Mechanically-Activated Microcapsules for 'On-Demand' Drug Delivery in Dynamically Loaded Musculoskeletal Tissues

Kelp and Cartilage Acellular Matrix Hybrid Microgel Assembly Realizes Articular Cartilage Repair Via ROS Scavenging, Endogenous BMSC Recruitment and Chondrogenic Differentiation

Articular cartilage repair remains challenging due to the inherent poor self-healing capacity and acute inflammation resulting from the over expression of intracellular reactive oxygen species (ROS). Although microfracture is frequently used in practical surgery, the newborn cartilage always exhibits fibrosis, mainly attributed to the weak ROS scavenging and mismatched microenvironment that fails to induce chondrogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). Herein, a novel simvastatin (SIM)-incorporated kelp and cartilage acellular matrix hybrid (labeled as SIM@KACM/CACM) microgel assembly with enhanced ROS scavenging, endogenous BMSC recruitment, and chondrogenic differentiation capabilities is constructed to improve microfracture-based articular cartilage repair. The kelp acellular matrix exhibits low immunogenicity, high biocompatibility, and ROS scavenging properties, whilst the sustained SIM release promotes BMSC recruitment from the bone marrow cavity. Meanwhile, the microenvironment and bioactive factors conferred by CACM facilitate the BMSC proliferation and differentiation into hyaline cartilage. In addition, the construction of porous microgel assembly via dynamic Schiff's bonds endows excellent injectability and tissue adhesion, which not only enhances its retention in the defect site after injection but also provides abundant sites for BMSC anchoring and infiltration. Due to the synergetic effect of the above-mentioned multiple factors, the articular cartilage repair is improved dramatically.

Artificial Intelligence-Empowered Automated Double Emulsion Droplet Library Generation

Double emulsions with core-shell structures are versatile materials used in applications such as cell culture, drug delivery, and materials synthesis. A droplet library with precisely controlled dimensions and properties would streamline screening and optimization for specific applications. While microfluidic droplet generation offers high precision, it is typically labor-intensive and sensitive to disturbances, requiring continuous operator intervention. To address these limitations, we present an artificial intelligence (AI)-empowered automated double emulsion droplet library generator. This system integrates a convolutional neural network (CNN)-based object detection model, decision-making, and feedback control algorithms to automate droplet generation and collection. The system monitors droplet generation every 171 ms-faster than a Formula 1 driver's reaction time-ensuring rapid response to disturbances and consistent production of single-core double emulsions. It autonomously generates libraries of 25 distinct monodisperse droplets with user-defined properties. This automation reduces labor and waste, enhances precision, and supports rapid and reliable droplet library generation. We anticipate that this platform will accelerate discovery and optimization in biomedical, biological, and materials research.

Mechano-Responsive Biomaterials for Bone Organoid Construction

Mechanical force is essential for bone development, bone homeostasis, and bone fracture healing. In the past few decades, various biomaterials have been developed to provide mechanical signals that mimic the natural bone microenvironment, thereby promoting bone regeneration. Bone organoids, emerging as a novel research approach, are 3D micro-bone tissues that possess the ability to self-renew and self-organize, exhibiting biomimetic spatial characteristics. Incorporating mechano-responsive biomaterials in the construction of bone organoids presents a promising avenue for simulating the mechanical bone microenvironment. Therefore, this review commences by elucidating the impact of mechanical force on bone health, encompassing both cellular interactions and alterations in bone structure. Furthermore, the most recent applications of mechano-responsive biomaterials within the realm of bone tissue engineering are highlighted. Three different types of mechano-responsive biomaterials are introduced with a focus on their responsive mechanisms, construction strategies, and efficacy in facilitating bone regeneration. Based on a comprehensive overview, the prospective utilization and future challenges of mechano-responsive biomaterials in the construction of bone organoids are discussed. As bone organoid technology advances, these biomaterials are poised to become powerful tools in bone regeneration.

Intraductal chemotherapy for triple-negative breast cancer: a pathway to minimally invasive clinical treatment

Triple-negative breast cancer (TNBC) is traditionally treated with systemic chemotherapy, often resulting in significant off-target toxicity. In this study, we assess the efficacy of intraductal chemotherapeutic delivery, aimed at reducing systemic side effects. Using an in situ TNBC model, created by intraductal injection of 4T1-luc cells, we identified day 3 post-tumor implantation as an optimal early intervention point. Echocardiographic analysis confirmed that intraductal administration of eribulin (ERI) or doxorubicin (DOX) did not cause cardiac dysfunction or apoptosis. Our results demonstrate that intraductal delivery of ERI and DOX significantly enhances anti-tumor and anti-metastatic effects. Mechanistically, ERI followed by DOX increased intratumoral perfusion, improved drug concentration, reversed epithelial-mesenchymal transition, and inhibited tumor cell invasion and metastasis. Additionally, this approach triggered immunogenic cell death and activated a systemic anti-tumor immune response. These findings underscore the potential of intraductal chemotherapy as a safe, highly effective approach, offering a preclinical foundation for minimally invasive TNBC therapies.

Injectable acellular matrix microgel assembly with stem cell recruitment and chondrogenic differentiation functions promotes microfracture-based articular cartilage regeneration

Articular cartilage repair and regeneration is still a significant challenge despite years of research. Although microfracture techniques are commonly used in clinical practice, the newborn cartilage is usually fibrocartilage rather than hyaline cartilage, which is mainly attributed to the inadequate microenvironment for effectively recruiting, anchoring, and inducing bone marrow mesenchymal stem cells (BMSCs) to differentiate into hyaline cartilage. This paper introduces a novel cartilage acellular matrix (CACM) microgel assembly with excellent microporosity, injectability, tissue adhesion, BMSCs recruitment and chondrogenic differentiation capabilities to improve the microfracture-based articular cartilage regeneration. Specifically, the sustained release of simvastatin (SIM) from the SIM@CACM microgel assembly efficiently recruits BMSCs in the early stage of cartilage regeneration, while the abundant interconnected micropores and high specific area assure the quick adhesion, proliferation and infiltration of BMSCs. Additionally, the active factors within the CACM matrix, appropriate mechanical properties of the microgel assembly, and excellent tissue adhesion provide a conductive environment for the continuous chondrogenic differentiation of BMSCs into hyaline cartilage. Owing to the synergistic effect of the above-mentioned factors, good articular cartilage repair and regeneration is achieved.

Multifunctional polymeric nanocapsules with enhanced cartilage penetration and retention for osteoarthritis treatment

Osteoarthritis (OA) is a prevalent joint disease characterized by cartilage degeneration and subchondral bone homeostasis imbalance. Effective topical OA therapy is challenging, as therapeutic drugs often suffer from insufficient penetration and rapid clearance. We develop miniature polydopamine (PDA) nanocapsules (sub-60 nm), which are conjugated with collagen-binding polypeptide (CBP) and loaded with an anabolic drug (i.e., parathyroid hormone 1-34, PTH 1-34) for efficient OA treatment. Such multifunctional polymeric nanocapsules, denoted as PDA@CBP-PTH, possess deformability when interacting with the dense collagen fiber networks, enabling the efficient penetration into 1 mm cartilage in 4 h and prolonged retention within the joints up to 28 days. Moreover, PDA@CBP-PTH nanocapsules exhibit excellent reactive oxygen species scavenging property in chondrocytes and enhance the anabolism in subchondral bone. The nanosystem, as dual-mode treatment for OA, demonstrates rapid penetration, long-lasting effects, and combinational therapeutic impact, paving the way for reversing the progression of OA for joint health care.

Microballoons: Osmotically-inflated elastomer shells for ultrafast release of encapsulants and mechanical energy

HYPOTHESIS

Microcapsules with osmotically-inflated elastic shells exhibit an ultrafast release of encapsulants while mechanically stimulating the microenvironments, akin to popping balloons.

EXPERIMENTS

To prepare elastic shells with uniform thickness and size, monodisperse water-in-oil-in-water (W/O/W) double-emulsion drops are produced in a capillary microfluidic device. The polydimethylsiloxane (PDMS)-containing oil phase is thermally cured to create the elastic shell. The elastic shells are inflated by pumping water into the lumen in hypotonic conditions. The inflated microcapsules produced undergo mechanical compression, and their release properties are studied.

FINDINGS

By controlling the osmotic pressure difference, Microballoons are inflated into a diameter of 200 μm - 316 μm and shell thickness of 7.8 μm - 0.7 µm, respectively. The inflated shell pops due to mechanical failure when subjected to mechanical stress above a certain threshold, resembling a balloon. During popping, the stretched shell rapidly retracts to the original uninflated state, resulting in an ultrafast release of encapsulants from the lumen within a millisecond. This process converts elastic potential energy stored in the shell into mechanical energy with substantial power. The microballoons mechanically stimulate the local environment, leading to the direct and rapid release of encapsulants. This has the potential to improve absorption efficiency.

A microfluidic platform for the synthesis of polymer and polymer-protein-based protocells

In this study, we demonstrate the fabrication of polymersomes, protein-blended polymersomes, and polymeric microcapsules using droplet microfluidics. Polymersomes with uniform, single bilayers and controlled diameters are assembled from water-in-oil-in-water double-emulsion droplets. This technique relies on adjusting the interfacial energies of the droplet to completely separate the polymer-stabilized inner core from the oil shell. Protein-blended polymersomes are prepared by dissolving protein in the inner and outer phases of polymer-stabilized droplets. Cell-sized polymeric microcapsules are assembled by size reduction in the inner core through osmosis followed by evaporation of the middle phase. All methods are developed and validated using the same glass-capillary microfluidic apparatus. This integrative approach not only demonstrates the versatility of our setup, but also holds significant promise for standardizing and customizing the production of polymer-based artificial cells.

Complex Emulsions as an Innovative Pharmaceutical Dosage form in Addressing the Issues of Multi-Drug Therapy and Polypharmacy Challenges

This review explores the intersection of microfluidic technology and complex emulsion development as a promising solution to the challenges of formulations in multi-drug therapy (MDT) and polypharmacy. The convergence of microfluidic technology and complex emulsion fabrication could herald a transformative era in multi-drug delivery systems, directly confronting the prevalent challenges of polypharmacy. Microfluidics, with its unparalleled precision in droplet formation, empowers the encapsulation of multiple drugs within singular emulsion particles. The ability to engineer emulsions with tailored properties-such as size, composition, and release kinetics-enables the creation of highly efficient drug delivery vehicles. Thus, this innovative approach not only simplifies medication regimens by significantly reducing the number of necessary doses but also minimizes the pill burden and associated treatment termination-issues associated with polypharmacy. It is important to bring forth the opportunities and challenges of this synergy between microfluidic-driven complex emulsions and multi-drug therapy poses. Together, they not only offer a sophisticated method for addressing the intricacies of delivering multiple drugs but also align with broader healthcare objectives of enhancing treatment outcomes, patient safety, and quality of life, underscoring the importance of dosage form innovations in tackling the multifaceted challenges of modern pharmacotherapy.

SCO-pH: Microfluidic dynamic phenotyping platform for high-throughput screening of single cell acidification

Studies on the dynamics of single cell phenotyping have been hampered by the lack of quantitative high-throughput metabolism assays. Extracellular acidification, a prominent phenotype, yields significant insights into cellular metabolism, including tumorigenicity. Here, we develop a versatile microfluidic system for single cell optical pH analysis (SCO-pH), which compartmentalizes single cells in 140-pL droplets and immobilizes approximately 40,000 droplets in a two-dimensional array for temporal extracellular pH analysis. SCO-pH distinguishes cells undergoing hyperglycolysis induced by oligomycin A from untreated cells by monitoring their extracellular acidification. To facilitate pH sensing in each droplet, we encapsulate a cell-impermeable pH probe whose fluorescence intensities are quantified. Using this approach, we can differentiate hyperglycolytic cells and concurrently observe single cell heterogeneity in extracellular acidification dynamics. This high-throughput system will be useful in applications that require dynamic phenotyping of single cells with significant heterogeneity.

Programmable Photoswitchable Microcapsules Enable Precise and Tailored Drug Delivery from Microfluidics

The development of precision personalized medicine poses a significant need for the next generation of advanced diagnostic and therapeutic technologies, and one of the key challenges is the development of highly time-, space-, and dose-controllable drug delivery systems that respond to the complex physiopathology of patient populations. In response to this challenge, an increasing number of stimuli-responsive smart materials are integrated into biomaterial systems for precise targeted drug delivery. Among them, responsive microcapsules prepared by droplet microfluidics have received much attention. In this study, we present a UV-visible light cycling mediated photoswitchable microcapsule (PMC) with dynamic permeability-switching capability for precise and tailored drug release. The PMCs were fabricated using a programmable pulsed aerodynamic printing (PPAP) technique, encapsulating an aqueous core containing magnetic nanoparticles and the drug doxorubicin (DOX) within a poly(lactic-co-glycolic acid) (PLGA) composite shell modified by PEG-b-PSPA. Selective irradiation of PMCs with ultraviolet (UV) or visible light (Vis) allows for high-precision time-, space-, and dose-controlled release of the therapeutic agent. An experimentally validated theoretical model was developed to describe the drug release pattern, holding promise for future customized programmable drug release applications. The therapeutic efficacy and value of patternable cancer cell treatment activated by UV radiation is demonstrated by our experimental results. After in vitro transcatheter arterial chemoembolization (TACE), PMCs can be removed by external magnetic fields to mitigate potential side effects. Our findings demonstrate that PMCs have the potential to integrate embolization, on-demand drug delivery, magnetic actuation, and imaging properties, highlighting their immense potential for tailored drug delivery and embolic therapy.

Tension-activated nanofiber patches delivering an anti-inflammatory drug improve repair in a goat intervertebral disc herniation model

Conventional microdiscectomy treatment for intervertebral disc herniation alleviates pain but does not repair the annulus fibrosus, resulting in a high incidence of recurrent herniation and persistent dysfunction. The lack of repair and the acute inflammation that arise after injury can further compromise the disc and result in disc-wide degeneration in the long term. To address this clinical need, we developed tension-activated repair patches (TARPs) for annulus fibrosus repair and local delivery of the anti-inflammatory factor anakinra (a recombinant interleukin-1 receptor antagonist). TARPs transmit physiologic strain to mechanically activated microcapsules embedded within the patch, which release encapsulated bioactive molecules in direct response to spinal loading. Mechanically activated microcapsules carrying anakinra were loaded into TARPs, and the effects of TARP-mediated annular repair and anakinra delivery were evaluated in a goat model of annular injury in the cervical spine. TARPs integrated with native tissue and provided structural reinforcement at the injury site that prevented aberrant disc-wide remodeling resulting from detensioning of the annular fibrosus. The delivery of anakinra by TARP implantation increased matrix deposition and retention at the injury site and improved maintenance of disc extracellular matrix. Anakinra delivery additionally attenuated the inflammatory response associated with TARP implantation, decreasing osteolysis in adjacent vertebrae and preserving disc cellularity and matrix organization throughout the annulus fibrosus. These results demonstrate the therapeutic potential of TARPs for the treatment of intervertebral disc herniation.

Asymmetry-Enhanced Motion of Urease-Powered Micromotors from Double Emulsion-Templated Microcapsules

Autonomous motion of enzyme-powered motors has important implications for drug delivery, cell-cell communication, and protocell engineering. Although many of these systems are inspired by the motion of biological cells, most of them lack key structural features, like micrometer-sized boundaries and aqueous compartments, and rely on bubble propulsion to generation motion. In this study, we use droplet microfluidics to generate large populations of cell-sized microcapsules with poly(lactic-co-glycolic acid) shells and functionalize their surfaces with the enzyme urease to drive their motion. We adjust the number of surface functional groups for urease conjugation by preparing microcapsules with two different surfactants, poly(vinyl alcohol) (PVA) and poly(ethylene-alt-maleic anhydride) (PEMA). We also tune the surface roughness of the microcapsules by varying the concentration of silica nanoparticles in the droplet middle phase. We find that PEMA plays a crucial role in increasing the grafting density of urease on the surface of smooth microcapsules, leading to active motion in the presence of urea. In addition, rough microcapsules prepared with PEMA and loaded with comparable amounts of urease move up to three times faster than their smooth counterparts, which we believe is due to an asymmetric distribution of urease on the surface, giving rise to a preferred direction of motion. Taken together, these results provide new insights into the role that various stabilizing agents play in the induction of motion by enzymatic motors prepared from microfluidics, which is a potentially powerful tool for future preparation of motile protocells in biomedicine.

Dynamically adaptive scaffolds for cartilage tissue engineering

Although cartilage regeneration is a continuously changing, complex process, most studies on cartilage tissue regeneration have focused on specific stages, thereby promoting regeneration in only a limited period rather than over the entire repair process. The ideal adaptive scaffolds for cartilage tissue engineering should exhibit dynamic and spatiotemporally controlled evolution according to the physiological microenvironments during each phase of cartilage repair. Moreover, scaffolds should have a specific feedback regulation capability, including long‐term feedback for the controlled delivery of multiple factors, which would better meet the requirements of cartilage regeneration. Adaptive scaffolds matching the whole evolving stages of cartilage repair are still under exploration. This review highlights the development of dynamically adaptive scaffolds to provide the appropriate microenvironments for cartilage regeneration, including scaffolds that manipulate the immune microenvironments from the inflammation stage to the regeneration stage, scaffolds that release cytokines on demand across several stages, and scaffolds that adapt according to the mechanical properties of extracellular matrices over time, and also discusses the future challenges and development directions of adaptive scaffolds in cartilage tissue regeneration. This understanding is expected to inspire the application of adaptive scaffolds for cartilage repair.

The Era of Biomaterials: Smart Implants?

Conditions, accidents, and aging processes have brought with them the need to develop implants with higher technology that allow not only the replacement of missing tissue but also the formation of tissue and the recovery of its function. The development of implants is due to advances in different areas such as molecular-biochemistry (which allows the understanding of the molecular/cellular processes during tissue repair), materials engineering, tissue regeneration (which has contributed advances in the knowledge of the properties of the materials used for their manufacture), and the so-called intelligent biomaterials (which promote tissue regeneration through inductive effects of cell signaling in response to stimuli from the microenvironment to generate adhesion, migration, and cell differentiation processes). The implants currently used are combinations of biopolymers with properties that allow the formation of scaffolds with the capacity to mimic the characteristics of the tissue to be repaired. This review describes the advances of intelligent biomaterials in implants applied in different dental and orthopedic problems; by means of these advances, it is expected to overcome limitations such as additional surgeries, rejections and infections in implants, implant duration, pain mitigation, and mainly, tissue regeneration.

Fabricating the cartilage: recent achievements

This review aims to describe the most recent achievements and provide an insight into cartilage engineering and strategies to restore the cartilage defects. Here, we discuss cell types, biomaterials, and biochemical factors applied to form cartilage tissue equivalents and update the status of fabrication techniques, which are used at all stages of engineering the cartilage. The actualized concept to improve the cartilage tissue restoration is based on applying personalized products fabricated using a full cycle platform: a bioprinter, a bioink consisted of ECM-embedded autologous cell aggregates, and a bioreactor. Moreover, in situ platforms can help to skip some steps and enable adjusting the newly formed tissue in the place during the operation. Only some achievements described have passed first stages of clinical translation; nevertheless, the number of their preclinical and clinical trials is expected to grow in the nearest future.

Pulmonary delivery of mucus-traversing PF127-modified silk fibroin nanoparticles loading with quercetin for lung cancer therapy

The mucosal barrier remains a major barrier in the pulmonary drug delivery system, as mucociliary clearance in the airway accelerates the removal of inhaled nanoparticles (NPs). Herein, we designed and developed the inhalable Pluronic F127-modified silk fibroin NPs loading with quercetin (marked as QR-SF (PF127) NPs), aiming to solve the airway mucus barrier and improve the cancer therapeutic effect of QR. The PF127 coating on the SF NPs could attenuate the interaction between NPs and mucin proteins, thus facilitating the diffusion of SF(PF127) NPs in the mucus layer. The QR-SF (PF127) NPs had particle sizes of approximately 200 nm with negatively charged surfaces and showed constant drug release properties. Fluorescence recovery after photobleaching (FRAP) assay and transepithelial transport test showed that QR-SF (PF127) NPs exhibited superior mucus-penetrating ability in artificial mucus and monolayer Calu-3 cell model. Notably, a large amount of QR-SF (PF127) NPs distributed uniformly in the mice airway section, indicating the good retention of NPs in the respiratory tract. The mice melanoma lung metastasis model was established, and the therapeutic effect of QR-SF (PF127) NPs was significantly improved in vivo. PF127-modified SF NPs may be a promising strategy to attenuate the interaction with mucin proteins and enhance mucus penetration efficiency in the pulmonary drug delivery system.

Smart Hydrogels for Bone Reconstruction via Modulating the Microenvironment

Rapid and effective repair of injured or diseased bone defects remains a major challenge due to shortages of implants. Smart hydrogels that respond to internal and external stimuli to achieve therapeutic actions in a spatially and temporally controlled manner have recently attracted much attention for bone therapy and regeneration. These hydrogels can be modified by introducing responsive moieties or embedding nanoparticles to increase their capacity for bone repair. Under specific stimuli, smart hydrogels can achieve variable, programmable, and controllable changes on demand to modulate the microenvironment for promoting bone healing. In this review, we highlight the advantages of smart hydrogels and summarize their materials, gelation methods, and properties. Then, we overview the recent advances in developing hydrogels that respond to biochemical signals, electromagnetic energy, and physical stimuli, including single, dual, and multiple types of stimuli, to enable physiological and pathological bone repair by modulating the microenvironment. Then, we discuss the current challenges and future perspectives regarding the clinical translation of smart hydrogels.

Smart Biomaterials for Articular Cartilage Repair and Regeneration

Articular cartilage defects bring about disability and worldwide socioeconomic loss, therefore, articular cartilage repair and regeneration is recognized as a global issue. However, due to its avascular and nearly acellular characteristic, cartilage tissue regeneration ability is limited to some extent. Despite the availability of various treatment methods, including palliative drugs and surgical regenerative therapy, articular cartilage repair and regeneration still face major challenges due to the lack of appropriate methods and materials. Smart biomaterials can regulate cell behavior and provide excellent tissue repair and regeneration microenvironment, thus inducing articular cartilage repair and regeneration. This process is adjusted by controlling drug/bioactive factors release via responding to exogenous/endogenous stimuli, tailoring materials’ structure and function similar to native cartilage or providing physiochemical and physical signaling factors. Herein, smart biomaterials, recently applied in articular cartilage repair and regeneration, are elaborated from two aspects: smart drug release system and smart scaffolds. Furthermore, articular cartilage and its defects and advanced manufacturing techniques of smart biomaterials are discussed in brief. Finally, perspectives for smart biomaterials used in articular cartilage repair and regeneration are presented and the clinical translation of smart biomaterials is emphasized.

Capsule-based colorimetric temperature monitoring system for customizable cold chain management

The COVID-19 pandemic and the resulting supply chain disruption have rekindled crucial needs for safe storage and transportation of essential items. Despite recent advances, existing temperature monitoring technologies for cold chain management fall short in reliability, cost, and flexibility toward customized cold chain management for various products with different required temperature. In this work, we report a novel capsule-based colorimetric temperature monitoring system with precise and readily tunable temperature ranges. Triple emulsion drop-based microfluidic technique enables rapid production of monodisperse microcapsules with an interstitial phase-change oil (PCO) layer with precise control over its dimension and composition. Liquid-solid phase transition of the PCO layer below its freezing point triggers the release of the encapsulated payload yielding drastic change in color, allowing user-friendly visual monitoring in a highly sensitive manner. Simple tuning of the PCO layer's compositions can further broaden the temperature range in a precisely controlled manner. The proposed simple scheme can readily be formulated to detect both temperature rise in the frozen environment and freeze detection as well as multiple temperature monitoring. Combined, these results support a significant step forward for the development of customizable colorimetric monitoring of a broad range of temperatures with precision.

Preclinical Use of FGF-18 Augmentation for Improving Cartilage Healing Following Surgical Repair: A Systematic Review

OBJECTIVE

To evaluate the efficacy of fibroblast growth factor-18 (FGF-18) augmentation for improving articular cartilage healing following surgical repair in preclinical (in vivo) animal models.

DESIGN

A systematic review was performed evaluating the efficacy of FGF-18 augmentation with cartilage surgery compared with cartilage surgery without FGF-18 augmentation in living animal models. Eligible intervention groups were FGF-18 treatment in conjunction with orthopedic procedures, including microfracture, osteochondral auto/allograft transplantation, and cellular-based repair. Outcome variables were: International Cartilage Repair Society (ICRS) score, modified O'Driscoll histology score, tissue infill score, qualitative histology, and adverse events. Descriptive statistics were recorded and summarized for each included study.

RESULTS

In total, 493 studies were identified and 4 studies were included in the final analysis. All studies were randomized controlled trials evaluating in vivo use of recombinant human FGF-18 (rhFGF-18). Animal models included ovine (n = 3) and equine (n = 1), with rhFGF-18 use following microfracture (n = 3) or osteochondral defect repair (n = 1). The rhFGF-18 was delivered via intra-articular injection (n = 2), collagen membrane scaffold (n = 1), or both (n = 1). All studies reported significant, positive improvements in cartilage defect repair with rhFGF-18 compared with controls based on ICRS score (n = 4), modified O'Driscoll score (n = 4), tissue infill (n = 3), and expression of collagen type II (n = 4) (P < 0.05). No adverse events were reported with the intra-articular administration of this growth factor, indicating short-term safety and efficacy of rhFGF-18 in vivo.

CONCLUSION

This systematic review provides evidence that rhFGF-18 significantly improves cartilage healing at 6 months postoperatively following microfracture or osteochondral defect repair in preclinical randomized controlled trials.

Flexible polymeric patch based nanotherapeutics against non-cancer therapy

Flexible polymeric patches find widespread applications in biomedicine because of their biological and tunable features including excellent patient compliance, superior biocompatibility and biodegradation, as well as high loading capability and permeability of drug. Such polymeric patches are classified into microneedles (MNs), hydrogel, microcapsule, microsphere and fiber depending on the formed morphology. The combination of nanomaterials with polymeric patches allows for improved advantages of increased curative efficacy and lowered systemic toxicity, promoting on-demand and regulated drug administration, thus providing the great potential to their clinic translation. In this review, the category of flexible polymeric patches that are utilized to integrate with nanomaterials is briefly presented and their advantages in bioapplications are further discussed. The applications of nanomaterials embedded polymeric patches in non-cancerous diseases were also systematically reviewed, including diabetes therapy, wound healing, dermatological disease therapy, bone regeneration, cardiac repair, hair repair, obesity therapy and some immune disease therapy. Alternatively, the limitations, latest challenges and future perspectives of such biomedical therapeutic devices are addressed.

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The most explored polymeric patches, such as microneedle, hydrogel, microsphere, microcapsule, and fiber are summarized.

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Polymeric patches integrated with a diversity of nanomaterials are systematically overviewed in non-cancer therapy.

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The future prospective for the development of polymeric patch based nanotherapeutics is discussed.

Physical and Soluble Cues Enhance Tendon Progenitor Cell Invasion into Injectable Synthetic Hydrogels

Synthetic hydrogels represent an exciting avenue in the field of regenerative biomaterials given their injectability, orthogonally tunable mechanical properties, and potential for modular inclusion of cellular cues. Separately, recent advances in soluble factor release technology have facilitated control over the soluble milieu in cell microenvironments via tunable microparticles. A composite hydrogel incorporating both of these components can robustly mediate tendon healing following a single injection. Here, a synthetic hydrogel system with encapsulated electrospun fiber segments and a novel microgel-based soluble factor delivery system achieves precise control over topographical and soluble features of an engineered microenvironment, respectively. It is demonstrated that three-dimensional migration of tendon progenitor cells can be enhanced via combined mechanical, topographical, and microparticle-delivered soluble cues in both a tendon progenitor cell spheroid model and an ex vivo murine Achilles tendon model. These results indicate that fiber reinforced hydrogels can drive the recruitment of endogenous progenitor cells relevant to the regeneration of tendon and, likely, a broad range of connective tissues.

Identifying small molecules for protecting chondrocyte function and matrix integrity after controlled compressive injury

Objective

Articular cartilage injury is central for the development of post-traumatic osteoarthritis (PTOA). With few disease-modifying therapies successful at offsetting progressive osteoarthritis (OA), our goal is to use a high throughput screening platform of cartilage injury to identify novel chondroprotective compounds. Targeting articular cartilage damage immediately after injury remains a promising therapeutic strategy to overcome irreversible tissue damage.

Method

We constructed a single impact-cartilage screening method using a multi-platen system that simultaneously impacts 48 samples and makes use of engineered cartilage tissue analogs (known as CTAs). Drug libraries were screened and assessed for their ability to alter two crucial biological responses to impact injuries, namely matrix degradation and cell stress.

Results

Over 500 small molecules were screened for their ability to alter proteoglycan loss, matrix metalloproteinase activity, and cell stress or death. Fifty-five compounds passed through secondary screening and were from commercial libraries of natural and redox, stem cell related compounds, as well as protease, kinase and phosphatase inhibitors. Through secondary screening, 16 promising candidates exhibited activity on one or more critical function of chondrocytes. While many are mechanistically known compounds, their function in joint diseases is not known.

Conclusion

This platform was validated for screening drug activity against a tissue engineered model of PTOA. Multiple compounds identified in this manner have potential application as early protective therapy for treating PTOA, and require further study. We propose this screening platform can identify novel molecules that act on early chondrocyte responses to injury and provide an invaluable tool for therapeutic development.

Biosensor-Integrated Drug Delivery Systems as New Materials for Biomedical Applications

Biosensor-integrated drug delivery systems are innovative devices in the health area, enabling continuous monitoring and drug administration. The use of smart polymer, bioMEMS, and electrochemical sensors have been extensively studied for these systems, especially for chronic diseases such as diabetes mellitus, cancer and cardiovascular diseases as well as advances in regenerative medicine. Basically, the technology involves sensors designed for the continuous analysis of biological molecules followed by drug release in response to specific signals. The advantages include high sensitivity and fast drug release. In this work, the main advances of biosensor-integrated drug delivery systems as new biomedical materials to improve the patients’ quality of life with chronic diseases are discussed.

Recent advances in mechanical force-responsive drug delivery systems

Mechanical force responsive drug delivery systems (in terms of mechanical force induced chemical bond breakage or physical structure destabilization) have been recently explored to exhibit a controllable pharmaceutical release behaviour at a molecular level. In comparison with chemical or biological stimulus triggers, mechanical force is not only an external but also an internal stimulus which is closely related to the physiological status of patients. However, although this mechanical force stimulus might be one of the most promising and feasible sources to achieve on-demand pharmaceutical release, current research in this field is still limited. Hence, this tutorial review aims to comprehensively evaluate the recent advances in mechanical force-responsive drug delivery systems based on different types of mechanical force, in terms of direct stimulation by compressive, tensile, and shear force, or indirect/remote stimulation by ultrasound and a magnetic field. Furthermore, the exciting developments and current challenges in this field will also be discussed to provide a blueprint for potential clinical translational research of mechanical force-responsive drug delivery systems.

Encapsulation of hygroscopic liquids via polymer precipitation in non-aqueous emulsions

HYPOTHESIS

Encapsulation of ionic liquids (ILs) and phase change materials (PCMs) can overcome limitations associated with bulk materials, e.g., slow mass transfer rates, high viscosities, or susceptibility to external environment. Single step soft-templated encapsulation methods commonly use interfacial polymerization for shell formation, with a multifunctional monomer in the continuous phase and another in the discontinuous phase, and thus do not give pristine core material. We posit that polymer precipitation onto emulsion droplets in non-aqueous emulsions could produce a robust shell without contamination of the core, ideal for the encapsulation of water-sensitive or water-miscible materials.

EXPERIMENTS

Solutions of commodity polymers were added to the continuous phase of non-aqueous Pickering emulsions stabilized by alkylated graphene oxide (GO) nanosheets such that the change in solubility of the polymer led to formation of robust shells and the production of capsules that could be isolated.

FINDINGS

We demonstrate that a polymer precipitation approach can produce capsules with pristine core of the IL 1-ethyl-3-methylimidazolium hexafluorophosphate [Emim][PF₆] or the salt hydrate PCM magnesium nitrate hexahydrate (MNH) and shell of nanosheets and polystyrene, poly(methyl methacrylate), or polyethylene. The capsules are approximately 80 wt% [Emim][PF₆] or >90 wt% MNH, and the core can undergo multiple cycles of solidification and melting without leakage or destruction. This novel, single-step methodology provides a distinct advantage to access capsules with pristine core composition and is amenable to different core and shell, paving the way for tailoring capsule composition for desired applications.

Monoporous Microsphere as a Dynamically Movable Drug Carrier for Osteoporotic Bone Remodeling

To repair systematically osteoporotic bone defects, it is significant to take effort on both the diminishment of osteoporosis and the enhancement of bone regeneration. Herein, a specifically monoporous microsphere carrier encapsulating dosage-sensitive and short half-time parathyroid hormone (PTH) has been constructed to tackle the issue. Compared with conventional microsphere carriers involving compact, porous, and mesoporous microspheres, the monoporous microsphere is desirable to achieve precisely in-situ delivery and to minimize topical accumulation. Our findings show that the PTH loaded inside MPMs can be gradually released from the single hole of MPMs to improve the initial drug concentration. Also, the MPMs can self-shift with the daily movement of experimental animals to effectively reduce the topical aggregation of released drugs in vitro. In vivo evaluation further confirms that the implant of MPMs-PTH plays a dual role in stimulating the regenerative repair of the cranial defect and relieving osteoporosis in the whole body. Consequently, our current work develops a dynamically movable drug delivery system to achieve precisely in-situ delivery, minimize topical accumulation, and systematically repair osteoporotic bone defects. This article is protected by copyright. All rights reserved.

Gravity-based patterning of osteogenic factors to preserve bone structure after osteochondral injury in a large animal model

Chondral and osteochondral repair strategies are limited by adverse bony changes that occur after injury. Bone resorption can cause entire scaffolds, engineered tissues, or even endogenous repair tissues to subside below the cartilage surface. To address this translational issue, we fabricated thick-shelled poly(D,L-lactide-co-glycolide) (PLGA) microcapsules containing the pro-osteogenic agents triiodothyronine and ß-glycerophosphate, and delivered these microcapsules in a large animal model of osteochondral injury to preserve bone structure. We demonstrate that the developed microcapsules ruptured in vitro under increasing mechanical loads, and readily sink within a liquid solution, enabling gravity-based patterning along the osteochondral surface. In a large animal, these mechanically-actived microcapsules (MAMCs) were assessed through two different delivery strategies. Intra-articular injection of control MAMCs enabled fluorescent quantification of MAMC rupture and cargo release in a synovial joint setting over time in vivo. This joint-wide injection also confirmed that the MAMCs do not elicit an inflammatory response. In the contralateral hindlimbs, chondral defects were created, MAMCs were patterned in situ, and nanofracture (Nfx), a clinically utilized method to promote cartilage repair, was performed. The NFx holes enabled marrow-derived stromal cells to enter the defect area and served as repeatable bone injury sites to monitor over time. Animals were evaluated 1 and 2 weeks after injection and surgery. Analysis of injected MAMCs showed that bioactive cargo was released in a controlled fashion over 2 weeks. A bone fluorochrome label injected at the time of surgery displayed maintenance of mineral labeling in the therapeutic group, but resorption in both control groups. Alkaline phosphatase (AP) staining at the osteochondral interface revealed higher AP activity in defects treated with therapeutic MAMCs. Overall, this study develops a gravity-based approach to pattern bioactive factors along the osteochondral interface, and applies this novel biofabrication strategy to preserve bone structure after osteochondral injury.

Recent advances in the microfluidic production of functional microcapsules by multiple-emulsion templating

Multiple-emulsion drops serve as versatile templates to design functional microcapsules due to their core-shell geometry and multiple compartments. Microfluidics has been used for the elaborate production of multiple-emulsion drops with a controlled composition, order, and dimensions, elevating the value of multiple-emulsion templates. Moreover, recent advances in the microfluidic control of the emulsification and parallelization of drop-making junctions significantly enhance the production throughput for practical use. Metastable multiple-emulsion drops are converted into stable microcapsules through the solidification of selected phases, among which solid shells are designed to function in a programmed manner. Functional microcapsules are used for the storage and release of active materials as drug carriers. Beyond their conventional uses, microcapsules can serve as microcompartments responsible for transmembrane communication, which is promising for their application in advanced microreactors, artificial cells, and microsensors. Given that post-processing provides additional control over the composition and construction of multiple-emulsion drops, they are excellent confining geometries to study the self-assembly of colloids and liquid crystals and produce miniaturized photonic devices. This review article presents the recent progress and current state of the art in the microfluidic production of multiple-emulsion drops, functionalization of solid shells, and applications of microcapsules.

Osmosis-Mediated Microfluidic Production of Submillimeter-Sized Capsules with an Ultrathin Shell for Cosmetic Applications

There is a demand for submillimeter-sized capsules with an ultrathin shell with high visibility and no tactile sensation after release for cosmetic applications. However, neither bulk emulsification nor droplet microfluidics can directly produce such capsules in a controlled manner. Herein, we report the microfluidic production of submillimeter-sized capsules with a spacious lumen and ultrathin biodegradable shell through osmotic inflation of water-in-oil-in-water (W/O/W) double-emulsion drops. Monodisperse double-emulsion drops are produced with a capillary microfluidic device to have an organic solution of poly(lactic-co-glycolic acid) (PLGA) in the middle oil layer. Hypotonic conditions inflate the drops, leading to core volume expansion and oil-layer thickness reduction. Afterward, the oil layer is consolidated to the PLGA shell through solvent evaporation. The degree of inflation is controllable with the osmotic pressure. With a strong hypotonic condition, the capsule radius increases up to 330 μm and the shell thickness decreases to 1 μm so that the ratio of the thickness to radius is as small as 0.006. The large capsules with an ultrathin shell readily release their encapsulant under an external force by shell rupture. In the mechanical test of single capsules, the threshold strain for shell rupture is reduced from 75 to 12%, and the threshold stress is decreased by two orders for highly inflated capsules in comparison with noninflated ones. During the shell rupture, the tactile sensation of capsules gradually disappears as the capsules lose volume and the residual shells are ultrathin.

Recent advances in smart stimuli-responsive biomaterials for bone therapeutics and regeneration

Bone defects combined with tumors, infections, or other bone diseases are challenging in clinical practice. Autologous and allogeneic grafts are two main traditional remedies, but they can cause a series of complications. To address this problem, researchers have constructed various implantable biomaterials. However, the original pathological microenvironment of bone defects, such as residual tumors, severe infection, or other bone diseases, could further affect bone regeneration. Thus, the rational design of versatile biomaterials with integrated bone therapy and regeneration functions is in great demand. Many strategies have been applied to fabricate smart stimuli-responsive materials for bone therapy and regeneration, with stimuli related to external physical triggers or endogenous disease microenvironments or involving multiple integrated strategies. Typical external physical triggers include light irradiation, electric and magnetic fields, ultrasound, and mechanical stimuli. These stimuli can transform the internal atomic packing arrangements of materials and affect cell fate, thus enhancing bone tissue therapy and regeneration. In addition to the external stimuli-responsive strategy, some specific pathological microenvironments, such as excess reactive oxygen species and mild acidity in tumors, specific pH reduction and enzymes secreted by bacteria in severe infection, and electronegative potential in bone defect sites, could be used as biochemical triggers to activate bone disease therapy and bone regeneration. Herein, we summarize and discuss the rational construction of versatile biomaterials with bone therapeutic and regenerative functions. The specific mechanisms, clinical applications, and existing limitations of the newly designed biomaterials are also clarified.

Mechanosignalling in cartilage: an emerging target for the treatment of osteoarthritis

Mechanical stimuli have fundamental roles in articular cartilage during health and disease. Chondrocytes respond to the physical properties of the cartilage extracellular matrix (ECM) and the mechanical forces exerted on them during joint loading. In osteoarthritis (OA), catabolic processes degrade the functional ECM and the composition and viscoelastic properties of the ECM produced by chondrocytes are altered. The abnormal loading environment created by these alterations propagates cell dysfunction and inflammation. Chondrocytes sense their physical environment via an array of mechanosensitive receptors and channels that activate a complex network of downstream signalling pathways to regulate several cell processes central to OA pathology. Advances in understanding the complex roles of specific mechanosignalling mechanisms in healthy and OA cartilage have highlighted molecular processes that can be therapeutically targeted to interrupt pathological feedback loops. The potential for combining these mechanosignalling targets with the rapidly expanding field of smart mechanoresponsive biomaterials and delivery systems is an emerging paradigm in OA treatment. The continued advances in this field have the potential to enable restoration of healthy mechanical microenvironments and signalling through the development of precision therapeutics, mechanoregulated biomaterials and drug systems in the near future.

A review of strategies for development of tissue engineered meniscal implants

The meniscus is a key stabilizing tissue of the knee that facilitates proper tracking and movement of the knee joint and absorbs stresses related to physical activity. This review article describes the biology, structure, and functions of the human knee meniscus, common tears and repair approaches, and current research and development approaches using modern methods to fabricate a scaffold or tissue engineered meniscal replacement. Meniscal tears are quite common, often resulting from sports or physical training, though injury can result without specific contact during normal physical activity such as bending or squatting. Meniscal injuries often require surgical intervention to repair, restore basic functionality and relieve pain, and severe damage may warrant reconstruction using allograft transplants or commercial implant devices. Ongoing research is attempting to develop alternative scaffold and tissue engineered devices using modern fabrication techniques including three-dimensional (3D) printing which can fabricate a patient-specific meniscus replacement. An ideal meniscal substitute should have mechanical properties that are close to that of natural human meniscus, and also be easily adapted for surgical procedures and fixation. A better understanding of the organization and structure of the meniscus as well as its potential points of failure will lead to improved design approaches to generate a suitable and functional replacement.

Stretch-responsive adhesive microcapsules for strain-regulated antibiotic release from fabric wound dressings

Bacterial infection of a wound is a major complication that can significantly delay proper healing and even necessitate surgical debridement. Conventional non-woven fabric dressings, including gauzes, bandages and cotton wools, often fail in treating wound infections in a timely manner due to their passive release mechanism of antibiotics. Here, we propose adhesive mechanically-activated microcapsules (MAMCs) capable of strongly adhering to a fibrous matrix to achieve a self-regulated release of antibiotics upon uniaxial stretching of non-woven fabric dressings. To achieve this, a uniform population of polydopamine (PDA)-coated MAMCs (PDA-MAMCs) are prepared using a microfluidics technique and subsequent oxidative dopamine polymerization. The PDA-MAMC allows for robust mechano-activation within the fibrous network through high retention and effective transmission of mechanical force under stretching. By validating the potential of a PDA-MAMCs-laden gauze to release antibiotics in a tensile strain-dependent manner, we demonstrate that PDA-MAMCs can be successfully incorporated into a woven material and create a smart wound dressing for control of bacterial infections. This new mechano-activatable delivery approach will open up a new avenue for a stretch-triggered, on-demand release of therapeutic cargos in skin-mountable or wearable biomedical devices.

Nanofibrous hyaluronic acid scaffolds delivering TGF-β3 and SDF-1α for articular cartilage repair in a large animal model

Focal cartilage injuries have poor intrinsic healing potential and often progress to osteoarthritis, a costly disease affecting almost a third of adults in the United States. To treat these patients, cartilage repair therapies often use cell-seeded scaffolds, which are limited by donor site morbidity, high costs, and poor efficacy. To address these limitations, we developed an electrospun cell-free fibrous hyaluronic acid (HA) scaffold that delivers factors specifically designed to enhance cartilage repair: Stromal Cell-Derived Factor-1α (SDF-1α; SDF) to increase the recruitment and infiltration of mesenchymal stem cells (MSCs) and Transforming Growth Factor-β3 (TGF-β3; TGF) to enhance cartilage tissue formation. Scaffolds were characterized in vitro and then deployed in a large animal model of full-thickness cartilage defect repair. The bioactivity of both factors was verified in vitro, with both SDF and TGF increasing cell migration, and TGF increasing matrix formation by MSCs. In vivo, however, scaffolds releasing SDF resulted in an inferior cartilage healing response (lower mechanics, lower ICRS II histology score) compared to scaffolds releasing TGF alone. These results highlight the importance of translation into large animal models to appropriately screen scaffolds and therapies, and will guide investigators towards alternative growth factor combinations. STATEMENT OF SIGNIFICANCE: This study addresses an area of orthopaedic medicine in which treatment options are limited and new biomaterials stand to improve patient outcomes. Those suffering from articular cartilage injuries are often destined to have early onset osteoarthritis. We have created a cell-free nanofibrous hyaluronic acid (HA) scaffold that delivers factors specifically designed to enhance cartilage repair: Stromal Cell-Derived Factor-1α (SDF-1α; SDF) to increase the recruitment and infiltration of mesenchymal stem cells (MSCs) and Transforming Growth Factor-β3 (TGF-β3; TGF) to enhance cartilage tissue formation. To our knowledge, this study is the first to evaluate such a bioactive scaffold in a large animal model and demonstrates the capacity for dual growth factor release.

Marginal sealing around integral bilayer scaffolds for repairing osteochondral defects based on photocurable silk hydrogels

Osteochondral repair remains a major challenge in current clinical practice despite significant advances in tissue engineering. In particular, the lateral integration of neocartilage into surrounding native cartilage is a difficult and inadequately addressed problem that determines the success of tissue repair. Here, a novel design of an integral bilayer scaffold combined with a photocurable silk sealant for osteochondral repair is reported. First, we fabricated a bilayer silk scaffold with a cartilage layer resembling native cartilage in surface morphology and mechanical strength and a BMP-2-loaded porous subchondral bone layer that facilitated the osteogenic differentiation of BMSCs. Second, a TGF-β3-loaded methacrylated silk fibroin sealant (Sil-MA) exhibiting biocompatibility and good adhesive properties was developed and confirmed to promote chondrocyte migration and differentiation. Importantly, this TGF-β3-loaded Sil-MA hydrogel provided a bridge between the cartilage layer of the scaffold and the surrounding cartilage and then guided new cartilage to grow towards and replace the degraded cartilage layer from the surrounding native cartilage in the early stage of knee repair. Thus, osteochondral regeneration and superior lateral integration were achieved in vivo by using this composite. These results demonstrate that the new approach of marginal sealing around the cartilage layer of bilayer scaffolds with Sil-MA hydrogel has tremendous potential for clinical use in osteochondral regeneration.

The future of meniscus science: international expert consensus

Purpose

The purpose of this study was to evaluate the main focus areas for research and development for furthering the state of meniscus science in 2021.

Methods

An electronic survey including 10 questions was sent in a blind fashion to the faculty members of the 5^th International Conference on Meniscus Science and Surgery. These faculty served as an expert consensus on the future of research and development areas of meniscus science. Survey responses were analyzed using descriptive statistics and ranking weighted averages were calculated to score survey questions.

Results

Of the 82 faculty, 76 (93%) from 18 different countries completed the survey (84% male, 16% female). The highest ranked future research and development focus areas were meniscus repair, biologics, osteotomy procedures, addressing meniscus extrusion, and the development of new therapies for the prevention of posttraumatic osteoarthritis. Currently, the most ‘valuable’ type of biologic reported for meniscus treatment was platelet-rich plasma. The main reported global research limitation was a lack of long-term clinical outcomes data. The most promising emerging medical technologies for improving meniscus science were 3-D printing, personalized medicine, and artificial implants.

Conclusions

This survey suggests that the future of meniscus science should be focused on meniscal preservation techniques through meniscus repair, addressing meniscal extrusion, and the use of orthobiologics. The lack of long-term clinical outcomes was the main reported research limitation globally for meniscus treatment. Future product development utilizing emerging medical technologies suggest the use of 3-D printing for meniscal transplants/scaffolds, personalized treatment, and bioengineering for artificial implants.

Level of Evidence

Level V.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40634-021-00345-y.

A synthetic mechanogenetic gene circuit for autonomous drug delivery in engineered tissues

Mechanobiologic signals regulate cellular responses under physiologic and pathologic conditions. Using synthetic biology and tissue engineering, we developed a mechanically responsive bioartificial tissue that responds to mechanical loading to produce a preprogrammed therapeutic biologic drug. By deconstructing the signaling networks induced by activation of the mechanically sensitive ion channel transient receptor potential vanilloid 4 (TRPV4), we created synthetic TRPV4-responsive genetic circuits in chondrocytes. We engineered these cells into living tissues that respond to mechanical loading by producing the anti-inflammatory biologic drug interleukin-1 receptor antagonist. Chondrocyte TRPV4 is activated by osmotic loading and not by direct cellular deformation, suggesting that tissue loading is transduced into an osmotic signal that activates TRPV4. Either osmotic or mechanical loading of tissues transduced with TRPV4-responsive circuits protected constructs from inflammatory degradation by interleukin-1α. This synthetic mechanobiology approach was used to develop a mechanogenetic system to enable long-term, autonomously regulated drug delivery driven by physiologically relevant loading.

Magneto-Driven Gradients of Diamagnetic Objects for Engineering Complex Tissues

Engineering complex tissues represents an extraordinary challenge and, to date, there have been few strategies developed that can easily recapitulate native-like cell and biofactor gradients in 3D materials. This is true despite the fact that mimicry of these gradients may be essential for the functionality of engineered graft tissues. Here, a non-traditional magnetics-based approach is developed to predictably position naturally diamagnetic objects in 3D hydrogels. Rather than magnetizing the objects within the hydrogel, the magnetic susceptibility of the surrounding hydrogel precursor solution is enhanced. In this way, a range of diamagnetic objects (e.g., polystyrene beads, drug delivery microcapsules, and living cells) are patterned in response to a brief exposure to a magnetic field. Upon photo-crosslinking the hydrogel precursor, object positioning is maintained, and the magnetic contrast agent diffuses out of the hydrogel, supporting long-term construct viability. This approach is applied to engineer cartilage constructs with a depth-dependent cellularity mirroring that of native tissue. These are thought to be the first results showing that magnetically unaltered cells can be magneto-patterned in hydrogels and cultured to generate heterogeneous tissues. This work provides a foundation for the formation of opposing magnetic-susceptibility-based gradients within a single continuous material.

Mechano-activated biomolecule release in regenerating load-bearing tissue microenvironments

Although mechanical loads are integral for musculoskeletal tissue homeostasis, overloading and traumatic events can result in tissue injury. Conventional drug delivery approaches for musculoskeletal tissue repair employ localized drug injections. However, rapid drug clearance and inadequate synchronization of molecule provision with healing progression render these methods ineffective. To overcome this, a programmable mechanoresponsive drug delivery system was developed that utilizes the mechanical environment of the tissue during rehabilitation (for example, during cartilage repair) to trigger biomolecule provision. For this, a suite of mechanically-activated microcapsules (MAMCs) with different rupture profiles was generated in a single fabrication batch via osmotic annealing of double emulsions. MAMC physical dimensions were found to dictate mechano-activation in 2D and 3D environments and their stability in vitro and in vivo, demonstrating the tunability of this system. In models of cartilage regeneration, MAMCs did not interfere with tissue growth and activated depending on the mechanical properties of the regenerating tissue. Finally, biologically active anti-inflammatory agents were encapsulated and released from MAMCs, which counteracted degradative cues and prevented the loss of matrix in living tissue environments. This unique technology has tremendous potential for implementation across a wide array of musculoskeletal conditions for enhanced repair of load-bearing tissues.

Guiding Cell Network Assembly using Shape-Morphing Hydrogels

Forces and relative movement between cells and extracellular matrix (ECM) are crucial to the self-organization of tissues during development. However, the spatial range over which these dynamics can be controlled in engineering approaches is limited, impeding progress toward the construction of large, structurally mature tissues. Herein, shape-morphing materials called "kinomorphs" that rationally control the shape and size of multicellular networks are described. Kinomorphs are sheets of ECM that change their shape, size, and density depending on patterns of cell contractility within them. It is shown that these changes can manipulate structure-forming behaviors of epithelial cells in many spatial locations at once. Kinomorphs are built using a new photolithographic technology to pattern single cells into ECM sheets that are >10× larger than previously described. These patterns are designed to partially mimic the branch geometry of the embryonic kidney epithelial network. Origami-inspired simulations are then used to predict changes in kinomorph shapes. Last, kinomorph dynamics are shown to provide a centimeter-scale program that sets specific spatial locations in which ≈50 µm-diameter epithelial tubules form by cell coalescence and structural maturation. The kinomorphs may significantly advance organ-scale tissue construction by extending the spatial range of cell self-organization in emerging model systems such as organoids.

Microfluidic Platforms toward Rational Material Fabrication for Biomedical Applications

The emergence of micro/nanomaterials in recent decades has brought promising alternative approaches in various biomedicine-related fields such as pharmaceutics, diagnostics, and therapeutics. These micro/nanomaterials for specific biomedical applications shall possess tailored properties and functionalities that are closely correlated to their geometries, structures, and compositions, therefore placing extremely high demands for manufacturing techniques. Owing to the superior capabilities in manipulating fluids and droplets at microscale, microfluidics has offered robust and versatile platform technologies enabling rational design and fabrication of micro/nanomaterials with precisely controlled geometries, structures and compositions in high throughput manners, making them excellent candidates for a variety of biomedical applications. This review briefly summarizes the progress of microfluidics in the fabrication of various micro/nanomaterials ranging from 0D (particles), 1D (fibers) to 2D/3D (film and bulk materials) materials with controllable geometries, structures, and compositions. The applications of these microfluidic-based materials in the fields of diagnostics, drug delivery, organs-on-chips, tissue engineering, and stimuli-responsive biodevices are introduced. Finally, an outlook is discussed on the future direction of microfluidic platforms for generating materials with superior properties and on-demand functionalities. The integration of new materials and techniques with microfluidics will pave new avenues for preparing advanced micro/nanomaterials with enhanced performance for biomedical applications.

Bioactive factors for cartilage repair and regeneration: Improving delivery, retention, and activity

Articular cartilage is a remarkable tissue whose sophisticated composition and architecture allow it to withstand complex stresses within the joint. Once injured, cartilage lacks the capacity to self-repair, and injuries often progress to joint wide osteoarthritis (OA) resulting in debilitating pain and loss of mobility. Current palliative and surgical management provides short-term symptom relief, but almost always progresses to further deterioration in the long term. A number of bioactive factors, including drugs, corticosteroids, and growth factors, have been utilized in the clinic, in clinical trials, or in emerging research studies to alleviate the inflamed joint environment or to promote new cartilage tissue formation. However, these therapies remain limited in their duration and effectiveness. For this reason, current efforts are focused on improving the localization, retention, and activity of these bioactive factors. The purpose of this review is to highlight recent advances in drug delivery for the treatment of damaged or degenerated cartilage. First, we summarize material and modification techniques to improve the delivery of these factors to damaged tissue and enhance their retention and action within the joint environment. Second, we discuss recent studies using novel methods to promote new cartilage formation via biofactor delivery, that have potential for improving future long-term clinical outcomes. Lastly, we review the emerging field of orthobiologics, using delivered and endogenous cells as drug-delivering "factories" to preserve and restore joint health. Enhancing drug delivery systems can improve both restorative and regenerative treatments for damaged cartilage. STATEMENT OF SIGNIFICANCE: Articular cartilage is a remarkable and sophisticated tissue that tolerates complex stresses within the joint. When injured, cartilage cannot self-repair, and these injuries often progress to joint-wide osteoarthritis, causing patients debilitating pain and loss of mobility. Current palliative and surgical treatments only provide short-term symptomatic relief and are limited with regards to efficiency and efficacy. Bioactive factors, such as drugs and growth factors, can improve outcomes to either stabilize the degenerated environment or regenerate replacement tissue. This review highlights recent advances and novel techniques to enhance the delivery, localization, retention, and activity of these factors, providing an overview of the cartilage drug delivery field that can guide future research in restorative and regenerative treatments for damaged cartilage.