17 novembre 2015 ~ 0 Commentaire

Twin Screw Extrusion Based Technologies Offer Novelty, Versatility, Reproducibility and Industrial Scalability for Fabrication of Tissue Engineering Scaffolds

Introduction

Porous, biodegradable and bioresorbable polymeric scaffolds are utilized in a variety of tissue engineering applications and so are shaped typically via 3-D printing, solvent casting, particulate leaching, phase separation, gas foaming, freeze drying, solidform and electrospinning fabrication. However, significant constraints and issues stay in the polymers and additives which you can use, cost, reproducibility of the microstructure and real estate of the fabricated scaffolds, and scalability of the fabrication operations to realistic manufacturing costs. These remaining major issues require the expansion of alternative elements processing methods. Recently, several novel fabrication methods based on the twin screw extrusion process have been developed and were found in the fabrication of various kinds of scaffolds for tissue engineering, especially focusing on bone and cartilage applications. These new techniques integrate twin screw extrusion with spiral winding, co-extrusion and electrospinning and offer significant advantages over conventional methods of scaffold fabrication. These advantages include commercial scalability, reproducibility and versatility.

Challenges in Fabrication of Scaffolds for Tissue Engineering

Tissue engineering depends on the use of porous, bioresorbable and biodegradable polymeric scaffolds to promote cell proliferation, differentiation, migration and extracellular matrix generation. Important criteria that need to be considered for scaffold development involve suitability of the top properties and biocompatibility, kinetics of biodegradation, and micro structural requirements such as porosity, pore size, and pore interconnectivity. The conventional methods that are applied to fabricate cells engineering scaffolds include 3-D printing, solvent casting, particulate leaching, phase separation, gas foaming, freeze drying, solid-form and electrospinning fabrication. In spite of the significant advancements made during the last decade significant issues and restrictions remain in the polymers and additives which you can use, cost, reproducibility of the microstructure and properties of the fabricated scaffolds, and scalability of the fabrication processes to realistic manufacturing prices. These remaining major issues require the creation of alternative components and materials processing methods for scaffold fabrication. Recently, numerous novel fabrication methods in line with the twin screw extrusion process have been developed and were used in the fabrication of different types of scaffolds for cells engineering applications. These latest operations integrate twin screw extrusion with spiral winding, co-extrusion and electrospinning and provide significant advantages over standard ways of scaffold fabrication. These advantages include industrial scalability, versatility and reproducibility.

Advantages Offered by Twin Screw Extrusion for Fabrication of Scaffolds

Twin screw extrusion procedures (two screws rotating in the opposite, i.e., counter-rotating or same, we.e., co-rotating guidelines), which plastic compounding machines can be fully-intermeshing, or non-intermeshing, are remarkably versatile and scalable continuous processing operations that generate reproducible mixtures and extrudates within rigid dimensional and structural tolerances. Twin screw extrusion enables multiple unit operations, including solids conveying, melting, distributive, and dispersive combining of contaminants and nanoparticles, deaeration, and shaping of the scaffolds, to take place within the confines of a single process. The screws possess modular designs generally, which permit the concomitant usage of multiple screw factors with varied functionalities, i.e., regularflighted conveying screws (both right-handed and left-handed) and lenticular components, i.e., the kneading disks. The kneading disks could be staggered at different stagger stagger and angles guidelines to supply a dispersive mixing capability, which permits the break-up of particle clusters, i.e., a capability not within conventional scaffold fabrication methods. A die that is designed to extrude the required scaffold shape is attached to the front-end of the twin screw extruder.

Twin Screw Extrusion Based Technology for Fabrication of Tissue Engineering Scaffolds

The twin screw extrusion based technologies which are recently produced for the fabrication of tissue engineering scaffolds principally contain five numerous fabrication methods. These are:

1. Twin screw extrusion and die combination

2. Twin screw co-extrusion and extrusion

3. Twin screw spiral and extrusion winding

4. Twin screw electrospinning and extrusion

5. Twin screw extrusion, electrospinning and spiral winding

All five strategies are amenable to industrial scale-up and generate scaffolds which are reproducible in geometry and properties. All of these five methods could also be used with and without solvents (dry out versus wet extrusion strategies). All five methods have already been applied in the specific area of interface cells engineering, targeting regenerative medication for bone and cartilage service and regeneration.

For processes #1-3, many polymeric resins including Poly(Glycolic Acid) (PGA), Poly(Lactic Acid) (PLA), and Poly(Caprolactone) (PCL) are compounded on the twin screw extruder with one or more porogens involving dissolvable salts and polymers, physical (typically supercritical CO2) or chemical substance blowing agents to facilitate the production of a porous structure. Various bioactives including nanoparticles, drugs, and proteins can also be incorporated. A die with a geometry that’s designed to enable the transformation of the mixture found in the twin screw extruder into a desired form is linked to the twin screw extruder. A co-extrusion die can also be used to allow multiple layers involving differences in materials of engineering, porosity, composition to come to be designed into scaffolds. For example, a co-extrudable cage/ key structure has been targeted for use in spinal arthrodesis. The twin screw extrusion and spiral winding process integrates the twin screw extrusion procedure with a modified filament winding method (designated right here as

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