Nerve guidance conduits (NGCs) are tubular scaffolds that act as a bridge between the proximal and distal ends of the native nerve to facilitate the nerve regeneration. The application of NGCs is mostly limited to nerve defects less than 3 mm due to the lack of sufficient cells in the lumen. The development of drug-release-system-embedded NGCs has the potential to improve the nerve regeneration performance by providing long-term release of growth factors. However, most of the past works only focused on one type of drug release system, limiting the variation in drug release system types and features. Therefore, in this study, computer-aided design (CAD) models were constructed and Computational Fluid Dynamics (CFD) simulations were carried out to investigate the effect of growth factor transporting efficiency on different drug release systems. To overcome the challenges posed by the current NGCs in treating long nerve gap injuries (>4 cm), a novel ‘relay’ NGC design is first proposed in this paper and has the potential to improve the nerve regeneration performance to next level. The intermediate cavities introduced along the length of the multi-channel NGCs act as a relay to further enhance the cell concentrations or growth factor delivery as well as the regeneration performance. Four different drug release systems, namely, a single-layer microsphere system, a double-layer microsphere system, bulk hydrogel, and hydrogel film, were chosen for the simulation. The results show that the double-layer microsphere system achieves the highest growth factor volume fraction among all the drug release systems. For the single-layer microsphere system, growth factor concentration can be significantly improved by increasing the microsphere quantities and decreasing the diameter and adjacent distance of microspheres. Bulk hydrogel systems hold the lowest growth factor release performance, and the growth factor concentration monotonically increased with the increase of film thickness in the hydrogel film system. Owing to the easy fabrication of hydrogel film and the even distribution of growth factors, the hydrogel film system can be regarded as a strong candidate in drug-eluting NGCs. The use of computational simulations can be regarded as a guideline for the design and application of drug release systems, as well as a promising tool for further nerve tissue engineering study.

Related Publications:

[1] Zhou, J., Vijayavenkataraman, S. (2022). A ‘relay’ type Drug-eluting Nerve Guide Conduit: Computational Fluid Dynamics Modelling of the Drug Eluting Efficiency of Various Drug Release Systems. Pharmaceutics, 14(2), 230. https://doi.org/10.3390/pharmaceutics14020230

Urochordates are the closest invertebrate relative to humans and commonly referred to as tunicates, a name ascribed to their leathery outer “tunic”. The tunic is the outer covering of the organism which functions as the exoskeleton and is rich in carbohydrates and proteins. Invasive or fouling tunicates pose a great threat to the indigenous marine ecosystem and governments spend several hundred thousand dollars for tunicate management, considering the huge adverse economic impact it has on the shipping and fishing industries. In this work, the environmentally destructive colonizing tunicate species of Polyclinum constellatum was successfully identified in the coast of Abu Dhabi and methods of sustainably using it as wound-dressing materials, decellularized extra-cellular matrix (dECM) scaffolds for tissue engineering applications and bioinks for bioprinting of tissue constructs for regenerative medicine are proposed. The intricate three-dimensional nanofibrous cellulosic networks in the tunic remain intact even after the multi-step process of decellularization and lyophilization. The lyophilized dECM tunics possess excellent biocompatibility and remarkable tensile modulus of 3.85 ± 0.93 MPa compared to ∼0.1–1 MPa of other hydrogel systems. This work demonstrates the use of lyophilized tunics as wound-dressing materials, having outperformed the commercial dressing materials with a capacity of absorbing 20 times its weight in the dry state. This work also demonstrates the biocompatibility of dECM scaffold and dECM-derived bioink (3D bioprinting with Mouse Embryonic Fibroblasts (MEFs)). Both dECM scaffolds and bioprinted dECM-based tissue constructs show enhanced metabolic activity and cell proliferation over time. Sustainable utilization of dECM-based biomaterials from ecologically-destructive fouling tunicates proposed in this work helps preserve the marine ecosystem, shipping and fishing industries worldwide, and mitigate the huge cost spent for tunicate management.

Related Publications:

[1] Govindharaj, M., Soman, S.S., Al Hashemi, N.S., Vijayavenkataraman, S. (2022). Bioprinting of bioactive tissue scaffolds from ecologically-destructive fouling tunicates. Journal of Cleaner Production, 330, 129923. https://doi.org/10.1016/j.jclepro.2021.129923

[2] Govindharaj, M., Al Hashemi, N.S., Soman, S.S., Kanwar.S, Vijayavenkataraman, S.* (2022). 3D Bioprinting of human Mesenchymal Stem Cells in a novel tunic decellularized ECM bioink for Cartilage Tissue Engineering. Materialia, 101457. https://doi.org/10.1016/j.mtla.2022.101457

[3] Soman, S.S., Govindharaj, M., Al Hashemi, N.S., Vijayavenkataraman, S.* (2022). Bioprinting of human neural tissues using a sustainable marine tunicate-derived bioink for translational medicine applications. International Journal of Bioprinting, 8 (4), 604. http://doi.org/10.18063/ijb.v8i3.0061

Bioprinting three-dimensional (3D) tissue equivalents have progressed tremendously over the last decade. This technique is currently being employed to develop larger and more physiologic models, and of particular interest is to generate vasculature in engineered tissues to aid better perfusion and transport of nutrition. Having the advantage over manual culture systems by bringing together biological scaffold materials and cells in precise 3D spatial orientation, bioprinting could assist in placing endothelial cells in specific spatial locations within a 3D matrix to promote vessel formation at these predefined areas. Hence, the present study investigated the use of bioprinting to generate capillary network-like structures in tissue constructs. A bioink was developed in-house using collagen type 1 supplemented with xanthan gum (XG) as a thickening agent. Using a commercial bioprinter and collagen-XG based bioink, endothelial cells and fibroblasts were bioprinted in spatially defined patterns. 3D bioprinted constructs thus generated were stable, maintained structural shape and form, with good cell viability when evaluated using live and dead staining. MTS assay showed satisfactory cell proliferation. Post-print culture of the bioprinted tissues resulted in sprouting of endothelial cells to form interconnected networks of vascular cord-like structures. In addition, 3D bioprinter-assisted spatial placement of endothelial cells resulted in their organization to form capillary network-like structures at specific locations. Overall, our study results will help in the fabrication of pre-vascularized constructs using 3D bioprinting which in future, could potentially be used to fabricate vascularized tissue grafts for regenerative applications.

Related Publications:

[1] Muthusamy, S., Kannan, S., Lee, M., Vijayavenkataraman, S., Lu, W.F., Fuh, J. Y. H., Sriram, G., Cao, T. (2021). 3D Bioprinting and Microscale Organization of Vascularized Tissue Constructs using Collagen-based Bioink. Biotechnology and Bioengineering. https://doi.org/10.1002/bit.27838

Skin regeneration through tissue engineering combines biomaterials compatible with living cells to build a niche of limited duration that can support recapitulating reconstruction of the key features of native human skin. Reconstructed full thickness human skin is a promising platform for studying skin biology and assessing the safety and efficacy of cosmeceutical and clinical skin care products. Yet, as a target tissue for synthetic reconstruction, skin still carries a unique set of challenges, in spite of its well-defined 3D architecture, cell composition, and the constantly improving biocompatible synthetic materials now available to bioengineers. Commercial in vitro skin models are mostly prepared via manual deposition of cells into and onto a suitable extracellular matrix, which is usually difficult to mold into irregular shapes. There is an unmet need to develop a process for systematic 3D bioprinting of biomimetic skin that demonstrates full and efficient differentiation with high reproducibility and good viability, within a practical time frame. This study presents a full-thickness biomimetic skin equivalent fabricated by extrusion-based bioprinting. The 3D bioprinted full thickness skin model has cellular collagen dermal layer that rests on an acellular PCL/collagen scaffold, and is overlaid by sequential extrusion of bioprinted keratinocytes before airlifting for stratification and differentiation. The bioprinted skin constructs are compared with full-thickness human skin constructs produced by manual seeding of cells, in terms of cell proliferation, viability, histology, immunostaining, and barrier properties, to identify quantitative and qualitative differences. This study identifies an opportunity to streamline specific 3D bioprinting approaches to deliver full thickness reconstructed human skin in a reproducible, consistent and potentially scalable manner.

Over the past decade, 3D printing has been explored as a means of producing human skin mimics for applications such as cosmetics testing, drug screening and wound healing. When it comes to the post-processing step of bioprinting skin, choices in recent times have mainly been the static culture of constructs or the use of perfusion and rotatory bioreactors. In this study, we investigated the feasibility of the use of a Taylor-Couette bioreactor in the maturation of bioprinted dermal constructs. Here, a set of bioprinted dermal constructs were cultured in a Taylor-Couette bioreactor up to a period of 7 days and was simultaneously compared with statically cultured constructs. Evaluation of cellular viability using MTS Assay and LIVE/DEAD Assay showed the capability of the Taylor-Couette bioreactor for improving maturation of fibroblasts in the dermal constructs. Histology and immunostaining revealed no adverse effect of the dynamic culture environment on fibroblasts in the constructs. This study thus demonstrates the possibility of utilizing the Taylor-Couette bioreactor as an alternative means for the maturation of the dermal layer in the skin bioprinting pipeline.

Related Publications:

[1] Srinivas, R., Pooya, D., Vijayavenkataraman, S., Jia Heng, T., Anbu Mozhi, T., Robinson, K.S., Bin, W., Fuh, J. Y. H., Dicolandrea, T., Zhao, H., Birgit, E.L., Wang, C.H. (2021). Optimized construction of a full thickness human skin equivalent using 3D bioprinting and a PCL/collagen dermal scaffold. Bioprinting, e00123. https://doi.org/10.1016/j.bprint.2020.e00123

[2] Jia Heng, T., Anbu Mozhi, T., Pooya, D., Srinivas, R., Vijayavenkataraman, S.,Yang, Q., Dicolandrea, T., Zhao, H., Fuh, J. Y. H., Liou, Y.C., Wang, C.H. (2019). Investigation of the Application of a Taylor-Couette Bioreactor in the Post-processing of Bioprinted Human Dermal Tissue. Biochemical Engineering Journal 151, 107317. https://doi.org/10.1016/j.bej.2019.107317

[3] Yan, W.C., Pooya, D., Vijayavenkataraman, S., Tian, Y., Ng, W.C., Fuh, J. Y. H., Robinson, K.S., & Wang, C.H. (2018). 3D-bioprinting of skin tissue: From pre-processing to final product evaluation. Advanced Drug Delivery Reviews, 132, 270-295. https://doi.org/10.1016/j.addr.2018.07.016

[4] Vijayavenkataraman, S., Lu, W. F., & Fuh, J. Y. H. (2016). 3D bioprinting of skin: a state-of-the-art review on modelling, materials, and processes. Biofabrication, 8(3), 032001.

Biomimetic scaffold design is gaining attention in the field of tissue engineering lately. Recently, triply periodic minimal surfaces (TPMSs) have attracted the attention of tissue engineering scientists for fabrication of biomimetic porous scaffolds. TPMS scaffolds offer several advantages, which include a high surface area to volume ratio, less stress concentration, and increased permeability compared to the traditional lattice structures, thereby aiding in better cell adhesion, migration, and proliferation. In literature, several design methods for TPMS scaffolds have been developed, which considered some of the important tissue-specific requirements, such as porosity, Young’s modulus, and pore size. However, only one of the requirements of a tissue engineering scaffold was investigated in these studies, and not all of the requirements were satisfied simultaneously. In this work, we develop a design method for TPMS sheet scaffolds, which is able to satisfy multiple requirements including the porosity, Young’s modulus, and pore size, based on a parametric optimization approach. Three TPMSs, namely, the primitive (P), gyroid (G), and diamond (D) surfaces, with cubic symmetry are considered. The versatility of the proposed design method is demonstrated by three different applications, namely, tissue-specific scaffolds, scaffolds for stem cell differentiation, and functionally graded scaffolds with biomimetic functional gradients.

Stress shielding is one of the main problems that lead to bone resorption and revision surgery after implantation. Most of the commercially available metallic non-porous bone implants have a much greater stiffness than the native human bones and are prone to cause stress-shielding. With an open cell structure and intricate architecture, hyperbolic minimal surfaces offer several advantages such as less stress concentration, high permeability and high surface area to volume ratio, thus providing an ideal environment for cell adhesion, migration, and proliferation. This paper explores the use of porous bone implant design based on Triply Periodic Minimal Surfaces (TPMS) which is additively manufactured with ceramic material (Alumina) using Lithography-based Ceramics Manufacturing (LCM) technology. A total of 12 different primitive surface structure unit cells with pore size in the range of 500–1000 μm and porosity above 50% were considered. This is one of the earliest studies reporting the 3D printing of TPMS-based structures using ceramic material. Our results suggest that the choice of material and a porous TPMS-based design led to fabrication of structures with a much lesser compressive modulus comparable with the native bone and hence could potentially be adopted for bone implant design to mitigate the stress-shielding effect.

Related Publications:

[1] Vijayavenkataraman, S., Zhang, L., Zhang, S., Fuh, J. Y. H., & Lu, W. F. (2018). Triply Periodic Minimal Surfaces Sheet Scaffolds for Tissue Engineering Applications: An Optimization Approach towards Biomimetic Scaffold Design. ACS Applied Bio Materials, 1 (2), 259-269. DOI: 10.1021/acsabm.8b00052

[2] Vijayavenkataraman, S., Lai, Y.K., & Lu, W. F. (2020). 3D-printed ceramic triply periodic minimal surface structures for design of functionally graded bone implants. Materials & Design, 108602. https://doi.org/10.1016/j.matdes.2020.108602

3D printing is one of the most innovative technologies in the current era, while 3D bioprinting is revolutionizing the medical technology industry. Bioprinting technology could help overcome the limitations of the current tissue engineering methods, including the problem of longer waiting times for treatment (especially with organ transplants). While fighting infectious diseases had been the main focus of medicine in the past, dealing with the consequences of a predominantly ageing population will be the priority in the future and bioprinting is a promising technology to tackle this challenge effectively. Bioprinting will not only cater the needs of ageing population but also in the field of paediatrics, where the bioprinted tissue or organ should possess the capability to grow with the patient. As researchers around the world are working on 3D bioprinting of tissues and organs, companies are burgeoning all over, making and marketing new bioprinters. While the research and commercialization are moving at such a rapid pace, the issues surrounding the technology, in terms of ethics, policies, regulations and social acceptance, are not addressed in commensurate. Identifying the ELSA (Ethical Legal and Social Aspects) concerns of this technology at an early stage is not only part of our social responsibility but also in the interest of the future of the technology itself. This paper reviews and foresees these challenges with pragmatism, thereby creating awareness to the researchers and policy makers and to urge a positive course of action in the foreseeable future. The significance of this work will be to address a broad audience, associated with this technology, from scientists to businessmen, engineers to clinicians, laymen to lawmakers. A ‘complete’ policy approach for this technology is recommended rather than a ‘piecemeal’ approach of the various constituents of this technology. An effective course of action will be to setup a multi-disciplinary international panel to work on the policy framework, which will look in to both ‘hard’ and ‘soft’ impacts of 3D bioprinting, the associated ethical challenges, legal measures including patenting and effective controls to prevent the misuse, as well as the social aspects encompassing the cultural and religious differences which accounts for the success of this technology. Setting up national level panels to assess the risk-benefit analysis, taking into consideration the cultural and religious view of its population and other legal and social aspects, might be a good starting point.

Related Publications:

[1] Vijayavenkataraman, S., Lu, W. F., & Fuh, J. Y. H. (2016). 3D bioprinting–An Ethical, Legal and Social Aspects (ELSA) framework. Bioprinting, 1, 11-21. https://doi.org/10.1016/j.bprint.2016.08.001

[1] Computational Design and Optimization of Nerve Guide Conduits

Nerve guidance conduits (NGCs) are tubular tissue engineering scaffolds used for nerve regeneration. The poor mechanical properties and porosity have always compromised their performances for guiding and supporting axonal growth. Therefore, in order to improve the properties of NGCs, the computational design approach was adopted to investigate the effects of different NGC structural features on their various properties, and finally, design an ideal NGC with mechanical properties matching human nerves and high porosity and permeability. Three common NGC designs, namely hollow luminal, multichannel, and microgrooved, were chosen in this study. Simulations were conducted to study the mechanical properties and permeability. The results show that pore size is the most influential structural feature for NGC tensile modulus. Multichannel NGCs have higher mechanical strength but lower permeability compared to other designs. Square pores lead to higher permeability but lower mechanical strength than circular pores. The study finally selected an optimized hollow luminal NGC with a porosity of 71% and a tensile modulus of 8 MPa to achieve multiple design requirements. The use of computational design and optimization was shown to be promising in future NGC design and nerve tissue engineering research.

Related Publication:

[1] Zhang, S., Vijayavenkataraman, S., Chong, G.L., Fuh, J. Y. H., & Lu, W. F. (2019). Computational Design and Optimization of Nerve Guidance Conduits for Improved Mechanical Properties and Permeability. ASME Journal of Biomechanical Engineering, 141(5), 051007. https://doi.org/10.1115/1.4043036

[2] Design of Three-Dimensional Scaffolds with Tunable Matrix Stiffness

Tissue engineering is a multi-disciplinary area of research bringing together the fields of engineering and life sciences with the aim of fabricating tissue constructs aiding in the regeneration of damaged tissues and organs. Scaffolds play a key role in tissue engineering, acting as the templates for tissue regeneration and guiding the growth of new tissue. The use of stem cells in tissue engineering and regenerative medicine becomes indispensable, especially for applications involving successful long-term restoration of continuously self-renewing tissues, such as skin. The differentiation of stem cells is controlled by a number of cues, of which the nature of the substrate and its innate stiffness plays a vital role in stem cell fate determination. By tuning the substrate stiffness, the differentiation of stem cells can be directed to the desired lineage. Many studies on the effect of substrate stiffness on stem cell differentiation has been reported, but most of those studies are conducted with two-dimensional (2D) substrates. However, the native in vivo tissue microenvironment is three-dimensional (3D) and life science researchers are moving towards 3D cell cultures. Porous 3D scaffolds are widely used by the researchers for 3D cell culture and the properties of such scaffolds affects the cell attachment, proliferation, and differentiation. To this end, the design of porous scaffolds directly influences the stem cell fate determination. There exists a need to have 3D scaffolds with tunable stiffness for directing the differentiation of stem cells into the desired lineage. Given the limited number of biomaterials with all the desired properties, the design of the scaffolds themselves could be used to tune the matrix stiffness. This paper is an in silico study, investigating the effect of various scaffold parameter, namely fiber width, porosity, number of unit cells per layer, number of layers, and material selection, on the matrix stiffness, thereby offering a guideline for design of porous tissue engineering scaffolds with tunable matrix stiffness for directing stem cell lineage specification.

Related Publication:

[1] Vijayavenkataraman, S., Shuo, Z., Fuh, J. Y., & Lu, W. F. (2017). Design of Three-Dimensional Scaffolds with Tunable Matrix Stiffness for Directing Stem Cell Lineage Specification: An In Silico Study. Bioengineering, 4(3), 66. https://doi.org/10.3390/bioengineering4030066