Bioresponsive microspheres for on-demand delivery of anti-inflammatory cytokines for articular cartilage repair

Bioresponsive Cytokine Delivery Responding to Matrix Metalloproteinases

Cytokines are regulated in acute and chronic inflammation, including rheumatoid arthritis (RA) and myocardial infarction (MI). However, the dynamic windows within which cytokine activity/inhibition is desirable in RA and MI change timely and locally during the disease. Therefore, traditional, static delivery regimens are unlikely to meet the idiosyncrasy of these highly dynamic pathophysiological and individual processes. Responsive delivery systems and biomaterials, sensing surrogate markers of inflammation (i.e., matrix metalloproteinases - MMPs) and answering with drug release, may present drug activity at the right time, manner, and place. This article discusses MMPs as surrogate markers for disease activity in RA and MI to clock drug discharge to MMP concentration profiles from MMP-responsive drug delivery systems and biomaterials.

Advancements in engineered mesenchymal stem cell exosomes for chronic lung disease treatment

Chronic lung diseases include an array of conditions that impact airways and lung structures, leading to considerable societal burdens. Mesenchymal stem cells (MSCs) and their exosomes (MSC-exos) can be used for cell therapy and exhibit a diverse spectrum of anti-inflammatory, antifibrotic, and immunomodulatory properties. Engineered MSC-exos possesses enhanced capabilities for targeted drug delivery, resulting in more potent targeting effects. Through various engineering modifications, these exosomes can exert many biological effects, resulting in specific therapeutic outcomes for many diseases. Moreover, engineered stem cell exosomes may exhibit an increased capacity to traverse physiological barriers and infiltrate protected lesions, thereby exerting their therapeutic effects. These characteristics render them a promising therapeutic agent for chronic pulmonary diseases. This article discusses and reviews the strategies and mechanisms of engineered MSC-exos in the treatment of chronic respiratory diseases based on many studies to provide new solutions for these diseases.

Recent advances in polymeric microparticle-based drug delivery systems for knee osteoarthritis treatment

Due to the poor bioavailability and high joint clearance of drugs, sustained delivery of therapeutic agents has proven difficult in the treatment of osteoarthritis (OA). Intra-articular (IA) drug delivery strategy is an attractive option for enhancing OA patients' prognosis, for which various polymer materials have been used as drug carriers due to their attractive delivery properties, to slow or even reverse the progress of OA by prolonging the duration of therapeutic agent residence in the joint. This article focuses on the recent developments in natural and synthetic polymer-based microsphere drug delivery systems for treating knee osteoarthritis. It evaluates the translational potential of some novel formulations for clinical application.

Engineered biochemical cues of regenerative biomaterials to enhance endogenous stem/progenitor cells (ESPCs)-mediated articular cartilage repair

As a highly specialized shock-absorbing connective tissue, articular cartilage (AC) has very limited self-repair capacity after traumatic injuries, posing a heavy socioeconomic burden. Common clinical therapies for small- to medium-size focal AC defects are well-developed endogenous repair and cell-based strategies, including microfracture, mosaicplasty, autologous chondrocyte implantation (ACI), and matrix-induced ACI (MACI). However, these treatments frequently result in mechanically inferior fibrocartilage, low cost-effectiveness, donor site morbidity, and short-term durability. It prompts an urgent need for innovative approaches to pattern a pro-regenerative microenvironment and yield hyaline-like cartilage with similar biomechanical and biochemical properties as healthy native AC. Acellular regenerative biomaterials can create a favorable local environment for AC repair without causing relevant regulatory and scientific concerns from cell-based treatments. A deeper understanding of the mechanism of endogenous cartilage healing is furthering the (bio)design and application of these scaffolds. Currently, the utilization of regenerative biomaterials to magnify the repairing effect of joint-resident endogenous stem/progenitor cells (ESPCs) presents an evolving improvement for cartilage repair. This review starts by briefly summarizing the current understanding of endogenous AC repair and the vital roles of ESPCs and chemoattractants for cartilage regeneration. Then several intrinsic hurdles for regenerative biomaterials-based AC repair are discussed. The recent advances in novel (bio)design and application regarding regenerative biomaterials with favorable biochemical cues to provide an instructive extracellular microenvironment and to guide the ESPCs (e.g. adhesion, migration, proliferation, differentiation, matrix production, and remodeling) for cartilage repair are summarized. Finally, this review outlines the future directions of engineering the next-generation regenerative biomaterials toward ultimate clinical translation.

Stimulus-Responsive Drug Delivery Nanoplatforms for Osteoarthritis Therapy

Osteoarthritis (OA) is one of the most prevalent age-related degenerative diseases. With an increasingly aging global population, greater numbers of OA patients are providing clear economic and societal burdens. Surgical and pharmacological treatments are the most common and conventional therapeutic strategies for OA, but often fall considerably short of desired or optimal outcomes. With the development of stimulus-responsive nanoplatforms has come the potential for improved therapeutic strategies for OA. Enhanced control, longer retention time, higher loading rates, and increased sensitivity are among the potential benefits. This review summarizes the advanced application of stimulus-responsive drug delivery nanoplatforms for OA, categorized by either those that depend on endogenous stimulus (reactive oxygen species, pH, enzyme, and temperature), or those that depend on exogenous stimulus (near-infrared ray, ultrasound, magnetic fields). The opportunities, restrictions, and limitations related to these various drug delivery systems, or their combinations, are discussed in areas such as multi-functionality, image guidance, and multi-stimulus response. The remaining constraints and potential solutions that are represented by the clinical application of stimulus-responsive drug delivery nanoplatforms are finally summarized.

In Vitro Comparison of 2 Clinically Applied Biomaterials for Autologous Chondrocyte Implantation: Injectable Hydrogel Versus Collagen Scaffold

OBJECTIVE

In autologous chondrocyte implantation (ACI), there is no consensus about used bioscaffolds. The aim of this study was to perform an in vitro comparative analysis of 2 clinically applied biomaterials for cartilage lesion treatment.

DESIGN

Monolayer expanded human chondrocytes (n = 6) were embedded in a collagen scaffold (CS) and a hyaluronic acid-based hydrogel (HA). Cells were cultured in chondropermissive medium supplemented with and without interleukin-10 (IL-10) and bone morphogenetic protein-2 (BMP-2). Gene expression of chondrogenic markers (COL1A1, COL2A1, COL10A1, ACAN, SOX9) was detected via quantitative real-time-polymerase chain reaction (RT-qPCR). Biosynthesis of matrix compounds, cell viability, morphology as well as migration from surrounding native bovine cartilage into cell-free scaffolds were analyzed histologically. Adhesion of the material to adjacent cartilage was investigated by a custom-made push-out test.

RESULTS

The shift of COL1/2 ratio toward COL2A1 was more pronounced in HA, and cells displayed a more spherical morphology compared with CS. BMP-2 and IL-10 significantly increased COL2A1, SOX9, and ACAN expression, which was paralleled by enhanced staining of glycosaminoglycans (GAGs) and type 2 collagen in histological sections of CS and HA. COL10A1 was not significantly expressed in HA and CS. Better interfacial integration and enhanced cell invasion was observed in CS. Push-out tests using CS showed higher bonding strength to native cartilage.

CONCLUSION

HA-based hydrogel revealed a more chondrocyte-like phenotype but only allowed limited cell invasion, whereas CS were advantageous in terms of cellular invasion and interfacial adhesion. These differences may be clinically relevant when treating cartilaginous or osteochondral defects.

Multicolor Light-Induced Immune Activation via Polymer Photocaged Cytokines

Cytokines act as potent, extracellular signals of the human immune system and can elicit striking treatment responses in patients with autoimmune disease, tissue damage, and cancer. Yet, despite their therapeutic potential, recombinant cytokine-mediated immune responses remain difficult to control as their administration is often systemic, whereas their intended sites of action are localized. To address the challenge of spatially and temporally constraining cytokine signals, we recently devised a strategy whereby recombinant cytokines are reversibly inactivated via chemical modification with photo-labile polymers that respond to visible LED light. Extending this approach to enable both in vivo and multicolor immune activation, here we describe a strategy whereby cytokines appended with heptamethine cyanine-polyethylene glycol are selectively re-activated ex vivo using tissue-penetrating near-infrared (NIR) light. We show that NIR LED light illumination of caged, pro-inflammatory cytokines restores cognate receptor signaling and potentiates the activity of T cell-engager cancer immunotherapies ex vivo. Using combinations of visible- and NIR-responsive cytokines, we further demonstrate multiwavelength optical control of T cell cytolysis ex vivo, as well as the ability to perform Boolean logic using multicolored light and orthogonally photocaged cytokine pairs as inputs and T cell activity as outputs. Together, this work demonstrates a novel approach to control extracellular immune cell signals using light, a strategy that in the future may improve our understanding of and ability to treat cancer and other diseases.

Adhesive hydrogels in osteoarthritis: from design to application

Osteoarthritis (OA) is the most common type of degenerative joint disease which affects 7% of the global population and more than 500 million people worldwide. One research frontier is the development of hydrogels for OA treatment, which operate either as functional scaffolds of tissue engineering or as delivery vehicles of functional additives. Both approaches address the big challenge: establishing stable integration of such delivery systems or implants. Adhesive hydrogels provide possible solutions to this challenge. However, few studies have described the current advances in using adhesive hydrogel for OA treatment. This review summarizes the commonly used hydrogels with their adhesion mechanisms and components. Additionally, recognizing that OA is a complex disease involving different biological mechanisms, the bioactive therapeutic strategies are also presented. By presenting the adhesive hydrogels in an interdisciplinary way, including both the fields of chemistry and biology, this review will attempt to provide a comprehensive insight for designing novel bioadhesive systems for OA therapy.

Targeted and responsive biomaterials in osteoarthritis

Osteoarthritis (OA) is a degenerative disease characterized by loss of articular cartilage and chronic inflammation, involving multiple cellular dysfunctions and tissue lesions. The non-vascular environment and dense cartilage matrix in the joints tend to block drug penetration, resulting in low drug bioavailability. There is a desire to develop safer and more effective OA therapies to meet the challenges of an aging world population in the future. Biomaterials have achieved satisfactory results in improving drug targeting, prolonging the duration of action, and achieving precision therapy. This article reviews the current basic understanding of the pathological mechanisms and clinical treatment dilemmas of OA, summarizes and discusses the advances for different kinds of targeted and responsive biomaterials in OA, seeking to provide new perspectives for the treatment of OA. Subsequently, limitations and challenges in clinical translation and biosafety are analyzed to guide the development of future therapeutic strategies for OA. As the need for precision medicine rises over time, emerging multifunctional biomaterials based on tissue targeting and controlled release will become an irreplaceable part of OA management.

Microcarriers in application for cartilage tissue engineering: Recent progress and challenges

Successful regeneration of cartilage tissue at a clinical scale has been a tremendous challenge in the past decades. Microcarriers (MCs), usually used for cell and drug delivery, have been studied broadly across a wide range of medical fields, especially the cartilage tissue engineering (TE). Notably, microcarrier systems provide an attractive method for regulating cell phenotype and microtissue maturations, they also serve as powerful injectable carriers and are combined with new technologies for cartilage regeneration. In this review, we introduced the typical methods to fabricate various types of microcarriers and discussed the appropriate materials for microcarriers. Furthermore, we highlighted recent progress of applications and general design principle for microcarriers. Finally, we summarized the current challenges and promising prospects of microcarrier-based systems for medical applications. Overall, this review provides comprehensive and systematic guidelines for the rational design and applications of microcarriers in cartilage TE.

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This review summarized fabrication techniques and cartilage repaired application of microcarriers.

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The appropriate materials and design principle for microcarriers in cartilage tissue engineering are discussed.

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Promising future perspectives and challenges in microcarriers fields are outlined.

Injectable nanoporous microgels generate vascularized constructs and support bone regeneration in critical-sized defects

Large and aberrant bone fractures require ossification and concomitant vascularization for proper healing. Evidence indicates that osteogenesis and vessel growth are coupled in bone fractures. Although the synergistic role of endothelial cells has been recognized, vascularizing large bone grafts remains a challenge and has apprehended the clinical translation of engineered bone constructs. Here, we describe a facile method to fabricate vascularized constructs using chitosan and gelatin-based microgels that promote osteogenesis of human mesenchymal stromal cells (MSC) while supporting endothelial sprouting and network formation. The microgels are enzymatically degradable and had a high hydration rate with a volume swelling ratio of ~ 493% and a polymer density of ~ 431 mg/cm3, which is comparable to that of native skeletal tissues. AFM indentation of the surface showed an average Young's modulus of 189 kPa, falling in a range that is conducive to both osteogenesis and vasculogenesis. The osteogenic microgel containing chitosan, gelatin, and hydroxyapatite, mimicking the bone matrix, supported robust attachment, proliferation, and differentiation of MSC. On the other hand, the vasculogenic microgels containing only gelatin, enriched endothelial phenotype and enabled vascular networks formation when embedded in 3D matrices. Combining the two types of microgels created a hybrid construct that sustained the functions of both osteogenic and vasculogenic microgels and enhanced one another. Using a murine model, we also show that the osteogenic microgels regenerate bone in a critical-sized defect with > 95% defect closure by week 12. These multifunctional microgels can be administered minimally invasively and can conformally fill large bone defects. This work lays the foundation to establish principles of designing multiphasic scaffolds with tissue-specific biophysical and biochemical properties for regenerating vascularized and interfacial tissues.

Licensing microgels prolong the immunomodulatory phenotype of mesenchymal stromal cells

Mesenchymal stromal cells (MSC) are sensors of inflammation, and they exert immunomodulatory properties through the secretion of cytokines and exosomes and direct cell-cell interactions. MSC are routinely used in clinical trials and effectively resolve inflammatory conditions. Nevertheless, inconsistent clinical outcomes necessitate the need for more robust therapeutic phenotypes. The immunomodulatory properties of MSC can be enhanced and protracted by priming (aka licensing) them with IFNγ and TNFα. Yet these enhanced properties rapidly diminish, and prolonged stimulation could tolerize their response. Hence a balanced approach is needed to enhance the therapeutic potential of the MSC for consistent clinical performance. Here, we investigated the concentration-dependent effects of IFNγ and TNFα and developed gelatin-based microgels to sustain a licensed MSC phenotype. We show that IFNγ treatment is more beneficial than TNFα in promoting an immunomodulatory MSC phenotype. We also show that the microgels possess integrin-binding sites to support adipose tissue-derived MSC (AD-MSC) attachment and a net positive charge to sequester the licensing cytokines electrostatically. Microgels are enzymatically degradable, and the rate is dependent on the enzyme concentration and matrix density. Our studies show that one milligram of microgels by dry mass can sequester up to 641 ± 81 ng of IFNγ. Upon enzymatic degradation, microgels exhibited a sustained release of IFNγ that linearly correlated with their degradation rate. The AD-MSC cultured on the IFNγ sequestered microgels displayed efficient licensing potential comparable to or exceeding the effects of bolus IFNγ treatment. When cultured with proinflammatory M1-like macrophages, the AD-MSC-seeded on licensing microgel showed an enhanced immunomodulatory potential compared to untreated AD-MSC and AD-MSC treated with bolus IFNγ treatment. Specifically, the AD-MSC seeded on licensing microgels significantly upregulated Arg1, Mrc1, and Igf1, and downregulated Tnfα in M1-like macrophages compared to other treatment conditions. These licensing microgels are a potent immunomodulatory approach that shows substantial promise in elevating the efficacy of current MSC therapies and may find utility in treating chronic inflammatory conditions.

The Role of Interleukin-4 and Interleukin-10 in Osteoarthritic Joint Disease: A Systematic Narrative Review

OBJECTIVE

A fusion protein of interleukin-4 and interleukin-10 (IL4-10 FP) was developed as a disease-modifying osteoarthritis drug (DMOAD), and chondroprotection, anti-inflammation, and analgesia have been suggested. To better understand the mechanisms behind its potential as DMOAD, this systematic narrative review aims to assess the potential of IL-4, IL-10 and the combination of IL-4 and IL-10 for the treatment of osteoarthritis. It describes the chondroprotective, anti-inflammatory, and analgesic effects of IL-4, IL-10, and IL4-10 FP.

DESIGN

PubMed and Embase were searched for publications that were published from 1990 until May 21, 2021 (moment of search). Key search terms were: Osteoarthritis, Interleukin-4, and Interleukin-10. This yielded 2,479 hits, of which 43 were included in this review.

RESULTS

IL-4 and IL-10 showed mainly protective effects on osteoarthritic cartilage in vitro and in vivo, as did IL4-10 FP. Both cytokines showed anti-inflammatory effects, but also proinflammatory effects. Only in vitro IL4-10 FP showed purely anti-inflammatory effects, indicating that proinflammatory effects of one cytokine can be counteracted by the other when given as a combination. Only a few studies investigated the analgesic effects of IL-4, IL-10 or IL4-10 FP. In vitro, IL-4 and IL4-10 FP were able to decrease pain mediators. In vivo, IL-4, IL-10, and IL4-10 FP were able to reduce pain.

CONCLUSIONS

In conclusion, this review describes overlapping, but also different modes of action for the DMOAD effects of IL-4 and IL-10, giving an explanation for the synergistic effects found when applied as combination, as is the case for IL4-10 FP.

Knee Osteoarthritis Therapy: Recent Advances in Intra-Articular Drug Delivery Systems

Drug delivery for osteoarthritis (OA) treatment is a continuous challenge because of their poor bioavailability and rapid clearance in joints. Intra-articular (IA) drug delivery is a common strategy and its therapeutic effects depend mainly on the efficacy of the drug-delivery system used for OA therapy. Different types of IA drug-delivery systems, such as microspheres, nanoparticles, and hydrogels, have been rapidly developed over the past decade to improve their therapeutic effects. With the continuous advancement in OA mechanism research, new drugs targeting specific cell/signaling pathways in OA are rapidly evolving and effective drug delivery is critical for treating OA. In this review, recent advances in various IA drug-delivery systems for OA treatment, OA targeted strategies, and related signaling pathways in OA treatment are summarized and analyzed based on current publications.

Cartilage tissue engineering: From proinflammatory and anti‑inflammatory cytokines to osteoarthritis treatments (Review)

Osteoarthritis (OA), one of the most common joint diseases, is characterized by fibrosis, rhagadia, ulcers and attrition of articular cartilage due to a number of factors. The etiology of OA remains unclear, but its occurrence has been associated with age, obesity, inflammation, trauma and genetic factors. Inflammatory cytokines are crucial for the occurrence and progression of OA. The intra-articular proinflammatory and anti-inflammatory cytokines jointly maintain a dynamic balance, in accordance with the physiological metabolism of articular cartilage. However, dynamic imbalance between proinflammatory and anti-inflammatory cytokines can cause abnormal metabolism in knee articular cartilage, which leads to deformation, loss and abnormal regeneration, and ultimately destroys the normal structure of the knee joint. The ability of articular cartilage to self-repair once damaged is limited, due to its inability to obtain nutrients from blood vessels, nerves and lymphatic vessels, as well as limitations in the extracellular matrix. There are several disadvantages inherent to conventional repair methods, while cartilage tissue engineering (CTE), which combines proinflammatory and anti-inflammatory cytokines, offers a new therapeutic approach for OA. The aim of the present review was to examine the proinflammatory factors implicated in OA, including IL-1β, TNF-α, IL-6, IL-15, IL-17 and IL-18, as well as the key anti-inflammatory factors reducing OA-related articular damage, including IL-4, insulin-like growth factor and TGF-β. The predominance of proinflammatory over anti-inflammatory cytokine effects ultimately leads to the development of OA. CTE, which employs mesenchymal stem cells and scaffolding technology, may prevent OA by maintaining the homeostasis of pro- and anti-inflammatory factors.

Controlled Growth Factor Delivery and Cyclic Stretch Induces a Smooth Muscle Cell-like Phenotype in Adipose-Derived Stem Cells

Adipose-derived stem cells (ASCs) are an abundant and easily accessible multipotent stem cell source with potential application in smooth muscle regeneration strategies. In 3D collagen hydrogels, we investigated whether sustained release of growth factors (GF) PDGF-AB and TGF-β1 from GF-loaded microspheres could induce a smooth muscle cell (SMC) phenotype in ASCs, and if the addition of uniaxial cyclic stretch could enhance the differentiation level. This study demonstrated that the combination of cyclic stretch and GF release over time from loaded microspheres potentiated the differentiation of ASCs, as quantified by protein expression of early to late SMC differentiation markers (SMA, TGLN and smooth muscle MHC). The delivery of GFs via microspheres produced large ASCs with a spindle-shaped, elongated SMC-like morphology. Cyclic strain produced the largest, longest, and most spindle-shaped cells regardless of the presence or absence of growth factors or the growth factor delivery method. Protein expression and cell morphology data confirmed that the sustained release of GFs from GF-loaded microspheres can be used to promote the differentiation of ASCs into SMCs and that the addition of uniaxial cyclic stretch significantly enhances the differentiation level, as quantified by intermediate and late SMC markers and a SMC-like elongated cell morphology.

A Review of the Use of Microparticles for Cartilage Tissue Engineering

Tissue and organ failure has induced immense economic and healthcare concerns across the world. Tissue engineering is an interdisciplinary biomedical approach which aims to address the issues intrinsic to organ donation by providing an alternative strategy to tissue and organ transplantation. This review is specifically focused on cartilage tissue. Cartilage defects cannot readily regenerate, and thus research into tissue engineering approaches is relevant as a potential treatment option. Cells, scaffolds, and growth factors are three components that can be utilized to regenerate new tissue, and in particular recent advances in microparticle technology have excellent potential to revolutionize cartilage tissue regeneration. First, microspheres can be used for drug delivery by injecting them into the cartilage tissue or joint space to reduce pain and stimulate regeneration. They can also be used as controlled release systems within tissue engineering constructs. Additionally, microcarriers can act as a surface for stem cells or chondrocytes to adhere to and expand, generating large amounts of cells, which are necessary for clinically relevant cell therapies. Finally, a newer application of microparticles is to form them together into granular hydrogels to act as scaffolds for tissue engineering or to use in bioprinting. Tissue engineering has the potential to revolutionize the space of cartilage regeneration, but additional research is needed to allow for clinical translation. Microparticles are a key enabling technology in this regard.

Engineering Strategies for Immunomodulatory Cytokine Therapies - Challenges and Clinical Progress

Cytokines are immunoregulatory proteins involved in many pathological states with promising potential as therapeutic agents. A diverse array of cytokines have been studied in preclinical disease models since the 1950s, some of which became successful biopharmaceutical products with the advancement of recombinant protein technology in the 1980s. However, following these early approvals, clinical translation of these natural immune signaling molecules has been limited due to their pleiotropic action in many cell types, and the fact that they have evolved to act primarily locally in tissues. These characteristics, combined with poor pharmacokinetics, have hindered the delivery of cytokines via systemic administration routes due to dose-limiting toxicities. However, given their clinical potential and recent clinical successes in cancer immunotherapy, cytokines continue to be extensively pursued in preclinical and clinical studies, and a range of molecular and formulation engineering strategies are being applied to reduce treatment toxicity while maintaining or enhancing therapeutic efficacy. This review provides a brief background on the characteristics of cytokines and their history as clinical therapeutics, followed by a deeper discussion on the engineering strategies developed for cytokine therapies with a focus on the translational relevance of these approaches.

Anti-Inflammatory Therapeutic Approaches to Prevent or Delay Post-Traumatic Osteoarthritis (PTOA) of the Knee Joint with a Focus on Sustained Delivery Approaches

Inflammation plays a central role in the pathogenesis of knee PTOA after knee trauma. While a comprehensive therapy capable of preventing or delaying post-traumatic osteoarthritis (PTOA) progression after knee joint injury does not yet clinically exist, current literature suggests that certain aspects of early post-traumatic pathology of the knee joint may be prevented or delayed by anti-inflammatory therapeutic interventions. We discuss multifaceted therapeutic approaches that may be capable of effectively reducing the continuous cycle of inflammation and concomitant processes that lead to cartilage degradation as well as those that can simultaneously promote intrinsic repair processes. Within this context, we focus on early disease prevention, the optimal timeframe of treatment and possible long-lasting sustained delivery local modes of treatments that could prevent knee joint-associated PTOA symptoms. Specifically, we identify anti-inflammatory candidates that are not only anti-inflammatory but also anti-degenerative, anti-apoptotic and pro-regenerative.

Inflammation-responsive delivery systems for the treatment of chronic inflammatory diseases

Inflammation is the biological response of immune system to protect living organisms from injurious factors. However, excessive and uncontrolled inflammation is implicated in a variety of devastating chronic diseases including atherosclerosis, inflammatory bowel disease (IBD), and rheumatoid arthritis (RA). Improved understanding of inflammatory response has unveiled a rich assortment of anti-inflammatory therapeutics for the treatment and management of relevant chronic diseases. Notwithstanding these successes, clinical outcomes are variable among patients and serious adverse effects are often observed. Moreover, there exist some limitations for clinical anti-inflammatory therapeutics such as aqueous insolubility, low bioavailability, off-target effects, and poor accessibility to subcellular compartments. To address these challenges, the rational design of inflammation-specific drug delivery systems (DDSs) holds significant promise. Moreover, as compared to normal tissues, inflamed tissue-associated pathological milieu (e.g., oxidative stress, acidic pH, and overexpressed enzymes) provides vital biochemical stimuli for triggered delivery of anti-inflammatory agents in a spatiotemporally controlled manner. In this review, we summarize recent advances in the development of anti-inflammatory DDSs with built-in pathological inflammation-specific responsiveness for the treatment of chronic inflammatory diseases.

Recent developments in natural and synthetic polymeric drug delivery systems used for the treatment of osteoarthritis

Osteoarthritis (OA), is a common musculoskeletal disorder that will progressively increase in older populations and is expected to be the most dominant cause of disability in the world population by 2030. The progression of OA is controlled by a multi-factorial pathway that has not been completely elucidated and understood yet. However, over the years, research efforts have provided a significant understanding of some of the processes contributing to the progression of OA. Both cartilage and bone degradation processes induce articular cells to produce inflammatory mediators that produce proinflammatory cytokines that block the synthesis of collagen type II and aggrecan, the major components of cartilage. Systemic administration and intraarticular injection of anti-inflammatory agents are the first-line treatments of OA. However, small anti-inflammatory molecules are rapidly cleared from the joint cavity which limits their therapeutic efficacy. To palliate this strong technological drawback, different types of polymeric materials such as microparticles, nanoparticles, and hydrogels, have been examined as drug carriers for the delivery of therapeutic agents to articular joints. The main purpose of this review is to provide a summary of recent developments in natural and synthetic polymeric drug delivery systems for the delivery of anti-inflammatory agents to arthritic joints. Furthermore, this review provides an overview of the design rules that have been proposed so far for the development of drug carriers used in OA therapy. Overall it is difficult to state clearly which polymeric platform is the most efficient one because many advantages and disadvantages could be pointed to both natural and synthetic formulations. That requires further research in the near future.

An Evidence-Based Systematic Review of Human Knee Post-Traumatic Osteoarthritis (PTOA): Timeline of Clinical Presentation and Disease Markers, Comparison of Knee Joint PTOA Models and Early Disease Implications

Understanding the causality of the post-traumatic osteoarthritis (PTOA) disease process of the knee joint is important for diagnosing early disease and developing new and effective preventions or treatments. The aim of this review was to provide detailed clinical data on inflammatory and other biomarkers obtained from patients after acute knee trauma in order to (i) present a timeline of events that occur in the acute, subacute, and chronic post-traumatic phases and in PTOA, and (ii) to identify key factors present in the synovial fluid, serum/plasma and urine, leading to PTOA of the knee in 23-50% of individuals who had acute knee trauma. In this context, we additionally discuss methods of simulating knee trauma and inflammation in in vivo, ex vivo articular cartilage explant and in vitro chondrocyte models, and answer whether these models are representative of the clinical inflammatory stages following knee trauma. Moreover, we compare the pro-inflammatory cytokine concentrations used in such models and demonstrate that, compared to concentrations in the synovial fluid after knee trauma, they are exceedingly high. We then used the Bradford Hill Framework to present evidence that TNF-α and IL-6 cytokines are causal factors, while IL-1β and IL-17 are credible factors in inducing knee PTOA disease progresssion. Lastly, we discuss beneficial infrastructure for future studies to dissect the role of local vs. systemic inflammation in PTOA progression with an emphasis on early disease.

Progress of gelatin-based microspheres (GMSs) as delivery vehicles of drug and cell

Gelatin has various attractive features as biomedical materials, for instance, biocompatibility, low immunogenicity, biodegradability, and ease of manipulation. In recent years, various gelatin-based microspheres (GMSs) have been fabricated with innovative technologies to serve as sustained delivery vehicles of drugs and genetic materials as well as beneficial bacteria. Moreover, GMSs have exhibited promising potentials to act as both cell carriers and 3D scaffold components in tissue engineering and regenerative medicine, which not only exhibit excellent injectability but also could be integrated into a macroscale construct with the laden cells. Herein, we aim to thoroughly summarize the recent progress in the preparations and biomedical applications of GMSs and then to point out the research direction in future. First, various methods for the fabrication of GMSs will be described. Second, the recent use of GMSs in tumor embolization and in the delivery of cells, drugs, and genetic material as well as bacteria will be presented. Finally, several key factors that may enhance the improvement of GMSs were suggested as delivery vehicles.

Potential and recent advances of microcarriers in repairing cartilage defects

Articular cartilage regeneration is one of the challenges faced by orthopedic surgeons. Microcarrier applications have made great advances in cartilage tissue engineering in recent years and enable cost-effective cell expansion, thus providing permissive microenvironments for cells. In addition, microcarriers can be loaded with proteins, factors, and drugs for cartilage regeneration. Some microcarriers also have the advantages of injectability and targeted delivery. The application of microcarriers with these characteristics can overcome the limitations of traditional methods and provide additional advantages. In terms of the transformation potential, microcarriers have not only many advantages, such as providing sufficient and beneficial cells, factors, drugs, and microenvironments for cartilage regeneration, but also many application characteristics; for example, they can be injected to reduce invasiveness, transplanted after microtissue formation to increase efficiency, or combined with other stents to improve mechanical properties. Therefore, this technology has enormous potential for clinical transformation. In this review, we focus on recent advances in microcarriers for cartilage regeneration. We compare the characteristics of microcarriers with other methods for repairing cartilage defects, provide an overview of the advantages of microcarriers, discuss the potential of microcarrier systems, and present an outlook for future development.

Translational potential of this article

We reviewed the advantages and recent advances of microcarriers for cartilage regeneration. This review could give many scholars a better understanding of microcarriers, which can provide doctors with potential methods for treating patients with cartilage injure.

An interleukin-4-loaded bi-layer 3D printed scaffold promotes osteochondral regeneration

Multilayer scaffolds fabricated by 3D printing or other techniques have been used to repair osteochondral defects. However, it remains a challenge to regenerate the articular cartilage and subchondral bone simultaneously with higher performance. In the present study, we enhanced the repair efficiency of osteochondral defects by developing a bi-layer scaffold: an interleukin-4 (IL-4)-loaded radially oriented gelatin methacrylate (GelMA) scaffold printed with digital light processing (DLP) in the upper layer and a porous polycaprolactone and hydroxyapatite (PCL-HA) scaffold printed with fused deposition modeling (FDM) in the lower layer. An in vitro test showed that both layers supported cell adhesion and proliferation, as the lower layer promoted osteogenic differentiation and the upper layer with IL-4 relieved the negative effects of inflammation on murine chondrocytes, which were induced by interleukin-1β (IL-1β) and M1 macrophages. In a rabbit osteochondral defect repair model, the IL-4-loaded bi-layer scaffold group obtained the highest histological score (24 ± 2) compared to the nontreated (11 ± 1) and pure bi-layer scaffold (16 ± 1) groups after 16 weeks of implantation, which showed that the IL-4-loaded bi-layer scaffold promoted regeneration of both cartilage and subchondral bone with increased formation of neocartilage and neobone tissues. Thus, the IL-4-loaded bi-layer scaffold is an attractive candidate for repair and regeneration of osteochondral defects.

Advanced Polymer-Based Drug Delivery Strategies for Meniscal Regeneration

The meniscus plays a critical role in maintaining knee joint homeostasis. Injuries to the meniscus, especially considering the limited self-healing capacity of the avascular region, continue to be a challenge and are often treated by (partial) meniscectomy, which has been identified to cause osteoarthritis. Currently, meniscus tissue engineering focuses on providing extracellular matrix (ECM)-mimicking scaffolds to direct the inherent meniscal regeneration process, and it has been found that various stimuli are essential. Numerous bioactive factors present benefits in regulating cell fate, tissue development, and healing, but lack an optimal delivery system. More recently, bioengineers have developed various polymer-based drug delivery systems (PDDSs), which are beneficial in terms of the favorable properties of polymers as well as novel delivery strategies. Engineered PDDSs aim to provide not only an ECM-mimicking microenvironment but also the controlled release of bioactive factors with release profiles tailored according to the biological concerns and properties of the factors. In this review, both different polymers and bioactive factors involved in meniscal regeneration are discussed, as well as potential candidate systems, with examples of recent progress. This article aims to summarize drug delivery strategies in meniscal regeneration, with a focus on novel delivery strategies rather than on specific delivery carriers. The current challenges and future prospects for the structural and functional regeneration of the meniscus are also discussed. Impact statement Meniscal injury remains a clinical Gordian knot owing to the limited healing potential of the region, restricted surgical approaches, and risk of inducing osteoarthritis. Existing tissue engineering scaffolds that provide mechanical support and a favorable microenvironment also lack biological cues. Advanced polymer-based delivery strategies consisting of polymers incorporating bioactive factors have emerged as a promising direction. This article primarily reviews the types and applications of biopolymers and bioactive factors in meniscal regeneration. Importantly, various carrier systems and drug delivery strategies are discussed with the hope of inspiring further advancements in this field.

Gelatin Microsphere for Cartilage Tissue Engineering: Current and Future Strategies

The gelatin microsphere (GM) provides an attractive option for tissue engineering due to its versatility, as reported by various studies. This review presents the history, characteristics of, and the multiple approaches to, the production of GM, and in particular, the water in oil emulsification technique. Thereafter, the application of GM as a drug delivery system for cartilage diseases is introduced. The review then focusses on the emerging application of GM as a carrier for cells and biologics, and biologics delivery within a cartilage construct. The influence of GM on chondrocytes in terms of promoting chondrocyte proliferation and chondrogenic differentiation is highlighted. Furthermore, GM seeded with cells has been shown to have a high tendency to form aggregates; hence the concept of using GM seeded with cells as the building block for the formation of a complex tissue construct. Despite the advancement in GM research, some issues must still be addressed, particularly the improvement of GM’s ability to home to defect sites. As such, the strategy of intraarticular injection of GM seeded with antibody-coated cells is proposed. By addressing this in future studies, a better-targeted delivery system, that would result in more effective intervention, can be achieved.

Pathomechanisms of Posttraumatic Osteoarthritis: Chondrocyte Behavior and Fate in a Precarious Environment

Traumatic injuries of the knee joint result in a wide variety of pathomechanisms, which contribute to the development of so-called posttraumatic osteoarthritis (PTOA). These pathogenetic processes include oxidative stress, excessive expression of catabolic enzymes, release of damage-associated molecular patterns (DAMPs), and synovial inflammation. The present review focuses on the underlying pathomechanisms of PTOA and in particular the behavior and fate of the surviving chondrocytes, comprising chondrocyte metabolism, regulated cell death, and phenotypical changes comprising hypertrophy and senescence. Moreover, possible therapeutic strategies, such as chondroanabolic stimulation, anti-oxidative and anti-inflammatory treatment, as well as novel therapeutic targets are discussed.