An overview of chitin or chitosan/nano ceramic composite scaffolds for bone tissue engineering

Chitin and chitosan based nanocomposite scaffolds have been widely used for bone tissue engineering. These chitin and chitosan based scaffolds were reinforced with nanocomponents viz Hydroxyapatite (HAp), Bioglass ceramic (BGC), Silicon dioxide (SiO₂), Titanium dioxide (TiO₂) and Zirconium oxide (ZrO₂) to develop nanocomposite scaffolds. Plenty of works have been reported on the applications and characteristics of the nanoceramic composites however, compiling the work done in this field and presenting it in a single article is a thrust area. This review is written with an aim to fill this gap and focus on the preparations and applications of chitin or chitosan/nHAp, chitin or chitosan/nBGC, chitin or chitosan/nSiO₂, chitin or chitosan/nTiO₂ and chitin or chitosan/nZrO₂ in the field of bone tissue engineering in detail. Many reports so far exemplify the importance of ceramics in bone regeneration. The effect of nanoceramics over native ceramics in developing composites, its role in osteogenesis etc. are the gist of this review.

The comparison study of bioactivity between composites containing synthetic non-substituted and carbonate-substituted hydroxyapatite

Apatite forming ability of hydroxyapatite (HAP) and carbonate hydroxyapatite (CHAP) containing composites was compared. Two composite materials, intended for filling bone defects, were made of polysaccharide polymer and one of two types of hydroxyapatite. The bioactivity of the composites was evaluated in vitro by soaking in a simulated body fluid (SBF), and the formation of the apatite layer was determined by scanning electron microscopy with energy-dispersive spectrometer and Raman spectroscopy. The results showed that both the composites induced the formation of apatite layer on their surface after soaking in SBF. In addition, the sample weight changes and the ion concentration of the SBF were scrutinized. The results showed the weight increase for both materials after SBF treatment, higher weight gain and higher uptake of calcium ions by HAP containing scaffolds. SBF solution analysis indicated loss of calcium and phosphorus ions during experiment. All these results indicate apatite forming ability of both biomaterials and suggest comparable bioactive properties of composite containing pure hydroxyapatite and carbonate-substituted one.

Effect of N/P ratios on physicochemical stability, cellular association, and gene silencing efficiency for trimethyl chitosan/small interfering RNA complexes

N,N,N-Trimethyl chitosan (TMC) with 40% quaternization was used as a vector for small interfering RNA (siRNA) delivery. Nano-sized complexes were formed in water by mixing siRNA with TMC; the smallest particle sizes were obtained at a N/P ratio of 10. The complexes had a positive surface charge that increased with increases in the N/P ratio and leveled off at +20 mV with N/P ratios > 10. The majority of particles had a diameter <100 nm under transmission electron microscope (TEM). When the N/P ratio was >10, the binding efficiency of TMC with siRNA was >90%. In 25% fetal bovine serum, the TMC/siRNA complexes with N/P ratios of 10 and 20 were intact for 12 and 48 h, respectively. TMC/siRNA complexes with an N/P ratio > 5 efficiently entered the human embryonic kidney (HEK) 293 cells and trapped initially in the lysosomes, which could then relocate in the cytoplasm. Gene silencing, tested by using enhanced green fluorescent protein (EGFP), was reduced to ~60% by the complexes with N/P ratios of 10 and 20. Specific silencing was confirmed by dose dependency and nonsilencing effect of sequence-mismatch siRNA. No significant cytotoxicity was detected for the TMC/siRNA complexes. In this study, the influence of the N/P ratio on TMC/siRNA complexes was systematically investigated and TMC was found to be an effective vector for siRNA delivery using optimized formulations.

Electrospun poly(lactic-co-glycolic acid)/wool keratin fibrous composite scaffolds potential for bone tissue engineering applications

Biocomposite scaffolds consist of poly(lactic- co-glycolic acid) and wool keratin were obtained by an electrospinning process. Scanning electron microscopy images showed that the poly(lactic- co-glycolic acid)/wool keratin fibers had relatively rougher surfaces and smaller diameters. Thermogravimetric analysis showed higher thermal stabilities of the developed biocomposites compared to neat poly(lactic- co-glycolic acid). Mechanical tests showed that when the wool keratin content increased from 0% to 0.5% w/v, the tensile strength and elongation at break of the poly(lactic- co-glycolic acid)/0.5% wool keratin scaffolds increased with maxima of 6.59 MPa and 104.44%, respectively, which was an increase of 8.2% and 570% over the poly(lactic- co-glycolic acid) scaffold. The biological response of bone mesenchymal stem cells to the poly(lactic- co-glycolic acid)/1.5% wool keratin biocomposites was superior when compared to pure poly(lactic- co-glycolic acid) scaffold in terms of improved cell attachment and higher proliferation. These observations suggest that the addition of wool keratin to a poly(lactic- co-glycolic acid) matrix can improve several properties of the electrospun poly(lactic- co-glycolic acid) fibers, and the poly(lactic- co-glycolic acid)/wool keratin biocomposites could make excellent materials for tissue engineering applications.

Chitosan-Based Macromolecular Biomaterials for the Regeneration of Chondroskeletal and Nerve Tissue

The use of materials, containing the biocompatible and bioresorbable biopolymer poly(1→4)-2-amino-2-deoxy-β-D-glucan, containing some N-acetyl-glucosamine units (chitosan, CHI) and/or its derivatives, to fabricate devices for the regeneration of bone, cartilage and nerve tissue, was reviewed. The CHI-containing devices, to be used for bone and cartilage regeneration and healing, were tested mainly for in vitro cell adhesion and proliferation and for insertion into animals; only the use of CHI in dental surgery has reached the clinical application. Regarding the nerve tissue, only a surgical repair of a 35 mm-long nerve defect in the median nerve of the right arm at elbow level with an artificial nerve graft, comprising an outer microporous conduit of CHI and internal oriented filaments of poly(glycolic acid), was reported. As a consequence, although many positive results have been obtained, much work must still be made, especially for the passage from the experimentation of the CHI-based devices, in vitro and in animals, to their clinical application.

Nano-hydroxyapatite/chitosan sponge-like biocomposite for repairing of rat calvarial critical-sized bone defect

A three-dimensional porous nano-hydroxyapatite (nHA)/chitosan (CS) biocomposite was synthesized. The rod-like nHA grains of 15—30 × 5—10 nm in size were observed by TEM and confirmed by characteristic XRD patterns. The diameters of the interconnecting pores of the nHA/CS biocomposite, determined by SEM, were 120—300 μm. Standard critical-sized calvarial bone defect ( = 6.5 mm) was created in Sprague-Dawley (SD) rats. In group 1, nHA/CS was implanted and in group 2, no implant was made in the defect. After 1 week, the histological assessment of group 1 clearly showed that a large number of living cells were anchored in the pores of the nHA/CS implants. New bone formation, both at the edge and in the center of implants, was found as early as 2 weeks. Histological assays confirmed that the newly formed bone tissue was bioactive and neovascularized. After 5 weeks, the mineral content and volume of the newly formed bone tissue in the defects were significantly greater in group 1 than in group 2 (p < 0.01). These results indicate that implantation of the nHA/CS enhanced the repair of bone defect and confirm the potential of this biocomposite as a bioactive bone grafting substitute.

Bioactivity of a Chitosan Based Nanocomposite

In this work, experiments to produce a series of nanocomposites based on natural chitosan and nano-clay (MMT) were conducted. Commercially available montmorillonite (MMT) was used as a nanofiller. CS-MMT nanocomposites were prepared using the casting method. Thin nanocomposite foils were neutralized in NaOH solution, then the nanocomposite foils were soaked in simulated body fluid (SBF). Kinetics of crystallization of the apatite structure was observed using PIXE, FTIR-ATR and SEM/EDS techniques. It was shown that high concentrations of calcium and phosphate ions were located inside the nanocomposite structure. Bioactivity phenomena was initiated first in the nanocomposite foils (CS/MMT) and then in pure chitosan foils. These results suggest that the nano-clay particles (MMT) distributed in the biopolymer matrix acted as nucleaction centers of apatite. An apatite layer on pure chitosan crystallized much more slowly than in the case of nanocomposite materials. The CS-MMT nanocomposites therefore seem to be promising materials for bone repair implants because of their inherent bioactivity.

Lipid-like Diblock Copolymer as an Additive for Improving the Blood Compatibility of Poly(lactide-co-glycolide)

To optimize the blood biocompatibility of poly(lactide-coglycolide) (PLGA), lipid-like diblock copolymer poly(DL-lactide)-block-poly(2-methacryloyloxyethyl phosphorylcholine) (PLA-b-PMPC) was employed as a surface-modifying additive. The blends of PLGA and PLA-b-PMPC coated poly(ethylene terephthalate) membranes were prepared by dip-coating. ATR-FTIR spectroscopy showed the incorporation of phosphorylcoline groups in the blends and contact angle results indicated that the hydrophilicity of the blends improved with increasing PLA-b-PMPC content. The plasma recalcification time of polymer coating was prolonged and the amount of adherent platelets on coating surface was decreased by introducing PLA-b-PMPC. The adhesion of polymer coating on the gold electrode of quartz crystal microbalance was monitored and PLGA containing PLA-b-PMPC additives showed excellent polymer—metal adhesion. These results show that the blends of PLGA and lipid-like PLA-b-PMPC could be used as high performance biodegradable polymer coatings for blood contact medical devices.

Preparation and In Vitro Evaluation of Chitosan Bioelectret Membranes for Guided Bone Regeneration

Chitosan bioelectret membranes were prepared from chitosan with the tape casting method and polarized in an electric field with grid-controlled corona charge. Surface potential tests revealed that the surface potential rapidly decayed within one day and gradually stabilized over the following 8 days. The bioelectret membranes exhibited similar mechanical properties as the unpolarized membranes. The negatively charged surface facilitated depolymerization by lysozyme in phosphate buffered saline solution and induced apatite crystals depositing on the surface in simulated body fluid. Osteoblasts adhered well to the negatively charged surface. Levels of osteoblast viability and alkaline phosphatase activity were higher on the bioelectret membranes than on the unpolarized membranes.

Chitosan composites for bone tissue engineering--an overview

Bone contains considerable amounts of minerals and proteins. Hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂] is one of the most stable forms of calcium phosphate and it occurs in bones as major component (60 to 65%), along with other materials including collagen, chondroitin sulfate, keratin sulfate and lipids. In recent years, significant progress has been made in organ transplantation, surgical reconstruction and the use of artificial protheses to treat the loss or failure of an organ or bone tissue. Chitosan has played a major role in bone tissue engineering over the last two decades, being a natural polymer obtained from chitin, which forms a major component of crustacean exoskeleton. In recent years, considerable attention has been given to chitosan composite materials and their applications in the field of bone tissue engineering due to its minimal foreign body reactions, an intrinsic antibacterial nature, biocompatibility, biodegradability, and the ability to be molded into various geometries and forms such as porous structures, suitable for cell ingrowth and osteoconduction. The composite of chitosan including hydroxyapatite is very popular because of the biodegradability and biocompatibility in nature. Recently, grafted chitosan natural polymer with carbon nanotubes has been incorporated to increase the mechanical strength of these composites. Chitosan composites are thus emerging as potential materials for artificial bone and bone regeneration in tissue engineering. Herein, the preparation, mechanical properties, chemical interactions and in vitro activity of chitosan composites for bone tissue engineering will be discussed.

Effects of Chitosan on Properties of Novel Human-like Collagen/Chitosan Hybrid Vascular Scaffold

Novel human-like collagen (HLC)/chitosan hybrid scaffolds were fabricated at blend ratios of 0%, 0.02%, 0.2% by crosslinking and freeze-drying process. The properties of the scaffolds were investigated, including morphology, mechanical strength, degradability, and cell biocompatibility. When the blend ratio was 0.02%, the morphology of the scaffolds was highly homogeneous with interconnected porous structure 46 ± 9 μm in size (SEM). The X-ray photoelectron spectroscopy analysis indicated intermolecular crosslinks between HLC and chitosan. The strain and stress of the scaffolds were 37.9 ± 3.3% and 309.7 ± 19.7 KPa, respectively. Human venous fibroblasts were expanded and seeded into the scaffolds in the density of 1 × 10 5 cells/cm3 under static conditions. The cell morphology and proliferation were investigated using SEM, H&E, and MTT assay, which showed that the optimal content of the chitosan was signifcantly enhanced the cells adhesion, proliferation, and viability, compared to pure HLC, pure chitosan, and 0.2% chitosan/HLC scaffolds. These hybrid scaffolds appear to have favorable characteristics for vascular tissue engineering application.

Injectable Poly(ethylene glycol) Dimethacrylate-based Hydrogels with Hydroxyapatite

Injectable hydrogels are attractive materials for tissue engineering as they provide fast reaction rates, low heat release, and biocompatibility for cell proliferation and permanent interface with surrounding tissue. A series of injectable poly(ethylene glycol) dimethacrylate (PEGDMA) hydrogels with four different weight fractions of hydroxyapatite (HA) particles were prepared and thermal and mechanical properties evaluated. The cytocompatibility was assessed by examining the viability and morphology of human mesenchymal stem cells (hMSCs) seeded on the hydrogels. The in situ crosslink process displayed a vast decrease in the maximal temperature and an increase in the maximal temperature time. Cytocompatibility evaluation by MTT assay, scanning electron microscopy (SEM) and laser scanning confocal microscopy (LSCM) showed that the cells on the composite hydrogels possessed better viability and adherence than the hydrogels without HA. The results indicated that composite hydrogels have potential as injectable materials for tissue engineering application.

Fabrication and in Vitro Evaluation of Calcium Phosphate Combined with Chitosan Fibers for Scaffold Structures

A rapid prototyping and rapid tool technique-based method was developed to fabricate chitosan fiber calcium phosphate cement composites (CF/CPC) for bone tissue engineering scaffold applications. The products were characterized and the in vitro performance with canine bone marrow stem cells (BMCs) on CF/CPC scaffold with controlled fiber structures evaluated. The X-ray diffraction analysis showed that about 91% of the inorganic part of the CF/CPC scaffold was hydroxyapatite (HA) and the variation in CF had little effect on the percentage of HA content. The results from in vitro study demonstrated that the interconnected macropores rapidly formed inside the CF/CPC scaffolds and that the patterns were related to the fiber structures used. The differences in the fiber structures altered the morphology of the BMCs without affecting the proliferation of the BMCs.

Preparation of Bioactive Hydroxyapatite on Pure Titanium

In this study, a hydroxyapatite (HA) was coated on a pure titanium surface by means of a complex oxidation and hydrothermal treatment. First an anodic oxidation was done on the titanium plates, followed by micro-arc oxidation. The HA-coated specimens and pure titanium specimens were immersed in SLB for 1, 5, and 10 days, respectively, to study their electrochemical behavior. The corrosion currents of HA-coated specimens were less than pure titanium specimens. This indicated that HA coating prevented surface metal ions of the implant from dissolving, thereby, reducing the tissue toxicity. The cytotoxic effect on fibroblasts L929 cells was measured by cell counting after being seeded for 2, 4, 8, 12, and 24 h. The number of surface cell attachments on the HA-coated specimens was much greater than on pure titanium specimens. The morphology of the cells on the HA coating had normal shapes and spread well with some cells climbing onto surface pores while cells on the pure titanium were oval shaped. The results confirm that the cell compatibility on HA-coated ion titanium surfaces is much better than pure titanium.