Evaluation of MC3T3 Cells Proliferation and Drug Release Study from Sodium Hyaluronate-1,4-butanediol Diglycidyl Ether Patterned Gel

Are We Overlooking Harms of BDDE-Cross-Linked Dermal Fillers? A Scoping Review

1,4-Butanediol ether (BDDE) is widely used as a cross-linker for hyaluronic acid in dermal fillers. The purpose of this scoping review was to determine the state of knowledge about the behaviour of cross-linked substances and safety of BDDE application. The rationale behind the review came from the clinical experience of one of the authors (KS), who noticed adverse reactions after BDDE-linked hyaluronan application. The scoping review was conducted according to PRISMA-ScR guidelines. Out of 399 articles, 52 met the inclusion criteria. Data on study design, sample/population, aims, methodology, outcomes and funding were extracted. Results were charted according to 6 subtopics: rheological properties, hydrogel stability, BDDE toxicity, immunogenicity, tissue interactions and clinical studies. In vitro, cross-linked hydrogels were characterized as effective fillers in terms of viscosity and elasticity; however, previously uncharacterized by-products of the cross-linking reaction were found. Most in vivo studies reported increased dermis regeneration, vascularization and anti-inflammatory cytokine release after implantation of BDDE-cross-linked substances. In clinical studies, BDDE was shown to sensitize subjects to 1,6-hexanediol ether and other substances found in epoxy resin systems. Occupational dermatitis and hypersensitivity reactions were documented. Our review shows that BDDE may have long-term adverse effects, which are overlooked in the safety assessment of fillers. Reviews on BDDE conducted so far have mostly been sponsored by the industry, potentially leading to incomplete reporting of adverse effects. A review of the occurrence of allergic reactions after commercial dermal filler use and analysis of possibly harmful by-products of BDDE hyaluronan degradation are needed.Level of Evidence III This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Tailorable mechanical and degradation properties of KCl-reticulated and BDDE-crosslinked PCL/chitosan/κ-carrageenan electrospun fibers for biomedical applications: Effect of the crosslinking-reticulation synergy

The development of intricated and interconnected porous mats is desired for many applications in biomedicine and other relevant fields. The mats that comprise the use of natural, bioactive, and biodegradable polymers are the focus of current research activities. In the present work, crosslinked fibers with improved characteristics were produced by incorporating 1,4-butanediol diglycidyl ether (BDDE) into a polymer formulation containing polycaprolactone (PCL), chitosan (CS), and κappa-carrageenan (κ-C). A slight variation of formic acid (FA)/acetic acid (AA) ratio used as a solvent system, significantly affected the characteristics of the produced fiber mats. Both polysaccharides and BDDE played a major role in tailoring mechanical properties when fibrous scaffolds were reticulated under KCl-mediated basic conditions for determined periods of time at 50 °C. In vitro biological assessment of the electrospun fiber mats revealed proliferation of MC3T3-E1 cells when incubated for 1 and 7 days. After staining the cells with 4',6-diamidino-2-phenylindole (DAPI)/rhodamine phalloidin an autofluorescence response was observed by fluorescence microscopy in the scaffold manufactured using a solvent with higher FA/AA ratio due to the formation of microfibers. The results demonstrated the potential of the BDDE-crosslinked PCL/CS/κ-C electrospun fibers as promising materials for biomedical applications that may include soft and bone tissue regeneration.

Microfluidic fabrication of X-ray-visible sodium hyaluronate microspheres for embolization

Catheter embolization is a minimally invasive technique that relies on embolic agents and is now widely used to treat various high-prevalence medical diseases. Embolic agents usually need to be combined with exogenous contrasts to visualize the embolotherapy process. However, the exogenous contrasts are quite simply washed away by blood flow, making it impossible to monitor the embolized location. To solve this problem, a series of sodium hyaluronate (SH) loaded with bismuth sulfide (Bi₂S₃) nanorods (NRs) microspheres (Bi₂S₃@SH) were prepared in this study by using 1,4-butaneglycol diglycidyl ether (BDDE) as a crosslinker through single-step microfluidics. Bi₂S₃@SH-1 microspheres showed the best performance among other prepared microspheres. The fabricated microspheres had uniform size and good dispersibility. Furthermore, the introduction of Bi₂S₃ NRs synthesized by a hydrothermal method as Computed Tomography (CT) contrast agents improved the mechanical properties of Bi₂S₃@SH-1 microspheres and endowed the microspheres with excellent X-ray impermeability. The blood compatibility and cytotoxicity test showed that the Bi₂S₃@SH-1 microspheres had good biocompatibility. In particular, the in vitro simulated embolization experiment results indicate that the Bi₂S₃@SH-1 microspheres had excellent embolization effect, especially for the small-sized blood vessels of 500-300 and 300 μm. The results showed the prepared Bi₂S₃@SH-1 microspheres have good biocompatibility and mechanical properties, as well as certain X-ray visibility and excellent embolization effects. We believe that the design and combination of this material has good guiding significance in the field of embolotherapy.

Control of maleic acid-propylene diepoxide hydrogel for 3D printing application for flexible tissue engineering scaffold with high resolution by end capping and graft polymerization

BACKGROUND

Control of 3D printing of highly tough hydrogel inks with adequate printability, scaffold fidelity and mechanical properties are highly desirable for biomedical and tissue engineering applications. However, developing a biocompatible tough ink with high-resolution printability, biodegradability, self-healing, adhesion, and integration with surrounding tissues is a big challenge in 3D printing. The aim of this study was to develop extrusion-based 3D printing of viscous hydrogel composing of maleic acid and propylene diepoxide by controlling continuous mechanisms of condensation and radical polymerization.

METHODS

The molecular weight of highly adhesive propagating poly(malate-co-propylene oxide) copolymer was controlled by capping its growing chain with mono-functional lipoic acid with different compositions during condensation reaction to form lipoic acid capped gel (LP-capped gel). Poly(ethylene oxide)-diacrylate, PEGDA, is graft-polymerized to the LP-capped backbone polymer (MPLE gel) by UV irradiation during 3D printing process to control the properties of gel printability, mechanical properties, and cell adhesiveness and post-printing fidelity of the printed scaffolds with high resolution and mechanical properties (MPLE scaffold). The scaffolds in complex geometries have been printed out in diverse forms with addition of model drugs with different molecular weights and chemical structures. Both the highly adhesive LP-capped gel and printing-controlled MPLE gel/scaffolds are diversely characterized and compared with for their applications to the extrusion-based printability, including biocompatibility, self-healing, drug releasing, adhesiveness, multi-layered high-resolution printing. Further in vitro/in vivo tests were done to observe cytotoxicity, immune response and tissue formation by using different cells in mice model.

RESULTS

LP-capped hydrogel from maleic acid and propylene diepoxide gel showed control of gel properties with lipoic acid with one function group of thiol during condensation reaction, and the ratio at 1:0.3 (w/v) between LP-capped gel and PEGDA was chosen for the optimal results during radical polymerization process for 3D printing at high resolution (90-140 μm in strut thickness) with various complex geometries (lattice, rhombus, and honeycomb). The hydrogel showed excellent properties of self-healing, mechanical strength, biocompatibility, etc. In addition, the long-term release profiles of bioactive molecules were well-controlled by incorporating drugs of high molecular bovine serum albumin (BSA, 21 days, 98.4 ± 0.69%), or small molecule ornidazole (ORN, 14 days, 97.1 ± 1.98%) into the MPLE gel scaffolds for the tests of potential therapeutic applications. More importantly, the MPLE gels represents excellent in vitro cyto-compatibility against osteoblast-like cells (MC3T3) with viability value at 96.43% ± 7.48% over 7 culturing days. For in-vivo studies, the flexible MPLE scaffolds showed significant improvement on angiogenesis with minor inflammatory response after 4-week implantation in mice.

CONCLUSION

The MPLE gel inks was well-controlled for the fabrication of flexible complex tissue engineering scaffold with high resolutions, shear-thinning, 3D printability and post-printing fidelity, by modulating the composition of the highly adhesive LP-capped gel and inert PEGDA as well as end capping of lipoic acid to the propagating poly(malate-co-propylene oxide) copolymer. The gel ink demonstrated its excellent printability, in vitro/in vivo biocompatibility and mechanical properties as well as sustained drug release from the gel.

Lyotropic Liquid Crystals: A Biocompatible and Safe Material for Local Cardiac Application

The regeneration of cardiac tissue is a multidisciplinary research field aiming to improve the health condition of the post-heart attack patient. Indeed, myocardial tissue has a poor ability to self-regenerate after severe damage. The scientific efforts focused on the research of a biomaterial able to adapt to heart tissue, thus guaranteeing the in situ release of active substances or growth promoters. Many types of hydrogels were proposed for this purpose, showing several limitations. The aim of this study was to suggest a new usage for glyceryl monooleate-based lyotropic liquid crystals (LLCs) as a biocompatible and inert material for a myocardial application. The main advantages of LLCs are mainly related to their easy in situ injection as lamellar phase and their instant in situ transition in the cubic phase. In vivo studies proved the biocompatibility and the inertia of LLCs after their application on the myocardial tissue of mice. In detail, the cardiac activity was monitored through 28 days, and no significant alterations were recorded in the heart anatomy and functionality. Moreover, gross anatomy showed the ability of LLCs to be bio-degraded in a suitable time frame. Overall, these results permitted us to suppose a potential use of LLCs as materials for cardiac drug delivery.

Hyaluronic acid-based interpenetrating network hydrogel as a cell carrier for nucleus pulposus repair

Hyaluronic acid (HA) is a key component of the intervertebral disc (IVD) that is widely investigated as an IVD biomaterial. One persisting challenge is introducing materials capable of supporting cell encapsulation and function, yet with sufficient mechanical stability. In this study, a hybrid interpenetrating polymer network (IPN) was produced as a non-covalent hydrogel, based on a covalently cross-linked HA (HA-BDDE) and HA-poly(N-isopropylacrylamide) (HA-pNIPAM). The hybrid IPN was investigated for its physicochemical properties, with histology and gene expression analysis to determine matrix deposition in vitro and in an ex vivo model. The IPN hydrogel displayed cohesiveness for at least one week and rheological properties resembling native nucleus pulposus (NP) tissue. When implanted in an ex vivo IVD organ culture model, the IPN supported cell viability, phenotype expression of encapsulated NP cells and IVD matrix production over four weeks under physiological loading. Overall, our results indicate the therapeutic potential of this HA-based IPN hydrogel for IVD regeneration.

The sodium hyaluronate microspheres fabricated by solution drying for transcatheter arterial embolization

Transcatheter arterial embolization (TAE) is an effective therapeutic method for several clinical ailments. Interminably, the polymer microsphere is reflected as one of the idyllic embolic materials due to the exceptional...

On-Chip Synthesis of Hyaluronic Acid-Based Nanoparticles for Selective Inhibition of CD44+ Human Mesenchymal Stem Cell Proliferation

In this study, an innovative microfluidics-based method was developed for one-step synthesis of hyaluronic acid (HA)-based nanoparticles (NPs), by exploiting polyelectrolytic interactions between HA and chitosan (CS), in order to improve reliability, reproducibility and possible scale-up of the NPs preparation. The on-chip synthesis, using a staggered herringbone micromixer, allowed to produce HA/CS NPs with tailored-made size and suitable for both parenteral (117.50 ± 4.51 nm) and loco-regional (349.15 ± 38.09 nm) administration, mainly composed by HA (more than 85% wt) with high negative surface charge (< −20 mV). HA/CS NPs were successfully loaded with a challenging water-insoluble molecule, Everolimus (EVE), an FDA- and EMA-approved anticancer drug able to lead to cell cycle arrest, reduced angiogenesis and promotion of apoptosis. HA/CS NPs resulted to be massively internalized in CD44+ human mesenchymal stem cells via CD44 receptor-mediated endocytosis. HA/CS NPs selectiveness towards CD44 was highlighted by blocking CD44 receptor by anti-CD44 primary antibody and by comparison to CS-based NPs cellular uptake. Eventually, high effectiveness in inhibiting cell proliferation was demonstrated on-chip synthetized EVE loaded HA/CS NPs by tracking in vitro DNA synthesis.

Self-assembling in situ gel based on lyotropic liquid crystals containing VEGF for tissue regeneration

Current tissue-regenerative biomaterials confront two critical issues: the uncontrollable delivery capacity of vascular endothelial growth factor (VEGF) for adequate vascularization and the poor mechanical properties of the system for tissue regeneration. To overcome these two issues, a self-assembling in situ gel based on lyotropic liquid crystals (LLC) was developed. VEGF-LLC was administrated as a precursor solution that would self-assemble into an in situ gel with well-defined internal inverse bicontinuous cubic phases when exposed to physiological fluid at a defect site. The inverse cubic phase with a 3D bicontinuous water channel enabled a 7-day sustained release of VEGF. The release profile of VEGF-LLC was controlled using octyl glucoside (OG) as a hydration-modulating agent, which could enlarge the water channel, yielding a 2-fold increase in water channel size and a 7-fold increase in VEGF release. For the mechanical properties, the elastic modulus was found to decrease from ∼100 kPa to ∼1.2 kPa, which might be more favorable for angiogenesis. Furthermore, the self-recovery ability of the VEGF-LLC gel was confirmed by quick recovery of the inner network in step-strain measurements. In vitro, VEGF-LLC considerably promoted the proliferation, migration, and tube formation of human umbilical vein endothelial cells (HUVECs) as compared to free VEGF (p < 0.05). Furthermore, angiogenesis was successfully induced in rats after subcutaneous injection of VEGF-LLC. The self-assembling LLC gel showed satisfactory degradability and mild inflammatory response with little impact on the surrounding tissue. The controllable release profile and unique mechanical properties of VEGF-LLC offer a new approach for tissue regeneration. STATEMENT OF SIGNIFICANCE: The potential clinical use of currently available biomaterials in tissue regeneration is limited by their uncontrollable drug delivery capacity and poor mechanical properties. Herein, a self-assembling in situ gel based on lyotropic liquid crystals (LLC) for induced angiogenesis was developed. The results showed that the addition of octyl glucoside (OG) could change the water channel size of LLC, which enabled the LLC system to release VEGF in a sustained manner and to possess a suitable modulus to favor angiogenesis simultaneously. Moreover, the self-recovery capability allowed the gel to match the deformation of surrounding tissues during body motion to maintain its properties and reduce discomfort. In vivo, angiogenesis was induced by VEGF-LLC 14 days after administering subcutaneous injection. These results highlight the potential of LLC as a promising sustained protein drug delivery system for vascular formation and tissue regeneration.

Fabrication of alginate-based stimuli-responsive, non-cytotoxic, terpolymric semi-IPN hydrogel as a carrier for controlled release of bovine albumin serum and 5-amino salicylic acid

Herein, we report a functionalized alginate(Alg)-based terpolymeric semi-interpenetrating (semi-IPN) hydrogel, synthesized via free radical polymerization for the delivery of bovine albumin serum (BSA) and 5-amino salicylic acid (5-ASA). To improve mechanical properties, and to modulate surface morphology of Alg, 2-hydroxyethyl acrylate (HEA) was grafted on alginate and then crosslinked using poly(ethylene glycol) diacrylate (PEGDA). The probable structure and compositions of the synthesized semi-IPN terpolymer were identified by FTIR, ¹H-HR-MAS NMR, and TGA analyses. Achievement of equilibrium swelling state (ESS) and higher elastic modulus values confirmed terpolymer gel formation in aqueous media. Differences in the ESS of the prepared gel at pH 2.5 and 7.4 signify its stimuli-responsive behaviour. The influence of PEGDA on swelling, mechanical properties, surface morphology, cell viability and proliferation, and BSA and 5-ASA delivery were characterized. SEM images show that higher % PEGDA resulted in smaller sized pores in the gel network. Texture analyses demonstrate that hardness, adhesiveness and chewiness of the gel were enhanced at higher PEGDA concentrations. Increases in PEGDA concentration also induced increases in osteoblastic cell viability and higher rates of cell proliferation compared with gels containing lower concentrations of PEGDA. The release results indicate that the gels containing higher concentrations of PEGDA more sustainably release BSA and 5-ASA at 5 days and 30 h, respectively. The experimental data revealed that the synthesized terpolymeric semi-IPN hydrogel may have useful biomedical applications, especially as a carrier of protein (BSA), or 5-ASA (a therapeutic option for conditions of the colon such as Crohn's Disease and Ulcerative Colitis).

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.

Hyaluronic Acid-Decorated Chitosan Nanoparticles for CD44-Targeted Delivery of Everolimus

Bronchiolitis obliterans syndrome (BOS), caused by lung allograft-derived mesenchymal cells' abnormal proliferation and extracellular matrix deposition, is the main cause of lung allograft rejection. In this study, a mild one-step ionotropic gelation method was set up to nanoencapsulate the everolimus, a key molecule in allograft organ rejection prevention, into hyaluronic acid-decorated chitosan-based nanoparticles. Rationale was the selective delivery of everolimus into lung allograft-derived mesenchymal cells; these cells are characterized by the CD44-overexpressing feature, and hyaluronic acid has proven to be a natural selective CD44-targeting moiety. The optimal process conditions were established by a design of experiment approach (full factorial design) aiming at the control of the nanoparticle size (≤200 nm), minimizing the size polydispersity (PDI 0.171 ± 0.04), and at the negative ζ potential maximization (-30.9 mV). The everolimus was successfully loaded into hyaluronic acid-decorated chitosan-based nanoparticles (95.94 ± 13.68 μg/100 mg nanoparticles) and in vitro released in 24 h. The hyaluronic acid decoration on the nanoparticles provided targetability to CD44-overexpressing mesenchymal cells isolated from bronchoalveolar lavage of BOS-affected patients. The mesenchymal cells' growth tests along with the nanoparticles uptake studies, at 37 °C and 4 °C, respectively, demonstrated a clear improvement of everolimus inhibitory activity when it is encapsulated in hyaluronic acid-decorated chitosan-based nanoparticles, ascribable to their active uptake mechanism.

Characterizations of hyaluronate-based terpolymeric hydrogel synthesized via free radical polymerization mechanism for biomedical applications

In the present study, a novel terpolymeric hydrogel was developed using sodium hyaluronate (HA), 2-hydroxyethyl acrylate (2-HEA), and poly(ethylene glycol) diacrylate (PEGDA) via free radical polymerization for biomedical applications. To achieve elasticity, swelling ability, porous architecture and sufficient gel strength, hyaluronate was chemically modified by grafting and crosslinking methods using 2-HEA and PEGDA, respectively. The structure and compositions of the fabricated terpolymer (HA-g-p(2-HEA)-x-PEGDA) were verified by FTIR, ¹H HR-MAS-NMR, and TGA analyses. The surface morphology and cross-section of the hydrogel was detected by SEM analysis. The gel nature of terpolymer in aqueous medium at 37 °C was confirmed from swelling study, and rheological experiment. Non-cytotoxicity and biocompatibility of the HA-g-p(2-HEA)-x-PEGDA hydrogel were ascertained by in vitro mouse osteoblastic cells (MC3T3) proliferation, and viability studies. Hematoxylin and eosin Y, and Masson's trichrome stainings were performed to show tissue regeneration ability on the prepared hydrogel. In vitro release results of proangiogenic drug-dimethyloxalylglycine (DMOG), and antibiotics-tetracycline (TCN) showed sustained release behaviour from the prepared hydrogel under different pHs at 37 °C. The mathematical models fitted data imply that both DMOG and TCN release follow first order kinetics, while, the release mechanism is primarily controlled by diffusion as well as erosion process. Finally, the novel biocompatible HA-g-p(2-HEA)-x-PEGDA gel, which showed sustained drugs release, and regeneration ability of extracellular matrix and collagen, could be employed in biomedical applications, especially, for the delivery of DMOG/TCN, and in tissue engineering.

Synthesis and Biocompatibility Characterizations of in Situ Chondroitin Sulfate-Gelatin Hydrogel for Tissue Engineering

Novel hydrogel composed of both chondroitin sulfate (CS) and gelatin was developed for better cellular interaction through two step double crosslinking of N-(3-diethylpropyl)-N-ethylcarbodiimide hydrochloride (EDC) chemistries and then click chemistry. EDC chemistry was proceeded during grafting of amino acid dihydrazide (ADH) to carboxylic groups in CS and gelatin network in separate reactions, thus obtaining CS-ADH and gelatin-ADH, respectively. CS-acrylate and gelatin-TCEP was obtained through a second EDC chemistry of the unreacted free amines of CS-ADH and gelatin-ADH with acrylic acid and tri(carboxyethyl)phosphine (TCEP), respectively. In situ CS-gelatin hydrogel was obtained via click chemistry by simple mixing of aqueous solutions of both CS-acrylate and gelatin-TCEP. ATR-FTIR spectroscopy showed formation of the new chemical bonds between CS and gelatin in CS-gelatin hydrogel network. SEM demonstrated microporous structure of the hydrogel. Within serial precursor concentrations of the CS-gelatin hydrogels studied, they showed trends of the reaction rates of gelation, where the higher concentration, the quicker the gelation occurred. In vitro studies, including assessment of cell viability (live and dead assay), cytotoxicity, biocompatibility via direct contacts of the hydrogels with cells, as well as measurement of inflammatory responses, showed their excellent biocompatibility. Eventually, the test results verified a promising potency for further application of CS-gelatin hydrogel in many biomedical fields, including drug delivery and tissue engineering by mimicking extracellular matrix components of tissues such as collagen and CS in cartilage.

Bioactive Molecules Release and Cellular Responses of Alginate-Tricalcium Phosphate Particles Hybrid Gel

In this article, a hybrid gel has been developed using sodium alginate (Alg) and α-tricalcium phosphate (α-TCP) particles through ionic crosslinking process for the application in bone tissue engineering. The effects of pH and composition of the gel on osteoblast cells (MC3T3) response and bioactive molecules release have been evaluated. At first, a slurry of Alg and α-TCP has been prepared using an ultrasonicator for the homogeneous distribution of α-TCP particles in the Alg network and to achieve adequate interfacial interaction between them. After that, CaCl2 solution has been added to the slurry so that ionic crosslinked gel (Alg-α-TCP) is formed. The developed hybrid gel has been physico-chemically characterized using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and a swelling study. The SEM analysis depicted the presence of α-TCP micro-particles on the surface of the hybrid gel, while cross-section images signified that the α-TCP particles are fully embedded in the porous gel network. Different % swelling ratio at pH 4, 7 and 7.4 confirmed the pH responsiveness of the Alg-α-TCP gel. The hybrid gel having lower % α-TCP particles showed higher % swelling at pH 7.4. The hybrid gel demonstrated a faster release rate of bovine serum albumin (BSA), tetracycline (TCN) and dimethyloxalylglycine (DMOG) at pH 7.4 and for the grade having lower % α-TCP particles. The MC3T3 cells are viable inside the hybrid gel, while the rate of cell proliferation is higher at pH 7.4 compared to pH 7. The in vitro cytotoxicity analysis using thiazolyl blue tetrazolium bromide (MTT), bromodeoxyuridine (BrdU) and neutral red assays ascertained that the hybrid gel is non-toxic for MC3T3 cells. The experimental results implied that the non-toxic and biocompatible Alg-α-TCP hybrid gel could be used as scaffold in bone tissue engineering.