Development of asymmetric gradational-changed porous chitosan membrane for guided periodontal tissue regeneration

A novel kind of guided tissue regeneration (GTR) barrier membrane has been fabricated using an immersion–precipitation phase inversion technique (IPPI) with biodegradable natural polymer–chitosan. The membrane had an asymmetric gradational-changed porous structure including a dense skin layer, a transition region and a sponge-like porous layer. The concentration of chitosan solution and solvent evaporated time were two key factors that had significant effect on the porosity, average pore size, absorbed water ratio and mechanical properties of the porous membrane. The porous membrane not only degraded but maintaining the structure integrity for 5–6 weeks in the enzyme solution that can meet the demand for GTR. The biological experiment results showed the asymmetric membranes did not cause anaphylactic reaction, hemolysis, cytotoxicity and pyrogenic effect. All of the results indicated that the porous chitosan membrane had excellent biocompatibility and biodegradation, which could be used as a barrier for preventing apical migration of gingival epithelial cells and promoting growth of periodontal ligament cells in periodontal therapy.     

In vitro corrosion resistance of Lotus-type porous Ni-free stainless steels

The corrosion behavior of three kinds of austenitic high nitrogen Lotus-type porous Ni-free stainless steels was examined in acellular simulated body fluid solutions and compared with type AISI 316L stainless steel. The corrosion resistance was evaluated by electrochemical techniques, the analysis of released metal ions was performed by inductively coupled plasma mass spectrometry (ICP-MS) and the cytotoxicity was investigated in a culture of murine osteoblasts cells. Total immunity to localized corrosion in simulated body fluid (SBF) solutions was exhibited by Lotus-type porous Ni-free stainless steels, while Lotus-type porous AISI 316L showed very low pitting corrosion resistance evidenced by pitting corrosion at a very low breakdown potential. Additionally, Lotus-type porous Ni-free stainless steels showed a quite low metal ion release in SBF solutions. Furthermore, cell culture studies showed that the fabricated materials were non-cytotoxic to mouse osteoblasts cell line. On the basis of these results, it can be concluded that the investigated alloys are biocompatible and corrosion resistant and a promising material for biomedical applications.     

In vitro apatite formation on polyamide containing carboxyl groups modified with silanol groups

Modification of organic polymer with silanol groups in combination with calcium salts enables the polymer to show bioactivity, that is, the polymer forms apatite on its surface after exposure to body environment. However, how modification with silanol groups influences ability of apatite formation on the polymer substrate and adhesive strength between polymer and apatite is not yet known. In the present study, polyamide containing carboxyl groups was modified with different amounts of silanol groups, and its apatite-forming ability in 1.5SBF, which contained ion concentrations 1.5 times those of simulated body fluid (SBF), was examined. The rate of apatite formation increased with increasing content of silanol groups in the polyamide films. This may be attributed to enhancement of dipole interactions. A tendency for the adhesive strength of the apatite layer on the polyamide film to be decreased with increasing content of silanol groups was observed. This may be attributed to swelling in 1.5SBF and having a high degree of shrinkage after drying. These findings clearly show that modification of organic polymers with the functional groups induces apatite deposition, and also determines the adhesive strength of the apatite layer to the organic substrates.     

In vitro formation of hydroxylapatite layer in a MgO-containing glass

In the present article, the behaviour of a biologically active glass (BAG) belonging to the system SiO₂–CaO–MgO–Na₂O–K₂O–P₂O₅, soaked in simulated body fluids (SBF_s), is studied. The amount of Ca, Mg and K leached from the glass, as well as variations in P concentration and pH of the solution were measured versus time. The formation of a hydroxylapatite (HA) layer on the glass surface was determined by XRD and SEM-EDX. The article reports the influence of pH variation of the medium on the crystallinity of the HA formed.     

In vitro apatite formation on organic polymers modified with a silane coupling reagent.

Gamma-methacryloxypropyltrimethoxysilane (gamma-MPS) was grafted to high-density polyethylene, polyamide and silicone rubber substrates by the emulsion polymerization procedure in order to provide these organic polymers with in vitro apatite-forming ability. The contact angles towards distilled water of the gamma-MPS-grafted specimens were lower than those of the original organic polymer specimens, indicating that the grafted substrates were more hydrophilic. The in vitro apatite formation in a simulated body fluid (Kokubo solution) was confirmed for several of the gamma-MPS-grafted specimens.     

In vitro degradation of porous poly(lactic acid)/quantum dots scaffolds

In this study, cadmium selenide/zinc sulfide (CdSe/ZnS) quantum dots (QDs) were introduced into poly(lactic acid) (PLA) for fabrication of photoluminescent PLA/QDs scaffolds. TEM images revealed that the QDs were uniformly dispersed in the PLA. Compressive modulus and thermal stability of the PLA/QDs scaffolds are higher than those of the unfilled PLA scaffold. Cytotoxicity test results confirmed the non-cytotoxicity of the PLA/QDs scaffolds. During the process of in vitro degradation, the degradation rate of the PLA was accelerated by the presence of the QDs, and the molecular weight distributions of the PLA/QDs scaffolds were much broader when compared with the unfilled PLA ones. During the first 84 weeks of the degradation process, the photoluminescence (PL) intensity of the PLA/QDs scaffolds decreased with almost the same degradation ratio. The results suggested that the CdSe/ZnS QDs have potential applications for monitoring in vivo degradation of tissue engineering scaffolds.     

Fiber-reinforced composites with polymer-derived matrix: processing,matrix formation and properties

Carbon and SiC fiber-reinforced ceramic matrix composites were prepared via infiltration of fiber preforms using the polymer infiltration technique and polymer pyrolysis. Suitable silazane (SiCN) precursors with appropriate thermosetting behavior, viscosity and ceramic yield were synthesized, starting from functionalized chlorosilanes. Microstructural development and fracture behavior was studied after various infiltration and pyrolysis cycles. Residual stresses induced during processing were evaluated. Mechanical and thermo-physical properties of the composites with polymer-derived matrix, i.e. 3-pt bending strength and thermal expansion coefficients (CTE), were measured dependent on reinfiltration cycles and fiber orientation. The oxidation resistance was investigated. Specific pyrolyzed samples were infiltrated via silicon melts in order to enhance corrosion and wear resistance.     

In vitro release of ketoprofen from hydrophilic matrix tablets containing cellulose polymer mixtures

The effect of cellulose ether polymer mixtures, containing both hydroxypropylcellulose (HPC) and hydroxypropylmethylcellulose (HPMC K15M or K100M), on ketoprofen (KTP) release from matrix tablets was investigated. In order to evaluate the compatibility between the matrix components, Raman spectroscopy, scanning electron microscopy (SEM), and X-ray powder diffraction (XRPD) experiments were performed. The results evidence the absence of significant intermolecular interactions that could eventually lead to an incompatibility between the drug and the different excipients. Formulations containing mixtures of polymers with both low and high viscosity grades were prepared by a direct compression method, by varying the polymer/polymer (w/w) ratio while keeping the drug amount incorporated in the solid dispersion constant (200?mg). The hardness values of different matrices were found within the range 113.8 to 154.9 N. HPLC analysis showed a drug content recovery between 99.3 and 102.1%, indicating that no KTP degradation occurred during the preparation process. All formulations attained a high hydration degree after the first hour, which is essential to allow the gel layer formation prior to tablet dissolution. Independent-model dissolution parameters such as t_10% and t_50% dissolution times, dissolution efficiency (DE), mean dissolution time (MDT), and area under curve (AUC) were calculated for all formulations. Zero-order, first-order, Higuchi, and Korsmeyer–Peppas kinetic models were employed to interpret the dissolution profiles: a predominantly Fickian diffusion release mechanism was obtained – with Korsmeyer–Peppas exponent values ranging from 0.216 to 0.555. The incorporation of HPC was thus found to play an essential role as a release modifier from HPMC containing tablets.     

A comparison study of different physical treatments on cartilage matrix derived porous scaffolds for tissue engineering applications

Native cartilage matrix derived (CMD) scaffolds from various animal and human sources have drawn attention in cartilage tissue engineering due to the demonstrable presence of bioactive components. Different chemical and physical treatments have been employed to enhance the micro-architecture of CMD scaffolds. In this study we have assessed the typical effects of physical cross-linking methods, namely ultraviolet (UV) light, dehydrothermal (DHT) treatment, and combinations of them on bovine articular CMD porous scaffolds with three different matrix concentrations (5%, 15% and 30%) to assess the relative strengths of each treatment. Our findings suggest that UV and UV–DHT treatments on 15% CMD scaffolds can yield architecturally optimal scaffolds for cartilage tissue engineering.     

In vitro evaluation of bioactive strontium-based ceramic with rabbit adipose-derived stem cells for bone tissue regeneration

The development of bone replacement materials is an important objective in the field of orthopaedic surgery. Due to the drawbacks of treating bone defects with autografts, synthetic bone graft materials have become optional. So in this work, a bone tissue engineering approach with radiopaque bioactive strontium incorporated calcium phosphate was proposed for the preliminary cytocompatibility studies for bone substitutes. Accumulating evidence indicates that strontium containing biomaterials promote enhanced bone repair and radiopacity for easy imaging. Hence, strontium calcium phosphate (SrCaPO₄) and hydroxyapatite scaffolds have been investigated for its ability to support and sustain the growth of rabbit adipose-derived mesenchymal stem cells (RADMSCs) in vitro. They were characterized via Micro-CT for pore size distribution. Cells used were isolated from New Zealand White rabbit adipose tissue, characterized by FACS and via differentiation into the osteogenic lineage by alkaline phosphatase, Masson’s trichome, Alizarin Red and von Kossa staining on day 28. Material-cell interaction was observed by SEM imaging of cell morphology on contact with material. Live–Dead analysis was done by confocal laser scanning microscopy and cell cluster analysis via μCT. The in vitro biodegradation, elution and nucleation of apatite formation of the material was evaluated using simulated body fluid and phosphate buffered saline in static regime up to 28 days at 37 °C. These results demonstrated that SrCaPO₄ is a good candidate for bone tissue engineering applications and with osteogenically-induced RADMSCs, they may serve as potential implants for the repair of critical-sized bone defects.     

Modulation of enamel matrix proteins on the formation and nano-assembly of hydroxyapatite in vitro

Natural enamel has a hierarchically nanoassembled architecture that is regulated by enamel matrix proteins (EMPs) during the formation of enamel crystals. To understand the role of EMPs on enamel mineralization, calcium phosphate (CaP) growth experiments in both the presence and absence of native rat EMPs in a single diffusion system were conducted. The morphology and organization of formed CaP crystals were examined by X-Ray Diffraction (XRD), High-Resolution Transmission Microscopy (HRTEM) and Selected Area Electron Diffraction (SAED). In the system containing the EMPs, hydroxyapatite (HAP) with hierarchical lamellar nanostructure can be formed and the aligned HAP assembly tightly bundled by 3–4 rod-like nanocrystals like an enamel prism. However, in the absence of EMPs, only a sheet-like structure of octacalcium phosphate (OCP) phase was presented. EMPs promote HAP formation and inhibit the growth of OCP on the (010) plane. It is discussed that the organized Amelogenin/Amorphous Calcium Phosphate might be the precursor to the bundled HAP crystal prism. The study benefits the understanding of biomineralization of tooth enamel.     

In vitro aging of mineralized collagen-based composite as guided tissue regeneration membrane

The technique of guided tissue regeneration (GTR) has been developed for the regeneration of periodontal tissues, bone around natural teeth and dental implants. The aim of this study is to investigate the biodegradability and mechanic behavior of a novel mineralized nano-hydroxyapatite/collagen/poly (lactic acid) (nHAC/PLA) composite as GTR membrane in vitro. The elastic modulus and maximum tensile strength of GTR film samples with different nHAC/PLA ratio were measured to get an optimal nHAC/PLA ratio. Thermogravimetric analysis was conducted to evaluate the change of the inorganic component in the samples during the process of in vitro aging. Morphology of samples was checked by using scanning electron microscopy. On the basis of the above results, it can be concluded that the GTR membranes maintained integrity and the original appearance throughout the 1-month in vitro aging. There is an active dissolution and deposition process of crystals which is propitious to the bone formation on the surface of the composite membrane. The optimal nHAC/PLA ratio of the novel membrane is 0.4:1. For a longer period of bone repair, PLA with higher molecular weight should be chosen as the scaffold for the GTR membrane.     

In vitro degradation of porous nano-hydroxyapatite/collagen/PLLA scaffold reinforced by chitin fibres

In this paper, a novel porous scaffold for bone tissue engineering was prepared with nano-hydroxyapatite/collagen/Poly-l-lactic acid (PLLA) composite reinforced by chitin fibres. To enhance the strength of the scaffold further, PLLA was linked with chitin fibres by Dicyclohexylcarbodimide (DCC). The structures of the reinforced scaffold with and without linking were characterized by Scanning Electron Microscopy (SEM). The chemical characteristics of the chitin fibres with and without linking were evaluated by Fourier-transformed infrared (FTIR) spectroscopy. The mechanical performance during degradation in vitro was investigated. The results indicated that the nano-hydroxyapatite/collagen/PLLA composite reinforced by chitin fibres with linking kept better mechanical properties than that of the composite without linking. These results denoted that the stronger interfacial bonding strength of the scaffold with linking could decrease the degradation rate in vitro. The reinforced composite with the link-treatment can be severed as a scaffold for bone tissue engineering.     

In vitro remineralization of human dental enamel by bioactive glasses

Different compositions of silicate-based bioactive glasses of the system SiO₂–CaO–P₂O₅ (45S, 58S, and 77S) were evaluated for teeth remineralization effect on the etched human dental enamel in simulate human oral environment. Enamel samples were subjected to demineralization in citric acid solution, then treated with different bioactive glass pastes, and finally soaked in simulated oral fluid (SOF) for 7 days before evaluation. The results indicated that enamel surface formed a homogenous and dense mineralized layer with the treatment of 45S and 58S samples. The average thickness was 4 and 2.5 μm, respectively. But 77S treatment showed a loose and uneven remineralized layer. Although the surface roughness decreased with the increase of silicon content, mechanical strength of enamel samples became less gradually. Taken together, 45S paste had the best remineralization ability, best mechanical strength, and satisfactory surface roughness. These results also indicated that the level of silicon content of bioactive glasses played a key role in dental enamel remineralization.     

Engineering cartilage tissue interfaces using a natural glycosaminoglycan hydrogel matrix — An in vitro study

Hydrogels are suitable matrices for cartilage tissue engineering on account of their resemblance to native extracellular matrix of articular cartilage and also considering its ease of application, they can be delivered to the defect site in a minimally invasive manner. In this study, we evaluate the suitability of a fast gelling natural biopolymer hydrogel matrix for articular cartilage tissue engineering. A hydrogel based on two natural polymers, chitosan and hyaluronic acid derivative was prepared and physicochemically characterized. Chondrocytes were then encapsulated within the hydrogel and cultured over a period of one month. Cartilage regeneration was assessed by histological, biochemical and gene expression studies. Chondrocytes maintained typical round morphology throughout the course of this investigation, indicating preservation of their phenotype with sufficient production of extracellular matrix and expression of typical chondrogenic markers Collagen type 2 and aggrecan. The results suggest that the natural polymer hydrogel matrix can be used as an efficient matrix for articular cartilage tissue engineering.     

Transdermal and buccal delivery of methylxanthines through human tissue in vitro

We examined the in vitro permeation of central nervous stimulants—caffeine, theophylline, and theobromine across human skin with the aid of six chemical enhancers. It was found that oleic acid was the most potent enhancer for all three methylxanthines. Further optimization studies with different solvents showed that caffeine transport could be enhanced to give flux values up to 585 μg/cm².hr^-1. Theobromine and theophylline delivery rates proved insufficient. An additional study involving a buccal tissue equivalent showed that this membrane was more permeable than skin for all model actives tested and would offer an alternate way of delivery.     

Collagenous tissue formation in association with medical implants

The host response to a biomaterial includes assembly of an effective collagenous matrix that is critical for the long-term performance of a medical implant. Despite the development of methods that allow detailed examination of the non-cellular matrix components, particularly collagens, relatively little information is available on the extent of molecular variability in the collagen matrix that is associated with various alternative implant materials.     

Fabrication and in vitro evaluations with osteoblast-like MG-63 cells of porous hyaluronic acid-gelatin blend scaffold for bone tissue engineering applications

In this study, hyaluronic acid–gelatin (HyA–Gel) scaffolds were prepared with HyA:Gel ratios of 15:85, 50:50, and 85:15 with the goal of obtaining a porous biocompatible scaffold for bone tissue engineering applications. Scanning electron microscopy and Fourier-transform infrared spectroscopy were done to characterize the morphological orientations of the scaffolds. The biocomposite structure was highly porous and the pores in the scaffolds were interconnected. The compressive strength of the scaffold was 7.39 ± 0.2 MPa for the HyA–Gel when fabricated at a ratio of 15:85. To assess the biocompatibility and cell behavior on the HyA–Gel biocomposite, the proliferation of MG-63 osteoblast cell on the scaffolds was examined using the MTT assay, optical microscopy, and confocal microscopy. Collagen type I and osteopontin expression of cells cultured on the scaffolds were examined using immunoblotting. The scaffolds fabricated with a 15:85—HyA:Gel ratio showed excellent biocompatibility, good mechanical properties, and high porosity, which suggest that the highly porous scaffold holds great promise for use in bone tissue engineering applications.