Key Engineering Materials Vols. 493-494

Abstract: The chemical compositions of calcium phosphate materials are similar to that of bone making them very attractive for use in the repair of critical size bone defects. The bioresorption of calcium phosphate occurs principally by dissolution. To determine the impact of composition and flow conditions on dissolution rates, calcium phosphate tablets were prepared by slip casting of ceramic slips with different ratios of hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP). Dissolution was evaluated at pH4 using both a static and dynamic flow regime. Both the composition of the HA:β-TCP tablet and flow regime noticeably influenced the rate of dissolution; the 50:50 HA:β-TCP composition demonstrating the greatest level of dissolution, and, exposure of the ceramic specimens to dynamic conditions producing the highest rate of dissolution. Understanding the impact of phase composition and flow condition with respect to the dissolution of calcium phosphate will aid in the development and improvement of materials for bone substitution.

Abstract: Chitin is a polysaccharide abundant in nature. Its’ deacetylation product-chitosan- in combination with gelatin (collagen product) is commonly used as biopolymer scaffold for tissue engineering. The aim of this study was to investigate diffrerences in surface characteristics of chitin (CHN CCS) and chitosan –gelatin (CHS-G CCS) composite ceramic scaffolds (CCS), during their incubation in culture medium (DMEM) with or without human periodontal ligament fibroblasts (HPDLF). CHN CCS and CHS- G CCS, with pore size 70-200μm, were fabricated on the surface of ceramic disks, being coated with a mixture of bioactive glass – ceramic (1:1 wt). Three CCSs of each type were constructed. Each CCS was incubated at 37 °C up to 10 days, either only in DMEM supplemented with 10% FCS or in DMEM with the presence of 10⁵ HPDLF. SEM microphotographs and EDS analysis, before and after incubation, were used to investigate CCSs’ surface alterations. Before incubation, all type of CCSs appeared to be macro porous with high interconnectivity. Exposed to incubation, CHN CCSs’ surface porosity seemed to be rapidly reduced and a rough surface without pores was observed with or without HPDLF. Attached HPDLF were rarely detected. CHS-G CCSs appeared to retain surface porosity in DMEM without cells. In HPDLF culture an almost uniform surface with organic aggregates and attached cells was observed. Until day 10, HPDLF could only be detected at CHS-G CCS’s surface. Conclusion: SEM microphotographs observations indicate that CHN CCSs’ incubation in DMEM led in early and rapid coalescence of surface pores, thus inhibiting HPDLF attachment. HPDLF attachment on CHS-G CCSs confirm the beneficial role of gelatin, while differences in CHS-G CCSs’ surface with and without HPDLF culture indicate that not only sedimentation of medium's ingredients, but cell attachment and function could decrease surface’s porosity, affecting consequently HPDLF proliferation.

Abstract: Tissue engineering is an important emerging area for creating biological alternatives for harvested tissues, implants, and prostheses. Biocompatible and biodegradable polymeric materials are considered an important class of materials that can be used as scaffolds in tissue engineering applications. In this work, the system studied was nanocomposites of hydroxyapatite (HA) dispersed in a matrix of PLLA. Scaffolds have to present similar structure and also function as an artificial extracellular matrix for cell attachment and growth. Hydroxyapatite is a bioactive ceramic and has been used in applications of repairing bone tissue due to its biocompatibility and osteoconductivity. Poly(L- lactic acid) is a biodegradable and biocompatible polymer and has been used in different applications in the biomedical field. In this work, polymer solutions were prepared with different percentages of hydroxyapatite and porous membranes consisting of non-woven nanostructured fibers were obtained by electrospinning. The process parameters were: voltage of 13kV, flow rate of 0.5 ml/h and distance from the tip of the needle to the collector of 12 cm. By using these process parameter, fibrous membranes were obtained with different concentrations of HA (1.96, 4.76, 9 [wt %]). The morphology of the samples was observed by SEM and the characteristic physic-chemical were analyzed by XRF, XRD, DSC and FTIR.

Abstract: Tissue engineering has been studied as a novel therapeutic technology which replaces organ transplantation. Tissue engineering consists of three factors “scaffolds”, “cells” and “growth factors”, and regenerates defecting tissue using them. We have successfully developed porous apatite-fiber scaffolds (AFSs) which have three-dimensional (3D) inter-connected pores using single-crystal apatite fibers and carbon beads; subsequently, we have clarified that the AFSs have an excellent bioactivity on the basis of both in vitro and in vivo evaluations. In addition, we have reconstructed the 3D tissue-engineered bone through 3D-cell culture of mesenchymal stem cells derived from rat bone marrow (RBMC) using the AFS settled into the radial-flow bioreactor (RFB). Aim in the present work is to examine the effect of flow rate of medium in the RFB on the differentiation of osteoblasts in tissue-engineered bone reconstructed using an AFS and RBMC. The flow rates were set to 1.3 and 6.3 cm³∙min^-1; tissue-engineered bones reconstructed by the two flow rates are defined as “bone#1” and “bone#2”, respectively. The ALP activity and OC amount normalized for DNA content of bone#2 were higher than those of bone#1. These results indicate that the faster flow rate may promote the differentiation into osteoblast. Thus, the physical irritation to cells, such as flow rates, may be effective for reconstruction of tissue-engineered bone.

Abstract: Scaffold-based tooth engineering is currently the most popular approach towards replacing dental tissues or even engineering a bio-tooth. Although, various scaffold materials have been employed in tooth regeneration, the scaffold-based tooth design has, until now, achieved only limited success. Recently, bioactive Mg-based ceramics have attracted interest as Mg plays an important role on skeletal metabolism and affects the quality and structure of hard dental tissues. Mg has been reported to improve the mechanical properties of calcium phosphate ceramics, control biodegradation rate and stabilize the cell-material interface improving cell attachment and growth. The aim of this study was the development of an experimental Mg-based ceramic material, with enhanced bioactivity and adequate mechanical properties, in order to be potentially used in dental tissue regeneration. The Mg-based ceramic was prepared by the sol-gel method, while the stabilization was performed at 1300, 1400 and 1450oC in order a fully crystalline material to be obtained. The characterization of the materials -before and after immersion is Simulated Body Fluid (SBF)- was performed by Fourier Tranform Infrared Spectroscopy (FTIR), X-Ray Diffractometry (XRD) and Scanning Electron Microscopy associated with an EDS analyzer (SEM-EDS), while the flexural strength of uniaxially pressed pellets was measured using a universal testing machine for 3- point bending tests (Instron 3344). FTIR spectra and XRD patterns of all powder samples before immersion in SBF solution confirmed the presence of three crystalline phases; akermanite, merwinite and diopside. The onset of apatite formation on the surface of all powders was observed even after three days of immersion, while the apatite formation on the surface of the sintered pellets was slightly delayed. Flexural strength values were in the range of 30Mpa. In conclusion, Mg-based glass-ceramics attain adequate mechanical integrity and high rate of bioactivity and could be potentially used in the construction of ceramic scaffolds for dental tissue regeneration.

Abstract: In this work a novel three-dimensional ostechondral substitute is proposed that is made of an inorganic/organic hybrid material, namely collagen/hydroxyapatite. The two components of the substitute have been characterized separately. The inorganic part, a hydroxyapatite scaffold, was fabricated by a polymer sponge templating method using a reactive sub-micron powder synthesized in our laboratory by hydroxide precipitation sol-gel route. The organic part, a collagen scaffold, was fabricated by a freeze-dying technique varying design parameters. Both the parts were analysed by scanning electron microscopy and their mechanical properties assessed by compression tests. The hydroxyapatite scaffold showed a high and highly interconnected porosity and a mechanical strength equal to 0.55 MPa, higher than those reported in literature. The collagen scaffolds were seeded by chondrocytes, processed for histology analysis and tested in compression. The biological tests proved the ability of the scaffolds to be positively populated by chondrocytes and the mechanical analysis showed that the mechanical strength of the scaffolds significantly increased after 3 weeks of culture.

Abstract: The biocompatibility of TiO₂ is due to the activity that it shown in front of oxygen and nitrogen reactive species. Some authors suggest that the mechanism go through oxidation reduction reactions where changes of oxidation state in the Titanium and phases are involve. For this reason, Anderson-Magnelli phases could present scavenging activity. Moreover, these materials are use as electrodes and in that way are proposed as electrodes for study their scavenging mechanism by electrochemical methods.

Abstract: Bone Tissue Engineering (BTE) composed of three main parts: scaffold, cells and signaling factors. Several materials and composites are suggested as a scaffold for BTE. Biocompatibility is one of the most important property of a BTE scaffold. In this work synthesis of a novel nanocomposite including layered double hydroxides (LDH) and gelatin is carried out and its biological properties were studied. The co-precipitation (pH=11) method was used to prepare the LDH powder, using calcium nitrate, Magesium nitrate and aluminum nitrate salts as starting materials. The resulted precipitates were dried. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) analyses were used to characterize the synthesized powders. The results demonstrated the presence of nanocrystals of Ca-LDH and Mg-LDH as Hexagonal and Layered Morphology. The obtained powders were composed to gelatin via solvent casting method then freez dried. The scaffold was prepared via membrane lamination method from the resulted layers that linked together with gelatin as binder. In order to investigate the scaffold cytotoxicity MTT assay was done with a osteosarcoma cell line. No toxic response was observed in specimens. As a major result, it was demonstrated that the specimen showed a significant cellular response. Then osteosarcoma cells were cultured for 7-day and 14-day extract of powders. The composites osteoconductivity was investigate with cells alkaline phosphatase extraction. The results demonstrated that the Ca-LDH/gelatin composite scaffold has a good potential for bone tissue engineering applications and Mg-LDH specimen has a better osteconductivity.

Abstract: Today, porous nanocomposite scaffolds play a key role in tissue engineering approaches and new processing methods and materials are constantly being developed to cater for the wide range of specifications and requirements. In addition, providing a structural support while maintaining bioactivity is one of the most important goals for these scaffolds, i.e. applying bioceramic into polymeric structures, facilitating the formation of functional tissues. In the last few years, hydroxyapatite (HAp) has been widely investigated as scaffolding material, mainly for its ability to bond to both hard and soft tissues. In this research, new bioactive scaffolds were successfully developed using poly(ε-caprolactone) (PCL), cross-linked gelatin and nanoparticles of HAp. After synthesis of nano HAp powder via chemical precipitation technique, the nanocomposites were prepared through layer solvent casting and lamination techniques. According to the obtained results, the amount of ultimate stress, stiffness and elastic modulus increased by addition of PCL. Also, the in vitro biocompatibility and cytocompatibility of the scaffolds were tested using mesenchymal stem cells (MSCs), and cells found to be attached to the scaffold walls.

Abstract: In this study, micro porous oxide layer was formed on a Ti6Al4V alloy by the micro arc oxidation process in an electrolyte containing (CH₃COO)₂CaH₂O + Na₃PO₄ with appropriate amount of silver containing agent. A wide spectrum antibiotic was also applied to the surface. Samples were subjected to antimicrobial activity tests in accordance with JIS Z 2801 standard against E.coli and the results were compared with those of original Ti6Al4V sample. First experimental results presented here showed that the micro arc oxidation process improve the antibacterial activity of Ti6Al4V alloy surface and further improvement could be obtained upon antibiotic application in addition to the micro arc oxidation process.