In situ formation of hydrophobic clusters to enhance mechanical performance of biodegradable poly(l-glutamic acid)/poly(ε-caprolactone) hydrogel towards meniscus tissue engineering

Preclinical Studies and Clinical Trials on Cell-Based Treatments for Meniscus Regeneration

This study aims at performing a thorough review of cell-based treatment strategies for meniscus regeneration in preclinical and clinical studies. The PubMed, Embase, and Web of Science databases were searched for relevant studies (both preclinical and clinical) published from the time of database construction to December 2022. Data related to cell-based therapies for in situ regeneration of the meniscus were extracted independently by two researchers. Assessment of risk of bias was performed according to the Cochrane Handbook for Systematic Reviews of Interventions. Statistical analyses based on the classification of different treatment strategies were performed. A total of 5730 articles were retrieved, of which 72 preclinical studies and 6 clinical studies were included in this review. Mesenchymal stem cells (MSCs), especially bone marrow MSCs (BMSCs), were the most commonly used cell type. Among preclinical studies, rabbit was the most commonly used animal species, partial meniscectomy was the most commonly adopted injury pattern, and 12 weeks was the most frequently chosen final time point for assessing repair outcomes. A range of natural and synthetic materials were used to aid cell delivery as scaffolds, hydrogels, or other morphologies. In clinical trials, there was large variation in the dose of cells, ranging from 16 × 106 to 150 × 106 cells with an average of 41.52 × 106 cells. The selection of treatment strategy for meniscus repair should be based on the nature of the injury. Cell-based therapies incorporating various "combination" strategies such as co-culture, composite materials, and extra stimulation may offer greater promise than single strategies for effective meniscal tissue regeneration, restoring natural meniscal anisotropy, and eventually achieving clinical translation. Impact Statement This review provides an up-to-date and comprehensive overview of preclinical and clinical studies that tested cell-based treatments for meniscus regeneration. It presents novel perspectives on studies published in the past 30 years, giving consideration to the cell sources and dose selection, delivery methods, extra stimulation, animal models and injury patterns, timing of outcome assessment, and histological and biomechanical outcomes, as well as a summary of findings for individual studies. These unique insights will help to shape future research on the repair of meniscus lesions and inform the clinical translation of new cell-based tissue engineering strategies.

Synthetic strain-stiffening hydrogels towards mechanical adaptability

Living organisms are made of wet, soft tissues. However, there is only one candidate to simultaneously replicate the mechanical and composition features of load-bearing tissues, that is, strain-stiffening hydrogels. The conventional mechanical match design principle is mostly limited to stiffness matching. However, this strategy cannot sufficiently and necessarily lead to mechanical matching over the whole physiologic deformation period for tissues and damages the tissues over time. In this review, we aim to provide a comprehensive summary of the reported synthetic strain-stiffening hydrogels and particularly focus on the relationship between their structure and performance. Initially, we present a brief introduction on the significance of strain-stiffening hydrogels in mimicking the mechanics of tissues, and then we discuss the qualitative evaluation of the strain-stiffening behaviors to guide the design of materials towards mimicking soft tissue. After distinguishing the mechanical testing methods, we focus on the methods for the preparation of typical strain-stiffening hydrogels based on categories, such as network without strand entanglement, semiflexible network, and anisotropic networks. Subsequently, we discuss the structural evolution of strain-stiffening hydrogels. We hope that this review will serve as an updated introduction and reference for researchers who are interested in exploring strain-stiffening hydrogels as tissue-mimics for addressing the societal needs at various frontiers.

Applications and prospects of different functional hydrogels in meniscus repair

The meniscus is a kind of fibrous cartilage structure that serves as a cushion in the knee joint to alleviate the mechanical load. It is commonly injured, but it cannot heal spontaneously. Traditional meniscectomy is not currently recommended as this treatment tends to cause osteoarthritis. Due to their good biocompatibility and versatile regulation, hydrogels are emerging biomaterials in tissue engineering. Hydrogels are excellent candidates in meniscus rehabilitation and regeneration because they are fine-tunable, easily modified, and capable of delivering exogenous drugs, cells, proteins, and cytokines. Various hydrogels have been reported to work well in meniscus-damaged animals, but few hydrogels are effective in the clinic, indicating that hydrogels possess many overlooked problems. In this review, we summarize the applications and problems of hydrogels in extrinsic substance delivery, meniscus rehabilitation, and meniscus regeneration. This study will provide theoretical guidance for new therapeutic strategies for meniscus repair.

Stereolithographic Visible-Light Printing of Poly(l-glutamic acid) Hydrogel Scaffolds

Bioprinting is a promising fabrication technique aimed at developing biologically functional, tissue-like constructs for various biomedical applications. Among the different bioprinting approaches, vat polymerization-based techniques offer the highest feature resolution compared to more commonly used extrusion-based methods and therefore have greater potential to be utilized for printing complex hierarchical tissue architectures. Although significant efforts have been directed toward harnessing digital light processing techniques for high-resolution bioprinting, the use of stereolithography (SLA) setups for producing distinct hydrogel filaments smaller than 20 μm has received less attention. Improving the bioprinting resolution is still a technical challenge that must consider both the practical limitations of the bioprinter apparatus and the formulation of the cytocompatible bioresin. In this study, we developed a novel bioresin compatible with SLA and capable of printing high-resolution features. This resin, composed of a biosynthetic polypeptide poly(l-glutamic acid) functionalized with tyramine moieties (PLGA-Tyr), was crosslinked using a visible-light photoinitiator system. Varying concentrations of PLGA-Tyr and the co-photoinitiator were evaluated for the hydrogel system's gelation ability, swelling characteristics, degradation profiles, mechanical properties, and cell viability post-encapsulation. This study introduces a custom-built, cost-effective, visible-light SLA bioprinting system named the "MicroNC". Using the newly developed visible-light bioresin, we demonstrated for the first time the ability to fabricate hydrogel scaffolds with well-resolved filaments (less than 8 μm in width) capable of supporting cell viability and proliferation and directing cellular morphology at the single-cell level for up to 14 days. Overall, these experiments have underscored the exciting potential of using the visible-light-photoinitiated PLGA-Tyr material system for developing physiologically relevant in vitro hydrogel scaffolds with feature resolutions comparable to the dimensions of individual human cells for a wide range of biomedical applications.

Ultrashort Peptides and Hyaluronic Acid-Based Injectable Composite Hydrogels for Sustained Drug Release and Chronic Diabetic Wound Healing

Peptide hydrogels are widely used for biomedical applications owing to their good biocompatibility and unique advantages in terms of amino acid-based structures and functions. However, the exploration of the peptide/saccharide composite hydrogels as potential biomaterials for chronic diabetic wound healing is still limited. Herein, hyaluronic acid (HA) was incorporated into diphenylalanine (FF) conjugated with different aromatic moieties by a one-pot reaction. Our results showed that the dipeptide derivatives modified by benzene (B), naphthalene (N), and pyrene (P) self-assembled into composite hydrogels with uniform distribution and good mechanical properties in the presence of HA. The obtained N-FF/HA composite hydrogel exhibited greatly improved self-healing properties via injection syringe needle operation and good biocompatibility on human skin fibroblast (HSF) cells. Besides, the structure of thinner nanofibers and honeycomb networks inside the composite hydrogel allowed for a longer sustained release of curcumin, a hydrophobic drug for anti-inflammation and wound healing. The curcumin-loaded N-FF/HA composite hydrogels could promote chronic wound healing in the streptozotocin-induced type I diabetic mouse model. The results suggested that our developed saccharide-peptide hydrogels could serve as very promising synthetic biomaterials for applications in both drug delivery and wound healing in the future.

From Residues to Added-Value Bacterial Biopolymers as Nanomaterials for Biomedical Applications

Bacterial biopolymers are naturally occurring materials comprising a wide range of molecules with diverse chemical structures that can be produced from renewable sources following the principles of the circular economy. Over the last decades, they have gained substantial interest in the biomedical field as drug nanocarriers, implantable material coatings, and tissue-regeneration scaffolds or membranes due to their inherent biocompatibility, biodegradability into nonhazardous disintegration products, and their mechanical properties, which are similar to those of human tissues. The present review focuses upon three technologically advanced bacterial biopolymers, namely, bacterial cellulose (BC), polyhydroxyalkanoates (PHA), and γ-polyglutamic acid (PGA), as models of different carbon-backbone structures (polysaccharides, polyesters, and polyamides) produced by bacteria that are suitable for biomedical applications in nanoscale systems. This selection models evidence of the wide versatility of microorganisms to generate biopolymers by diverse metabolic strategies. We highlight the suitability for applied sustainable bioprocesses for the production of BC, PHA, and PGA based on renewable carbon sources and the singularity of each process driven by bacterial machinery. The inherent properties of each polymer can be fine-tuned by means of chemical and biotechnological approaches, such as metabolic engineering and peptide functionalization, to further expand their structural diversity and their applicability as nanomaterials in biomedicine.

Ultrasound-targeted microbubble destruction augmented synergistic therapy of rheumatoid arthritis via targeted liposomes

Rheumatoid arthritis (RA) can lead to joint destruction and deformity, which is a significant cause of the loss of the young and middle-aged labor force. However, the treatment of RA is still filled with challenges. Though dexamethasone, one of the glucocorticoids, is commonly used in the treatment of RA, its clinical use is limited because of the required high-dose and long-term use, unsatisfactory therapeutic effects, and various side-effects. Ultrasound-targeted microbubble destruction (UTMD) can augment the ultrasonic cavitation effects and trigger drug release from targeted nanocarriers in the synovial cavity, which makes it a more effective synergistic treatment strategy for RA. In this work, we aim to utilize the UTMD effect to augment the synergistic therapy of RA by using polyethylene glycol (PEG)-modified folate (FA)-conjugated liposomes (LPs) loaded with dexamethasone sodium phosphate (DexSP) (DexSP@LPs-PEG-FA). The UTMD-mediated DexSP@LPs-PEG-FA for targeted delivery of DexSP including a synergistic ultrasonic cavitation effect and drug therapy were investigated through in vitro RAW264.7 cell experiments and in vivo collagen-induced arthritis SD rat model animal experiments. The results show the DexSP release from targeted liposomes was improved under the UTMD effect. Likewise, the folate-conjugated liposomes displayed targeting association to RAW264.7 cells. Together with the application of ultrasound and microbubbles, liposomes-delivered DexSP potently reduced joints swelling, bone erosion, and inflammation in both joints and serum with a low dose. These results demonstrated that UTMD-mediated folate-conjugated liposomes are not only a promising method for targeted synergistic treatment of RA but also may show high potential for serving as nanomedicines for many other biomedical fields.

Amphiphilic copolymers in biomedical applications: Synthesis routes and property control

The request of new materials, matching strict requirements to be applied in precision and patient-specific medicine, is pushing for the synthesis of more and more complex block copolymers. Amphiphilic block copolymers are emerging in the biomedical field due to their great potential in terms of stimuli responsiveness, drug loading capabilities and reversible thermal gelation. Amphiphilicity guarantees self-assembly and thermoreversibility, while grafting polymers offers the possibility of combining blocks with various properties in one single material. These features make amphiphilic block copolymers excellent candidates for fine tuning drug delivery, gene therapy and for designing injectable hydrogels for tissue engineering. This manuscript revises the main techniques developed in the last decade for the synthesis of amphiphilic block copolymers for biomedical application. Strategies for fine tuning the properties of these novel materials during synthesis are discussed. A deep knowledge of the synthesis techniques and their effect on the performance and the biocompatibility of these polymers is the first step to move them from the lab to the bench. Current results predict a bright future for these materials in paving the way towards a smarter, less invasive, while more effective, medicine.

Hydrogel scaffolds for tissue engineering: the importance of polymer choice

We explore the design and synthesis of hydrogel scaffolds for tissue engineering from the perspective of the underlying polymer chemistry. The key polymers, properties and architectures used, and their effect on tissue growth are discussed.