Unraveling the role of carboxylate groups and elastin particle size in medial calcification.

While it is known that calcium phosphate (CaP) minerals deposit in elastin-rich medial layers of arteries during medial calcification, their nucleation and growth sites are still debated. Neutral carbonyl groups and carboxylate groups are possible candidates. Also, while it is known that elastin degradation leads to calcification, it is unclear whether this is due to formation of new carboxylate groups or elastin fragmentation. In this work, we disentangle effects of carboxylate groups and particle size on elastin calcification; in doing so, we shed light on CaP mineralization sites on elastin. We find carboxylate groups accelerate calcification only in early stages; they mainly function as Ca2+ ion chelation sites but not calcification sites. Their presence promotes formation (likely on Ca2+ ions adsorbed on nearby carbonyl groups) of CaP minerals with high calcium-to-phosphate ratio as intermediate phases. Larger elastin particles calcify slower but reach similar amounts of CaP minerals in late stages; they promote direct formation of hydroxyapatite and CaP minerals with low calcium-to-phosphate ratio as intermediate phases. This work provides new perspectives on how carboxylate groups and elastin particle size influence calcification; these parameters can be tuned to study the mechanism of medial calcification and design drugs to inhibit the process.

Upconverting Nanoparticles Coated with Light-Breakable Mesoporous Silica for NIR-Triggered Release of Hydrophobic Molecules.

Upconverting nanoparticles (UCNPs) doped with Yb3+ and Tm3+ are near-infrared (NIR) to ultraviolet (UV) transducers that can be used for NIR-controlled drug delivery. However, due to the low quantum yield of upconversion, high laser powers and long irradiation times are required to trigger this drug release. In this work, we report the one-step synthesis of a nanocomposite consisting of a LiYbF4:Tm3+@LiYF4 UCNP coated with mesoporous UV-breakable organosilica shells of various thicknesses. We demonstrate that a thin shell accelerates the breakage of the shell at 1 W/cm2 NIR light exposure, a laser power up to 9 times lower than that of conventional systems. When the mesopores are loaded with hydrophobic vitamin D3 precursor 7-dehydrocholesterol (7-DH), shell breakage results in subsequent cargo release. Its minimal toxicity in HeLa cells and successful internalization into the cell cytoplasm demonstrate its biocompatibility and potential application in biological systems. The tunability of this system due to its simple, one-step synthesis process and its ability to operate at low laser powers opens up avenues in UCNP-powered NIR-triggered drug delivery toward a more scalable, flexible, and ultimately translational option.

Directed Assembly of Elastic Fibers via Coacervate Droplet Deposition on Electrospun Templates.

Elastic fibers provide critical elasticity to the arteries, lungs, and other organs. Elastic fiber assembly is a process where soluble tropoelastin is coacervated into liquid droplets, cross-linked, and deposited onto and into microfibrils. While much progress has been made in understanding the biology of this process, questions remain regarding the timing of interactions during assembly. Furthermore, it is unclear to what extent fibrous templates are needed to guide coacervate droplets into the correct architecture. The organization and shaping of coacervate droplets onto a fiber template have never been previously modeled or employed as a strategy for shaping elastin fiber materials. Using an in vitro system consisting of elastin-like polypeptides (ELPs), genipin cross-linker, electrospun polylactic-co-glycolic acid (PLGA) fibers, and tannic acid surface coatings for fibers, we explored ELP coacervation, cross-linking, and deposition onto fiber templates. We demonstrate that integration of coacervate droplets into a fibrous template is primarily influenced by two factors: (1) the balance of coacervation and cross-linking and (2) the surface energy of the fiber templates. The success of this integration affects the mechanical properties of the final fiber network. Our resulting membrane materials exhibit highly tunable morphologies and a range of elastic moduli (0.8-1.6 MPa) comparable to native elastic fibers.

Altered Foreign Body Response at the Posterior Surface Compared to the Anterior Surface of Human Silicone Breast Implants.

Soft implantable devices are crucial to optimizing form and function for many patients. However, periprosthetic capsule fibrosis is one of the major challenges limiting the use of implants. Currently, little is understood about how spatial and temporal factors influence capsule physiology and how the local capsule environment affects the implant structure. In this work, we analyzed breast implant capsule specimens with staining, immunohistochemistry, and real-time polymerase chain reaction to investigate spatiotemporal differences in inflammation and fibrosis. We demonstrated that in comparison to the anterior capsule against the convex surface of breast implants, the posterior capsule against the flat surface of the breast implant displays several features of a dysregulated foreign body reaction including increased capsule thickness, abnormal extracellular remodeling, and infiltration of macrophages. Furthermore, the expression of pro-inflammatory cytokines increased in the posterior capsule across the lifespan of the device, but not in the anterior capsule. We also analyzed the surface oxidation of breast explant samples with XPS analysis. No significant differences in surface oxidation were identified either spatially or temporally. Collectively, our results support spatiotemporal heterogeneity in inflammation and fibrosis within the breast implant capsule. These findings presented here provide a more detailed picture of the complexity of the foreign body reaction surrounding implants destined for human use and could lead to key research avenues and clinical applications to treat periprosthetic fibrosis and improve device longevity.

A Bioglass-Poly(lactic-co-glycolic Acid) Scaffold@Fibrin Hydrogel Construct to Support Endochondral Bone Formation.

Bone tissue engineering using stem cells to build bone directly on a scaffold matrix often fails due to lack of oxygen at the injury site. This may be avoided by following the endochondral ossification route; herein, a cartilage template is promoted first, which can survive hypoxic environments, followed by its hypertrophy and ossification. However, hypertrophy is so far only achieved using biological factors. This work introduces a Bioglass-Poly(lactic-co-glycolic acid@fibrin (Bg-PLGA@fibrin) construct where a fibrin hydrogel infiltrates and encapsulates a porous Bg-PLGA. The hypothesis is that mesenchymal stem cells (MSCs) loaded in the fibrin gel and induced into chondrogenesis degrade the gel and become hypertrophic upon reaching the stiffer, bioactive Bg-PLGA core, without external induction factors. Results show that Bg-PLGA@fibrin induces hypertrophy, as well as matrix mineralization and osteogenesis; it also promotes a change in morphology of the MSCs at the gel/scaffold interface, possibly a sign of osteoblast-like differentiation of hypertrophic chondrocytes. Thus, the Bg-PLGA@fibrin construct can sequentially support the different phases of endochondral ossification purely based on material cues. This may facilitate clinical translation by decreasing in-vitro cell culture time pre-implantation and the complexity associated with the use of external induction factors.

How to Design Catechol-Containing Hydrogels for Cell Encapsulation Despite Catechol Toxicity.

Catechol (cat) is a highly adhesive diphenol that can be chemically grafted to polymers such as chitosan (CH) to make them adhesive as well. However, catechol-containing materials experimentally show a large variability of toxicity, especially in vitro. While it is unclear how this toxicity emerges, most concerns are directed toward the oxidation of catechol into quinone that releases reactive oxygen species (ROS) which can, in turn, cause cell apoptosis through oxidative stress. To better understand the mechanisms at play, we examined the leaching profiles, hydrogen peroxide (H2O2) production, and in vitro cytotoxicity of several cat-chitosan (cat-CH) hydrogels that were prepared with different oxidation levels and cross-linking methods. To create cat-CH with different propensities toward oxidation, we grafted either hydrocaffeic acid (HCA, more prone to oxidation) or dihydrobenzoic acid (DHBA, less prone to oxidation) to the backbone of CH. Hydrogels were cross-linked either covalently, using sodium periodate (NaIO4) to trigger oxidative cross-linking, or physically, using sodium bicarbonate (SHC). While using NaIO4 as a cross-linker increased the oxidation levels of the hydrogels, it also significantly reduced in vitro cytotoxicity, H2O2 production, and catechol and quinone leaching in the media. For all gels tested, cytotoxicity could be directly related to the release of quinones rather than H2O2 production or catechol release, showing that oxidative stress may not be the main reason for catechol cytotoxicity, as other pathways of quinone toxicity come into play. Results also suggest that the indirect cytotoxicity of cat-CH hydrogels fabricated through carbodiimide chemistry can be reduced if (i) catechol groups are chemically bound to the polymer backbone to prevent leaching or (ii) the chosen cat-bearing molecule has a high resistance to oxidation. Coupled with the use of other cross-linking chemistries or more efficient purification methods, these strategies can be adopted to synthesize various types of cytocompatible cat-containing scaffolds.

Supramolecular temperature responsive assembly of polydopamine reduced graphene oxide.

Graphene oxide (GO) and reduced graphene oxide (rGO) colloidal systems can directly respond to environmental stimuli such as pH, ionic strength, and light by themselves, but not to temperature. Here we show that surface modification of rGO with polydopamine (PDA) leads to a temperature-responsive composite material, even though neither rGO nor PDA have intrinsic temperature responsiveness. Reducing GO with dopamine results in rGO/PDA flakes with hydrophilic PDA clusters attached to hydrophobic rGO domains, which mimics the amphiphilic structure of temperature responsive poly(N-isopropylacrylamide) (PNIPAM). The rGO/PDA flakes self-assemble at temperature higher than 30 °C, causing flake aggregation and precipitation in suspensions with concentration of 0.05 g L-1, which is reversible upon cooling, shaking, and re-heating. A solution-to-gelation transition occurs upon heating suspensions with concentration of 10 g L-1. Nacre-like films and porous monoliths are obtained by drying rGO/PDA suspensions at different concentrations. Films and porous monoliths obtained by drying suspensions that are previously self-assembled through heat have more compact structures compared to those obtained with suspensions that are not heated. Overall, this work introduces the concept of supramolecular temperature responsive assembly of nanomaterials (STRAN), i.e., that temperature response can be introduced in nanomaterials by combining non-responsive components that function cooperatively in supramolecules, whose interactions with solvents can be modulated by temperature changes, mimicking what happens in macromolecular systems such as PNIPAM. STRAN could be applied to nanomaterials beyond GO to develop responsive systems whose self-assembly in suspension and architectural features realized upon drying can be controlled by temperature.

Structural Integrity of Absorbable Gelatin Sponges for Middle Ear Packing in Otologic Surgery.

OBJECTIVE: This study investigates the physical properties upon immersion of two gelatin sponges commonly used in otologic surgery. BACKGROUND: Absorbable gelatin sponges are often used in middle ear surgery to achieve hemostasis and, perhaps more importantly, to provide a "scaffolding" to support ossicular chain and/or tympanic membrane reconstructions. Their rate of dissolution may therefore affect the success of tympanic membrane closure. METHODS: An in vitro study was conducted to quantify the material changes of two absorbable gelatin sponges, a standard-density sponge and one with fewer collagen cross-linkages (low-density sponge). Volume loss (%) in 0.9% saline, 0.3% ciprofloxacin, and/or 0.1% dexamethasone as single-agent otic drops in a combination formulation was measured at 15-minute intervals for the first hour and at days 1, 3, and 5 postimmersion. Secondary end points included compressibility, porosity under microscopy, and infrared spectroscopy analysis. RESULTS: The low-density sponge immersed in any of the three otic solutions showed a statistically significant greater volume loss at all time points when compared with the standard-density sponge (27.2% ± 5.4% vs. 15.4% ± 6.0% at 15 minutes and 44.8% ± 5.1% vs. 34.6% ± 2.9% at 5 days, p < 0.001). Interestingly, both sponges immersed in normal saline had lost almost half of their original volume after 15 minutes when compared with samples immersed in an otic solution (48.3% ± 4.6% vs. 21.3% ± 8.3%, respectively, p < 0.001). CONCLUSION: The standard-density sponge immersed in an otic solution of ciprofloxacin, dexamethasone, or a combination formulation best maintained its structural integrity. Ancillary in vivo studies are required to assess the hemostatic properties, surgical outcomes, and middle ear synechiae of the above study conditions. LEVEL OF EVIDENCE: Foundational evidence.

Biomimetic Strategy to Enhance Epithelial Cell Viability and Spreading on PEEK Implants.

Polyetheretherketone (PEEK) is a biocompatible material widely used in spinal and craniofacial implants, with potential use in percutaneous implants. However, its inertness prevents it from forming a tight seal with the surrounding soft tissue, which can lead to infections and implant failure. Conversely, the surface chemistry of percutaneous organs (i.e., teeth) helps establish a strong interaction with the epithelial cells of the contacting soft tissues, and hence a tight seal, preventing infection. The seal is created by adsorption of basement membrane (BM) proteins, secreted by epithelial cells, onto the percutaneous organ surfaces. Here, we aim to create a tight seal between PEEK and epithelial tissues by mimicking the surface chemistry of teeth. Our hypothesis is that collagen I, the most abundant tooth protein, enables integration between the epithelial tissue and teeth by promoting adsorption of BM proteins. To test this, we immobilized collagen I via EDC/NHS coupling on a carboxylated PEEK surface modified using diazonium chemistry. We used titanium alloy (Ti-6Al-4V) for comparison, as titanium is the most widely used percutaneous biomaterial. Both collagen-modified PEEK and titanium showed a larger adsorption of key BM proteins (laminin, nidogen, and fibronectin) compared to controls. Keratinocyte epithelial cell viability on collagen-modified PEEK was twice that of control PEEK and ∼1.5 times that of control titanium after 3 days of cell seeding. Both keratinocytes and fibroblasts spread more on collagen-modified PEEK and titanium compared to controls. This work introduces a versatile and biomimetic surface modification technique that may enhance PEEK-epithelial tissue sealing with the potential of extending PEEK applications to percutaneous implants, making it competitive with titanium.

Light intensity defines growth and photopigment content of a mixed culture of purple phototrophic bacteria.

Purple bacteria (PPB), anoxygenic photoorganoheterotrophic organisms with a hyper-versatile metabolism and high biomass yields over substrate, are promising candidates for the recovery of nutrient resources from wastewater. Infrared light is a pivotal parameter to control and design PPB-based resource recovery. However, the effects of light intensities on the physiology and selection of PPB in mixed cultures have not been studied to date. Here, we examined the effect of infrared irradiance on PPB physiology, enrichment, and growth over a large range of irradiance (0 to 350 W m-2) in an anaerobic mixed-culture sequencing batch photobioreactor. We developed an empirical mathematical model that suggests higher PPB growth rates as response to higher irradiance. Moreover, PPB adapted to light intensity by modulating the abundances of their phototrophic complexes. The obtained results provide an in-depth phylogenetic and metabolic insight the impact of irradiance on PPB. Our findings deliver the fundamental information for guiding the design of light-driven, anaerobic mixed-culture PPB processes for wastewater treatment and bioproduct valorization.

Selective Catalytic Electro-Oxidation of Water with Cobalt Oxide in Ion Impermeable Reduced Graphene Oxide Porous Electrodes.

The direct electrolysis of seawater is greatly inhibited by the oxidation of Cl- to free chlorine, an undesirable, corrosive byproduct. To suppress the parasitic interference of Cl- and any other ion, we developed a freestanding, electrically conducting, 3D macroporous reduced graphene oxide (rGO) scaffold with cobalt oxide particles selectively deposited on the internal walls of its closed pores (with an average diameter of ∼180 µm). The pore walls act as membranes composed of stacked rGO flakes; the nanochannels between rGO layers (size <1 nm) are permeable to water and gases while preventing the diffusion of dissolved ions such as Cl-. Due to this, the catalytic particles are selectively accessible to water molecules but not to ions, allowing electrolysis to occur without chlorine evolution. The electrodes developed exhibit a stable generation of O2 from simulated seawater at pH 14, reaching a specific current density of up to 25 A g-1 during continuous electrolysis with 89-98% Faradaic efficiency, while chlorine generation is below 6 ppm h-1, the sensitivity limit of the detection method employed. The strategy here proposed can be generalized to build electrodes that are inherently selective thanks to their architecture, with catalytically active particles loaded into closed pores with selective ion transport properties.

Layered Assembly of Graphene Oxide Paper for Mechanical Structures.

Graphene oxide (GO) paper is an attractive material because of high stiffness and strength, light weight, and multiple functionalities. While these properties are now widely exploited in nanoinclusions or flat sheets, three-dimensional (3D) structures from GO paper are not widely studied because of a lack of suitable processing methods. In this study, we report a layered assembly method to make stiff and strong 3D GO structures with the aid of a sodium tetraborate (borax) solution. By comparing mechanical properties of assembled GO paper using water or borax solution, we found that the borax-assembled layers had the highest stiffness. To demonstrate the versatility of our assembly protocol, we then fabricated a variety of 3D structures including I-beams, cylindrical tubes, and bridge-like structures from GO paper. These GO structures were stiff and light weight, and the stiffness to mass ratio was around 2-4 times higher than other polymer samples including cellulose, fluorinated ethylene propylene, and poly(vinyl alcohol). The versatile processing method to make stiff and strong GO structures will enable new engineering applications where nonplanar GO structures are required.

Globule and fiber formation with elastin-like polypeptides: a balance of coacervation and crosslinking.

Elastic fiber assembly is a complex process that requires the coacervation and cross-linking of the protein building block tropoelastin. To date, the order, timing, and interplay of coacervation and crosslinking is not completely understood, despite a great number of advances into understanding the molecular structure and functions of the many proteins involved in elastic fiber assembly. With a simple in vitro model using elastin-like polypeptides and the natural chemical crosslinker genipin, we demonstrate the strong influence of the timing and kinetics of crosslinking reaction on the coacervation, crosslinking extent, and resulting morphology of elastin. We also outline a method for analyzing elastin droplet network formation as a heuristic for measuring the propensity for elastic fiber formation. From this we show that adding crosslinker during peak coacervation dramatically increases the propensity for droplet network formation.

The Role of Surface Chemistry in the Osseointegration of PEEK Implants.

Poly(etheretherketone) (PEEK) implants suffer from poor osseointegration because of chronic inflammation. In this study, we hypothesized that adding NH2 and COOH groups to the surface of PEEK could modulate macrophage responses by altering protein adsorption and improve its osseointegration. NH2 and COOH-functionalized PEEK surfaces induced pro- and anti-inflammatory macrophage responses, respectively, and differences in protein adsorption patterns on these surfaces were related to the varied inflammatory responses. The macrophage responses to NH2 surfaces significantly reduced the osteogenic differentiation of mesenchymal stem cells (MSCs). MSCs cultured on NH2 surfaces differentiated less than those on COOH surfaces even though NH2 surfaces promoted the most mineralization in simulated body fluid solutions. After 14 days in rat tibia unicortical defects, the bone around NH2 surfaces had thinner trabeculae and higher specific bone surface than the bone around unmodified implants; surprisingly, the NH2 implants significantly increased bone-binding over the unmodified implants, while COOH implants only showed a trend for increasing bone-binding. Taken together, these results suggest that both mineral-binding and immune responses play a role in osseointegration, and PEEK implant integration may be improved with mixtures of these two functional groups to harness the ability to reduce inflammation and bind bone strongly.

Amniotic stromal stem cell-loaded hydrogel repairs cardiac tissue in infarcted rat hearts via paracrine mediators.

The use of stem cells to repair the heart after a myocardial infarction (MI) remains promising, yet clinical trials over the past 20 years suggest that cells fail to integrate into the native tissue, resulting in limited improvements in cardiac function. Here, we demonstrate the cardioprotective potential of a composite inserting human amniotic stromal mesenchymal stem cells (ASMCs) in a chitosan and hyaluronic acid (C/HA) based hydrogel in a rat MI model. Mechanical characterization of the C/HA platform indicated a swift elastic conversion at 40°C and a rapid sol-gel transition time at 37°C. Cell viability assay presented active and proliferating AMSCs in the C/HA. The ASMCs + C/HA injected composite significantly increased left ventricular ejection fraction, fractional shortening, and neovessel formation. The encapsulated AMSCs were abundantly detected in the infarcted myocardium 6 weeks post-administration and co-expressed cardiac proteins and notably proliferative markers. Proteomic profiling revealed that extracellular vesicles released from hypoxia preconditioned ASMCs contained proteins involved in cytoprotection, angiogenesis, cardiac differentiation and non-canonical Wnt-signaling. Independent activation of non-canonical Wnt-signaling pathways in ASMCs induced cardiogenesis. Despite a low injected cellular density at baseline, the encapsulated AMSCs were abundantly retained and increased cardiac function. Furthermore, the C/HA hydrogel provided an active milieu for the AMSCs to proliferate, co-express cardiac proteins, and induce new vessel formation. Hence, this novel composite of AMSCs + C/HA scaffold is a conceivable candidate that could restore cardiac function and reduce remodeling.

Titanium-Containing Silicate-Based Sol-Gel Bioactive Glass: Development, Characterization, and Applications.

Bioactive glasses are surface-reactive glasses that, when placed in physiological fluid, undergo a transformation from glass to hydroxyapatite. Doping the bioactive glass with metallic ions can impart desirable and unique properties that are not inherent to natural hydroxyapatite. Once such ion is titanium. Titanium exists in trace amounts in native dental enamel, and its presence has been correlated with increased tooth hardness and brightness, both desirable clinical properties. Synthetic titanium-substituted hydroxyapatite exhibits better mechanical and antibacterial properties and demonstrates potential for an improved cellular response when compared to unmodified hydroxyapatite with applications in the broader field of bone tissue engineering. In this work, we use the sol-gel method to synthesize a titanium-containing silicate-based bioactive glass aimed at generating titanium-substituted hydroxyapatite on the glass surface upon immersion in body fluid. Titanium is homogeneously distributed throughout our glass, which keeps its amorphous nature. After 14 days of immersion in simulated body fluid, the glass forms a titanium-substituted hydroxyapatite on its surface. Enamel surfaces treated with the titanium-containing glass show significantly increased microhardness compared to enamel surfaces treated with a control glass, confirming the potential for the proposed glass in enamel remineralization. We also show that the presence of titanium in the glass promotes cell differentiation toward bone formation, suggesting further applications for this material in the broader field of bone tissue engineering.

A catechol-chitosan-based adhesive and injectable hydrogel resistant to oxidation and compatible with cell therapy.

Injectable hydrogels designed for cell therapy need to be adhesive to the surrounding tissues to maximize their retention and the communication between the host and the encapsulated cells. Catechol grafting is an efficient and well-known strategy to improve the adhesive properties of various polymers, including chitosan. However, catechol groups are also known to be cytotoxic as they oxidize into quinones in alkaline environments. Usually, hydrogels made from catechol-grafted chitosan (cat-CH) oxidize quickly, which tends to limit adhesion and prevent cell encapsulation. In this work, we limited oxidation and improved the cytocompatibility of cat-CH hydrogels by grafting chitosan with dihydroxybenzoic acid (DHBA), a small cat-bearing molecule known to have a high resistance to oxidation. We show that DHBA-grafted CH (dhba-CH) oxidized significantly slower and to a lesser extent that cat-CH made with hydrocaffeic acid (hca-CH). By combining dhba-CH with sodium bicarbonate and phosphate buffer, we fabricated thermosensitive injectable hydrogels with higher mechanical properties, quicker gelation and significantly lower oxidation than previously designed cat-CH systems. The resulting gels are highly adhesive on inorganic substrates and support L929 fibroblast encapsulation with high viability (≥90% after 24 hours), something that was not possible in any previously designed cat-CH gel system. These properties make the dhba-CH hydrogels excellent candidates for minimally invasive and targeted cell therapy in applications that require high adhesive strength.

High toughness resorbable brushite-gypsum fiber-reinforced cements.

The ideal bone substitute material should be mechanically strong, biocompatible with a resorption rate matching the rate of new bone formation. Brushite (dicalcium phosphate dihydrate) cement is a promising bone substitute material but with limited resorbability and mechanical properties. To improve the resorbability and mechanical performance of brushite cements, we incorporated gypsum (calcium sulfate dihydrate) and diazonium-treated polyglactin fibers which are well-known for their biocompatibility and bioresorbability. Here we show that by combining brushite and gypsum, we were able to fabricate biocompatible composite cements with high fracture toughness (0.47 MPa·m1/2) and a resorption rate that matched the rate of new bone formation. Adding functionalized polyglactin fibers to this composite cement further improved the fracture toughness up to 1.00 MPa·m1/2. XPS and SEM revealed that the improvement in fracture toughness is due to the strong interfacial bonding between the functionalized fibers and the cement matrix. This study shows that adding gypsum and functionalized polyglactin fibers to brushite cements results in composite biomaterials that combine high fracture toughness, resorbability, and biocompatibility, and have great potential for bone regeneration.

Operational Strategies to Selectively Produce Purple Bacteria for Microbial Protein in Raceway Reactors.

Purple non-sulfur bacteria (PNSB) show potential for microbial protein production on wastewater as animal feed. They offer good selectivity (i.e., low microbial diversity and high abundance of one species) when grown anaerobically in the light. However, the cost of closed anaerobic photobioreactors is prohibitive for protein production. Although open raceway reactors are cheaper, their feasibility to selectively grow PNSB is thus far unexplored. This study developed operational strategies to boost PNSB abundance in the biomass of a raceway reactor fed with volatile fatty acids. For a flask reactor run at a 2 day sludge retention time (SRT), matching the chemical oxygen demand (COD) loading rate to the removal rate in the light period prevented substrate availability during the dark period and increased the PNSB abundance from 50-67 to 88-94%. A raceway reactor run at a 2 day SRT showed an increased PNSB abundance from 14 to 56% when oxygen supply was reduced (no stirring at night). The best performance was achieved at the highest surface-to-volume ratio (10 m2 m-3 increased light availability) showing productivities up to 0.2 g protein L-1 day-1 and a PNSB abundance of 78%. This study pioneered in PNSB-based microbial protein production in raceway reactors, yielding high selectivity while avoiding the combined availability of oxygen, COD, and darkness.

Protein Adsorption on Surfaces Functionalized with COOH Groups Promotes Anti-inflammatory Macrophage Responses.

Implants can induce a foreign body reaction that leads to chronic inflammation and fibrosis in the surrounding tissue. Macrophages help detect the foreign material, play a role in the inflammatory response, and may promote fibrosis instead of the desired tissue regeneration around implants. Implant surface properties impact macrophage responses by changing the nature of the adsorbed protein layer, but conflicting studies highlight the complexity of this relationship. In this study, the effect of surface chemistry on macrophage behavior was investigated with poly(styrene) surfaces containing common functional groups at similar surface densities. The protein layer was characterized to identify the proteins that adsorbed on the surfaces from the medium and the proteins secreted onto the surfaces by adherent macrophages. Of the surface chemistries studied, carboxylic acid (COOH) groups promoted anti-inflammatory responses from unstimulated macrophages and did not exacerbate inflammation upon stimulation. These surfaces also enhanced the adsorption of proteins involved in integrin signaling and promoted the secretion of proteins related to angiogenesis, integrin signaling, and cytokine signaling, which have been previously associated with improved biomaterial integration. Therefore, this study suggests that surface modification with COOH groups may help improve the integration of implants in the body by enhancing anti-inflammatory macrophage responses through altered protein adsorption.