Functionally-Graded Polymeric Grat Substitutes and Scafolds for Tissue Engineering can be Fabricated via Various Extrusion Methods Dilhan M Kalyon 1,2* , Cevat Erisken 1,3 , Seher Ozkan 1,4 , Asli Ergun-Butros 1,5 , Xiaojun Yu 2 , Hongjun Wang 2 , Antonio Valdevit 2 and Arthur Ritter 2 1 Chemical Engineering and Materials Science, Stevens Institute of Technology, USA 2 Chemistry, Chemical Biology and Biomedical Engineering Department, Stevens Institute of Technology, USA 3 Tissue Engineering and Regenerative Medicine Laboratory, Columbia University Medical Center, USA 4 Ashland Specialty Ingredients, Ashland Inc., Bridgewater, USA 5 24 M Company, Cambridge, MA *Corresponding author: Dilhan M Kalyon, Chemistry, Chemical Biology and Biomedical Engineering Department, Stevens Institute of Technology, Hoboken, NJ, USA, Tel: 201-216-8225; Email: dkalyon@stevens.edu Received date: March 25, 2014, Accepted date: March 27, 2014, Published date: March 29, 2014 Copyright: © 2014 Kalyon DM, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Abstract he design and fabrication of bioresorbable polymeric grat substitutes and porous scafolds for regenerative medicine are challenged by the complexities in structure and composition found in native tissues. he mimicking of complex gradations found in native tissues requires correspondingly complex gradations in bone grat substitutes and tissue engineering scafolds. Extrusion based processing methods ofer signiicant advantages for the fabrication of scafolds and polymeric grat substitutes functionally-graded in various directions for porosity, composition as well as distributions of other tissue relevant properties. Challenges of Regenerative Medicine he design and fabrication of bioresorbable polymeric grat substitutes and porous scafolds for regenerative medicine are challenged by the complex structural and compositional gradations found in human tissues [1-6] and tissue-tissue transitions such as the interfaces between cartilage and bone, ligament and bone, and tendon and bone. For example, it would be desirable for the bone grat substitutes used in the repair of critical sized defects in long bones like femur and tibia to accommodate changes in porosities and moduli along their transverse and axial directions. he mimicking of complex gradations found in native tissues requires correspondingly complex gradations in bone grat substitutes and tissue engineering scafolds. Generally, eforts to generate grat substitutes and scafolds which exhibit tailored three-dimensional distributions in composition, structure and properties are constrained by the myriad shortcomings of conventional scafold fabrication methodologies. Examples of such eforts [1-6] include the multilayered scafolds that were fabricated via electrospinning of separate meshes and pressing them under hydraulic pressure, layer-by-layer casting, freeze-drying, phase separation, and rapid prototyping techniques, including fused deposition modeling, 3- D printing, selective laser sintering, and stereo lithography. Among these, the 3-D printing method ofers signiicant promise but is handicapped by the unavailability of the mixing and dispersion capability, and its typical requirement of high temperature processing for some polymers that could be detrimental for biological additives. hus, additional methods that can process a wide family of polymers and additives (including bioactives) and that would allow the reproducible and industrially-scalable grading of grat substitutes and tissue engineering scafolds for a wide range of compositions, porosities and mechanical properties are needed. Extrusion based fabrication methods ofer signiicant advantages for the fabrication of graded scafolds and polymeric grat substitutes as described in the following. Such methods have been largely overlooked in spite of their advantages for generating graded structures over conventional methods of fabrication. Processing and Shaping of Polymer Melts and Solution and Polymeric Compounds via Extrusion Methods Extruders can be of the single or the twin screw extruder type with the twin screw extruders further subdivided into co-rotating (rotation directions of the two screws are similar) or counter-rotating. Twin screw extruders can also be of the fully-intermeshing or non- intermeshing, i.e., tangential types. Twin screw extruders are preferred over the single screw extruders due to their superior mixing capabilities and greater versatility. Extruders allow multiple ingredients to be fed, polymers to be molten, various ingredients to be mixed, air/ gases to be removed and the mixtures to be pressurized to be forced through dies for being shaped into extrudates. he screw elements can have diferent functionalities, i.e., regular-lighted conveying screws and lenticular elements, i.e., the kneading disks. he kneading disks provide chaotic mixing dynamics as well as generate a dispersive mixing capability, to enable the break-up of particle agglomerates, i.e., a capability not found in conventional scafold fabrication methods [7, 8]. A die is attached to the exit of the extruder to generate the desired shape. Instead of a die an electrospinning head can also be utilized. To generate porosity either porogens like dissolvable polymers or salts or foaming methods based on chemical and physical blowing agents, including supercritical luid technologies [9], can be utilized. he extrusion process can provide functionally graded extrudates to serve as graded scafolds or polymeric implants simply via time- dependent changes in the operating conditions and feed rates during the process. Rendering the input rates and process conditions cyclic gives rise to corresponding cyclic changes in the composition, porosity and physical properties either as a function of the axial or the transverse to low direction or as functions of both axial and transverse to low directions. Tissue Science & Engineering Kalyon DM, et al., J Tissue Sci Eng 2014, 5:1 http://dx.doi.org/10.4172/2157-7552.1000e128 Editorial Article open access J Tissue Sci Eng ISSN:2157-7552 JTSE, an open access journal Volume 5 • Issue 1 • 1000e128