Enriched mesoporous bioactive glass scaffolds as bone substitutes in critical diaphyseal bone defects in rabbits.

In the field of orthopedic surgery, there is an increasing need for the development of bone replacement materials for the treatment of bone defects. One of the main focuses of biomaterials engineering are advanced bioceramics like mesoporous bioactive glasses (MBG´s). The present study compared the new bone formation after 12 weeks of implantation of MBG scaffolds with composition 82,5SiO2-10CaO-5P2O5-x 2.5SrO alone (MBGA), enriched with osteostatin, an osteoinductive peptide, (MBGO) or enriched with bone marrow aspirate (MBGB) in a long bone critical defect in radius bone of adult New Zealand rabbits. New bone formation from the MBG scaffold groups was compared to the gold standard defect filled with iliac crest autograft and to the unfilled defect. Radiographic follow-up was performed at 2, 6, and 12 weeks, and microCT and histologic examination were performed at 12 weeks. X-Ray study showed the highest bone formation scores in the group with the defect filled with autograft, followed by the MBGB group, in addition, the microCT study showed that bone within defect scores (BV/TV) were higher in the MBGO group. This difference could be explained by the higher density of newly formed bone in the osteostatin enriched MBG scaffold group. Therefore, MBG scaffold alone and enriched with osteostatin or bone marrow aspirate increase bone formation compared to defect unfilled, being higher in the osteostatin group. The present results showed the potential to treat critical bone defects by combining MBGs with osteogenic peptides such as osteostatin, with good prospects for translation into clinical practice. STATEMENT OF SIGNIFICANCE: Treatment of bone defects without the capacity for self-repair is a global problem in the field of Orthopedic Surgery, as evidenced by the fact that in the U.S alone it affects approximately 100,000 patients per year. The gold standard of treatment in these cases is the autograft, but its use has limitations both in the amount of graft to be obtained and in the morbidity produced in the donor site. In the field of materials engineering, there is a growing interest in the development of a bone substitute equivalent. Mesoporous bioactive glass (MBG´s) scaffolds with three-dimensional architecture have shown great potential for use as a bone substitutes. The osteostatin-enriched Sr-MBG used in this long bone defect in rabbit radius bone in vivo study showed an increase in bone formation close to autograft, which makes us think that it may be an option to consider as bone substitute.

In vivo behavior in rabbit radius bone defect of scaffolds based on nanocarbonate hydroxyapatite.

Bone defects treatment may require the use of biomaterials that behave as a support and promote bone regeneration. Limitations associated with the use of autografts and allografts make it necessary to design new synthetic bone substitutes. Some of the most promising biomaterials currently under investigation are based on nanocarbonate hydroxyapatite (nCHA). In this study, we studied the bone-inducing capacity of nCHA-based scaffolds alone (SAG) and enriched with osteostatin (SAGO) or with bone marrow aspirate(SAGB) after implantation for 12 weeks in a 15-mm long critical defect performed in the radius of New Zealand rabbits. Bone formation obtained was compared with a group with the unfilled defect (CE), as control group, and other with the defect filed with iliac crest autograft (GS), as gold standard. X-ray follow-up was performed at 2, 4, 6 and 12 weeks and µCT and histological studies at 12 weeks. The radiological results showed a greater increment in bone formation in the GS group (75%-100%), followed by the SAG and SAGB groups (50%-75%). µCT results showed an increase of bone volume/tissue volume values in GS group followed by SAG and SAGB groups (0.53, 0.40, and 0.31 respectively) compared with CE group (0.26). Histological results showed limited resorption of the nCHA scaffolds and partial osseointegration in the SAG and SAGB groups. However, in the SAGO group, the presence of connective tissue encapsulating the scaffold was detected. In SAG, SAGB, and increase of bone formation were observed compared with CE group, but less than the GS group. Thus, the investigated materials represent a significant advance in the design of synthetic materials for bone grafting, but further studies are needed to bring their in vivo behavior closer to autograft, the gold standard.

New Photocrosslinked 3D Foamed Scaffolds Based on GelMA Copolymers: Potential Application in Bone Tissue Engineering.

The production of customized polymeric hydrogels in the form of 3D scaffolds with application in bone tissue engineering is currently a topic of great interest. Based on gelatin methacryloyl (GelMa) as one of the most popular used biomaterials, GelMa with two different methacryloylation degrees (DM) was obtained, to achieve crosslinked polymer networks by photoinitiated radical polymerization. In this work, we present the obtention of new 3D foamed scaffolds based on ternary copolymers of GelMa with vinylpyrrolidone (VP) and 2-hydroxyethylmethacrylate (HEMA). All biopolymers obtained in this work were characterized by infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA), whose results confirm the presence of all copolymers in the crosslinked biomaterial. In addition, scanning electron microscopy (SEM) pictures were obtained verifying the presence of the porosity created by freeze-drying process. In addition, the variation in its swelling degree and its enzymatic degradation in vitro was analyzed as a function of the different copolymers obtained. This has allowed us to observe good control of the variation in these properties described above in a simple way by varying the composition of the different comonomers used. Finally, with these concepts in mind, biopolymers obtained were tested through assessment of several biological parameters such as cell viability and differentiation with MC3T3-E1 pre-osteoblastic cell line. Results obtained show that these biopolymers maintain good results in terms of cell viability and differentiation, along with tunable properties in terms of hydrophilic character, mechanical properties and enzymatic degradation.

In Vitro and In Vivo Response of Zinc-Containing Mesoporous Bioactive Glasses in a Sheep Animal Model.

Zinc-enriched mesoporous bioactive glasses (MBGs) are bioceramics with potential antibacterial and osteogenic properties. However, few assays have been performed to study these properties in animal models. In this study, MBGs enriched with up to 5% ZnO were synthesized, physicochemically characterized, and evaluated for their osteogenic activity both in vitro and in vivo. The ZnO MBGs showed excellent textural properties despite ZnO incorporation. However, the release of Zn2+ ions inhibited the mineralization process when immersed in simulated body fluid. In vitro assays showed significantly higher values of viability and expression of early markers of cell differentiation and angiogenesis in a ZnO-content-dependent manner. The next step was to study the osteogenic potential in a sheep bone defect model. Despite their excellent textural properties and cellular response in vitro, the ZnO MBGs were not able to integrate into the bone tissue, which can be explained in terms of inhibition of the mineralization process caused by Zn2+ ions. This work highlights the need to develop nanostructured materials for bone regeneration that can mineralize to interact with bone tissue and induce the processes of implant acceptance, cell colonization by osteogenic cells, and regeneration of lost bone tissue.

Cu-Doped Hollow Bioactive Glass Nanoparticles for Bone Infection Treatment.

In search of new approaches to treat bone infection and prevent drug resistance development, a nanosystem based on hollow bioactive glass nanoparticles (HBGN) of composition 79.5SiO2-(18-x)CaO-2.5P2O5-xCuO (x = 0, 2.5 or 5 mol-% CuO) was developed. The objective of the study was to evaluate the capacity of the HBGN to be used as a nanocarrier of the broad-spectrum antibiotic danofloxacin and source of bactericidal Cu2+ ions. Core-shell nanoparticles with specific surface areas close to 800 m2/g and pore volumes around 1 cm3/g were obtained by using hexadecyltrimethylammonium bromide (CTAB) and poly(styrene)-block-poly(acrylic acid) (PS-b-PAA) as structure-directing agents. Flow cytometry studies showed the cytocompatibility of the nanoparticles in MC3T3-E1 pre-osteoblastic cell cultures. Ion release studies confirmed the release of non-cytotoxic concentrations of Cu2+ ions within the therapeutic range. Moreover, it was shown that the inclusion of copper in the system resulted in a more gradual release of danofloxacin that was extended over one week. The bactericidal activity of the nanosystem was evaluated with E. coli and S. aureus strains. Nanoparticles with copper were not able to reduce bacterial viability by themselves and Cu-free HBGN failed to reduce bacterial growth, despite releasing higher antibiotic concentrations. However, HBGN enriched with copper and danofloxacin drastically reduced bacterial growth in sessile, planktonic and biofilm states, which was attributed to a synergistic effect between the action of Cu2+ ions and danofloxacin. Therefore, the nanosystem here investigated is a promising candidate as an alternative for the local treatment of bone infections.

Strontium-Modified Scaffolds Based on Mesoporous Bioactive Glasses/Polyvinyl Alcohol Composites for Bone Regeneration.

In the search of a new biomaterial for the treatment of bone defects resulting from traumatic events, an osteoporosis scenario with bone fractures, tumor removal, congenital pathologies or implant revisions for infection, we developed 3D scaffolds based on mesoporous bioactive glasses (MBGs) (85-x)SiO2-5P2O5-10CaO-xSrO (x = 0, 2.5 and 5 mol.%). The scaffolds with meso-macroporosity were fabricated by pouring a suspension of MBG powders in polyvinyl alcohol (PVA) into a negative template of polylactic acid (PLA), followed by removal of the template by extraction at low temperature. SrO-containing MBGs exhibited excellent properties for bone substitution including ordered mesoporous structure, high textural properties, quick in vitro bioactive response in simulated body fluid (SBF) and the ability of releasing concentrations of strontium ions able to stimulate expression of early markers of osteoblastic differentiation. Moreover, the direct contact of MC3T3-E1 pre-osteoblastic cells with the scaffolds confirmed the cytocompatibility of the three compositions investigated. Nevertheless, the scaffold containing 2.5% of SrO induced the best cellular proliferation showing the potential of this scaffold as a candidate to be further investigated in vitro and in vivo, aiming to be clinically used for bone regeneration applications in non-load bearing sites.