Without functionalization, reconstituted collagen gels demonstrate poor mineralization in vitro and in vivo. Due to their high reactivity, bioactive sol-gel-derived borate-glasses (SGBGs) rapidly convert to carbonated hydroxyapatite (CHA) in vitro....

Reconstituted hydrogels based on the self-assembly of acid-solubilized collagen molecules have been extensively used as in vitro models and precursors in biofabrication processes. This study investigated the effect of fibrillization pH—ranging from 4 to 11—on real-time rheological property changes during the gelation of collagen hydrogels and its interplay with the properties of subsequently biofabricated dense collagen matrices generated via automated gel aspiration-ejection (GAE). A contactless, nondestructive technique was used to characterize the temporal progression in shear storage modulus (G’, or stiffness) during collagen gelation. There was a relative increase in G′ of the hydrogels from 36 to 900 Pa with an increase in gelation pH. Automated GAE, which simultaneously imparts collagen fibrillar compaction and alignment, was then applied to these precursor collagen hydrogels to biofabricate native extracellular matrix-like densified gels. In line with viscoelastic properties, only hydrogels fibrillized in the 6.5 < pH ≤ 10 range could be densified via GAE. There was an increase in both fibrillar density and alignment in the GAE-derived matrices with an increase in gelation pH. These factors, combined with a higher G′ in the alkaline precursor hydrogels, led to a significant increase in the micro-compressive modulus of GAE-densified gels of pH 9 and 10. Furthermore, NIH/3T3 fibroblast-seeded GAE-derived matrices densified from gels fibrillized in the pH range of 7 to 10 exhibited low cell mortality with >80% viability. It is anticipated that the results of this study can be potentially applicable to other hydrogel systems, as well as biofabrication techniques involving needles or nozzles, such as injection and bioprinting.

Introduction/Purpose Existing metal flow-diverting stents are limited in their use mainly for sidewall aneurysms and restrict re-treatment options should the aneurysm fail to occlude. In this study, we sought to pre-clinically validate a novel hybrid polymer-metal flow-diverting stent ('ReSolvTM') in terms of in vivo safety and efficacy, deployment in multiple aneurysm types, and an ability to employ adjunctive or re-treatment techniques typically unavailable for metal stents. Materials and Methods The ReSolvTM stent was deployed in 30 rabbit models, including 24 aortas (with up to 18 months of follow-up) and 6 elastase-induced saccular aneurysms (with at least 6 months of follow-up). Optical coherence tomography (OCT) was used to characterize neointima formation while angiography was used to evaluate parent vessel/jailed side branch patency, as well as aneurysm occlusion at follow-up time points. Patient-specific models of ophthalmic, posterior communicating, cavernous, and basilar tip aneurysms were used to study deployment characteristics, wall apposition (by 3D AngioCT), and mesh crossability of the BRS. Results In animal models, OCT showed smooth neointima formation over the stent in as early as 7 days, and all parent vessels (30/30) and angiographically visible jailed side branches (58/58) were patent at follow-up. O'Kelly-Marotta scores at a mean of 7.5 months indicated aneurysm occlusion or near-occlusion in 5/6 (83%) animals. The stent was successfully deployed using the push-pull technique in patient-specific aneurysm models with good wall apposition, and with an ability to shape the stent to improve neck coverage of bifurcation aneurysms. Microcatheter access to the aneurysm could be obtained across the mesh of the stent for coiling after flow diversion. Conclusions The ReSolvTM stent demonstrates safety and effectiveness as a stand-alone flow diverter in animal models. The device is uniquely versatile in its potential ability to treat both sidewall and bifurcation aneurysms, and by permitting microcatheter access across the mesh for adjunctive coiling or future re-treatment, thereby expanding therapeutic strategies in the treatment of brain aneurysms. Disclosures E. Rezabeigi: 5; C; Fluid Biomed. M. Eesa: 4; C; Fluid Biomed. J. Wong: 4; C; Fluid Biomed. A. Mitha: 1; C; Stryker Neurovascular, Fluid Biomed. 2; C; Cerus Endovascular. 4; C; Fluid Biomed.

Hemorrhaging is the main cause of death among combat and civilian injuries and has significant clinical and economic consequences. Despite their vital roles in bleeding management, an optimal topical hemostatic agent (HA) has yet to be developed for a particular scenario. This is partly due to a lack of an overarching quantitative testing technology to characterize the various classes of HAs in vitro. Herein, the feasibility of a novel, contactless, and nondestructive technique to quantitatively measure the shear storage modulus (G') and clotting properties of whole blood in contact with different dosages of eight topical HAs, including particulates and gauze-like and sponge-like systems, was assessed. The real-time G'-time profiles of these blood/HA systems revealed their distinct biomechanical behavior to induce and impact coagulation. These were analyzed to characterize the clot initiation time, clotting rate, clotting time, and apparent stiffness of the formed clots (both immediately and temporally), which were correlated with their reported hemostatic mechanisms of action. Moreover, the HAs that worked independently from the natural blood clotting cascade were identified and quantified through this technology. In sum, this study indicated that the nondestructive nature of the technology may offer a promising tool for accurate, quantitative in vitro measurements of the clotting properties of various classes of HAs, which may be used to better predict their in vivo outcomes.

Although the incorporation of bioactive glasses into glass ionomer cements (GICs) has led to promising results, using a bioactive glass as the only solid component of GICs has never been investigated. In this study, we developed an Al-free GIC with standard compressive strength using various combinations of 45S5 Bioglass ® and its glass-ceramic as the solid component. The glass-ceramic particles with 74% crystallinity were used for this purpose as they can best act as both remineralizing and reinforcing agents. Strengthening mechanisms including crack deflection and crack-tip shielding were activated for the GICs containing 50–50 wt% bioglass and bioglass-ceramic as the optimum ratio. The progression of the GIC setting reaction at its early stages was also monitored and verified. We also discussed that our bimodal particle size distribution containing both micron- and nanosized particles may enhance the packing density and integrity of the structure of the cements after setting. In such GICs produced in this study, the toxic effects of Al are avoided while chemical bonds are expected to form between the cement and the surrounding hard tissue(s) through interfacial biomineralization and adhesion.

Bone is a representative hybrid tissue found in the native body and composed of collagen type I and hydroxycarbonated apatite that exhibits highly organised hierarchical structures from the nano- to the macroscale. Bone tissue engineering aims to overcome risks associated with current clinical bone repair strategies by providing alternative graft materials. A successful scaffold should ideally reflect bone, in terms of both composition and structure. Therefore, in this chapter, the defining characteristics of bone and the potential for hybrid scaffold materials, in particular mineralised collagen constructs, are discussed, to review the materials and manufacturing methods for effective biomimicry within bone tissue engineering.

Recent convergence of the 3D printing of tissue-like bioinks and regenerative medicine offers promise in the high-throughput engineering of in vitro tissue models and organoids for drug screening and discovery research, and of potentially implantable neo-tissues with tailored structural, biological, and mechanical properties. However, the current printing approaches are not compatible with collagen, the native scaffolding material. Herein, a unique biofabrication approach that uses automated gel aspiration-ejection (GAE) is reported to potentially overcome these challenges. Automated-GAE generates highly defined, aligned, dense collagen gel bioinks of various geometries (i.e., cylindrical, quadrangular, and tubular), dimensions, as well as tunable microstructural and mechanical properties that modulate seeded cellular responses. By densifying initial naturally derived reconstituted collagen hydrogels incorporating cells, automated-GAE generates mini-tissue building blocks with tailored protein fibril density and alignment, as well as cell loading, density and orientation according to the intended use. Surprisingly, a simple mathematical relationship defining the bioink compaction factor is found to be highly effective in predicting the initial and temporal properties of the bioinks in culture. Therefore, automated-GAE will potentially also enable a fourth dimension to biofabrication, where cell-cell communications and cell-extracellular matrix interactions as a function of time in culture can be predicted and modeled.

This study reports on the production and characterization of highly porous (up to 91%) composite foams for potential bone tissue engineering (BTE) applications. A calcium phosphate-based glass particulate (PGP) filler of the formulation 50P2O5-40CaO-10TiO2 mol.%, was incorporated into biodegradable poly(d,l-lactic acid) (PDLLA) at 5, 10, 20, and 30 vol.%. The composites were fabricated by melt compounding (extrusion) and compression molding, and converted into porous structures through solid-state foaming (SSF) using high-pressure gaseous carbon dioxide. The morphological and mechanical properties of neat PDLLA and composites in both nonporous and porous states were examined. Scanning electron microscopy micrographs showed that the PGPs were well dispersed throughout the matrices. The highly porous composite systems exhibited improved compressive strength and Young's modulus (up to >2-fold) and well-interconnected macropores (up to ~78% open pores at 30 vol.% PGP) compared to those of the neat PDLLA foam. The pore size of the composite foams decreased with increasing PGPs content from an average of 920 µm for neat PDLLA foam to 190 µm for PDLLA-30PGP. Furthermore, the experimental data was in line with the Gibson and Ashby model, and effective microstructural changes were confirmed to occur upon 30 vol.% PGP incorporation. Interestingly, the SSF technique allowed for a high incorporation of bioactive particles (up to 30 vol.%-equivalent to ~46 wt.%) while maintaining the morphological and mechanical criteria required for BTE scaffolds. Based on the results, the SSF technique can offer more advantages and flexibility for designing composite foams with tunable characteristics compared to other methods used for the fabrication of BTE scaffolds.

There is a need for reliable and quantitative real-time assessment of blood properties to study and treat a broad spectrum of disorders and cardiovascular diseases as well as to test the efficacy of hemostatic agents. In this study, the real-time changes in viscoelastic/rheological properties of bovine whole blood during coagulation induced by different concentrations of calcium chloride (CaCl2; 15, 25, 35 and 45 mM) was investigated. For this purpose, a novel, contactless technique was used to accurately measure the clotting characteristics under controlled and sterile conditions. It was demonstrated that, increasing the calcium concentration from low values (i.e., 15 and 25 mM), led to shorter reaction time; however, a further increase in calcium concentration (i.e., 35 and 45 mM) favored longer reaction times. Additionally, increasing the CaCl2 concentration resulted in higher shear storage modulus (i.e., stiffer clots). These results were also comparable to those generated by thromboelastrograph, a clinically established technique, as well as a conventional rheometer, which quantitatively verified the high correlation of the shear storage modulus data. In sum, the non-destructive testing technique used in this study is reproducible and sensitive in measuring clot formation kinetics, which could be applied to assess the efficacy of hemostatic agents, and may also contribute to better diagnosing relevant circulatory system diseases and conditions.

The clinical applications of glass ionomer cements (GICs) are limited by their relatively poor mechanical properties and insufficient remineralizing capacity. In this study, we developed hybrid GICs with improved mechanical and remineralizing properties via incorporation of an optimum amount (5 wt%) of 45S5 bioglass-ceramic particles. Also, we found that bioglass-ceramic particles with 74% crystallinity best act as both re mineralizing and reinforcing agents. The degree of crystallinity of the additives, is overlooked in this context in other research. At around 74% crystallinity, there is sufficient amount of combeite and an amorphous phosphorous-rich phase in the 45S5 bioglass-ceramic particles to respectively promote their reinforcing role and allow them to effectively partake in the setting process creating an excellent interfacial bond with the GIC matrix. As a result, several strengthening mechanisms such as crack deflection and crack-tip shielding are activated within the hybrid GIC containing 5 wt% bioglass-ceramic with 74% crystallinity, contributing to its improved mechanical properties. The enhanced remineralizing and mechanical properties of such hybrid GICs can potentially Improve their in vivo performance and broaden their clinical applications.

Electrospinning of nonsolvent-induced phase-separated ternary (NIPST) systems has gained a lot of interest due to its potential to produce (nano)fibers, which are superficially and internally porous with nanoscale surface roughness. Membranes produced from such systems are expected to have a high specific surface area (SSA; e.g., more than 50 m(2) g(-1)), an essential requirement for many of their applications. In spite of their advantages and potential, there are major issues regarding the electrospinning of NIPST systems that are not systematically addressed in the literature. In this paper, the most recent developments are reported and the potential and challenges associated with the electrospinning of NIPST systems are discussed. Furthermore, the essential steps to improve and optimize the electrospinning process of these systems are concisely discussed. By developing a modified time-dependent rheological model, a time range can be defined for NIPST systems as electrospinnability window, in which fiber functionality and characteristics can be tailored through aging of the systems prior to electrospinning. Some potential post-treatment processes are also proposed based on the results of recent studies to stabilize as-electrospun membranes without damaging their highly porous fibers, which can guarantee their in-service mechanical and morphological stability.

The acoustic properties of highly porous polylactic acid (PLA) foams with very low densities (as low as 0.12 g/cm 3 ) are evaluated using an impedance tube. PLA foams with a mesoporous or a combined meso/macroporous morphology exhibiting different mechanical and physical properties, are produced via nonsolvent induced phase separation (NIPS). The resulting foams exhibit an interesting resonance-like acoustic absorption behavior providing the opportunity to design acoustic materials to target specific frequency bands by controlling their microstructure. Despite very low densities, plane wave tube measurements suggest that these PLA foams may have the potential for sound barrier applications. Using the transfer matrix approach on multilayer configurations, we showed that the combined meso/macroporous morphology has the most significant impact on the absorption and transmission capacity of the foams. The knowledge produced from this study helps to understand the correlation between the characteristics of highly porous NIPS-derived foams and their acoustic properties.

Osteochondral tissue engineering (OTE) for joint reconstruction ideally requires a scaffold system that provides both the articular cartilage and the underlying, supportive subchondral bone. In this study, to mimic the osteochondral arrangement of diarthrodial joints, a bilayered dense hydrogel construct was developed using two defined collagen/chitosan weight ratios which approach the ratio of collagen/glycosaminoglycans observed in the native extracellular matrices (ECMs) of the cartilage and bone. RCJ3.1C5.18 chondroprogenitor cells, and MC3T3-E1 osteoprogenitor cells, were selected as well-defined models of cell differentiation and activity (to chondrocytes and osteoblasts, respectively) that could be sequentially seeded within adjacent hydrogel layers. Culture conditions were optimized to support the simultaneous growth and differentiation of both cell types as determined by gene expression and biochemical analyses. Chondrogenesis was observed within the cartilage-ECM-like layer, as indicated by the expression of Col2a1 and Acan, safranin O staining, and quantification of glycosaminoglycans, as well as by observing type II collagen and aggrecan immunoreactivity. In the bone-ECM-like layer, biomarkers included elevated alkaline phosphatase enzymatic activity, mineral deposition, and expression of Akp2, Col1a1, and Mmp-13. This study describes an integrated, bilayered hydrogel tissue model to investigate cell-cell and cell-matrix/mineral interactions in a multi-layered construct potentially useful for joint repair.

Abstract Sol-gel derived bioactive borate glasses (SGBGs) rapidly convert to hydroxycarbonated apatite (HCA) in simulated body fluid (SBF), in vitro. While previous studies have examined the influence of processing and composition on bioactivity, the effect of the in vitro dissolution media has not been well examined for these glasses. In this study, the mineral conversion of a SGBG substituted 45S5 Bioglass® formulation (“B46”, (46.1)B2O3-(26.9)CaO-(24.4)Na2O-(2.6)P2O5, mol%), was examined in six different dissolution media: SBF, tris(hydroxymethyl)aminomethane (TRIS, pH 7.4) buffer, Dulbecco’s phosphate buffered saline (PBS, 1X), Dulbecco’s Modified Eagle Medium (DMEM, 1X), 0.9% Saline (SAL), and deionized water (DIW) at 1.5 mg/mL for 10 min, 2h, and 1d. All media underwent a rapid increase in pH as a result of glass dissolution and ion release. B46 in SBF, TRIS, and PBS converted to HCA while B46 in DMEM, SAL, and DIW converted to calcite according to attenuated total reflectance-Fourier-transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. The ratio of B46 to SBF was also examined at 3, 6, 12, and 24 mg/mL for 1d. These results help elucidate the dissolution and mineral conversion of borate glasses and help provide insights into optimizing pre-conditioning treatments for both in vitro and in vivo analyses.

Combeite (Na2Ca2Si3O9) is a mechanically strong phase that crystallizes from 45S5 Bioglass (R) during heat treatments. 4555 glass-ceramics are expected to not only retain desirable levels of bioactivity but also exhibit improved mechanical properties compared to those of the amorphous 45S5 Bioglass (R). However, producing crystalline 45S5 glass-ceramics containing solely combeite is challenging since other phase(s) may also form during the heat treatment process. In this study, we developed a comprehensive set of heat treatment regimes that can be used to control the formation of combeite in order to tailor the crystallinity of 45S5 glass-ceramics over a wide range of 5% to 95%. These heat treatments were designed based on controlling the nucleation and growth temperatures and times of the combeite phase, also preventing other potential phases from forming. The activation energy for crystallization of combeite was calculated based on three different analytical methods and then used to obtain the Avrami exponent of the Bioglass (R) powder (n = 0.71). The results indicated that the crystallization of combeite occurred mainly on the surface of the particles. Depending on the target application, different levels of mechanical properties and bioactivity in bioglasses may be required. The crystallinity of 45S5 Bioglass (R) can be adjusted by applying the appropriate heat treatment regime selected from the profiles developed in this study.

Electrospinning of ternary systems containing a nonsolvent is of interest because it can produce fibers that are highly porous on the surface and in the core. Despite the growing interest and applications, electrospinning of such ternary systems is challenging due to their evolving viscoelastic properties prior to electrospinning. In this study, we produce porous/rough poly(lactic acid) (PLA) fibers via electrospinning of binary and ternary systems of PLA, dichloromethane (solvent) and hexane (nonsolvent). We introduce a rheological approach to determine the appropriate time for electrospinning of ternary systems which is within at most 10% of their induction time of crystallization, when incipient crystals are formed within the polymer-rich phase. These incipient crystals act as nucleators for further crystallization during the process leading to higher crystallinity and more a form crystals. Surprisingly, the pore morphology and crystallinity of the as- electrospun fibers are drastically changed after a room temperature solvent exchange. During this process, cold crystallization and a' to a recrystallization occur for all systems. Also, the surface porosity of the fibers is decreased after the solvent exchange, except for the fibers produced from the ternary systems with higher PLA concentrations. Our results indicate that the crystallinity and surface texture of electrospun membranes and thus their performance may change during subsequent analysis and in-service applications, even when a highly volatile solvent is used as a spinning medium.

ABSTRACT In this study, porous micron‐sized fibers of polylactic acid (PLA) are fabricated via electrospinning of PLA‐dichloromethane (DCM)‐hexane systems with no post treatment involved. Several compositions from the liquid‐liquid phase separated region of the phase diagram of this ternary system are selected and their electrospinnability are investigated throughout their phase separation process before gelation. We show that under constant processing and ambient parameters, there is a phase separation shelf time for each composition wherein the viscoelasticity of the systems is optimum to produce long, uniform porous fibers. For the first time, we investigate the effect of aging time during phase separation on the morphology of the electrospun fibers using scanning electron microscopy (SEM). Based on our results, certain phase separated systems provide a range of viscosity allowing for the production of porous spherical micro beads or fibers via electrospraying and electrospinning, respectively. It is also shown that obtaining long, uniform fibers from electrospinning of highly phase separated systems, e.g., a gel, is not feasible due to the high degree of crystallinity of their polymer‐rich domains and the solid‐like yielding behavior. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44862.

In this study, we produce highly porous (up to ∼91%) composite scaffolds of polylactic acid (PLA) containing 2 wt % sol-gel-derived 45S5 Bioglass® particles via nonsolvent induced phase separation at -23°C with no sacrificial phases involved. Before the incorporation of the bioglass with PLA, the particles are surface modified with a silane coupling agent which effectively diminishes agglomeration between them leading to a better dispersion of bioactive particles throughout the scaffold. Interestingly, the incorporation route (via solvent dichloromethane or nonsolvent hexane) of the surface modified particles in the foaming process has the greatest impact on porosity, crystallinity, and morphology of the scaffolds. The composite scaffolds with a morphology consisting of both mesopores and large macropores, which is potentially beneficial for bone regeneration applications, are examined further. SEM images show that the surface modified bioglass particles take-up a unique configuration within the mesoporous structure of these scaffolds ensuring that the particles are well interlocked but not completely covered by PLA such that they can be in contact with physiological fluids. The results of preliminary in vitro tests confirm that this PLA/bioglass configuration promotes the interaction of the bioactive phase with physiological fluids. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2433-2442, 2017.