Endothelialization of Whey Protein Isolate-Based Scaffolds for Tissue Regeneration.

BACKGROUND: Whey protein isolate (WPI) is a by-product from the dairy industry, whose main component is ß-lactoglobulin. Upon heating, WPI forms a hydrogel which can both support controlled drug delivery and enhance the proliferation and osteogenic differentiation of bone-forming cells. This study makes a novel contribution by evaluating the ability of WPI hydrogels to support the growth of endothelial cells, which are essential for vascularization, which in turn is a pre-requisite for bone regeneration. METHODS: In this study, the proliferation and antioxidant levels in human umbilical vascular endothelial cells (HUVECs) cultured with WPI supplementation were evaluated using real-time cell analysis and flow cytometry. Further, the attachment and growth of HUVECs seeded on WPI-based hydrogels with different concentrations of WPI (15%, 20%, 30%, 40%) were investigated. RESULTS: Supplementation with WPI did not affect the viability or proliferation of HUVECs monitored with real-time cell analysis. At the highest used concentration of WPI (500 µg/mL), a slight induction of ROS production in HUVECs was detected as compared with control samples, but it was not accompanied by alterations in cellular thiol levels. Regarding WPI-based hydrogels, HUVEC adhered and spread on all samples, showing good metabolic activity. Notably, cell number was highest on samples containing 20% and 30% WPI. CONCLUSIONS: The demonstration of the good compatibility of WPI hydrogels with endothelial cells in these experiments is an important step towards promoting the vascularization of hydrogels upon implantation in vivo, which is expected to improve implant outcomes in the future.

Phloroglucinol-enhanced whey protein isolate hydrogels with antimicrobial activity for tissue engineering.

Aging populations in developed countries will increase the demand for implantable materials to support tissue regeneration. Whey Protein Isolate (WPI), derived from dairy industry by-products, can be processed into hydrogels with the following desirable properties for applications in tissue engineering: (i) ability to support adhesion and growth of cells; (ii) ease of sterilization by autoclaving and (iii) ease of incorporation of poorly water-soluble drugs with antimicrobial activity, such as phloroglucinol (PG), the fundamental phenolic subunit of marine polyphenols. In this study, WPI hydrogels were enriched with PG at concentrations between 0 and 20% w/v. PG solubilization in WPI hydrogels is far higher than in water. Enrichment with PG did not adversely affect mechanical properties, and endowed antimicrobial activity against a range of bacteria which occur in healthcare-associated infections (HAI). WPI-PG hydrogels supported the growth of, and collagen production by human dental pulp stem cells and - to a lesser extent - of osteosarcoma-derived MG-63 cells. In summary, enrichment of WPI with PG may be a promising strategy to prevent microbial contamination while still promoting stem cell attachment and growth.

Mineralization of gellan gum hydrogels with calcium and magnesium carbonates by alternate soaking in solutions of calcium/magnesium and carbonate ion solutions.

Mineralization of hydrogels is desirable prior to applications in bone regeneration. CaCO3 is a widely used bone regeneration material, and Mg, when used as a component of calcium phosphate biomaterials, has promoted bone-forming cell adhesion and proliferation and bone regeneration. In this study, gellan gum hydrogels were mineralized with carbonates containing different amounts of calcium (Ca) and magnesium (Mg) by alternate soaking in, firstly, a calcium and/or magnesium ion solution and, secondly, a carbonate ion solution. This alternate soaking cycle was repeated five times. Five different calcium and/or magnesium ion solutions, containing different molar ratios of Ca to Mg ranging from Mg free to Ca free were compared. Carbonate mineral formed in all sample groups subjected to the alternate soaking cycle. Ca : Mg elemental ratio in the mineral formed was higher than in the respective mineralizing solution. Mineral formed in the absence of Mg was predominantly CaCO3 in the form of a mixture of calcite and vaterite. Increasing the Mg content in the mineral formed led to the formation of magnesian calcite and decreased the total amount of the mineral formed and its crystallinity. Hydrogel mineralization and increasing Mg content in mineral formed did not obviously improve proliferation of MC3T3-E1 osteoblast-like cells or differentiation after 7 days.

Gentamicin-Loaded Polysaccharide Membranes for Prevention and Treatment of Post-operative Wound Infections in the Skeletal System.

PURPOSE: To develop polysaccharide-based membranes that allow controlled and localized delivery of gentamicin for the treatment of post-operative bone infections. METHODS: Membranes made of gellan gum (GUM), sodium alginate (ALG), GUM and ALG crosslinked with calcium ions (GUM + Ca and ALG + Ca, respectively) as well as reference collagen (COL) were produced by freeze-drying. Mechanical properties, drug release, antimicrobial activity and cytocompatibility of the membranes were assessed. RESULTS: The most appropriate handling and mechanical properties (Young's modulus, E = 92 ± 4 MPa and breaking force, F MAX  = 2.6 ± 0.1 N) had GUM + Ca membrane. In contrast, COL membrane showed F MAX  = 0.14 ± 0.02 N, E = 1.0 ± 0.3 MPa and was deemed to be unsuitable for antibiotic delivery. The pharmacokinetic data demonstrated a uniform and sustainable delivery of gentamicin from GUM + Ca (44.4 ± 1.3% within 3 weeks), while for COL, ALG and ALG + Ca membranes the most of the drug was released within 24 h (55.3 ± 1.9%, 52.5 ± 1.5% and 37.5 ± 1.8%, respectively). Antimicrobial activity against S. aureus and S. epidermidis was confirmed for all the membranes. GUM + Ca and COL membranes supported osteoblasts growth, whereas on ALG and ALG + Ca membranes cell growth was reduced. CONCLUSIONS: GUM + Ca membrane holds promise for effective treatment of bone infections thanks to favorable pharmacokinetics, bactericidal activity, cytocompatibility and good mechanical properties.

Ca:Mg:Zn:CO3 and Ca:Mg:CO3-tri- and bi-elemental carbonate microparticles for novel injectable self-gelling hydrogel-microparticle composites for tissue regeneration.

Injectable composites for tissue regeneration can be developed by dispersion of inorganic microparticles and cells in a hydrogel phase. In this study, multifunctional carbonate microparticles containing different amounts of calcium, magnesium and zinc were mixed with solutions of gellan gum (GG), an anionic polysaccharide, to form injectable hydrogel-microparticle composites, containing Zn, Ca and Mg. Zn and Ca were incorporated into microparticle preparations to a greater extent than Mg. Microparticle groups were heterogeneous and contained microparticles of differing shape and elemental composition. Zn-rich microparticles were 'star shaped' and appeared to consist of small crystallites, while Zn-poor, Ca- and Mg-rich microparticles were irregular in shape and appeared to contain lager crystallites. Zn-free microparticle groups exhibited the best cytocompatibility and, unexpectedly, Zn-free composites showed the highest antibacterial activity towards methicilin-resistant Staphylococcus aureus. Composites containing Zn-free microparticles were cytocompatible and therefore appear most suitable for applications as an injectable biomaterial. This study proves the principle of creating bi- and tri-elemental microparticles to induce the gelation of GG to create injectable hydrogel-microparticle composites.

Novel injectable, self-gelling hydrogel-microparticle composites for bone regeneration consisting of gellan gum and calcium and magnesium carbonate microparticles.

The suitability of hydrogel biomaterials for bone regeneration can be improved by incorporation of an inorganic phase in particle form, thus maintaining hydrogel injectability. In this study, carbonate microparticles containing different amounts of calcium (Ca) and magnesium (Mg) were added to solutions of the anionic polysaccharide gellan gum (GG) to crosslink GG by release of Ca2+ and Mg2+ from microparticles and thereby induce formation of hydrogel-microparticle composites. It was hypothesized that increasing Mg content of microparticles would promote GG hydrogel formation. The effect of Mg incorporation on cytocompatibility and cell growth was also studied. Microparticles were formed by mixing Ca2+ and Mg2+ and [Formula: see text] ions in varying concentrations. Microparticles were characterized physiochemically and subsequently mixed with GG solution to form hydrogel-microparticle composites. The elemental Ca:Mg ratio in the mineral formed was similar to the Ca:Mg ratio of the ions added. In the absence of Mg, vaterite was formed. At low Mg content, magnesian calcite was formed. Increasing the Mg content further caused formation of amorphous mineral. Microparticles of vaterite and magnesium calcite did not induce GG hydrogel formation, but addition of Mg-richer amorphous microparticles induced gelation within 20 min. Microparticles were dispersed homogeneously in hydrogels. MG-63 osteoblast-like cells were cultured in eluate from hydrogel-microparticle composites and on the composites themselves. All composites were cytocompatible. Cell growth was highest on composites containing particles with an equimolar Ca:Mg ratio. In summary, carbonate microparticles containing a sufficient amount of Mg induced GG hydrogel formation, resulting in injectable, cytocompatible hydrogel-microparticle composites.

Enrichment of enzymatically mineralized gellan gum hydrogels with phlorotannin-rich Ecklonia cava extract Seanol(®) to endow antibacterial properties and promote mineralization.

Hydrogels offer several advantages as biomaterials for bone regeneration, including ease of incorporation of soluble substances such as mineralization-promoting enzymes and antibacterial agents. Mineralization with calcium phosphate (CaP) increases bioactivity, while antibacterial activity reduces the risk of infection. Here, gellan gum (GG) hydrogels were enriched with alkaline phosphatase (ALP) and/or Seanol(®), a seaweed extract rich in phlorotannins (brown algae-derived polyphenols), to induce mineralization with CaP and increase antibacterial activity, respectively. The sample groups were unmineralized hydrogels, denoted as GG, GG/ALP, GG/Seanol and GG/Seanol/ALP, and hydrogels incubated in mineralization medium (0.1 M calcium glycerophosphate), denoted as GG/ALP_min, GG/Seanol_min and GG/Seanol/ALP_min. Seanol(®) enhanced mineralization with CaP and also increased compressive modulus. Seanol(®) and ALP interacted in a non-covalent manner. Release of Seanol(®) occurred in a burst phase and was impeded by ALP-mediated mineralization. Groups GG/Seanol and GG/ALP/Seanol exhibited antibacterial activity against methicillin-resistant Staphylococcus aureus. GG/Seanol/ALP_min, but not GG/Seanol_min, retained some antibacterial activity. Eluates taken from groups GG/ALP_min, GG/Seanol_min and GG/ALP/Seanol_min displayed comparable cytotoxicity towards MG-63 osteoblast-like cells. These results suggest that enrichment of hydrogel biomaterials with phlorotannin-rich extracts is a promising strategy to increase mineralizability and antibacterial activity.

Enrichment of thermosensitive chitosan hydrogels with glycerol and alkaline phosphatase for bone tissue engineering applications.

Thermosensitive injectable chitosan hydrogels can be formed by neutralization of acidic chitosan solutions with sodium betaglycerophosphate (Na-ß-GP) coupled with increasing temperature to body temperature. Such hydrogels have been considered for applications in bone regeneration. In this study, chitosan hydrogels were enriched with glycerol and the enzyme alkaline phosphatase (ALP) with a view to improving their suitability as materials for bone tissue engineering. Mineral formation was confirmed by infrared spectroscopy (FTIR) and increases in the mass fraction of the hydrogel not consisting of water. Incorporation of ALP in hydrogels followed by incubation in a solution containing calcium ions and glycerophosphate, a substrate for ALP, led to formation of calcium phosphate within the hydrogel. MG-63 osteoblast-like cells were cultivated in eluates from hydrogels containing ALP and without ALP at different dilutions and directly on the hydrogel samples. Hydrogels containing ALP exhibited superior cytocompatibility to ALP-free hydrogels. These results pave the way for the use of glycerol- and ALP-enriched hydrogels in bone regeneration.

Visualizing changes in electron distribution in coupled chains of cytochrome bc(1) by modifying barrier for electron transfer between the FeS cluster and heme c(1).

Cytochrome c(1) of Rhodobacter (Rba.) species provides a series of mutants which change barriers for electron transfer through the cofactor chains of cytochrome bc(1) by modifying heme c(1) redox midpoint potential. Analysis of post-flash electron distribution in such systems can provide useful information about the contribution of individual reactions to the overall electron flow. In Rba. capsulatus, the non-functional low-potential forms of cytochrome c(1) which are devoid of the disulfide bond naturally present in this protein revert spontaneously by introducing a second-site suppression (mutation A181T) that brings the potential of heme c(1) back to the functionally high levels, yet maintains it some 100 mV lower from the native value. Here we report that the disulfide and the mutation A181T can coexist in one protein but the mutation exerts a dominant effect on the redox properties of heme c(1) and the potential remains at the same lower value as in the disulfide-free form. This establishes effective means to modify a barrier for electron transfer between the FeS cluster and heme c(1) without breaking disulfide. A comparison of the flash-induced electron transfers in native and mutated cytochrome bc(1) revealed significant differences in the post-flash equilibrium distribution of electrons only when the connection of the chains with the quinone pool was interrupted at the level of either of the catalytic sites by the use of specific inhibitors, antimycin or myxothiazol. In the non-inhibited system no such differences were observed. We explain the results using a kinetic model in which a shift in the equilibrium of one reaction influences the equilibrium of all remaining reactions in the cofactor chains. It follows a rather simple description in which the direction of electron flow through the coupled chains of cytochrome bc(1) exclusively depends on the rates of all reversible partial reactions, including the Q/QH2 exchange rate to/from the catalytic sites.