Enzymatically gellable gelatin improves nano-hydroxyapatite-alginate microcapsule characteristics for modular bone tissue formation

Betulin Stimulates Osteogenic Differentiation of Human Osteoblasts-Loaded Alginate-Gelatin Microbeads

Osteoporosis, a terminal illness, has emerged as a global public health problem in recent years. The long-term use of bone anabolic drugs to treat osteoporosis causes multi-morbidity in elderly patients. Alternative therapies, such as allogenic and autogenic tissue grafts, face important issues, such as a limited source of allogenic grafts and tissue rejection in autogenic grafts. However, stem cell therapy has been shown to increase bone regeneration and decrease osteoporotic bone formation. Stem cell therapy combined with betulin (BET) supplementation might be adequate for bone remodeling and new bone tissue generation. In this study, the effect of BET on the viability and osteogenic differentiation of hFOB 1.19 cells was investigated. The cells were encapsulated in alginate-gelatin (AlGel) microbeads. In vitro tests were conducted during the 12 d of incubation. While BET showed cytotoxic activity (>1 µM) toward non-encapsulated hFOB 1.19 cells, encapsulated cells retained their functionality for up to 12 days, even at 5 µM BET. Moreover, the expression of osteogenic markers indicates an enhanced osteo-inductive effect of betulin on encapsulated hFOB 1.19, compared to the non-encapsulated cell culture. The 3D micro-environment of the AlGel microcapsules successfully protects the hFOB 1.19 cells against BET cytotoxicity, allowing BET to improve the mineralization and differentiation of osteoblast cells.

3D bioprinting technology to construct bone reconstruction research model and its feasibility evaluation

Objective: To explore and construct a 3D bone remodeling research model displaying stability, repeatability, and precise simulation of the physiological and biochemical environment in vivo. Methods: In this study, 3D bioprinting was used to construct a bone reconstruction model. Sodium alginate (SA), hydroxyapatite (HA) and gelatin (Gel) were mixed into hydrogel as scaffold material. The osteoblast precursor cells MC3T3-E1 and osteoclast precursor cells RAW264.7 were used as seed cells, which may or may not be separated by polycarbonate membrane. The cytokines osteoprotegerin (OPG) and receptor activator of NF-κB ligand (RANKL) were used to induce cell differentiation. The function of scaffolds in the process of bone remodeling was analyzed by detecting the related markers of osteoblasts (alkaline phosphatase, ALP) and osteoclasts (tartrate resistant acid phosphatase, TRAP). Results: The scaffold showed good biocompatibility and low toxicity. The surface morphology aided cell adhesion and growth. The scaffold had optimum degradability, water absorption capacity and porosity, which are in line with the conditions of biological experiments. The effect of induced differentiation of cells was the best when cultured alone. After direct contact between the two types of cells at 2D or 3D level, the induced differentiation of cells was inhibited to varying degrees, although they still showed osteogenesis and osteoclast. After the cells were induced by indirect contact culture, the effect of induced differentiation improved when compared with direct contact culture, although it was still not as good as that of single culture. On the whole, the effect of inducing differentiation at 3D level was the same as that at 2D level, and its relative gene expression and enzyme activity were higher than that in the control group. Hence the scaffold used in this study could induce osteogenesis as well as osteoclast, thereby rendering it more effective in inducing new bone formation. Conclusion: This method can be used to construct the model of 3D bone remodeling mechanism.

In-vitro and in-vivo evaluation for the bio-natural Alginate/nano-Hydroxyapatite (Alg/n-HA) injectable hydrogel for critical size bone substitution

Currently, bio-natural injectable hydrogels are receiving a lot of attention due to their ability to control, adjust, and adapt to random bone defects, in addition, to their ability to mimic the composition of natural bones. From such a viewpoint, this study goal is to prepare and characterize the injectable hydrogels paste based on the natural alginate (Alg) derived from brown sea algae as a polysaccharide polymer, which coupled with nano biogenic-hydroxyapatite (n-HA) prepared from eggshells and enriched with valuable trace elements. The viscosity and mechanical properties of the paste were investigated. As well as the in-vitro study in terms of water absorption and biodegradability in the PBS, biocompatibility and the capability of the injectable Alginate/n-Hydroxyapatite (Alg/n-HA) to regenerate bone for the most suitable injectable form. The injectable hydrogel (BP -B sample) was chosen for the study as it had an appropriate setting time for injecting (13 mins), and suitable compressive strength reached 6.3 MPa. The in vivo study was also carried out including a post-surgery follow-up test of the newly formed bone (NB) in the defect area after 10 and 20 weeks using different techniques such as (SEM/EDX) and histological analysis, the density of the newly formed bone by Dual x-ray absorptiometry (DEXA), blood biochemistry and the radiology test. The results proved that the injectable hydrogels Alginate/n-Hydroxyapatite (Alg/n-HA) had an appreciated biodegradability and bioactivity, which allow the progress of angiogenesis, endochondral ossification, and osteogenesis throughout the defect area, which positively impacts the healing time and ensures the full restoration for the well-mature bone tissue that similar to the natural bone.

Phenolated alginate hydrogel induced osteogenic properties of mesenchymal stem cells via Wnt signaling pathway

Osteogenic properties of phenolated alginate (1.2 %) hydrogel containing collagen (0.5 %)/nano-hydroxyapatite (1 %) were studied on human mesenchymal stem cells in vitro. The phenolation rate and physical properties of the hydrogel were assessed using nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM), swelling ratio, gelation time, mechanical assay, and degradation rate. The viability of encapsulated cells was monitored on days 7, 14, and 21 using an MTT assay. Osteoblast differentiation was studied using western blotting, and real-time PCR. Using PCR array analysis, the role of the Wnt signaling pathway was also investigated. Data showed that the combination of alginate/collagen/nanohydroxyapatite yielded proper mechanical features. The addition of nanohydroxyapatite, and collagen reduced degradation, swelling rate coincided with increased stiffness. Elasticity and pore size were also diminished. NMR and FTIR revealed suitable incorporation of collagen and nanohydroxyapatite in the structure of alginate. Real-time PCR analysis and western blotting indicated the expression of osteoblast-related genes such as Runx2 and osteocalcin. PCR array revealed the induction of numerous genes related to Wnt signaling pathways during the maturation of human stem cells toward osteoblast-like cells. In vivo data indicated that transplantation of phenolated alginate/collagen/nanohydroxyapatite hydrogel led to enhanced de novo bone formation in rats with critical-sized calvarial defects. Phenolated alginate hydrogel can promote the osteogenic capacity of human amniotic membrane mesenchymal stem cells in the presence of nanohydroxyapatite and collagen via engaging the Wnt signaling pathway.

Primary human hepatocytes-laden scaffolds for the treatment of acute liver failure

Cell-based liver therapies based on retrieving and steadying failed metabolic function(s) for acute and chronic diseases could be a valuable substitute for liver transplants, even though they are limited by the low engraftment capability and reduced functional quality of primary human hepatocytes (PHH). In this paper we propose the use of gelatin-hyaluronic acid (Gel-HA) scaffolds seeded with PHH for the treatment of liver failure. We first optimized the composition using Gel-HA hydrogels, looking for the mechanical properties closer to the human liver and determining HepG2 cells functionality. Gel-HA scaffolds with interconnected porosity (pore size 102 μm) were prepared and used for PHH culture and evaluation of key hepatic functions. PHH cultured in Gel-HA scaffolds exhibited increased albumin and urea secretion and metabolic capacity (CYP and UGT activity levels) compared to standard monolayer cultures. The transplant of the scaffold containing PHH led to an improvement in liver function (transaminase levels, necrosis) and ameliorated damage in a mouse model of acetaminophen (APAP)-induced liver failure. The study provided a mechanistic understanding of APAP-induced liver injury and the impact of transplantation by analyzing cytokine production and oxidative stress induction to find suitable biomarkers of cell therapy effectiveness.

Melatonin and endothelial cell-loaded alginate-fibrin hydrogel promoted angiogenesis in rat cryopreserved/thawed ovaries transplanted to the heterotopic sites

BACKGROUND

Ischemic niche can promote follicular atresia following the transplantation of cryopreserved/thawed ovaries to the heterotopic sites. Thus, the promotion of blood supply is an effective strategy to inhibit/reduce the ischemic damage to ovarian follicles. Here, the angiogenic potential of alginate (Alg) + fibrin (Fib) hydrogel enriched with melatonin (Mel) and CD144⁺ endothelial cells (ECs) was assessed on encapsulated cryopreserved/thawed ovaries following transplantation to heterotopic sites in rats.

METHODS

Alg + Fib hydrogel was fabricated by combining 2% (w/v) sodium Alg, 1% (w/v) Fib, and 5 IU thrombin at a ratio of 4: 2: 1, respectively. The mixture was solidified using 1% CaCl₂. Using FTIR, SEM, swelling rate, and biodegradation assay, the physicochemical properties of Alg + Fib hydrogel were evaluated. The EC viability was examined using an MTT assay. Thirty-six adult female rats (aged between 6 and 8 weeks) with a normal estrus cycle were ovariectomized and enrolled in this study. Cryopreserved/thawed ovaries were encapsulated in Alg + Fib hydrogel containing 100 µM Mel + CD144⁺ ECs (2 × 10⁴ cells/ml) and transplanted into the subcutaneous region. Ovaries were removed after 14 days and the expression of Ang-1, and Ang-2 was monitored using real-time PCR assay. The number of vWF⁺ and α-SMA⁺ vessels was assessed using IHC staining. Using Masson's trichrome staining, fibrotic changes were evaluated.

RESULTS

FTIR data indicated successful interaction of Alg with Fib in the presence of ionic cross-linker (1% CaCl₂). Data confirmed higher biodegradation and swelling rates in Alg + Fib hydrogel compared to the Alg group (p < 0.05). Increased viability was achieved in encapsulated CD144⁺ ECs compared to the control group (p < 0.05). IF analysis showed the biodistribution of Dil⁺ ECs within hydrogel two weeks after transplantation. The ratio of Ang-2/Ang-1 was statistically up-regulated in the rats that received Alg + Fib + Mel hydrogel compared to the control-matched groups (p < 0.05). Based on the data, the addition of Mel and CD144⁺ ECs to Alg + Fib hydrogel reduced fibrotic changes. Along with these changes, the number of vWF⁺ and α-SMA⁺ vessels was increased in the presence of Mel and CD144⁺ ECs.

CONCLUSIONS

Co-administration of Alg + Fib with Mel and CD144⁺ ECs induced angiogenesis toward encapsulated cryopreserved/thawed ovarian transplants, resulting in reduced fibrotic changes.

Biomimetic biphasic scaffolds in osteochondral tissue engineering: Their composition, structure and consequences

Approaches to the design and construction of biomimetic scaffolds for osteochondral tissue, show increasing advances. Considering the limitations of this tissue in terms of repair and regeneration, there is a need to develop appropriately designed scaffolds. A combination of biodegradable polymers especially natural polymers and bioactive ceramics, shows promise in this field. Due to the complicated architecture of this tissue, biphasic and multiphasic scaffolds containing two or more different layers, could mimic the physiology and function of this tissue with a higher degree of similarity. The purpose of this review article is to discuss the approaches focused on the application of biphasic scaffolds for osteochondral tissue engineering, common methods of combining layers and the ultimate consequences of their use in patients were discussed.

Influence of gelatin modification on enzymatically-gellable pectin-gelatin hydrogel properties for soft tissue engineering applications

Injectable in situ-forming hydrogels appears to be a promising approach for tissue engineering applications. In this study, the effect of phenol moiety (Ph) addition to gelatin in enzymatically-gellable modified pectin hydrogel (Pec-Ph) was studied. Addition of gelatin-Ph to Pec-Ph (Pec-Ph/Gel-Ph) altered the physical properties of Pec-Ph-based hydrogels as compared to unmodified gelatin (Pec-Ph/Gel) addition. Swelling ratio and degradation rates of the Pec-Ph/Gel-Ph hydrogel decreased 35% and 50%, respectively, and the elasticity of Pec-Ph/Gel-Ph hydrogel was higher than the Pec-Ph/Gel hydrogels. Scanning electron microscopy images showed that the existence of phenolic groups in gelatin decreased the pore size of Pec-Ph/Gel-Ph hydrogels. Culture of chondrocyte cells in the Pec-Ph/Gel-Ph hydrogels showed more metabolic activity (4×) during a 14-day culture period. Hydrogels subcutaneously implanted in rats could also be identified readily without complete absorption and signs of toxicity or any untoward reactions after 1 month. The work showed the potential of Pec-Ph/Gel-Ph hydrogels as a promising in situ injectable hydrogel for soft tissue engineering applications.

Interaction of alginate with nano-hydroxyapatite-collagen using strontium provides suitable osteogenic platform

Background

Hydrogels based on organic/inorganic composites have been at the center of attention for the fabrication of engineered bone constructs. The establishment of a straightforward 3D microenvironment is critical to maintaining cell-to-cell interaction and cellular function, leading to appropriate regeneration. Ionic cross-linkers, Ca²⁺, Ba²⁺, and Sr²⁺, were used for the fabrication of Alginate-Nanohydroxyapatite-Collagen (Alg-nHA-Col) microspheres, and osteogenic properties of human osteoblasts were examined in in vitro and in vivo conditions after 21 days.

Results

Physicochemical properties of hydrogels illustrated that microspheres cross-linked with Sr²⁺ had reduced swelling, enhanced stability, and mechanical strength, as compared to the other groups. Human MG-63 osteoblasts inside Sr²⁺ cross-linked microspheres exhibited enhanced viability and osteogenic capacity indicated by mineralization and the increase of relevant proteins related to bone formation. PCR (Polymerase Chain Reaction) array analysis of the Wnt (Wingless-related integration site) signaling pathway revealed that Sr²⁺ cross-linked microspheres appropriately induced various signaling transduction pathways in human osteoblasts leading to osteogenic activity and dynamic growth. Transplantation of Sr²⁺ cross-linked microspheres with rat osteoblasts into cranium with critical size defect in the rat model accelerated bone formation analyzed with micro-CT and histological examination.

Conclusion

Sr²⁺ cross-linked Alg-nHA-Col hydrogel can promote functionality and dynamic growth of osteoblasts.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01511-9.

Collagen and nano-hydroxyapatite interactions in alginate-based microcapsule provide an appropriate osteogenic microenvironment for modular bone tissue formation

The addition of nano-hydroxyapatite (nHA) and collagen (Col) to the alginate (Alg) microcapsule hydrogel reduced swelling and degradation ratios while the compressive strength increased compared to Alg, Alg-Col, and Alg-nHA groups. MTT assay and Calcein-AM staining revealed an enhanced MG-63 osteoblasts viability in the Alg-nHA-Col hydrogel compared to the other groups. SEM showed the attachment of MG-63 osteoblasts inside Alg-Col hydrogels. Non-significant differences were found in antioxidant capacity of cells inside the Alg-nHA-Col hydrogel compared to the Alg group. Hematoxylin-Eosin staining showed the distribution of MG-63 osteoblasts inside microspheres. Calcium deposits, alkaline phosphatase (ALP) activity with the increase of intracellular calcium were found in Alg-nHA-Col group. Western blotting showed that levels of osteocalcin, ColA2, Sox-9, and ColA1 also significantly increased compared to the Alg, Alg-Col, Alg-nHA groups. The present study demonstrated that the addition of mineral nHA and protein (Col) into the Alg improves osteogenic potential and provides a 3D platform for modular bone tissue engineering.

Alginic Acid Polymer-Hydroxyapatite Composites for Bone Tissue Engineering

Natural bone is a composite organic-inorganic material, containing hydroxyapatite (HAP) as an inorganic phase. In this review, applications of natural alginic acid (ALGH) polymer for the fabrication of composites containing HAP are described. ALGH is used as a biocompatible structure directing, capping and dispersing agent for the synthesis of HAP. Many advanced techniques for the fabrication of ALGH-HAP composites are attributed to the ability of ALGH to promote biomineralization. Gel-forming and film-forming properties of ALGH are key factors for the development of colloidal manufacturing techniques. Electrochemical fabrication techniques are based on strong ALGH adsorption on HAP, pH-dependent charge and solubility of ALGH. Functional properties of advanced composite ALGH-HAP films and coatings, scaffolds, biocements, gels and beads are described. The composites are loaded with other functional materials, such as antimicrobial agents, drugs, proteins and enzymes. Moreover, the composites provided a platform for their loading with cells for the fabrication of composites with enhanced properties for various biomedical applications. This review summarizes manufacturing strategies, mechanisms and outlines future trends in the development of functional biocomposites.

Hybrid Gelatin Hydrogels in Nanomedicine Applications

Gelatin based hydrogels are often incorporated with supporting materials such as chitosan, poly(vinyl alcohol), alginate, carbon nanotubes, and hyaluronic acid. These hybrid materials are specifically of interest in diversified nanomedicine fields as they exhibit unique physicochemical properties, antimicrobial activity, biodegradability, and biocompatibility. The applications include drug delivery, wound healing, cell culture, and tissue engineering. This paper reviews the various up-to-date methods to fabricate gelatin-based hydrogels, including UV photo-cross-linking, electrospinning, and 3D bioprinting. This paper also includes physical, chemical, mechanical, and biocompatibility characterization studies of several hybrid gelatin hydrogels and discusses their relevance in nanomedicine based applications. Challenges associated with the fabrication of hybrid materials for nanotechnology implementation, specifically in nanomedicine development, are critically discussed, and some future recommendations are provided.

The osteogenic differentiation of human dental pulp stem cells in alginate-gelatin/Nano-hydroxyapatite microcapsules

Background

Microcapsule is considered as a promising 3D microenvironment for Bone Tissue Engineering (BTE) applications. Microencapsulation of cells in an appropriate scaffold not only protected the cells against excess stress but also promoted cell proliferation and differentiation. Through the current study, we aimed to microcapsulate the human Dental Pulp Stem Cells (hDPSCs) and evaluated the proliferation and osteogenic differentiation of those cells by using MTT assay, qRT-PCR, Alkaline phosphatase, and Alizarine Red S.

Results

The SEM results revealed that Alg/Gel microcapsules containing nHA showed a rough and more compact surface morphology in comparison with the Alg/Gel microcapsules. Moreover, the microencapsulation by Alg/Gel/nHA could improve cell proliferation and induce osteogenic differentiation. The cells cultured in the Alg/Gel and Alg/Gel/nHA microcapsules showed 1.4-fold and 1.7-fold activity of BMP-2 gene expression more in comparison with the control group after 21 days. The mentioned amounts for the BMP-2 gene were 2.5-fold and 4-fold more expression for the Alg/Gel and Alg/Gel/nHA microcapsules after 28 days. The nHA, addition to hDPSCs-laden Alg/Gel microcapsule, could up-regulate the bone-related gene expressions of osteocalcin, osteonectin, and RUNX-2 during the 21 and 28 days through the culturing period, too. Calcium deposition and ALP activities of the cells were observed in accordance with the proliferation results as well as the gene expression analysis.

Conclusion

The present study demonstrated that microencapsulation of the hDPSCs inside the Alg/Gel/nHA hydrogel could be a potential approach for regenerative dentistry in the near future.

Graphical abstract

Influence of gelatin and collagen incorporation on peroxidase-mediated injectable pectin-based hydrogel and bioactivity of fibroblasts

Pectin has recently attracted increasing attention for biomedical and pharmaceutical applications. Due to the lack of adhesion molecules in polysaccharides, phenolic hydroxyl conjugated gelatin was added to enzymatically-gellable peroxidase-modified pectin derivative and compared with phenolic hydroxyl -pectin/collagen. Both pectin and gelatin were modified by tyramine hydrochloride in the presence of EDC/NHS. The phenolic hydroxyl -pectin/phenolic hydroxyl -gelatin, phenolic hydroxyl-pectin/collagen, and phenolic hydroxyl -pectin hydrogels were prepared using horseradish peroxidase and hydrogen peroxide_. The hydrogels were characterized by gelation time analysis. Morphology, enzymatic biodegradation, mechanical and swelling properties as well as water vapor transmission rate were also evaluated. Fibroblasts were cultured for 7 days, and the survival rate was evaluated using conventional MTT assay. Hydrogels composed of Ph-pectin/Ph-gelatin showed decreased biodegradation rate, and WVTR and further improved mechanical performance in comparison with other groups. Both phenolic hydroxyl -pectin/collagen and phenolic hydroxyl -pectin/phenolic hydroxyl -gelatin hydrogels exhibited porous structures. The hydrogels composed of collagen promoted cell survival rate 1.4 and 3.5 times compared to phenolic hydroxyl -gelatin and phenolic hydroxyl -pectin based hydrogels at the end of 7 days, respectively (p < 0.001). The study demonstrated the potential of enzymatically-gellable pectin-based hydrogels as cost-effective frameworks for use in tissue engineering applications.

Microspheres containing biosynthesized silver nanoparticles with alginate-nano hydroxyapatite for biomedical applications

Scaffolding system plays an important role in the development of artificial bone for treatment of defective or diseased bone tissue. In the present work, we have developed microspheres (COS-Ag-Alg-HA) containing chitooligosaccharide (COS) coated silver nanoparticles (Ag NPs) with alginate (Alg) and hydroxyapatite (HA) as bone graft substitutes. The developed microspheres were characterized through various analytical techniques such as UV-visible spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction, field emission scanning electron microscopy with EDX and evaluated the mechanical strength by using universal testing machine. In addition to this, antimicrobial activity and biocompatibility of the developed microspheres were evaluated with pathogenic microbes and osteoblast-like cells, respectively. Results suggest that microspheres are rigid, and strong chemical interactions were observed between the materials. The size of the microspheres was ranging from 1.5 ± 0.5 to 4.0 ± 0.5 mm. Significant microbial inhibition was observed against Staphylococcus aureus, and the developed microspheres are biocompatible with osteoblast-like cells. Based on the aforementioned finding results, the developed microsphere is proposed to be a potential candidate for bone tissue repair and regeneration.