Radzali Othman

Macroporous bioceramics: A remarkable material for bone regeneration

This review summarises the major developments of macroporous bioceramics used mainly for repairing bone defects. Porous bioceramics have been receiving attention ever since their larger surface area was reported to be beneficial for the formation of more rigid bonds with host tissues. The study of porous bioceramics is important to overcome the less favourable bonds formed between dense bioceramics and host tissues, especially in healing bone defects. Macroporous bioceramics, which have been studied extensively, include hydroxyapatite, tricalcium phosphate, alumina, and zirconia. The pore size and interconnections both have significant effects on the growth rate of bone tissues. The optimum pore size of hydroxyapatite scaffolds for bone growth was found to be 300 µm. The existence of interconnections between pores is critical during the initial stage of tissue ingrowth on porous hydroxyapatite scaffolds. Furthermore, pore formation on β-tricalcium phosphate scaffolds also allowed the impregnation of growth factors and cells to improve bone tissues growth significantly. The formation of vascularised tissues was observed on macroporous alumina but did not take place in the case of dense alumina due to its bioinert nature. A macroporous alumina coating on scaffolds was able to improve the overall mechanical properties, and it enabled the impregnation of bioactive materials that could increase the bone growth rate. Despite the bioinertness of zirconia, porous zirconia was useful in designing scaffolds with superior mechanical properties after being coated with bioactive materials. The pores in zirconia were believed to improve the bone growth on the coated system. In summary, although the formation of pores in bioceramics may adversely affect mechanical properties, the advantages provided by the pores are crucial in repairing bone defects.

Carbonate Hydroxyapatite and Silicon-Substituted Carbonate Hydroxyapatite: Synthesis, Mechanical Properties, and Solubility Evaluations

The present study investigates the chemical composition, solubility, and physical and mechanical properties of carbonate hydroxyapatite (CO3Ap) and silicon-substituted carbonate hydroxyapatite (Si-CO3Ap) which have been prepared by a simple precipitation method. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF) spectroscopy, and inductively coupled plasma (ICP) techniques were used to characterize the formation of CO3Ap and Si-CO3Ap. The results revealed that the silicate (SiO4 4−) and carbonate (CO3 2−) ions competed to occupy the phosphate (PO4 3−) site and also entered simultaneously into the hydroxyapatite structure. The Si-substituted CO3Ap reduced the powder crystallinity and promoted ion release which resulted in a better solubility compared to that of Si-free CO3Ap. The mean particle size of Si-CO3Ap was much finer than that of CO3Ap. At 750°C heat-treatment temperature, the diametral tensile strengths (DTS) of Si-CO3Ap and CO3Ap were about 10.8 ± 0.3 and 11.8 ± 0.4 MPa, respectively.

Nanoporous biomaterials for uremic toxin adsorption in artificial kidney systems: A review

Hemodialysis, one of the earliest artificial kidney systems, removes uremic toxins via diffusion through a semipermeable porous membrane into the dialysate fluid. Miniaturization of the present hemodialysis system into a portable and wearable device to maintain continuous removal of uremic toxins would require that the amount of dialysate used within a closed-system is greatly reduced. Diffused uremic toxins within a closed-system dialysate need to be removed to maintain the optimum concentration gradient for continuous uremic toxin removal by the dialyzer. In this dialysate regenerative system, adsorption of uremic toxins by nanoporous biomaterials is essential. Throughout the years of artificial kidney development, activated carbon has been identified as a potential adsorbent for uremic toxins. Adsorption of uremic toxins necessitates nanoporous biomaterials, especially activated carbon. Nanoporous biomaterials are also utilized in hemoperfusion for uremic toxin removal. Further miniaturization of artificial kidney system and improvements on uremic toxin adsorption capacity would require high performance nanoporous biomaterials which possess not only higher surface area, controlled pore size, but also designed architecture or structure and surface functional groups. This article reviews on various nanoporous biomaterials used in current artificial kidney systems and several emerging nanoporous biomaterials.

Sol–gel hydrothermal synthesis of microstructured CaO-based adsorbents for CO2 capture

In this study, microstructured CaO-based adsorbents were synthesized by a sol–gel hydrothermal method using calcium nitrate tetrahydrate, citric acid and sodium hydroxide as precursors. Experiments with different NaOH concentrations (2, 6 and 10 M) were carried out to investigate the effects on the morphologies and CO2 adsorption activities of the synthesized adsorbents. X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM) results showed that different NaOH concentrations resulted in different crystal phases and morphologies. A novel three-dimensional (3D) hierarchical calcite (CaCO3) hollow microspherical adsorbent composed of one-dimensional (1D) spike-shaped nanorods was obtained with 2 M NaOH. XRD analyses confirmed that the hierarchical CaCO3 hollow microspheres were characteristic of the calcite phase. The FESEM image revealed that the microspheres were composed of 1D spike-shaped nanorods with an average length of 500 nm. The cross-sectional FESEM image showed that the microspheres had hollow structures with an average inner cavity of 2 μm and a shell thickness of approximately 0.5 μm. The CO2 adsorption performance of the synthesized adsorbents was investigated using thermogravimetry-differential thermal analysis (TG-DTA) apparatus. The results indicated that the novel hierarchical calcite (CaCO3) hollow microspherical adsorbent composed of one-dimensional (1D) spike-shaped nanorods possessed higher carbonation conversion of 45% after 15 cycles, which was about 22% higher than that of other adsorbents synthesized with 6 and 10 M NaOH concentration and limestone. This property could be attributed to the 3D hierarchical hollow microsphere structure, 1D spike-shaped nanorod structure, trimodal pore size distribution and large BET surface area (44.85 m2 g−1) of the novel adsorbent.

Development of a bone substitute material based on alpha-tricalcium phosphate scaffold coated with carbonate apatite/poly-epsilon-caprolactone.

Interconnected porous tricalcium phosphate ceramics are considered to be potential bone substitutes. However, insufficient mechanical properties when using tricalcium phosphate powders remain a challenge. To mitigate these issues, we have developed a new approach to produce an interconnected alpha-tricalcium phosphate (α-TCP) scaffold and to perform surface modification on the scaffold with a composite layer, which consists of hybrid carbonate apatite / poly-epsilon-caprolactone (CO3Ap/PCL) with enhanced mechanical properties and biological performance. Different CO3Ap combinations were tested to evaluate the optimal mechanical strength and in vitro cell response of the scaffold. The α-TCP scaffold coated with CO3Ap/PCL maintained a fully interconnected structure with a porosity of 80% to 86% and achieved an improved compressive strength mimicking that of cancellous bone. The addition of CO3Ap coupled with the fully interconnected microstructure of the α-TCP scaffolds coated with CO3Ap/PCL increased cell attachment, accelerated proliferation and resulted in greater alkaline phosphatase (ALP) activity. Hence, our bone substitute exhibited promising potential for applications in cancellous bone-type replacement.

Synthesis of Nanoporous Carbonated Hydroxyapatite Using Non-Ionic Pluronics Surfactant

Hydroxyapatite (HA) is a bioceramics that commonly used as bone substitute materials, coating materials and scaffolds in orthopedics. It is well known for its remarkable biocompatibility with natural human tissue. However, synthetic HA is different from biological apatite whereby apatites contain carbonate ion which is about 3-8wt% of the hard tissues of human body which described as carbonated hydroxyapatite (CHA). Hence, synthetic CHA may have a better bioactivity than HA and more widely used as biomaterials. This study described the synthesis and characterization of nanoporous carbonated hydroxyapatite (CHA) by co-precipitation method through self-organization mechanism with different type of non-ionic surfactants (P123 and F127). Diammonium hydrogen phosphate, (NH4)2HPO4 and calcium nitrate tetrahydrate, Ca (NO3)2.4H2O were used as starting materials for preparing the precursor for CHA powder. The ammonium carbonate, NH4HCO3 was used as the main source for carbonate ion. Synthesized powder was characterized using XRD, FESEM, EDS and FTIR. From the XRD result, pure HA phase was obtained for all samples. FTIR analysis results obviously showed the substitution of carbonate ion into the apatite and confirm the formation of CHA. The FTIR results also demonstrated that the surfactants had been removed completely through calcination process. SEM image revealed a sphere-like particle shape of CHA was produced after the calcinations. The mesoporous CHA with pore size 2-12 nm (F127) and 2-8 nm (P123) was synthesized.

Comparison of Two Powder Processing Techniques on the Properties of Cu-NbC Composites

An in situ Cu-NbC composite was successfully synthesized from Cu, Nb, and C powders using ball milling and high pressure torsion (HPT) techniques. The novelty of the new approach, HPT, is the combination of high compaction pressure and large shear strain to simultaneously refine, synthesize, and consolidate composite powders at room temperature. The HPTed Cu-NbC composite was formed within a short duration of 20 min without Fe contamination from the HPT’s die. High porosity of 3–9%, Fe and niobium oxidations, from grinding media and ethanol during ball milling led to low electrical conductivity of the milled Cu-NbC composite. The electrical conductivity of the HPTed Cu-NbC composite showed a value 50% higher than that of milled Cu-NbC composite of the same composition.

Formation of Titanium Carbide Reinforced Copper Matrix Composite by In Situ Processing

Composite materials with copper matrix and ceramic particle reinforcements provide basis for producing relatively high hardness and electrical conductivity materials. Most of the work on copper-based composites has involved transition metal carbide reinforcement, which is introduced in the copper matrix through a powder metallurgy (P/M) route. TiC particle is one of the interesting candidates for the reinforcement of the Cu composite. This is because of its high melting point, high hardness, good oxidation and corrosion resistance combined with good electrical and thermal conductivity. In this study, in situ prepared copper-titanium carbide using high energy ball milling was addressed. Cu-Ti-C mixture powder was mechanically alloyed by high energy ball milling at 400 rpm speed for 4 hours to investigate the formation of TiC phase during milling. Then, MA was continued for 5, 20, 40,60 and 80 hours in order to determine the formation of titanium carbide phase by milling time. Then the as-milled powders were compacted at 400 MPa and sintered at 900°C for one hour. As-milled powder was characterized by x-ray diffraction for phase identification. From the XRD result, TiC peaks were found at 35.9˚, 41.7˚and 60.4˚.

Comparison of Silica Sand Properties from Kandal Province, Cambodia and Tapah, Perak, Malaysia and Characterization of Soda Lime Silicate Glass Produced From Cambodian Silica Sand

Silica sand from Kandal province, Cambodia and Tapah Perak, Malaysia was grounded into an average micron size of 128.12 and 132.68µm. Both sands were characterized by X-ray fluorescence (XRF), X-ray Diffraction, particle Size Analysis, Differential Thermal Analysis and Thermogravimetric Analysis (DTA/TGA). Malaysian silica sand was designated SDMTP and Cambodian Silica sand as SDCK. From theanalysis, XRF showed that the major impurities in SDMTP were Al2O3, K2O and TiO2. On the other hand, SDCK had impurities of Al2O3,K2O and Na2O. DTA results from SDMTP and SDCK showedthere is an endothermic peak occurring at 572°C which can be attributed to β-quartz transformation into α-quartz. TGA for SDMTP showed that maximum weight lost was at 441°C with a weight percent (wt%) change of 0.48%. The TGA for SDCK showed a wt% change of 1.298% at temperature of 1000°C. From XRD analysis, the main phase of SDCK and SDMTP were quartz. The impurities of both sands play an important role in determining the optical and mechanical properties of the soda lime silicate (SLS) glass formed. Particle size of silica sand affects the mechanical properties such as compression, hardness, and transmittance of SLS glass. The smaller particle size would be ideal choice for glassmaking. Melting temperature, soaking time, and melt accelerant can also affect the mechanical properties of SLS glass. The best result obtained for Vickers hardness in this study was the SLS glass sample designated as Run No 12 with a value of 525.02 kg.mm-2. It had a particle size range from 500-600µm, a furnace soaking time of 4 hours at a melting temperature of 1500°C with 1.0 wt% of Sodium Chloride (NaCl) as meltingaccelerant. On the other hand, the highest compressive strength of 356.22 MPa was found in sample designated as Run No 1. It had a particle size range from 75-1800µm, a soaking time of 5 hours at a melting temperature of 1550°C with 0.5 wt% of NaCl. Lastly,the highest UV-VIS transmittance at 520 nm was obtained from sample designated as Run No 5 within the value of 84.26 %Transmittance (T). It had a particle size range of 75-1800µm, soaking time of 3 hours at a melting temperature of 1550°C with 1.5 wt% of NaCl. .

Activated Carbon Fiber Derived from Pyrolysis of Palm Fiber

Palm empty fruit bunch (EFB) is an abundant by-product resulted from massive palm oil production in Malaysia as one of the worlds largest exporter and second largest producer of palm oil. This agricultural waste is usually disposed in nature, burnt in opened atmospheres, or used as a fuel for boilers. Such conventional handlings of EFB have created environmental concerns to Malaysia such as air pollution and release of green house gases (CH4 and CO2). This study made use of such biomass in the production of cost effective nanoporous material, namely activated carbon fiber (ACF) which able to diminish the problem of waste disposal, and at the same time to turn waste into wealth. This is especially beneficial when the ACF is used for environmental friendly application such as adsorbed natural gas (ANG) technology. ACF was formed from carbonaceous materials via process of carbonisation and activation. Both chemical and physical activations were carried out by using H2SO4 and CO2, respectively. In pyrolysis, carbonisation was conducted at temperatures i.e. 400, 600, 800 and 1000 °C in nitrogen (N2) atmosphere. Surface morphologies, microstructures, pore structures and surface chemistry of these samples were investigated for the characterisation of EFB fiber-derived ACF. Above 80% of the total pore volumes for the samples were contributed by the micropore as the major pore components in the ACF produced. The samples exhibited an high BET surface area , dominant micropore volume up and narrow pore size distribution in micro range (< 1.5 nm).