Degradation, bioactivity, and osteogenic potential of composites made of PLGA and two different sol-gel bioactive glasses

Ultrastable PLGA-Coated 177Lu-Microspheres for Radioembolization Therapy of Hepatocellular Carcinoma

Transarterial radioembolization (TARE) is a highly effective localized radionuclide therapy that has been successfully used to treat hepatocellular carcinoma (HCC). Extensive research has been conducted on the use of radioactive microspheres (MSs) in TARE, and the development of ideal radioactive MSs is crucial for clinical trials and patient treatment. This study presents the development of a radioactive MS for TARE of HCC. These MSs, referred to as 177Lu-MS@PLGA, consist of poly(lactic-co-glycolic acid) (PLGA) copolymer and radioactive silica MSs, labeled with 177Lu and then coated with PLGA. It has an extremely high level of radiostability. Cellular experiments have shown that it can cause DNA double-strand breaks, leading to cell death. In vivo radiostability of 177Lu-MS@PLGA is demonstrated by microSPECT/CT imaging. In addition, the antitumor study has shown that TARE of 177Lu-MS@PLGA can effectively restrain tumor growth without harmful side effects. Thus, 177Lu-MS@PLGA exhibits significant potential as a radioactive MS for the treatment of HCC.

Bioactive Glasses Enriched with Strontium or Zinc with Different Degrees of Structural Order as Components of Chitosan-Based Composite Scaffolds for Bone Tissue Engineering

The development of innovative biomaterials with improved integration with bone tissue and stimulating regeneration processes is necessary. Here, we evaluate the usefulness of bioactive glasses from the SiO2-P2O5-CaO system enriched with 2 wt.% SrO or ZnO in the manufacturing of chitosan-based scaffolds. Bioglasses produced using the sol-gel method were subjected to thermal treatment in different regimes. Chitosan/bioglass composites were produced with a weight ratio. Bioglasses were evaluated via TG-DTA, FTIR, and SEM-EDS before and after incubation in simulated body fluid (SBF). The release of ions was tested. The cytocompatibility of the composites in contact with MG63 osteoblast-like cells was evaluated. The results showed that the presence of the crystalline phase decreased from 41.2-44.8% for nonmodified bioglasses to 24.2-24.3% for those modified with ZnO and 22.0-24.2% for those modified with SrO. The samples released Ca2+, Zn2+, and/or Sr2+ ions and were bioactive according to the SBF test. The highest cytocompatibility was observed for the composites containing nonmodified bioglasses, followed by those enriched with SrO bioglasses. The least cytocompatible were the composites containing ZnO bioglasses that released the highest amount of Zn2+ ions (0.58 ± 0.07 mL/g); however, those that released 0.38 ± 0.04 mL/g were characterised by acceptable cytocompatibility. The study confirmed that it is feasible to control the biological performance of chitosan/bioglass composites by adjusting the composition and heat treatment parameters of bioglasses.

Chemical Compounds Released from Specific Osteoinductive Bioactive Materials Stimulate Human Bone Marrow Mesenchymal Stem Cell Migration

In this work, a poly(L-lactide-co-glycolide) (PLGA)-based composite was enriched with one of the following sol-gel bioactive glasses (SBG) at 50 wt.%: A1—40 mol% SiO2, 60 mol% CaO, CaO/SiO2 ratio of 1.50; S1—80 mol% SiO2, 20 mol% CaO, CaO/SiO2 ratio of 0.25; A2—40 mol% SiO2, 54 mol% CaO, 6 mol% P2O5, CaO/SiO2 ratio of 1.35; S2—80 mol% SiO2,16 mol% CaO, 4 mol% P2O5, CaO/SiO2 ratio of 0.20. The composites and PLGA control sheets were then soaked for 24 h in culture media, and the obtained condition media (CM) were used to treat human bone marrow stromal cells (hBMSCs) for 72 h. All CMs from the composites increased ERK 1/2 activity vs. the control PLGA CM. However, expressions of cell migration-related c-Fos, osteopontin, matrix metalloproteinase-2, C-X-C chemokine receptor type 4, vascular endothelial growth factor, and bone morphogenetic protein 2 were significantly increased only in cells treated with the CM from the A1/PLGA composite. This CM also significantly increased the rate of human BMSC migration but did not affect cell metabolic activity. These results indicate important biological markers that are upregulated by products released from the bioactive composites of a specific chemical composition, which may eventually prompt osteoprogenitor cells to colonize the bioactive material and accelerate the process of tissue regeneration.

Drug infused Al2O3-bioactive glass coatings toward the cure of orthopedic infection

A unique implant coated substrate with dual-drug-eluting system exhibiting antibacterial, anti-inflammatory, and bone regenerative capacity has been fabricated using spray pyrolysis deposition (SPD) method. Bioglass (BG) and BG-alumina (BG-Al) composites coatings with different concentrations of Al incorporated on BG network over the Cp-Ti substrate were fabricated using SPD technique. Phase purity of BG and BG-Al composites were analyzed by XRD in which Na₂Ca₂Si₃O₉ and β-Na₂Ca₄(PO₄)₂SiO₄) and Na_7.15(Al_7.2Si_8.8O₃₂) phases were formed. Surface morphology of the coated substrates was analyzed by SEM. Uniformity of the coatings were evaluated by surface profilometer and the uniform distribution the nanoparticles were confirmed with Elemental mapping. Systematically, each apatite layer formation on coated substrate was confirmed by immersing the samples for 1, 3, and 7 days in simulated body fluid and the needle-like structure was characterized using SEM. Cumulative release of Tetracycline hydrochloride (Tet) antibiotic and Dexamethasone (Dex) anti-inflammatory drug-loaded BG-Al and BG-Al composite-coated substrate were studied for 24 h. Antibacterial activity of the coated substrates were evaluated by time-dependent growth inhibition and minimal inhibitory concentration (MIC) assays in which BG-Al and BG-Al composite loaded with Tet showed considerable growth inhibition against S. aureus. Osteoblast-like cells (MG-63) exhibited profound proliferation with no cytotoxic effects which was due to release of Dex drug-coated substrates. Thus, surface modification of Cp-Ti substrate with BG, BG-Al composites coatings loaded with Tet and Dex drug can be considered for post-operative orthopedic implant infection application.

Lysine-functionalized chondroitin sulfate improves the biological properties of collagen/chitosan-based injectable hydrogels

Novel bioactive collagen/chitosan/lysine-functionalized chondroitin sulfate (CS_mod) injectable hydrogels are presented. The modification of CS with amine groups introduced with lysine moieties (the degree of substitution about 21%) guarantees its covalent binding with the hydrogel network while genipin crosslinking. Both the physicochemical and biological features of developed hydrogels might be adjusted by playing with CS_mod and crosslinking agent concentrations. It was revealed that materials became more hydrophobic with increased CS_mod content, while crosslinking degree and enzymatic degradation studies established the influence of CS_mod concentration and Ch:CS_mod ratio on the crosslinking process. In situ rheological experiments verified the injectability of resulted systems. The biological in vitro evaluation demonstrated that all designed materials are biocompatible as they supported proliferation and adhesion of MG-63 cell line. In vitro biomineralization study employing simulated body fluid model revealed CS_mod-content dependent bioactivity of obtained hydrogels. Importantly for pristine collagen/chitosan materials, the formation of apatite-like structures was not observed. Our findings demonstrate that developed injectable ColChCS_mod hydrogels particularly system with the greatest CS_mod concentration exhibits high bioactive potential, without the need of applying additional inducers what renders them promising materials within tissue engineering applications.

Amniotic Epithelial Stem Cells Counteract Acidic Degradation By-Products of Electrospun PLGA Scaffold by Improving Their Immunomodulatory Profile In Vitro

Electrospun poly(lactic-co-glycolic acid) (PLGA) scaffolds with highly aligned fibers (ha-PLGA) represent promising materials in the field of tendon tissue engineering (TE) due to their characteristics in mimicking fibrous extracellular matrix (ECM) of tendon native tissue. Among these properties, scaffold biodegradability must be controlled allowing its replacement by a neo-formed native tendon tissue in a controlled manner. In this study, ha-PLGA were subjected to hydrolytic degradation up to 20 weeks, under di-H₂O and PBS conditions according to ISO 10993-13:2010. These were then characterized for their physical, morphological, and mechanical features. In vitro cytotoxicity tests were conducted on ovine amniotic epithelial stem cells (oAECs), up to 7 days, to assess the effect of non-buffered and buffered PLGA by-products at different concentrations on cell viability and their stimuli on oAECs’ immunomodulatory properties. The ha-PLGA scaffolds degraded slowly as evidenced by a slight decrease in mass loss (14%) and average molecular weight (35%), with estimated degradation half-time of about 40 weeks under di-H₂O. The ultrastructure morphology of the scaffolds showed no significant fiber degradation even after 20 weeks, but alteration of fiber alignment was already evident at week 1. Moreover, mechanical properties decreased throughout the degradation times under wet as well as dry PBS conditions. The influence of acid degradation media on oAECs was dose-dependent, with a considerable effect at 7 days’ culture point. This effect was notably reduced by using buffered media. To a certain level, cells were able to compensate the generated inflammation-like microenvironment by upregulating IL-10 gene expression and favoring an anti-inflammatory rather than pro-inflammatory response. These in vitro results are essential to better understand the degradation behavior of ha-PLGA in vivo and the effect of their degradation by-products on affecting cell performance. Indeed, buffering the degradation milieu could represent a promising strategy to balance scaffold degradation. These findings give good hope with reference to the in vivo condition characterized by physiological buffering systems.

Advances in the Fabrication of Scaffold and 3D Printing of Biomimetic Bone Graft

The need for bone grafts is tremendous, and that leads to the use of autograft, allograft, and bone graft substitutes. The biology of the bone is quite complex regarding cellular composition and architecture, hence developing a mineralized connective tissue graft is challenging. Traditionally used bone graft substitutes including metals, biomaterial coated metals and biodegradable scaffolds, suffer from persistent limitations. With the advent and rise of additive manufacturing technologies, the future of repairing bone trauma and defects seems to be optimistic. 3D printing has significant advantages, the foremost of all being faster manipulation of various biocompatible materials and live cells or tissues into the complex natural geometries necessary to mimic and stimulate cellular bone growth. The advent of new-generation bioprinters working with high-precision, micro-dispensing and direct digital manufacturing is aiding in ground-breaking organ and tissue printing, including the bone. The future bone replacement for patients holds excellent promise as scientists are moving closer to the generation of better 3D printed bio-bone grafts that will be safer and more effective. This review aims to summarize the advances in scaffold fabrication techniques, emphasizing 3D printing of biomimetic bone grafts.

Novel Eco-Friendly Tannic Acid-Enriched Hydrogels-Preparation and Characterization for Biomedical Application

Sodium alginate and tannic acid are natural compounds that can be mixed with each other. In this study, we propose novel eco-friendly hydrogels for biomedical applications. Thus, we conducted the following assessments including (i) observation of the structure of hydrogels by scanning electron microscope; (ii) bioerosion and the concentration of released tannic acid from subjected material; (iii) dehydrogenase activity assay to determine antibacterial activity of prepared hydrogels; and (iv) blood and cell compatibility. The results showed that hydrogels based on sodium alginate/tannic acid exert a porous structure. The immersion in simulated body fluid (SBF) results in the biomineralization process occurring on their surface while the bioerosion studies revealed that the addition of tannic acid improves hydrogels’ stability proportional to its concentration. Besides, tannic acid release concentration depends on the type of hydrogels and the highest amount was noticed for those based on sodium alginate with the content of 30% tannic acid. Antibacterial activity of hydrogels was proven for both Gram-negative and Gram-positive bacteria, the hemolysis rate was below 5% and the viability of the cells was elevated with an increasing amount of tannic acid in hydrogels. Collectively, we assume that obtained materials make the imperative to consider them for biomedical applications.

Enhancement of hydrophilicity, biocompatibility and biodegradability of poly(ε-caprolactone) electrospun nanofiber scaffolds using poly(ethylene glycol) and poly(L-lactide-co-ε-caprolactone-co-glycolide) as additives for soft tissue engineering

In this study, poly(ε-caprolactone) (PCL) has been blended with a more hydrophilic poly(ethylene glycol) (PEG) and with a biocompatible block-co-polymer: poly(L-lactide-co-ε-caprolactone-co-glycolide) (PLCG) in order to improve hydrophilicity, biocompatibility and biodegradability of PCL. PCL and the blend solutions were subjected to electrospinning to produce nanofiber scaffolds by the addition of only 1 wt% of PEG and PLCG either singly or in combination in PCL to retain the mechanical properties of the scaffolds. PCL-PEG-PLCG ternary and two binary (PCL-PEG and PCL-PLCG) blend nanofiber scaffolds have been prepared for comparison. The resulting nanofibers showed a smooth and flaw-free surface and the diameter of the nanofibers displayed a normal distribution. The PCL-PEG nanofiber scaffold showed improved hydrophilicity [water contact angle (WCA) ∼84°] over pristine PCL (WCA ∼127°); while PCL-PLCG and PCL-PEG-PLCG scaffolds exhibited absolute wetting by water, likely due to high porosity. In vitro biocompatibility studies using gingival mesenchymal stem cells (gMSCs) suggested that, both the PCL and the blend scaffolds were biocompatible supporting cell-viability and growth of gMSCs following their seeding on these scaffolds. Biodegradation studies in phosphate buffer solution showed that the addition of PEG and PLCG in PCL increased the weight loss of scaffolds with time, indicating higher extent of biodegradation in the blend scaffolds and the weight loss followed the power law curve with time.

In-vivo histocompatibility and osteogenic potential of biodegradable PLDLA composites containing silica-based bioactive glass fiber

The purpose of this two-year study was to evaluate the histocompatibility and osteogenic properties of a composite material consisting of poly(l-co-d,l lactide) (PLDLA) and silica-based bioactive glass fibers in vivo. PLDLA and PLDLA/silica-based bioactive glass fibers pins were implanted into the erector spinae muscles and femurs of beagles. Muscle and bone tissue samples were harvested 6, 12, 16, 26, 52, 78, and 104 weeks after implantation. Histology analysis was used to assess the histocompatibility, angiogenesis, and bone-implant contact. Micro-computed tomography was used to evaluate bone formation around the pins. Immunohistochemistry and western blotting revealed the expression level of the osteogenesis-related proteins. Addition of bioactive glass was demonstrated to possess better histocompatibility and reduce the inflammatory reactions in vivo. Moreover, PLDLA/silica-based bioactive glass fibers pins were demonstrated to promote angiogenesis and increase osteogenesis-related proteins expression, and thus played a positive role in osteogenesis and osseointegration after implantation. Our findings indicated that a composite of PLDLA and silica-based bioactive glass fiber is a promising biodegradable material for clinical use.

Mechanical and degradative properties of PLDLA biodegradable pins with bioactive glass fibers in a beagle model

The present study aimed to evaluate the mechanical and degradative properties of poly(L-co-D,L-lactic acid)/silicate bioactive glass fibers (PLDLA/SGFs) composite pins in vivo. Both PLDLA and PLDLA/SGFs pins were inserted into the erector spinae muscles and femurs of beagle dogs and were harvested 6, 12, 16, 26, 52, 78, and 104 weeks after insertion. Bone formation around the pins was evaluated by micro-computed tomography. Mechanical properties were measured by the shear strength test. Thermogravimetric analysis, differential scanning calorimetry, and gel permeation chromatography were used to assess the degradation of these materials. The surface and cross-sectional morphology of both pins were observed using a scanning electron microscope. The experimental data demonstrated that PLDLA/SGFs pins can support new bone formation due to the influence of bioactive glass fibers. PLDLA/SGFs composite pins had higher initial shear strength and were relatively stable for at least 26 weeks. The addition of bioactive glass fibers accelerated the degradation rate of the composite pins. Thus, PLDLA/SGFs composite pins have promising potential for bone fixation applications.

The effect of ethenyltrimethoxysilane modification of nano bioactive glass on the physiochemical and mechanical properties and in vitro bioactivity of poly(lactide-co-glycolide)/poly(trimethylene carbonate) composite

The new biodegradable PLGA/PTMC/YDH-NBG composite with excellent mechanical properties and good in vitro bioactivity.

The role of CaO/SiO2 ratio and P2O5 content in gel-derived bioactive glass-polymer composites in the modulation of their bioactivity and osteoinductivity in human BMSCs

We obtained a range of PLGA-based composites containing sol-gel bioactive glasses (SBG) from the SiO₂-CaO and SiO₂-CaO-P₂O₅ systems. Eight SBGs with different CaO/SiO₂ ratios with and without P₂O₅ were incorporated at 50% w/w to PLGA matrix and structured into thin films suitable for cell culture. The SBG/PLGA composites were examined for their bioactivity in simulated body fluid (SBF), ion release profile in culture media with and without cells, and osteoinductivity in standard human bone marrow stromal cell (hBMSC) cultures without osteogenic growth factors. Our results indicate different surface activity of composites depending on the presence/absence of P₂O₅ in SBG composition. Furthermore, ion release profile to culture medium differed depending on the presence/absence of cells. Direct culture of hBMSC on the SiO₂-CaO/PLGA composite films resulted in elevated Runx-2 mRNA, opposite to low Runx-2 mRNA levels on SiO₂-CaO-P₂O₅/PLGA films. All studied composites increased Osx mRNA levels. Whereas some of SiO₂-CaO/PLGA composites did not elevate BMP-2 and -6 proteins in hBMSC cultures, high levels of these BMPs were present in all cultures on SiO₂-CaO-P₂O₅/PLGA composites. All composites induced BMP-related Tak1 signalling, whereas Smad1 signalling was restricted mostly to composites containing three-component SBGs. ALP activity of hBMSC and BMP-related luciferase activity of mouse BRITE cells differed depending on whether the cells were stimulated with culture medium conditioned with SBG/PLGA composites or the cells were directly cultured on the composite surfaces. Altogether, beyond bioactivity and osteoinductivity of SBG/PLGA composites, our studies show key differences in the biological response to both the bioactive material dissolution products and upon direct cell-material contacts.

Bioglass/PLGA associated to photobiomodulation: effects on the healing process in an experimental model of calvarial bone defect

Bioactive glasses (BG) are known for their ability to bond to bone tissue. However, in critical situations, even the osteogenic properties of BG may be not enough to induce bone consolidation. Thus, the enrichment of BG with polymers such as Poly (D, L-lactic-co-glycolic) acid (PLGA) and associated to photobiomodulation (PBM) may be a promising strategy to promote bone tissue healing. The aim of the present study was to investigate the in vivo performance of PLGA supplemented BG, associated to PBM therapy, using an experimental model of cranial bone defect in rats. Rats were distributed in 4 different groups (Bioglass, Bioglass/PBM, Bioglas/PLGA and BG/PLGA/PBM). After the surgical procedure to induce cranial bone defects, the pre-set samples were implanted and PBM treatment (low-level laser therapy) started (808 nm, 100 mW, 30 J/cm²). After 2 and 6 weeks, animals were euthanized, and the samples were retrieved for the histopathological, histomorphometric, picrosirius red staining and immunohistochemistry analysis. At 2 weeks post-surgery, it was observed granulation tissue and areas of newly formed bone in all experimental groups. At 6 weeks post-surgery, BG/PLGA (with or without PBM) more mature tissue around the biomaterial particles. Furthermore, there was a higher deposition of collagen for BG/PLGA in comparison with BG/PLGA/PBM, at second time-point. Histomorphometric analysis demonstrated higher values of BM.V/TV for BG compared to BG/PLGA (2 weeks post-surgery) and N.Ob/T.Ar for BG/PLGA compared to BG and BG/PBM (6 weeks post-surgery). This current study concluded that the use of BG/PLGA composites, associated or not to PBM, is a promising strategy for bone tissue engineering.

Incorporation of Ca ions into anodic oxide coatings on the Ti-13Nb-13Zr alloy by plasma electrolytic oxidation

The present work concerns the surface modification of The Ti-13Nb-13Zr alloy by electropolishing and plasma electrolytic oxidation (PEO) process in Ca-containing electrolytes: calcium formate and calcium lactate solutions (0.1-1.0 mol dm^-3) under voltages of 200 and 400 V. As a result of the PEO process, a porous oxide layer containing incorporated calcium compounds was formed on the Ti-13Nb-13Zr alloy surface. The morphology and chemical composition of the modified Ti-13Nb-13Zr alloy were investigated using scanning electron microscopy (SEM + EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). An increase in the applied voltage caused an increase in the number of pores and an increase in the amount of calcium incorporated in the oxide layer. Analysis showed that all samples were covered by titanium oxide, which was present in the form of anatase and/or rutile. In course of the experiments, it was showed that the proposed procedure has a positive effect on the overall bioactivity of the Ti-13Nb-13Zr alloy. Bioactivity investigations using simulated body fluid (SBF) confirmed the formation of apatite on the anodized surfaces. The cell adhesion results obtained by the use of human bone marrow mesenchymal stem cells (hBMSC) demonstrated that the PEO coatings on the Ti-13Nb-13Zr alloy remarkably enhanced the cytocompatibility of the substrate, indicating a potential application in orthopedic surgeries. The incorporation of Ca into the oxide layer proceeded to a higher extent when the PEO treatment was performed in the calcium lactate bath. The oxide layers formed in the calcium lactate solution exhibited also superior biological behavior towards hBMSC. This can be ascribed to the presence of carboxylic groups onto coatings' surface (as identified by XPS), which facilitated the anchoring of cells and tissues.

A comprehensive review of biodegradable synthetic polymer-ceramic composites and their manufacture for biomedical applications

The application of various materials in biomedical procedures has recently experienced rapid growth. One area that is currently receiving significant attention from the scientific community is the treatment of a number of different types of bone-related diseases and disorders by using biodegradable polymer-ceramic composites. Biomaterials, the most common materials used to repair or replace damaged parts of the human body, can be categorized into three major groups: metals, ceramics, and polymers. Composites can be manufactured by combining two or more materials to achieve enhanced biocompatibility and biomechanical properties for specific applications. Biomaterials must display suitable properties for their applications, about strength, durability, and biological influence. Metals and their alloys such as titanium, stainless steel, and cobalt-based alloys have been widely investigated for implant-device applications because of their excellent mechanical properties. However, these materials may also manifest biological issues such as toxicity, poor tissue adhesion and stress shielding effect due to their high elastic modulus. To mitigate these issues, hydroxyapatite (HA) coatings have been used on metals because their chemical composition is similar to that of bone and teeth. Recently, a wide range of synthetic polymers such as poly (l-lactic acid) and poly (l-lactide-co-glycolide) have been studied for different biomedical applications, owing to their promising biocompatibility and biodegradability. This article gives an overview of synthetic polymer-ceramic composites with a particular emphasis on calcium phosphate group and their potential applications in tissue engineering. It is hoped that synthetic polymer-ceramic composites such as PLLA/HA and PCL/HA will provide advantages such as eliminating the stress shielding effect and the consequent need for revision surgery.

Formation of calcium phosphate coatings within polycaprolactone scaffolds by simple, alkaline phosphatase based method

The paper presents a novel approach to the production of calcium phosphate coatings of scaffolds. Mineral deposits were formed during incubation of polycaprolactone (PCL) scaffolds with bovine intestinal alkaline phosphatase in sodium glycerophosphate and calcium chloride medium. To modify hydrophobic surface of scaffolds and intensify attachment of coating, scaffolds were incubated at 50 °C (thermal activation, TA) or at 37 °C after short exposition to lipase (lipase activation, LA). Micro-computed tomography observations demonstrated that both methods resulted in deposition of mineral on the surface of external and internal walls of the scaffolds. Precipitate formed after thermal and lipase activation contained particles with average size of 200-400 nm, and the shape of donuts. In thermal activated PCL coatings X-ray diffraction disclosed peaks typical for hydroxyapatite (HAp), while after lipase activation these peaks could be precisely defined only if left for 6 days in the incubation medium. The Fourier-transform infrared spectroscopy suggested crystalline structure of HAp both after thermal and lipase activation. The adherence of bone marrow mesenchymal stem cells was initially higher on coated than pristine PCL, but during 7 days of culture the cell number increased and was similar on all tested samples. Alkaline phosphatase activity, considered as a sign of osteogenic differentiation, measured on PCL samples after 7 days was 2-3 times lower on pristine PCL than on the coated samples, but after 2 weeks increased significantly and reached similar value as on the calcium phosphate substrates.

Nonunion fractures, mesenchymal stem cells and bone tissue engineering

Depending on the duration of healing process, 5-10% of bone fractures may result in either nonunion or delayed union. Because nonunions remain a clinically important problem, there is interest in the utilization of tissue engineering strategies to augment bone fracture repair. Three basic biologic elements that are required for bone regeneration include cells, extracellular matrix scaffolds and biological adjuvants for growth, differentiation and angiogenesis. Mesenchymal stem cells (MSCs) are capable to differentiate into various types of the cells including chondrocytes, myoblasts, osteoblasts, and adipocytes. Due to their potential for multilineage differentiation, MSCs are considered important contributors in bone tissue engineering research. In this review we highlight the progress in the application of biomaterials, stem cells and tissue engineering in promoting nonunion bone fracture healing. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A:2551-2561, 2018.

Biodegradable ceramic-polymer composites for biomedical applications: A review

The present work focuses on the state-of-the-art of biodegradable ceramic-polymer composites with particular emphasis on influence of various types of ceramic fillers on properties of the composites. First, the general needs to create composite materials for medical applications are briefly introduced. Second, various types of polymeric materials used as matrices of ceramic-containing composites and their properties are reviewed. Third, silica nanocomposites and their material as well as biological characteristics are presented. Fourth, different types of glass fillers including silicate, borate and phosphate glasses and their effect on a number of properties of the composites are described. Fifth, wollastonite as a composite modifier and its effect on composite characteristics are discussed. Sixth, composites containing calcium phosphate ceramics, namely hydroxyapatite, tricalcium phosphate and biphasic calcium phosphate are presented. Finally, general possibilities for control of properties of composite materials are highlighted.

A single short session of media perfusion induces osteogenesis in hBMSCs cultured in porous scaffolds, dependent on cell differentiation stage

Perfusing culture media through porous cell-seeded scaffolds is now a common approach within many tissue engineering strategies. Human bone-marrow derived mesenchymal stem cells (hBMSC) are a clinically valuable source of osteoprogenitors that respond to mechanical stimuli. However, the optimal mechanical conditions for their osteogenic stimulation in vitro have not been defined. Whereas the effects of short durations of media fluid flow have been studied in monolayers of osteoblastic cells, in 3D culture continuous or repeated perfusion is usually applied. Here, we investigated whether a short, single perfusion session applied to hBMSCs cultured in 3D would enhance their osteogenesis in vitro. We cultured hBMSCs on gelatine-coated, porous polyurethane scaffolds with osteogenic supplements and stimulated them with a single 2-h session of unidirectional, steady, 2.5 mL/min media perfusion, at either early or late stages of culture in 3D. Some cells were pre-treated in monolayer with osteogenic supplements to advance cell differentiation, followed by 3D culture also with the osteogenic supplements. We report that this single, short session of media perfusion can markedly enhance the expression of bone-related transcription and growth factors, and matrix components, by hBMSCs but that it is more effective when cells reach the pre-osteoblast or osteoblast differentiation stage. These findings could aid in the optimization of 3D culture protocols for efficient bone tissue engineering. Biotechnol. Bioeng. 2016;113: 1814-1824. © 2016 Wiley Periodicals, Inc.

Fabrication and characterization of bioactive glass/alginate composite scaffolds by a self-crosslinking processing for bone regeneration

Bioactive glass/alginate composite scaffolds were fabricated through a self-crosslinking process by bioactive glass microspheres provided Ca²⁺completely.

Improved dimensional stability with bioactive glass fibre skeleton in poly(lactide-co-glycolide) porous scaffolds for tissue engineering

Bone tissue engineering requires highly porous three-dimensional (3D) scaffolds with preferable osteoconductive properties, controlled degradation, and good dimensional stability. In this study, highly porous 3D poly(d,l-lactide-co-glycolide) (PLGA) - bioactive glass (BG) composites (PLGA/BG) were manufactured by combining highly porous 3D fibrous BG mesh skeleton with porous PLGA in a freeze-drying process. The 3D structure of the scaffolds was investigated as well as in vitro hydrolytic degradation for 10weeks. The effect of BG on the dimensional stability, scaffold composition, pore structure, and degradation behaviour of the scaffolds was evaluated. The composites showed superior pore structure as the BG fibres inhibited shrinkage of the scaffolds. The BG was also shown to buffer the acidic degradation products of PLGA. These results demonstrate the potential of these PLGA/BG composites for bone tissue engineering, but the ability of this kind of PLGA/BG composites to promote bone regeneration will be studied in forthcoming in vivo studies.

In situ nanomechanical characterization of the early stages of swelling and degradation of a biodegradable polymer

The interactions of a biodegradable scaffold with cells or living tissues depend on the time-evolution of the nanoscale properties of the scaffold. We present an in situ quantitative study on the early-stage swelling and degradation of poly(lactic-co-glycolic acid) (PLGA). A novel metrology scheme based on force microscopy measurements of the patterns of PLGA nanostructures is developed to characterize the evolution of topography, volume and nanomechanical properties. The volume and nanoscale roughness show an oscillating behaviour during the first eight days of immersion; at a later stage, we observe a continuous decrease of the volume. The effective Young's modulus exhibits a monotonic decrease from an initial value of about 2.4 GPa down to 9 MPa at day 14. The oscillating behaviour of the volume before the onset of full degradation is explained by a coupled diffusion-swelling mechanism. The appearance of a second maximum in the volume evolution results from the competition between swelling and degradation.

Injectable self-gelling composites for bone tissue engineering based on gellan gum hydrogel enriched with different bioglasses

Hydrogels of biocompatible calcium-crosslinkable polysaccharide gellan gum (GG) were enriched with bioglass particles to enhance (i) mineralization with calcium phosphate (CaP); (ii) antibacterial properties and (iii) growth of bone-forming cells for future bone regeneration applications. Three bioglasses were compared, namely one calcium-rich and one calcium-poor preparation both produced by a sol-gel technique (hereafter referred to as A2 and S2, respectively) and one preparation of composition close to that of the commonly used 45S5 type (hereafter referred to as NBG). Incubation in SBF for 7 d, 14 d and 21 d caused apatite formation in bioglass-containing but not in bioglass-free samples, as confirmed by FTIR, XRD, SEM, ICP-OES, and measurements of dry mass, i.e. mass attributable to polymer and mineral and not water. Mechanical testing revealed an increase in compressive modulus in samples containing S2 and NBG but not A2. Antibacterial testing using biofilm-forming meticillin-resistant staphylococcus aureus (MRSA) showed markedly higher antibacterial activity of samples containing A2 and S2 than samples containing NBG and bioglass-free samples. Cell biological characterization using rat mesenchymal stem cells (rMSCs) revealed a stimulatory effect of NBG on rMSC differentiation. The addition of bioglass thus promotes GG mineralizability and, depending on bioglass type, antibacterial properties and rMSC differentiation.

Comparative in vitro study regarding the biocompatibility of titanium-base composites infiltrated with hydroxyapatite or silicatitanate

BACKGROUND

The development of novel biomaterials able to control cell activities and direct their fate is warranted for engineering functional bone tissues. Adding bioactive materials can improve new bone formation and better osseointegration. Three types of titanium (Ti) implants were tested for in vitro biocompatibility in this comparative study: Ti6Al7Nb implants with 25% total porosity used as controls, implants infiltrated using a sol-gel method with hydroxyapatite (Ti HA) and silicatitanate (Ti SiO2). The behavior of human osteoblasts was observed in terms of adhesion, cell growth and differentiation.

RESULTS

The two coating methods have provided different morphological and chemical properties (SEM and EDX analysis). Cell attachment in the first hour was slower on the Ti HA scaffolds when compared to Ti SiO2 and porous uncoated Ti implants. The Alamar blue test and the assessment of total protein content uncovered a peak of metabolic activity at day 8-9 with an advantage for Ti SiO2 implants. Osteoblast differentiation and de novo mineralization, evaluated by osteopontin (OP) expression (ELISA and immnocytochemistry), alkaline phosphatase (ALP) activity, calcium deposition (alizarin red), collagen synthesis (SIRCOL test and immnocytochemical staining) and osteocalcin (OC) expression, highlighted the higher osteoconductive ability of Ti HA implants. Higher soluble collagen levels were found for cells cultured in simple osteogenic differentiation medium on control Ti and Ti SiO2 implants. Osteocalcin (OC), a marker of terminal osteoblastic differentiation, was most strongly expressed in osteoblasts cultivated on Ti SiO2 implants.

CONCLUSIONS

The behavior of osteoblasts depends on the type of implant and culture conditions. Ti SiO2 scaffolds sustain osteoblast adhesion and promote differentiation with increased collagen and non-collagenic proteins (OP and OC) production. Ti HA implants have a lower ability to induce cell adhesion and proliferation but an increased capacity to induce early mineralization. Addition of growth factors BMP-2 and TGFβ1 in differentiation medium did not improve the mineralization process. Both types of infiltrates have their advantages and limitations, which can be exploited depending on local conditions of bone lesions that have to be repaired. These limitations can also be offset through methods of functionalization with biomolecules involved in osteogenesis.

Scaffold design for bone regeneration

The use of bone grafts is the standard to treat skeletal fractures, or to replace and regenerate lost bone, as demonstrated by the large number of bone graft procedures performed worldwide. The most common of these is the autograft, however, its use can lead to complications such as pain, infection, scarring, blood loss, and donor-site morbidity. The alternative is allografts, but they lack the osteoactive capacity of autografts and carry the risk of carrying infectious agents or immune rejection. Other approaches, such as the bone graft substitutes, have focused on improving the efficacy of bone grafts or other scaffolds by incorporating bone progenitor cells and growth factors to stimulate cells. An ideal bone graft or scaffold should be made of biomaterials that imitate the structure and properties of natural bone ECM, include osteoprogenitor cells and provide all the necessary environmental cues found in natural bone. However, creating living tissue constructs that are structurally, functionally and mechanically comparable to the natural bone has been a challenge so far. This focus of this review is on the evolution of these scaffolds as bone graft substitutes in the process of recreating the bone tissue microenvironment, including biochemical and biophysical cues.

Strong and tough mineralized PLGA nanofibers for tendon-to-bone scaffolds

Engineering complex tissues such as the tendon-to-bone insertion sites require a strong and tough biomimetic material system that incorporates both mineralized and unmineralized tissues with different strengths and stiffnesses. However, increasing strength without degrading toughness is a fundamental challenge in materials science. Here, we demonstrate a promising nanofibrous polymer-hydroxyapatite system, in which, a continuous fibrous network must function as a scaffold for both mineralized and unmineralized tissues. It is shown that the high toughness of this material system could be maintained without compromising on the strength with the addition of hydroxyapatite mineral. Individual electrospun poly (lactide-co-glycolide) (PLGA) nanofibers demonstrated outstanding strain-hardening behavior and ductility when stretched uniaxially, even in the presence of surface mineralization. This highly desirable hardening behavior which results in simultaneous nanofiber strengthening and toughening was shown to depend on the initial cross-sectional morphology of the PLGA nanofibers. For pristine PLGA nanofibers, it was shown that ellipsoidal cross-sections provide the largest increase in fiber strength by almost 200% compared to bulk PLGA. This exceptional strength accompanied by 100% elongation was shown to be retained for thin and strongly bonded conformal mineral coatings, which were preserved on the nanofiber surface even for such very large extensions.

Preconditioned 70S30C bioactive glass foams promote osteogenesis in vivo

Bioactive glass scaffolds (70S30C; 70% SiO2 and 30% CaO) produced by a sol-gel foaming process are thought to be suitable matrices for bone tissue regeneration. Previous in vitro data showed bone matrix production and active remodelling in the presence of osteogenic cells. Here we report their ability to act as scaffolds for in vivo bone regeneration in a rat tibial defect model, but only when preconditioned. Pretreatment methods (dry, pre-wetted or preconditioned without blood) for the 70S30C scaffolds were compared against commercial synthetic bone grafts (NovaBone® and Actifuse®). Poor bone ingrowth was found for both dry and wetted sol-gel foams, associated with rapid increase in pH within the scaffolds. Bone ingrowth was quantified through histology and novel micro-CT image analysis. The percentage bone ingrowth into dry, wetted and preconditioned 70S30C scaffolds at 11 weeks were 10±1%, 21±2% and 39±4%, respectively. Only the preconditioned sample showed above 60% material-bone contact, which was similar to that in NovaBone and Actifuse. Unlike the commercial products, preconditioned 70S30C scaffolds degraded and were replaced with new bone. The results suggest that bioactive glass compositions should be redesigned if sol-gel scaffolds are to be used without preconditioning to avoid excess calcium release.

pH-dependent antibacterial effects on oral microorganisms through pure PLGA implants and composites with nanosized bioactive glass

Biomaterials made of biodegradable poly(α-hydroxyesters) such as poly(lactide-co-glycolide) (PLGA) are known to decrease the pH in the vicinity of the implants. Bioactive glass (BG) is being investigated as a counteracting agent buffering the acidic degradation products. However, in dentistry the question arises whether an antibacterial effect is rather obtained from pure PLGA or from BG/PLGA composites, as BG has been proved to be antimicrobial. In the present study the antimicrobial properties of electrospun PLGA and BG45S5/PLGA fibres were investigated using human oral bacteria (specified with mass spectrometry) incubated for up to 24 h. BG45S5 nanoparticles were prepared by flame spray synthesis. The change in colony-forming units (CFU) of the bacteria was correlated with the pH of the medium during incubation. The morphology and structure of the scaffolds as well as the appearance of the bacteria were followed bymicroscopy. Additionally, we studied if the presence of BG45S5 had an influence on the degradation speed of the polymer. Finally, it turned out that the pH increase induced by the presence of BG45S5 in the scaffold did not last long enough to show a reduction in CFU. On the contrary, pure PLGA demonstrated antibacterial properties that should be taken into consideration when designing biomaterials for dental applications.

Accelerated calcium phosphate cement degradation due to incorporation of glucono-delta-lactone microparticles

Injectable calcium phosphate cements (CPC) are frequently used for filling of bone defects due to their excellent osteocompatibility. Their poor degradability, however, limits complete regeneration of bone defects. Organic additives that produce acid by-products are particularly attractive to create macroporosity in situ since CPC degrade by acid dissolution. The aim of the current study was to investigate whether glucono-delta-lactone (GDL) can be used as acid-producing microparticles for incorporation into CPC without compromising its osteocompatibility. Characterization studies confirmed that CPCs containing either low or high amounts of GDL were injectable and self-setting, while a considerable amount of porosity was formed already within 1 day of incubation in phosphate buffered saline due to dissolution of GDL. Histomorphometrical evaluation after 2 weeks of implantation revealed that CPC containing 10% of GDL degraded faster and was replaced by more bone tissue than CPCs containing either Poly (lactic-co-glycolic acid) (PLGA) or gelatin microspheres. Summarizing, the current study showed that CPCs containing appropriate amounts of GDL display accelerated degradation and new bone formation compared with CPCs containing microparticles made of conventional polymers such as PLGA or gelatin.

Physicochemical properties and applications of poly(lactic-co-glycolic acid) for use in bone regeneration

Poly(lactic-co-glycolic acid) (PLGA) is the most often used synthetic polymer within the field of bone regeneration owing to its biocompatibility and biodegradability. As a consequence, a large number of medical devices comprising PLGA have been approved for clinical use in humans by the American Food and Drug Administration. As compared with the homopolymers of lactic acid poly(lactic acid) and poly(glycolic acid), the co-polymer PLGA is much more versatile with regard to the control over degradation rate. As a material for bone regeneration, the use of PLGA has been extensively studied for application and is included as either scaffolds, coatings, fibers, or micro- and nanospheres to meet various clinical requirements.