Key Engineering Materials Vols. 330-332

Abstract: The use of 3D osteoconductive scaffolds provides an informative substrate serving as a physical support matrix for in vivo tissue regeneration. In the last few years the use of bioengineered 3D scaffolds has been becoming the most promising experimental approach for the regeneration of living tissues. Stem cells are typically used, in combination with 3D substrates, to promote in vivo bone regeneration and repair. For tissue engineering applications, biomaterials should therefore be able to support the functional properties of osteo-progenitor cells, giving them the optimal microenvironment to perform their physiological activity. Inorganic biomaterials are particularly relevant for bone regeneration; calcium phosphate ceramics have in fact been shown to strongly interact with bone tissue. The aim of the present work was to evaluate two different scaffolds with a defined design and different composition developed to guide/promote tissue repair.

Abstract: The complex porous materials, Hydroxyapatite(HA)/silk fibroin, were prepared using ultrasonic vibration gel method in this paper. The mechanical properties decreased with the increase of HA while the porosity increased. The pore size become bigger than 100μm when adding silk fiber in the complex materials, and the breaking energy increased evidently from 10 to 1000 J/m2 when fiber content increased from 0 to 4 wt.%. It was observed from SEM that all composites have interconnected micropores.

Abstract: The present study was designed to investigate whether porous titanium (Ti) having Young’s modulus similar to bone has osteoconductive characteristics in rat critical-sized calvarial bone defect. The effect of coating by octacalcium phosphate (OCP) was also examined. OCP is known as a precursor of initial mineral crystals of biological apatite in bones and teeth. Ti powder was prepared by plasma rotating electrode process in an Ar atmosphere. Then, porous Ti disks, 8 mm in diameter with 1 mm thick, were obtained using the particles ranging from 300 to 500 +m, by sintering at 1573 K without applied pressure. The disks had about 35 vol% in porosity and about 10 GPa in Young’s modulus which corresponds to that of human cortical bone. Newly formed bone was observed so as to fill the pore up at 12 weeks, confirming the ability to conduct the ingrowths of the bone tissue. Although in vitro study showed that proliferation of mouse bone marrow stromal ST-2 cells was inhibited on the dishes coated by OCP rather than the control dish, OCP coating on porous Ti seemed to stimulate the bone formation in vivo. Taken together, it seems likely that porous Ti having Young’s modulus similar to bone shows osteoconductive characteristics to conduct bone ingrowths. OCP could be a potential coating agent to assist bone regeneration on porous Ti.

Abstract: Porous HA/TCP bioceramics were immersed in pure dog serum to observe apatite formation. Deposited crystals were examined using SEM. Results showed that beamed sheet-like crystals formed on the surface of ceramics granules, and after postponement immersion time, crystals extended and became bigger. EDS and IR results suggested formed crystals were defect-calcium type carbonated hydroxyapatite. HRTEM photograph suggested formation process of new-formed crystals from non-crystal to crystal in serum. Directional organisms acted maybe as a template in process of crystals formation, so new crystals developed along certain direction.

Abstract: A new method of design and manufacturing of bone graft substitutes is introduced. For the first time it is possible to prepare bone graft substitutes with a directed and controlled pore structure. Furthermore, the formation of sophisticated geometries is feasible. First in vitro investigations with cell cultures show a vital cell growing on the synthetic bone graft material. Numerous applications are possible.

Abstract: Bone tissue engineering is a promising way to repair of bone defects. To choose a proper scaffold is still a disputable problem in bone tissue engineering. This study aimed to compare the effects of repairing critical calvarial defects with the compounds of autogenous bone marrow stromal cells (BMSCs) and coral hydroxyapatite(CHA), hydroxyapatite/ tricalcium phosphate (HA/TCP), poly(lactide-co-glycolide) (PLGA) and alginate (AG). The results showed that CHA and AG were satisfactory bone tissues engineering scaffolds among the four kinds of materials. BMSCs/CHA and BMSCs/AG are promising techniques for reconstruction of bone defects.

Abstract: A porous structure comprises pores and pore throats with a complex three-dimensional network structure, and many investigators have described the relationship between average pore size and the amount of bone ingrowth. However, the influence of network structure or pore throats for tissue ingrowth has rarely been discussed. Bioactive porous titanium implants with 48% porosity were analyzed using specific algorithms for three-dimensional analysis of interconnectivity based on a micro focus X-ray computed tomography system. In vivo histological analysis was performed using the very same implants implanted into the femoral condyles of male rabbits for 6 weeks. This matching study revealed that more poorly differentiated pores tended to have narrow pore throats, especially in their shorter routes to the outside. Data obtained suggest that this sort of novel analysis is useful for evaluating bone and tissue ingrowth into porous biomaterials.

Abstract: The porous scaffolds of silk fibroin-chitosan /nano-hydroxyapatite (SF-CS / n-HA) were fabricated through the freeze- drying technique. Component, structure and morphology of scaffolds were studied by infrared (IR), X-ray diffusion (XRD) and scanning electron microscope (SEM), and the mechanical properties of the scaffolds were measured. The simulated body fluid (SBF) experiments were conducted to assess the bioactivity of the scaffolds. Results indicate that chemical binding is formed between HA and organics, the macropore diameter of the scaffolds varies from 150 to 400μm. The porous scaffolds with interconnected pores possess a high porosity of 78%-91% and compressive strength of 0.26 -1.96MPa, which can be controlled by adjusting the concentration of organic phases and prefreezing temperature. In the SBF tests, a layer of randomly oriented bone-like apatite crystals formed on the scaffold surface, which suggested that the composite material had good bioactivity. Studies suggest the feasibility of using SF-CS /n-HA composite scaffolds for bone tissue engineering.

Abstract: An environmentally friendly direct foaming method was investigated to produce porous alumina ceramics. Egg white protein was used as a binder and foaming agent. The microstructures show that pores are interconnected with pore size of a few hundreds μm and pore window size of ca. 50 μm. The compressive strength of alumina foam is up to 100 MPa depending on porosity. Bioactivation of alumina was carried out using an alkaline solution treatment. Hydroxylation of alumina was achieved using 5M NaOH at 80°C for 4 days. In vitro assessments of the alumina in a human osteoblast cell-like cell (MG63) culture showed that the bioactivated alumina foams exhibited better cellularity and alkaline phosphatase (ALP) activity compared to untreated alumina foams. The results indicate that it is possible to improve the osseointgration of alumina ceramics by structural and surface modifications and to extend the applications of biocompatible alumina ceramics in biomedical implants and tissue engineering scaffolds.

Abstract: Porous CaO-P2O5-SiO2 monolithics with double-pore structure were prepared from tetraethoxysilane, triethylephosphate and calcium nitrate by a sol-gel method. Polyethylene glycol and starch were used as mesopore-making agent and as macropore-making agent, respectively. The porous monolithics, having mesopores with ~20 nm pore size and macropores with 7~20 μm pore size, could be formed from the removal of organic components after heated at 600°C for 2 hours. After soaked in simulated body fluid (SBF) at 37°C for 7 days, bonelike apatite was formed on the surface of the samples. The porous samples were degraded gradually in SBF solution.