Bioprinting of Human Musculoskeletal Interface

Bioprinting of Stable Bionic Interfaces Using Piezoresistive Hydrogel Organoelectronics

Bionic tissues offer an exciting frontier in biomedical research by integrating biological cells with artificial electronics, such as sensors. One critical hurdle is the development of artificial electronics that can mechanically harmonize with biological tissues, ensuring a robust interface for effective strain transfer and local deformation sensing. In this study, a highly tissue-integrative, soft mechanical sensor fabricated from a composite piezoresistive hydrogel. The composite not only exhibits exceptional mechanical properties, with elongation at the point of fracture reaching up to 680%, but also maintains excellent biocompatibility across multiple cell types. Furthermore, the material exhibits bioadhesive qualities, facilitating stable cell adhesion to its surface. A unique advantage of the formulation is the compatibility with 3D bioprinting, an essential technique for fabricating stable interfaces. A multimaterial sensorized 3D bionic construct is successfully bioprinted, and it is compared to structures produced via hydrogel casting. In contrast to cast constructs, the bioprinted ones display a high (87%) cell viability, preserve differentiation ability, and structural integrity of the sensor-tissue interface throughout the tissue development duration of 10 d. With easy fabrication and effective soft tissue integration, this composite holds significant promise for various biomedical applications, including implantable electronics and organ-on-a-chip technologies.

Designing of gradient scaffolds and their applications in tissue regeneration

Gradient scaffolds are isotropic/anisotropic three-dimensional structures with gradual transitions in geometry, density, porosity, stiffness, etc., that mimic the biological extracellular matrix. The gradient structures in biological tissues play a major role in various functional and metabolic activities in the body. The designing of gradients in the scaffold can overcome the current challenges in the clinic compared to conventional scaffolds by exhibiting excellent penetration capacity for nutrients & cells, increased cellular adhesion, cell viability & differentiation, improved mechanical stability, and biocompatibility. In this review, the recent advancements in designing gradient scaffolds with desired biomimetic properties, and their implication in tissue regeneration applications have been briefly explained. Furthermore, the gradients in native tissues such as bone, cartilage, neuron, cardiovascular, skin and their specific utility in tissue regeneration have been discussed in detail. The insights from such advances using gradient-based scaffolds can widen the horizon for using gradient biomaterials in tissue regeneration applications.

Design and bioprinting for tissue interfaces

Tissue interfaces include complex gradient structures formed by transitioning of biochemical and mechanical properties in micro-scale. This characteristic allows the communication and synchronistic functioning of two adjacent but distinct tissues. It is particularly challenging to restore the function of these complex structures by transplantation of scaffolds exclusively produced by conventional tissue engineering methods. Three-dimensional (3D) bioprinting technology has opened an unprecedented approach for precise and graded patterning of chemical, biological and mechanical cues in a single construct mimicking natural tissue interfaces. This paper reviews and highlights biochemical and biomechanical design for 3D bioprinting of various tissue interfaces, including cartilage-bone, muscle-tendon, tendon/ligament-bone, skin, and neuro-vascular/muscular interfaces. Future directions and translational challenges are also provided at the end of the paper.

Biomaterial-based 3D bioprinting strategy for orthopedic tissue engineering

The advent of three-dimensional (3D) bioprinting has enabled impressive progress in the development of 3D cellular constructs to mimic the structural and functional characteristics of natural tissues. Bioprinting has considerable translational potential in tissue engineering and regenerative medicine. This review highlights the rational design and biofabrication strategies of diverse 3D bioprinted tissue constructs for orthopedic tissue engineering applications. First, we elucidate the fundamentals of 3D bioprinting techniques and biomaterial inks and discuss the basic design principles of bioprinted tissue constructs. Next, we describe the rationale and key considerations in 3D bioprinting of tissues in many different aspects. Thereafter, we outline the recent advances in 3D bioprinting technology for orthopedic tissue engineering applications, along with detailed strategies of the engineering methods and materials used, and discuss the possibilities and limitations of different 3D bioprinted tissue products. Finally, we summarize the current challenges and future directions of 3D bioprinting technology in orthopedic tissue engineering and regenerative medicine. This review not only delineates the representative 3D bioprinting strategies and their tissue engineering applications, but also provides new insights for the clinical translation of 3D bioprinted tissues to aid in prompting the future development of orthopedic implants. STATEMENT OF SIGNIFICANCE: 3D bioprinting has driven major innovations in the field of tissue engineering and regenerative medicine; aiming to develop a functional viable tissue construct that provides an alternative regenerative therapy for musculoskeletal tissue regeneration. 3D bioprinting-based biofabrication strategies could open new clinical possibilities for creating equivalent tissue substitutes with the ability to customize them to meet patient demands. In this review, we summarize the significance and recent advances in 3D bioprinting technology and advanced bioinks. We highlight the rationale for biofabrication strategies using 3D bioprinting for orthopedic tissue engineering applications. Furthermore, we offer ample perspective and new insights into the current challenges and future direction of orthopedic bioprinting translation research.

The translational paradigm of nanobiomaterials: Biological chemistry to modern applications

Recently nanotechnology has evolved as one of the most revolutionary technologies in the world. It has now become a multi-trillion-dollar business that covers the production of physical, chemical, and biological systems at scales ranging from atomic and molecular levels to a wide range of industrial applications, such as electronics, medicine, and cosmetics. Nanobiomaterials synthesis are promising approaches produced from various biological elements be it plants, bacteria, peptides, nucleic acids, etc. Owing to the better biocompatibility and biological approach of synthesis, they have gained immense attention in the biomedical field. Moreover, due to their scaled-down sized property, nanobiomaterials exhibit remarkable features which make them the potential candidate for different domains of tissue engineering, materials science, pharmacology, biosensors, etc. Miscellaneous characterization techniques have been utilized for the characterization of nanobiomaterials. Currently, the commercial transition of nanotechnology from the research level to the industrial level in the form of nano-scaffolds, implants, and biosensors is stimulating the whole biomedical field starting from bio-mimetic nacres to 3D printing, multiple nanofibers like silk fibers functionalizing as drug delivery systems and in cancer therapy. The contribution of single quantum dot nanoparticles in biological tagging typically in the discipline of genomics and proteomics is noteworthy. This review focuses on the diverse emerging applications of Nanobiomaterials and their mechanistic advancements owing to their physiochemical properties leading to the growth of industries on different biomedical measures. Alongside the implementation of such nanobiomaterials in several drug and gene delivery approaches, optical coding, photodynamic cancer therapy, and vapor sensing have been elaborately discussed in this review. Different parameters based on current challenges and future perspectives are also discussed here.

3D Bioprinting: An Enabling Technology to Understand Melanoma

Melanoma is a potentially fatal cancer with rising incidence over the last 50 years, associated with enhanced sun exposure and ultraviolet radiation. Its incidence is highest in people of European descent and the ageing population. There are multiple clinical and epidemiological variables affecting melanoma incidence and mortality, such as sex, ethnicity, UV exposure, anatomic site, and age. Although survival has improved in recent years due to advances in targeted and immunotherapies, new understanding of melanoma biology and disease progression is vital to improving clinical outcomes. Efforts to develop three-dimensional human skin equivalent models using biofabrication techniques, such as bioprinting, promise to deliver a better understanding of the complexity of melanoma and associated risk factors. These 3D skin models can be used as a platform for patient specific models and testing therapeutics.

Bioinks and Bioprinting Strategies for Skeletal Muscle Tissue Engineering

Skeletal muscles play important roles in critical body functions and their injury or disease can lead to limitation of mobility and loss of independence. Current treatments result in variable functional recovery, while reconstructive surgery, as the gold-standard approach, is limited due to donor shortage, donor-site morbidity, and limited functional recovery. Skeletal muscle tissue engineering (SMTE) has generated enthusiasm as an alternative solution for treatment of injured tissue and serves as a functional disease model. Recently, bioprinting has emerged as a promising tool for recapitulating the complex and highly organized architecture of skeletal muscles at clinically relevant sizes. Here, skeletal muscle physiology, muscle regeneration following injury, and current treatments following muscle loss are discussed, and then bioprinting strategies implemented for SMTE are critically reviewed. Subsequently, recent advancements that have led to improvement of bioprinting strategies to construct large muscle structures, boost myogenesis in vitro and in vivo, and enhance tissue integration are discussed. Bioinks for muscle bioprinting, as an essential part of any bioprinting strategy, are discussed, and their benefits, limitations, and areas to be improved are highlighted. Finally, the directions the field should expand to make bioprinting strategies more translational and overcome the clinical unmet needs are discussed.

Reversible, Selective, Ultrawide-Range Variable Stiffness Control by Spatial Micro-Water Molecule Manipulation

Evolution has decided to gift an articular structure to vertebrates, but not to invertebrates, owing to their distinct survival strategies. An articular structure permits kinematic motion in creatures. However, it is inappropriate for creatures whose survival strategy depends on the high deformability of their body. Accordingly, a material in which the presence of the articular structure can be altered, allowing the use of two contradictory strategies, will be advantageous in diverse dynamic applications. Herein, spatial micro-water molecule manipulation, termed engineering on variable occupation of water (EVO), that is used to realize a material with dual mechanical modes that exhibit extreme differences in stiffness is introduced. A transparent and homogeneous soft material (110 kPa) reversibly converts to an opaque material embodying a mechanical gradient (ranging from 1 GPa to 1 MPa) by on-demand switching. Intensive theoretical analysis of EVO yields the design of spatial transformation scheme. The EVO gel accomplishes kinematic motion planning and shows great promise for multimodal kinematics. This approach paves the way for the development and application of smart functional materials.

Review of Bioprinting in Regenerative Medicine: Naturally Derived Bioinks and Stem Cells

Regenerative medicine offers the potential to repair or substitute defective tissues by constructing active tissues to address the scarcity and demands for transplantation. The method of forming 3D constructs made up of biomaterials, cells, and biomolecules is called bioprinting. Bioprinting of stem cells provides the ability to reliably recreate tissues, organs, and microenvironments to be used in regenerative medicine. 3D bioprinting is a technique that uses several biomaterials and cells to tailor a structure with clinically relevant geometries and sizes. This technique's promise is demonstrated by 3D bioprinted tissues, including skin, bone, cartilage, and cardiovascular, corneal, hepatic, and adipose tissues. Several bioprinting methods have been combined with stem cells to effectively produce tissue models, including adult stem cells, embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), and differentiation techniques. In this review, technological challenges of printed stem cells using prevalent naturally derived bioinks (e.g., carbohydrate polymers and protein-based polymers, peptides, and decellularized extracellular matrix), recent advancements, leading companies, and clinical trials in the field of 3D bioprinting are delineated.

Hydroxyethyl Cellulose As a Rheological Additive for Tuning the Extrusion Printability and Scaffold Properties

Bioink, a key element of three-dimensional (3D) bioprinting, is frequently engineered to achieve improved printing performance. Viscoelasticity related to rheological properties is correlative of the printability of bioink for extrusion bioprinting, which affects the complexity of printing 3D structures. This article shows the use of hydroxyethyl cellulose (HEC) as a rheological additive for engineering bioink to improve the printability without reducing the biocompatibility. Different concentrations of HEC were added to four types of bioink, namely, reagent-crosslinked, temperature-dependent phase change, ultraviolet-polymerized, and composite hydrogel bioinks, to investigate the effect on the viscoelasticity properties, print fidelity, and other printed scaffold properties. The results indicate that HEC is able to increase the rheological properties by 100 times to stabilize complex structures and improve the printing fidelity to narrow the gap between the design value and theoretical value, even converting nonviscous ink into directly printable ink, as well as tune the swelling ratio for better molecular permeability. The degradation of bioink can also be tuned by the addition of HEC. Moreover, this bioink is biocompatible for cell lines and primary cells. HEC is expected to be widely used in 3D extrusion-based bioprinting.

The emerging role of microfluidics in multi-material 3D bioprinting

To assist the transition of 3D bioprinting technology from simple lab-based tissue fabrication, to fully functional and implantable organs, the technology must not only provide shape control, but also functional control. This can be accomplished by replicating the cellular composition of the native tissue at the microscale, such that cell types interact to provide the desired function. There is therefore a need for precise, controllable, multi-material printing that could allow for high, possibly even single cell, resolution. This paper aims to draw attention to technological advancements made in 3D bioprinting that target the lack of multi-material, and/or multi cell-type, printing capabilities of most current devices. Unlike other reviews in the field, which largely focus on variations in single-material 3D bioprinting involving the standard methods of extrusion-based, droplet-based, laser-based, or stereolithographic methods; this review concentrates on sophisticated multi-material 3D bioprinting using multi-cartridge printheads, co-axial nozzles and microfluidic-enhanced printing nozzles.

Regeneration of skeletal system with genipin crosslinked biomaterials

Natural biomaterials, such as collagen, gelatin, and chitosan, are considered as promising candidates for use in tissue regeneration treatment, given their similarity to natural tissues regarding components and structure. Nevertheless, only receiving a crosslinking process can these biomaterials exhibit sufficient strength to bear high tensile loads for use in skeletal system regeneration. Recently, genipin, a natural chemical compound extracted from gardenia fruits, has shown great potential as a reliable crosslinking reagent, which can reconcile the crosslinking effect and biosafety profile simultaneously. In this review, we briefly summarize the genipin extraction process, biosafety, and crosslinking mechanism. Subsequently, the applications of genipin regarding aiding skeletal system regeneration are discussed in detail, including the advances and technological strategies for reconstructing cartilage, bone, intervertebral disc, tendon, and skeletal muscle tissues. Finally, based on the specific pharmacological functions of genipin, its potential applications, such as its use in bioprinting and serving as an antioxidant and anti-tumor agent, and the challenges of genipin in the clinical applications in skeletal system regeneration are also presented.