The quest for mechanically and biologically functional soft biomaterials via soft network composites

3D printing of heart valves

3D printing technologies have the potential to revolutionize the manufacture of heart valves through the ability to create bespoke, complex constructs. In light of recent technological advances, we review the progress made towards 3D printing of heart valves, focusing on studies that have utilised these technologies beyond manufacturing patient-specific moulds. We first overview the key requirements of a heart valve to assess functionality. We then present the 3D printing technologies used to engineer heart valves. By referencing International Organisation for Standardisation (ISO) Standard 5840 (Cardiovascular implants - Cardiac valve prostheses), we provide insight into the achieved functionality of these valves. Overall, 3D printing promises to have a significant positive impact on the creation of artificial heart valves and potentially unlock full complex functionality.

Chemical and Structural Engineering of Gelatin-Based Delivery Systems for Therapeutic Applications: A Review

As a biodegradable and biocompatible protein derived from collagen, gelatin has been extensively exploited as a fundamental component of biological scaffolds and drug delivery systems for precise medicine. The easily engineered gelatin holds great promise in formulating various delivery systems to protect and enhance the efficacy of drugs for improving the safety and effectiveness of numerous pharmaceuticals. The remarkable biocompatibility and adjustable mechanical properties of gelatin permit the construction of active 3D scaffolds to accelerate the regeneration of injured tissues and organs. In this Review, we delve into diverse strategies for fabricating and functionalizing gelatin-based structures, which are applicable to gene and drug delivery as well as tissue engineering. We emphasized the advantages of various gelatin derivatives, including methacryloyl gelatin, polyethylene glycol-modified gelatin, thiolated gelatin, and alendronate-modified gelatin. These derivatives exhibit excellent physicochemical and biological properties, allowing the fabrication of tailor-made structures for biomedical applications. Additionally, we explored the latest developments in the modulation of their physicochemical properties by combining additive materials and manufacturing platforms, outlining the design of multifunctional gelatin-based micro-, nano-, and macrostructures. While discussing the current limitations, we also addressed the challenges that need to be overcome for clinical translation, including high manufacturing costs, limited application scenarios, and potential immunogenicity. This Review provides insight into how the structural and chemical engineering of gelatin can be leveraged to pave the way for significant advancements in biomedical applications and the improvement of patient outcomes.

Hutmacher D, Medeiros Savi F. 3D-Printed Medical-Grade Polycaprolactone (mPCL) Scaffold for the Surgical Treatment of Vaginal Prolapse and Abdominal Hernias

The expected outcome after a scaffold augmented hernia repair is the regeneration of a tissue composition strong enough to sustain biomechanical function over long periods. It is hypothesised that melt electrowriting (MEW) medical-grade polycaprolactone (mPCL) scaffolds loaded with platelet-rich plasma (PRP) will enhance soft tissue regeneration in fascial defects in abdominal and vaginal sheep models. A pre-clinical evaluation of vaginal and abdominal hernia reconstruction using mPCL mesh scaffolds and polypropylene (PP) meshes was undertaken using an ovine model. Each sheep was implanted with both a PP mesh (control group), and a mPCL mesh loaded with PRP (experimental group) in both abdominal and vaginal sites. Mechanical properties of the tissue-mesh complexes were assessed with plunger tests. Tissue responses to the implanted meshes were evaluated via histology, immunohistochemistry and histomorphometry. At 6 months post-surgery, the mPCL mesh was less stiff than the PP mesh, but stiffer than the native tissue, while showing equitable collagen and vascular ingrowth when compared to PP mesh. The results of this pilot study were supportive of mPCL as a safe and effective biodegradable scaffold for hernia and vaginal prolapse repair, hence a full-scale long-term study (over 24-36 months) with an adequate sample size is recommended.

Fabrication and Evaluation of Electrospun Silk Fibroin/Halloysite Nanotube Biomaterials for Soft Tissue Regeneration

The production of nanofibrous materials for soft tissue repair that resemble extracellular matrices (ECMs) is challenging. Electrospinning uniquely produces scaffolds resembling the ultrastructure of natural ECMs. Herein, electrospinning was used to fabricate Bombyx mori silk fibroin (SF) and SF/halloysite nanotube (HNT) composite scaffolds. Different HNT loadings were examined, but 1 wt% HNTs enhanced scaffold hydrophilicity and water uptake capacity without loss of mechanical strength. The inclusion of 1 wt% HNTs in SF scaffolds also increased the scaffold’s thermal stability without altering the molecular structure of the SF, as revealed by thermogravimetric analyses and Fourier transform infrared spectroscopy (FTIR), respectively. SF/HNT 1 wt% composite scaffolds better supported the viability and spreading of 3T3 fibroblasts and the differentiation of C2C12 myoblasts into aligned myotubes. These scaffolds coated with decellularised ECM from 3T3 cells or primary human dermal fibroblasts (HDFs) supported the growth of primary human keratinocytes. However, SF/HNT 1 wt% composite scaffolds with HDF-derived ECM provided the best microenvironment, as on these, keratinocytes formed intact monolayers with an undifferentiated, basal cell phenotype. Our data indicate the merits of SF/HNT 1 wt% composite scaffolds for applications in soft tissue repair and the expansion of primary human keratinocytes for skin regeneration.

Progress in the Development of Graphene-Based Biomaterials for Tissue Engineering and Regeneration

Over the last few decades, tissue engineering has become an important technology for repairing and rebuilding damaged tissues and organs. The scaffold plays an important role and has become a hot pot in the field of tissue engineering. It has sufficient mechanical and biochemical properties and simulates the structure and function of natural tissue to promote the growth of cells inward. Therefore, graphene-based nanomaterials (GBNs), such as graphene and graphene oxide (GO), have attracted wide attention in the field of biomedical tissue engineering because of their unique structure, large specific surface area, good photo-thermal effect, pH response and broad-spectrum antibacterial properties. In this review, the structure and properties of typical GBNs are summarized, the progress made in the development of GBNs in soft tissue engineering (including skin, muscle, nerve and blood vessel) are highlighted, the challenges and prospects of the application of GBNs in soft tissue engineering have prospected.

Gelatin Methacryloyl Hydrogels for the Localized Delivery of Cefazolin

The tuneability of hydrogels renders them promising candidates for local drug delivery to prevent and treat local surgical site infection (SSI) while avoiding the systemic side-effects of intravenous antibiotic injections. Here, we present a newly developed gelatin methacryloyl (GelMA)-based hydrogel drug delivery system (GelMA-DDS) to locally deliver the broad-spectrum antibiotic cefazolin for SSI prophylaxis and treatment. Antibiotic doses from 3 µg to 90 µg were loaded in photocrosslinked GelMA hydrogel discs with 5 to 15% w/v polymer concentration and drug encapsulation efficiencies, mechanical properties, crosslinking and release kinetics, as well as bacterial growth inhibition were assessed. Our results demonstrate that all GelMA groups supported excellent drug encapsulation efficiencies of up to 99%. Mechanical properties of the GelMA-DDS were highly tuneable and unaffected by the loading of small to medium doses of cefazolin. The diffusive and the proteolytic in vitro drug delivery of all investigated cefazolin doses was characterized by a burst release, and the delivered cefazolin amount was directly proportional to the encapsulated dose. Accelerated enzymatic degradation of the GelMA-DDS followed zero-order kinetics and was dependent on both the cefazolin dose and GelMA concentration (3-13 h). Finally, we demonstrate that cefazolin delivered from GelMA induced a dose-dependent antibacterial efficacy against S. aureus, in both a broth and a diffusive assay. The cefazolin-loaded GelMA-DDS presented here provides a highly tuneable and easy-to-use local delivery system for the prophylaxis and treatment of SSI.

Vascular Tissue Engineering: Challenges and Requirements for an Ideal Large Scale Blood Vessel

Since the emergence of regenerative medicine and tissue engineering more than half a century ago, one obstacle has persisted: the in vitro creation of large-scale vascular tissue (>1 cm³) to meet the clinical needs of viable tissue grafts but also for biological research applications. Considerable advancements in biofabrication have been made since Weinberg and Bell, in 1986, created the first blood vessel from collagen, endothelial cells, smooth muscle cells and fibroblasts. The synergistic combination of advances in fabrication methods, availability of cell source, biomaterials formulation and vascular tissue development, promises new strategies for the creation of autologous blood vessels, recapitulating biological functions, structural functions, but also the mechanical functions of a native blood vessel. In this review, the main technological advancements in bio-fabrication are discussed with a particular highlights on 3D bioprinting technologies. The choice of the main biomaterials and cell sources, the use of dynamic maturation systems such as bioreactors and the associated clinical trials will be detailed. The remaining challenges in this complex engineering field will finally be discussed.

Supramolecular Host-Guest Hydrogels for Corneal Regeneration

Over 6.2 million people worldwide suffer from moderate to severe vision loss due to corneal disease. While transplantation with allogenic donor tissue is sight-restoring for many patients with corneal blindness, this treatment modality is limited by long waiting lists and high rejection rates, particularly in patients with severe tissue damage and ocular surface pathologies. Hydrogel biomaterials represent a promising alternative to donor tissue for scalable, nonimmunogenic corneal reconstruction. However, implanted hydrogel materials require invasive surgeries and do not precisely conform to tissue defects, increasing the risk of patient discomfort, infection, and visual distortions. Moreover, most hydrogel crosslinking chemistries for the in situ formation of hydrogels exhibit off-target effects such as cross-reactivity with biological structures and/or result in extractable solutes that can have an impact on wound-healing and inflammation. To address the need for cytocompatible, minimally invasive, injectable tissue substitutes, host-guest interactions have emerged as an important crosslinking strategy. This review provides an overview of host-guest hydrogels as injectable therapeutics and highlights the potential application of host-guest interactions in the design of corneal stromal tissue substitutes.

Thoughts on cartilage tissue engineering: A 21st century perspective

In mature individuals, hyaline cartilage demonstrates a poor intrinsic capacity for repair, thus even minor defects could result in progressive degeneration, impeding quality of life. Although numerous attempts have been made over the past years for the advancement of effective treatments, significant challenges still remain regarding the translation of in vitro cartilage engineering strategies from bench to bedside. This paper reviews the latest concepts on engineering cartilage tissue in view of biomaterial scaffolds, tissue biofabrication, mechanobiology, as well as preclinical studies in different animal models. The current work is not meant to provide a methodical review, rather a perspective of where the field is currently focusing and what are the requirements for bridging the gap between laboratory-based research and clinical applications, in light of the current state-of-the-art literature. While remarkable progress has been accomplished over the last 20 years, the current sophisticated strategies have reached their limit to further enhance healthcare outcomes. Considering a clinical aspect together with expertise in mechanobiology, biomaterial science and biofabrication methods, will aid to deal with the current challenges and will present a milestone for the furtherance of functional cartilage engineering.

Mechanobiological Interactions between Dynamic Compressive Loading and Viscoelasticity on Chondrocytes in Hydrazone Covalent Adaptable Networks for Cartilage Tissue Engineering

Mechanobiological cues influence chondrocyte biosynthesis and are often used in tissue engineering applications to improve the repair of articular cartilage in load-bearing joints. In this work, the biophysical effects of an applied dynamic compression on chondrocytes encapsulated in viscoelastic hydrazone covalent adaptable networks (CANs) is explored. Here, hydrazone CANs exhibit viscoelastic loss tangents ranging from (9.03 ± 0.01) 10-4 to (1.67 ± 0.09) 10-3 based on the molar percentages of alkyl-hydrazone and benzyl-hydrazone crosslinks. Notably, viscoelastic alkyl-hydrazone crosslinks improve articular cartilage specific gene expression showing higher SOX9 expression in free swelling hydrogels and dynamic compression reduces hypertrophic chondrocyte markers (COL10A1, MMP13) in hydrazone CANs. Interestingly, dynamic compression also improves matrix biosynthesis in elastic benzyl-hydrazone controls but reduces biosynthesis in viscoelastic alkyl-hydrazone CANs. Additionally, intermediate levels of viscoelastic adaptability demonstrate the highest levels of matrix biosynthesis in hydrazone CANs, demonstrating on average 70 ± 4 µg of sulfated glycosaminoglycans per day and 31 ± 3 µg of collagen per day over one month in dynamic compression bioreactors. Collectively, the results herein demonstrate the role of matrix adaptability and viscoelasticity on chondrocytes in hydrazone CANs during dynamic compression, which may prove useful for tissue engineering applications in load-bearing joints.

Recent Advances in Fiber-Hydrogel Composites for Wound Healing and Drug Delivery Systems

In the last decades, much research has been done to fasten wound healing and target-direct drug delivery. Hydrogel-based scaffolds have been a recurrent solution in both cases, with some reaching already the market, even though their mechanical stability remains a challenge. To overcome this limitation, reinforcement of hydrogels with fibers has been explored. The structural resemblance of fiber-hydrogel composites to natural tissues has been a driving force for the optimization and exploration of these systems in biomedicine. Indeed, the combination of hydrogel-forming techniques and fiber spinning approaches has been crucial in the development of scaffolding systems with improved mechanical strength and medicinal properties. In this review, a comprehensive overview of the recently developed fiber-hydrogel composite strategies for wound healing and drug delivery is provided. The methodologies employed in fiber and hydrogel formation are also highlighted, together with the most compatible polymer combinations, as well as drug incorporation approaches creating stimuli-sensitive and triggered drug release towards an enhanced host response.

A modular design strategy to integrate mechanotransduction concepts in scaffold-based bone tissue engineering

Repair or regeneration of load-bearing bones has long been an incentive for the tissue engineering community to develop a plethora of synthetic bone scaffolds. Despite the key role of physical forces and the mechanical environment in bone regeneration, the mechanotransduction concept has rarely been incorporated in structural design of bone tissue scaffolds, particularly those made of bioactive materials such as hydrogels and bioceramics. Herein, we introduce a modular design strategy to fabricate a load bearing device that can support a wide range of hydrogel- and ceramic-based scaffolds against complex in-vivo loading conditions to induce desirable mechanical strains for bone regeneration within the scaffolds. The device is comprised of a fenestrated polymeric shell and ceramic structural pillars arranged in a sophisticated configuration to provide ample internal space for the scaffold, also enabling it to purposely regulate the levels of strains and stresses within the scaffolds. Utilizing this top-down design approach, we demonstrate that the failure load of alginate hydrogels increases 3200-fold in compression, 300-fold in shear and 75-fold in impact, achieving the values that enable them to withstand physiological loads in weight-bearing sites, while allowing generation of osteoinductive strains (i.e., 0.2-0.4%) in the hydrogel. This modular design approach opens a broad range of opportunities to utilize various bioactive but mechanically weak scaffolds for the treatment of load-bearing defects and exploiting mechanobiology strategies to improve bone regeneration.

Designing Outside the Box: Unlocking the Geometric Freedom of Melt Electrowriting using Microscale Layer Shifting

Melt electrowriting, a high-resolution additive manufacturing technology, has so far been developed with vertical stacking of fiber layers, with a printing trajectory that is constant for each layer. In this work, microscale layer shifting is introduced through deliberately offsetting the printing trajectory for each printed layer. Inaccuracies during the printing of sinusoidal walls are corrected via layer shifting, resulting in accurate control of their geometry and mechanical properties. Furthermore, more substantial layer shifting allows stacking of fiber layers in a horizontal manner, overcoming the electrostatic autofocusing effect that favors vertical layer stacking. Novel nonlinear geometries, such as overhangs, wall texturing and branching, and smooth and abrupt changes in printing trajectory are presented, demonstrating the flexibility of the layer shifting approach beyond the state-of-the-art. The practice of microscale layer shifting for melt electrowriting enables more complex geometries that promise to have a profound impact on the development of products in a broad range of applications.

Fiber reinforced GelMA hydrogel to induce the regeneration of corneal stroma

Regeneration of corneal stroma has always been a challenge due to its sophisticated structure and keratocyte-fibroblast transformation. In this study, we fabricate grid poly (ε-caprolactone)-poly (ethylene glycol) microfibrous scaffold and infuse the scaffold with gelatin methacrylate (GelMA) hydrogel to obtain a 3 D fiber hydrogel construct; the fiber spacing is adjusted to fabricate optimal construct that simulates the stromal structure with properties most similar to the native cornea. The topological structure (3 D fiber hydrogel, 3 D GelMA hydrogel, and 2 D culture dish) and chemical factors (serum, ascorbic acid, insulin, and β-FGF) are examined to study their effects on the differentiation of limbal stromal stem cells to keratocytes or fibroblasts and the phenotype maintenance, in vitro and in vivo tissue regeneration. The results demonstrate that fiber hydrogel and serum-free media synergize to provide an optimal environment for the maintenance of keratocyte phenotype and the regeneration of damaged corneal stroma.

Regeneration of corneal stroma has been a challenge due to its sophisticated structure and the easy transformation of the keratocyte. Here, the authors use a hydrogel reinforced with orthogonally aligned fibres and serum free medium to maintain keratocyte phenotype for the in vivo stromal regeneration.

Gelatin Methacryloyl Hydrogels Control the Localized Delivery of Albumin-Bound Paclitaxel

Hydrogels are excellent candidates for the sustained local delivery of anticancer drugs, as they possess tunable physicochemical characteristics that enable to control drug release kinetics and potentially tackle the problem of systemic side effects in traditional chemotherapeutic delivery. Yet, current systems often involve complicated manufacturing or covalent bonding processes that are not compatible with regulatory or market reality. Here, we developed a novel gelatin methacryloyl (GelMA)-based drug delivery system (GelMA-DDS) for the sustained local delivery of paclitaxel-based Abraxane®, for the prevention of local breast cancer recurrence following mastectomy. GelMA-DDS readily encapsulated Abraxane® with a maximum of 96% encapsulation efficiency. The mechanical properties of the hydrogel system were not affected by drug loading. Tuning of the physical properties, by varying GelMA concentration, allowed tailoring of GelMA-DDS mesh size, where decreasing the GelMA concentration provided overall more sustained cumulative release (significant differences between 5%, 10%, and 15%) with a maximum of 75% over three months of release, identified to be released by diffusion. Additionally, enzymatic degradation, which more readily mimics the in vivo situation, followed a near zero-order rate, with a total release of the cargo at various rates (2-14 h) depending on GelMA concentration. Finally, the results demonstrated that Abraxane® delivery from the hydrogel system led to a dose-dependent reduction of viability, metabolic activity, and live-cell density of triple-negative breast cancer cells in vitro. The GelMA-DDS provides a novel and simple approach for the sustained local administration of anti-cancer drugs for breast cancer recurrence.

An electrospun polyurethane scaffold-reinforced zwitterionic hydrogel as a biocompatible device

An electrospun scaffold-reinforced zwitterionic hydrogel achieved both high tensile strength and mechano-induced self-enhancement while maintaining excellent hemocompatibility.