Exploratory Testing of Diatom Silica to Map the Role of Material Attributes on Cell Fate

Self-locomotive, antimicrobial microrobot (SLAM) swarm for enhanced biofilm elimination

Biofilm is a major cause of infections and infrastructure deterioration, largely due to molecular diffusion restrictions that hamper the antimicrobial activity of traditional antibiotics and disinfectants. Here, we present a self-locomotive, antimicrobial microrobot (SLAM) swarm that can penetrate, fracture, and detach biofilm and, in turn, nullify bacterial resistance to antibiotics. The SLAM is assembled by loading a controlled mass of manganese oxide nanosheets on diatoms with the polydopamine binder. In hydrogen peroxide solution, SLAMs produce oxygen bubbles that generate thrust to penetrate the rigid and dense Pseudomonas aeruginosa biofilm and self-assemble into a swarm that repeatedly surrounds, expands, and bursts oxygen bubbles. The resulting cavities continue to deform and fracture extracellular polymeric substances from microgrooved silicone substrates and wounded skin explants while decreasing the number of viable bacterial cells. Additionally, SLAM allows irrigating water or antibiotics to access the residual biofilm better, thus enhancing the synergistic efficacy in killing up to 99.9% of bacterial cells.

Atmospheric Processing of Iron-Bearing Mineral Dust Aerosol and Its Effect on Growth of a Marine Diatom, Cyclotella meneghiniana

Iron (Fe) is a growth-limiting micronutrient for phytoplankton in major areas of oceans and deposited wind-blown desert dust is a primary Fe source to these regions. Simulated atmospheric processing of four mineral dust proxies and two natural dust samples followed by subsequent growth studies of the marine planktic diatom Cyclotella meneghiniana in artificial sea-water (ASW) demonstrated higher growth response to ilmenite (FeTiO₃) and hematite (α-Fe₂O₃) mixed with TiO₂ than hematite alone. The processed dust treatment enhanced diatom growth owing to dissolved Fe (DFe) content. The fresh dust-treated cultures demonstrated growth enhancements without adding such dissolved Fe. These significant growth enhancements and dissolved Fe measurements indicated that diatoms acquire Fe from solid particles. When diatoms were physically separated from mineral dust particles, the growth responses become smaller. The post-mineralogy analysis of mineral dust proxies added to ASW showed a diatom-induced increased formation of goethite, where the amount of goethite formed correlated with observed enhanced growth. The current work suggests that ocean primary productivity may not only depend on dissolved Fe but also on suspended solid Fe particles and their mineralogy. Further, the diatom C. meneghiniana benefits more from mineral dust particles in direct contact with cells than from physically impeded particles, suggesting the possibility for alternate Fe-acquisition mechanism/s.

Filament extrusion of bioresorbable PDLGA for additive manufacturing utilising diatom biosilica to inhibit process-induced thermal degradation

Bone scaffolds are often fabricated by initially producing custom-made filaments by twin-screw extruder and subsequently fabricating into 3D scaffolds using fused deposition modelling. This study aims to directly compare the effect of two alternative silica-rich filler materials on the thermo-mechanical properties of such scaffolds after extrusion and printing. Poly (DL-lactide-co-glycolide) (PDLGA) was blended with either 45S5 Bioglass (5 wt %) or Biosilica (1 and 5 wt%) isolated from Cyclotella meneghiniana a freshwater diatom were tested. Diatom-PDLGA was found to have similar mechanical strength and ductility to pure-PDLGA, whereas Bioglass-PDLGA was found induce a more brittle behaviour. Bioglass-PDLGA was also found to have the lowest toughness in terms of energy absorption to failure. The TGA results suggested that significant thermal degradation in both the Bioglass filaments and scaffolds had occurred as a result of processing. However, diatom biosilica was found to inhibit thermal degradation of the PDLGA. Furthermore, evidence suggested the agglomeration of Bioglass particles occurred during processing the Bioglass-PDLGA filaments. Overall, diatom biosilica was found to be a promising candidate as a bone filler additive in 3D printed PDLGA scaffolds, whereas Bioglass caused some potentially detrimental effects on performance.

Nanoplastics exposure modulate lipid and pigment compositions in diatoms

The impact of nanoplastics (NP) using model polystyrene nanoparticles amine functionalized (PS-NH₂) has been investigated on pigment and lipid compositions of the marine diatom Chaetoceros neogracile, at two growth phases using a low (0.05 μg mL^-1) and a high (5 μg mL^-1) concentrations for 96 h. Results evidenced an impact on pigment composition associated to the light-harvesting function and photoprotection mainly at exponential phase. NP also impacted lipid composition of diatoms with a re-adjustment of lipid classes and fatty acids noteworthy. Main changes upon NP exposure were observed in galactolipids and triacylglycerol's at both growth phases affecting the thylakoids membrane structure and cellular energy reserve of diatoms. Particularly, exponential cultures exposed to high NP concentration showed an impairment of long chain fatty acids synthesis. Changes in pigment and lipid content of diatom' cells revealed that algae physiology is determinant in the way cells adjust their thylakoid membrane composition to cope with NP contamination stress. Compositions of reserve and membrane lipids are proposed as sensitive markers to assess the impact of NP exposure, including at potential predicted environmental doses, on marine organisms.

Do transparent exopolymeric particles (TEP) affect the toxicity of nanoplastics on Chaetoceros neogracile?

The potential presence of nanoplastics (NP) in aquatic environments represents a growing concern regarding their possible effects on aquatic organisms. The objective of this study was to assess the impact of polystyrene (PS) amino-modified particles (50  nm PSNH₂) on the cellular and metabolic responses of the diatom Chaetoceros neogracile cultures at two essential phases of the growth cycle, i.e. exponential (division) and stationary (storage) phases. Both cultures were exposed for 4 days to low (0.05 μg mL^-1) and high (5 μg mL^-1) concentrations of PS-NH_2. Exposure to NP impaired more drastically the major cellular and physiological parameters during exponential phase than during the stationary phase. Only an increase in ROS production was observed at both culture phases following NP exposures. In exponential phase cultures, large decreases in chlorophyll content, esterase activity, cellular growth and photosynthetic efficiency were recorded upon NP exposure, which could have consequences on the diatoms life cycle and higher food-web levels. The observed differential responses to NP exposure according to culture phase could reflect i) the higher concentration of Transparent Exopolymer Particles (TEP) at stationary phase leading to NP aggregation and thus, probably minimizing NP effects, and/or ii) the fact that dividing cells during exponential phase may be intrinsically more sensitive to stress. This work evidenced the importance of algae physiological state for assessing the NP impacts with interactions between NP and TEP being one key factor affecting the fate of NP in algal media and their impact to algal' cells.

Bioactive diatomite and POSS silica cage reinforced chitosan/Na-carboxymethyl cellulose polyelectrolyte scaffolds for hard tissue regeneration

Recently, natural polymers are reinforced with silica particles for hard tissue engineering applications to induce bone regeneration. In this study, as two novel bioactive agents, effects of diatomite and polyhedral oligomeric silsesquioxanes (POSS) on chitosan (CS)/Na-carboxymethylcellulose (Na-CMC) polymer blend scaffolds are examined. In addition, the effect of silica reinforcements was compared with Si-substituted nano-hydroxyapatite (Si-Hap) particles. The morphology, physical and chemical structures of the scaffolds were characterized with SEM, liquid displacement, FT-IR, mechanical analysis, swelling and degradation studies. The particle size and the crystal structure of diatomite, POSS and Si-Hap particles were determined with DLS and XRD analyses. In vitro studies were performed to figure out the cytotoxicity, proliferation, ALP activity, osteocalcin production and biomineralization to demonstrate the promising use of natural silica particles in bone regeneration. Freeze-dried scaffolds showed 190-307 μm pore size range and 61-70% porosity. Both inorganic reinforcements increased the mechanical strength, enhanced the water uptake capacity and fastened the degradation rate. The nanocomposite scaffolds did not show any cytotoxic effect and enhanced the surface mineralization in osteogenic medium. Thus, diatomite and POSS cage structures can be potential reinforcements for nanocomposite design in hard tissue engineering applications.

Characterization and Cytotoxicity Evaluation of a Marine Sponge Biosilica

Bone fractures characterize an important event in the medical healthcare, being related to traumas, aging, and diseases. In critical conditions, such as extensive bone loss and osteoporosis, the tissue restoration may be compromised and culminate in a non-union consolidation. In this context, the osteogenic properties of biomaterials with a natural origin have gained prominence. Particularly, marine sponges are promising organisms that can be exploited as biomaterials for bone grafts. Thus, the objectives of this study were to study the physicochemical and morphological properties of biosilica (BS) from sponges by using scanning electron microscopy, Fourier-transform infrared, X-ray diffraction (SEM, FTIR and XRD respectively), mineralization, and pH. In addition, tests on an osteoblast precursor cell line (MC3T3-E1) were performed to investigate its cytotoxicity and proliferation in presence of BS. Bioglass (BG) was used as gold standard material for comparison purposes. Sponge BS was obtained, and this fact was proven by SEM, FTIR, and XRD analysis. Calcium assay showed a progressive release of this ion from day 7 and a more balanced pH for BS was maintained compared to BG. Cytotoxicity assay indicated that BS had a positive influence on MC3T3-E1 cells viability and qRT-PCR showed that this material stimulated Runx2 and BMP4 gene expressions. Taken together, the results indicate a potential use of sponge biosilica for tissue engineering applications.