Combinatorial Approaches to Controlling Cell Behaviour and Tissue Formation in 3D via Rapid-Prototyping and Smart Scaffold Design

The understanding of fundamental phenomena involved in tissue engineering and regenerative medicine is continuously growing and leads to the demand for three-dimensional (3D) models that better represent tissue architecture and direct cells into the proper lineage for specific tissue repair. Porous 3D scaffolds are used in tissue engineering as templates to allow cell attachment and tissue formation. Scaffold design plays a central role in guiding cells to synthesize and maintain new tissues. While a number of techniques have been developed and are now in use for high-throughput screening of combinatorial factors involved in biotechnology in two-dimensions, high-throughput screening in 3D is still in its infancy. There is a broad interest in developing similar techniques to assess which variables are critical in designing 3D scaffolds to achieve proper and lasting tissue regeneration. We describe, herein, a number of studies adopting smart scaffold design and in vitro and in vivo analysis as the basis for 3D model systems for evaluating combinatorial factors influencing cell differentiation and tissue formation

Tissue attenuation characteristics of acoustic emission signals for wear and degradation of total hip arthoplasty implants

6-pagesRecent research has investigated the use of Acoustic Emission (AE) monitoring of patients with Total Joint Replacement (TJR) implants. This technique involves using a set of four passive ultrasonic receivers to monitor the acoustic events that are created when a TJR implant is articulated through a range of motion. Both ¬in-vitro and in-vivo monitoring of implants is possible. The soft-tissue attenuation characteristics are a very important aspect of how these two signal types are related as the aim of AE monitoring is to provide in-vivo diagnosis of implant degradation. This manuscript presents the results of in vivo monitoring of patients with Total Hip Replacement (THR) implants. The corresponding Bode plots are presented to approximate the soft tissue attenuation characteristics. Overall averages are taken across 45 patient data sets and each of the four sensors, located against the skin surface, from the greater trochanter to mid-femur. Each sensor set is also analysed individually to delineate different tissues attenuation at the different locations. These results of this research can be used to determine the maximum likely frequency of interest present on the skin surface during AE monitoring, even if higher frequencies may be observed in-vitro

Predictive Value of In Vitro and In Vivo Assays in Bone and Cartilage Repair -What do They Really Tell Us about the Clinical Performance?

The continuous increase of life expectancy leads to an expanding demand for repair and replacement of damaged and degraded organs and tissues. Recent completion of a first version of the human genome sequence is a great breakthrough for the field of pharmaceutics. It is conceivable that new developments in pharmaceutical research will result in a large number of novel and improved medicines. A similar development is expected in the field of biomaterials designed for bone and cartilage repair and replacement. Spinal fusions and repairs of bone defects caused by trauma, tumors, infections, biochemical disorders and abnormal skeletal development, are some examples of the frequently performed surgeries in the clinic. For most of these surgeries, there is a great need for bone graft substitutes. Similarly, the number of patients worldwide experiencing joint pain and loss of mobility through trauma or degenerative cartilage conditions is considerable, and yet, few approaches employed clinically are capable of restoring long-term function to damaged articular cartilage1, 2. Therefore, new materials and techniques need to be developed

Polymer Scaffolds Fabricated with Pore-Size Gradients as a Model for Studying the Zonal Organization within Tissue-Engineered Cartilage Constructs

The zonal organization of cells and extracellular matrix (ECM) constituents within articular cartilage is important for its biomechanical function in diarthroidal joints. Tissue-engineering strategies adopting porous three-dimensional (3D) scaffolds offer significant promise for the repair of articular cartilage defects, yet few approaches have accounted for the zonal structural organization as in native articular cartilage. In this study, the ability of anisotropic pore architectures to influence the zonal organization of chondrocytes and ECM components was investigated. Using a novel 3D fiber deposition (3DF) technique, we designed and produced 100% interconnecting scaffolds containing either homogeneously spaced pores (fiber spacing, 1 mm; pore size, about 680 µm in diameter) or pore-size gradients (fiber spacing, 0.5–2.0 mm; pore size range, about 200–1650 µm in diameter), but with similar overall porosity (about 80%) and volume fraction available for cell attachment and ECM formation. In vitro cell seeding showed that pore-size gradients promoted anisotropic cell distribution like that in the superficial, middle, and lower zones of immature bovine articular cartilage, irrespective of dynamic or static seeding methods. There was a direct correlation between zonal scaffold volume fraction and both DNA and glycosaminoglycan (GAG) content. Prolonged tissue culture in vitro showed similar inhomogeneous distributions of zonal GAG and collagen type II accumulation but not of GAG:DNA content, and levels were an order of magnitude less than in native cartilage. In this model system, we illustrated how scaffold design and novel processing techniques can be used to develop anisotropic pore architectures for instructing zonal cell and tissue distribution in tissue-engineered cartilage constructs

The effect of PEGT/PBT scaffold architecture on the composition of tissue engineered cartilage

A highly interconnecting and accessible pore network has been suggested as one of a number of prerequisites in the design of scaffolds for tissue engineering. In the present study, two processing techniques, compression-molding/particulate-leaching (CM), and 3D fiber deposition (3DF), were used to develop porous scaffolds from biodegradable poly(ethylene glycol)-terephthalate/ poly(butylene terephthalate) (PEGT/PBT) co-polymers with varying pore architectures. Three-dimensional micro-computed tomography (muCT) was used to characterize scaffold architectures and scaffolds were seeded with articular chondrocytes to evaluate tissue formation. Scaffold porosity ranged between 75% and 80%. Average pore size of tortuous CM scaffolds (182 pm) was lower than those of organized 3DF scaffolds (525 mum). The weight ratio of glycosaminoglycans (GAG)/DNA, as a measure of cartilage like tissue formation, did not change after 14 days of culture whereas, following subcutaneous implantation, GAG/DNA increased significantly and was significantly higher in 3DF constructs than in CM constructs, whilst collagen type II was present within both constructs. In conclusion, 3DF PEGT/PBT scaffolds create an environment in vivo that enhances cartilaginous matrix deposition and hold particular promise for treatment of articular cartilage defects. (C) 2004 Elsevier Ltd. All rights reserved

Light-Activated Decellularized Extracellular Matrix-Based Bioinks for Volumetric Tissue Analogs at the Centimeter Scale

Tissue engineering requires not only tissue-specific functionality but also a realistic scale. Decellularized extracellular matrix (dECM) is presently applied to the extrusion-based 3D printing technology. It has demonstrated excellent efficiency as bioscaffolds that allow engineering of living constructs with elaborate microarchitectures as well as the tissue-specific biochemical milieu of target tissues and organs. However, dECM bioinks have poor printability and physical properties, resulting in limited shape fidelity and scalability. In this study, new light-activated dECM bioinks with ruthenium/sodium persulfate (dERS) are introduced. The materials can be polymerized via a dityrosine-based cross-linking system with rapid reaction kinetics and improved mechanical properties. Complicated constructs with high aspect ratios can be fabricated similar to the geometry of the desired constructs with increased shape fidelity and excellent printing versatility using dERS. Furthermore, living tissue constructs can be safely fabricated with excellent tissue regenerative capacity identical to that of pure dECM. dERS may serve as a platform for a wider biofabrication window through building complex and centimeter-scale living constructs as well as supporting tissue-specific performances to encapsulated cells. This capability of dERS opens new avenues for upscaling the production of hydrogel-based constructs without additional materials and processes, applicable in tissue engineering and regenerative medicine. ? 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH11Nsciescopu