A bibliometric analysis of published literature on membrane photobioreactors for wastewater treatment from 2000 to 2022.

With the focus on limiting greenhouse gas emissions, microalgae-based technology is a promising approach for wastewater treatment, combining cost-effective operation, nutrient recovery, and assimilation of CO2. In addition, membrane technology supports process intensification and wastewater reclamation. Based on a bibliometric analysis, this paper evaluated the literature on membrane photobioreactors to highlight promising areas for future research. Specifically, efforts should be made on advancing knowledge of interactions between algae and bacteria, analysing different strategies for membrane fouling control and determining the conditions for the most cost-effective operation. The Scopus® database was used to select documents from 2000 to 2022. A set of 126 documents were found. China is the country with the highest number of publications, whereas the most productive researchers belong to the Universitat Politècnica de València (Spain). The analysis of 50 selected articles provides a summary of the main parameters investigated, that focus in increasing the biomass productivity and nutrient removal. In addition, microalgal-bacterial membrane photobioreactor seems to have the greatest commercialisation potential. S-curve fitting confirms that this technology is still in its growth stage.

PLGA-BMP-2 and PLA-17ß-Estradiol Microspheres Reinforcing a Composite Hydrogel for Bone Regeneration in Osteoporosis.

The controlled release of active substances-bone morphogenetic protein 2 (BMP-2) and 17ß-estradiol-is one of the main aspects to be taken into account to successfully regenerate a tissue defect. In this study, BMP-2- and 17ß-estradiol-loaded microspheres were combined in a sandwich-like system formed by a hydrogel core composed of chitosan (CHT) collagen, 2-hidroxipropil γ-ciclodextrin (HP-γ-CD), nanoparticles of hydroxyapatite (nano-HAP), and an electrospun mesh shell prepared with two external electrospinning films for the regeneration of a critical bone defect in osteoporotic rats. Microspheres were made with poly-lactide-co-glycolide (PLGA) to encapsulate BMP-2, whereas the different formulations of 17ß-estradiol were prepared with poly-lactic acid (PLA) and PLGA. The in vitro and in vivo BMP-2 delivered from the system fitted a biphasic profile. Although the in vivo burst effect was higher than in vitro the second phases (lasted up to 6 weeks) were parallel, the release rate ranged between 55 and 70 ng/day. The in vitro release kinetics of the 17ß-estradiol dissolved in the polymeric matrix of the microspheres depended on the partition coefficient. The 17ß-estradiol was slowly released from the core system using an aqueous release medium (Deff = 5.58·10-16 ± 9.81·10-17m2s-1) and very fast in MeOH-water (50:50). The hydrogel core system was injectable, and approximately 83% of the loaded dose is uniformly discharged through a 20G needle. The system placed in the defect was easily adapted to the defect shape and after 12 weeks approximately 50% of the defect was refilled by new tissue. None differences were observed between the osteoporotic and non-osteoporotic groups. Despite the role of 17ß-estradiol on the bone remodeling process, the obtained results in this study suggest that the observed regeneration was only due to the controlled rate released of BMP-2 from the PLGA microspheres.

In situ gel-forming system for dual BMP-2 and 17ß-estradiol controlled release for bone regeneration in osteoporotic rats.

The aim of this study was to evaluate the bone regeneration capacity of a Pluronic® F127 (P)-Tetronic®1307 (T) and α-cyclodextrin (CD) supramolecular gel (P-T-CD) in a 11/7/7 ratio containing BMP-2 and 17ß-estradiol pre-encapsulated in poly-lactide-co-glycolide (PLGA) and poly-lactic acid (PLA-S) microspheres, respectively. Ovariectomy combined with dexamethasone treatment was used to induce an osteoporotic (OP) animal model of calvaria critical size defect in female rats to test the system. The two active substances showed a biphasic in vitro release profile characterized by an initial fast phase followed by a slow and prolonged release. The bone morphogenetic protein-2 (BMP-2) in vivo release was faster than in vitro. The in vivo experimental design included four groups of sham rats and other four groups of OP rats treated with the blank system, BMP-2, and one or two doses of BMP-2 combined with 17ß-estradiol. After 12 weeks, histological and histomorphometric analyses showed that the combined treatment with BMP-2 and 17ß-estradiol did not improve the repair response in sham, whereas in OP animals, a significant increase in the repair rate was observed with respect to the group treated with BMP-2 alone. However, the low values of osteocalcin, showed an immature and poorly mineralized new bone in OP animals. The second dose of the system with BMP-2 and 17ß-estradiol did not improve the repair response in any case.

Bone regeneration in osteoporosis by delivery BMP-2 and PRGF from tetronic-alginate composite thermogel.

As the life expectancy of the world population increases, osteoporotic (OP) fracture risk increase. Therefore in the present study a novel injectable thermo-responsive hydrogel loaded with microspheres of 17ß-estradiol, microspheres of bone morphogenetic protein-2 (BMP-2) and plasma rich in growth factors (PRGF) was applied locally to regenerate a calvaria critical bone defect in OP female rats. Three systems were characterized: Tetronic® 1307 (T-1307) reinforced with alginate (T-A), T-A with PRGF and T-A-PRGF with microspheres. The addition of the microspheres increased the viscosity but the temperature for the maximum viscosity did not change (22-24 °C). The drugs were released during 6 weeks in one fast phase (three days) followed by a long slow phase. In vivo evaluation was made in non-OP and OP rats treated with T-A, T-A with microspheres of 17ß-estradiol (T-A-ßE), T-A-ßE prepared with PRGF (T-A-PRGF-ßE), T-A-ßE with microspheres of BMP-2 (T-A-ßE-BMP-2) and the combination of the three (T-A-PRGF-ßE-BMP). After 12 weeks, histological and histomorphometric analyzes showed a synergic effect due to the addition of BMP-2 to the T-A-ßE formulation. The PRGF did not increased the bone repair. The new bone filling the OP defect was less mineralized than in the non-OP groups.

Mobility of Water and Polymer Species and Rheological Properties of Supramolecular Polypseudorotaxane Gels Suitable for Bone Regeneration.

The aim of this work was to prepare polypseudorotaxane-based supramolecular gels combining αCD with two temperature-responsive copolymers of different architecture (i.e., linear poloxamer P and X-shaped poloxamine T), at the lowest concentration as possible to form syringeable depots, and to shed light on the self-diffusion and spatial closeness of all components (including water) which in turn may determine the cooperative self-assembly phenomena and the performance of the gels at the macroscopic level. The exchange rate between bound water and bulk water was measured with a novel NMR experiment Water Diffusion Exchange-Diffusion Optimized Spectroscopy (WDE-DOSY). Polypseudorotaxane formation caused opposite effects on the mobility of αCD species (decreased) and internal water (increased) but did not affect PPO-water interaction. Consequently, designed ternary P/T/αCD supramolecular gels exhibited in situ gelling at body temperature could host large amounts of PLA/PLGA microspheres and behaved as porous 3D-scaffolds for mesenchymal stem cells (MSCs) supporting their osteogenic differentiation. Interestingly, the gels withstood freeze-drying and reconstitution with minor changes in inner structure and rheological properties. The gathered information may help to understand better the supramolecular gels and provide tools for the rational design of syringeable bone scaffolds that can simultaneously accommodate cells and drug microcarriers for efficient tissue regeneration.