Bioactive materials: the potential for tissue regeneration

Applications of Bioactive Strontium Compounds in Dentistry

Divalent cations have captured the interest of researchers in biomedical and dental fields due to their beneficial effects on bone formation. These metallic elements are similar to trace elements found in human bone. Strontium is a divalent cation commonly found in various biomaterials. Since strontium has a radius similar to calcium, it has been used to replace calcium in many calcium-containing biomaterials. Strontium has the ability to inhibit bone resorption and increase bone deposition, making it useful in the treatment of osteoporosis. Strontium has also been used as a radiopacifier in dentistry and has been incorporated into a variety of dental materials to improve their radiopacity. Furthermore, strontium has been shown to improve the antimicrobial and mechanical properties of dental materials, promote enamel remineralization, alleviate dentin hypersensitivity, and enhance dentin regeneration. The objective of this review is to provide a comprehensive review of the applications of strontium in dentistry.

Effects of cerium-doped bioactive glass incorporation on an alginate/gelatin scaffold for bone tissue engineering: In vitro characterizations

Bioactive glasses (BGs) have been extensively employed in treating bone defects due to their capacity to bond and integrate with hard and soft tissues. To promote their characteristics, BGs are doped with therapeutic inorganic ions; Among these, Cerium (Ce) is of special attention because of its material and biological properties. This study aimed to investigate the effects of the addition of Ce to BG on the physicochemical and biological properties of the alginate/gelatin (Alg-Gel) scaffold compared with a similar scaffold that only contains BG45S5. The scaffolds were characterized for their biocompatibility using human bone marrow-derived mesenchymal stem cells (hBM-MSCs) by MTT analysis. The osteogenic differentiation of hBM-MSCs cultured on the scaffolds was assessed by evaluating the alkaline phosphatase (ALP) activity and the expression of osteogenic-related genes. Scanning electron microscopy of the prepared scaffolds showed an interconnected porous structure with an average diameter of 212-272 μm. The Young's modulus of the scaffolds significantly increased from 13 ± 0.82 MPa for Alg-Gel to 91 ± 1.76 MPa for Alg-Gel-BG/Ce. Ce doping improved the osteogenic differentiation of hBM-MSCs and ALP secretion compared to the other samples, even without adding an osteogenic differentiation medium. The obtained results demonstrated the biocompatibility and osteo-inductive potentials of the Alg-Gel-BG/Ce scaffold for bone tissue engineering.

Biomimetic Approaches in Clinical Endodontics

In the last few decades, biomimetic concepts have been widely adopted in various biomedical fields, including clinical dentistry. Endodontics is an important sub-branch of dentistry which deals with the different conditions of pulp to prevent tooth loss. Traditionally, common procedures, namely pulp capping, root canal treatment, apexification, and apexigonesis, have been considered for the treatment of different pulp conditions using selected materials. However, clinically to regenerate dental pulp, tissue engineering has been advocated as a feasible approach. Currently, new trends are emerging in terms of regenerative endodontics which have led to the replacement of diseased and non-vital teeth into the functional and healthy dentine-pulp complex. Root- canal therapy is the standard management option when dental pulp is damaged irreversibly. This treatment modality involves soft-tissue removal and then filling that gap through the obturation technique with a synthetic material. The formation of tubular dentine and pulp-like tissue formation occurs when stem cells are transplanted into the root canal with an appropriate scaffold material. To sum up tissue engineering approach includes three components: (1) scaffold, (2) differentiation, growth, and factors, and (3) the recruitment of stem cells within the pulp or from the periapical region. The aim of this paper is to thoroughly review and discuss various pulp-regenerative approaches and materials used in regenerative endodontics which may highlight the current trends and future research prospects in this particular area.

Bioactive glass-collagen/poly (glycolic acid) scaffold nanoparticles exhibit improved biological properties and enhance osteogenic lineage differentiation of mesenchymal stem cells

Today’s using tissue engineering and suitable scaffolds have got attention to increase healing of non-union bone fractures. In this study, we aimed to prepare and characterize scaffolds with functional and mechanical properties suitable for bone regeneration. Porous scaffolds containing collagen-poly glycolic acid (PGA) blends and various quantities of bioactive glass (BG) 45S5 were fabricated. Scaffolds with different compositions (BG/collagen-PGA ratios (w/w): 0/100; 40/60; 70/30) were characterized for their morphological properties, bioactivity, and mechanical behavior. Then, biocompatibility and osteogenic differentiation potential of the scaffolds were analyzed by seeding mesenchymal stem cells (MSCs). Scaffolds made with collagen-PGA combined with the BG (45S5) were found to have interconnected pores (average pore diameter size 75–115 µm) depending on the percentage of the BG added. Simulated body fluid (SBF) soaking experiments indicated the stability of scaffolds in SBF regardless of their compositions, while the scaffolds retained their highly interconnected structure. The elastic moduli, cell viability, osteogenic differentiation of the BG/collagen-PGA 40/60 and 70/30 scaffolds were superior to the original BG/collagen-PGA (0/100). These results suggest that BG incorporation enhanced the physical stability of our collagen-PGA scaffold previously reported. This new scaffold composition provides a promising platform to be used as a non-toxic scaffold for bone regeneration and tissue engineering.

Assessment of protein adhesion behaviour and biocompatibility of magnesium/Co-substituted HA-based composites for orthopaedic application

Protein adsorption has a great influence on Mg-based metallic implants, which affects cell attachment and cell growth. Adsorption of the proteins (via electrostatic interaction, hydrophobic/hydrophilic, and hydrogen-bonding) on the implant surface is greatly influenced by the surface chemistry of the implant. Hydroxyapatite (HA) is a class of CaP ceramic, beneficial for protein adsorption as it possesses Ca²⁺ and PO₄^3- in it, which are believed to be the protein binding sites on the HA surface. Moreover, HA is the popular choice for reinforcement in the magnesium matrix owing to its similarity with bone mineral composition. However, negligible interaction between HA and Mg particles during sintering is the major limitation for frequent usage of Mg-HA implants. Doping of HA with Mg²⁺ and Zn²⁺ (CoHA) ions leads to its chemistry similar to natural apatite in human bone and facilitates comparatively better bonding with the MgZn matrix. This study mainly aims to delve into the protein adsorption behaviour of Magnesium/Co-substituted HA-based Composites (M3Z-CoHA) along with their biocompatibility. Qualitative and quantitative protein adsorption analysis shows that the addition of 15 wt% CoHA to Mg matrix enhanced protein adsorption by ~60% and renders cell viability >90% after day 1, supporting cellular growth and proliferation. The implants also initiated osteogenic differentiation of the cells after day 7. The leached-out products from all the composites showed no toxicity. The morphology of the cells in all the composites was found as healthy as the control cells. Overall, the composite with 15 wt% HA reinforcement (M3Z-15CoHA) has shown favourable protein adsorption behaviour and cytocompatibility.

Effect of Ce-doped bioactive glass/collagen/chitosan nanocomposite scaffolds on the cell morphology and proliferation of rabbit’s bone marrow mesenchymal stem cells-derived osteogenic cells

Background

Cerium-containing materials have wide applications in the biomedical field, because of the mimetic catalytic activities of cerium. The study aims to deeply estimate the biocompatibility of different scaffolds based on Ce-doped nanobioactive glass, collagen, and chitosan using the first passage of rabbit bone marrow mesenchymal stem cells (BM-MSCs) directed to osteogenic lineage by direct and indirect approach. One percentage of glass filler was used (30 wt. %) in the scaffold, while the percentage of CeO₂ in the glass was ranged from 0 to 10 mol. %. Cytotoxicity was evaluated by monitoring of cell morphological changes and reduction in cell proliferation activity of BMMSCs maintained under osteogenic condition using proliferation assays, MTT assay for the direct contact of cells/scaffolds twice in a week, trypan blue and hemocytometer cell counting for indirect contact of cells/scaffolds extracts at day 7. Cell behaviors growth, morphology characteristics were monitored daily under a microscope and cell counting were conducted after 1 week of the incubation of the cells with the extracts of the four composite scaffolds in the osteogenic medium at the end of the week.

Results

Showed that at 24 h after direct contact with composite scaffold, all scaffolds showed proliferation of cells > 50% and increased in cell density on day 7. The scaffold of the highest percentage of CeO₂ in bioactive glass nanoparticles (sample CL/CH/C10) showed the lowest inhibition of cell proliferation (< 25%) at day 7. Moreover, the indirect cell viability test showed that all extracts from the four composite scaffolds did not demonstrate a toxic effect on the cells (inhibition value < 25%).

Conclusion

The addition of CeO₂ to the glass composition improved the biocompatibility of the composite scaffold for the proliferation of rabbit bone marrow mesenchymal stem cells directed to osteogenic lineage.

Supplementary Information

The online version contains supplementary material available at 10.1186/s43141-022-00302-x.

Antibacterial and Fluorescence Staining Properties of an Innovative GTR Membrane Containing 45S5BGs and AIE Molecules In Vitro

This study aimed to add two functional components-antibacterial 45S5BGs particles and AIE nanoparticles (TPE-NIM⁺) with bioprobe characteristics-to the guided tissue regeneration (GTR) membrane, to optimize the performance. The PLGA/BG/TPE-NIM⁺ membrane was synthesized. The static water contact angle, morphologies, and surface element analysis of the membrane were then characterized. In vitro biocompatibility was tested with MC3T3-E1 cells using CCK-8 assay, and antibacterial property was evaluated with Streptococcus mutans and Porphyromonas gingivalis by the LIVE/DEAD bacterial staining and dilution plating procedure. The fluorescence staining of bacteria was observed by Laser Scanning Confocal Microscope. The results showed that the average water contact angle was 46°. In the cytotoxicity test, except for the positive control group, there was no significant difference among the groups (p > 0.05). The antibacterial effect in the PLGA/BG/TPE-NIM⁺ group was significantly (p < 0.01), while the sterilization rate was 99.99%, better than that in the PLGA/BG group (98.62%) (p < 0.01). Confocal images showed that the membrane efficiently distinguished G⁺ bacteria from G^- bacteria. This study demonstrated that the PLGA/BG/TPE-NIM⁺ membrane showed good biocompatibility, efficient sterilization performance, and surface mineralization ability and could be used to detect pathogens in a simple, fast, and wash-free protocol.

Nanocomposite electrospun fibers of poly(ε-caprolactone)/bioactive glass with shape memory properties

Electrospun fibers of shape memory triethoxysilane-terminated poly(epsilon-caprolactone) (PCL-TES) loaded with bioactive glasses (BG) are here presented. Unloaded PCL-TES, as well as PCL/BG nanocomposite fibers, are also considered for comparison. It is proposed that hydrolysis and condensation reactions take place between triethoxysilane groups of the polymer and the silanol groups at the BG particle surface, thus generating additional crosslinking points with respect to those present in the PCL-TES system. The as-spun PCL-TES/BG fibers display excellent shape memory properties, in terms of shape fixity and shape recovery ratios, without the need of a thermal crosslinking treatment. BG particles confer in vitro bioactivity to PCL-based nanocomposite fibers and favor the precipitation of hydroxycarbonate apatite on the fiber surface. Preliminary cytocompatibility tests demonstrate that the addition of BG particles to PCL-based polymer does not inhibit ST-2 cell viability. This novel approach of using bioactive glasses not only for their biological properties, but also for the enhancement of shape memory properties of PCL-based polymers, widens the versatility and suitability of the obtained composite fibers for a huge portfolio of biomedical applications.

The effect of vanadium ferrite doping on the bioactivity of mesoporous bioactive glass-ceramics

Bioactive glasses are highly reactive surface materials synthesized by melting or sol–gel techniques. In this study, mesoporous bioactive glass-ceramics doped with different amounts of vanadium and iron ((60−(x + y)) SiO₂–36CaO–4P₂O₅–xV₂O₅–yFe₂O₃, x and y between 0, 5 and, 10 mole%) were synthesized using a sol–gel method. Then, their effects on particle morphology and the biomineralization process were examined in simulated body fluid (SBF). N2 adsorption isotherm analysis proved that the samples have a mesoporous structure. In addition, the Fourier-transform infrared spectroscopy (FTIR) spectra of the samples after soaking in SBF for various periods (7, 14, and 21 days) confirmed the presence of new chemical bonds related to the apatite phase, which is in accordance with scanning electron microscopy (SEM) observations. X-ray diffraction (XRD) patterns of the samples after SBF soaking showed that lower amounts of vanadium and iron were associated with the formation of a stable and more crystalline phase of hydroxyapatite. The MTT results showed that the cell viability of mesoporous bioactive glass containing 5% V₂O₅ remains more than 90% over 7 days, which indicates the biocompatibility of the samples. To conclude, further studies on these formulations are going to be carried out in future investigations for chemohyperthermia application.

Bioactive glasses are highly reactive surface materials synthesized by melting or sol–gel techniques.

Advanced bioactive nanomaterials for biomedical applications

Bioactive materials are a kind of materials with unique bioactivities, which can change the cellular behaviors and elicit biological responses from living tissues. Bioactive materials came into the spotlight in the late 1960s when the researchers found that the materials such as bioglass could react with surrounding bone tissue for bone regeneration. In the following decades, advances in nanotechnology brought the new development opportunities to bioactive nanomaterials. Bioactive nanomaterials are not a simple miniaturization of macroscopic materials. They exhibit unique bioactivities due to their nanoscale size effect, high specific surface area, and precise nanostructure, which can significantly influence the interactions with biological systems. Nowadays, bioactive nanomaterials have represented an important and exciting area of research. Current and future applications ensure that bioactive nanomaterials have a high academic and clinical importance. This review summaries the recent advances in the field of bioactive nanomaterials, and evaluate the influence factors of bioactivities. Then, a range of bioactive nanomaterials and their potential biomedical applications are discussed. Furthermore, the limitations, challenges, and future opportunities of bioactive nanomaterials are also discussed.

Microstructure, corrosion rate, and mechanical properties of unidirectionally and cross-rolled Mg-0.375Ga and Mg-0.750Ga alloys

The effect of unidirectional and cross rolling on the corrosion rate, texture, tensile properties and hemolysis of the Mg-0.375Ga and Mg-0.750Ga alloys was evaluated. Pure Mg and as-cast alloys were processed by unidirectional and cross rolling at 400°C to obtain a total thickness reduction of 50%. The corrosion rate was measured by the weight loss method in simulated body fluid. Determination of the hemolysis percentage was carried out by direct contact of specimens with diluted blood. After hot rolling, the mechanical properties of the alloys were improved. The cross-rolled Mg-0.750Ga alloy showed the highest grain refinement (55 μm) and the highest ultimate tensile strength (240 MPa), however, lower elongation (13.9%) than the rolled Mg-0.375Ga alloy. While unidirectional rolling creates a strong basal texture, cross rolling weakens considerably this texture. The Ga addition weakens the basal texture. Corrosion rate of the Mg-Ga alloys was significantly reduced (<1 mm/yr) after heat treatment and hot rolling due the homogenization of the microstructure and the presence of gallium as alloying element. The cross-rolled samples showed higher corrosion than the heat-treated and unidirectionally rolled samples. After rolling, alloys showed hemolysis percentages between 7.1 and 9.3%, values lower than those presented by pure magnesium (>22.7%) and as-cast alloys (>24.2%); however, the alloys are still hemolytic (>5%).

Bioactive Glass Applications: A Literature Review of Human Clinical Trials

The use of bioactive glasses in dentistry, reconstructive surgery, and in the treatment of infections can be considered broadly beneficial based on the emerging literature about the potential bioactivity and biocompatibility of these materials, particularly with reference to Bioglass® 45S5, BonAlive® and 19-93B3 bioactive glasses. Several investigations have been performed (i) to obtain bioactive glasses in different forms, such as bulk materials, powders, composites, and porous scaffolds and (ii) to investigate their possible applications in the biomedical field. Although in vivo studies in animals provide us with an initial insight into the biological performance of these systems and represent an unavoidable phase to be performed before clinical trials, only clinical studies can demonstrate the behavior of these materials in the complex physiological human environment. This paper aims to carefully review the main published investigations dealing with clinical trials in order to better understand the performance of bioactive glasses, evaluate challenges, and provide an essential source of information for the tailoring of their design in future applications. Finally, the paper highlights the need for further research and for specific studies intended to assess the effect of some specific dissolution products from bioactive glasses, focusing on their osteogenic and angiogenic potential.

Electrophoretic deposition of collagen/chitosan films with copper-doped phosphate glasses for orthopaedic implants

Coatings with bioactive properties play a key role in the success of orthopaedic implants. Recent studies focused on composite coatings incorporating biocompatible elements that can increase the nucleation of hydroxyapatite (HA), the mineral component of bone, and have promising bioactive and biodegradable properties. Here we report a method of fabricating composite collagen, chitosan and copper-doped phosphate glass (PG) coatings for biomedical applications using electrophoretic deposition (EPD). The use of collagen and chitosan (CTS) allows for the co-deposition of PG particles at standard ambient temperature and pressure (1 kPa, 25 °C), and the addition of collagen led to the steric stabilization of PG in solution. The coating composition was varied by altering the collagen/CTS concentrations in the solutions, as well as depositing PG with 0, 5 and 10 mol% CuO dopant. A monolayer of collagen/CTS containing PG was obtained on stainless steel cathodes, showing that deposition of PG in conjunction with a polymer is feasible. The mass of the monolayer varied depending on the polymer (collagen, CTS and collagen/CTS) and combination of polymer + PG (collagen-PG, CTS-PG and collagen/CTS-PG), while the presence of copper led to agglomerates during deposition at higher concentrations. The deposition yield was studied at different time points and showed a profile typical of constant voltage deposition. Increasing the concentration of collagen in the PG solution allows for a higher deposition yield, while pure collagen solutions resulted in hydrogen gas evolution at the cathode. The ability to deposit polymer-PG coatings that can mimic native bone tissue allows for the potential to fabricate orthopaedic implants with tailored biological properties with lower risk of rejection from the host and exhibit increased bioactivity.

Sol-gel based synthesis and biological properties of zinc integrated nano bioglass ceramics for bone tissue regeneration

Bone is a flexible and electro active tissue that is vulnerable to various traumatic injuries. The self-healing of damaged bone tissue towards reconstruction is limited due to the lack of proper niche compliances. Nevertheless, the classical grafting techniques like autograft/allograft for bone repair pose challenges like bacterial infections and donor-site morbidity with unsatisfactory outcomes. The use of appropriate biomaterial with osteogenic potential can meet these challenges. In this regard, bioactive glass ceramics is widely used as a bone filler or graft material because of its bonding affinity to bone leading towards bone reconstruction applications without the challenge of post implant infections. Hence, the current study is aimed at addressing this potentiality of zinc (Zn) for doped the bioglass at nano-scale advantages for bone tissue repair. Since, Zn has been demonstrated to have not only antibacterial property but also the stimulatory effect on osteoblasts differentiation, mineralization by enhancing the osteogenic genes expression. In view of these, the present study is focused on sol-gel synthesis and pysico-chemical characterization of Zinc-doped bioglass nanoparticles (Zn-nBGC) and also analyzing its biological implications. The surface morphological and physiochemical characterizations using SEM, EDX, FT-IR and XRD analysis has shown the increased surface area of Zn-nBGC particles providing a great platform for biomolecular interaction, cytocompatibility, cell proliferation and osteogenic differentiation. The obtaining hydroxy apatite groups have initiated in vitro mineralization towards osteogenic lineage formation. Zn has not only involved in enhancing cellular actions but also strengthen the ceramic nanoparticles towards antibacterial application. Hence the finding suggests a biomaterial synthesis of better biomaterial for bone tissue engineering application by preventing post-operative bacterial infection.

Innovative Molecular and Cellular Therapeutics in Cleft Palate Tissue Engineering

Clefts of the lip and/or palate are the most prevalent orofacial birth defects occurring in about 1:700 live human births worldwide. Early postnatal surgical interventions are extensive and staged to bring about optimal growth and fusion of palatal shelves. Severe cleft defects pose a challenge to correct with surgery alone, resulting in complications and sequelae requiring life-long, multidisciplinary care. Advances made in materials science innovation, including scaffold-based delivery systems for precision tissue engineering, now offer new avenues for stimulating bone formation at the site of surgical correction for palatal clefts. In this study, we review the present scientific literature on key developmental events that can go awry in palate development and the common surgical practices and challenges faced in correcting cleft defects. How key osteoinductive pathways implicated in palatogenesis inform the design and optimization of constructs for cleft palate correction is discussed within the context of translation to humans. Finally, we highlight new osteogenic agents and innovative delivery systems with the potential to be adopted in engineering-based therapeutic approaches for the correction of palatal defects. Impact statement Tissue-engineered scaffolds supplemented with osteogenic growth factors have attractive, largely unexplored possibilities to modulate molecular signaling networks relevant to driving palatogenesis in the context of congenital anomalies (e.g., cleft palate). Constructs that address this need may obviate current use of autologous bone grafts, thereby avoiding donor-site morbidity and other regenerative challenges in patients afflicted with palatal clefts. Combinations of biomaterials and drug delivery of diverse regenerative cues and biologics are currently transforming strategies exploited by engineers, scientists, and clinicians for palatal cleft repair.

Dual delivery of platelet-derived growth factor and bone morphogenetic factor-6 on titanium surface to enhance the early period of implant osseointegration

OBJECTIVE

To test the surface properties and in vitro effects of a new sequential release system on MC3T3-E1 cells for improved osseointegration.

BACKGROUND

BMP6-loaded anodized titanium coated with PDGF containing silk fibroin (SF) may improve osseointegration.

METHODS

Titanium surfaces were electrochemically anodized, and SF layer was covered via electrospinning. Five experimental groups (unanodized Ti (Ti), anodized Ti (AnTi), anodized + BMP6-loaded Ti (AnTi-BMP6), anodized + BMP6 loaded + silk fibroin-coated Ti (AnTi-BMP6-SF), and anodized + BMP6-loaded + silk fibroin with PDGF-coated Ti (AnTi-BMP6-PDGF-SF)) were tested. After SEM characterization, contact angle analysis, and FTIR analysis, the amount of released PDGF and BMP6 was detected using ELISA. Cell proliferation (XTT), mineralization, and gene expression (RUNX2 and ALPL) were also evaluated.

RESULTS

After successful anodization and loading of PDGF and BMP6, contact angle measurements showed hydrophobicity for TiO₂ and hydrophilicity for protein-adsorbed surfaces. In FTIR, protein-containing surfaces exhibited amide-I, amide-II, and amide-III bands at 1600 cm^-1 -1700 cm^-1 , 1520 cm^-1 -1540 cm^-1 , and 1220 cm^-1 -1300 cm^-1 spectrum levels with a significant peak in BMP6- and/or SF-loaded groups at 1100 cm^-1 . PDGF release and BMP6 release were delayed, and relatively slower release was detected in SF-coated surfaces. Higher MC3T3-E1 proliferation and mineralization and lower gene expression of RUNX2 and ALPL were detected in AnTi-BMP6-PDGF-SF toward day 28.

CONCLUSION

The new system revealed a high potential for an improved early osseointegration period by means of a better factor release curve and contribution to the osteoblastic cell proliferation, mineralization, and associated gene expression.

Cytotoxic Effect of Niobium Phosphate Glass-based Gutta-Percha Points on Periodontal Ligament Fibroblasts In Vitro

INTRODUCTION

The outcome of root canal obturation might be affected by the chemical components of the chosen filling materials. Niobium phosphate glass-based gutta-percha (GNB) was proposed as a biomaterial-based obturation point. This study aimed to investigate the cytotoxic and cell modulation effects of GNB points on human periodontal ligament fibroblasts (PDLFs) in vitro.

METHODS

Human PDLFs were cultured for the assays. Extracts of regular gutta-percha (GP) points and GNB were obtained, serially diluted (1:5, 1:10, and 1:25), and used to stimulate PDLFs. A cell viability assay was performed using alamarBlue reagent (Molecular Probes, Waltham, MA), and reverse transcription quantitative polymerase chain reaction was used to assess the gene expression for collagen type I and cementum protein 1. One-way analysis of variance followed by the Tukey post hoc test was performed (P < .05).

RESULTS

Regular GP reduced cell viability only in pure extracts, whereas GNB exhibited cytotoxicity to PDLFs in pure extracts as well as 1/5 and 1/10 dilutions. The gene expression of collagen type I was down-regulated only in the GNB group (P < .05). The expression of cementum protein 1 remained unaltered by both tested materials.

CONCLUSIONS

The addition of niobium phosphate glass to GP points increased cytotoxicity, affecting PDLF viability and partially disturbing physiological cell function.

Natural Polymeric Scaffolds in Bone Regeneration

Despite considerable advances in microsurgical techniques over the past decades, bone tissue remains a challenging arena to obtain a satisfying functional and structural restoration after damage. Through the production of substituting materials mimicking the physical and biological properties of the healthy tissue, tissue engineering strategies address an urgent clinical need for therapeutic alternatives to bone autografts. By virtue of their structural versatility, polymers have a predominant role in generating the biodegradable matrices that hold the cells in situ to sustain the growth of new tissue until integration into the transplantation area (i.e., scaffolds). As compared to synthetic ones, polymers of natural origin generally present superior biocompatibility and bioactivity. Their assembly and further engineering give rise to a wide plethora of advanced supporting materials, accounting for systems based on hydrogels or scaffolds with either fibrous or porous architecture. The present review offers an overview of the various types of natural polymers currently adopted in bone tissue engineering, describing their manufacturing techniques and procedures of functionalization with active biomolecules, and listing the advantages and disadvantages in their respective use in order to critically compare their actual applicability potential. Their combination to other classes of materials (such as micro and nanomaterials) and other innovative strategies to reproduce physiological bone microenvironments in a more faithful way are also illustrated. The regeneration outcomes achieved in vitro and in vivo when the scaffolds are enriched with different cell types, as well as the preliminary clinical applications are presented, before the prospects in this research field are finally discussed. The collection of studies herein considered confirms that advances in natural polymer research will be determinant in designing translatable materials for efficient tissue regeneration with forthcoming impact expected in the treatment of bone defects.

OPTIMIZATION OF COLLAGEN-ELASTIN-LIKE POLYPEPTIDE-BIOGLASS SCAFFOLD COMPOSITION FOR OSTEOGENIC DIFFERENTIATION OF ADIPOSE-DERIVED STEM CELLS

We have developed a multicomponent hydrogel scaffold that can mimic the bone extracellular matrix by incorporating collagen, elastin-like polypeptide (ELP), and Bioglass. We examined the effects of Bioglass addition to collagen-ELP scaffolds on mechanical properties, physical characteristics, and in vitro osteogenic differentiation, by varying the Bioglass amount and particle size. Response surface methodology with a central composite design predicted 5 mg (6.6 mg/mL) Bioglass with a particle size of 142 ± 5 μm as the optimal amount and particle size to be mixed with 6 mg/mL collagen and 18 mg/mL ELP to obtain a combination of maximized compressive properties. Swelling ratio and FTIR spectroscopy indicated lower hydrophilicity and the presence of hydrophobic and secondary interactions between collagen, ELP, and Bioglass. Scanning electron microscopy showed a nanofibrous morphology of intermingled collagen-ELP-Bioglass network. In vitro osteogenic characterization using human adipose-derived stem cells revealed increased cell attachment and proliferation with increased ALP activity, osteocalcin content, and mineralized deposit formation during a three-week culture. Numerous mineralized deposits composed of calcium and phosphorous were shown by energy dispersive spectroscopy. Overall, our results show that the collagen-ELP-Bioglass multicomponent composites have enhanced mechanical properties with adequate physical features and cell culture properties for bone tissue engineering.

Fibrin biopolymer as scaffold candidate to treat bone defects in rats

BACKGROUND

Bone tissue repair remains a challenge in tissue engineering. Currently, new materials are being applied and often integrated with live cells and biological scaffolds. The fibrin biopolymer (FBP) proposed in this study has hemostatic, sealant, adhesive, scaffolding and drug-delivery properties. The regenerative potential of an association of FBP, biphasic calcium phosphate (BCP) and mesenchymal stem cells (MSCs) was evaluated in defects of rat femurs.

METHODS

Adult male Wistar rats were submitted to a 5-mm defect in the femur. This was filled with the following materials and/or associations: BPC; FBP and BCP; FBP and MSCs; and BCP, FBP and MSCs. Bone defect without filling was defined as the control group. Thirty and sixty days after the procedure, animals were euthanatized and subjected to computed tomography, scanning electron microscopy and qualitative and quantitative histological analysis.

RESULTS

It was shown that FBP is a suitable scaffold for bone defects due to the formation of a stable clot that facilitates the handling and optimizes the surgical procedures, allowing also cell adhesion and proliferation. The association between the materials was biocompatible. Progressive deposition of bone matrix was higher in the group treated with FBP and MSCs. Differentiation of mesenchymal stem cells into osteogenic lineage was not necessary to stimulate bone formation.

CONCLUSIONS

FBP proved to be an excellent scaffold candidate for bone repair therapies due to application ease and biocompatibility with synthetic calcium-based materials. The satisfactory results obtained by the association of FBP with MSCs may provide a more effective and less costly new approach for bone tissue engineering.

Green synthesis of bacterial cellulose/bioactive glass nanocomposites: Effect of glass nanoparticles on cellulose yield, biocompatibility and antimicrobial activity

Despite the advantages of bacterial cellulose (BC) over traditional cellulose, its low yield and little bioactivity makes a limitation to be used in an industrial scale. This paper was mainly dual aimed to increase the BC yield using a nanobioactive glass (NBG), and in situ synthesize BC/NBG bioactive nanocomposites by a novel and simple green method. Accordingly, the composites were prepared via in situ fermentation approach by incorporation of NBG particles into BC producing culture medium. The effect of NBG addition on the production process of cellulose, biocompatibility, bioactivity and antimicrobial activity were investigated. The results showed that NBG was enhanced and increased the BC yield and this has been achieved by maintaining these NBG on the pH value of the culture medium during the fermentation period. Moreover, it was effectively improved biocompatibility and antimicrobial properties of BC. This study evidenced that BC/NBG composite can be expected to be widely applied in biomedical industries such as bone regeneration and wound healing with the unique of being not harmful to humans.

Calcium carbonate: Adored and ignored in bioactivity assessment

The title of this article could sound a bit curious to some readers since a layer of apatite - and not calcium carbonate - is well-known to form on the surface of bioactive glasses upon immersion in simulated body fluids. However, calcium carbonate (commonly reported as calcite crystals) can form on the surface of bioactive glasses as well, instead of or in competition with hydroxyapatite, during in vitro tests. Major factors that govern calcium carbonate formation are a high concentration of Ca²⁺ ions in the testing solution - and, in this regard, glass composition/texture and type of medium play key roles - along with the volume of solution used during in vitro tests. To date, this phenomenon has received relatively little attention and is still partly unexplored. This article provides a critical overview of the available literature on this topic in order to stimulate constructive discussion among biomaterials scientists and further research for better understanding the mechanisms involved in glass bioactivity. STATEMENT OF SIGNIFICANCE: A literature search indicates that a layer of apatite - and not calcium carbonate - is well known to form on the surface of biomaterials during the bioactivity assessment. However, calcium carbonate can form on the surface as well, instead of or in competition with apatite. To date, this phenomenon has received relatively little attention and is still partly unexplored. This review provides a critical overview of the available literature on this topic in order to stimulate constructive discussions that can be further useful for clinical success.

The bone regeneration capacity of 3D-printed templates in calvarial defect models: A systematic review and meta-analysis

3D-printed templates are being used for bone tissue regeneration (BTR) as temporary guides. In the current review, we analyze the factors considered in producing potentially bioresorbable/degradable 3D-printed templates and their influence on BTR in calvarial bone defect (CBD) animal models. In addition, a meta-analysis was done to compare the achieved BTR for each type of template material (polymer, ceramic or composites). Database collection was completed by January 2018, and the inclusion criteria were all titles and keywords combining 3D printing and BTR in CBD models. Clinical trials and poorly-documented in vivo studies were excluded from this study. A total of 45 relevant studies were finally included and reviewed, and an additional check list was followed before inclusion in the meta-analysis, where material type, porosity %, and the regenerated bone area were collected and analyzed statistically. Overall, the capacity of the printed templates to support BTR was found to depend in large part on the amount of available space (porosity %) provided by the printed templates. Printed ceramic and composite templates showed the best BTR capacity, and the optimum printed template structure was found to have total porosity >50% with a pore diameter between 300 and 400 µm. Additional features and engineered macro-channels within the printed templates increased BTR capacity at long time points (12 weeks). Although the size of bone defects in rabbits was larger than in rats, BTR was greater in rabbits (almost double) at all time points and for all materials used. STATEMENT OF SIGNIFICANCE: In the present study, we reviewed the factors considered in producing degradable 3D-printed templates and their influence on bone tissue regeneration (BTR) in calvarial bone defects through the last 15 years. A meta-analysis was applied on the collected data to quantify and analyze BTR related to each type of template material. The concluded data states the importance of 3D-printed templates for BTR and indicates the ideal design required for an effective clinical translation. The evidence-based guidelines for the best BTR capacity endorse the use of printed composite and ceramic templates with total porosity >50%, pore diameter between 300 and 400 µm, and added engineered macro-channels within the printed templates.

Indirect 3D printing technology for the fabrication of customised β-TCP/chitosan scaffold with the shape of rabbit radial head-an in vitro study

Background

With the development of indirect three-dimensional (3D) printing technology, it is possible to customise individual scaffolds to be used in bone transplantation and regeneration. In addition, materials previously limited to the 3D printing (3DP) process due to their own characteristics can also be used well in indirect 3DP. In this study, customised β-TCP/chitosan scaffolds with the shape of rabbit radial head were produced by indirect 3D printing technology.

Methods

Swelling ability, porosity, mechanical characterisation, and degradation rate analysis were performed, and in vitro studies were also implemented to evaluate the proliferation and osteogenic differentiation of bone marrow mesenchymal stem cells (MSCs) on the scaffolds. CCK8 cell proliferation assay kit and alkaline phosphatase (ALP) staining solution were used to study cell proliferation and early ALP content at the scaffold surface. Moreover, the osteogenic differentiation of MSCs on scaffolds was also evaluated through the scanning electron microscopy analysis.

Results

β-TCP/chitosan scaffold has good performance and degradation rate, and in vitro cell experiments also confirm that the scaffold has adequate cytocompatibility and bioactivity.

Conclusion

This study provides a promising new strategy for the design of customised scaffolds for the repair of complex damaged tissues.

Enhanced osteoconductivity on electrically charged titanium implants treated by physicochemical surface modifications methods

Biomimetic design is a key tenet of orthopedic device technology, and in particular the development of responsive surfaces that promote ion exchange with interfacing tissues, facilitating the ionic events that occur naturally during bone repair, hold promise in orthopedic fixation strategies. Non-bioactive nanostructured titanium implants treated by shot-blasting and acid-etching (AE) induced higher bone implant contact (BIC=52% and 65%) compared to shot-blasted treated (SB) implants (BIC=46% and 47%) at weeks 4 and 8, respectively. However, bioactive charged implants produced by plasma (PL) or thermochemical (BIO) processes exhibited enhanced osteoconductivity through specific ionic surface-tissue exchange (PL, BIC= 69% and 77% and BIO, BIC= 85% and 87% at weeks 4 and 8 respectively). Furthermore, bioactive surfaces (PL and BIO) showed functional mechanical stability (resonance frequency analyses) as early as 4 weeks post implantation via increased total bone area (BAT=56% and 59%) ingrowth compared to SB (BAT=35%) and AE (BAT=35%) surfaces.

Carbon Nanotubes and Graphene as Nanoreinforcements in Metallic Biomaterials: a Review

Current challenges in existing metallic biomaterials encourage undertaking research in the development of novel materials for biomedical applications. This paper critically reviews the potential of carbon nanotubes (CNT) and graphene as nanoreinforcements in metallic biomaterials for bone tissue engineering. Unique and remarkable mechanical, electrical, and biological properties of these carbon nanomaterials allow their use as secondary-phase reinforcements in monolithic biomaterials. The nanoscale dimensions and extraordinarily large surface areas of CNT and graphene make them suitable materials for purposeful reaction with living organisms. However, the cytocompatibility of CNT and graphene is still a controversial issue that impedes advances in utilizing these promising materials in clinical orthopedic applications. The interaction of CNT and graphene with biological systems including proteins, nucleic acids, and human cells is critically reviewed to assess their cytocompatibity in vitro and in vivo. It is revealed that composites reinforced with CNT and graphene show enhanced adhesion of osteoblast cells, which subsequently promotes bone tissue formation in vivo. This potential is expected to pave the way for developing ground-breaking technologies in regenerative medicine and bone tissue engineering. In addition, current progress and future research directions are highlighted for the development of CNT and graphene reinforced implants for bone tissue engineering.

Comparative evaluation of magnetic hyperthermia performance and biocompatibility of magnetite and novel Fe-doped hardystonite nanoparticles for potential bone cancer therapy

Hyperthermia-increasing temperature of cancerous tissue for a short period of time-is considered as an effective treatment for various cancer types such as malignant bone tumors. Superparamagnetic and ferromagnetic particles have been studied for their hyperthermic properties in treating various types of cancers. The activation of magnetic nanoparticles by an alternating magnetic field is currently being explored as a technique for targeted therapeutic heating of different tumors and is being studied as an adjuvant to conventional chemotherapy and radiation therapy. In the case of bone cancers, to increase the efficiency of treatment in the hyperthermia therapy, employed materials should support bone regeneration as well. Magnetite is one of the most attractive magnetic nanoceramics used in hyperthermia application. However, biocompatibility and bioactivity of this material have raised questions. There is a high demand for extremely efficient hyperthermia materials which are equally biocompatible to non-tumor cells and tissues. We report the development of a biocompatible and bioactive material with desirable magnetic properties that show excellent hyperthermia properties and can be used for destruction of the cancerous tissue in addition to supporting tissue regeneration for treatment of bone tumors. In the current study, iron (Fe³⁺)-containing HT nanostructured material was prepared, and its biocompatibility, bioactivity, and hyperthermia abilities were studied. The developed materials showed effective hyperthermic properties with increased biocompatibility as compared to magnetite.

Synthesis and characterization of Barium-Iron containing magnetic bioactive glasses: The effect of magnetic component on structure and in vitro bioactivity

CaO-P₂O₅-SiO₂-BaO-Fe₂O₃ magnetic bioactive glasses were prepared via an optimized sol-gel method. This study is focused on investigating effects of magnetic content addition on the bioactive glass properties. To this aim, we evaluate the physical, rheological, and biocompatibility properties of synthesized magnetic bioactive glass. The morphology and composition of these glasses were studied using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The particle size was also determined using Laser Particle Size Analyzer (LPSA). The thermal measurements were carried out using Differential Thermal Analysis (DTA). For assessing the in-vitro bioactive character of synthesized glasses, the ability for apatite formation on their surface upon immersion in simulated body fluid (SBF) was checked using SEM, EDX and pH measurements. Furthermore, the Ca, Si, Ba and Fe ions in SBF were monitored using Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES). The results showed that the addition of Ba and Fe in the glass composition affect formation of apatite layer onto the glass surfaces. Morphologies of the apatite layers were also different in which the bioactivity decreased with increasing Fe concentration, but the increase of Ba concentration led to an increase in bioactivity. However all of the synthesized glasses are still highly bioactive. Finally, this research demonstrates that the synthesized magnetic bioactive glasses are nontoxic and biocompatible and they can be used as thermoseeds for cancer hyperthermia studies.

Multifunctional polymer coatings for titanium implants

The aim of this work was to modify the surface of the titanium implants by application of multifunctional polymer coatings based on polyurethane and its composites with graphene and β-TCP. Graphene was used as an antibacterial agent, TCP as a bioactive component, and polymer coating as a corrosion protection of metal. As a result, materials with different surface characteristic, from hydrophilic to hydrophobic, varying in bioactivity and biocompatibility, were obtained. Wettability of the materials was tested by the sessile drop method; surface roughness was assessed on the basis of R_a parameter, measured by contact profilometry. The surface characteristic was complemented by microhardness testing. Also, in vitro immersion tests in fluids and cell tests were performed. Obtained results suggest that it is possible to fabricate, on the surface of titanium implants, multifunctional composite coatings based on polyurethane, with optimal composition for bone surgery and dentistry applications. The study further showed that the chemical structure (composition) of the polymer and the graphene content are crucial in terms of biocompatibility of the final material, while addition of tricalcium phosphate affects its bioactivity.

Enhancing the Cell-Biological Performances of Hydroxyapatite Bioceramic by Constructing Silicate-Containing Grain Boundary Phases via Sol Infiltration

Hydroxyapatite (HA) is well-known as one of the excellent bone repair biomaterials because of its chemical similarity with biological apatite. However, weak bioactivity obstructs its application. Although the bioactivity of HA bioceramic could be enhanced by the incorporation of bioactive glass (BG), the dramatic decrease of its mechanical property is consistently a disturbance to the reliable efficacy of traditional modified HA bioceramic. In this study, HA bioceramic was modified by infiltration of BG sol and formation of silicate-containing grain boundary phases during subsequent sintering. The phase compositions, microstructure, mechanical performance, in vitro degradation behaviors, and osteogenesis of the bioceramic were investigated. The modified HA bioceramic exhibited an interesting phenomenon in which the HA grains were uniformly enveloped by the small silicate-containing grains in the boundaries of HA grains. The microporosity of modified HA bioceramics was up to 25.27% ± 0.01%, much higher than that of unmodified HA bioceramic (1.74% ± 0.27%). The compressive strength of the modified HA bioceramic via BG sol infiltration was much higher than that of the HA bioceramic modified by BG via mechanical blending method, though slightly lower than that of the blank. Moreover, mouse bone mesenchymal stem cells (mBMSCs) cultured on modified bioceramic displayed better adhesion morphology and proliferation, and had an enhanced expression of osteogenesis-related genes. This study offers a new strategy to improve the bioactivity of HA bioceramic without obvious deterioration in mechanical strength.

In Vitro and In Vivo Characterization of N-Acetyl-L-Cysteine Loaded Beta-Tricalcium Phosphate Scaffolds

Beta-tricalcium phosphate bioceramics are widely used as bone replacement scaffolds in bone tissue engineering. The purpose of this study is to develop beta-tricalcium phosphate scaffold with the optimum mechanical properties and porosity and to identify the effect of N-acetyl-L-cysteine loaded to beta-tricalcium phosphate scaffold on the enhancement of biocompatibility. The various interconnected porous scaffolds were fabricated using slurries containing various concentrations of beta-tricalcium phosphate and different coating times by replica method using polyurethane foam as a passing material. It was confirmed that the scaffold of 40 w/v% beta-tricalcium phosphate with three coating times had optimum microstructure and mechanical properties for bone tissue engineering application. The various concentration of N-acetyl-L-cysteine was loaded on 40 w/v% beta-tricalcium phosphate scaffold. Scaffold group loaded 5 mM N-acetyl-L-cysteine showed the best viability of MC3T3-E1 preosteoblastic cells in the water-soluble tetrazolium salt assay test.

Biodegradable Scaffolds for Bone Regeneration Combined with Drug-Delivery Systems in Osteomyelitis Therapy

A great deal of research is ongoing in the area of tissue engineering (TE) for bone regeneration. A possible improvement in restoring damaged tissues involves the loading of drugs such as proteins, genes, growth factors, antibiotics, and anti-inflammatory drugs into scaffolds for tissue regeneration. This mini-review is focused on the combination of the local delivery of antibiotic agents with bone regenerative therapy for the treatment of a severe bone infection such as osteomyelitis. The review includes a brief explanation of scaffolds for bone regeneration including scaffolds characteristics and types, a focus on severe bone infections (especially osteomyelitis and its treatment), and a literature review of local antibiotic delivery by the combination of scaffolds and drug-delivery systems. Some examples related to published studies on gentamicin sulfate-loaded drug-delivery systems combined with scaffolds are discussed, and future perspectives are highlighted.

Sensitivity of novel silicate and borate-based glass structures on in vitro bioactivity and degradation behaviour

Three novel glass compositions, identified as NCL2 (SiO2-based), NCL4 (B2O3-based) and NCL7 (SiO2-based), along with apatite-wollastonite (AW) were processed to form sintered dense pellets, and subsequently evaluated for their in vitro bioactive potential, resulting physico-chemical properties and degradation rate. Microstructural analysis showed the carbonated hydroxyapatite (HCA) precipitate morphology following SBF testing to be composition-dependent. AW and the NCL7 formulation exhibited greater HCA precursor formation than the NCL2 and NCL4-derived pellets. Moreover, the NCL4 borate-based samples showed the highest biodegradation rate; with silicate-derived structures displaying the lowest weight loss after SBF immersion. The results of this study suggested that glass composition has significant influence on apatite-forming ability and also degradation rate, indicating the possibility to customise the properties of this class of materials towards the bone repair and regeneration process.

Novel bioglasses for bone tissue repair and regeneration: Effect of glass design on sintering ability, ion release and biocompatibility

Eight novel silicate, phosphate and borate glass compositions (coded as NCLx, where x = 1 to 8), containing different oxides (i.e. MgO, MnO2, Al2O3, CaF2, Fe2O3, ZnO, CuO, Cr2O3) were designed and evaluated alongside apatite-wollastonite (used as comparison material), as potential biomaterials for bone tissue repair and regeneration. Glass frits of all the formulations were processed to have particle sizes under 53 μm, with their morphology and dimensions subsequently investigated by scanning electron microscopy (SEM). In order to establish the nature of the raw glass powders, X-ray diffraction (XRD) analysis was also performed. The sintering ability of the novel materials was determined by using hot stage microscopy (HSM). Ionic release potential was assessed by inductively coupled plasma optical emission spectroscopy (ICP-OES). Finally, the cytotoxic effect of the novel glass powders was evaluated for different glass concentrations via a colorimetric assay, on which basis three formulations are considered promising biomaterials.

Quantitative Kinetics Evaluation of Blocks Versus Granules of Biphasic Calcium Phosphate Scaffolds (HA/β-TCP 30/70) by Synchrotron Radiation X-ray Microtomography: A Human Study

INTRODUCTION

Successful bone regeneration using both granules and blocks of biphasic calcium phosphate materials has been reported in the recent literature, in some clinical applications for maxillary sinus elevation, but the long-term kinetics of bone regeneration has still not been fully investigated.

MATERIALS AND METHODS

Twenty-four bilateral sinus augmentation procedures were performed and grafted with hydroxyapatite/β-tricalcium phosphate 30/70, 12 with granules and 12 with blocks. The samples were retrieved at different time points and were evaluated for bone regeneration, graft resorption, neovascularization, and morphometric parameters by computed microtomography and histology.

RESULTS

A large amount of newly formed bone was detected in the retrieved specimens, together with a good rate of biomaterial resorption and the formation of a homogeneous and rich net of new vessels. The morphometric values were comparable at 5/6 months from grafting but, 9 months after grafting, revealed that the block-based specimens mimicked slightly better than granule-based samples the healthy native bone of the maxillary site.

CONCLUSION

The scaffold morphology was confirmed to influence the long-term kinetics of bone regeneration.

Self-assembled high-strength hydroxyapatite/graphene oxide/chitosan composite hydrogel for bone tissue engineering

Graphene hydrogel has shown greatly potentials in bone tissue engineering recently, but it is relatively weak in the practical use. Here we report a facile method to synthesize high strength composite graphene hydrogel. Graphene oxide (GO), hydroxyapatite (HA) nanoparticles (NPs) and chitosan (CS) self-assemble into a 3-dimensional hydrogel with the assistance of crosslinking agent genipin (GNP) for CS and reducing agent sodium ascorbate (NaVC) for GO simultaneously. The dense and oriented microstructure of the resulted composite gel endows it with high mechanical strength, high fixing capacity of HA and high porosity. These properties together with the good biocompatibility make the ternary composite gel a promising material for bone tissue engineering. Such a simultaneous crosslinking and reduction strategy can also be applied to produce a variety of 3D graphene-polymer based nanocomposites for biomaterials, energy storage materials and adsorbent materials.

Three-dimensional bioprinting speeds up smart regenerative medicine

Biological materials can actively participate in the formation of bioactive organs and can even control cell fate to form functional tissues that we name as the smart regenerative medicine (SRM). The SRM requires interdisciplinary efforts to finalize the pre-designed organs. Three-dimensional (3D) printing, as an additive manufacturing technology, has been widely used in various fields due to its high resolution and individuation. In SRM, with the assistance of 3D printing, cells and biomaterials could be precisely positioned to construct complicated tissues. This review summarizes the state of the SRM advances and focuses in particular on the 3D printing application in biofabrication. We further discuss the issues of SRM development and finally propose some approaches for future 3D printing, which involves SRM.