Multi-functional P(3HB) microsphere/45S5 Bioglass®-based composite scaffolds for bone tissue engineering

Novel multi-functional P(3HB) microsphere/45S5 Bioglass®-based composite scaffolds exhibiting potential for drug delivery were developed for bone tissue engineering. 45S5 Bioglass®-based glass–ceramic scaffolds of high interconnected porosity produced using the foam-replication technique were coated with biodegradable microspheres (size < 2 μm) made from poly(3-hydroxybutyrate), P(3HB), produced using Bacillus cereus SPV. A solid-in-oil-in-water emulsion solvent extraction/evaporation technique was used to produce these P(3HB) microspheres. A simple slurry-dipping method, using a 1 wt.% suspension of P(3HB) microspheres in water, dispersed by an ultrasonic bath, was used to coat the scaffold, producing a uniform microsphere coating throughout the three-dimensional scaffold structure. Compressive strength tests confirmed that the microsphere coating slightly enhanced the scaffold mechanical strength. It was also confirmed that the microsphere coating did not inhibit the bioactivity of the scaffold when immersed in simulated body fluid (SBF) for up to 4 weeks. The hydroxyapatite (HA) growth rate on P(3HB) microsphere-coated 45S5 Bioglass® composite scaffolds was very similar to that on the uncoated control sample, qualitatively indicating similar bioactivity. However, the surface topography of the HA surface layer was affected as shown by results obtained from white light interferometry. The roughness of the surface was much higher for the P(3HB) microsphere-coated scaffolds than for the uncoated samples, after 7 days in SBF. This feature would facilitate cell attachment and proliferation. Finally, gentamycin was successfully encapsulated into the P(3HB) microspheres to demonstrate the drug delivery capability of the scaffolds. Gentamycin release kinetics was determined using liquid chromatography–mass spectrometry. The release of the drug from the coated composite scaffolds was slow and controlled when compared to the observed fast and relatively uncontrolled drug release from the bone scaffold (without microsphere coating). Thus, this unique multifunctional bioactive composite scaffold has the potential to enhance cell attachment and to provide controlled delivery of relevant drugs for bone tissue engineering.     

Repairing a critical-sized bone defect with highly porous modified and unmodified baghdadite scaffolds

This is the first reported study to prepare highly porous baghdadite (Ca₃ZrSi₂O₉) scaffolds with and without surface modification and investigate their ability to repair critical-sized bone defects in a rabbit radius under normal load. The modification was carried out to improve the mechanical properties of the baghdadite scaffolds (particularly to address their brittleness) by coating their surfaces with a thin layer (～400 nm) of polycaprolactone (PCL)/bioactive glass nanoparticles (nBGs). The β-tricalcium phosphate/hydroxyapatite (TCP/HA) scaffolds with and without modification were used as the control groups. All of the tested scaffolds had an open and interconnected porous structure with a porosity of ～85% and average pore size of 500 μm. The scaffolds (six per scaffold type and size of 4 mm × 4 mm × 15 mm) were implanted (press-fit) into the rabbit radial segmental defects for 12 weeks. Micro-computed tomography and histological evaluations were used to determine bone ingrowth, bone quality, and implant integration after 12 weeks of healing. Extensive new bone formation with complete bridging of the radial defect was evident with the baghdadite scaffolds (modified/unmodified) at the periphery and in close proximity to the ceramics within the pores, in contrast to TCP/HA scaffolds (modified/unmodified), where bone tended to grow between the ulna adjacent to the implant edge. Although the modification of the baghdadite scaffolds significantly improved their mechanical properties, it did not show any significant effect on in vivo bone formation. Our findings suggest that baghdadite scaffolds with and without modification can serve as a potential material to repair critical sized bone defects.     

Mechanical properties and dual drug delivery application of poly(lactic-co-glycolic acid) scaffolds fabricated with a poly(β-amino ester) porogen

Polymeric scaffolds that are biocompatible and biodegradable are widely used for tissue engineering applications. Scaffolds can be further enhanced by enabling the release of one or more drugs to stimulate regeneration or for the treatment of a specific disease or condition. In this study, poly(lactic-co-glycolic acid) (PLGA) microspheres were mixed with poly(β-amino ester) (PBAE) particles to create novel hybrid scaffolds capable of dual release of drug and growth factor. Fast-degrading PBAE particles loaded with the drug ketoprofen acted as porogens that provided a rapid 12 h release. The PLGA microspheres were loaded with a growth factor, bone morphogenetic protein 2, and fused together around the porogens to create a slow-degrading matrix that provided sustained release lasting 70 days. Drug release was further tailored by varying the amount of porogen added to the scaffold. Bioactivity measurements demonstrated that the scaffold fabrication technique did not damage the drug or protein. The compressive modulus was affected by the amount of porogen added, extending from 50 to 111 MPa for loadings from 60 to 40% PBAE, and after 5 days of degradation, it decreased to 0.6 to 1.1 kPa when the porogen was gone. PLGA containing a quick-degrading porogen can be used to release two drugs while developing a porous microarchitecture for cell ingrowth with in a matrix capable of maintaining a compressive modulus applicable for soft tissue implants.     

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.     

Comparative studies on ectopic bone formation in porous hydroxyapatite scaffolds with complementary pore structures

Vascularized bone grafts were constructed by implanting hydroxyapatite (HA) scaffolds with complementary macro-pore structures into the dorsal muscle of dogs. The relationship between pore structures and ectopic bone formation properties was investigated. Two types of scaffolds with complementary porous structures were fabricated by spherulite-accumulating and porogen-preparing methods, and were named spherulite HA-positive and porogen HA-negative, respectively. After implantation for 1 month, histological observation showed that all the scaffolds were encapsulated by normal muscle tissue and multiple vascular net with cells, indicating excellent biocompatibility and pore interconnectivity of the scaffolds. In the spherulite HA-positive scaffolds, a number of osteoclasts and osteoblasts coupled with new bone tissues were found after 3 and 6 months’ implantations, which was better than those in the porogen HA-negative scaffolds. Similarly, the improvement of mechanical properties and the reconstruction of materials in the spherulite HA-positive scaffolds were superior to those in the porogen HA-negative scaffolds. The different ectopic bone formation induced by different macro-pore structures after intramuscular implantation demonstrated the significant effect of macro-pore structures of scaffolds on osteoinduction and vascularization.     

Modified PHBV scaffolds by in situ UV polymerization: Structural characteristic,mechanical properties and bone mesenchymal stem cell compatibility

An ideal scaffold provides an interface for cell adhesion and maintains enough biomechanical support during tissue regeneration. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) scaffolds with pore sizes ranging from 100 to 500 μm and porosity ～90% were prepared by the particulate-leaching method, and then modified by the introduction of polyacrylamide (PAM) on the inner surface of scaffolds using in situ UV polymerization, with the aim of enhancing the biological and mechanical properties of the PHBV scaffolds. The modified PHBV scaffolds had interconnected pores with porosity of 75.4–78.6% and pore sizes at peak volume from 20 to 50 μm. The compressive load and modulus were up to 62.45 N and 1.06 MPa, respectively. The water swelling percentage (WSP) of the modified PHBV scaffolds increased notably compared with that of the PHBV scaffolds, with the maximum WSP at 537%. Sheep bone mesenchymal stem cells (BMSC) were cultured on the PHBV and modified PHBV. The hydrophilic PAM chains did not influence BMSC viability or proliferation index, but the initial cell adhesion at 1 h of culture was enhanced significantly. Framing PHBV scaffold along with gel-like PAM chains inside is a novel model of inner surface modification for PHBV scaffolds, which shows potential in tissue engineering applications.     

Unique microstructural design of ceramic scaffolds for bone regeneration under load

During the past two decades, research on ceramic scaffolds for bone regeneration has progressed rapidly; however, currently available porous scaffolds remain unsuitable for load-bearing applications. The key to success is to apply microstructural design strategies to develop ceramic scaffolds with mechanical properties approaching those of bone. Here we report on the development of a unique microstructurally designed ceramic scaffold, strontium–hardystonite–gahnite (Sr–HT–gahnite), with 85% porosity, 500 μm pore size, a competitive compressive strength of 4.1 ± 0.3 MPa and a compressive modulus of 170 ± 20 MPa. The in vitro biocompatibility of the scaffolds was studied using primary human bone-derived cells. The ability of Sr–HT–gahnite scaffolds to repair critical-sized bone defects was also investigated in a rabbit radius under normal load, with β-tricalcium phosphate/hydroxyapatite scaffolds used in the control group. Studies with primary human osteoblast cultures confirmed the bioactivity of these scaffolds, and regeneration of rabbit radial critical defects demonstrated that this material induces new bone defect bridging, with clear evidence of regeneration of original radial architecture and bone marrow environment.     

Nanostructured biocomposite substrates by electrospinning and electrospraying for the mineralization of osteoblasts

Nanotechnology has enabled the engineering of nanostructured materials to meet current challenges in bone replacement therapies. Biocomposite nanofibrous scaffolds of poly(l-lactic acid)-co-poly(?-caprolactone), gelatin and hydroxyapatite (HA) were fabricated by combining the electrospinning and electrospraying techniques in order to create a better osteophilic environment for the growth and mineralization of osteoblasts. Electrospraying of HA nanoparticles on electrospun nanofibers helped to attain rough surface morphology ideal for cell attachment and proliferation and also achieve improved mechanical properties than HA blended nanofibers. Nanofibrous scaffolds showed high pore size and porosity up to 90% with fiber diameter in the range of 200–700 nm. Nanofibrous scaffolds were characterized for their functional groups and chemical structure by FTIR and XRD analysis. Studies on cell–scaffold interaction were carried out by culturing human fetal osteoblast cells (hFOB) on both HA blended and sprayed PLACL/Gel scaffolds and assessing their growth, proliferation, mineralization and enzyme activity. The results of MTS, ALP, SEM and ARS studies confirmed, not only did HA sprayed biocomposite scaffolds showed better cell proliferation but also enhanced mineralization and alkaline phosphatase activity (ALP) proving that electrospraying in combination with electrospinning produced superior and more suitable biocomposite nanofibrous scaffolds for bone tissue regeneration.     

Electrospun nanostructured scaffolds for bone tissue engineering

The current challenge in bone tissue engineering is to fabricate a bioartificial bone graft mimicking the extracellular matrix (ECM) with effective bone mineralization, resulting in the regeneration of fractured or diseased bones. Biocomposite polymeric nanofibers containing nanohydroxyapatite (HA) fabricated by electrospinning could be promising scaffolds for bone tissue engineering. Nanofibrous scaffolds of poly-l-lactide (PLLA, 860 ± 110 nm), PLLA/HA (845 ± 140 nm) and PLLA/collagen/HA (310 ± 125 nm) were fabricated, and the morphology, chemical and mechanical characterization of the nanofibers were evaluated using scanning electron microscopy, Fourier transform infrared spectroscopy and tensile testing, respectively. The in vitro biocompatibility of different nanofibrous scaffolds was also assessed by growing human fetal osteoblasts (hFOB), and investigating the proliferation, alkaline phosphatase activity (ALP) and mineralization of cells on different nanofibrous scaffolds. Osteoblasts were found to adhere and grow actively on PLLA/collagen/HA nanofibers with enhanced mineral deposition of 57% higher than the PLLA/HA nanofibers. The synergistic effect of the presence of an ECM protein, collagen and HA in PLLA/collagen/HA nanofibers provided cell recognition sites together with apatite for cell proliferation and osteoconduction necessary for mineralization and bone formation. The results of our study showed that the biocomposite PLLA/collagen/HA nanofibrous scaffold could be a potential substrate for the proliferation and mineralization of osteoblasts, enhancing bone regeneration.     

Finite element analysis on the biomechanical stability of open porous titanium scaffolds for large segmental bone defects under physiological load conditions

Repairing large segmental defects in long bones caused by fracture, tumour or infection is still a challenging problem in orthopaedic surgery. Artificial materials, i.e. titanium and its alloys performed well in clinical applications, are plenary available, and can be manufactured in a wide range of scaffold designs. Although the mechanical properties are determined, studies about the biomechanical behaviour under physiological loading conditions are rare. The goal of our numerical study was to determine the suitability of open-porous titanium scaffolds to act as bone scaffolds. Hence, the mechanical stability of fourteen different scaffold designs was characterized under both axial compression and biomechanical loading within a large segmental distal femoral defect of 30 mm. This defect was stabilized with an osteosynthesis plate and physiological hip reaction forces as well as additional muscle forces were implemented to the femoral bone. Material properties of titanium scaffolds were evaluated from experimental testing. Scaffold porosity was varied between 64 and 80%. Furthermore, the amount of material was reduced up to 50%. Uniaxial compression testing revealed a structural modulus for the scaffolds between 3.5 GPa and 19.1 GPa depending on porosity and material consumption. The biomechanical testing showed defect gap alterations between 0.03 mm and 0.22 mm for the applied scaffolds and 0.09 mm for the intact bone. Our results revealed that minimizing the amount of material of the inner core has a smaller influence than increasing the porosity when the scaffolds are loaded under biomechanical loading. Furthermore, an advanced scaffold design was found acting similar as the intact bone.     

Evaluation of bone regeneration in implants composed of hollow HA microspheres loaded with transforming growth factor β1 in a rat calvarial defect model

Implants that serve simultaneously as an osteoconductive matrix and as a device for local growth factor delivery may be required for optimal bone regeneration in some applications. In the present study, hollow hydroxyapatite (HA) microspheres (106–150 μm) in the form of three-dimensional (3-D) scaffolds or individual (loose) microspheres were created using a glass conversion process. The capacity of the implants, with or without transforming growth factor β1 (TGF-β1), to regenerate bone in a rat calvarial defect model was compared. The 3-D scaffolds supported the proliferation and alkaline phosphatase activity of osteogenic MLO-A5 cells in vitro, showing their cytocompatibility. Release of TGF-β1 from the 3-D scaffolds into phosphate-buffered saline ceased after 2–3 days when ～30% of the growth factor was released. Bone regeneration in the 3-D scaffolds and the individual microspheres increased with time from 6 to 12 weeks, but it was significantly higher (23%) in the individual microspheres than in the 3-D scaffolds (15%) after 12 weeks. Loading with TGF-β1 (5 μg per defect) enhanced bone regeneration in the 3-D scaffolds and individual microspheres after 6 weeks, but had little effect after 12 weeks. 3-D scaffolds and individual microspheres with larger HA diameter (150–250 μm) showed better ability to regenerate bone. Based on these results, implants composed of hollow HA microspheres show promising potential as an osteoconductive matrix for local growth factor delivery in bone regeneration.     

Fabrication of HA/TCP scaffolds with a graded and porous structure using a camphene-based freeze-casting method

A room temperature camphene-based freeze-casting method was used to fabricate hydroxyapatite/tricalcium phosphate (HA/TCP) ceramic scaffolds. By varying the solid loading of the mixture and the freezing temperature, a range of structures with different pore sizes and strength characteristics were achieved. The macropore size of the HA/TCP bioceramics was in the range of 100–200 μm, 40–80 μm and less than 40 μm at solid loadings of 10, 20 and 30 vol.%, respectively. The initial level of solid loading played a primary role in the resulting porosity of the scaffolds. The porosity decreased from 72.5 to 31.4 vol.% when the solid loading was increased from 10 to 30 vol.%. This resulted in an increase in the compressive strength from 2.3 to 36.4 MPa. The temperature gradient, rather than the percentage porosity, influenced the pore size distribution. The compressive strength increased from 1.95 to 2.98 MPa when samples were prepared at 4 °C as opposed to 30 °C. The results indicated that it was possible to manufacture porous HA/TCP bioceramics, with compressive strengths comparable to cancellous bone, using the freeze-casting manufacturing technique, which could be of significant clinical interest.     

A study of vascular smooth muscle cell function under cyclic mechanical loading in a polyurethane scaffold with optimized porosity

High porosity and pore interconnectivity are important features of a successful tissue engineering scaffold. The objective of this work was to optimize the pore interconnectivity and to increase the porosity of an elastomeric degradable/polar/hydrophobic/ionic (D-PHI) polyurethane porous scaffold while maintaining its mechanical integrity in order to allow for the transfer of mechanical stimulus to vascular smooth muscle cells (VSMCs) seeded onto the scaffold. The effect of varying porogen (sodium bicarbonate (salt) and polyethylene glycol (PEG)) composition and concentration on the mechanical properties, degree of swelling and porosity of the scaffolds was investigated. It was found that the use of 10 wt.% PEG and 65 wt.% salt in scaffold fabrication (D-PHI-75T) resulted in micropore (1–5 μm) formation, a high porosity (79 ± 3%) and mechanical properties (elastic modulus = 0.16 ± 0.03 MPa, elongation-at-yield = 31 ± 5% and tensile strength = 0.04 ± 0.01 MPa) required to withstand the physiologically relevant mechanical strain experienced by VMSCs in vivo. This study also investigated the influence of cyclic mechanical strain (CMS) on select molecular markers of A10 VSMCs when seeded into the optimized D-PHI scaffold. To study the interaction of A10 cells with the optimized D-PHI-75T scaffold in the presence of uniaxial strain (10%, 1 Hz), a CMS bioreactor was designed and constructed. Molecular marker studies showed a statistical increase in DNA mass and calponin expression after 3 and 7 days of CMS when compared to static samples, indicating that the translation of mechanical loading from the novel polyurethane elastomeric scaffold onto VSMCs will be important to consider with regard to modulating cell phenotype.     

Incorporation of bioactive polyvinylpyrrolidone–iodine within bilayered collagen scaffolds enhances the differentiation and subchondral osteogenesis of mesenchymal stem cells

Polyvinylpyrrolidone–iodine (Povidone-iodine, PVP-I) is widely used as an antiseptic agent for lavation during joint surgery; however, the biological effects of PVP–I on cells from joint tissue are unknown. This study examined the biocompatibility and biological effects of PVP–I on cells from joint tissue, with the aim of optimizing cell-scaffold based joint repair. Cells from joint tissue, including cartilage derived progenitor cells (CPC), subchondral bone derived osteoblast and bone marrow derived mesenchymal stem cells (BM-MSC) were isolated. The concentration-dependent effects of PVP–I on cell proliferation, migration and differentiation were evaluated. Additionally, the efficacy and mechanism of a PVP–I loaded bilayer collagen scaffold for osteochondral defect repair was investigated in a rabbit model. A micromolar concentration of PVP–I was found not to affect cell proliferation, CPC migration or extracellular matrix production. Interestingly, micromolar concentrations of PVP–I promote osteogenic differentiation of BM-MSC, as evidenced by up-regulation of RUNX2 and Osteocalcin gene expression, as well as increased mineralization on the three-dimensional scaffold. PVP–I treatment of collagen scaffolds significantly increased fibronectin binding onto the scaffold surface and collagen type I protein synthesis of cultured BM-MSC. Implantation of PVP–I treated collagen scaffolds into rabbit osteochondral defect significantly enhanced subchondral bone regeneration at 6 weeks post-surgery compared with the scaffold alone (subchondral bone histological score of 8.80 ± 1.64 vs. 3.8 ± 2.19, p < 0.05). The biocompatibility and pro-osteogenic activity of PVP–I on the cells from joint tissue and the enhanced subchondral bone formation in PVP–I treated scaffolds would thus indicate the potential of PVP–I for osteochondral defect repair.     

Mesoporous bioactive scaffolds prepared with cerium-, gallium- and zinc-containing glasses

Mesoporous bioactive glass scaffolds (MBG_Scs), based on 80% SiO₂–15% CaO–5% P₂O₅ (in mol.%) mesoporous sol–gel glasses substituted with Ce₂O₃, Ga₂O₃ (both 0.2% or 1.0%) and ZnO (0.4% or 2.0%), were synthesized by combination of evaporation-induced self-assembly and rapid prototyping techniques. Cerium, gallium and zinc trace elements were selected because of their inherent beneficial biological properties. Fabricated scaffolds were characterized and compared with unsubstituted scaffold (B_Sc). All of them contained well interconnected ultralarge pores (pores >400 μm) ideal for vascular ingrowth and proliferation of cells. Macropores of size 100–400 μm were present inside the scaffolds. In addition, low-angle X-ray diffraction showed that B_Sc and scaffolds with substituent contents up to 0.4% exhibited ordered mesoporosity useful for hosting molecules with biological activity. The textural properties of B_Sc were a surface area of 398 m² g^?1, a pore diameter of 4.3 nm and a pore volume of 0.43 cm³ g^?1. A slight decrease in surface area and pore volume was observed upon substitution with no distinct effect on pore diameter. In addition, all the MBG_Scs except 2.0% ZnO_Sc showed quite quick in vitro bioactive response. Hence, the present study is a positive addition to ongoing research into preparing bone tissue engineering scaffolds from bioceramics containing elements of therapeutic significance.     

Microporous bacterial cellulose as a potential scaffold for bone regeneration

Nanoporous cellulose biosynthesized by bacteria is an attractive biomaterial scaffold for tissue engineering due to its biocompatibility and good mechanical properties. However, for bone applications a microscopic pore structure is needed to facilitate osteoblast ingrowth and formation of a mineralized tissue. Therefore, in this study microporous bacterial cellulose (BC) scaffolds were prepared by incorporating 300–500 μm paraffin wax microspheres into the fermentation process. The paraffin wax microspheres were subsequently removed, and scanning electron microscopy confirmed a microporous surface of the scaffolds while Fourier transform infrared spectroscopy verified the elimination of paraffin and tensile measurements showed a Young’s modulus of approximately 1.6 MPa. Microporous BC and nanoporous (control) BC scaffolds were seeded with MC3T3-E1 osteoprogenitor cells, and examined by confocal microscopy and histology for cell distribution and mineral deposition. Cells clustered within the pores of microporous BC, and formed denser mineral deposits than cells grown on control BC surfaces. This work shows that microporous BC is a promising biomaterial for bone tissue engineering applications.     

Fabrication of porous polysaccharide-based scaffolds using a combined freeze-drying/cross-linking process

Biocompatible three-dimensional (3-D) porous scaffolds are of great interest for tissue engineering applications. We here present a novel combined freeze-drying/cross-linking process to prepare porous polysaccharide-based scaffolds. This process does not require an organic solvent or porogen agent. We unexpectedly found that cross-linking of biomacromolecules such as pullulan and dextran with sodium trimetaphosphate could be performed during freeze-drying. We have demonstrated that the freeze-drying pressure modulates the degree of porosity. High freeze-drying pressure scaffolds presented pores with a mean diameter of 55 ± 4 μm and a porosity of 33 ± 12%, whereas low freeze-drying pressure scaffolds contained larger pores with a mean diameter of 243 ± 14 μm and a porosity of 68 ± 3%. Porous scaffolds of the desired shape could be easily obtained and were stable in culture medium for weeks. In vitro viable mesenchymal stem cells were found associated with porous scaffolds in higher proportions than with non-porous scaffolds. Moreover, cells penetrated deeper into scaffolds with larger pores. This novel combined freeze-drying/cross-linking processing of polysaccharides enabled the fabrication of biocompatible scaffolds with controlled porosity and architectures suitable for 3-D in vitro culture and biomedical applications.     

Electrospun microfiber meshes of silicon-doped vaterite/poly(lactic acid) hybrid for guided bone regeneration

Silicon-releasable microfiber meshes consisting of silicon-doped vaterite (SiV) particles and poly(lactic acid) (PLA) hybrids were prepared by electrospinning. Due to their flexibility and porosity they formed ideal membranes or scaffolds for guided bone regeneration. In addition, a trace amount of silicon species has been reported to stimulate osteogenic cells to mineralize and enhance bone formation. We propose a new method of preparation of silicon-releasing microfiber meshes by electrospinning. Their structure and hydroxyapatite (HA)-forming abilities in simulated body fluid were examined. In addition, we studied their stimulatory effects on osteoblast-like cells in vitro and bone-forming ability in vivo, with a special emphasis on their ability to release silicon. The meshes consisted of a hybrid of carboxy groups in PLA and amino groups in siloxane, derived from aminopropyltriethoxysilane or calcium ions on the SiV surface. This hybrid exhibited an enhanced ability to form HA. The meshes coated with HA released 0.2–0.7 mg l^?1 silicon species into the culture medium over 7 days. Enhanced proliferation of osteoblast-like cells was observed using the meshes and new bone formed on the meshes when implanted into the calvaria of rabbits. These meshes, therefore, provide an excellent substrate for bone regeneration and exhibit enhanced bone-forming ability under both in vitro and in vivo conditions.     

Density–property relationships in collagen–glycosaminoglycan scaffolds

Collagen–glycosaminoglycan scaffolds for the regeneration of skin have previously been fabricated by freeze-drying a slurry containing a co-precipitate of collagen and glycosaminoglycan. The mechanical properties of the scaffold are low (e.g. the dry compressive Young’s modulus is roughly 30 kPa and the dry compressive strength is roughly 5 kPa). There is interest in using these scaffolds for tendon and ligament regeneration where there is a need for improved mechanical properties. Previous attempts to increase the mechanical properties of the scaffold by increasing the solid volume fraction of the scaffolds were limited by the increasing viscosity of the slurry, making it more difficult to mix and giving inhomogeneous scaffolds. Our recent work on mineralized collagen–glycosaminoglycan scaffolds used a vacuum filtration technique to increase the volume fraction of solids in the slurry, thereby increasing the density and mechanical properties of the scaffolds. In this work, we used this technique to fabricate collagen–glycosaminoglycan scaffolds with dry densities between 0.0076 and 0.0311 g cm^?3 and pore sizes between 250 and 350 μm, values appropriate for soft tissue growth. The compressive Young’s modulus and strength in the dry state increased from 32 to 127 kPa and from 5 to 19 kPa, respectively, with increasing density. The tensile Young’s modulus in the dry state increased from 295 to 3.1 MPa with increasing density. Finally, we showed that the attachment of cells onto the scaffold was directly proportional to the specific surface area of the scaffold, which defines the total internal surface area per volume of scaffold.