Polymeric Sponge Method Research Articles

Microstructure and properties of LZSA glass-ceramic foams

Commercial polyurethane foams with a monomodal pore size distribution were used to produce LZSA glass-ceramic foams by the polymeric sponge method. A suspension containing LZSA glass powder, bentonite and sodium silicate was prepared in isopropanol to impregnate the polymeric foams by dip coating. The sintering conditions were varied in the range of 700–850 °C for 30–180 min. The cellular microstructure of glass-ceramic foams was characterized by scanning electron microscopy (SEM) and micro-computer X-ray tomography (μCT). Optimum physical, mechanical and fluidynamic properties of the LZSA glass-ceramic foams were obtained at 750 °C for 60 min. Main crystalline phases detected were β-spodumene and zirconium silicate. The compressive strength of the foams (0.1–10 MPa) is strongly dependent on their overall porosity and their behaviour could be explained using the Gibson-Ashby model. The Darcyan permeability of LZSA foams was found to be in the range of 0.1–4 × 10 −9 m 2, which is in the order of magnitude of cellular supports for aerosol filters, and, therefore, suitable for several other technological applications.

Effect of Reaction Conditions on Pore Configuration and Mechanical Property for Porous Hydroxyapatite Prepared by Polymer Sponge Method

Porous HAp scaffolds have been prepared by using the slurry including HAp and magnesia based on the replication of polymer sponge substrate. The influence of HAp and MgO content in slurry on the pore morphology and size, and density, porosity, and mechanical strength of porous HAp scaffolds was investigated. The obtained scaffolds with average pore sizes ranging 150 to 300 μm had open, relatively uniform, and interconnected porous structure regardless of HAp and MgO content. As the MgO content increased, the pore network frame of scaffolds became to be relatively stronger, even though the pore size was not much changed. The compressive strength of the scaffolds increased rapidly with the increase of MgO content at a fixed HAp content because of increasing the pore wall thickness and density of the scaffolds. As a result, the porosity, density, and compressive strength of the porous HAp scaffolds scaffolds prepared by the sponge method were significantly affected by the addition of MgO.

Tissue-engineered bone formation using human bone marrow stromal cells and novel β-tricalcium phosphate**This work was supported by the National Basic Research Program of China (G1999054300, 2005CB522700) and Shanghai Science and Technology Development Foundation.

In this study we investigated not only the cellular proliferation and osteogenic differentiation of human bone marrow stromal cells (hBMSCs) on the novel β-tricalcium phosphate (β-TCP) scaffolds in vitro but also bone formation by ectopic implantation in athymic mice in vivo. The interconnected porous β-TCP scaffolds with pores of 300–500 µm in size were prepared by the polymeric sponge method. β-TCP scaffolds with the dimension of 3 mm × 3 mm × 3 mm were combined with hBMSCs, and incubated with (+) or without (−) osteogenic medium in vitro. Cell proliferation and osteogenic differentiation on the scaffolds were evaluated by scanning electron microscopy (SEM) observation, MTT assay, alkaline phosphatase (ALP) activity and osteocalcin (OCN) content measurement. SEM observation showed that hBMSCs attached well on the scaffolds and proliferated rapidly. No significant difference in the MTT assay could be detected between the two groups, but the ALP activity and OCN content of scaffolds (+) were much higher than those of the scaffolds (−) (p < 0.05). These results indicated that the novel porous β-TCP scaffolds can support the proliferation and subsequent osteogenic differentiation of hBMSCs in vitro. After being cultured in vitro for 14 days, the scaffolds (+) and (−) were implanted into subcutaneous sites of athymic mice. In β-TCP scaffolds (+), woven bone formed after 4 weeks of implantation and osteogenesis progressed with time. Furthermore, tissue-engineered bone could be found at 8 weeks, and remodeled lamellar bone was also observed at 12 weeks. However, no bone formation could be found in β-TCP scaffolds (−) at each time point checked. The above findings illustrate that the novel porous β-TCP scaffolds developed in this work have prominent osteoconductive activity and the potential for applications in bone tissue engineering.

A novel bioactive porous bredigite (Ca7MgSi4O16) scaffold with biomimetic apatite layer for bone tissue engineering

The aim of this study was to develop a novel bioactive, degradable and cytocompatible bredigite (Ca(7)MgSi(4)O(16)) scaffold with biomimetic apatite layer for bone tissue engineering. Porous bredigite scaffolds were prepared using polymer sponge method. The bredigite scaffolds with biomimetic apatite layer (BTAP) were obtained by soaking bredigite scaffolds in simulated body fluid (SBF) for 10 days. The porosity and in vitro degradability of BTAP scaffolds were investigated. In addition, osteoblast-like cell morphology, proliferation and differentiation on BTAP scaffolds were evaluated and compared with beta-tricalcium phosphate (beta-TCP) scaffolds. The results showed that BTAP scaffolds possessed 90% of porosity. The degradation of BTAP scaffolds was comparable to that of beta-TCP scaffolds. Cells on BTAP scaffolds spread well and presented a higher proliferation rate and differentiation level as compared with those on beta-TCP scaffolds. Our results indicated that BTAP scaffolds were degradable and possessed the function to enhance cell proliferation and differentiation, and might be used as bone tissue engineering materials.

Porous hydroxyapatite for artificial bone applications

Hydroxyapatite (HA) has been used clinically for many years. It has good biocompatibility in bone contact as its chemical composition is similar to that of bone material. Porous HA ceramics have found enormous use in biomedical applications including bone tissue regeneration, cell proliferation, and drug delivery. In bone tissue engineering it has been applied as filling material for bone defects and augmentation, artificial bone graft material, and prosthesis revision surgery. Its high surface area leads to excellent osteoconductivity and resorbability providing fast bone ingrowth. Porous HA can be produced by a number of methods including conversion of natural bones, ceramic foaming technique, polymeric sponge method, gel casting of foams, starch consolidation, microwave processing, slip casting, and electrophoretic deposition technique. Some of these methods have been combined to fabricate porous HA with improved properties. These combination methods have yielded some promising results. This paper discusses briefly fundamental aspects of porous HA for artificial bone applications as well as various techniques used to prepare porous HA. Some of our recent results on development of porous HA will be presented as well.

The Effect of MgO Content on the Preparation of Porous Hydroxyapaite Scaffolds by Polymer Sponge Method

Porous hydroxyapatite (HAp) scaffolds have been prepared by using the slurry including HAp and magnesia based on the replication of polymer sponge substrate. The influence of MgO content in slurry on the pore morphology and size, density, porosity, and mechanical strength of porous HAp scaffolds was investigated. The obtained scaffolds with average pore sizes ranging 150 to 300 mm had open, relatively uniform, and interconnected porous structure regardless of MgO content. As the MgO content increased, the pore network frame of scaffolds became to be relatively stronger, even though the pore size was not much changed. The compressive strength of the scaffolds increased rapidly with the increase of MgO content because of increasing the pore wall thickness and density of the scaffolds. As a result, the porosity, density, and compressive strength of the porous HAp scaffolds prepared by the sponge method were significantly affected by the addition of MgO.

Processing of Cellular Glass Ceramics

Commercial polyurethane foams with a monomodal pore size distribution were chosen to produce LZSA (Li2O–ZrO2–SiO2–Al2O3 system) glass–ceramic foams by the polymeric sponge method. A suspension containing LZSA glass–ceramic, bentonite, and sodium silicate was prepared in water and isopropanol to impregnate the polymeric foams by dip coating. The suspension was characterized by rheological measurements. The effect of the solvent on the microstructure and physical properties on the LZSA foams was evaluated. The cellular microstructure of the glass–ceramic foams was characterized by scanning electron microscopy (SEM) and micro‐computer X‐ray tomography (μ‐CT). LZSA foams prepared with isopropanol suspension exhibited higher mechanical strength under compression than those prepared with water.

Application of X-Ray Micro-Computed Tomography on Macroporous Calcium Phosphate Glass Scaffolds

A numerous techniques have been applied to fabricate three-dimensional scaffolds of high porosity and surface area. And X-ray micro computed tomography can be used studying the architecture of scaffold. In this study, we fabricated three-dimensional macroporous scaffold by polymeric sponge method using calcium phosphate glass. Calcium phosphate glass slurry was prepared by dissolving the glass powder in water polyvinyl alcohol, polyethylene glycol and dimethyl formamide. Reticulated polyurethane sponges were used as a template and were coated with the prepared slurry by infiltration technique several times. Sintering at 950oC exhibited dense microstructure as well as entire elimination of organic additives. By repeating the coating and sintering process, it was possible to decrease the pore size and be thick the strut of the structure. The unique feature of the micro computed tomography is that the three dimensions computed reconstruction can be sliced along any direction to gain accurate information on the internal geometric properties and structural parameters of scaffold. Porosity, surface area per unit volume and mean thickness of strut were evaluated through imaging and computer software of scaffold scan data.

In vivo study of novel biodegradable and osteoconductive CaO‐SiO2‐B2O3 glass‐ceramics

To evaluate the possibility of novel CaO-SiO2-B2O3 glass-ceramics (CS10B) as a new bone replacement material, we compared the biodegradation and osteoconduction properties of CS10B, hydroxyapatite (HA), and tricalcium phosphate (TCP). Porous CS10B implants were prepared by the polymer sponge method. L5-6 single-level posterolateral spinal fusions were performed on 30 New Zealand white male rabbits. The animals were divided into three groups by implant material: CS10B, HA, and TCP. Radiographs were performed every 2 weeks. All animals were euthanized 12 weeks after surgery. The ratio of the area occupied by the ceramics by final and initial radiographs was calculated using radiomorphometric analysis. Uniaxial tensile strength was determined from seven cases in each group. The ratio of the area occupied by HA (88.7%+/-16.1%) was significantly higher than the others (p<0.005), and the ratio of the area occupied by CS10B (28.2%+/-9.3%) was significantly lower than those of HA and TCP (37%+/-9.6%, p<0.05). The mean values of the tensile strengths of the CS10B (182.7+/-19.9 N) and HA (191.4+/-33.5 N) were significantly higher (p<0.05) than that of TCP (141.1+/-28.2 N). CS10B had a fusion mass tensile strength similar to that of HA. Histological analysis confirmed that CS10B was well incorporated into the fusion mass. These findings suggest that CS10B is a possible bone replacement material.

Factors affecting the microstructure of porous ceramics

In this study, porous ceramics were produced by using two methods: the polymeric sponge and foam method. A study of the effect of viscosity on the characteristics of the final product produced using the polymeric sponge method revealed that the microstructure of porous ceramics is highly affected by the viscosity of the slurry. The optimal ratio between porosity and the strength of the porous material was achieved by subsequently repeating the immersing and drying processes. A study of the porous material obtained using the foam method revealed that the pore size and foam volume can be controlled by varying the amounts of anhydride and thermal blowing agent. The problem related to foam collapsing was solved by using a thermal blowing agent. The microstructure of the samples was characterized by SEM.

Porous akermanite scaffolds for bone tissue engineering: Preparation, characterization, and in vitro studies

The aim of this study was to develop a bioactive, degradable, and cytocompatible akermanite (Ca2MgSi2O7) scaffold with high porosity and pore interconnectivity. In brief, porous akermanite scaffolds were prepared using polymer sponge method. The porosity and corresponding compressive strength were evaluated. The in vitro degradability was investigated by soaking the scaffolds in Ringer's solution. Hydroxyapatite (HAp)-formation ability of akermantite scaffolds in simulated body fluid (SBF) and the effect of ionic products from the scaffolds dissolution on osteoblasts were investigated. In addition, bone marrow stromal cells (BMSC) adhesion and proliferation on the scaffolds were evaluated. Differentiation of the cells was assessed by measuring alkaline phosphatase (ALP) activity. The results showed that akermanite scaffolds possessed 63.5-90.3% of porosity, with a corresponding compressive strength between 1130 and 530 kPa. The weight loss of the scaffolds and ionic content of the Ringer's solution increased with the increase in soaking time, indicating the degradability of scaffolds. HAp was formed on the scaffolds in SBF and the ionic products from akermanite scaffolds dissolution stimulated osteoblasts proliferation, indicating good in vitro bioactivity. Furthermore, BMSC adhered and spread well on akermanite scaffolds and proliferated with the increase in the culture time, and the differentiation rate of osteoblasts on scaffolds was comparable to that on blank culture plate control. Our results suggested that akermanite scaffolds were bioactive, degradable, and cytocompatible, and might be used as bone tissue engineering materials.

Biomechanical, Radiomorphometric Evaluation of CaO-SiO&lt;sub&gt;2&lt;/sub&gt;-B&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Glass-Ceramics in a Rabbit Lumbar Fusion Model

The purpose of our study is to compare the biodegradation and osteoconduction between CaO-SiO2-B2O3 glass-ceramics(CS10B) and hydroxyapatite(HA), tricalcium phosphate(TCP). Porous CS10B implants were prepared by polymer sponge method. Single-level posterolateral spinal fusions were performed on thirty rabbits. The animals were divided into three groups by implant material: HA, TCP and CS10B. Radiographs checked every two weeks. All animals were sacrificed 12 weeks after surgery. The proportion of the area occupied by ceramics in final radiography on the initial radiography was calculated. Uniaxial tensile strength was measured on 7 cases in each group. The proportion of the area of HA(88.7%±16.1) was significantly higher than those of the others(p&lt;0.05), and the proportion of the area of CS10B(28.2%±9.3) was significantly lower than those of HA and TCP(37%±9.6)(p&lt;0.05). The mean values of tensile strength of the HA(191.4±33.5 N) and CS10B(182.7±19.9 N) were significantly higher(p&lt;0.05) than those of the TCP(141.1±28.2 N). CS10B showed the tensile strength of fusion masses similar to those of the HA, however, more rapid biodegradation than HA and TCP. These findings suggest that CS10B grafts have the possibility as a bone graft substitute.

Evaluation of Osteosynthesis in CaO-SiO2-P2O5-B2O3Glass-ceramics by Posterolateral Fusion of Rabbit Lumbar vertebrae

Study Design: A comparative in vivo study between ceramics with different compositions. Objectives: To compare the biodegradation and osteoconduction properties of CaO-SiO2P2O5B2O3 glass-ceramics and CeraboneA W . Summary of Literature Review: Bioglass ceramics can be used as bone graft substitutes. However, no study has been undertaken to investigate the possibility of CaO-S i O2-P2O5-B2O3 glass-ceramics as a bone graft substitute. Materials and Methods: Porous CSPB2 implants (44.07% CaO, 40.28% SiO2, 8.1% P2O5 and 5.0% B2O3), porous CSPB3 implants (43.76% CaO, 43.41% SiO2, 4.05% P2O5 and 7.5% B2O3) and porous Cerabone-AW were prepared by the polymer sponge method. Single-level posterolateral spinal fusions were performed on sixty New Zealand white male rabbits. The animals were divided into four groups (9 of autograft, 17 per 3 kind of porous implant group) according to the implant material used: autograft, CSPB2, CSPB3 and Cerabone-AW. Radiographs were performed every two weeks. All animals were sacrificed 12 weeks after surgery. Manual palpation and uniaxial tensile strength were determined. The proportion of the area occupied by the ceramics in the final compared to the initial radiographs was calculated. Decalcified and undecalcified histological sections were evaluated by light microscopy. R e s u l t s: Fifty one rabbits were evaluated. The union rates were 100 (9 out of 9), 80 (8 out of 8), 81.1 (9 out of 11) and 90.9% (10 out of 11) in the autograft, Cerabone-AW, CSPB2 and CSPB3 groups, respectively. The proportion of the area occupied by CeraboneA W ( 9 0 . 8 %±14.0) was significantly higher than for CSPB2 (73.1%±11.5) and CSPB3 (73.5%±10.0)(p=0.0011). The mean values of the tensile strengths of Cerabone-AW (214.±57.3N), CSPB2 (214.±57.3 N) and CSPB3 (217±70.1 N) were not significantly different (p>0.05). Conclusion: CSPB2 and CSPB3 had similar tensile strengths and fusion rates of the fusion masses as those of Cerabone-AW; however, they degraded more rapidly than Cerabone-AW. These findings suggest that CSPB2 and CSPB3 grafts can be used as a more ideal new bone graft substitutes than Cerabone-AW.

Preparation of porous hydroxyapatite scaffolds by combination of the gel-casting and polymer sponge methods

A new technique of combining the gel-casting and polymer sponge methods is introduced in this study to prepare macroporous hydroxyapatite scaffolds, which provides a better control over the microstructures of scaffolds and enhances their mechanical properties. With this technique, we were able to produce scaffolds with mechanical and structural properties that cannot be attained by either the polymer sponge or gel-casting method. The scaffolds prepared have an open, uniform and interconnected porous structure with a pore size of 200–400 μm. A compressive yield strength of ∼5 MPa equivalent to that of cancellous bone and a compressive modulus of ∼8 GPa similar to that of cortical bone were achieved. The pore morphology, size, and distribution of the scaffolds were characterized using a scanning electron microscope. X-ray diffraction and Fourier transform infrared spectroscopy were used to determine the crystal structure and chemical composition of scaffolds, respectively. Scaffolds with desired porosity, pore size, and geometry can be prepared by using polymer sponges of appropriate structures.

Evaluation of Biodegradation and Osteosynthesis in CaO-SiO2-B2O3 Glass-ceramics by Posterolateral Fusion of Rabbit Lumbar vertebrae

Purpose: To compare the biodegradation and osteoconduction properties of glass-ceramics (CS10B), hydroxyapatite (HA), and tricalcium phosphate (TCP). Materials and Methods: Porous CS10B implants were prepared by the polymer sponge method. Single-level posterolateral spinal fusions were performed on thirty rabbits. The animals were divided into three groups by implant material: HA, TCP and CS10B. Radiographs were performed every two weeks. All animals were sacrificed 12 weeks after surgery. The proportion of the area occupied by the ceramics in the final over the initial radiographs was calculated. Uniaxial tensile strength was determined from 7 cases in each group. Results: The proportion of the area occupied by HA was significantly higher than the others (p was significantly lower than those of HA and TCP (p and CS10B were significantly higher (p. Conclusion: CS10B had similar tensile strengths of the fusion masses as HA, however, it degraded more rapidly than HA or TCP. These findings suggest CS10B grafts as possible bone replacement materials.

A study on the factors involved in collapse of macroporous α-Al 2O 3 structure

Collapse is the major problem in preparing macroporous ceramics by the polymeric sponge method. The contributions of slurry viscosity, slurry-solid loading and heating rate to collapse are analyzed. The viscosity of slurry should be the highest possible before this parameter prevents slurry entry to all parts of the sponge. Higher viscosity leads to more solid particles of α-Al 2O 3 being taken into the sponge and this is required to avoid collapse prior to and during sintering. Heating rate is another important factor controlling collapse. To maintain pore structure, a controlled slow heating at the beginning of sintering program is needed.

Preparation and characterization of ceramic foam supported nanocrystalline zeolite catalysts

The influence of the viscosity of the ceramic slip on the manufacture of ceramic foams by the polymer sponge method was studied. The foams were coated with silicalite (100nm) and HZSM-5 (650nm) crystals by dipping them in a zeolite suspension without binder additives. The amount of zeolite loaded can be controlled through the zeolite content of the dipping suspension. Uniform coatings are achieved starting with about 1g zeolite/m2 foam.