Hierarchical porous materials made by stereolithographic printing of photo-curable emulsions

Porous materials are relevant for a broad range of technologies from catalysis and filtration, to tissue engineering and lightweight structures. Controlling the porosity of these materials over multiple length scales often leads to enticing new functionalities and higher efficiency but has been limited by manufacturing challenges and the poor understanding of the properties of hierarchical structures. Here, we report an experimental platform for the design and manufacturing of hierarchical porous materials via the stereolithographic printing of stable photo-curable Pickering emulsions. In the printing process, the micron-sized droplets of the emulsified resins work as soft templates for the incorporation of microscale porosity within sequentially photo-polymerized layers. The light patterns used to polymerize each layer on the building stage further generate controlled pores with bespoke three-dimensional geometries at the millimetre scale. Using this combined fabrication approach, we create architectured lattices with mechanical properties tuneable over several orders of magnitude and large complex-shaped inorganic objects with unprecedented porous designs.

3D printing of concentrated emulsions into multiphase biocompatible soft materials

3D printing via direct ink writing (DIW) is a versatile additive manufacturing approach applicable to a variety of materials ranging from ceramics over composites to hydrogels. Due to the mild processing conditions compared to other additive manufacturing methods, DIW enables the incorporation of sensitive compounds such as proteins or drugs into the printed structure. Although emulsified oil-in-water systems are commonly used vehicles for such compounds in biomedical, pharmaceutical, and cosmetic applications, printing of such emulsions into architectured soft materials has not been fully exploited and would open new possibilities for the controlled delivery of sensitive compounds. Here, we 3D print concentrated emulsions into soft materials, whose multiphase architecture allows for site-specific incorporation of both hydrophobic and hydrophilic compounds into the same structure. As a model ink, concentrated emulsions stabilized by chitosan-modified silica nanoparticles are studied, because they are sufficiently stable against coalescence during the centrifugation step needed to create a bridging network of droplets. The resulting ink is ideal for 3D printing as it displays high yield stress, storage modulus and elastic recovery, through the formation of networks of droplets as well as of gelled silica nanoparticles in the presence of chitosan. To demonstrate possible architectures, we print biocompatible soft materials with tunable hierarchical porosity containing an encapsulated hydrophobic compound positioned in specific locations of the structure. The proposed emulsion-based ink system offers great flexibility in terms of 3D shaping and local compositional control, and can potentially help address current challenges involving the delivery of incompatible compounds in biomedical applications.

3D Printing of Emulsions and Foams into Hierarchical Porous Ceramics

Bulk hierarchical porous ceramics with unprecedented strength-to-weight ratio and tunable pore sizes across three different length scales are printed by direct ink writing. Such an extrusion-based process relies on the formulation of inks in the form of particle-stabilized emulsions and foams that are sufficiently stable to resist coalescence during printing.

Can aortocoronary and peripheral venous bypass graft patency be improved by the administration of pentoxifylline on a long-term basis?

BACKGROUND

Venous bypass grafts to coronary and peripheral arteries have a high rate of occlusion at follow-up. Pentoxifylline, known to reduce blood viscosity, has the potential theoretically to reduce venous graft occlusion. We tested this hypothesis in this study.

METHODS

The effect of pentoxifylline (Trental) on the early and late failure of venous bypass grafts was studied on 107 patients who underwent a total of 159 aortocoronary and 55 peripheral venous bypass grafts. Pentoxifylline was initially administered in the prime of the heart-lung machine in coronary patients and intra-arterially in peripheral vascular patients. All patients were treated postoperatively with oral administration of pentoxifylline at a dose of 400 mg daily, during the 2-year follow-up period. The short- and long-term graft patency in this unit was compared to that of an identical placebo unit, composed of 105 patients (141 aortocoronary and 55 peripheral venous bypass grafts). The patients of the placebo unit had the same operative treatment but were not treated with pentoxifylline. These patients were pre- and postoperatively examined by the same methods as the patients of the pentoxifylline unit.

RESULTS

The 2-year follow-up demonstrated that in cardiac patients aortocoronary graft patency was 92.5% in the pentoxifylline unit, and 80.6% in the placebo unit. Similar results were observed in peripheral vascular patients, as well as in a small group of patients with multifocal arterial disease.

CONCLUSIONS

These results indicate that pentoxifylline affects favorably the patency of both aortocoronary and peripheral bypass grafts.