Bioreactor cultivation of anatomically shaped human bone grafts

Spatial Growth Factor Delivery for 3D Bioprinting of Vascularized Bone with Adipose-Derived Stem/Stromal Cells as a Single Cell Source

Encapsulating multiple growth factors within a scaffold enhances the regenerative capacity of engineered bone grafts through their localization and controls the spatiotemporal release profile. In this study, we bioprinted hybrid bone grafts with an inherent built-in controlled growth factor delivery system, which would contribute to vascularized bone formation using a single stem cell source, human adipose-derived stem/stromal cells (ASCs) in vitro. The strategy was to provide precise control over the ASC-derived osteogenesis and angiogenesis at certain regions of the graft through the activity of spatially positioned microencapsulated BMP-2 and VEGF within the osteogenic and angiogenic bioink during bioprinting. The 3D-bioprinted vascularized bone grafts were cultured in a perfusion bioreactor. Results proved localized expression of osteopontin and CD31 by the ASCs, which was made possible through the localized delivery activity of the built-in delivery system. In conclusion, this approach provided a methodology for generating off-the-shelf constructs for vascularized bone regeneration and has the potential to enable single-step, in situ bioprinting procedures for creating vascularized bone implants when applied to bone defects.

Personalized Volumetric Tissue Generation by Enhancing Multiscale Mass Transport through 3D Printed Scaffolds in Perfused Bioreactors

Engineered tissues provide an alternative to graft material, circumventing the use of donor tissue such as autografts or allografts and non-physiological synthetic implants. However, their lack of vasculature limits the growth of volumetric tissue more than several millimeters thick which limits their success post-implantation. Perfused bioreactors enhance nutrient mass transport inside lab-grown tissue but remain poorly customizable to support the culture of personalized implants. Here, a multiscale framework of computational fluid dynamics (CFD), additive manufacturing, and a perfusion bioreactor system are presented to engineer personalized volumetric tissue in the laboratory. First, microscale 3D printed scaffold pore geometries are designed and 3D printed to characterize media perfusion through CFD and experimental fluid testing rigs. Then, perfusion bioreactors are custom-designed to combine 3D printed scaffolds with flow-focusing inserts in patient-specific shapes as simulated using macroscale CFD. Finally, these computationally optimized bioreactor-scaffold assemblies are additively manufactured and cultured with pre-osteoblast cells for 7, 20, and 24 days to achieve tissue growth in the shape of human calcaneus bones of 13 mL volume and 1 cm thickness. This framework enables an intelligent model-based design of 3D printed scaffolds and perfusion bioreactors which enhances nutrient transport for long-term volumetric tissue growth in personalized implant shapes. The novel methods described here are readily applicable for use with different cell types, biomaterials, and scaffold microstructures to research therapeutic solutions for a wide range of tissues.

Manufacturing artificial bone allografts: a perspective

Bone grafts have traditionally come from four sources: the patients' own tissue (autograft), tissue from a living or cadaveric human donor (allograft), animal donors (xenograft) and synthetic artificial biomaterials (ceramics, cement, polymers, and metal). However, all of these have advantages and drawbacks. The most commercially successful bone grafts so far are allografts, which hold 57% of the current bone graft market; however, disease transmission and scarcity are still significant drawbacks limiting their use. Tissue-engineered grafts have great potential, in which human stem cells and synthetical biomaterials are combined to produce bone-like tissue in vitro, but this is yet to be approved for widespread clinical practice. It is hypothesised that artificial bone allografts can be mass-manufactured to replace conventional bone allografts through refined bone tissue engineering prior to decellularisation. This review article aims to review current literature on (1) conventional bone allograft preparation; (2) bone tissue engineering including the use of synthetic biomaterials as bone graft substitute scaffolds, combined with osteogenic stem cells in vitro; (3) potential artificial allograft manufacturing processes, including mass production of engineered bone tissue, osteogenic enhancement, decellularisation, sterilisation and safety assurance for regulatory approval. From these assessments, a practical route map for mass production of artificial allografts for clinical use is proposed.

Developing a novel resorptive hydroxyapatite-based bone substitute for over-critical size defect reconstruction: physicochemical and biological characterization and proof of concept in segmental rabbit's ulna reconstruction

The aim of this study was to develop novel hydroxyapatite (HAP)-based bioactive bone replacement materials for segmental osteotomy reconstruction. Customized three-dimensional (3D) bone construct was manufactured from nanohydroxyapatite (nHAP) with poly(lactide-co-glycolide) (PLGA) coating using 3D models derived from the computed tomography (CT) scanning of the rabbit's ulna and gradient 3D printing of the bone substitute mimicking the anatomical shape of the natural bone defect. Engineered construct revealed adequate micro-architectural design for successful bone regeneration having a total porosity of 64% and an average pore size of 256 μm. Radiography and micro-CT analysis depicted new bone apposition through the whole length of the reconstructed ulna with a small area of non-resorbed construct in the central area of defect. Histological analysis revealed new bone formation with both endochondral and endesmal type of ossification. Immunohistochemistry analysis depicted the presence of bone formation indicators - bone morphogenetic protein (BMP), osteocalcin (OCN) and osteopontin (OPN) within newly formed bone. Manufactured personalized construct acts as a "smart" responsive biomaterial capable of modulating the functionality and potential for the personalized bone reconstruction on a clinically relevant length scale.

Fabrication of Decellularized Engineered Extracellular Matrix through Bioreactor-Based Environment for Bone Tissue Engineering

Extracellular matrix (ECM)-contained grafts can be achieved by decellularization of native bones or synthetic scaffolds. Limitations associated with harvesting the native bone has raised interest in preparing in vitro ECM bioscaffold for bone tissue engineering. Here, we intend to develop an ECM-contained construct via decellularizing an engineered gelatin-coated β-tricalcium phosphate (gTCP) scaffold. In order to find an optimal protocol for decellularization of cell-loaded gTCP scaffolds, they were seeded with buccal fat pad-derived stem cells. Then, four decellularization protocols including sodium dodecyl sulfate, trypsin, Triton X-100, and combined solution methods were compared for the amounts of residual cells and remnant collagen and alteration of scaffold structure. Then, the efficacy of the selected protocol in removing cells from gTCP scaffolds incubated in a rotating and perfusion bioreactor for 24 days was evaluated and compared with static condition using histological analysis. Finally, decellularized scaffolds, reloaded with cells, and their cytotoxicity and osteoinductive capability were evaluated. Complete removal of cells from gTCP scaffolds was achieved from all protocols. However, treatment with Triton X-100 showed significantly higher amount of remnant ECM. Bioreactor-incubated scaffolds possessed greater magnitude of ECM proteins including collagen and glycosaminoglycans. Reseeding the decellularized scaffolds also represented higher osteoinductivity of bioreactor-based scaffolds. Application of Triton X-100 as decellularization protocol and usage of bioreactors are suggested as a suitable technique for designing ECM-contained grafts for bone tissue engineering.

Regenerative Potential of Mandibular Condyle Cartilage and Bone Cells Compared to Costal Cartilage Cells When Seeded in Novel Gelatin Based Hydrogels

The field of temporomandibular joint (TMJ) condyle regeneration is hampered by a limited understanding of the phenotype and regeneration potential of cells in mandibular condyle cartilage. It has been shown that chondrocytes derived from hyaline and costal cartilage exhibit a greater chondro-regenerative potential in vitro than those from mandibular condylar cartilage. However, our recent in vivo studies suggest that mandibular condyle cartilage cells do have the potential for cartilage regeneration in osteochondral defects, but that bone regeneration is inadequate. The objective of this study was to determine the regeneration potential of cartilage and bone cells from goat mandibular condyles in two different photocrosslinkable hydrogel systems, PGH and methacrylated gelatin, compared to the well-studied costal chondrocytes. PGH is composed of methacrylated poly(ethylene glycol), gelatin, and heparin. Histology, biochemistry and unconfined compression testing was performed after 4 weeks of culture. For bone derived cells, histology showed that PGH inhibited mineralization, while gelatin supported it. For chondrocytes, costal chondrocytes had robust glycosaminoglycan (GAG) deposition in both PGH and gelatin, and compression properties on par with native condylar cartilage in gelatin. However, they showed signs of hypertrophy in gelatin but not PGH. Conversely, mandibular condyle cartilage chondrocytes only had high GAG deposition in gelatin but not in PGH. These appeared to remain dormant in PGH. These results show that mandibular condyle cartilage cells do have innate regeneration potential but that they are more sensitive to hydrogel material than costal cartilage cells.

Bioreactor cultivation condition for engineered bone tissue: Effect of various bioreactor designs on extra cellular matrix synthesis

Dynamic-based systems are bio-designed in order to mimic the micro-environments of the bone tissue. There is limited direct comparison between perfusion and perfusion-rotation forces in designing a bioreactor. Hence, in current study, we aimed to compare given bioreactors for bone regeneration. Two types of bioreactors including rotating & perfusion and perfusion bioreactors were designed. Mesenchymal stem cells derived from buccal fat pad were loaded on a gelatin/β-Tricalcium phosphate scaffold. Cell-scaffold constructs were subjected to different treatment condition and place in either of the bioreactors. Effect of different dynamic conditions on cellular behavior including cell proliferation, cell adhesion, and osteogenic differentiation were assessed. Osteogenic assessment of scaffolds after 24 days revealed that rotating & perfusion bioreactor led to significantly higher expression of OCN and RUNX2 genes and also greater amount of ALP and collagen I protein production compared to static groups and perfusion bioreactor. Observation of cellular sheets which filled the scaffold porosities in SEM images, approved the better cell responses to rotating & perfusion forces of the bioreactor. The outcomes demonstrated that rotating & perfusion bioreactor action on bone regeneration is much preferable than perfusion bioreactor. Therefore, it seems that exertion of multi-stimuli is more effective for bone engineering.

Mimetic Hierarchical Approaches for Osteochondral Tissue Engineering

In order to engineer biomimetic osteochondral (OC) construct, it is necessary to address both the cartilage and bone phase of the construct, as well as the interface between them, in effect mimicking the developmental processes when generating hierarchical scaffolds that show gradual changes of physical and mechanical properties, ideally complemented with the biochemical gradients. There are several components whose characteristics need to be taken into account in such biomimetic approach, including cells, scaffolds, bioreactors as well as various developmental processes such as mesenchymal condensation and vascularization, that need to be stimulated through the use of growth factors, mechanical stimulation, purinergic signaling, low oxygen conditioning, and immunomodulation. This chapter gives overview of these biomimetic OC system components, including the OC interface, as well as various methods of fabrication utilized in OC biomimetic tissue engineering (TE) of gradient scaffolds. Special attention is given to addressing the issue of achieving clinical size, anatomically shaped constructs. Besides such neotissue engineering for potential clinical use, other applications of biomimetic OC TE including formation of the OC tissues to be used as high-fidelity disease/healing models and as in vitro models for drug toxicity/efficacy evaluation are covered.

HIGHLIGHTS

Biomimetic OC TE uses "smart" scaffolds able to locally regulate cell phenotypes and dual-flow bioreactors for two sets of conditions for cartilage/bone Protocols for hierarchical OC grafts engineering should entail mesenchymal condensation for cartilage and vascular component for bone Immunomodulation, low oxygen tension, purinergic signaling, time dependence of stimuli application are important aspects to consider in biomimetic OC TE.

Bone Marrow Stromal Stem Cells in Tissue Engineering and Regenerative Medicine

Bone marrow stromal stem cells (BMSCs) are adult multipotent cells, which have the potential to differentiate into cell types of mesodermal origin, namely osteocytes, adipocytes, and chondrocytes. Due to their accessibility and expansion potential, BMSCs have historically held therapeutic promise in tissue engineering and regenerative medicine applications. More recently, it has been demonstrated that not only can bone marrow stromal stem cells directly participate in tissue regeneration, but they also have the capacity to migrate to distant sites of tissue injury, where they can participate in tissue repair either directly through their differentiation or indirectly through paracrine mechanisms. Additionally, they can elicit various immunomodulatory signals, which can attenuate the inflammatory and immune responses. As such, bone marrow stromal stem cells have been explored clinically for treatment of a wide variety of different conditions including bone defects, graft-vs.-host disease, cardiovascular diseases, autoimmune diseases, diabetes, neurological diseases, and liver and kidney diseases. This review provides an overview of current clinical applications of bone marrow stromal stem cells and discusses their therapeutic properties, while also addressing limitations of their use. PubMed, Ovid, and Google Scholar online databases were searched using several keywords, including "stem cells", "tissue engineering", tissue regeneration" and "clinical trials". Additionally, Clinical trials.gov was used to locate completed clinical trials using bone marrow derived stem cells.

The potential impact of bone tissue engineering in the clinic

Bone tissue engineering (BTE) intends to restore structural support for movement and mineral homeostasis, and assist in hematopoiesis and the protective functions of bone in traumatic, degenerative, cancer, or congenital malformation. While much effort has been put into BTE, very little of this research has been translated to the clinic. In this review, we discuss current regenerative medicine and restorative strategies that utilize tissue engineering approaches to address bone defects within a clinical setting. These approaches involve the primary components of tissue engineering: cells, growth factors and biomaterials discussed briefly in light of their clinical relevance. This review also presents upcoming advanced approaches for BTE applications and suggests a probable workpath for translation from the laboratory to the clinic.

Challenges in engineering osteochondral tissue grafts with hierarchical structures

INTRODUCTION

A major hurdle in treating osteochondral (OC) defects is the different healing abilities of two types of tissues involved - articular cartilage and subchondral bone. Biomimetic approaches to OC-construct engineering, based on recapitulation of biological principles of tissue development and regeneration, have potential for providing new treatments and advancing fundamental studies of OC tissue repair.

AREAS COVERED

This review on state of the art in hierarchical OC tissue graft engineering is focused on tissue engineering approaches designed to recapitulate the native milieu of cartilage and bone development. These biomimetic systems are discussed with relevance to bioreactor cultivation of clinically sized, anatomically shaped human cartilage/bone constructs with physiologic stratification and mechanical properties. The utility of engineered OC tissue constructs is evaluated for their use as grafts in regenerative medicine, and as high-fidelity models in biological research.

EXPERT OPINION

A major challenge in engineering OC tissues is to generate a functionally integrated stratified cartilage-bone structure starting from one single population of mesenchymal cells, while incorporating perfusable vasculature into the bone, and in bone-cartilage interface. To this end, new generations of advanced scaffolds and bioreactors, implementation of mechanical loading regimens and harnessing of inflammatory responses of the host will likely drive the further progress.

Three-dimensional osteogenic and chondrogenic systems to model osteochondral physiology and degenerative joint diseases

Tissue engineered constructs have the potential to function as in vitro pre-clinical models of normal tissue function and disease pathogenesis for drug screening and toxicity assessment. Effective high throughput assays demand minimal systems with clearly defined performance parameters. These systems must accurately model the structure and function of the human organs and their physiological response to different stimuli. Musculoskeletal tissues present unique challenges in this respect, as they are load-bearing, matrix-rich tissues whose functionality is intimately connected to the extracellular matrix and its organization. Of particular clinical importance is the osteochondral junction, the target tissue affected in degenerative joint diseases, such as osteoarthritis (OA), which consists of hyaline articular cartilage in close interaction with subchondral bone. In this review, we present an overview of currently available in vitro three-dimensional systems for bone and cartilage tissue engineering that mimic native physiology, and the utility and limitations of these systems. Specifically, we address the need to combine bone, cartilage and other tissues to form an interactive microphysiological system (MPS) to fully capture the biological complexity and mechanical functions of the osteochondral junction of the articular joint. The potential applications of three-dimensional MPSs for musculoskeletal biology and medicine are highlighted.