RESUMO
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.
Assuntos
Elastina , Copolímero de Ácido Poliláctico e Ácido Poliglicólico , Copolímero de Ácido Poliláctico e Ácido Poliglicólico/química , Elastina/química , Ácido Láctico/química , Ácido Poliglicólico/química , Iridoides/química , Tropoelastina/química , Reagentes de Ligações Cruzadas/química , Taninos/química , Peptídeos/química , ElasticidadeRESUMO
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.
RESUMO
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.
Assuntos
Elastina , Tropoelastina , Elastina/química , Cinética , Peptídeos/química , Tropoelastina/química , Tropoelastina/metabolismoRESUMO
Medial calcification has been associated with diabetes, chronic kidney disease, and genetic disorders like pseudoxanthoma elasticum. Recently, we showed that genetic reduction of arterial elastin content reduces the severity of medial calcification in matrix Gla protein (MGP)-deficient and Eln haploinsufficient Mgp-/-;Eln+/- mice. This study suggests that there might be a direct effect of elastin amount on medial calcification. We studied this using novel in vitro systems, which are based on elastin or elastin-like polypeptides. We first examined the mineral deposition properties of a transfected pigmented epithelial cell line that expresses elastin and other elastic lamina proteins. When grown in inorganic phosphate-supplemented medium, these cells deposited calcium phosphate minerals, which could be prevented by an N'-terminal peptide of MGP (m3pS) carrying phosphorylated serine residues. We next confirmed these findings using a cell-free elastin-like polypeptide (ELP3) scaffold, where the peptide prevented mineral maturation. Overall, this work describes a novel cell culture model for elastocalcinosis and examines the inhibition of mineral deposition by the m3pS peptide in this and a cell-free elastin-based scaffold. Our study provides strong evidence suggesting the critical functional roles of MGP's phosphorylated serine residues in the prevention of elastin calcification and proposes a possible mechanism of their action.
Assuntos
Calcinose/metabolismo , Proteínas de Ligação ao Cálcio/metabolismo , Elastina/metabolismo , Proteínas da Matriz Extracelular/metabolismo , Peptídeos/metabolismo , Humanos , Minerais/metabolismo , Proteína de Matriz GlaRESUMO
Biowaste-derived substances isolated from green compost (BBS-GC) are environmentally friendly reactants similar to humic substances, which contain multiple functionalities, that are suitable for adsorbing different kinds of pollutants in wastewater. Herein, sodium alginate (derived from brown algae) cross-linked with both Ca2+ ions and BBS-GC in the form of hydrogels and dried films are proposed as green, easy-to-form, and handleable materials for tertiary water treatments. The results show that both hydrogels and films are mechanically stable and can effectively remove differently charged dyes through an adsorption mechanism that can be described by the Freundlich model. BBS-GC-containing gels always performed better than samples prepared without BBS-GC, revealing that such unconventional materials can integrate waste valorization and water decontamination, potentially providing social and environmental benefits.
Assuntos
Alginatos/química , Hidrogéis/química , Águas Residuárias/química , Poluentes Químicos da Água/isolamento & purificação , Purificação da Água/métodos , Água/química , Adsorção , Química Verde , Phaeophyceae/química , Poluentes Químicos da Água/químicaRESUMO
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.
Assuntos
Vidro , Titânio , Durapatita , Osteogênese , SilicatosRESUMO
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.
Assuntos
Proteobactérias , Águas Residuárias , Análise da Demanda Biológica de Oxigênio , Reatores Biológicos , Fotobiorreatores , EsgotosRESUMO
PURPOSE: A new type of diazonium-based adhesive has been recently developed by our team to bind dental alloys (Titanium, stainless steel, and cobalt chromium) to dental polymers. Here, we explored the endurance of the resulting adhesive after thermal-cycling and autoclave aging. MATERIALS AND METHODS: Polished samples of titanium (Ti), stainless steel (SS) and cobalt chromium (Co-Cr) were coated with a diazonium-based adhesive. Untreated samples served as controls (n = 12 per each condition). X-ray photoelectron spectroscopy (XPS) was performed to characterize the elemental compositions of the different surfaces. Biocompatibility of the coated alloys was assessed with human gingival fibroblasts (HGF). Inductively coupled plasma (ICP) and total organic carbon (TOC) analyses were used to quantify the ions and organic matters released from the diazonium coated alloys. Endurance of the adhesives was assessed by exposing the samples to autoclaving and thermal-cycling. The tensile strength of the poly(methylmethacrylate) (PMMA)-alloy bond was also tested. RESULTS: Results of mechanical testing demonstrated a higher endurance of the coated CoCr, Ti, and SS compared to the uncoated alloys. The human fibroblasts cultured on the substrates remained alive and metabolically active, and the coatings did not release significant amounts of toxic chemicals in solutions. CONCLUSIONS: The results further support the use of diazonium-based adhesives as new coupling agents for dental applications.
Assuntos
Ligas Dentárias , Cimentos Dentários , Ligas , Ligas de Cromo , Humanos , Teste de Materiais , Propriedades de Superfície , TitânioRESUMO
Deposition of calcium phosphate minerals on the elastin-rich medial layers of arteries can cause severe cardiovascular complications. There are no available treatments for medial calcification, and the mechanism of mineral formation on elastin layers is still unknown. We recently developed an in vitro model of medial calcification using cross-linked elastin-like polypeptide (ELP) membranes immersed in simulated body fluid (SBF). While mineral phase evolution matched that observed in a mouse model of medial calcification, the long incubation required was a practical limitation of this model. Using higher SBF ion concentrations could be a solution to speed up mineral deposition, but its effect on the mineralization process is still not well understood. Here we analyze mineral formation and phase transformation on ELP membranes immersed in high concentration SBF. We show that while mineral deposition is significantly accelerated in these conditions, the chemistry and morphology of the minerals deposited on the ELP membranes and the overall mineralization process are strongly affected. Overall, this work suggests that while the use of low concentration SBF in this in vitro model is more appropriate to study medial calcification associated with the loss of calcification inhibitors, higher SBF ion concentration may be more relevant to study medial calcification in patients with life-threatening diseases such as chronic kidney disease.
Assuntos
Apatitas/química , Cristalização , Membranas Artificiais , Peptídeos/química , Materiais Biomiméticos/química , Cálcio/química , Elastina/química , Escherichia coli/genética , Iridoides/química , Peptídeos/genética , Sódio/químicaRESUMO
Calcium phosphate minerals deposit on the elastin-rich medial layers of arteries in the majority of seniors, diabetic, and chronic kidney disease patients, causing severe cardiovascular complications. There is no cure for medial calcification, and the mechanism of mineral formation on elastin layers is unknown. Here we propose cross-linked elastin-like polypeptide membranes as models to study medial calcification. Calcium phosphates deposit first on fibers and filaments and then spread to globular structures present in the membranes. Mineral phase evolution analyzed by near-edge X-ray spectroscopy matches that previously observed in a mouse model of medial calcification, showing that this simple system captures some of the key in vivo findings. This work shows how minerals form and evolve upon nucleation on elastin and provides an in vitro model that can be tuned to study hypotheses related to arterial calcification mechanisms and test drugs to stop or revert mineralization.
Assuntos
Elastina/metabolismo , Membranas Artificiais , Modelos Cardiovasculares , Calcificação Vascular/metabolismo , Animais , Elastina/química , Humanos , CamundongosRESUMO
OBJECTIVE: Vascular calcification significantly increases morbidity in life-threatening diseases, and no treatments are available because of lack of understanding of the underlying molecular mechanism. Here, we study the physicochemical details of mineral nucleation and growth in an animal model that faithfully recapitulates medial arterial calcification in humans, to understand how pathological calcification is initiated on the vascular extracellular matrix. APPROACH AND RESULTS: MGP (matrix Gla protein) is a potent mineralization inhibitor. We study the evolution of medial calcification in MGP-deficient mice over the course of 5 weeks using a combination of material science techniques and find that mineral composition and crystallinity evolve over time and space. We show that calcium is adsorbed first and then amorphous calcium phosphate and octacalcium phosphate forms, which then transform into hydroxyapatite and carbonated apatite. These events are repeated after each nucleation event, providing a snapshot of the overall mineral evolution at each time point analyzed. CONCLUSIONS: Our results show that an interdisciplinary approach combining animal models and materials science can provide insights into the mechanism of vascular calcification and suggest the importance of analyzing mineral phases, rather than just overall mineralization extent, to diagnose and possibly prevent disease development.
Assuntos
Aorta Abdominal/metabolismo , Aorta Torácica/metabolismo , Doenças da Aorta/metabolismo , Proteínas de Ligação ao Cálcio/metabolismo , Cálcio/metabolismo , Proteínas da Matriz Extracelular/metabolismo , Matriz Extracelular/metabolismo , Calcificação Vascular/metabolismo , Animais , Aorta Abdominal/ultraestrutura , Aorta Torácica/ultraestrutura , Doenças da Aorta/genética , Doenças da Aorta/patologia , Apatitas/metabolismo , Fosfatos de Cálcio/metabolismo , Proteínas de Ligação ao Cálcio/deficiência , Proteínas de Ligação ao Cálcio/genética , Cristalização , Modelos Animais de Doenças , Progressão da Doença , Durapatita/metabolismo , Matriz Extracelular/patologia , Proteínas da Matriz Extracelular/deficiência , Proteínas da Matriz Extracelular/genética , Camundongos Endogâmicos C57BL , Camundongos Knockout , Fatores de Tempo , Calcificação Vascular/genética , Calcificação Vascular/patologia , Proteína de Matriz GlaRESUMO
Efficient control over drug release is critical to increasing drug efficacy and avoiding side effects. An ideal drug delivery system would deliver drugs in the right amount, at the right location and at the right time noninvasively. This can be achieved using light-triggered delivery: light is noninvasive, spatially precise and safe if appropriate wavelengths are chosen. However, the use of light-controlled delivery systems has been limited to areas that are not too deep inside the body because ultraviolet (UV) or visible (Vis) light, the typical wavelengths used for photoreactions, have limited penetration and are toxic to biological tissues. The advent of upconverting nanoparticles (UCNPs) has made it possible to overcome this crucial challenge. UCNPs can convert near-infrared (NIR) radiation, which can penetrate deeper inside the body, to shorter wavelength NIR, Vis and UV radiation. UCNPs have been used as bright, in situ sources of light for on-demand drug release and bioimaging applications. These remote-controlled, NIR-triggered drug delivery systems are especially attractive in applications where a drug is required at a specific location and time such as in anesthetics, postwound healing, cardiothoracic surgery and cancer treatment. In this Perspective, we discuss recent progress and challenges as well as propose potential solutions and future directions, especially with regard to their translation to the clinic.
Assuntos
Sistemas de Liberação de Medicamentos , Nanopartículas/química , Liberação Controlada de Fármacos , Humanos , Luz , Raios UltravioletaRESUMO
OBJECTIVE: The mechanisms underlying the pathogenesis of aortic valve calcification remain unclear. With accumulating evidence demonstrating that valve calcification recapitulates bone development, the crucial roles of noncanonical Wnt ligands WNT5a, WNT5b, and WNT11 in osteogenesis make them critical targets in the study of aortic valve calcification. APPROACH AND RESULTS: Using immunohistochemistry, real-time qPCR, Western blotting, and tissue culture, we examined the tissue distribution of WNT5a, WNT5b, and WNT11 in noncalcified and calcified aortic valves and their effects on human aortic valve interstitial cells (HAVICs). Only focal strong immunostaining for WNT5a was seen in and around areas of calcification. Abundant immunostaining for WNT5b and WNT11 was seen in inflammatory cells, fibrosis, and activated myofibroblasts in areas of calcified foci. There was significant correlation between WNT5b and WNT11 overall staining and presence of calcification, lipid score, fibrosis, and microvessels (P<0.05). Real-time qPCR and Western blotting revealed abundant expression of both Wnts in stenotic aortic valves, particularly in bicuspid valves. Incubation of HAVICs from noncalcified valves with the 3 noncanonical Wnts significantly increased cell apoptosis and calcification (P<0.05). Treatment of HAVICs with the mitogen-activated protein kinase-38ß and GSK3ß inhibitors significantly reduced their mineralization (P<0.01). Raman spectroscopy identified the inorganic phosphate deposits as hydroxyapatite and showed a significant increase in hydroxyapatite deposition in HAVICs in response to WNT5a and WNT11 (P<0.05). Similar crystallinity was seen in the deposits found in HAVICs treated with Wnts and in calcified human aortic valves. CONCLUSIONS: These findings suggest a potential role for noncanonical Wnt signaling in the pathogenesis of aortic valve calcification.
Assuntos
Estenose da Valva Aórtica/metabolismo , Valva Aórtica/metabolismo , Valva Aórtica/patologia , Calcinose/metabolismo , Osteogênese , Proteínas Wnt/metabolismo , Via de Sinalização Wnt , Proteína Wnt-5a/metabolismo , Idoso , Idoso de 80 Anos ou mais , Fosfatase Alcalina/metabolismo , Estenose da Valva Aórtica/genética , Estenose da Valva Aórtica/patologia , Apoptose , Calcinose/genética , Calcinose/patologia , Células Cultivadas , Durapatita/metabolismo , Feminino , Fibrose , Regulação da Expressão Gênica , Glicogênio Sintase Quinase 3 beta/metabolismo , Humanos , Imuno-Histoquímica , Masculino , Pessoa de Meia-Idade , Proteínas Quinases Ativadas por Mitógeno/metabolismo , Osteogênese/genética , Fosforilação , Análise Espectral Raman , Proteínas Wnt/genética , Proteína Wnt-5a/genéticaRESUMO
Lanthanide-doped upconverting nanoparticles (UCNPs) have emerged as excellent nanotransducers for converting longer wavelength near-infrared (NIR) light to shorter wavelengths spanning the ultraviolet (UV) to the visible (Vis) regions of the spectrum via a multiphoton absorption process, known as upconversion. Here, we report the development of NIR to UV-Vis-NIR UCNPs consisting of LiYF4:Yb(3+)/Tm(3+)@SiO2 individually coated with a 10 ± 2 nm layer of chitosan (CH) hydrogel cross-linked with a photocleavable cross-linker (PhL). We encapsulated fluorescent-bovine serum albumin (FITC-BSA) inside the gel. Under 980 nm excitation, the upconverted UV emission cleaves the PhL cross-links and instantaneously liberates the FITC-BSA under 2 cm thick tissue. The release is immediately arrested if the excitation source is switched off. The upconverted NIR light allows for the tracking of particles under the tissue. Nucleus pulposus (NP) cells cultured with UCNPs are viable both in the presence and in the absence of laser irradiation. Controlled drug delivery of large biomolecules and deep tissue imaging make this system an excellent theranostic platform for tissue engineering, biomapping, and cellular imaging applications.
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Reagentes de Ligações Cruzadas/química , Sistemas de Liberação de Medicamentos , Hidrogéis/química , Raios Infravermelhos , Nanopartículas/química , Fotólise , Nanomedicina Teranóstica , Animais , Bovinos , Sobrevivência Celular , Células Cultivadas , Quitosana/química , Fluorescência , Fluoretos/química , Lítio/química , Neurônios/citologia , Neurônios/metabolismo , Soroalbumina Bovina/química , Dióxido de Silício/química , Tecnécio/química , Ítrio/químicaRESUMO
During the intraerythrocytic stage of malaria, the parasite digests hemoglobin and aggregates the released heme as an insoluble crystalline material called hemozoin. This detoxification step is an excellent drug target for developing new antimalarials, which can bind to hemozoin surface to inhibit further growth. Although the bulk crystalline properties of hemozoin are well-known, the surface properties remain poorly defined. Here, we use a combination of spectroscopic and adsorption techniques to study the surface of synthetic hemozoin, hematin anhydride, produced by two different methods. We show that the two synthetic methods produce crystals with major differences, such as the amount of water adsorbed on the surface and surface carboxylate groups. These results imply that the methodology to produce hematin anhydride affects its surface reactivity; this information needs to be considered whenever hematin anhydride is used as a model to study host immune response or to design new antimalarials.
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Hemina/química , Hemina/síntese química , Adsorção , Técnicas de Química Sintética , Propriedades de SuperfícieRESUMO
Graphene hydrogels/aerogels are emerging three-dimensional graphene macroscopic assemblies of potential use in many applications including energy storage, pollutant adsorption, and gas sensing. In this Letter, we identify, characterize and control the formation of the exterior shell structure of graphene hydrogels prepared via hydrothermal reduction of graphene oxide. Unlike the porous bulk of the hydrogel, the shell is a compact, highly ordered layer with a higher electrical conductivity. Shell formation is dependent upon the surface anchoring of graphene oxide at the liquid-air and liquid-container interfaces. By purposefully weakening surface anchoring of graphene oxide using mild thermal or chemical prereduction method prior to hydrothermal reduction, we have succeeded in completely suppressing shell formation in the graphene hydrogel. The resulting graphene hydrogel shows a lower volume reduction with a porous bulk structure immediately accessible from the surface, in contrast to graphene hydrogels prepared under conventional conditions.
RESUMO
Genesis of natural biocomposite-based materials, such as bone, cartilage, and teeth, involves interactions between organic and inorganic systems. Natural biopolymers, such as peptide motif sequences, can be used as a template to direct the nucleation and crystallization of hydroxyapatite (HA). In this study, a natural motif sequence consisting of 13 amino acids present in the first helix of osteocalcin was selected based on its calcium binding ability and used as substrate for nucleation of HA crystals. The acidic (acidic osteocalcin-derived peptide (OSC)) and amidic (amidic osteocalcin-derived peptide (OSN)) forms of this sequence were synthesized to investigate the effects of different C termini on the process of biomineralization. Electron microscopy analyses show the formation of plate-like HA crystals with random size and shape in the presence of OSN. In contrast, spherical amorphous calcium phosphate is formed in the presence of OSC. Circular dichroism experiments indicate conformational changes of amidic peptide to an open and regular structure as a consequence of interaction with calcium and phosphate. There is no conformational change detectable in OSC. It is concluded that HA crystal formation, which only occurred in OSN, is attributable to C-terminal amidation of a natural peptide derived from osteocalcin. It is also proposed that natural peptides with the ability to promote biomineralization have the potential to be utilized in hard tissue regeneration.
Assuntos
Durapatita/química , Osteocalcina/química , Sequência de Aminoácidos , Animais , Desenvolvimento Ósseo , Cálcio/química , Físico-Química/métodos , Dicroísmo Circular , Cristalização , Humanos , Microscopia Eletrônica/métodos , Microscopia Eletrônica de Varredura/métodos , Microscopia Eletrônica de Transmissão/métodos , Dados de Sequência Molecular , Osseointegração , Peptídeos/química , Próteses e Implantes , Estrutura Terciária de Proteína , RegeneraçãoRESUMO
Rubinstein-Taybi syndrome (RTS) is a rare multiple congenital anomalies-intellectual disability syndrome. The diagnosis is made after birth and based on the detection of signs such as growth and developmental delay, minor facial anomalies, and broad thumbs and halluces. It is rare to suspect RTS during the prenatal period. We report here the approach to a patient with RTS whose pregnancy was complicated by multiple congenital anomalies. However, in the presence of the broad thumb and facial anomalies, we were able to suggest the correct diagnosis. The RTS was confirmed at birth and the molecular analysis of the major causative gene revealed a previously unreported heterozygous truncating mutation of CREBBP. This report provides new knowledge of the fetal phenotype of RTS.
Assuntos
Anormalidades Múltiplas/genética , Feto/anormalidades , Síndrome de Rubinstein-Taybi/genética , Humanos , Masculino , Fenótipo , Diagnóstico Pré-Natal/métodosRESUMO
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.
Assuntos
Fosfatos de Cálcio , Elastina , Tamanho da Partícula , Elastina/metabolismo , Elastina/química , Fosfatos de Cálcio/química , Fosfatos de Cálcio/metabolismo , Animais , Ácidos Carboxílicos/química , Calcificação Vascular/metabolismo , Calcificação Vascular/patologia , Cálcio/metabolismo , Durapatita/químicaRESUMO
Bioactive glasses (BGs) bond with bone by forming hydroxy carbonate apatite (HCA) upon reaction in physiological fluid, a phenomenon known as bioactivity. BGs structural network connectivity determines their bioactivity. Sol-gel BGs are synthesized through the hydrolysis and condensation of metal alkoxide precursors in the presence of a catalyst, in aqueous environments. Several sol-gel synthesis parameters directly impact BG network connectivity: pH (i.e. acid or basic catalysis), water to alkoxide ratio (Rw), alkoxide type and presence of dopant ions. However, the relationship between bioactivity and these parameters remains surprisingly unexplored. This study highlights the relationship between synthesis pH, Rw, network connectivity and bioactivity in silica-based sol-gel BGs and BGs doped with titanium (Ti) ions (TiBGs), the latter selected for their known ability to enhance network connectivity. BGs and TiBGs are synthesized with various Rw values under acidic and basic conditions, and their bioactivity is assessed in simulated body fluid for 7 days. Increasing Rw decreases network connectivity and increases bioactivity of BGs with high network connectivity, as observed for base-catalyzed BGs and for both acid and base catalyzed TiBGs, but not in BGs with lower connectivity as evidenced in acid-catalyzed BGs. Basic catalysis of TiBGs prevents crystalline TiO2 domain formation, which was instead consistently observed in TiBGs synthesized under acidic catalysis. These findings help the design of BGs for applications where ion release needs to be enhanced even in the presence of dopants that slow down HCA formation, and of BGs with specific properties, e.g. TiO2-containing BGs with potential bactericidal activity. STATEMENT OF SIGNIFICANCE: Bioactive glasses (BGs) bond with bone by dissolving and forming hydroxycarbonate apatite (HCA) on their surface, offering applications in medicine and dentistry. BG's network connectivity influences its dissolution rate, and hence HCA formation. While solution-gelation (sol-gel) is commonly used for BG production, the effect of sol gel synthesis parameters on HCA formation remains unexplored. We studied the relationship between synthesis parameters (water-to-alkoxide ratio (Rw), catalyst, and dopant ions, particularly titanium), BG network connectivity, and HCA formation. We find that increasing Rw with any catalyst enhances HCA formation, particularly in glasses with high network connectivity. This understanding allows tailoring BG synthesis for different applications, e.g. those requiring doping with ions that increase network connectivity and fills a crucial gap in BG literature.