Biomanufacturing: A US-China National Science Foundation–Sponsored Workshop

3D printing- creating a blueprint for the future of orthopedics: Current concept review and the road ahead!

The use of 3D printing in Orthopedics is set to transform the way surgeries are planned and executed. The development of X rays and later the CT scan and MRI enabled surgeons to understand the anatomy and condition better and helped plan surgeries on images obtained. 3DGraphy a term used for 3D printed orthopedic patient models and Jigs has gone a step further by providing surgeons with a physical copy of the patient's affected part that can not only be seen but also felt and moved around spatially. Similarly 3D printed Jigs are patient specific devices that are used to ensure optimal screw trajectory and implant placement with minimal exposure. While the use of 3D printed models and Jigs have now become routine, a similar revolution is happening in the field of designing and printing patient specific implants. Metal printing along with enhanced capability to print other biocompatible materials like PEEK and PLA is likely to improve the current implant manufacturing process. On the horizon is another interesting development related to this field - 3D Bio printing. Printing human tissues and organs is considered the final frontier and impressive strides have been made in printing bone graft substitutes and cartilage like material. This paper is an overview of all the current developments and the road ahead in this invigorating field.

Essential design considerations for the resazurin reduction assay to noninvasively quantify cell expansion within perfused extracellular matrix scaffolds

Precise measurement of cellularity within bioartificial tissues and extracellular matrix (ECM) scaffolds is necessary to augment rigorous characterization of cellular behavior, as accurate benchmarking of tissue function to cell number allows for comparison of data across experiments and between laboratories. Resazurin, a soluble dye that is reduced to highly fluorescent resorufin in proportion to the metabolic activity of a cell population, is a valuable, noninvasive tool to measure cell number. We investigated experimental conditions in which resazurin reduction is a reliable indicator of cellularity within three-dimensional (3D) ECM scaffolds. Using three renal cell populations, we demonstrate that correlation of viable cell numbers with the rate of resorufin generation may deviate from linearity at higher cell densities, lower resazurin working volumes, or longer incubation times that all contribute to depleting the pool of resazurin. In conclusion, while the resazurin reduction assay provides a powerful, noninvasive readout of metrics enumerating cellularity and growth within ECM scaffolds, assay conditions may strongly influence its applicability for accurate quantification of cell number. The approach and methodological recommendations presented herein may be used as a guide for application-specific optimization of this assay to obtain rigorous and accurate measurement of cellular content in bioengineered tissues.

Characterization of tissue scaffolds for time-dependent biotransport criteria - a novel computational procedure

This study aims to establish a new computational framework that allows modeling transient oxygen diffusion in tissue scaffolds more efficiently. It has been well known that the survival of cells strongly relies on continuous oxygen/nutrient supply and metabolite removal. With optimal design in scaffold architecture, its ability to sustain long distance oxygen supply could be improved considerably. In this study, finite element based homogenization procedure is first used to characterize the initial effective biotransport properties in silico. These initial properties are proper indicators to prediction of the on-going performance of tissue scaffolds over time. The transient model by adopting an edge-based smoothed finite element method with combination of mass-redistributed method is then established to more efficiently simulate the transient oxygen transfer process in tissue scaffolds. The proposed new method allows large time steps to model the oxygen diffusion process without losing numerical accuracy, thereby enhancing the computational efficiency significantly, in particular for the design optimization problems which typically require numerous analysis iterations. A number of different scaffold designs are examined either under net diffusion without cell seeding, or under cellular oxygen/nutrient uptake with or without considering cell viability. The association between the homogenized effective diffusivity of net scaffold microstructures and corresponding transient diffusion and time-dependent cellular activities is divulged. This study provides some insights into scaffold design.

Design and preparation of polymeric scaffolds for tissue engineering

Polymeric scaffolds for tissue engineering can be prepared with a multitude of different techniques. Many diverse approaches have recently been under development. The adaptation of conventional preparation methods, such as electrospinning, induced phase separation of polymer solutions or porogen leaching, which were developed originally for other research areas, are described. In addition, the utilization of novel fabrication techniques, such as rapid prototyping or solid free-form procedures, with their many different methods to generate or to embody scaffold structures or the usage of self-assembly systems that mimic the properties of the extracellular matrix are also described. These methods are reviewed and evaluated with specific regard to their utility in the area of tissue engineering.

Tissue engineering: A new vista in periodontal regeneration

Tissue engineering is a highly promising field of reconstructive biology that draws on recent advances in medicine, surgery, molecular and cellular biology, polymer chemistry, and physiology. The objective of using tissue engineering as therapeutic application has been to harness its ability to exploit selected and primed cells together with an appropriate mix of regulatory factors, to allow growth and specialization of cells and matrix. The authors reviewed controlled clinical trials which also included histological studies that evaluated the potential of tissue engineering as a clinical tool in regeneration. PubMed/MEDLINE databases were searched for studies up to and including June 2010 to identify appropriate articles. A comprehensive search was designed, and the articles were independently screened for eligibility. Articles with authentic controls and proper randomization and pertaining specifically to their role in periodontal regeneration were included. Studies demonstrated that the periodontal regeneration with the use of combination of tissue engineered products with an osteoconductive matrix improve the beneficial effect of these materials by accelerating cellular in growth and revascularization of the wound site. Studies have suggested the use of rh Platelet-derived growth factor + beta tricalcium phosphate for regeneration of the periodontal attachment apparatus in combination with collagen membranes as an acceptable alternative to connective tissue graft for covering gingival recession defects. The studies concluded that growth factors promote true regeneration of the periodontal attachment apparatus and the use of combination protein therapeutics which is commercially available can provide more predictable, faster, less invasive, less traumatic, and efficient outcome for the patient.

Biofabrication of a three-dimensional liver micro-organ as an in vitro drug metabolism model

In their normal in vivo matrix milieu, tissues assume complex well-organized three-dimensional architectures. Therefore, the primary aim in the tissue engineering design process is to fabricate an optimal analog of the in vivo scenario. This challenge can be addressed by applying emerging layered biofabrication approaches in which the precise configuration and composition of cells and bioactive matrix components can recapitulate the well-defined three-dimensional biomimetic microenvironments that promote cell-cell and cell-matrix interactions. Furthermore, the advent of and refinements in microfabricated systems can present physical and chemical cues to cells in a controllable and reproducible fashion unmatched with conventional cultures, resulting in the precise construction of engineered biomimetic microenvironments on the cellular length scale in geometries that are readily parallelized for high throughput in vitro models. As such, the convergence of layered solid freeform fabrication (SFF) technologies along with microfabrication techniques enables the creation of a three-dimensional micro-organ device to serve as an in vitro platform for cell culture, drug screening or to elicit further biological insights, particularly for NASA's interest in a flight-suitable high-fidelity microscale platform to study drug metabolism in space and planetary environments. The proposed model in this paper involves the combinatorial setup of an automated syringe-based, layered direct cell writing bioprinting process with micro-patterning techniques to fabricate a microscale in vitro device housing a chamber of bioprinted three-dimensional liver cell-encapsulated hydrogel-based tissue constructs in defined design patterns that biomimic the cell's natural microenvironment for enhanced biological functionality. In order to assess the structural formability and biological feasibility of such a micro-organ, reproducibly fabricated tissue constructs were biologically characterized for liver cell-specific function. Another key facet of the in vivo microenvironment that was recapitulated with the in vitro system included the necessary dynamic perfusion of the three-dimensional microscale liver analog with cells probed for their collective drug metabolic function and suitability as a drug metabolism model. This paper details the principles and methods that undergird the direct cell writing biofabrication process development and adaptation of microfluidic devices for the creation of a drug screening model, thereby establishing a novel drug metabolism study platform for NASA's interest to adopt a microfluidic microanalytical device with an embedded three-dimensional microscale liver tissue analog to assess drug pharmacokinetic profiles in planetary environments.

Bioprinting Endothelial Cells With Alginate for 3D Tissue Constructs

Advanced solid freeform fabrication (SFF) techniques have been an interest for constructing tissue engineered polymeric scaffolds because of its repeatability and capability of high accuracy in fabrication resolution at the scaffold macro- and microscales. Among many important scaffold applications, hydrogel 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. Such fabrication techniques not only enable the reconstruction of scaffolds with accurate anatomical architectures but also enable the ability to incorporate bioactive species such as growth factors, proteins, and living cells. This paper presents a bioprinting system designed for the freeform fabrication of porous alginate scaffolds with encapsulated endothelial cells. The bioprinting fabrication system includes a multinozzle deposition system that utilizes SFF techniques and a computer-aided modeling system capable of creating heterogeneous tissue scaffolds. The manufacturing process is biologically compatible and is capable of functioning at room temperature and relatively low pressures to reduce the fluidic shear forces that could deteriorate biologically active species. The deposition system resolution is 10 μm in the three orthogonal directions XYZ and has minimum velocity of 100 μm/s. The ideal concentrations of sodium alginate and calcium chloride were investigated to determine a viable bioprinting process. The results indicated that the suitable fabrication parameters were 1.5% (w/v) sodium alginate and 0.5% (w/v) calcium chloride. Degradation studies via mechanical testing showed a decrease in the elastic modulus by 35% after 3 weeks. Cell viability studies were conducted on the cell encapsulated scaffolds for validating the bioprinting process and determining cell viability of 83%. This work exhibits the potential use of accurate cell placement for engineering complex tissue regeneration using computer-aided design systems.

Biofabrication: a 21st century manufacturing paradigm

Biofabrication can be defined as the production of complex living and non-living biological products from raw materials such as living cells, molecules, extracellular matrices, and biomaterials. Cell and developmental biology, biomaterials science, and mechanical engineering are the main disciplines contributing to the emergence of biofabrication technology. The industrial potential of biofabrication technology is far beyond the traditional medically oriented tissue engineering and organ printing and, in the short term, it is essential for developing potentially highly predictive human cell- and tissue-based technologies for drug discovery, drug toxicity, environmental toxicology assays, and complex in vitro models of human development and diseases. In the long term, biofabrication can also contribute to the development of novel biotechnologies for sustainable energy production in the future biofuel industry and dramatically transform traditional animal-based agriculture by inventing 'animal-free' food, leather, and fur products. Thus, the broad spectrum of potential applications and rapidly growing arsenal of biofabrication methods strongly suggests that biofabrication can become a dominant technological platform and new paradigm for 21st century manufacturing. The main objectives of this review are defining biofabrication, outlining the most essential disciplines critical for emergence of this field, analysis of the evolving arsenal of biofabrication technologies and their potential practical applications, as well as a discussion of the common challenges being faced by biofabrication technologies, and the necessary conditions for the development of a global biofabrication research community and commercially successful biofabrication industry.

Neurovascular modeling: small-batch manufacturing of silicone vascular replicas

BACKGROUND AND PURPOSE

Realistic, population based cerebrovascular replicas are required for the development of neuroendovascular devices. The objective of this work was to develop an efficient methodology for manufacturing realistic cerebrovascular replicas.

MATERIALS AND METHODS

Brain MR angiography data from 20 patients were acquired. The centerline of the vasculature was calculated, and geometric parameters were measured to describe quantitatively the internal carotid artery (ICA) siphon. A representative model was created on the basis of the quantitative measurements. Using this virtual model, we designed a mold with core-shell structure and converted it into a physical object by fused-deposit manufacturing. Vascular replicas were created by injection molding of different silicones. Mechanical properties, including the stiffness and luminal coefficient of friction, were measured.

RESULTS

The average diameter, length, and curvature of the ICA siphon were 4.15 +/- 0.09 mm, 22.60 +/- 0.79 mm, and 0.34 +/- 0.02 mm(-1) (average +/- standard error of the mean), respectively. From these image datasets, we created a median virtual model, which was transformed into a physical replica by an efficient batch-manufacturing process. The coefficient of friction of the luminal surface of the replica was reduced by up to 55% by using liquid silicone rubber coatings. The modulus ranged from 0.67 to 1.15 MPa compared with 0.42 MPa from human postmortem studies, depending on the material used to make the replica.

CONCLUSIONS

Population-representative, smooth, and true-to-scale silicone arterial replicas with uniform wall thickness were successfully built for in vitro neurointerventional device-testing by using a batch-manufacturing process.

Effects of dispensing pressure and nozzle diameter on cell survival from solid freeform fabrication-based direct cell writing

Novel technologies are emerging that incorporate cells as part of the building blocks for various biomanufacturing processes, such as solid freeform fabricated tissue constructs for tissue regeneration, three-dimensional pharmacokinetic models, cell-based microelectromechanical systems, sensors, and microfluidic devices. However, the effects of these biomanufacturing processes on cells have not been fully studied. This paper examines the effect of solid freeform fabrication-based direct cell writing process, focusing on dispensing pressure and nozzle size, on the viability and functional behavior of HepG2 cells encapsulated within alginate. Our experimental results revealed a process-induced mechanical damage to cell membrane integrity, causing a quantifiable loss in cell viability due to incremental increases and decreases in the studied process parameters of dispensing pressure and nozzle size, respectively. The experimental results also suggested that cells may require a recovery period following direct cell writing biofabrication. The general finding of this study may be applicable to freeform fabrication of cell-based tissue constructs and three-dimensional biological models.

Translation from Research to Applications

The article summarizes the collective views expressed at the fourth session of the workshop Tissue Engineering--the Next Generation, which was devoted to the translation of results of tissue engineering research into applications. Ernst Hunziker described the paradigm of a dual translational approach, and argued that tissue engineering should be guided by the dimensions and physiological setting of the bodily compartment to be repaired. Myron Spector discussed collagen-glycosaminoglycan (GAG) scaffolds for musculoskeletal tissue engineering. Jeanette Libera focused on the biological and clinical aspects of cartilage tissue engineering, and described a completely autologous procedure for engineering cartilage using the patient's own chondrocytes and blood serum. Arthur Gertzman reviewed the applications of allograft tissues in orthopedic surgery, and outlined the potential of allograft tissues as models for biological and medical studies. Savio Woo discussed a list of functional tissue engineering approaches designed to restore the biochemical and biomechanical properties of injured ligaments and tendons to be closer to that of the normal tissues. Specific examples of using biological scaffolds that have chemoattractants as well as growth factors with unique contact guidance properties to improve their healing process were shown. Anthony Ratcliffe discussed the translation of the results of research into products that are profitable and meet regulatory requirements. Michael Lysaght challenged the proposition that commercial and clinical failures of early tissue engineering products demonstrate a need for more focus on basic research. Arthur Coury described the evolution of tissue engineering products based on the example of Genzyme, and how various definitions of success and failure can affect perceptions and policies relative to the status and advancement of the field of tissue engineering.