Sub-100-micron calcium-alginate microspheres: Preparation by nitrogen flow focusing, dependence of spherical shape on gas streams and a drug carrier using acetaminophen as a model drug

3D bioprinting approaches for spinal cord injury repair

Regenerative healing of spinal cord injury (SCI) poses an ongoing medical challenge by causing persistent neurological impairment and a significant socioeconomic burden. The complexity of spinal cord tissue presents hurdles to successful regeneration following injury, due to the difficulty of forming a biomimetic structure that faithfully replicates native tissue using conventional tissue engineering scaffolds. 3D bioprinting is a rapidly evolving technology with unmatched potential to create 3D biological tissues with complicated and hierarchical structure and composition. With the addition of biological additives such as cells and biomolecules, 3D bioprinting can fabricate preclinical implants, tissue or organ-like constructs, andin vitromodels through precise control over the deposition of biomaterials and other building blocks. This review highlights the characteristics and advantages of 3D bioprinting for scaffold fabrication to enable SCI repair, including bottom-up manufacturing, mechanical customization, and spatial heterogeneity. This review also critically discusses the impact of various fabrication parameters on the efficacy of spinal cord repair using 3D bioprinted scaffolds, including the choice of printing method, scaffold shape, biomaterials, and biological supplements such as cells and growth factors. High-quality preclinical studies are required to accelerate the translation of 3D bioprinting into clinical practice for spinal cord repair. Meanwhile, other technological advances will continue to improve the regenerative capability of bioprinted scaffolds, such as the incorporation of nanoscale biological particles and the development of 4D printing.

Alginates Combined with Natural Polymers as Valuable Drug Delivery Platforms

Alginates (ALG) have been used in biomedical and pharmaceutical technologies for decades. ALG are natural polymers occurring in brown algae and feature multiple advantages, including biocompatibility, low toxicity and mucoadhesiveness. Moreover, ALG demonstrate biological activities per se, including anti-hyperlipidemic, antimicrobial, anti-reflux, immunomodulatory or anti-inflammatory activities. ALG are characterized by gelling ability, one of the most frequently utilized properties in the drug form design. ALG have numerous applications in pharmaceutical technology that include micro- and nanoparticles, tablets, mucoadhesive dosage forms, wound dressings and films. However, there are some shortcomings, which impede the development of modified-release dosage forms or formulations with adequate mechanical strength based on pure ALG. Other natural polymers combined with ALG create great potential as drug carriers, improving limitations of ALG matrices. Therefore, in this paper, ALG blends with pectins, chitosan, gelatin, and carrageenans were critically reviewed.

Effect of the Biopolymer Carrier on Staphylococcus aureus Bacteriophage Lytic Activity

The use of implant materials is always associated with the risk of infection. Moreover, the effectiveness of antibiotics is reduced due to antibiotic-resistant pathogens. Thus, selecting the appropriate alternative antimicrobials for local delivery systems is correlated with successful infection management. We evaluated immobilization of the S. aureus specific bacteriophages in clinically recognized biopolymers, i.e., chitosan and alginate, to control the release profile of the antimicrobials. The high-titre S. aureus specific bacteriophages were prepared from commercial bacteriophage cocktails. The polymer mixtures with the propagated bacteriophages were then prepared. The stability of the S. aureus bacteriophages in the biopolymer solutions was assessed. In the case of chitosan, no plaques indicating the presence of the lytic bacteriophages were observed. The titre reduction of the S. aureus bacteriophages in the Na-alginate was below 1 log unit. Furthermore, the bacteriophages retained their lytic activity in the alginate after crosslinking with Ca²⁺ ions. The release of the lytic S. aureus bacteriophages from the Ca-alginate matrices in the TRIS-HCl buffer solution (pH 7.4 ± 0.2) was determined. After 72 h-0.292 ± 0.021% of bacteriophages from the Ca-alginate matrices were released. Thus, sustained release of the lytic S. aureus bacteriophages can be ensured.

Environmentally friendly microbeads to model the dispersal of particulates in aquatic systems

The transport of particulate matter including the gametes, larvae and propagules of reproducing organisms and other organic matter involved in nutrient/contaminant transport are important processes, yet there are few environmentally friendly methods available to examine dispersal empirically. Herein we report on the development and application of a biodegradable and non-toxic physical model, based on alginate microbeads with modifiable size, density (ρ), and colour for use in dispersal studies. Specifically, the microbeads were designed to model the size and ρ of parasitic juvenile freshwater mussels (Unionidae; ρ = 1200 kg m^-3), which undergo dispersal upon excystment from fish hosts. We released the juvenile-mussel and neutrally buoyant microbeads (ρ = 1000 kg m^-3) in a local river and captured them in drift nets downstream. The concentration of microbeads declined with downstream distance, but neutrally buoyant microbeads were transported farther. Analysis of microbead capture rates could be described using the patterns of several mathematical models (negative exponential, power, and turbulent transport), which were consistent with the reported dispersal of mussel larvae and other benthic macroinvertebrates. These results support the use of alginate microbeads in dispersal studies, because their environmentally friendly and customizable properties offer improvements over non-biodegradable alternatives.

Survivability of probiotics encapsulated in kelp nanocellulose/alginate microcapsules on microfluidic device

Probiotics are living microorganisms that can produce health benefits to the host only when they are ingested in sufficient quantities and reach the intestines active state. However, the external environment that probiotics face for a long time before administration and the low pH environment in the stomach after administration can greatly reduce their activity. In this work, we proposed a simple microfluidic encapsulation strategy to efficiently prepare the probiotics-loaded nanocellulose/alginate delivery system, which can improve the storage stability and gastrointestinal survival rate of probiotics. The microcapsules were found to be monodisperse, and the average particle size was<500 μm by observing the microstructure and macroscopic morphology. The kelp nanocellulose was cross-linked in the microcapsule and formed a dense surface with alginate. Through the simulated gastrointestinal digestion experiment, it was found that the survival of probiotics in microcapsules containing 0.5 % and 1.5 % kelp nanocellulose decreased by 1.77 log CFU/g and 1.65 log CFU/g respectively, which was significantly lower than that of nanocellulose-free microcapsules (3.70 log CFU/g). And all the treated groups could release probiotics above 7 log CFU/g after digesting intestinal juice for 6 h. Furthermore, through the storage experiment, it was found that the microcapsules with 1.5 % kelp nanocellulose could still release 8.07 log CFU/g probiotics after four weeks. The results provide a new strategy for probiotics processing and extensive high-value utilization of marine natural products.

Natural Biopolymers as Additional Tools for Cell Microencapsulation Applied to Cellular Therapy

One of the limitations in organ, tissue or cellular transplantations is graft rejection. To minimize or prevent this, recipients must make use of immunosuppressive drugs (IS) throughout their entire lives. However, its continuous use generally causes several side effects. Although some IS dose reductions and withdrawal strategies have been employed, many patients do not adapt to these protocols and must return to conventional IS use. Therefore, many studies have been carried out to offer treatments that may avoid IS administration in the long term. A promising strategy is cellular microencapsulation. The possibility of microencapsulating cells originates from the opportunity to use biomaterials that mimic the extracellular matrix. This matrix acts as a support for cell adhesion and the syntheses of new extracellular matrix self-components followed by cell growth and survival. Furthermore, by involving the cells in a polymeric matrix, the matrix acts as an immunoprotective barrier, protecting cells against the recipient’s immune system while still allowing essential cell survival molecules to diffuse bilaterally through the polymer matrix pores. In addition, this matrix can be associated with IS, thus diminishing systemic side effects. In this context, this review will address the natural biomaterials currently in use and their importance in cell therapy.

Smart Bioinks for the Printing of Human Tissue Models

3D bioprinting has tremendous potential to revolutionize the field of regenerative medicine by automating the process of tissue engineering. A significant number of new and advanced bioprinting technologies have been developed in recent years, enabling the generation of increasingly accurate models of human tissues both in the healthy and diseased state. Accordingly, this technology has generated a demand for smart bioinks that can enable the rapid and efficient generation of human bioprinted tissues that accurately recapitulate the properties of the same tissue found in vivo. Here, we define smart bioinks as those that provide controlled release of factors in response to stimuli or combine multiple materials to yield novel properties for the bioprinting of human tissues. This perspective piece reviews the existing literature and examines the potential for the incorporation of micro and nanotechnologies into bioinks to enhance their properties. It also discusses avenues for future work in this cutting-edge field.

How Microgels Can Improve the Impact of Organ-on-Chip and Microfluidic Devices for 3D Culture: Compartmentalization, Single Cell Encapsulation and Control on Cell Fate

The Organ-on-chip (OOC) devices represent the new frontier in biomedical research to produce micro-organoids and tissues for drug testing and regenerative medicine. The development of such miniaturized models requires the 3D culture of multiple cell types in a highly controlled microenvironment, opening new challenges in reproducing the extracellular matrix (ECM) experienced by cells in vivo. In this regard, cell-laden microgels (CLMs) represent a promising tool for 3D cell culturing and on-chip generation of micro-organs. The engineering of hydrogel matrix with properly balanced biochemical and biophysical cues enables the formation of tunable 3D cellular microenvironments and long-term in vitro cultures. This focused review provides an overview of the most recent applications of CLMs in microfluidic devices for organoids formation, highlighting microgels' roles in OOC development as well as insights into future research.