Nanostructured raspberry-like gelatin microspheres for local delivery of multiple biomolecules

Functional microspheres for tissue regeneration

As a new type of injectable biomaterials, functional microspheres have attracted increasing attention in tissue regeneration because they possess some advantageous properties compared to other biomaterials, including hydrogels. A variety of bio-inspired microspheres with unique structures and properties have been developed as cellular carriers and drug delivery vehicles in recent years. In this review, we provide a comprehensive summary of the progress of functional and biodegradable microspheres that have been used for tissue regeneration over the last two decades. First, we briefly introduce the biomaterials and general methods for microsphere fabrication. Next, we focus on the newly developed technologies for preparing functional microspheres, including macroporous microspheres, nanofibrous microspheres, hollow microspheres, core-shell structured microspheres, and surface-modified functional microspheres. After that, we discuss the application of functional microspheres for tissue regeneration, specifically for bone, cartilage, dental, neural, cardiac, and skin tissue regeneration. Last, we present our perspectives and future directions of functional microspheres as injectable carriers for the future advancement of tissue regeneration.

Hybrid colloidal gels with tunable elasticity formed by charge-driven assembly between spherical soft nanoparticles and discotic nanosilicates

Colloidal gels based on electrostatic interparticle attractions hold unexploited potential for tailoring their microstructure and properties. Here, we demonstrate that hetero-aggregation between oppositely charged particles with different geometries is a viable strategy for controlling their properties. Specifically, we studied hybrid colloidal gels prepared by the charge-driven assembly of oppositely charged spherical gelatin nanoparticles and two-dimensional (2D) nanosilicates. We show that the asymmetry between the building blocks and the resulting anisotropic interparticle interactions produces a variety of nanostructures and hybrid colloidal gels that exhibit high elasticity at low colloidal volume fractions. Tuning the competition between different attractive interactions in the system by varying the spatial charge heterogeneity on the 2D nanosheets, composition, and ionic strength was found to alter the mechanism of gel formation and their rheological properties. Remarkably, increasing the mass ratio of 2D nanosheets to spherical nanoparticles at a constant total mass fraction affords hybrid gels that exhibit an inverse relationship between elasticity and volume fraction. However, these hybrid gels are easily fluidized and exhibit rapid structural recovery once the stress is removed. These features allow for the engineering of versatile 3D-printable hybrid colloidal gels, whose structure and viscoelastic response are governed by parameters that have not been explored before.

Controlled and localized antibiotics delivery using magnetic-responsive beads for synergistic treatment of orthopedic infection

Antibiotic-loaded bone cement beads have been a reliable passive delivery system for the localized treatment of osteomyelitis; however, low, and unregulated drug release rates limit the ability of this system to maintain therapeutic concentrations. This problem is further amplified by drug-resistant pathogens that might invade or evolve under these conditions. Furthermore, currently available bone cements are incompatible with some antibiotics. The proposed device resembles conventional bone cement beads but contains an on-demand drug delivery magnetic sponge that provides actively controlled release of antibiotics. The slightly porous structure facilitates some drug diffusion while further drug release may be controlled remotely via magnetic actuation. Additionally, a combination of silver nitrate and gentamicin are used in the device as these agents are shown to display a synergistic antibacterial activity in vitro using checkerboard and time-kill assays. The device releases gentamicin and silver in both actuation and diffusion modes over 7 days. The in vitro bacterial studies demonstrate the efficacy of the released agents alone, and synergistically in combination, against Methicillin-resistant Staphylococcus aureus and Escherichia coli. The proposed device offers a facile fabrication process which allows control of the release profile by engineering hole configurations or manipulating magnetic field strength to provide the most effective therapy.

Potent Particle-Based Vehicles for Growth Factor Delivery from Electrospun Meshes: Fabrication and Functionalization Strategies for Effective Tissue Regeneration

Functionalization of electrospun meshes with growth factors (GFs) is a common strategy for guiding specific cell responses in tissue engineering. GFs can exert their intended biological effects only when they retain their bioactivity and can be subsequently delivered in a temporally controlled manner. However, adverse processing conditions encountered in electrospinning can potentially disrupt GFs and diminish their biological efficacy. Further, meshes prepared using conventional approaches often promote an initial burst and rely solely on intrinsic fiber properties to provide extended release. Sequential delivery of multiple GFs─a strategy that mimics the natural tissue repair cascade─is also not easily achievable with traditional fabrication techniques. These limitations have hindered the effective use and translation of mesh-based strategies for tissue repair. An attractive alternative is the use of carrier vehicles (e.g., nanoparticles, microspheres) for GF incorporation into meshes. This review presents advances in the development of particle-integrated electrospun composites for safe and effective delivery of GFs. Compared to traditional approaches, we reveal how particles can protect GF activity, permit the incorporation of multiple GFs, decouple release from fiber properties, help achieve spatiotemporal control over delivery, enhance surface bioactivity, exert independent biological effects, and augment matrix mechanics. In presenting innovations in GF functionalization and composite engineering strategies, we also discuss specific in vitro and in vivo biological effects and their implications for diverse tissue engineering applications.

Utilization of diverse protein sources for the development of protein-based nanostructures as bioactive carrier systems: A review of recent research findings (2010-2021)

Consumer awareness of the relationship between health and nutrition has caused a substantial increase in the demand for nutraceuticals and functional foods containing bioactive compounds (BACs) with potential health benefits. However, the direct incorporation of many BACs into commercial food and beverage products is challenging because of their poor matrix compatibility, chemical instability, low bioavailability, or adverse impact on food quality. Advanced encapsulation technologies are therefore being employed to overcome these problems. In this article, we focus on the utilization of plant and animal derived proteins to fabricate micro and nano-particles that can be used for the oral delivery of BACs such as omega-3 oils, vitamins and nutraceuticals. This review comprehensively discusses different methods being implemented for fabrications of protein-based delivery vehicles, types of proteins used, and their compatibility for the purpose. Finally, some of the challenges and limitations of different protein matrices for encapsulation of BACs are deliberated upon. Various approaches have been developed for the fabrication of protein-based microparticles and nanoparticles, including injection-gelation, controlled denaturation, and antisolvent precipitation methods. These methods can be used to construct particle-based delivery systems with different compositions, sizes, surface hydrophobicity, and electrical characteristics, thereby enabling them to be used in a wide range of applications.

3D printed colloidal biomaterials based on photo-reactive gelatin nanoparticles

Biomaterials-based strategies have shown great promise for tissue regeneration. 3D printing technologies can deliver unprecedented control over architecture and properties of biomaterial constructs when combined with innovative material design strategies. Colloidal gels made of polymeric nanoparticles are attractive injectable and self-healing systems, but their use as bio-inks for extrusion-based printing is largely unexplored. Here, we report 3D printing of novel biomaterial constructs with shape memory behavior using photo-reactive gelatin nanoparticles as colloidal building blocks. These nanoparticles are stabilized with intraparticle covalent crosslinks, and also contain pendant methacryloyl groups as photo-reactive moieties. While non-covalent interactions between nanoparticles enable formation of colloidal gel inks that are printable at room temperature, UV-induced covalent interparticle crosslinks based on methacryloyl moieties significantly enhance mechanical properties of printed constructs. Additionally, the UV crosslinking modality enables remarkable control over swelling, degradation, and biomolecule release behavior of 3D constructs. Finally, by exploiting the mechanical properties of colloidal biomaterials after UV crosslinking, 3D constructs can be designed with shape memory properties, returning to their original programmed geometry upon re-hydration. Accordingly, these novel colloidal inks exhibit great potential to serve as bio-inks for 3D printing of biomaterials with shape-morphing features for a wide range of tissue engineering and regenerative medicine applications.

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.

Therapeutics and delivery vehicles for local treatment of osteomyelitis

Osteomyelitis, or the infection of the bone, presents a major complication in orthopedics and may lead to prolonged hospital visits, implant failure, and in more extreme cases, amputation of affected limbs. Typical treatment for this disease involves surgical debridement followed by long-term, systemic antibiotic administration, which contributes to the development of antibiotic-resistant bacteria and has limited ability to eradicate challenging biofilm-forming pathogens including Staphylococcus aureus-the most common cause of osteomyelitis. Local delivery of high doses of antibiotics via traditional bone cement can reduce systemic side effects of an antibiotic. Nonetheless, growing concerns over burst release (then subtherapeutic dose) of antibiotics, along with microbial colonization of the nondegradable cement biomaterial, further exacerbate antibiotic resistance and highlight the need to engineer alternative antimicrobial therapeutics and local delivery vehicles with increased efficacy against, in particular, biofilm-forming, antibiotic-resistant bacteria. Furthermore, limited guidance exists regarding both standardized formulation protocols and validated assays to predict efficacy of a therapeutic against multiple strains of bacteria. Ideally, antimicrobial strategies would be highly specific while exhibiting a broad spectrum of bactericidal activity. With a focus on S. aureus infection, this review addresses the efficacy of novel therapeutics and local delivery vehicles, as alternatives to the traditional antibiotic regimens. The aim of this review is to discuss these components with regards to long bone osteomyelitis and to encourage positive directions for future research efforts.

Recent advances in gelatin-based therapeutics

INTRODUCTION

Biomaterials have provided a wide range of exciting opportunities in tissue engineering and regenerative medicine. Gelatin, a collagen-derived natural biopolymer, has been extensively used in regenerative medicine applications over the years, due to its cell-responsive properties and the capacity to deliver a wide range of biomolecules.

AREAS COVERED

The most relevant properties of gelatin as biomaterial are presented together with its main therapeutic applications. The latter includes drug delivery systems, tissue engineering approaches, potential uses as ink for 3D/4D Bioprinting, and its relevance in organ-on-a-chip platforms.

EXPERT OPINION

Advances in polymer chemistry, mechanobiology, imaging technologies, and 3D biofabrication techniques have expanded the application of gelatin in multiple biomedical research applications ranging from bone and cartilage tissue engineering, to wound healing and anti-cancer therapy. Here, we highlight the latest advances in gelatin-based approaches within the fields of biomaterial-based drug delivery and tissue engineering together with some of the most relevant challenges and limitations.