Preparation and Characterization of Collagen/Chitosan Matrices As Potential Biomaterials

Chitosan was covalently coupled to type I collagen by using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide in morpholinoethane sulfonic acid buffer. The physico-chemical characteristics of the collagen/chitosan matrices (CCM) were evaluated by electron spectroscopy and tensile mechanical strength. The platelet deposition and endothelial cell culture experiments showed that the CCM have good cell compatibility and excellent blood compatibility. The results suggest that the CCM creates an appropriate environment for the regeneration of endothelial cells and are promising candidates as biomaterials for the tissue regeneration scaffolds.

Sodium Alginate as a Scaffold Material for Hepatic Tissue Engineering

Sodium alginate, which has excellent biocompatibility, was evaluated as a scaffold material for hepatic tissue engineering. It is found that hepatocyte cells attached and proliferated well on films made from sodium alginate. Furthermore, the attached hepatocytes had normal functions, such as synthesizing albumin which was detected by immunohistochemical staining for albumin.

The Effects of S-Chitosan on the Physical Properties of Calcium Phosphate Cements

Water-soluble disodium (1→4)-2-deoxy-2-sulfoamino-β-d-glucopyranuronan (S-chitosan) was prepared from chitin by successive N-deacetylation, specific carboxylation at C-6 and sulfonation. Its structure was characterized by IR spectra and elemental analysis. The S-chitosan was added to two easily developed calcium phosphate cements (CPCs). One cement was monocalcium phosphate monohydrate (MPCM) with calcium oxide (CaO) in a 1M phosphate buffer (pH 7.4)(CPC-I); the other cement was dicalcium phosphate dihydrate (DCPD) with calcium hydroxide [Ca(OH)2] in a 1M Na2HPO4 solution (CPC-II). In vitro experiments showed that when S-chitosan where added to the liquid phases that the resulting S-chitosan containing CPCs had higher mechanical strengths and slightly prolonged setting times. The polyanion enhanced the mechanical strength of the CPCs by increasing the dissolubility of the cement start materials and binding the calcium ions strongly afterwards. An excess of the polyanion destroys the balances of the formulations of CPCs and lead to very slow setting processes or no setting at all.

In Vivo Evaluation of S-Chitosan Enhanced Calcium Phosphate Cements

Calcium phosphate cements (CPC), made from dicalcium phosphate dihydrate and calcium hydroxide and reinforced with water soluble S-chitosan, were investigated in vivo. Cylinders of these cements were prepared and prehardened before implantation into preformed radial defects in rabbits. Histological observations after 1, 4, 14 and 22 weeks, respectively, were performed on thin decalcified sections. No inflammation or other negative response was found in the S-chitosan containing cements (S-CPCs). After 4 weeks, newly formed trabeculae contacted with the implant directly in the lower S-chitosan sample, while a thin layer of fibers had formed between the newly formed bone and the implant in the higher S-chitosan samples. The degradation rates of the S-CPCs were significantly lower than the original CPC cement alone. Most of the S-chitosan cements were still present at the end of the 22 weeks. The implant material and the surrounding infiltrated fluid layer were examined by back scattered scanning electron microscopy and X-ray energy-dispersive spectrometry.

In Vitro Cytocompatibility and Osteoinduction of Phosphorylated Chitosan with Osteoblasts

The cytocompatibility and osteoinduction of water-soluble phosphorylated chitosan (P-chitosan), that was modified by PO23 groups, with neonatal rat osteoblasts in vitro was studied. To identify the biocompatibility of P-chitosan with osteoblasts, the biofunctions of osteoblast cells, in the presence of three different concentrations of P-chitosan solutions as culture media and DMEM with 10% FBS as controls, were determined. The osteoblast differences in the P-chitosan solutions and on chitosan films were also investigated with immunocytochemistry. It was found, based on the ALP activity and mineralization assay that water-soluble P-chitosan has excellent cytocompatibility compared to the chitosan without phosphorylated modification. P-chitosan concentrations as high as 2% had a significant influence on cytocompatibility and osteoinduction; one tissue (or derived product) caused a second undifferentiated tissue to differentiate into bone. Water-soluble P-chitosan could be a promising osteoinductive biomaterial for tissue engineering and orthopedic uses.

A New Method of Heparinizing PLLA Film by Surface Entrapment

A new method of surface heparinizing biodegradable polymers was designed. A heparin-modified poly(L-lactic acid) (PLLA) system was developed by physically entrapping the heparin on the PLLA surface. The surface characterization and biological performance of these materials were carried out by SEM, attenuated-total-reflection spectroscopy, contact angle measurements, and platelet adhesion evaluations. The modification strategy was performed by reversible swelling of the PLLA surface following exposure to a solvent–nonsolvent mixture. This process resulted in the localized physical entrapment of the diffused heparin. X-ray photoelectron spectroscopy was used to confirm that control over the heparin surface density can be achieved by using set polymer treatment times. Platelet adhesion tests showed significant improvement in blood compatibility by the PLLA surfaces after modification.

Biocompatible Fibroin Blended Films with Recombinant Human-like Collagen for Hepatic Tissue Engineering

Recombinant human-like collagen (RHLC) was blended with fibroin to prepare a novel biocompatible film as a scaffold material for hepatic tissue engineering applications. Solution blending was used to incorporate RHLC with silk fibroin to enhance the blend films biocompatibility and hydrophilicity while maintaining elasticity. FTIR and XRD analysis indicated that hydrogen bonds had formed between fibroin and RHLC, while SEM microscopy data confirmed that homogeneous microstructures were still retained after the introduction of RHLC with fibroin. Contact angle measurements indicated that the hydrophilicity of the fibroin/RHLC films was greater after RHLC was added. The elongation at break in the wet state was not markedly changed after blending the recombinant human-like collagen, which implied that flexibility was maintained. The proliferation and viability of the cell cultures on fibroin/RHLC films were significantly enhanced compared to pure fibroin films or tissue culture plates.

Osteoblasts Adherence and Migration through Three-dimensional Porous Mineralized Collagen Based Composite: nHAC/PLA

Osteoblast cells were separated from the neonatal rat calvaria and co-cultured on a novel mineralized hydroxyapatite/collagen/poly(lactic acid) composite scaffold. By using this static cell culture, a three-dimensional osteoblasts/composite bone-like was constructed in vitro. The culture process was observed by scanning electron microscopy, fluorescence microscopy, confocal laser scanning microscopy, and histological analysis. Cells were observed to spread and proliferate throughout the inner-pores of the scaffold material. After a 12-day culture, the cells had grown into the interior scaffold about 200–400 μm depth of the composite by histological section observation. This mobile behavior of osteoblasts appeared to be similar to the composition and hierarchical structure of bone tissue. The adherence and migration of osteoblast cells in this three-dimensional composite is clinically important for large bone defect repair based on tissue engineering.

Repair of Segmental Defects with Nano-hydroxyapatite/Collagen/PLA Composite Combined with Mesenchymal Stem Cells

The aim of the present study was to investigate and compare the capacity of fresh-frozen allogeneic bone, nano-hydroxyapatite/collagen/PLA (nHAC/PLA) scaffold, and nHAC/PLA scaffold loaded with bone marrow mesenchymal stem cells (BMSCs) in inducing bone formation. A 10mm segmental rabbit radial defect was surgically created. The animals were divided into four groups in which the defect was either left untreated, or filled with the abovementioned three grafts. The animals were euthanized at 2, 4, 6, 8, 12, and 18 weeks. Radiographic and histologic analyses were performed on the harvested tissue. We show that nHAC/PLA composite combined with mesenchymal stem cells could enhance and accelerate bone formation in segmental defects of rabbits. nHAC/PLA composite is an ideal bone graft; implanting nHAC/PLA composite combined with mesenchymal stem cells is a potential method for surgical treatment of bone defects.

Cerebrum Repair with PHPMA Hydrogel Immobilized with Neurite-Promoting Peptides in Traumatic Brain Injury of Adult Rat Model

A poly[N-(2-hydroxypropyl) methacrylamide] (PHPMA) hydrogel immobilized with the neurite-promoting peptide sequence of xIKVAVx was synthesized and its structure was characterized. The PHPMA-IKVAV hydrogel displayed an interconnected porous structure. The ability of the hydrogel to support axonal outgrowth in the injured adult rats cerebrum cavity and to promote tissue regeneration was evaluated. After implantation for 4, 6, 12 and 18 weeks, the brain sections were processed for histological staining. The observations of the sections showed that the polymer hydrogel provided a structural, three-dimensional continuity across the defect and favoured reorganization of local wound-repair cells, angiogenesis and axonal growth into the hydrogel scaffold. Compared with the unmodified PHPMA hydrogel, the PHPMA-IKVAV hydrogel displayed greater ability to repair tissue defects in the cerebrum nervous system.

Osteoblast MC3T3-E1 Culture on a Fast-setting Carbonated Hydroxyapatite Bone-like Material

Using ultra-fine grain technology, a fast-setting type of carbonated hydroxyapatite (CHA) material from Ca3(PO4)2·3H2O (ACP), CaCO3, Ca(H2PO4)2 (MCPA) and Na3PO4 was prepared. The ultra-fine particles (3 m) shortens the setting time, to form bone like material with 5.2wt% carbonation. Osteoblastic MC3T3-E1 cells were cultured with CHA material to observe cell adhesion, proliferation and differentiation. There were no obvious differences in adhesion and proliferation rate of MC3T3-E1 cells between the CHA and the control group. MC3T3-E1 cells on the surface of CHA observed by a scanning electron microscope (SEM). The alkaline phosphatase (ALP) activity of the cells on the CHA was higher than the control, and collagen I (COL 1) mRNA expressed on the CHA was also significantly higher than the control. This CHA bone material exhibited biocompatibility and osteo-conductive properties that are sought for bone repair and scaffolding for tissue engineering. *Author to whom correspondence should be addressed.

Responses of Osteo- and Fibroblast Cells to Phosphorylated Chitin

The cell responses of rat osteoblasts and fibroblasts to water-soluble phosphorylated chitin (P-chitin) were examined in vitro. Cell morphology was observed at 1, 4 and 7 days, respectively. A wide range of measurements, including the percentages of viable cells, total intracellular protein content, and 3-[4,5-dimethylthiazol-2-yl]-2, 5-diphenyl tetrasodium bromide (MTT) assay on osteoblasts and fibroblasts, as well as alkaline phosphatase activity assay on osteoblasts at the end of 7 days culture, were conducted. P-chitin had no cytotoxity on either cell lines. An increase of viability and protein content of both cell types was found in media containing 0.10 g/mL of P-chitin after 7 days culture. The positive effects were especially significant for osteoblasts. Water-soluble P-chitin could be a promising biomaterial for tissue engineering.

PLLA Morphology Controlled by Dry-cast Process

The influence of solvent evaporation rate, in the dry-casting process, on crystallinity and morphology of crystallizable polymeric membrane was studied. Poly-l-lactic acid (PLLA) was taken as an example. The membranes were characterized by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). By controlling the solvent evaporation rate, samples with various crystallinities were prepared. From higher to lower crystallinity the membranes exhibit three types of surface morphology in sequence: granule, stripe and smooth.

In vivo biocompatibility and degradation behavior of Mg alloy coated by calcium phosphate in a rabbit model

This study is conducted to investigate the biocompatibility and biodegradation behavior of calcium phosphate-coated Mg alloy in vivo. Calcium phosphate (Ca-P) was coated on the Mg alloy (AZ31) by a chemical process. Samples of Ca-P coated rods, the naked alloy rods, and degradable polymer as controls were implanted into the thighbone of rabbits to investigate the bone response at the early stage. The reduction in implant volume was determined by micro-computed tomography and three-dimensional reconstruction of the remaining Mg alloy segmented from the bone matrix. It was observed that the biodegradation rate of naked Mg implant is faster than that of the coated ones. The bone-implant interface was characterized in sections by scanning electron microscopy with energy-dispersive spectroscopy. Biodegradation or reaction layer was formed on the surface of Mg alloy implants and direct contact with the surrounding bone. The layer was mainly composed of Ca, P, O, and Mg. After 8 weeks of post-operation, paraffin sections were generated for histomorphologic analysis; 100% implants were fixed and no inflammation was observed. Histological analysis showed that new bone tissue is formed around the Mg implants, and no fibrous capsule was found. Blood examination showed that the biodegradation of the Mg implant caused little change to blood composition. Ca-P coating on Mg alloy substrate might be an effective method to reduce the biodegradation rate of Mg alloy in vivo and improve the surface bioactivity of Mg alloy implants.

Comparison on Regulation of Calcium Phosphate by Organic Monolayer, Unilamellar Phospholipid Vesicles and Hydrothermal Self-Assembly

Biomineralization centers on the idea that organics control the nucleation, growth and final form of inorganics. The present studies investigated the deposition or precipitation of inorganics templated by organic monolayer films, unilamellar phospholipid vesicles, and selfassembled hexadecylamine, with the emphasis on the regulation of template on phase, orientation and microstructure of minerals. The obtained calcium phosphate varied from the thin layer precipitated on the organic monolayer to the confined particles formed inside the lipid vesicles to the mesolamellar structure self-organized in the precursor sol-gel. The typically regulated features of these three systems have been revealed. Consequently, the different phases of calcium phosphate can be obtained through variation of controllable parameters.

Application of nerve growth factor by gel increases formation of bone in mandibular distraction osteogenesis in rabbits

The long period of bony consolidation is a concern in mandibular distraction osteogenesis (DO). We have previously shown that repeated local injections of human nerve growth factor beta (NGFβ) can appreciably improve bony consolidation in a rabbit model of DO. The present study was designed to test the effect of a single injection of human NGFβ delivered by collagen/nano-hydroxyapatite/kappa-carrageenan gels to sites of new bony formation in DO. Rabbits underwent mandibular DO at a rate of 0.75 mm/12h for 6 days. At the end of the distraction period, the following injections were given percutaneously into the callus (n=6 in each of the four groups): human NGFβ in the gel; human NGFβ in saline; the gels alone; and saline alone. Fourteen days after the end of distraction, mechanical testing, histological and histomorphometric variables of the new bone were evaluated. Histologically, the NGFβ group had more advanced consolidation than the other three groups. Both maximal load and bone volume/total volume in this group were significantly higher than in the other three (P<0.05). In conclusion, the delivery of human NGFβ in the gels results in better acceleration of new bone formation than when it is given in saline, and may be a possible way to shorten the duration of craniofacial DO.

Electrospun collagen-chitosan nanofiber: a biomimetic extracellular matrix for endothelial cell and smooth muscle cell

Electrospinning of collagen and chitosan blend solutions in a 1,1,1,3,3,3-hexafluoroisopropanol/trifluoroacetic acid (v/v, 90/10) mixture was investigated for the fabrication of a biocompatible and biomimetic nanostructure scaffold in tissue engineering. The morphology of the electrospun collagen-chitosan nanofibers was observed by scanning electron microscopy (SEM) and stabilized by glutaraldehyde (GTA) vapor via crosslinking. Fourier transform infrared spectra analysis showed that the collagen-chitosan nanofibers do not change significantly, except for enhanced stability after crosslinking by GTA vapor. X-ray diffraction analysis implied that both collagen and chitosan molecular chains could not be crystallized in the course of electrospinning and crosslinking, and gave an amorphous structure in the nanofibers. The thermal behavior and mechanical properties of electrospun collagen-chitosan fibers were also studied by differential scanning calorimetry and tensile testing, respectively. To assay the biocompatibility of electrospun fibers, cellular behavior on the nanofibrous scaffolds was also investigated by SEM and methylthiazol tetrazolium testing. The results show that both endothelial cells and smooth muscle cells proliferate well on or within the nanofiber. The results indicate that a collagen-chitosan nanofiber matrix may be a better candidate for tissue engineering in biomedical applications such as scaffolds.

Bone regeneration by using scaffold based on mineralized recombinant collagen

Bone regeneration was achieved in the 15-mm segmental defect model in the radius of rabbit by using the scaffold based on mineralized recombinant collagen for the first time. The recombinant collagen was recombinant human-like type I collagen, which was produced by cloning a partial cDNA that was reversed by mRNA from human collagen alpha1(I) and transferred to E. coli. The scaffold material nano-hydroxyapatite/recombinant human-like collagen/poly(lactic acid) (nHA/RHLC/PLA) was developed by biomimetic synthesis. Thermo gravimetric analysis, X-ray diffraction and scanning electron microscopy were applied to exhibit that the scaffold showed some features of natural bone both in main component and hierarchical microstructure. The percentages of organic phase and inorganic phase of nHA/RHLC were similar to that of natural bone. The three-dimensional porous scaffold materials mimic the microstructure of cancellous bone. In the implantation experiment, the segmental defect was healed 24 weeks after surgery, and the implanted composite was completely substituted by new bone tissue. The results of the implantation experiment were very comparable with that of the scaffold based on mineralized animal-sourced collagen. It is concluded that the scaffold based on mineralized recombinant collagen maintains the advantages of mineralized animal-sourced collagen, while avoids potential virus-dangers. The scaffold is a promising material for bone tissue engineering.

Modification of bone graft by blending with lecithin to improve hydrophilicity and biocompatibility

Lecithin was blended to improve the hydrophilicity and biocompatibility of bone graft containing poly(l-lactic acid) (PLLA). Solution blending and freeze drying were used to fabricate symmetrical scaffolds containing different percentages of lecithin (lecithin: PLLA = 0, 5, 10 wt%). Scanning electron microscopy showed that the scaffolds maintained the three-dimensional porous structure. A water uptake experiment proved the significant improvement of hydrophilicity of the blend scaffold. With the addition of lecithin, the compressive strength and compressive modulus decreased. When the weight ratio of lecithin to PLLA was up to 10%, the compressive strength was still more than the lower limit of natural cancellous bone. To test the biocompatibility of the scaffolds, cell culture in vitro and subcutaneous implantation in vivo were performed. MC3T3-E1 preosteoblastic cells were cultured on the scaffolds for 7 days. Methylthiazol tetrazolium assay and laser scanning confocal microscopy were used to exhibit proliferation and morphology of the cells. The subcutaneous implantation in rats tested inflammatory response to the scaffolds. The results proved the better biocompatibility and milder inflammatory reactions of the blend scaffold (lecithin: PLLA = 5%) compared with the scaffold without lecithin. The modified scaffold containing lecithin is promising for bone tissue engineering.

Atomic force and confocal microscopy for the study of cortical cells cultured on silicon wafers

The primary cortical cells were selected as a model to study the adherence and neural network development on chemically roughened silicon substrates without any coatings using confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM). The silicon substrates have a nano-range roughness (RMS) achieved by chemical etching using hydrofluoric (HF) acid. After 7 days of culturing, the neurons were observed to connect together and form dense neural networks. Furthermore, AFM results revealed that some porous structures at a few micrometer range existed between the neuron cells and the silicon substrates. It is suggested that the porous structures are made of extracellular matrix (ECM) components and play an important role in the neuronal adhesion and neurite outgrowth on the inert silicon wafers.

Biomedical modification of poly(L-lactide) by blending with lecithin

Lecithin was, for the first time, blended with PLLA to prepare scaffold material for tissue engineering applications in the present study. Solution blending was used to incorporate Lecithin (containing 0-10 wt %) with PLLA to enhance the blend films biocompatibility, hydrophilicity and toughness while maintaining mechanical strength of PLLA. The results of FTIR-ATR analysis indicated that the amino groups of lecitin existed in the films. DSC analysis indicated that T(g) decreased with the increase of lecithin content in the blend films. The percentage elongation markedly increased with increase of lecithin content. The proliferation and viability of the vascular smooth muscle cell cultures on PLLA/Lecithin (containing 3-7 wt %) films were significantly enhanced compared to pure PLLA on tissue culture plates.

Hyaluronic acid hydrogel immobilized with RGD peptides for brain tissue engineering

In this paper, hyaluronic acid hydrogels with open porous structure have been developed for scaffold of brain tissue engineering. A short peptide sequence of arginine-glycine-aspartic acid (RGD) was immobilized on the backbone of the hydrogels. Both unmodified hydrogels and those modified with RGD were implanted into the defects of cortex in rats and evaluated for their ability to improve tissue reconstruction. After 6 and 12 weeks, sections of brains were processed for DAB and Glees staining. They were also labeled with GFAP and ED1 antibodies, and observed under the SEM for ultrastructral examination. After implanting into the lesion of cortex, the porous hydrogels functioned as a scaffold to support cells infiltration and angiogenesis, simultaneously inhibiting the formation of glial scar. In addition, HA hydrogels modified with RGD were able to promote neurites extension. Our experiments showed that the hyaluronic acid-RGD hydrogel provided a structural, three-dimensional continuity across the defect and favoured reorganization of local wound-repair cells, angiogenesis and axonal growth into the hydrogel scaffold, while there was little evidence of axons regeneration in unmodified hydrogel.

Regulation of charged groups and laminin patterns for selective neuronal adhesion

Primary neuronal cultures on substrates patterned with extracellular matrix proteins such as laminin have yielded much information regarding the physiological characteristics of neuronal cells in vitro. Surface charge also influences neuronal adherence, and a positive charge can have stimulatory effects. The attraction between laminin patterns and polycation films are of interest in the study of neuronal adhesion. We cultured primary hippocampal neurons on poly(ethylenimine) (PEI) films with laminin grids and evaluated their viability and morphology by means of fluorescent microscopy after 5-7 days. The results showed that the neurons did not form networks on the laminin grids. It is inferred that the PEI films were more favourable for neuronal adhesion than the laminin grid.

Hyaluronic acid-poly-D-lysine-based three-dimensional hydrogel for traumatic brain injury

Brain tissue engineering in the postinjury brain represents a promising option for cellular replacement and rescue, providing a cell scaffold for either transplanted or resident cells. In this article, a hyaluronic acid (HA)-poly-D-lysine (PDL) copolymer hydrogel with an open porous structure and viscoelastic properties similar to neural tissue has been developed for brain tissue engineering. The chemicophysical properties of the hydrogel with HA:PDL ratios of 10:1, 5:1, and 4:1 were investigated by scanning electron microscopy (SEM) and X-ray photoelectron spectrometry. Neural cells cultured in the hydrogel were studied by phase-contrast microscope and SEM. The incorporation of PDL peptides into the HA-PDL hydrogel allowed for the modulation of neuronal cell adhesion and neural network formation. Macrophages and multinucleated foreign body giant cells found at the site of implantation of the hydrogel in the rat brain within the first weeks postimplantation decreased in numbers after 6 weeks, consistent with the host response to inert implants in numerous tissues. Of importance was the infiltration of the hydrogel by glial fibrillary acidic protein-positive cells-reactive astrocytes-by immunohistochemistry and the contiguity between the hydrogel and the surrounding tissue demonstrated by SEM. These findings indicated the compatibility of this hydrogel with brain tissue. Collectively, the results demonstrate the promise of an HA-PDL hydrogel as a scaffold material for the repair of defects in the brain.

AFM study of hippocampal cells cultured on silicon wafers with nano-scale surface topograph

The rat hippocampal cells were selected as model to study the interaction between the neural cells and silicon substrates using atomic force microscopy (AFM). The hippocampal cells show tight adherence on silicon wafers with nano-scale surface topograph. The lateral friction force investigated by AFM shows significant increase on the boundary around the cellular body. It is considered to relate to the cytoskeleton and cellular secretions. After ultrasonic wash in ethanol and acetone step by step, the surface of silicon wafers was observed by AFM sequentially. We have found that the culture leftovers form tight porous networks and a monolayer on the silicon wafers. It is concluded that the leftovers overspreading on the silicon substrates are the base of cell adherence on such smooth inert surfaces.

Property variations in the prism and the organic sheath within enamel by nanoindentation

Atomic force microscopy (AFM) combined with nanoindentation technique was used to definitely, site-specifically, test the nanomechanical properties, including nanohardness and elastic modulus, of the isolated domains within single enamel, the prisms and the surrounding sheaths, of mature human maxillary third molars. In this way, it is for the first time that evident differences of nanomechanical properties were revealed between these domains. The nanohardness and elastic modulus of the sheaths were about 73.6% and 52.7% lower than those of the prisms, respectively. Measuring the residual impressions with AFM supported the similar conclusion. The variations of mechanical properties in these domains are considered to be mainly relative to their different component and fibrils arrangement.

Hyaluronic acid hydrogel as Nogo-66 receptor antibody delivery system for the repairing of injured rat brain: in vitro

Nogo-66 and NgR are important receptors inhibiting neuronal regeneration and therefore are targets for treating CNS injury. Antagonists of this receptor including blocking antibodies are potential therapeutic agents for CNS axonal injuries such as spinal cord and brain trauma. A new antibody (IgG) releasing system has been developed by covalently attaching IgG to the biodegradable hyaluronic acid (HA) hydrogel via the hydrolytically unstable hydrazone linkage, aiming to deliver the antibody of CNS regeneration inhibitors to the injured brain. In this paper we describe the synthesis, physico-chemical characteristics and test results of biological activity of antibody released from hyluronic acid hydrogel. To form the conjugates the antibody is attached to the polymer backbone using a condensation reaction between aldehyde group of the antibody and hydrazide group of the HA hydrogel. Furthermore, pH sensitive linkage-hydrozone has been formed between hydrogel and antibody. The amount of conjugated antibodies can reach 135 microg antibody/mg hydrogel in the dry state. At low pH, the antibodies released quite fast. However, the antibodies released much slower in neutral and alkaline environment. The bioactivity of antibody released from hydrogel was retained as demonstrated by indirect immunofluorescence technique.

Hierarchical structural comparisons of bones from wild-type and liliput(dtc232) gene-mutated Zebrafish

The alterations of hierarchical structures of bone by gene mutation in the zebrafish, which is associated with abnormal bone mineralization and bone disease, were reported for the first time in this paper. Bone samples from the liliput(dtc232) (lil) mutants as well as normal controls were studied by polarized light microscope, scanning electron microscope (SEM), transmission electron microscope (TEM), and atomic force microscope (AFM). Light microscopy examinations reveal that the lil bone has asymmetric mineralization and much thinner bone wall. The SEM studies show a lot of microcracks in lil bone wall. And the plywood-like structure of the normal bone does not exist in the lil bone, which is confirmed by the measurements of polarized light microscope. Furthermore, the TEM investigations display the collagen fibrils with two typical diameters. For the thinner collagen fibrils, the diameter of lil bone is about twice larger than that of the wild-type bone. And for the thicker one, there is a small increase in diameter after mutation and the band periodicity of the lil bone is similar with that of wild-type bone, which is consistent with the result of AFM. The morphologies of the minerals revealed that the mutated mineral was in bigger size and the shape was irregular but not plate-shaped.

In vitro and in vivo degradation of mineralized collagen-based composite scaffold: nanohydroxyapatite/collagen/poly(L-lactide)

The objective of this article was to investigate the in vitro and in vivo biodegradation of a novel biomimetic bone scaffold composite, nanohydroxyapatite/collagen/poly(L-lactide), that could be used for bone tissue engineering. For evaluation of in vitro degradation specimens were immersed into 1% trypsin/phosphate-buffered saline solution at 37 degrees C. In vivo evaluation involved the implantation of samples into the posterolateral lumbar spine of rabbits, and the retrieved specimens were analyzed by Fourier transform-infrared spectroscopy. The results demonstrated that weight loss increased continuously in vitro with a reduction in mass of 19.6% after 4 weeks. During the experimental period in vitro, the relative rate of reduction of the three components in this material was shown to differ greatly: collagen decreased the fastest, from 40% by weight to 20% in the composite; hydroxyapatite content increased from 45 to 60%; and PLA changed little. The pore structure was maintained throughout the whole experimental period in vitro; however, the thickness of the walls of the pores decreased and the surface of the walls increased in roughness. In vivo, the ratio of collagen to hydroxyapatite appeared to be slightly higher near the transverse process than in the central part of the intertransverse process. This finding may have been due to new bone matrix formation extending from the transverse to the intertransverse process.

Covalent immobilization of chitosan and heparin on PLGA surface

Chitosan and heparin were covalently immobilized onto a poly(lactic acid-co-glycolic acid) (PLGA) surface using N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC), N-hydroxysuccinimide (NHS) in a 2-morpholinoethane sulfonic acid (MES) buffer system. The properties of the modified PLGA surface and the control were investigated by water contact angle measurement and electron spectroscopy for chemical analysis (ESCA). The water contact angle of the modified film was greatly decreased and the element content on the surface of the films changed correspondingly. Platelet adhesion assay showed that blood compatibility of the chitosan/heparin modified film was improved while hepatocyte culture indicated that the cell compatibility of the modified film was enhanced.

Measuring membrane potential and electric field of brainstem neurons in vitro by confocal microscopy

A method of measuring transmembrane potential and electric field of neural cells cultured in vitro is described in this paper. The high resolution and scanning speed of the method make it considerable to be used to observe the viability of the neurons cultured on opaque substrate. Rhodamine 123 was used to stain the cells in order to display different intensity corresponding to transmembrane potential. The fluorescence data were collected by confocal laser scanning microscopy (CLSM). Then the data were processed to create the graphs of transmembrane potential and electric field. This is the first paper describes a reliable method for three-dimensional visualization of potential voltage of neurons at the best of our knowledge.

Hierarchically biomimetic bone scaffold materials: Nano-HA/collagen/PLA composite

A bone scaffold material (nano-HA/ collagen/PLA composite) was developed by biomimetic synthesis. It shows some features of natural bone both in main composition and hierarchical microstructure. Nano-hydroxyapatite and collagen assembled into mineralized fibril. The three-dimensional porous scaffold materials mimic the microstructure of cancellous bone. Cell culture and animal model tests showed that the composite material is bioactive. The osteoblasts were separated from the neonatal rat calvaria. Osteoblasts adhered, spread, and proliferated throughout the pores of the scaffold material within a week. A 15-mm segmental defect model in the radius of the rabbit was used to evaluate the bone-remodeling ability of the composite. Combined with 0.5 mg rhBMP-2, the material block was implanted into the defect. The segmental defect was integrated 12 weeks after surgery, and the implanted composite was partially substituted by new bone tissue. This scaffold composite has promise for the clinical repair of large bony defects according to the principles of bone tissue engineering.

Effect of spinal cord injury on urinary bladder spinal neural pathway: a retrograde transneuronal tracing study with pseudorabies virus

OBJECTIVES

To determinate the effect of acute and chronic spinal cord injury (SCI) resulting from thoracic cord transection on the urinary bladder spinal neural pathway.

METHODS

Seventy-six adult Sprague-Dawley rats were randomly divided into four groups, non-SCI (normal rats undergoing no surgical procedure except pseudorabies virus [PRV] injection), SCI(b) (SCI and PRV injected immediately after SCI), SCI(c) (SCI and PRV injected at 3 weeks after SCI), and SCI(d) (SCI and PRV injected at 3 months after SCI). Transcardiac perfusion fixation was done at appropriate survival periods after PRV injection into the bladder wall tissue. Sections of the dorsal root ganglion, spinal cord, and brain were processed for visualization of the virus by the streptavidin-peroxidase immunohistochemical procedure.

RESULTS

The bladder weight of the non-SCI, SCI(b), SCI(c), SCI(d) rats was 144 +/- 9 mg, 142 +/- 8 mg, 486 +/- 51 mg, and 656 +/- 69 mg, respectively. The time-ordered flow charts of PRV tracing were similar in the non-SCI and SCI rats. The cross-sectional area of the labeled dorsal root ganglion cell profiles increased significantly after SCI (P <0.001): 593 +/- 40 microm2, 588 +/- 39 microm2, 815 +/- 53 microm2, and 902 +/- 57 microm2 in the non-SCI, SCI(b), SCI(c), SCI(d) rats, respectively. The number of labeled cells in the dorsal horn in the L6 and S1 segments 3 days after PRV injection markedly increased in chronic SCI rats, as did the number of labeled motor neurons 4 days after injection.

CONCLUSIONS

Acute and chronic SCI have no effect on the process of virus transneuronal transport below the level of the lesion. Subsequent to chronic SCI, reorganization of the micturition reflex pathways may occur.

Lumbar spinal fusion with a mineralized collagen matrix and rhBMP-2 in a rabbit model

STUDY DESIGN

A new mineralized collagen matrix combined with or without growth factor was used for the posterolateral spinal fusion in the rabbit lumbar spine.

OBJECTIVES

The availability of a new osteoconductive matrix with or without recombinant osteoinductive growth factors offers a possible alternative to the use of autogenous bone for grafting indications. This study evaluated the bone-forming activity of the biomimetic matrix: nano-hydroxyapatite/collagen/polylactic acid (nHAC/PLA) combined without or with recombinant human bone morphogenetic protein-2 (rhBMP-2) in a rabbit posterolateral spinal fusion.

SUMMARY OF BACKGROUND DATA

Many bone grafting materials such as titanium alloy, ceramics, and polymers were used to repair bony defects. However, each has specific disadvantaged. The permanent implantation still has possibility to be eroded in vivo, which is caused by late breakdown and abscess formation. The acidic outcome of polymer biodegradation was also negatively affected in the later-stage results of bone repair. It needed a promising material for an alternative to the use of autogenous bone for grafting indications.

MATERIALS AND METHODS

Sixty-four rabbits were randomly divided into four groups: autologous iliac crest bone group (ACB), nHAC/PLA composite group (nHAC/PLA), autologous iliac crest bone mixed with nHAC/PLA composite group (ACB + nHAC/PLA), nHAC/PLA composite with recombinant human BMP-2 group (nHAC/PLA + rhBMP-2). The lumbar intertransverse process fusions were assessed by manual palpation, radiographic, histologic, and mechanical strength, and scanning electronic microscopy (SEM) in a 10-week observation.

RESULTS

Optimal formulations of the ACB + nHAC/PLA and nHAC/PLA + rhBMP-2 groups were shown to perform similar to ACB in both the fusion ratio and mechanical strength in the 6 and 10 weeks after surgery. From the microstructure analysis of the samples, there was no negative effect when the compound implanted this composite with autogenous iliac crest, and there was also new bone-like tissue formation implanted this composite without combined rhBMP-2 early at the second week after surgery.

CONCLUSIONS

This study shows the effective results of nHAC/PLA in rabbit posterolateral spinal fusion combined with rhBMP-2. It is an alternative method to autograft by compounding this osteoconductive matrix with growth factors.

Crosslinked collagen/chitosan matrix for artificial livers

Matrices composed of collagen and chitosan may create an appropriate environment for the regeneration of livers. In this study, we have prepared, characterized and evaluated a new collagen/chitosan matrix (CCM). The CCM was made by using crosslinking agent 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) in N-hydroxysuccinimide (NHS) and a 2-morpholinoethane sulfonic acid (MES) buffer system. The chemical characteristics were evaluated by Fourier-transformed infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The mechanical strength was measured by tensile tests. The platelet deposition and hepatocyte culture experiments show that CCM has excellent blood and cell compatibility. The results suggest that the CCM is a promising candidate matrix for implantable bioartificial livers.

Synthesis and biocompatibility of porous nano-hydroxyapatite/collagen/alginate composite

Porous nano-hydroxyapatite/collagen/alginate (nHAC/Alginate) composite containing nHAC and Ca-crosslinked alginate is synthesized biomimetically. This composite shows a significant improvement in mechanical properties over nHAC material. Mechanical test results show that the compressive modulus and yield strength of this composite are in direct proportion to the percentage of Ca-crosslinked alginate in the composite. Primary biocompatibility experiments in vitro including fibroblasts and osteoblasts co-culture with nHAC/alginate composite indicated the high biocompatibility of this composite. Therefore the composite can be a promising candidate of scaffold material for bone tissue engineering.

Organization of apatite crystals in human woven bone

The organization of collagen fibrils differs in woven bone and lamellar bone, and it reflects certain aspects of the nature of the mineral crystals associated with them. In order to investigate the morphology and distribution of apatite crystals in woven bone, mineralized collagen fibrils and isolated crystals from the mid-diaphyses of human fetal femurs were observed with scanning and transmission electron microscopy and high-resolution electron microscopy. A number of features of woven bone were observed for the first time by these means. Similar to mature crystals from lamellar bone, the apatite crystals in woven bone are also platelet-shaped. However, most likely because of a high rate of old bone resorption and new bone formation in woven material, the average crystal dimensions are considerably smaller than those of mature crystals in lamellar bone. Apatite crystals were noted on the surface of collagen fibrils in woven bone. In densely packed woven bone, the periodicity of mineral deposited on individual fibrils is in registration over many fibrils. In addition to their association with collagen surfaces, crystals also appear distributed in both extrafibrillar and intrafibrillar collagen regions. In both cases, the minerals are crystalline and defect-free. These characteristics provide insight into the spatial and temporal relation between collagen and mineral that is the basis for the structure and organization of the mineral comprising human woven bone.

Bone growth in biomimetic apatite coated porous Polyactive 1000PEGT70PBT30 implants

We recently, developed a simple one-day one-step incubation method to obtain bone-like apatite coating on flexible and biodegradable Polyactive 1000PEGT70PBT30. The present study reports a preliminary biological evaluation on the coated polymer after implantation in rabbit femurs. The porous cylindrical implants were produced from a block fabricated by injection molding and salt leaching. This technique provided the block necessary mechanical integrity to make small cylinders (diameter 3.5 x 5 mm2) that were suitable for implantation in rabbits. The coating continuously covered the surface of the polymer, preserving the porous architecture of outer contour of the cylinders. Two defects with a diameter of 3.5 or 4 mm were drilled in the proximal and distal part of femur diaphysis. The implants were inserted as press-fit or undersized into the cortex as well as in the marrow cavity. The polymer swelled after implantation due to hydration, leading to a tight contact with the surrounding bone in both defects. The adherence of the coating on the polymer proved to be sufficient to endure a steam sterilization process as well as the 15% swelling of the polymer in vivo. The coated Polyactive 1000PEGT70PBT30 has a good osteoconductive property, as manifested by abundant bone growth into marrow cavity along the implant surface during 4-week implantation. A favorable bioactive effect of the coating with an intimate bone contact and extensive bone bonding with this polymer was qualitatively confirmed. Concerning the bone ingrowth into the porous implant in the defect of 4 mm diameter, only marginal bone formation was observed up to 8 weeks with a maximal penetration depth of about 1 mm. The pore interconnectivity is important not only for producing a coating inside the porous structure but also for bone ingrowth into this biodegradable material. This preliminary study provided promising evidence for a further study using a bigger animal model.

Variation of nanomechanical properties of bone by gene mutation in the zebrafish

Significant variations of nanomechanical properties and fracture morphology between gene-mutated liliput(dtc232) (lil/lil) zebrafish skeletal bone and wild-type bone have been observed. Nanoindentation measurement disclosed that lil/lil bone has 36% lower nanohardness and 32% lower elastic modulus. The standard deviations of hardness and elastic modulus of lil/lil bone were both much higher than those of wild-type bone. SEM morphology of fracture surfaces further revealed that in bones after gene mutation, formative microcracks make the performance reduction and the increasing of brittleness. What is more, the plywood-like structure of the normal bone does not exist in the lil/lil bone.

Culture of neural cells on silicon wafers with nano-scale surface topograph

The adherence and viability of central neural cells (substantia nigra) on a thin layer of SiO(2) on Si wafers with different surface roughness were investigated. Variable roughness of the Si wafer surface was achieved by etching. The nano-scale surface topography was evaluated by atomic force microscopy. The adherence and subsequent viability of the cells on the wafer were examined by scanning electron microscopy (SEM) and fluorescence immunostaining of tyrosine hydroxylase (TH). It is found that the surface roughness significantly affected cell adhesion and viability. Cells survived for over 5 days with normal morphology and expressed neuronal TH when grown on surfaces with an average roughness (Ra) ranging from 20 to 50 nm. However, cell adherence was adversely affected when surfaces with Ra less than 10 nm and rough surfaces with Ra above 70 nm were used as the substrate. Such a simple preparation procedure may provide a suitable interface surface for silicon-based devices and neurones or other living tissues.

Mechanical properties of skeletal bone in gene-mutated stöpsel(dtl28d) and wild-type zebrafish (Danio rerio) measured by atomic force microscopy-based nanoindentation

An atomic force microscopy (AFM)-based nanoindenter was used to evaluate the mechanical properties of skeletal bones in wild-type and gene-mutated zebrafish (Danio rerio), stöpsel(dtl28d). Both skeletons were isolated from adult zebrafish and tested under a load of 5 mN. It was found that stp/stp bone has a similar nanohardness but significantly greater elastic modulus compared with that of wild-type bone. The residual indenter impressions using AFM and the fracture surfaces of both bones using scanning electron microscopy were examined and showed that the bone of zebrafish becomes more brittle after the stp mutation. This first observation of the alteration of bone mechanical behavior by gene mutation in zebrafish system is of scientific and clinical relevance to many areas of study, such as bone fracture and fragility mechanisms in human heritable disorders and bone-materials fabrication via gene engineering.

Biomimetic calcium phosphate coatings on Polyactive 1000/70/30

Precalcification of Polyactive 1000/70/30 with a biomimetic calcium phosphate coating is expected to enhance the bioactivity of this biodegradable polymer for the application as bone filler or scaffold of bone tissue engineering. This study presents a 1-day one-step incubation method to obtain either amorphous or bone-like apatitic calcium phosphate coating on Polyactive 1000/70/30. Either dense plates or three-dimensional porous blocks of the polymer were incubated in a simplified but concentrated simulated body fluid-derived solution at 37 degrees C. By bubbling CO2 gas, a solution was prepared with calcium and phosphate ion concentrations five times of that of regular simulated body fluid. With controlled stirring, the CO2 was released out of the solution and exchanged by air. The pH of the solution increased to induce coating formation. Adjusting stirring rate and CO2/air exchange rate controlled the process kinetics. The reaction kinetics had little influence on the crystallographic structure of the final coating mineral for a given solution composition as shown by Fourier transform infrared spectroscopy and X-ray diffraction. However, the interface structure between the coating and substrate was kinetics-dependent. A fast precipitation condition resulted in a uniform but superficial calcification pattern at the surface of polymer. A slow process by selecting either a slow stirring or a slow CO2/air exchange, on the contrary, induced a localized but deep inside calcification pattern. A tensile test showed no statistically significant difference in the mechanical properties among uncoated and coated polymers. The cracking behavior of coatings from different kinetics, however, exhibited different manners, as can be attributed to different interface structures and interfacial strengths.

Connective tissue orientation around dental implants in a canine model

The objective of this study was to evaluate the orientation of collagen in the canine gingival connective tissue to a titanium surface (TI), and to hydroxyapatite coatings applied by plasma-spraying (HAPS) and ion beam assisted deposition (IBAD), on the supracrestal region of dental implants after 3 and 4 months. The effects of induced peri-implantitis on the soft connective tissue apposed to the implant were also evaluated. The use of these three surface types allowed for the evaluation of the effects of chemical composition (TI vs. IBAD; same topography) and topography (HAPS vs. IBAD; similar chemical composition) on the collagen fiber orientation. The majority of collagen fibers were found to be parallel to the implant surface, and there was no significant effect of surface type on orientation. There was a significant effect of inflammation on the connective tissue attachment length. The loss of bone height and concomitant gingival recession reduced the length of soft connective tissue apposed to the implant zone designed for collagen fiber attachment.

A mechanistic study of the antibacterial effect of silver ions on Escherichia coli and Staphylococcus aureus

To investigate the mechanism of inhibition of silver ions on microorganisms, two strains of bacteria, namely Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus), were treated with AgNO(3) and studied using combined electron microscopy and X-ray microanalysis. Similar morphological changes occurred in both E. coli and S. aureus cells after Ag(+) treatment. The cytoplasm membrane detached from the cell wall. A remarkable electron-light region appeared in the center of the cells, which contained condensed deoxyribonucleic acid (DNA) molecules. There are many small electron-dense granules either surrounding the cell wall or depositing inside the cells. The existence of elements of silver and sulfur in the electron-dense granules and cytoplasm detected by X-ray microanalysis suggested the antibacterial mechanism of silver: DNA lost its replication ability and the protein became inactivated after Ag(+) treatment. The slighter morphological changes of S. aureus compared with E. coli recommended a defense system of S. aureus against the inhibitory effects of Ag(+) ions.

High-resolution transmission electron microscopy investigations of a highly adhesive hydroxyapatite coating/titanium interface fabricated by ion-beam-assisted deposition

An atomic intermixing layer, 25 nm in width, has been identified by high-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray spectroscopy (EDS) analysis at the ceramic/metal interface of a hydroxyapatite (HA) coating/titanium implant prepared by an ion-beam-assisted deposition (IBAD) technique and post-heat-treatment process. The detailed interfacial microstructure revealed a gradient evolution of both the structure and composition of the interfacial phases from the titanium substrate to HA coatings. An enhancement of the tensile bond strength was found and was attributed to the possible chemical bonding at the ceramic/metal interface.