Assessment of alginate hydrogel degradation in biological tissue using viscosity-sensitive fluorescent dyes

3D-bioprinted alginate-based bioink scaffolds with β-tricalcium phosphate for bone regeneration applications

Background/purpose

3D-printed bone tissue engineering is becoming recognized as a key approach in dentistry for creating customized bone regeneration treatments fitting patients bone defects requirements. 3D bioprinting offers an innovative method to fabricate detailed 3D structures, closely emulating the native bone micro-environment and better bone regeneration. This study aimed to develop an 3D-bioprintable scaffold using a combination of alginate and β-tricalcium phosphate (β-TCP) with the Cellink® BioX printer, aiming to advance the field of tissue engineering.

Materials and methods

The physical and biological properties of the resulting 3D-printed scaffolds were evaluated at 10 %, 12 %, and 15 % alginate combined with 10 % β-TCP. The scaffolds were characterized through printability, swelling behavior, degradability, and element analysis. The biological assessment included cell viability, alkaline phosphatase (ALP) activity.

Results

10 % alginate/β-TCP 3D printed at 25 °C scaffold demonstrated the optimal condition for printability, swelling capability, and degradability of cell growth and nutrient diffusion. Addition of β-TCP particles significantly improved the 3D printed material viscosity over only alginate (P < 0.05). 10 % alginate/β-TCP enhanced MG-63 cell's proliferation (P < 0.05) and alkaline phosphatase activity (P < 0.001).

Conclusion

This study demonstrated in vitro that 10 % alginate/β-TCP bioink characteristic for fabricating 3D acellular bioprinted scaffolds was the best approach. 10 % alginate/β-TCP bioink 3D-printed scaffold exhibited superior physical properties and promoted enhanced cell viability and alkaline phosphatase activity, showing great potential for personalized bone regeneration treatments.

Application of locally responsive design of biomaterials based on microenvironmental changes in myocardial infarction

Morbidity and mortality caused by acute myocardial infarction (AMI) are on the rise, posing a grave threat to the health of the general population. Up to now, interventional, surgical, and pharmaceutical therapies have been the main treatment methods for AMI. Effective and timely reperfusion therapy decreases mortality, but it cannot stimulate myocardial cell regeneration or reverse ventricular remodeling. Cell therapy, gene therapy, immunotherapy, anti-inflammatory therapy, and several other techniques are utilized by researchers to improve patients' prognosis. In recent years, biomaterials for AMI therapy have become a hot spot in medical care. Biomaterials furnish a microenvironment conducive to cell growth and deliver therapeutic factors that stimulate cell regeneration and differentiation. Biomaterials adapt to the complex microenvironment and respond to changes in local physical and biochemical conditions. Therefore, environmental factors and material properties must be taken into account when designing biomaterials for the treatment of AMI. This article will review the factors that need to be fully considered in the design of biological materials.

A Minireview of Microfluidic Scaffold Materials in Tissue Engineering

In 2020, nearly 107,000 people in the U.S needed a lifesaving organ transplant, but due to a limited number of donors, only ∼35% of them have actually received it. Thus, successful bio-manufacturing of artificial tissues and organs is central to satisfying the ever-growing demand for transplants. However, despite decades of tremendous investments in regenerative medicine research and development conventional scaffold technologies have failed to yield viable tissues and organs. Luckily, microfluidic scaffolds hold the promise of overcoming the major challenges associated with generating complex 3D cultures: 1) cell death due to poor metabolite distribution/clearing of waste in thick cultures; 2) sacrificial analysis due to inability to sample the culture non-invasively; 3) product variability due to lack of control over the cell action post-seeding, and 4) adoption barriers associated with having to learn a different culturing protocol for each new product. Namely, their active pore networks provide the ability to perform automated fluid and cell manipulations (e.g., seeding, feeding, probing, clearing waste, delivering drugs, etc.) at targeted locations in-situ. However, challenges remain in developing a biomaterial that would have the appropriate characteristics for such scaffolds. Specifically, it should ideally be: 1) biocompatible—to support cell attachment and growth, 2) biodegradable—to give way to newly formed tissue, 3) flexible—to create microfluidic valves, 4) photo-crosslinkable—to manufacture using light-based 3D printing and 5) transparent—for optical microscopy validation. To that end, this minireview summarizes the latest progress of the biomaterial design, and of the corresponding fabrication method development, for making the microfluidic scaffolds.

Multicomponent polysaccharide alginate-based bioinks

3D-Bioprinting has seen a rapid expansion in the last few years, with an increasing number of reported bioinks. Alginate is a natural biopolymer that forms hydrogels by ionic cross-linking with calcium ions. Due to its biocompatibility and ease of gelation, it is an ideal ingredient for bioinks. This review focuses on recent advances on bioink formulations based on the combination of alginate with other polysaccharides. In particular, the molecular weight of the alginate and its loading level have an impact on the material's performance, as well as the loading of the divalent metal salt and its solubility, which affects the cross-linking of the gel. Alginate is often combined with other polysaccharides that can sigificantly modify the properties of the gel, and can optimise alginate for use in different biological applications. It is also possible to combine alginate with sacrificial polymers, which can temporarily reinforce the 3D printed construct, but then be removed at a later stage. Other additives can be formulated into the gels to enhance performance, including nanomaterials that tune rheological properties, peptides to encourage cell adhesion, or growth factors to direct stem cell differentiation. The ease of formulating multiple components into alginate gels gives them considerable potential for further development. In summary, this review will facilitate the identification of different alginate-polysaccharide bioink formulations and their optimal applications, and help inform the design of second generation bioinks, allowing this relatively simple gel system to achieve more sophisticated control over biological processes.

Dual cross-linked honey coupled 3D antimicrobial alginate hydrogels for cutaneous wound healing

We report potentiation of healing efficacy of alginate by value addition at its structural level. Dual crosslinked (ionically and covalently) sodium alginate hydrogel coupled with honey (HSAG) brings about an intermediate stiffness in the fabric, confers consistent swelling property and limits erratic degradation of the polymer which ultimately provides conducive milieu to cellular growth and proliferation. In this work honey concentrations in HSAGs are varied from 2% to 10%. FTIR, XRD and nanoindentation studies on the HSAGs exhibited physicochemical integrity. In vitro degradation study provided the crucial finding on 4% HSAG having controlled degradation rate up to 12 days with a weight loss of 87.36 ± 1.14%. This particular substrate also has an ordered crystalline surface morphology with decent cellular viability (HaCaT and 3T3) and antimicrobial potential against Methicillin Resistant Staphylococcus aureus (MRSA) and Escherichia coli. The in vivo wound contraction kinetics on murine models (4% HSAG treated wound contraction: 94.56 ± 0.1%) has been monitored by both invasive (histopathology) and noninvasive (Swept Source Optical Coherence Tomography) imaging and upon corroborating them it evidenced that 4% HSAG treated wound closure achieved epithelial thickness resembling to that of unwounded skin. Thus, the work highlights structurally modified alginate hydrogel embedded with honey as a potential antimicrobial healing agent.

Poly(3-hydroxybutyrate)/hydroxyapatite/alginate scaffolds seeded with mesenchymal stem cells enhance the regeneration of critical-sized bone defect

A critical-sized calvarial defect in rats is employed to reveal the osteoinductive properties of biomaterials. In this study, we investigate the osteogenic efficiency of hybrid scaffolds based on composites of a biodegradable and biocompatible polymer, poly(3-hydroxybutyrate) (PHB) with hydroxyapatite (HA) filled with alginate (ALG) hydrogel containing mesenchymal stem cells (MSCs) on the regeneration of the critical-sized radial defect of the parietal bone in rats. The scaffolds based on PHB and PHB/HA with desired shapes were prepared by two-stage salt leaching technique using a mold obtained by three-dimensional printing. To obtain PHB/HA/ALG/MSC scaffolds seeded with MSCs, the scaffolds were filled with ALG hydrogel containing MSCs; acellular PHB/ALG and PHB/ALG filled with empty ALG hydrogel were prepared for comparison. The produced scaffolds have high porosity and irregular interconnected pore structure. PHB/HA scaffolds supported MSC growth and induced cell osteogenic differentiation in a regular medium in vitro that was manifested by an increase in ALP activity and expression of the CD45 phenotype marker. The data of computed tomography and histological studies showed 94% and 92%, respectively, regeneration of critical-sized calvarial bone defect in vivo at 28th day after implantation of MSC-seeded PHB/HA/ALG/MSC scaffolds with 3.6 times higher formation of the main amount of bone tissue at 22-28 days in comparison with acellular PHB/HA/ALG scaffolds that was shown at the first time by fluorescent microscopy using the original technique of intraperitoneal administration of fluorescent dyes to living postoperative rats. The obtained in vivo results can be associated with the MSC-friendly microstructure and in vitro osteogenic properties of PHB/HA base-scaffolds. Thus, the obtained data demonstrate the potential of MSCs encapsulated in the bioactive biopolymer/mineral/hydrogel scaffold to improve the bone regeneration process in critical-sized bone defects.

Quantifying compressive forces between living cell layers and within tissues using elastic round microgels

Increasing evidence shows that mechanical stresses are critical in regulating cell functions, fate, and diseases. However, no methods exist that can quantify isotropic compressive stresses. Here we describe fluorescent nanoparticle-labeled, monodisperse elastic microspheres made of Arg-Gly-Asp-conjugated alginate hydrogels (elastic round microgels, ERMGs). We generate 3D displacements and calculate strains and tractions exerted on an ERMG. Average compressive tractions on an ERMG are 570 Pa within cell layers and 360 Pa in tumor-repopulating cell (TRC) colonies grown in 400-Pa matrices. 3D compressive tractions on a 1.4-kPa ERMG are applied by surrounding cells via endogenous actomyosin forces but not via mature focal adhesions. Compressive stresses are substantially heterogeneous on ERMGs within a uniform cell colony and do not increase with TRC colony sizes. Early-stage zebrafish embryos generate spatial and temporal differences in local normal and shear stresses. This ERMG method could be useful for quantifying stresses in vitro and in vivo.

Increasing importance is placed upon the effect of mechanical forces on cell regulation, fate and disease states. Here, the authors describe a deformable fluorescent nanoparticle labeled elastic microsphere which can be used to calculate strain and traction forces in vitro and in vivo.

A self-healable fluorescence active hydrogel based on ionic block copolymers prepared via ring opening polymerization and xanthate mediated RAFT polymerization

In this work we report a facile method to prepare a fluorescence active self-healable hydrogel via the incorporation of fluorescence responsive ionic block copolymers (BCPs).

One-pot carbonization synthesis of europium-doped carbon quantum dots for highly selective detection of tetracycline

The detection of tetracycline is of great significance because of its damaging effects on human health, such as renal toxicity and hemolytic anemia. Any release of tetracycline into the surrounding environment can produce bacterial drug resistance. We develop a new sensitive and selective detection approach for tetracycline in complex water samples by preparing europium-doped carbon quantum dots (Eu-CQDs) through a simple and rapid carbonization method operating at 200 °C for 5 min. The Eu-CQDs are characterized by blue photoluminescence, excitation-wavelength-dependent emission and excellent stability. Importantly, the fluorescence of the Eu-CQDs can be quenched efficiently by tetracycline, based on the strong inner filter effect mechanism between Eu-CQDs and tetracycline, making the fluorescence intensity ratio (I ₀/I) of the Eu-CQDs at 465 nm correlate linearly with the concentration of tetracycline in the range of 0.5-200 μM, with a limit of detection of 0.3 μM. This shows the broad applicability of the Eu-CQDs in pursuing the concepts of simplicity and specificity for analytical purposes.