Key Engineering Materials Vol. 751

Abstract: High porosity in porous concretes contributes to benefits in terms of lightweight, high water permeability, and superior insulation properties in the concretes. Nevertheless, excessive porosity can lead to diminished compressive strength. This study, therefore, aimed at fabricating porous concretes with porosity and compressive strength in the range suitable for practical applications. Since addition of aluminium powder is a well-known technique for porosity production, this study also assessed effects of aluminium addition on properties of porous concretes. Relationships among concentrations of aluminium, porosity, and compressive strength of the specimens were examined. Microstructural analysis from scanning electron microscope (SEM) images and compressive strength testing according to ASTM C109 revealed that the specimens with 0.15 wt% Al demonstrated porosity and compressive strength were in an acceptable range. Additionally, porosity production and specimen strengthening were discussed with respect to chemical compositions.

Abstract: This paper focuses on industrial thermosetting plastic waste reduction by recycling as the material for natural coarse aggregate replacement in concrete. This substitution of aggregate is an integration approach to preserve the natural resources and environment as well as develop the alternative recycled aggregate material to meet 3R principle and sustainable development. Bakelite waste is prohibited from disposing of sanitary landfill and direct burning because of hazardous disposal and emission reasons .There are many studies of plastic aggregate to substitute natural coarse aggregate especially PET and PE aggregate. However, there is no study of Waste Bakelite Aggregate (WBA) mixed in concrete in Thailand. This study aim is investigating the mechanical properties of Waste Bakelite Aggregate Concrete (WBAC) compare to conventional concrete (CC).The methodology is based on an experimental program by testing of concrete specimens. The data obtained from sample test according to BS standard. These test results present compressive strength of all samples both CC and WBAC. The relationship charts between mechanical properties and the waste Bakelite aggregate replacement percentage will be illustrated including the compressive strength predictable equation model. Furthermore, the chemical extraction test of waste Bakelite aggregate concrete and the durability of WBAC are notified for the utilization. WBAC is an alternative material that can be applied to the non-structural concrete product to replace the natural aggregate and helpful in waste plastic pollution mitigation.

Abstract: The objective of this study was to investigate sericin-polyurethane nanofiber cover (SUC) for wound dressing materials in a rat skin. Sericin-polyurethane blended nanofibers were fabricated by using electrospinning. The composition of 3%w/v polyurethane in ethanol and 19% w/v sericin were blended and electrospun at 15 kV, 20 cm from tip to collector with a feed rate of 6.2 ml/hr. The mats, approximately 1.5 mm thick, were sterile by gamma irradiation with a radiation dose of 15 kGy. The samples of in vitro and in vivo testing were separated into three groups; gauze, polyurethane nanofiber cover (UC), and SUC. In vitro cultured L929 cell lines were investigated with inverted microscope. It was found that cells migrated to SCU. For in vivo tests, the remaining wound in rats was measured on day 2-14 after excision. Compared to original size of wound samples, the size of the wound remained 24% for SUC, 33% for gauze, and 34% for UC at day 8. The sericin, an active agent, contained in SUC mats was about 5 µl at 1.5 ×1.5 cm. It can be concluded that sericin is non-toxic to cells and can promote wound healing process in rats.

Abstract: The aim of this study was to examine the effects of active filler in resin-based pit and fissure sealant on fluoride release and recharge abilities. Mesoporous silica was synthesized from tetraethyl orthosilicate (TEOS) using sol-gel method. Resin-based sealant was incorporated with 5% w/w of filler (<45 μm): synthesized mesoporous silica (S), calcium carbonate (C), and fluoro-alumino silicate glass (F). Resin-based sealant without filler added was the control. Ten specimens of each group were separately stored in 3 mL of deionized water and the fluoride concentration, before and after fluoride recharge, were measured every 3 days (from day 3 to day 27). Fluoride release before recharge was only found in F (0.1024±0.0077 ppm) and then gradually decreased to baseline. After two recharges, the highest fluoride release was found in S (0.0804±0.0095 ppm after first recharge and 0.0601±0.0092 after second recharge), followed by F (0.0386±0.0024 ppm after first recharge and 0.0313±0.0027 ppm after second recharge), and then decreased to baseline. Fluoride recharge was not found in C and control. This result suggested that resin-based pit and fissure sealant containing synthesized mesoporous silica filler has fluoride recharge ability which might prevent secondary caries at material-enamel interface.

Abstract: Aloe vera extracts, consisting of active compounds that decrease pain and inflammation and stimulate skin growth and repair, are selected as a drug model in this work. Polyvinyl alcohol (PVA) was used as base material. Release profiles of Aloe vera extracts from PVA electrospun fibers were compared to those from PVA hydrogel films prepared by freezing/thawing method. This method provided a physical crosslinked polymer. The concentration of PVA solution used for electrospinning and hydrogel preparation was 10% wt with different contents of Aloe vera extracts (0, 30, 50, 70 and 90% w/w). The properties of electrospun fibers and hydrogel films were evaluated in terms of morphology, chemical structure, swelling behavior and release profiles. The morphological properties of electrospun fibers and hydrogel film were observed by SEM. Electrospun fibers were smoothly round, high surface area, and non-woven, while hydrogel film possessed rough surface and was covered with porous. Fourier transform infrared spectroscopic measurement exhibited the existence of relevant functional groups of both PVA and Aloe vera extracts. The results showed relevant functional groups of Aloe vera extracts in both electrospun fibers and hydrogel film. The release of Aloe vera extracts from both electrospun fibers and hydrogel film was evaluated in phosphate buffer of pH 5.5 at 25 °C and was monitored by UV–vis spectroscopy. It was revealed that as the content of Aloe vera increased, the amount of Aloe vera extracts released from electrospun fibers decreased. This result contrasts with the release of aloe vera from hydrogel film which increased when the content of aloe vera increased. It was also noticed that the amount of Aloe vera extracts released from electrospun fibers was more than that from hydrogel films at 600 minutes. The results also showed that the releasing rate of Aloe vera from electrospun fibers was faster than that from hydrogel films. This is probably because electrospun fibers had much higher surface area than that of hydrogel film thus, the release was faster.

Abstract: Factors influencing calcium phosphate deposition on three dimensional printed hydroxyapatite (3D printed HA) by biomimetic process including soaking times (2, 4 and 6 hrs), solution temperatures (23, 37 and 50 °C) and solution refreshment (refreshed and non-refreshed) were studied. It was found that the weight change of the samples increased with increasing soaking times at all temperatures regardless of solution refreshment. Using refreshed solution resulted in greater increase in weight change than using non-refreshed solution. In the case of solution temperature, two opposite trends were observed depending on the solution refreshment. Increasing solution temperatures in non-refreshed solution exhibited a decrease in the weight change whereas the increase in the weight change was observed when using refreshed solution. This could be related to the competition between the dissolution of 3D printed HA and the deposition of new calcium phosphate crystals during biomimetic process. Octacalcium phosphate and HA were found to be the main phases of biomimetically deposited 3D printed HA.

Abstract: Silk fibroin is a natural biodegradable polymer that has been demonstrated for use as scaffolds for bone tissue engineering. To improve the osteoconductivity and the osteoinductivity of silk fibroin scaffolds, ceramics were added. α-tricalcium phosphate (α-TCP) is the expected ceramic that useful for scaffolds for bone tissue engineering either alone or blended with silk fibroin. From the previous study, we evaluated the mechanical properties of three-dimensional porous silk fibroin/ α-TCP scaffolds and concluded that the scaffolds containing 8% (w/w) α-TCP exhibited the highest compressive modulus. The objective of this study was to evaluate the biological properties of three-dimensional porous silk fibroin/α-TCP scaffolds. The scaffolds were constructed using a solvent casting and salt leaching technique. The hybrid strain of degummed Thai silk fibroin, Nangnoi Srisaket 1 x Mor, was dissolved in hexafluoroisopropanol at 16% (w/v). α-TCP was incorporated to produce 4, 8, 12, and 16 wt% solution. Sucrose (particle size 250-450 μm; sucrose/silk fibroin = 8.5/1 w/w) was used as a porogen. Human gingival fibroblasts (passage 5) were cultured in these scaffolds. After 72 h, the biocompatibility of seeded scaffolds was evaluated under the inverted phase contrast microscopy. Cell proliferation was determined by DNA assays and scanning electron microscopy. The images from inverted phase contrast microscopy revealed the human gingival fibroblasts can be attached at the surface of scaffolds in all groups. The results from the DNA assays showed that the number of human gingival fibroblasts was increased as the culture period was prolonged but was not as the increasing of α-TCP. At 120 h, the scaffolds containing 8% (w/w) α-TCP exhibited the highest cell number. The scanning electron microscope images at 24, 72, and 120 h after cell culturing presented human gingival fibroblasts can be expanded well and exhibited the normal morphology. The results suggested that the scaffolds containing 8% (w/w) α-TCP may be a potential candidate for bone tissue engineering applications.

Abstract: The overall aim of this study is to establish the inter-relationships between phase formations, mechanical properties and magnetic properties of the novel ceramic in hydroxyapatite system for biomaterial applications. First, barium hexaferrite and strontium hexaferrite powders were prepared as M-type hexaferrite phases. Hydroxyapatite was prepared from cockle shells via co-precipitation method. After that, a combination between hydroxyapatite+barium hexaferrite and hydroxyapatite+strontium hexaferrite was mixed together then shaping and sintering at 1200 °C for 2 h. The sintered samples were characterized phase formation, mechanical and magnetic properties by using X-ray diffraction (XRD), Universal testing and VSM measurements, respectively. XRD patterns for all samples showed a combination between hydroxyapatite and hexaferrite phases. Compressive strength of all samples tends to increase with increasing of the amount of hexaferrite phases due to densification mechanism. However, the increasing of these values, it appears that there is no difference in the statistical significant. For magnetic properties, the coexistence of barium hexaferrite and strontium hexaferrite phases reveals magnetic hysteresis loops, showing the change from diamagnetic to ferromagnetic behavior.

Abstract: Synthesis and characterization of bioglass^® of general composition (45-X-Y) SiO₂, 24.5 Na₂O, 24.5 CaO and 6.0 P₂O₅ (wt %) was modified by addition of X= (0-1) wt % of CeO₂ and Y= (0-1) wt % of La₂O₃ respectively. These five samples were prepared in alumina crucible via melting route at a temperature of 1400±5 °C with air as a furnace atmosphere. These glass samples were immersed in simulated body fluid (SBF) for different time period and their bioactivity were determined by Fourier transform infrared spectroscopy (FTIR) analysis. Surface morphology was studied by using Scanning electron microscope (SEM). Bioactivity, pH measurement of bioactive glass was carried out and mechanical properties of these glasses increased with increasing concentration of CeO₂ and La₂O₃.

Abstract: Attributed to its biocompatibility and osteoconductivity, hydroxyapatite (HAp, Ca₁₀(PO₄)₆(OH)₂) has been extensively utilized as a bioactive material. As the implant material, HAp is required to be fabricated into a porous form. The present study was therefore aimed at synthesizing HAp powder by solution combustion technique and at fabricating porous HAp specimens. Calcium nitrate and ammonium dihydrogenphosphate (NH₄H₂PO₄), with Ca/P ratio equal to 2.3, were used as initial reagents in the HAp synthesis process. X-ray diffraction analysis confirmed that HAp was present as the primary phase, while minor secondary phases, Tri-calcium phosphaste (TCP) and CaO, were also observed. To prepare porous specimens, HAp slip with solids loadings ranging from 15 to 25 vol% was cast into acrylic molds and sintered. The sintering temperatures were 1350°C and 1450°C, and sintering periods ranged from 2 to 4 hours. Results from microstructural analysis revealed that high solids loadings, sintering temperatures and sintering periods resulted in decreasing of porosity. Porosity in the range between 30 and 90%, which was in an acceptable range for orthopedic applications, was observed.