cells exhibited higher levels of enkephalins and catecholamines on PLGA scaffold compared with their monolayer cultures. By the use of 3-D PLGA as support for ACCs, it is possible to upregulate metabolic function and localize a high number of morphologically healthy-looking cells. Highly purified ACCs cultured on PLGA scaffold may have promise in transplantation studies, because these cells are less immunogenic and may be applied to in vivo settings by using short-term immunosuppression.

Potential use of chitosan as a cell scaffold material for cartilage tissue engineering

One of the most important factors in any tissue-engineering application is the cell substrate. The purpose of this study was the initial evaluation of chitosan, a derivative of the abundant, naturally occurring biopolymer chitin, as a cell scaffold for cartilage tissue engineering. Chitosan scaffolds having an interconnecting porous structure were easily fabricated by simple freezing and lyophilization of a chitosan solution. After rehydration of scaffolds, porcine chondrocytes were seeded onto scaffolds and cultured for up to 28 days in a rotating-wall bioreactor. Chitosan scaffolds supported cell attachment and maintenance of a rounded cell morphology. After 18 days, cells within the scaffolds had synthesized extracellular matrix in which proteoglycan and type II collagen were detected by toluidine blue staining and immunohistochemistry, respectively. Abundant extracellular matrix was found almost exclusively in the periphery of the scaffolds, as scaffold microstructure prevented cells from penetrating to interior regions. Nonetheless, the results suggest that chitosan scaffolds may be a useful alternative to synthetic cell scaffolds for cartilage tissue engineering.

Recent development on computer aided tissue engineering--a review

The utilization of computer-aided technologies in tissue engineering has evolved in the development of a new field of computer-aided tissue engineering (CATE). This article reviews recent development and application of enabling computer technology, imaging technology, computer-aided design and computer-aided manufacturing (CAD and CAM), and rapid prototyping (RP) technology in tissue engineering, particularly, in computer-aided tissue anatomical modeling, three-dimensional (3-D) anatomy visualization and 3-D reconstruction, CAD-based anatomical modeling, computer-aided tissue classification, computer-aided tissue implantation and prototype modeling assisted surgical planning and reconstruction.

Biocompatible hydrogel supports the growth of respiratory epithelial cells: possibilities in tracheal tissue engineering

Extensive tracheal defect reconstruction is a major challenge in plastic and reconstructive surgery. The lack of an epithelial lining on the luminal surfaces of tracheal prostheses is among the major causes of their failure. Chitosan-gelatin hydrogels were synthesized for the development of biocompatible, growth-supportive substrata for respiratory epithelial cells. We employed J774 macrophages to test the immunocompatibility of this gel. The hydrogel did not exert a cytotoxic effect on macrophages, as confirmed by tetrazolium reduction and neutral red uptake assay. Flow cytometric analysis of macrophages cultured on the hydrogel showed a comparable expression of activation markers CD11b/CD18, CD45, and CD14 to the control. Semiquantitative RT-PCR results showed an absence of upregulation of interleukin-6 (IL-6) and TNF-alpha in these macrophages with respect to the controls. Primary human respiratory epithelial cells cultured on the hydrogel showed proper attachment, normal morphology, and growth. A small proportion of cells on the hydrogel showed synchronously beating cilia. RT-PCR analysis showed that cells on the hydrogel expressed mucins 2 and 5 and cytokeratin 13, which are markers for secretory goblet and squamous cells, respectively. All these results demonstrate that the hydrogel supports the growth of a mixed population of differentiated epithelial cells. This hydrogel is suitable as a culture substratum for respiratory epithelial cells and could be used as a potential candidate for coating tracheal prostheses.

Application of chitosan-based polysaccharide biomaterials in cartilage tissue engineering: a review

Once damaged, articular cartilage has very little capacity for spontaneous healing because of the avascular nature of the tissue. Although many repair techniques have been proposed over the past four decades, none has sucessfully regenerated long-lasting hyaline cartilage tissue to replace damaged cartilage. Tissue engineering approaches, such as transplantation of isolated chondrocytes, have recently demonstrated tremendous clinical potential for regeneration of hyaline-like cartilage tissue and treatment of chondral lesions. As such a new approach emerges, new important questions arise. One of such questions is: what kinds of biomaterials can be used with chondrocytes to tissue-engineer articular cartilage? The success of chondrocyte transplantation and/or the quality of neocartilage formation strongly depend on the specific cell-carrier material. The present article reviews some of those biomaterials, which have been suggested to promote chondrogenesis and to have potentials for tissue engineering of articular cartilage. A new biomaterial, a chitosan-based polysaccharide hydrogel, is also introduced and discussed in terms of the biocompatibility with chondrocytes.

Chitosan supports the expression of extracellular matrix proteins in human osteoblasts and chondrocytes

The search for biocompatible materials that can support the growth and phenotypic expression of osteoblasts and chondrocytes is a major challenge in the application of tissue engineering techniques for the repair of bone and cartilage defects. Chitosan, a copolymer of glucosamine and N-acetylglucosamine, may provide an answer to this search. Chitosan is the deacetylated product of chitin, a ubiquitous biopolymer found in the exoskeleton of insects and marine invertebrates. Little is known about the utility of chitosan in propagating human osteoblasts and chondrocytes. In this study, we test the hypothesis that chitosan promotes the survival and function of osteoblasts and chondrocytes. Chitosan (4%, w/v in 2% HAc) was coated onto plastic coverslips that had been fitted into 24-well plates. Human osteoblasts and articular chondrocytes were seeded on either uncoated or chitosan-coated coverslips at 1 x 10(5)/cells per well. Cultures were incubated at 37 degrees C, 5% CO(2) for a period of 7 days. Cell viability was assessed at that time using a fluorescent molecular probe. The phenotypic expression of osteoblasts and chondrocytes was analyzed by reverse transcriptase-polymerase chain reaction and immunocytochemistry. Osteoblasts and chondrocytes appeared spherical and refractile on chitosan-coated coverslips. In contrast, greater than 90% of cells on plastic coverslips were elongated and spindle shaped after 7 days of culture. Similar to cells propagated on uncoated control wells, greater than 90% of human osteoblasts and chondrocytes propagated on chitosan remained viable. Human osteoblasts propagated on chitosan films continued to express collagen type I whereas chondrocytes expressed collagen type II and aggrecan, as shown by reverse transcriptase-polymerase chain reaction analysis and immunostaining. The present in vitro work demonstrates the biocompatibility of chitosan as a substrate for the growth and continued function of human osteoblasts and chondrocytes. Chitosan may have potential use as a tissue engineering tool for the repair of osseous and chondral defects.