Gelatin and Bioactive Glass Composites for Tissue Engineering: A Review

Nano-/micron-sized bioactive glass (BG) particles are attractive candidates for both soft and hard tissue engineering. They can chemically bond to the host tissues, enhance new tissue formation, activate cell proliferation, stimulate the genetic expression of proteins, and trigger unique anti-bacterial, anti-inflammatory, and anti-cancer functionalities. Recently, composites based on biopolymers and BG particles have been developed with various state-of-the-art techniques for tissue engineering. Gelatin, a semi-synthetic biopolymer, has attracted the attention of researchers because it is derived from the most abundant protein in the body, viz., collagen. It is a polymer that can be dissolved in water and processed to acquire different configurations, such as hydrogels, fibers, films, and scaffolds. Searching "bioactive glass gelatin" in the tile on Scopus renders 80 highly relevant articles published in the last ~10 years, which signifies the importance of such composites. First, this review addresses the basic concepts of soft and hard tissue engineering, including the healing mechanisms and limitations ahead. Then, current knowledge on gelatin/BG composites including composition, processing and properties is summarized and discussed both for soft and hard tissue applications. This review explores physical, chemical and mechanical features and ion-release effects of such composites concerning osteogenic and angiogenic responses in vivo and in vitro. Additionally, recent developments of BG/gelatin composites using 3D/4D printing for tissue engineering are presented. Finally, the perspectives and current challenges in developing desirable composites for the regeneration of different tissues are outlined.

PLGA Membranes Functionalized with Gelatin through Biomimetic Mussel-Inspired Strategy

Electrospun membranes have been widely used as scaffolds for soft tissue engineering due to their extracellular matrix-like structure. A mussel-inspired coating approach based on 3,4-dihydroxy-DL-phenylalanine (DOPA) polymerization was proposed to graft gelatin (G) onto poly(lactic-co-glycolic) acid (PLGA) electrospun membranes. PolyDOPA coating allowed grafting of gelatin to PLGA fibers without affecting their bulk characteristics, such as molecular weight and thermal properties. PLGA electrospun membranes were dipped in a DOPA solution (2 mg/mL, Tris/HCl 10 mM, pH 8.5) for 7 h and then incubated in G solution (2 mg/mL, Tris/HCl 10 mM, pH 8.5) for 16 h. PLGA fibers had an average diameter of 1.37 ± 0.23 µm. Quartz crystal microbalance with dissipation technique (QCM-D) analysis was performed to monitor DOPA polymerization over time: after 7 h the amount of deposited polyDOPA was 71 ng/cm2. After polyDOPA surface functionalization, which was, also revealed by Raman spectroscopy, PLGA membranes maintained their fibrous morphology, however the fiber size and junction number increased. Successful functionalization with G was demonstrated by FTIR-ATR spectra, which showed the presence of G adsorption bands at 1653 cm-1 (Amide I) and 1544 cm-1 (Amide II) after G grafting, and by the Kaiser Test, which revealed a higher amount of amino groups for G functionalized membranes. Finally, the biocompatibility of the developed substrates and their ability to induce cell growth was assessed using Neonatal Normal Human Dermal Fibroblasts.

Importance of crosslinking strategies in designing smart biomaterials for bone tissue engineering: A systematic review

Biomaterials are of significant importance in biomedical applications as these biological macromolecules have moderately replaced classical tissue grafting techniques owing to its beneficial properties. Despite of its favourable advantages, poor mechanical and degradative properties of biomaterials are of great concern. To this regard, crosslinkers have emerged as a smart and promising tool to augment the biological functionality of biopolymers. Different crosslinkers have been extensively used in past decades to develop bone substitutes, but the implications of toxic response and adverse reactions are truly precarious after implantation. Traditional crosslinker like glutaraldehyde has been widely used in numerous bio-implants but the potential toxicity is largely being debated with many disproving views. As alternative, green chemicals, enzymatic and non-enzymatic chemicals, bi-functional epoxies, zero-length crosslinkers and physical crosslinkers have been introduced to achieve the desired properties of a bone substitute. In this review, systematic literature search was performed on PubMed database to identify the most commonly used crosslinkers for developing promising bone like materials. The relevant articles were identified, analysed and reviewed in this paper giving due importance to different crosslinking methodologies and comparing their effectiveness and efficacy in regard to material composition, scaffold production, crosslinker dosage, toxicity and immunogenicity. This review summarizes the recent developments in crosslinking mechanism with an emphasis placed on their ability to link proteins through bonding reactions. Finally, this study also covers the convergent and divergent methodologies of crosslinking strategies also giving special importance in retrieving the current limitations and future opportunities of crosslinking modalities in bone tissue engineering.

Combining Calcium Phosphates with Polysaccharides: A Bone-Inspired Material Modulating Monocyte/Macrophage Early Inflammatory Response

The use of inorganic calcium/phosphate supplemented with biopolymers has drawn lots of attention in bone regenerative medicine. While inflammation is required for bone healing, its exacerbation alters tissue regeneration/implants integration. Inspired by bone composition, a friendly automated spray-assisted system was used to build bioactive and osteoinductive calcium phosphate/chitosan/hyaluronic acid substrate (CaP-CHI-HA). Exposing monocytes to CaP-CHI-HA resulted in a secretion of pro-healing VEGF and TGF-β growth factors, TNF-α, MCP-1, IL-6 and IL-8 pro-inflammatory mediators but also IL-10 anti-inflammatory cytokine along with an inflammatory index below 1.5 (versus 2.5 and 7.5 following CaP and LPS stimulation, respectively). Although CD44 hyaluronic acid receptor seems not to be involved in the inflammatory regulation, results suggest a potential role of chemical composition and calcium release from build-up substrates, in affecting the intracellular expression of a calcium-sensing receptor. Herein, our findings indicate a great potential of CaP-CHI-HA in providing required inflammation-healing balance, favorable for bone healing/regeneration.

Incorporation of Cu-Containing Bioactive Glass Nanoparticles in Gelatin-Coated Scaffolds Enhances Bioactivity and Osteogenic Activity

Bioactive glass scaffolds (BGS) of 45S5 composition exhibit desired bioactivity, osteogenesis, and angiogenesis potential, being promising biomaterials for bone repair/regeneration. Natural polymer-based coatings, e.g., gelatin coating, are effective to enhance the mechanical properties of BGS. However, the presence of a coating may reduce the bioactivity and osteogenesis activity of the scaffolds. To address the issue of reduced osteogenic properties induced by polymer coatings, in this study, we incorporated Cu-containing bioactive glass nanoparticles (Cu-BGN: 95SiO₂-2.5CaO-2.5CuO, in mol %), as bioactive fillers, into the gelatin coating. The bioactivity (apatite-forming ability) of the gelatin coated BGS was improved after the incorporation of Cu-BGN in the coating. Hydroxyapatite could form on the Cu-BGN/gelatin nanocomposite coated BGS within 1 day of immersion in simulated body fluid. The osteogenic activity as indicated by the ALP activity of MC3T3-E1 cells on the coated BGS was also significantly enhanced after the incorporation of Cu-BGN. In addition, the incorporation of Cu-BGN in the coating did not affect the highly porous and interconnected pore structure of BGS while the mechanical improvement induced by the gelatin coating remained after the addition of Cu-BGN. The attachment of MC3T3-E1 cells on the scaffolds was not influenced by the presence of Cu-BGN in the gelatin coating, while the cell proliferation was enhanced. In conclusion, the incorporation of bioactive nanoparticles into polymer coating is presented as a solution to the reduced bioactivity and osteogenic activity of polymer coated 45S5 BGS. The Cu-BGN/gelatin nanocomposite coated BGS exhibiting high bioactivity, appropriate mechanical properties, and osteogenic potential are candidate biomaterials for bone tissue engineering/regeneration.

Alginate-based hydrogels functionalised at the nanoscale using layer-by-layer assembly for potential cartilage repair

Injuries to articular cartilage are frequently difficult to repair, in part because of the poor regenerative capacity of this tissue. To date, no successful system for complete regeneration of the most challenging cartilage defects has been demonstrated. The aim of this work was to develop functionalised hydrogels at the nanoscale by Layer-by-Layer (LbL) assembly to promote cartilage healing. Hydrogels, based on sodium alginate (NaAlg) and gelatin (G), were prepared by an external gelation method consisting of CaCl₂ diffusion and genipin addition for G crosslinking. Successively, hydrogels were coated with G to obtain a positive charge on the surface, then functionalised by LbL assembly to create 16 nanolayers, based on poly(styrene sulfonate)/poly(allyl amine) (PSS/PAH), including a specific peptide sequence (CTATVHL) and transforming growth factors β1 (TGF-β1). Physico-chemical properties were evaluated by XPS, ATR-FTIR and rheological analyses while in vitro cytocompatibility was studied using bovine articular chondrocytes (BAC). XPS spectra showed N_1s and S_2p peaks, indicating that PAH and PSS have been introduced with success. ATR-FTIR indicated the specific PAH and PSS absorption peaks. Finally, the biomolecule incorporation influenced positively the processes of BAC adhesion and proliferation, and glycosamynoglycan secretion. The functionalised alginate-based hydrogels described here are ideally suited to chondral regeneration in terms of their integrity, stability, and cytocompatibility.

* Engineering Membranes for Bone Regeneration

This review is focused on the use of membranes for the specific application of bone regeneration. The first section focuses on the relevance of membranes in this context and what are the specifications that they should possess to improve the regeneration of bone. Afterward, several techniques to engineer bone membranes by using "bulk"-like methods are discussed, where different parameters to induce bone formation are disclosed in a way to have desirable structural and functional properties. Subsequently, the production of nanostructured membranes using a bottom-up approach is discussed by highlighting the main advances in the field of bone regeneration. Primordial importance is given to the promotion of osteoconductive and osteoinductive capability during the membrane design. Whenever possible, the films prepared using different techniques are compared in terms of handability, bone guiding ability, osteoinductivity, adequate mechanical properties, or biodegradability. A last chapter contemplates membranes only composed by cells, disclosing their potential to regenerate bone.

Composite scaffolds loaded with bone mesenchymal stem cells promote the repair of radial bone defects in rabbit model

This study aimed to investigate the efficacy of three-dimensional scaffolds of silk fibroin/chitosan/nano-hydroxyapatite (SF/CS/nHA) and bone marrow derived mesenchymal stem cells (BMSCs) on the repair of long segmental bone defects in rabbits. BMSCs were cultured with SF/CS/nHA in vitro, and cell proliferation, alkaline phosphatase activity and Ca2+ content were examined. A 15mm segmental defect in the radius was generated in 12 New Zealand White rabbits, which were divided randomly into three groups (n=4): experimental group with SF/CS/nHA scaffold of induced BMSCs; control group with SF/CS/nHA scaffold; and blank group without any materials. Postoperatively at 12 weeks, osteogenesis effect and the degradation and absorption of SF/CS/nHA were evaluated by X-ray, hematoxylin eosin staining, and scanning electron microscopy. In vitro, SF/CS/nHA scaffolds exhibited good biocompatibility and no toxicity. SF/CS/nHA promoted adhesion, growth, and calcium nodule formation of BMSCs compared to control (P<0.05). In vivo, we observed gradual new bone formation and bone defect gradually recovered at 12 weeks in experimental and control group, but more new bone was formed in experimental group (P<0.05). In blank group, limited bone formation was observed and bone defect was obvious. In conclusion, SF/CS/nHA scaffolds loaded with BMSCs achieve high efficacy to repair segmental defect in the radius.

Release characteristics of bone‑like hydroxyapatite/poly amino acid loaded with rifapentine microspheres in vivo

Bone-like hydroxyapatite/poly amino acid (BHA/PAA) is a potential bone repair material. Rifapentine-loaded poly(lactic‑co‑glycolic acid) microspheres (RPMs) are bioactive and efficient controlled‑release delivery systems used in vitro. The aim of the present study was to investigate the in vivo drug release characteristics of RPM‑loaded BHA/PAA on a rabbit model of bone defect. RPM was combined with BHA/PAA to obtain the drug‑loaded, slow‑releasing bioactive material. Bone defects were generated in New Zealand white rabbits and the rabbits were then implanted with RPM‑loaded BHA/PAA. High‑performance liquid chromatography (HPLC) was used to determine the concentrations of rifapentine in the plasma and the local muscle tissues of the treated rabbits. Hematoxylin and eosin (H&E) staining and biochemical analyses were performed to elucidate potential side effects of RPM‑loaded BHA/PAA on the heart, liver and kidney histopathology and functions of the treated rabbits. The biocompatibility and osteogenic ability of RPM‑loaded BHA/PAA was evaluated by H&E staining. The results demonstrated that the material was completely degraded and absorbed at 12 weeks following implantation and new trabecular bone and cartilage tissues had formed. The in vivo release tests revealed that RPM‑loaded BHA/PAA exhibited sustained release profiles of rifapentine and the drug concentration in the muscle tissues remained higher than the minimum inhibitory concentration of rifapentine against Mycobacterium tuberculosis for as long as 12 weeks. In addition, RPM‑loaded BHA/PAA had no long‑term side effects to the heart, liver and kidney of the treated rabbits. In conclusion, the present study demonstrated that RPM‑loaded BHA/PAA slowly and continuously released rifapentine in vivo and exhibited no side effects on heart, liver and kidney tissues and function. Furthermore, RPM‑loaded BHA/PAA promoted new bone formation, while it was gradually degraded and absorbed. The present study provided a theoretical basis for the potential advancement in developing novel treatments for osteoarticular tuberculosis.

Cell viability and hemocompatibility evaluation of a starch-based hydrogel loaded with hydroxyapatite or calcium carbonate for maxillofacial bone regeneration

The objective of this study is to evaluate the cell viability and hemocompatibility of starch-based hydrogels for maxillofacial bone regeneration. Seven starch-based hydrogels were prepared: three loaded with 0.5, 1 and 2% calcium carbonate (Sigma Aldrich, St. Louis, MO, USA); three loaded with 2, 3 and 4% hydroxyapatite (Sigma Aldrich); and one not loaded as a control. A 10 M NaOH was then added to induce hydrogel formation. Human osteoblasts were cultured on each hydrogel for 72 h. An MTS assay (Cell Titer96; PROMEGA, Madison, WI, USA) was used to assess cell viability. Hemocompatibility testing was conducted with normal human blood in the following conditions: 100 mg of each hydrogel in contact with 900 µL of whole blood for 15 min at 37 °C under lateral stirring. Higher percentages of cell viability were observed in starch-based hydrogels loaded with hydroxyapatite as compared with the control. The hemolysis test showed a hemolysis level lower than 2%. Activated partial thromboplastin time and prothrombin time were unchanged, while platelet counting showed a slight decrease when compared with controls.

Effect of bone-like hydroxyapatite/poly amino acid loaded with rifapentine microspheres on bone and joint tuberculosis in vitro

Rifapentine-loaded poly(lactic-co-glycolic acid) microspheres (RPMs)-loaded bone-like hydroxyapatite/poly amino acid (BHA/PAA) is effective in curing Staphylococcus aureus-induced chronic osteomyelitis. This study continues to investigate the effect of RPM-loaded BHA/PAA on the bacterial growth of Mycobacterium tuberculosis (MTB), cell proliferation and differentiation in MTB H37Rv-infected MG63 cells. Furthermore, whether Wnt/β-catenin signaling pathway was activated by RPM-loaded BHA/PAA was explored. We found the bactec growth index of H37Rv was significantly inhibited by RPM-loaded BHA/PAA. The MTT assay showed that RPM-loaded BHA/PAA could promote the cell proliferation of H37Rv-infected MG63 cells, as determined by MTT assay. The alkaline phosphatase (ALP) activity and the expression of runt-related transcription factor 2 (Runx2) and osteocalcin (OCN) was examined by commercial kit and Western blot analysis to determine the effect of RPM-loaded BHA/PAA on MTB H37Rv-infected MG63 cell differentiation. It was revealed that RPM-loaded BHA/PAA could promote cell differentiation of H37Rv-infected MG63 cells. Furthermore, we found the expression of Wnt1, LDL receptor related protein 6 (Lrp6) and β-catenin was significantly increased in H37Rv-infected MG63 cells following treatment with RPM-loaded BHA/PAA, as determined by Western blot analysis. In conclusion, this study demonstrated that RPM-loaded BHA/PAA has an effective activity against MTB. RPM-loaded BHA/PAA promoted cell proliferation and cell differentiation of H37Rv-infected MG63 cells. Wnt/β-catenin signaling could be activated by RPM-loaded BHA/PAA in MG63 cells infected with H37Rv. This study demonstrated the potential value of RPM-loaded BHA/PAA in treating bone and joint TB, and suggested Wnt/β-catenin signaling may be an important pathway underlying its function.

Study of bone-like hydroxyapatite/polyamino acid composite materials for their biological properties and effects on the reconstruction of long bone defects

Purpose

The purpose of this study was to investigate the effect of bone-like hydroxyapatite/polyamino acid (BHA/PAA) in the osteogenesis and reconstruction of long segmental bone defects.

Methods

In vitro, MG63 cells were cultured with BHA/PAA. The osteoinductive activity of the BHA/PAA material was evaluated using inverted microscopy, scanning electron microscopy, MTT proliferation assay, and the determination of alkaline phosphatase activity and Ca²⁺ content. In vivo, the radial bone defect was made in 20 New Zealand White rabbits, and then these animal were randomly divided into two groups (n=10), the experimental group (with BHA/PAA) and the control group (without BHA/PAA). Postoperatively, the osteogenesis effect of BHA/PAA was evaluated through X-ray, hematoxylin–eosin staining, observation of the gross bone specimen, immunohistochemistry, and fluorescent confocal scanning microscopy.

Results

In vitro, BHA/PAA promoted the adhesion, growth, and calcium nodule formation of MG63 cells, and it had good osteogenesis activity. In vivo, with BHA/PAA material degradation and absorption, the new bone gradually formed, and the bone defect gradually recovered in the experimental group. In the control group, a limited bone formation was found at the bone broken ends, and the bone defect was obviously visible.

Conclusion

In vitro and in vivo, we confirmed that BHA/PAA was effective in inducing osteogenesis and reconstructing a long segmental bone defect.

Localised controlled release of simvastatin from porous chitosan-gelatin scaffolds engrafted with simvastatin loaded PLGA-microparticles for bone tissue engineering application

Localised controlled release of simvastatin from porous freeze-dried chitosan-gelatin (CH-G) scaffolds was investigated by incorporating simvastatin loaded poly-(dl-lactide-co-glycolide) acid (PLGA) microparticles (MSIMs) into the scaffolds. MSIMs at 10% w/w simvastatin loading were prepared using a single emulsion-solvent evaporation method. The MSIM optimal amount to be incorporated into the scaffolds was selected by analysing the effect of embedding increasing amounts of blank PLGA microparticles (BL-MPs) on the scaffold physical properties and on the in vitro cell viability using a clonal human osteoblastic cell line (hFOB). Increasing the BL-MP content from 0% to 33.3% w/w showed a significant decrease in swelling degree (from 1245±56% to 570±35%). Scaffold pore size and distribution changed significantly as a function of BL-MP loading. Compressive modulus of scaffolds increased with increasing BL-MP amount up to 16.6% w/w (23.0±1.0kPa). No significant difference in cell viability was observed with increasing BL-MP loading. Based on these results, a content of 16.6% w/w MSIM particles was incorporated successfully in CH-G scaffolds, showing a controlled localised release of simvastatin able to influence the hFOB cell proliferation and the osteoblastic differentiation after 11 days.

Treatment of Staphylococcus aureus-induced chronic osteomyelitis with bone-like hydroxyapatite/poly amino acid loaded with rifapentine microspheres

Purpose

The purpose of this study was to investigate the curative effect of bone-like hydroxyapatite/poly amino acid (BHA/PAA) as a carrier for poly(lactic-co-glycolic acid)-coated rifapentine microsphere (RPM) in the treatment of rabbit chronic osteomyelitis induced by Staphylococcus aureus.

Methods

RPM was prepared through an oil-in-water emulsion solvent evaporation method, and RPM was combined with BHA/PAA to obtain drug-loaded, slow-releasing materials. Twenty-six New Zealand white rabbits were induced to establish the animal model of chronic osteomyelitis. After debridement, the animals were randomly divided into three groups (n=8): the experimental group (with RPM-loaded BHA/PAA), the control group (with BHA/PAA), and the blank group. The RPM-loaded BHA/PAA was evaluated for antibacterial activity, dynamics of drug release, and osteogenic ability through in vitro and in vivo experiments.

Results

In vitro, RPM-loaded BHA/PAA released the antibiotics slowly, inhibiting the bacterial growth of S. aureus for up to 5 weeks. In vivo, at week 4, the bacterial colony count was significantly lower in the experimental group than in the control and blank groups (P<0.01). At week 12, the chronic osteomyelitis was cured and the bone defect was repaired in the experimental group, whereas the infection and bone defect persisted in the control and blank groups.

Conclusion

In vitro and in vivo experiments demonstrated that RPM-loaded BHA/PAA effectively cured S. aureus-induced chronic osteomyelitis. Therefore, BHA/PAA has potential value as a slow-releasing material in clinical setting. Further investigation is needed to determine the optimal dosage for loading rifapentine.

Review and the state of the art: Sol-gel and melt quenched bioactive glasses for tissue engineering

Biomaterial development is currently the most active research area in the field of biomedical engineering. The bioglasses possess immense potential for being the ideal biomaterials due to their high adaptiveness to the biological environment as well as tunable properties. Bioglasses like 45S5 has shown great clinical success over the past 10 years. The bioglasses like 45S5 were prepared using melt-quenching techniques but recently porous bioactive glasses have been derived through sol-gel process. The synthesis route exhibits marked effect on the specific surface area, as well as degradability of the material. This article is an attempt to provide state of the art of the sol-gel and melt quenched bioactive bioglasses for tissue regeneration. Fabrication routes for bioglasses suitable for bone tissue engineering are highlighted and the effect of these fabrication techniques on the porosity, pore-volume, mechanical properties, cytocompatibilty and especially apatite layer formation on the surface of bioglasses is analyzed in detail. Drug delivery capability of bioglasses is addressed shortly along with the bioactivity of mesoporous glasses. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1248-1275, 2016.

Composite scaffolds for controlled drug release: role of the polyurethane nanoparticles on the physical properties and cell behaviour

Localised delivery of appropriate biomolecule/drug(s) can be suitable to prevent postoperative infections and inflammation after scaffold implantation in vivo. In this study composite shell scaffolds, based on an internally produced bioactive glass and a commercial hydroxyapatite, were surface coated with a uniform polymeric layer, embedded with thermo-stable polyesterurethane (PU)-based nanoparticles (NPs), containing an anti-inflammatory drug (indomethacin; IDCM). The obtained functionalised scaffolds were subjected to physico-mechanical and biological characterisations. The results indicated that NPs incorporation into the gelatin coating of the composite scaffolds: 1) not changed significantly the micro-architecture of the scaffolds in terms of mean pore diameter and pore size distribution; 2) increased the compressive modulus; and 3) allowed to a sustained IDMC release (65-70% of the loaded-drug) within the first week of incubation in physiological solution. On the other hand, the NPs incorporation did not affect the biocompatibility of composite scaffolds, as evidenced by viability and alkaline phosphatase (ALP) activity of MG63 human osteoblast-like cells.

Biomimetic materials for medical application through enzymatic modification

Living organisms synthesize functional materials, based on proteins and polysaccharides, using enzyme-catalyzed reactions. According to the biomimetic approach, biomaterial matrices for tissue engineering are designed to be able to mimic the properties and the functions of the extracellular matrix (ECM). In this chapter, the most significant research efforts dedicated to the study and the preparation of biomimetic materials through enzymatic modifications were reviewed. The functionalizations of different polymeric matrices obtained through the catalytic activity of two enzymes (Transglutaminase, TGase and Tyrosinase, TYRase) were discussed. Specifically, the biomimetic applications of TGase and TYRase to confer appropriate biomimetic properties to the biomaterials, such as the possibility to obtain in situ gelling hydrogels and the incorporation of bioactive molecules (growth factors) and cell-binding peptides into the scaffolds, were reviewed.

Current progress in bioactive ceramic scaffolds for bone repair and regeneration

Bioactive ceramics have received great attention in the past decades owing to their success in stimulating cell proliferation, differentiation and bone tissue regeneration. They can react and form chemical bonds with cells and tissues in human body. This paper provides a comprehensive review of the application of bioactive ceramics for bone repair and regeneration. The review systematically summarizes the types and characters of bioactive ceramics, the fabrication methods for nanostructure and hierarchically porous structure, typical toughness methods for ceramic scaffold and corresponding mechanisms such as fiber toughness, whisker toughness and particle toughness. Moreover, greater insights into the mechanisms of interaction between ceramics and cells are provided, as well as the development of ceramic-based composite materials. The development and challenges of bioactive ceramics are also discussed from the perspective of bone repair and regeneration.

[Membranes in pre-implantation surgery]

The use of membranes in pre-implantation surgery is part of the guided bone regeneration (GBR) concept, one of the usual bone augmentation techniques. Membranes for GBR procedures have two main uses: a mechanical function to maintain bone regeneration space and a physical function as cellular barrier. The goal is to promote colonization of the regeneration space located under the membrane, by osteogenic cells from the residual bone walls. GBR was the subject of numerous publications and protocols since its first use in the 1980s. These protocols are mainly supported by team experience and the level of evidence is poor. Few indications are truly validated. The goal of our study was to review the recent literature on membrane use for pre-implantations surgery, and, in the absence of any consensus, to provide some arguments for their rational use.

Enhanced osteoinductivity and osteoconductivity through hydroxyapatite coating of silk-based tissue-engineered ligament scaffold

Hybrid silk scaffolds combining knitted silk fibers and silk sponge have been recently developed for use as ligament-alone grafts. Incorporating an osteoinductive phase into the ends of a ligament scaffold may potentially generate an integrated "bone-ligament-bone" graft and improve graft osteointegration with host bone. To explore the possible application of hydroxyapatite (HA) coating in the fabrication of osteoinductive ends of silk-based scaffold, HA was coated on the hybrid silk scaffold and the effects to the bone-related cells were evaluated. HA could be coated in a uniform and controlled manner on the silk sponge, using an alternate soaking technology, with the amount deposited being dependent on the number of soaking cycles. HA coating also progressively reduced the hydrophobicity of silk surface (decreasing water contact angle from 87° to 42-76°, after 1-3 soaking cycles), making the HA-coated silk scaffold less favorable for initial cell attachments; but the attached cells showed viability and sustained proliferation on the HA-coated scaffold. As demonstrated by real-time polymerase chain reaction and alkaline phosphatase assay, the osteoinductivity of HA-coated silk scaffolds resulted in the osteogenic differentiation of bone marrow mesenchymal stem cells, and the osteoconductivity of HA-coated silk scaffolds supported osteoblasts growth and maintained the properties of mature osteoblasts. These properties of HA-coating demonstrated its possible application in fabricating osteoinductive ends of the silk-based ligament graft to potentially enhance graft-to-host bone integration.

Bioactive glass/polymer composite scaffolds mimicking bone tissue

The aim of this work was the preparation and characterization of scaffolds with mechanical and functional properties able to regenerate bone. Porous scaffolds made of chitosan/gelatin (POL) blends containing different amounts of a bioactive glass (CEL2), as inorganic material stimulating biomineralization, were fabricated by freeze-drying. Foams with different compositions (CEL2/POL 0/100; 40/60; 70/30 wt %/wt) were prepared. Samples were crosslinked using genipin (GP) to improve mechanical strength and thermal stability. The scaffolds were characterized in terms of their stability in water, chemical structure, morphology, bioactivity, and mechanical behavior. Moreover, MG63 osteoblast-like cells and periosteal-derived stem cells were used to assess their biocompatibility. CEL2/POL samples showed interconnected pores having an average diameter ranging from 179 ± 5 μm for CEL2/POL 0/100 to 136 ± 5 μm for CEL2/POL 70/30. GP-crosslinking and the increase of CEL2 amount stabilized the composites to water solution (shown by swelling tests). In addition, the SBF soaking experiment showed a good bioactivity of the scaffold with 30 and 70 wt % CEL2. The compressive modulus increased by increasing CEL2 amount up to 2.1 ± 0.1 MPa for CEL2/POL 70/30. Dynamical mechanical analysis has evidenced that composite scaffolds at low frequencies showed an increase of storage and loss modulus with increasing frequency; furthermore, a drop of E' and E″ at 1 Hz was observed, and for higher frequencies both moduli increased again. Cells displayed a good ability to interact with the different tested scaffolds which did not modify cell metabolic activity at the analyzed points. MTT test proved only a slight difference between the two cytotypes analyzed.

Stem cell-biomaterial interactions for regenerative medicine

The synergism of stem cell biology and biomaterial technology promises to have a profound impact on stem-cell-based clinical applications for tissue regeneration. Biomaterials development is rapidly advancing to display properties that, in a precise and physiological fashion, could drive stem-cell fate both in vitro and in vivo. Thus, the design of novel materials is trying to recapitulate the molecular events involved in the production, clearance and interaction of molecules within tissue in pathologic conditions and regeneration of tissue/organs. In this review we will report on the challenges behind translating stem cell biology and biomaterial innovations into novel clinical therapeutic applications for tissue and organ replacements (graphical abstract).