Tissue Engineering Cartilage with Deep Zone Cytoarchitecture by High-Resolution Acoustic Cell Patterning

Acoustofluidic-based therapeutic apheresis system

Therapeutic apheresis aims to selectively remove pathogenic substances, such as antibodies that trigger various symptoms and diseases. Unfortunately, current apheresis devices cannot handle small blood volumes in infants or small animals, hindering the testing of animal model advancements. This limitation restricts our ability to provide treatment options for particularly susceptible infants and children with limited therapeutic alternatives. Here, we report our solution to these challenges through an acoustofluidic-based therapeutic apheresis system designed for processing small blood volumes. Our design integrates an acoustofluidic device with a fluidic stabilizer array on a chip, separating blood components from minimal extracorporeal volumes. We carried out plasma apheresis in mouse models, each with a blood volume of just 280 μL. Additionally, we achieved successful plasmapheresis in a sensitized mouse, significantly lowering preformed donor-specific antibodies and enabling desensitization in a transplantation model. Our system offers a new solution for small-sized subjects, filling a critical gap in existing technologies and providing potential benefits for a wide range of patients.

FLight Biofabrication Supports Maturation of Articular Cartilage with Anisotropic Properties

Tissue engineering approaches that recapitulate cartilage biomechanical properties are emerging as promising methods to restore the function of injured or degenerated tissue. However, despite significant progress in this research area, the generation of engineered cartilage constructs akin to native counterparts still represents an unmet challenge. In particular, the inability to accurately reproduce cartilage zonal architecture with different collagen fibril orientations is a significant limitation. The arrangement of the extracellular matrix (ECM) plays a fundamental role in determining the mechanical and biological functions of the tissue. In this study, it is shown that a novel light-based approach, Filamented Light (FLight) biofabrication, can be used to generate highly porous, 3D cell-instructive anisotropic constructs that lead to directional collagen deposition. Using a photoclick-based photoresin optimized for cartilage tissue engineering, a significantly improved maturation of the cartilaginous tissues with zonal architecture and remarkable native-like mechanical properties is demonstrated.

Physical-property-based patterning: simply engineering complex tissues

The field of biofabrication is rapidly expanding with the advent of new technologies and material systems to engineer complex tissues. In this opinion article, we introduce an emerging tissue patterning method, physical-property-based patterning, that has strong translational potential given its simplicity and limited dependence on external hardware. Physical-property-based patterning relies solely on the intrinsic density, magnetic susceptibility, or compressibility of an object, its surrounding solution, and the noncontact application of a remote field. We discuss how physical properties can be exploited to pattern objects and design a variety of biologic tissues. Finally, we pose several open questions that, if addressed, could transform the status quo of biofabrication, pushing us one step closer to patterning tissues in situ.

Acoustofluidic Actuation of Living Cells

Acoutofluidics is an increasingly developing and maturing technical discipline. With the advantages of being label-free, non-contact, bio-friendly, high-resolution, and remote-controllable, it is very suitable for the operation of living cells. After decades of fundamental laboratory research, its technical principles have become increasingly clear, and its manufacturing technology has gradually become popularized. Presently, various imaginative applications continue to emerge and are constantly being improved. Here, we introduce the development of acoustofluidic actuation technology from the perspective of related manipulation applications on living cells. Among them, we focus on the main development directions such as acoustofluidic sorting, acoustofluidic tissue engineering, acoustofluidic microscopy, and acoustofluidic biophysical therapy. This review aims to provide a concise summary of the current state of research and bridge past developments with future directions, offering researchers a comprehensive overview and sparking innovation in the field.

X-Ray Visible Protein Scaffolds by Bulk Iodination

Protein-based biomaterial use is expanding within medicine, together with the demand to visualize their placement and behavior in vivo. However, current medical imaging techniques struggle to differentiate between protein-based implants and surrounding tissue. Here a fast, simple, and translational solution for tracking transplanted protein-based scaffolds is presented using X-ray CT-facilitating long-term, non-invasive, and high-resolution imaging. X-ray visible scaffolds are engineered by selectively iodinating tyrosine residues under mild conditions using readily available reagents. To illustrate translatability, a clinically approved hernia repair mesh (based on decellularized porcine dermis) is labeled, preserving morphological and mechanical properties. In a mouse model of mesh implantation, implants retain marked X-ray contrast up to 3 months, together with an unchanged degradation rate and inflammatory response. The technique's compatibility is demonstrated with a range of therapeutically relevant protein formats including bovine, porcine, and jellyfish collagen, as well as silk sutures, enabling a wide range of surgical and regenerative medicine uses. This solution tackles the challenge of visualizing implanted protein-based biomaterials, which conventional imaging methods fail to differentiate from endogenous tissue. This will address previously unanswered questions regarding the accuracy of implantation, degradation rate, migration, and structural integrity, thereby accelerating optimization and safe translation of therapeutic biomaterials.

3D printed osteochondral scaffolds: design strategies, present applications and future perspectives

Articular osteochondral (OC) defects are a global clinical problem characterized by loss of full-thickness articular cartilage with underlying calcified cartilage through to the subchondral bone. While current surgical treatments can relieve pain, none of them can completely repair all components of the OC unit and restore its original function. With the rapid development of three-dimensional (3D) printing technology, admirable progress has been made in bone and cartilage reconstruction, providing new strategies for restoring joint function. 3D printing has the advantages of fast speed, high precision, and personalized customization to meet the requirements of irregular geometry, differentiated composition, and multi-layered boundary layer structures of joint OC scaffolds. This review captures the original published researches on the application of 3D printing technology to the repair of entire OC units and provides a comprehensive summary of the recent advances in 3D printed OC scaffolds. We first introduce the gradient structure and biological properties of articular OC tissue. The considerations for the development of 3D printed OC scaffolds are emphatically summarized, including material types, fabrication techniques, structural design and seed cells. Especially from the perspective of material composition and structural design, the classification, characteristics and latest research progress of discrete gradient scaffolds (biphasic, triphasic and multiphasic scaffolds) and continuous gradient scaffolds (gradient material and/or structure, and gradient interface) are summarized. Finally, we also describe the important progress and application prospect of 3D printing technology in OC interface regeneration. 3D printing technology for OC reconstruction should simulate the gradient structure of subchondral bone and cartilage. Therefore, we must not only strengthen the basic research on OC structure, but also continue to explore the role of 3D printing technology in OC tissue engineering. This will enable better structural and functional bionics of OC scaffolds, ultimately improving the repair of OC defects.

Acousto-optofluidic 3D single cell imaging of macrophage phagocytosis of Pseudomonas Aeruginosa

Understanding how immune cells such as monocytes or macrophages within our blood and tissue engulf and destroy foreign organisms is important for developing new therapies. The process undertaken by these cells, called phagocytosis, has yet to be observed in real-time at the single cell level. Microfluidic-based imaging platforms offer a wide range of tools for precise fluid control and biomolecule manipulation that makes regulating long term experiments and data collection possible. With the compatibility between acoustofluidics and light-sheet fluorescent microscopy (LSFM) previously demonstrated, here an acousto-optfluidic device with on-chip fluid flow direction control was developed. The standing surface acoustic waves (SSAWs) were used to trap, load and safeguard individual cells within a highly controllable fluid loop, created via the triggering of on-chip PDMS valves, to demonstrate multiple rounds of live single cell imaging. The valves allowed for the direction of the fluid flow to be changed (between forward and reverse operation) without altering the inlet flow rate, an important factor for performing reproducible and comparable imaging of samples over time. With this high-resolution imaging system, volumetric reconstructions of phagocytosed bacteria within macrophages could be resolved over a total of 9 rounds of imaging: totalling 19 reconstructed images of the cell membrane with visible intracellular bacteria.

Straightforward Cell Patterning with Ultra-Low Background Using Polydimethylsiloxane Through-Hole Membranes

Micropatterning is becoming an increasingly popular tool to realize microscale cell positioning and decipher cell activities and functions under specific microenvironments. However, a facile methodology for building a highly precise cell pattern still remains challenging. In this study, A simple and straightforward method for stable and efficient cell patterning with ultra-low background using polydimethylsiloxane through-hole membranes is developed. The patterning process is conveniently on the basis of membrane peeling and routine pipetting. Cell patterning in high quality involving over 97% patterning coincidence and zero residue on the background is achieved. The high repeatability and stability of the established method for multiple types of cell arrangements with different spatial profiles is demonstrated. The customizable cell patterning with ultra-low background and high diversity is confirmed to be quite feasible and reliable. Furthermore, the applicability of the patterning method for investigating the fundamental cell activities is also verified experimentally. The authors believe this microengineering advancement has valuable applications in many microscale cell manipulation-associated research fields including cell biology, cell engineering, cell imaging, and cell sensing.

Acoustofluidic Engineering of Functional Vessel-on-a-Chip

Construction of in vitro vascular models is of great significance to various biomedical research, such as pharmacokinetics and hemodynamics, and thus is an important direction in the tissue engineering field. In this work, a standing surface acoustic wave field was constructed to spatially arrange suspended endothelial cells into a designated acoustofluidic pattern. The cell patterning was maintained after the acoustic field was withdrawn within the solidified hydrogel. Then, interstitial flow was provided to activate vessel tube formation. In this way, a functional vessel network with specific vessel geometry was engineered on-chip. Vascular function, including perfusability and vascular barrier function, was characterized by microbead loading and dextran diffusion, respectively. A computational atomistic simulation model was proposed to illustrate how solutes cross the vascular membrane lipid bilayer. The reported acoustofluidic methodology is capable of facile and reproducible fabrication of the functional vessel network with specific geometry and high resolution. It is promising to facilitate the development of both fundamental research and regenerative therapy.

Acoustic-propelled micro/nanomotors and nanoparticles for biomedical research, diagnosis, and therapeutic applications

Acoustic manipulation techniques have gained significant attention across various fields, particularly in medical diagnosis and biochemical research, due to their biocompatibility and non-contact operation. In this article, we review the broad range of biomedical applications of micro/nano-motors that use acoustic manipulation methods, with a specific focus on cell manipulation, targeted drug release for cancer treatment and genetic disease diagnosis. These applications are facilitated by acoustic-propelled micro/nano-motors and nanoparticles which are manipulated by acoustic tweezers. Acoustic systems enable high precision positioning and can be effectively combined with magnetic manipulation techniques. Furthermore, acoustic propulsion facilitates faster transportation speeds, making it suitable for tasks in blood flow, allowing for precise positioning and in-body manipulation of cells, microprobes, and drugs. By summarizing and understanding these acoustic manipulation methods, this review aims to provide a summary and discussion of the acoustic manipulation methods for biomedical research, diagnostic, and therapeutic applications.

Acoustic quasi-periodic bioassembly based diverse stem cell arrangements for differentiation guidance

Arrangement patterns and geometric cues have been demonstrated to influence cell function and fate, which calls for efficient and versatile cell patterning techniques. Despite constant achievements that mainly focus on individual cells and uniform cell patterns, simultaneously constructing cellular arrangements with diverse patterns and positional relationships in a flexible and contact-free manner remains a challenge. Here, stem cell arrangements possessing multiple geometries and structures are proposed based on powerful and diverse pattern-building capabilities of quasi-periodic acoustic fields, with advantages of rich patterns and structures and flexibility in structure modulation. Eight-fold waves' interference produces regular potentials that result in higher rotational symmetry and more complex arrangement of geometric units. Moreover, through flexible modulation of the phase relations among these wave vectors, a wide variety of cellular pattern units are arranged in this potential, such as circular-, triangular- and square-shape, simultaneously. It is proved that these diverse cellular patterns conveniently build human mesenchymal stem cell (hMSC) models, for research on the effect of cellular arrangement on stem cell differentiation. This work fills the gap of acoustic cell patterning in quasi-periodic patterns and shows promising potential in tissue engineering and regenerative medicine.

Correlative Imaging of Three-Dimensional Cell Culture on Opaque Bioscaffolds for Tissue Engineering Applications

Three-dimensional (3D) tissue engineering (TE) is a prospective treatment that can be used to restore or replace damaged musculoskeletal tissues, such as articular cartilage. However, current challenges in TE include identifying materials that are biocompatible and have properties that closely match the mechanical properties and cellular microenvironment of the target tissue. Visualization and analysis of potential 3D porous scaffolds as well as the associated cell growth and proliferation characteristics present additional problems. This is particularly challenging for opaque scaffolds using standard optical imaging techniques. Here, we use graphene foam (GF) as a 3D porous biocompatible substrate, which is scalable, reproducible, and a suitable environment for ATDC5 cell growth and chondrogenic differentiation. ATDC5 cells are cultured, maintained, and stained with a combination of fluorophores and gold nanoparticles to enable correlative microscopic characterization techniques, which elucidate the effect of GF properties on cell behavior in a 3D environment. Most importantly, the staining protocol allows for direct imaging of cell growth and proliferation on opaque scaffolds using X-ray MicroCT, including imaging growth of cells within the hollow GF branches, which is not possible with standard fluorescence and electron microscopy techniques.

Acoustofluidic Engineering Functional Vessel-on-a-Chip

Construction of in vitro vascular models is of great significance to various biomedical research, such as pharmacokinetics and hemodynamics, thus is an important direction in tissue engineering. In this work, a standing surface acoustic wave field was constructed to spatially arrange suspended endothelial cells into a designated patterning. The cell patterning was maintained after the acoustic field was withdrawn by the solidified hydrogel. Then, interstitial flow was provided to activate vessel tube formation. Thus, a functional vessel-on-a-chip was engineered with specific vessel geometry. Vascular function, including perfusability and vascular barrier function, was characterized by beads loading and dextran diffusion, respectively. A computational atomistic simulation model was proposed to illustrate how solutes cross vascular lipid bilayer. The reported acoustofluidic methodology is capable of facile and reproducible fabrication of functional vessel network with specific geometry. It is promising to facilitate the development of both fundamental research and regenerative therapy.

Rational Design and Acoustic Assembly of Human Cerebral Cortex-Like Microtissues from hiPSC-Derived Neural Progenitors and Neurons

Development of biologically relevant and clinically relevant human cerebral cortex models is demanded by mechanistic studies of human cerebral cortex-associated neurological diseases and discovery of preclinical neurological drug candidates. Here, rational design of human-sourced brain-like cortical tissue models is demonstrated by reverse engineering and bionic design. To implement this design, the acoustic assembly technique is employed to assemble hiPSC-derived neural progenitors and neurons separately in a label-free and contact-free manner followed by subsequent neural differentiation and culture. The generated microtissues encapsulate the neuronal microanatomy of human cerebral-cortex tissue that contains six-layered neuronal architecture, a 400-µm interlayer distance, synaptic connections between interlayers, and neuroelectrophysiological transmission. Furthermore, these microtissues are infected with herpes simplex virus type I (HSV-1) virus, and the HSV-induced pathogenesis associated with Alzheimer's disease is determined, including neuron loss and the expression of Aβ. Overall, a high-fidelity human-relevant in vitro histotypic model is provided for the cerebral cortex, which will facilitate wide applications in probing the mechanisms of neurodegenerative diseases and screening the candidates for neuroprotective agents.

Development of a Nanohybrid Peptide Hydrogel for Enhanced Intervertebral Disc Repair and Regeneration

Effective therapeutic approaches to overcome the heterogeneous pro-inflammatory and inhibitory extracellular matrix (ECM) microenvironment are urgently needed to achieve robust structural and functional repair of severely wounded fibrocartilaginous tissues. Herein we developed a dynamic and multifunctional nanohybrid peptide hydrogel (NHPH) through hierarchical self-assembly of peptide amphiphile modified with biodegradable two-dimensional nanomaterials with enzyme-like functions. NHPH is not only injectable, biocompatible, and biodegradable but also therapeutic by catalyzing the scavenging of pro-inflammatory reactive oxygen species and promoting ECM remodeling. In addition, our NHPH method facilitated the structural and functional recovery of the intervertebral disc (IVD) after severe injuries by delivering pro-regenerative cytokines in a sustained manner, effectively suppressing immune responses and eventually restoring the regenerative microenvironment of the ECM. In parallel, the NHPH-enhanced nucleus pulposus cell differentiation and pain reduction in a rat nucleotomy model further validated the therapeutic potential of NHPH. Collectively, our advanced nanoscaffold technology will provide an alternative approach for the effective treatment of IVD degeneration as well as other fibrocartilaginous tissue injuries.

Compact holographic sound fields enable rapid one-step assembly of matter in 3D

Acoustic waves exert forces when they interact with matter. Shaping ultrasound fields precisely in 3D thus allows control over the force landscape and should permit particulates to fall into place to potentially form whole 3D objects in "one shot." This is promising for rapid prototyping, most notably biofabrication, since conventional methods are typically slow and apply mechanical or chemical stress on biological cells. Here, we realize the generation of compact holographic ultrasound fields and demonstrate the one-step assembly of matter using acoustic forces. We combine multiple holographic fields that drive the contactless assembly of solid microparticles, hydrogel beads, and biological cells inside standard labware. The structures can be fixed via gelation of the surrounding medium. In contrast to previous work, this approach handles matter with positive acoustic contrast and does not require opposing waves, supporting surfaces or scaffolds. We envision promising applications of 3D holographic ultrasound fields in tissue engineering and additive manufacturing.

Recent Advances in "Functional Engineering of Articular Cartilage Zones by Polymeric Biomaterials Mediated with Physical, Mechanical, and Biological/Chemical Cues"

Articular cartilage (AC) plays an unquestionable role in joint movements but unfortunately the healing capacity is restricted due to its avascular and acellular nature. While cartilage tissue engineering has been lifesaving, it is very challenging to remodel the complex cartilage composition and architecture with gradient physio-mechanical properties vital to proper tissue functions. To address these issues, a better understanding of the intrinsic AC properties and how cells respond to stimuli from the external microenvironment must be better understood. This is essential in order to take one step closer to producing functional cartilaginous constructs for clinical use. Recently, biopolymers have aroused much attention due to their versatility, processability, and flexibility because the properties can be tailored to match the requirements of AC. This review highlights polymeric scaffolds developed in the past decade for reconstruction of zonal AC layers including the superficial zone, middle zone, and deep zone by means of exogenous stimuli such as physical, mechanical, and biological/chemical signals. The mimicked properties are reviewed in terms of the biochemical composition and organization, cell fate (morphology, orientation, and differentiation), as well as mechanical properties and finally, the challenges and potential ways to tackle them are discussed.