Polymer Membranes as Innovative Means of Quality Restoring for Wastewater Bearing Heavy Metals

The problem that has aroused the interest of this review refers to the harmful effect of heavy metals on water sources due to industrial development. In this respect, the review is aimed at achieving a literature survey on the outstanding results and advancements in membranes and membrane technologies for the advanced treatment of heavy metal-loaded wastewaters. Particular attention is given to synthetic polymer membranes, for which the proper choice of precursor material can provide cost benefits while ensuring good decontamination activity. Furthermore, it was also found that better removal efficiencies of heavy metals are achieved by combining the membrane properties with the adsorption properties of inorganic powders. The membrane processes of interest from the perspective of industrial applications are also discussed. A noteworthy conclusion is the fact that the main differences between membranes, which refer mainly to the definition and density of the pore structure, are the prime factors that affect the separation process of heavy metals. Literature studies reveal that applying UF/MF approaches prior to RO leads to a better purification performance.

Gelatin-based cellular solids: Fabrication, structure and properties

Although most cellular polymers are made from thermoplastics using different foaming technologies, gelatin and many other natural polymers can form hydrogels and convert them to cellular solids using various techniques, many of which differ from traditional plastic foaming, and so does their resulting structures. Cellular solids from natural hydrogels are porous materials that often exhibit a combination of desirable properties, including high specific surface area, biochemical activity, as well as thermal and acoustic insulation properties. Among natural hydrogels, gelatin-based porous materials are widely explored due to their availability, biocompatibility, biodegradability and relatively low cost. In addition, gelatin-based cellular solids have outstanding properties and are currently subject to increasing scientific research due to their potential in many applications, such as biocompatible cellular materials or biofoams to facilitate waste treatment. This article aims at providing a comprehensive review of gelatin cellular solids processing and their processing-properties-structure relationship. The fabrication techniques covered include aerogels production, mechanical foaming, blowing agents use, 3D printing, electrospinning and particle leaching methods. It is hoped that the assessment of their characteristics provides compiled information and guidance for selecting techniques and optimization of processing conditions to control material structure and properties to meet the needs of the finished products.

A two-compartment bone tumor model to investigate interactions between healthy and tumor cells

We produced a novel three-dimensional (3D) bone tumor model (BTM) to study the interactions between healthy and tumor cells in a tumor microenvironment, the migration tendency of the tumor cells, and the efficacy of an anticancer drug, Doxorubicin, on the cancer cells. The model consisted of two compartments: (a) a healthy bone tissue mimic, made of poly(lactic acid-co-glycolic acid) (PLGA)/beta-tricalcium phosphate (β-TCP) sponge seeded with human fetal osteoblastic cells (hFOB) and human umbilical vein endothelial cells (HUVECs), and (b) a tumor mimic, made of lyophilized collagen sponge seeded with human osteosarcoma cells (Saos-2). The tumor mimic component was placed into a central cavity created in the healthy bone mimic and together they constituted the complete 3D bone tumor model (3D-BTM). The porosities of both sponges were higher than 85% and the diameters of the pores were 199 ± 52 μm for the PLGA/TCP and 50-150 μm for the collagen scaffolds. The compression Young's modulus of the PLGA/TCP and the collagen sponges were determined to be 4.76 MPa and 140 kPa, respectively. Cell proliferation, morphology, calcium phosphate forming capacity and alkaline phosphatase production were studied separately on both the healthy and tumor mimics. All cells demonstrated cellular extensions and spread well in porous scaffolds indicating good cell-material interactions. Confocal microscopy analysis showed direct contact between the cells present in different parts of the 3D-BTM. Migration of HUVECs from the healthy bone mimic to the tumor compartment was confirmed by the increase in the levels of angiogenic factors vascular endothelial growth factor, basic fibroblast growth factor, and interleukin 8 in the tumor component. Doxorubicin (2.7 μg.ml^-1) administered to the 3D-BTM caused a seven-fold decrease in the cell number after 24 h of interaction with the anticancer drug. Caspase-3 enzyme activity assay results demonstrated apoptosis of the osteosarcoma cells. This novel 3D-BTM has a high potential for use in studying the metastatic capabilities of cancer cells, and in determining the effective drug types and combinations for personalized treatments.

Temperature-driven processing techniques for manufacturing fully interconnected porous scaffolds in bone tissue engineering

The development of structures with a predefined multiscale pore network is a major challenge in designing tissue engineering (TE) scaffolds. To address this, several strategies have been investigated to provide biocompatible, biodegradable porous materials that would be suitable for use as scaffolds, and able to guide and facilitate the cell activity involved in the generation of new tissue regeneration. This study seeks to provide an overview of different temperature-driven process technologies for developing scaffolds with tailored porosity, in which pore size distribution is strictly defined and pores are fully interconnected. Here, three-dimensional (3D) porous composite scaffolds based on poly(∊-caprolactone) (PCL) were fabricated by thermally induced phase separation (TIPS) and by melt co-continuous polymer blending (MCPB). The combination of these processes with a salt leaching technique enables the establishment of bimodal porosity within the polymer network. This feature may be exploited in the development of substrates with fully interconnected pores, which can be used effectively for tissue regeneration. Various combinations of the proposed techniques provide a range of procedures for the preparation of porous scaffolds with an appropriate combination of morphological and mechanical properties to reproduce the requisite features of the extracellular matrix (ECM) of hard tissues such as bone.

Open-pore biodegradable foams prepared via gas foaming and microparticulate templating

Open-pore biodegradable foams with controlled porous architectures were prepared by combining gas foaming and microparticulate templating. Microparticulate composites of poly(epsilon-caprolactone) (PCL) and micrometric sodium chloride particles (NaCl), in concentrations ranging from 70/30 to 20/80 wt.-% of PCL/NaCl were melt-mixed and gas-foamed using carbon dioxide as physical blowing agent. The effects of microparticle concentration, foaming temperature, and pressure drop rate on foam microstructure were surveyed and related to the viscoelastic properties of the polymer/microparticle composite melt. Results showed that foams with open-pore networks can be obtained and that porosity, pore size, and interconnectivity may be finely modulated by optimizing the processing parameters. Furthermore, the ability to obtain a spatial gradient of porosity embossed within the three-dimensional polymer structure was exploited by using a heterogeneous microparticle filling. Results indicated that by foaming composites with microparticle concentration gradients, it was also possible to control the porosity and pore-size spatial distribution of the open-pore PCL foams.

Preparation of porous apatite granules from calcium phosphate cement

A versatile method for preparing spherical, micro- and macroporous (micro: 2-10 and macro: 150-550 microm pores), carbonated apatitic calcium phosphate (Ap-CaP) granules (2-4 mm in size) was developed by using NaCl crystals as the porogen. The entire granule production was performed between 21 and 37 degrees C. A CaP cement powder, comprising alpha-Ca3(PO4)2 (61 wt.%), CaHPO4 (26%), CaCO3 (10%) and precipitated hydroxyapatite, Ca10(PO4)6(OH)2 (3%), was dry mixed with NaCl crystals varying in size from 420 microm to 1 mm. Cement powder (35 wt.%) and NaCl (65 wt.%) mixture was kneaded with an ethanol-Na2HPO4 initiator solution, and the formed dough was immediately agitated on an automatic sieve shaker for a few minutes to produce the spherical granules. Embedded NaCl crystals were then leached out of the granules by soaking them in deionized water. CaP granules were micro- and macroporous with a total porosity of 50% or more. Granules were composed of carbonated, poorly crystallized, apatitic CaP phase. These were the first spherical and porous CaP granules ever produced from a self-setting calcium phosphate cement. The granules reached their final handling strength at the ambient temperature through the cement setting reaction, without having a need for sintering.