When bottom-up meets top-down

Bridging the Gap: Advances and Challenges in Heart Regeneration from In Vitro to In Vivo Applications

Cardiovascular diseases, particularly ischemic heart disease, area leading cause of morbidity and mortality worldwide. Myocardial infarction (MI) results in extensive cardiomyocyte loss, inflammation, extracellular matrix (ECM) degradation, fibrosis, and ultimately, adverse ventricular remodeling associated with impaired heart function. While heart transplantation is the only definitive treatment for end-stage heart failure, donor organ scarcity necessitates the development of alternative therapies. In such cases, methods to promote endogenous tissue regeneration by stimulating growth factor secretion and vascular formation alone are insufficient. Techniques for the creation and transplantation of viable tissues are therefore highly sought after. Approaches to cardiac regeneration range from stem cell injections to epicardial patches and interposition grafts. While numerous preclinical trials have demonstrated the positive effects of tissue transplantation on vasculogenesis and functional recovery, long-term graft survival in large animal models is rare. Adequate vascularization is essential for the survival of transplanted tissues, yet pre-formed microvasculature often fails to achieve sufficient engraftment. Recent studies report success in enhancing cell survival rates in vitro via tissue perfusion. However, the transition of these techniques to in vivo models remains challenging, especially in large animals. This review aims to highlight the evolution of cardiac patch and stem cell therapies for the treatment of cardiovascular disease, identify discrepancies between in vitro and in vivo studies, and discuss critical factors for establishing effective myocardial tissue regeneration in vivo.

Advances in the Treatment of Partial-Thickness Cartilage Defect

Partial-thickness cartilage defects (PTCDs) of the articular surface is the most common problem in cartilage degeneration, and also one of the main pathogenesis of osteoarthritis (OA). Due to the lack of a clear diagnosis, the symptoms are often more severe when full-thickness cartilage defect (FTCDs) is present. In contrast to FTCDs and osteochondral defects (OCDs), PTCDs does not injure the subchondral bone, there is no blood supply and bone marrow exudation, and the nearby microenvironment is unsuitable for stem cells adhesion, which completely loses the ability of self-repair. Some clinical studies have shown that partial-thickness cartilage defects is as harmful as full-thickness cartilage defects. Due to the poor effect of conservative treatment, the destructive surgical treatment is not suitable for the treatment of partial-thickness cartilage defects, and the current tissue engineering strategies are not effective, so it is urgent to develop novel strategies or treatment methods to repair PTCDs. In recent years, with the interdisciplinary development of bioscience, mechanics, material science and engineering, many discoveries have been made in the repair of PTCDs. This article reviews the current status and research progress in the treatment of PTCDs from the aspects of diagnosis and modeling of PTCDs, drug therapy, tissue transplantation repair technology and tissue engineering ("bottom-up").

Flower-like Photonic Hydrogel with Superstructure Induced via Modulated Shear Field

Biological tissues usually have complex superstructures and elaborated functionalities. However, creating superstructures in soft and wet hydrogels is challenging because of the absence of effective approaches to control the molecular orientation. Here we introduce a method to create superstructures in photonic hydrogels comprising lamellar bilayers intercalated in the cross-linked polymer network. The orientation of lamellar bilayers in the photonic gel, which are sensitive to shear, is modulated by applying a gradient shear field on the precursor solution using a customized rheometer. The difference in orientation of lamellar bilayers leads to swelling mismatch in the radial direction, endowing the disk-shape hydrogel with a macroscopic flower-like shape with a central dome and an edge petal, along with a bright photonic color. By characterization of the swelling anisotropy of the radial profile, the shear rate required for the unidirectional orientation of lamellar bilayers was extracted. Moreover, a delayed polymerization experiment was designed to measure the lifetime of aligned lamellar bilayers, which reveals the domain size of lamellar bilayers in the precursor solution. Furthermore, we also demonstrated that the hydrogel flowers could fade and rebloom reversibly in response to external stimuli. This work presents a strategy to develop superstructures in hydrogels and sheds light on designing biomimetic materials with intricately architectural superstructure.

3D Bioprinted Cardiac Tissues and Devices for Tissue Maturation

Cardiovascular diseases are the leading cause of mortality worldwide. Given the limited endogenous regenerative capabilities of cardiac tissue, patient-specific anatomy, challenges in treatment options, and shortage of donor tissues for transplantation, there is an urgent need for novel approaches in cardiac tissue repair. 3D bioprinting is a technology based on additive manufacturing which allows for the design of precisely controlled and spatially organized structures, which could possibly lead to solutions in cardiac tissue repair. In this review, we describe the basic morphological and physiological specifics of the heart and cardiac tissues and introduce the readers to the fundamental principles underlying 3D printing technology and some of the materials/approaches which have been used to date for cardiac repair. By summarizing recent progress in 3D printing of cardiac tissue and valves with respect to the key features of cardiovascular tissue (such as contractility, conductivity, and vascularization), we highlight how 3D printing can facilitate surgical planning and provide custom-fit implants and properties that match those from the native heart. Finally, we also discuss the suitability of this technology in the design and fabrication of custom-made devices intended for the maturation of the cardiac tissue, a process that has been shown to increase the viability of implants. Altogether this review shows that 3D printing and bioprinting are versatile and highly modulative technologies with wide applications in cardiac regeneration and beyond.

Advanced Bottom-Up Engineering of Living Architectures

Bottom-up tissue engineering is a promising approach for designing modular biomimetic structures that aim to recapitulate the intricate hierarchy and biofunctionality of native human tissues. In recent years, this field has seen exciting progress driven by an increasing knowledge of biological systems and their rational deconstruction into key core components. Relevant advances in the bottom-up assembly of unitary living blocks toward the creation of higher order bioarchitectures based on multicellular-rich structures or multicomponent cell-biomaterial synergies are described. An up-to-date critical overview of long-term existing and rapidly emerging technologies for integrative bottom-up tissue engineering is provided, including discussion of their practical challenges and required advances. It is envisioned that a combination of cell-biomaterial constructs with bioadaptable features and biospecific 3D designs will contribute to the development of more robust and functional humanized tissues for therapies and disease models, as well as tools for fundamental biological studies.

All-Organic Conductive Biomaterial as an Electroactive Cell Interface

Various attractive materials are being used in bioelectronics recently. In this paper, hydroxymethyl-3,4-ethylenedioxythiophene (EDOT-OH) has been in situ integrated and polymerized on the surface of the regenerated silk fibroin (RSF) film to construct a biocompatible electrode. In order to improve the efficiency of in situ polymerization, sodium dodecyl sulfate (SDS) was adopted as surfactant to construct a well-organized and stable poly(hydroxymethyl-3,4-ethylenedioxythiophene) (PEDOT-OH) coating, whereas ammonium persulfate was used as oxidant. The effects of dosages of surfactant and oxidant, initial pH value, and monomer concentration on the polymerization were studied. Under the optimal conditions, the RSF/PEDOT-OH film exhibited a square resistance of 3.28 × 10⁵ Ω corresponding to a conductance of 6.1 × 10^-3 S/cm. Scanning electron microscope images indicated that PEDOT-OH was deposited uniformly on the surface of the RSF film with SDS. Furthermore, Fourier transform infrared spectroscopy confirmed that interactions existed between the peptide linkages of silk fibroin (SF) macromolecules and PEDOT-OH. The RSF/PEDOT-OH film displayed favorable electrochemical stability, biocompatibility, and fastness. This study provides a feasible method to endow conductivity to RSF materials in various forms. In addition, the conductive layer and biocompatible silk substrate make the RSF/PEDOT-OH biomaterial highly suitable for potential applications in bioelectric devices, sensors, and tissue engineering.