Nanocellulose-based porous materials: Regulation and pathway to commercialization in regenerative medicine.

We review the recent progress that have led to the development of porous materials based on cellulose nanostructures found in plants and other resources. In light of the properties that emerge from the chemistry, shape and structural control, we discuss some of the most promising uses of a plant-based material, nanocellulose, in regenerative medicine. Following a brief discussion about the fundamental aspects of self-assembly of nanocellulose precursors, we review the key strategies needed for material synthesis and to adjust the architecture of the materials (using three-dimensional printing, freeze-casted porous materials, and electrospinning) according to their uses in tissue engineering, artificial organs, controlled drug delivery and wound healing systems, among others. For this purpose, we map the structure-property-function relationships of nanocellulose-based porous materials and examine the course of actions that are required to translate innovation from the laboratory to industry. Such efforts require attention to regulatory aspects and market pull. Finally, the key challenges and opportunities in this nascent field are critically reviewed.

Synergistic Antimicrobial Metal Oxide-Doped Phosphate Glasses; a Potential Strategy to Reduce Antimicrobial Resistance and Host Cell Toxicity.

The emergence of antimicrobial resistant strains bacteria and a decline in the discovery of new antibiotics has led to the idea of combining various antimicrobials to treat resistant strains and/or polymicrobial infections. Metal oxide-doped glasses have been extensively investigated for their antimicrobial potential; however to date, most experiments have focused on single metal species in isolation. The present study investigates the antimicrobial potential of sodium calcium phosphates (P2O5)50(Na2O)20(CaO)30-X(MO)X, where M is cobalt, copper, or zinc as single species. In addition, this work studied the effect of co-doping glasses containing two different metal ions (Co + Cu, Co + Zn, and Cu + Zn). The antimicrobial efficacy of all glasses was tested against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacterial strains, as well as a fungal strain (Candida albicans). Minimum inhibitory and bactericidal concentrations and time kill/synergy assays were used to assess the antimicrobial activity. An enhanced antimicrobial effect, at 5 mg/mL concentration, was exhibited by cobalt, copper, and zinc oxide glasses alone and in combinations. A synergistic antimicrobial effect was observed by Cu + Co and Cu + Zn against E. coli and Cu + Zn against S. aureus.

In vitro and in vivo osteogenic potential of niobium-doped 45S5 bioactive glass: A comparative study.

In vitro and in vivo experiments were undertaken to evaluate the solubility, apatite-forming ability, cytocompatibility, osteostimulation, and osteoinduction for a series of Nb-containing bioactive glass (BGNb) derived from composition of 45S5 Bioglass. Inductively coupled plasma optical emission spectrometry (ICP-OES) revealed that the rate at which Na, Ca, Si, P, and Nb species are leached from the glass decrease with the increasing concentration of the niobium oxide. The formation of apatite as a function of time in simulated body fluid was monitored by 31P Magic Angle Spinning (MAS) Nuclear magnetic resonance spectroscopy. Results showed that the bioactive glasses: Bioglass 45S5 (BG45S5) and 1 mol%-Nb-containing-bioactive glass (BGSN1) were able to grow apatite layer on their surfaces within 3 h, while glasses with higher concentrations of Nb2 O5 (2.5 and 5 mol%) took at least 12 h. Nb-substituted glasses were shown to be compatible with bone marrow-derived mesenchymal stem cells (BMMSCs). Moreover, the bioactive glass with 1 mol% Nb2 O5 significantly enhanced cell proliferation after 4 days of treatment. Concentrations of 1 and 2.5 mol% Nb2 O5 stimulated osteogenic differentiation of BMMSCs after 21 days of treatment. For the in vivo experiments, trial glass rods were implanted into circular defects in rat tibia in order to evaluate their osteoconductivity and osteostimulation. Two morphometric parameters were analyzed: (a) thickness of new-formed bone layer and (b) area of new-formed subperiostal bone. Results showed that BGNb bioactive glass is osteoconductive and osteostimulative. Therefore, these results indicate that Nb-substituted glass is suitable for biomedical applications.

Evaluation of effectiveness of 45S5 bioglass doped with niobium for repairing critical-sized bone defect in in vitro and in vivo models.

Here, we investigated the biocompatibility of a bioactive sodium calcium silicate glass containing 2.6 mol% Nb2 O5 (denoted BGPN2.6) and compare the results with the archetypal 45S5 bioglass. The glass bioactivity was tested using a range of in vitro and in vivo experiments to assess its suitability for bone regeneration applications. in vitro studies consisted of assessing the cytocompatibility of the BGPN2.6 glass with bone-marrow-derived mesenchymal stem cells (BM-MSCs). Systemic biocompatibility was verified by means of the quantification of biochemical markers and histopathology of liver, kidneys, and muscles. The glass genotoxicity was assessed using the micronucleus test. The regeneration of a calvarial defect was assessed using both qualitative and quantitative analysis of three-dimensional microcomputed tomography images. The BGPN2.6 glass was not cytotoxic to BM-MSCs. It is systemically biocompatible causing no signs of damage to high metabolic and excretory organs such as the liver and kidneys. No mutagenic potential was observed in the micronucleus test. MicroCT images showed that BGPN2.6 was able to nearly fully regenerate a critical-sized calvarial defect and was far superior to standard 45S5 Bioglass. Defects filled with BGPN2.6 glass showed over 90% coverage compare to just 66% for 45S5 Bioglass. For one animal the defect was completely filled in 8 weeks. These results clearly show that Nb-containing bioactive glasses are a safe and effective biomaterial for bone replacement.

Nanocellulose/bioactive glass cryogels as scaffolds for bone regeneration.

A major challenge exists in the preparation of scaffolds for bone regeneration, namely, achieving simultaneously bioactivity, biocompatibility, mechanical performance and simple manufacturing. Here, cellulose nanofibrils (CNF) are introduced for the preparation of scaffolds taking advantage of their biocompatibility and ability to form strong 3D porous networks from aqueous suspensions. CNF are made bioactive for bone formation through a simple and scalable strategy that achieves highly interconnected 3D networks. The resultant materials optimally combine morphological and mechanical features and facilitate hydroxyapatite formation while releasing essential ions for in vivo bone repair. The porosity and roughness of the scaffolds favor several cell functions while the ions act in the expression of genes associated with cell differentiation. Ion release is found critical to enhance the production of the bone morphogenetic protein 2 (BMP-2) from cells within the fractured area, thus accelerating the in vivo bone repair. Systemic biocompatibility indicates no negative effects on vital organs such as the liver and kidneys. The results pave the way towards a facile preparation of advanced, high performance CNF-based scaffolds for bone tissue engineering.