S. Khalil

Multi‐nozzle deposition for construction of 3D biopolymer tissue scaffolds

Purpose – To introduce recent research and development of biopolymer deposition for freeform fabrication of three‐dimensional tissue scaffolds that is capable of depositing bioactive ingredients.Design/methodology/approach – A multi‐nozzle biopolymer deposition system is developed, which is capable of extruding biopolymer solutions and living cells for freeform construction of 3D tissue scaffolds. The deposition process is biocompatible and occurs at room temperature and low pressures to reduce damage to cells. In contrast with other systems, this system is capable of, simultaneously with scaffold construction, depositing controlled amount of cells, growth factors, or other bioactive compounds with precise spatial position to form complex cell‐seeded tissue constructs. The examples shown are based on sodium alginate solutions and poly‐e‐caprolactone (PCL). Studies of the biopolymer deposition feasibility, structural formability, and different material deposition through a multi‐nozzle heterogeneous system...

Precision extruding deposition and characterization of cellular poly‐ε‐caprolactone tissue scaffolds

Successes in scaffold guided tissue engineering require scaffolds to have specific macroscopic geometries and internal architectures to provide the needed biological and biophysical functions. Freeform fabrication provides an effective process tool to manufacture many advanced scaffolds with designed properties. This paper reports our recent study on using a novel precision extruding deposition (PED) process technique to directly fabricate cellular poly‐e_rm;‐caprolactone (PCL) scaffolds. Scaffolds with a controlled pore size of 250 μm and designed structural orientations were fabricated.

Characterization of cell viability during bioprinting processes

Bioprinting is an emerging technology in the field of tissue engineering and regenerative medicine. The process consists of simultaneous deposition of cells, biomaterial and/or growth factors under pressure through a micro-scale nozzle. Cell viability can be controlled by varying the parameters like pressure and nozzle diameter. The process itself can be a very useful tool for evaluating an in vitro cell injury model. It is essential to understand the cell responses to process-induced mechanical disturbances because they alter cell morphology and function. We carried out analysis and quantification of the degree of cell injury induced by bioprinting process. A parametric study with different process parameters was conducted to analyze and quantify cell injury as well as to optimize the parameters for printing viable cells. A phenomenological model was developed correlating the percentage of live, apoptotic and necrotic cells to the process parameters. This study incorporates an analytical formulation to predict the cell viability through the system as a function of the maximum shear stress in the system. The study shows that dispensing pressure has a more significant effect on cell viability than the nozzle diameter. The percentage of live cells is reduced significantly (by 38.75%) when constructs are printed at 40 psi compared to those printed at 5 psi.

Intrinsic fiber optic chemical sensor for the detection of dimethyl methylphosphonate

We report the early stage development of an intrinsic fiber optic sensor to detect the presence of nerve agent sarin simulant dim- ethyl methylphosphonate (DMMP). The sensor design is based on the modified cladding or coating approach. Conducting polymer polypyrrole is the chemo-optic transducer, i.e., is used as a modified cladding mate- rial. Sensitivity to approximately 134 ppm of DMMP is demonstrated in the developed sensor, with a sensor response of 20 mV and a response time of 2 sec. Morphology characterization of the polypyrrole is per- formed by scanning electron microscopy. Selectivity study of the devel- oped sensor is presented by exposing the sensing element to other gases like acetone and ammonia. Influence of temperature and humidity on the developed sensor is investigated, along with ambient aging of polypyrrole films.

Fiber optic neurotoxin sensor

Nerve agents are chemicals that attack the central nervous system. A release of a nerve agent has the potential to rapidly affect a large number of people. The majority of nerve agents belong to a class of compounds called Organophosphates. The presence of these compounds cannot be sensed by hydrolysis. A combination of a conducting polymer and optical fiber provides with an effective medium to sense organophosphates. This paper describes the development of an optical fiber sensor to detect the presence of organophosphate dimethylmethylphosphonate.

Biopolymer deposition for freeform fabrication of tissue engineered scaffolds

Polymeric scaffolds have been utilized in tissue engineering as a technique to confide the desired proliferation of seeded cells in vitro and in vivo into its architecturally porous three-dimensional structures. Novel freeform fabrication methods for tissue engineering polymeric scaffolds have been an interest because of its repeatability and capability of high accuracy in fabrication resolution at the macro and micro scales. A multi-nozzle biopolymer deposition system which is capable of extruding biopolymer solutions and living cells for freeform construction of 3D tissue scaffolds is presented. The deposition process is biocompatible and occurs at room temperature and low pressures to reduce damage to cells. This paper presents three types of nozzle systems that can be used to deposit sodium alginate using three-dimensional deposition (3D-D) to fabricate three-dimensional scaffold structures, in addition to cell/alginate deposition.

Characterization of integrated fiber optic sensors in smart textiles

Smart textiles with integrated fiber optic sensors have been studied for various applications including in-situ measurement of load/deformation on the textiles. Two types of silica multimode optical fibers were successfully integrated into 4/4 Twill-woven and Plain-woven textiles along the warp direction of the textile structures for sensing of applied load conditions. The sensing mechanism is based on the MPD (Modal Power Distribution) technique, which employs the principle of intensity modulation based on modal power redistribution of the propagating light within multimode fibers caused by external perturbations. In the presence of transverse load applied to an integrated optical fiber, the redistribution of the modal power is an indication of the applied load. The spatial modal power redistribution was clearly recorded as a function of the optical intensity profile. Based on the uni-axial tensile test results, the relationship between the mechanical behavior of the textile and the output of the embedded fiber-optic sensor was established and understood. It is clearly demonstrated that the sensitivity and dynamic range of this type of intensity-based sensor is determined by the interaction between the fabric yarns and optical fibers, which are closely related with the textile structure and the type of optical fiber.

Development of smart textiles with embedded fiber optic chemical sensors

Smart textiles are defined as textiles capable of monitoring their own health conditions or structural behavior, as well as sensing external environmental conditions. Smart textiles appear to be a future focus of the textile industry. As technology accelerates, textiles are found to be more useful and practical for potential advanced technologies. The majority of textiles are used in the clothing industry, which set up the idea of inventing smart clothes for various applications. Examples of such applications are medical trauma assessment and medical patients monitoring (heart and respiration rates), and environmental monitoring for public safety officials. Fiber optics have played a major role in the development of smart textiles as they have in smart structures in general. Optical fiber integration into textile structures (knitted, woven, and non-woven) is presented, and defines the proper methodology for the manufacturing of smart textiles. Samples of fabrics with integrated optical fibers were processed and tested for optical signal transmission. This was done in order to investigate the effect of textile production procedures on optical fiber performance. The tests proved the effectiveness of the developed methodology for integration of optical fibers without changing their optical performance or structural integrity.

Scaffold informatics: multi-material strategies for tissue scaffolds

The dominant approach in 3D tissue engineering is to construct a scaffold of biocompatible material, to seed the scaffold with an appropriate cell type, to culture these cells in a bioreactor, and to implant the resulting tissue construct. Numerous individual materials have been investigated, but no single material has proven ideal for tissue culture. We advocate the use of multiple materials within a single scaffold. Such scaffolds would be produced using a 3D positioning system possessing multiple heads, capable of both fused deposition and droplet deposition of multiple materials. Our candidate materials for heterogenous deposition include poly-/spl epsiv/-caprolactone(PCL), alginate, fibrin, and chitosan. This paper discusses 1) the design of the hardware necessary to perform this operation, 2) the considerations in selecting candidate materials, and 3) the anticipated benefits to design and construction of tissue scaffolds.

Freeform fabrication of bioactive tissue scaffolds

Biopolymeric scaffolds have been utilized in tissue engineering as a technique to confide the desired proliferation of seeded cells in vitro and in vivo into its architecturally porous three-dimensional structures. Novel freeform fabrication methods for tissue engineering polymeric scaffolds have been an interest because of its repeatability and capability of high accuracy in fabrication resolution at the macro and micro scales. A multinozzle biopolymer deposition system which is capable of extruding biopolymer solutions and living cells for bioactive fabrication of 3D tissue scaffolds is presented. The deposition process is biocompatible and occurs at room temperature and low pressures to reduce damage to cells. Sodium alginate aqueous solution is deposited into calcium chloride solution using three-dimensional dispensing (3DD) to form hydrogel structures. The flow rate, nozzle diameter, and nozzle velocity were studied and a model was developed to design 3D scaffolds with controlled strut diameters and pore sizes. In addition, cells were deposited through the system with alginate to form gel scaffold structures with encapsulated cells in a bioactive fabricated manor. Cell viability studies were conducted on the cell encapsulated scaffolds for validating the bioactive freeform fabrication process.