Biomimetic calcium phosphate coatings on Polyactive 1000/70/30

Biomineralization of poly-l-lactide spongy bone scaffolds obtained by freeze-extraction method

Implants in the form of polymer scaffolds are commonly used to regenerate bone tissue after traumas or tooth extractions. However, few implant formation methods enable building polymer scaffolds allowing to reconstruct larger bone losses without immune response. Spacious, porous poly-l-lactide implants with considerable volume were obtained using the phase inversion method with the freeze-extraction variant. The calcium phosphate (CaP) coating was deposited on implant surfaces with the biomimetic method to improve the implant's osteoconductivity. The substitues morphology was characterized-porosity, size and shape of pores; mechanical properties, mass absorbability of implants before and after mineralization. The characteristics were provided with scanning electron microscopy (SEM), static compression test and hydrostatic weighing, respectively. The presence of CaPs in the entire volume of the implant was confirmed with SEM and infrared spectroscopy with Fourier transform (FTIR). The biocompatibility of scaffolds was confirmed with in vitro quantitative test and microscopic observations. The obtained results show that the implants can be used in tissue engineering as a vehicle of platelet-rich plasma to regenerate critical spongy bone losses.

Influence of in vitro differentiation status on the in vivo bone regeneration of cell/chitosan microspheres using a rat cranial defect model

The aim of this study was to investigate the influence of the in vitro osteogenic differentiation status on the in vivo bone regeneration of cell/chitosan microspheres qualitatively and quantitatively. To this end, rat bone-marrow-derived mesenchymal stromal cells (BMSCs) were seeded onto apatite-coated chitosan microspheres. The constructs were osteogenically differentiated for 0, 7, 14, and 21 days followed by calvarial defect implantation in vivo for up to 8 weeks. In vitro studies showed that BMSCs in the constructs proliferated from day 0 to day 7. The activity and gene expression of alkaline phosphatise increased from day 0 to day 14 and then decreased. The gene expression of collagen type I and osteocalcin peaked at day 21. In vivo, constructs retrieved from day 0 group were filled with fibrous tissues and capillaries, but no bone formation was observed. Constructs retrieved from day 7 and day 21 groups showed progressive bone formation, whereas those retrieved from day 14 group had the highest percentage of bone formation. These data suggested that to generate a substantial amount of bone in vivo, not only the in vitro osteogenic differentiation was necessary, but also the period of pre-differentiation was important for the cell-scaffold constructs. The period of pre-differentiation for 14 days was found to be the most suitable for chitosan microspheres.

Nanoparticles Embedded in Amphiphilic Membranes for Carbon Dioxide Separation and Dehumidification

Polymers containing ethylene oxide (EO) groups have gained significant interest as the EO groups have favorable interactions with polar molecules such as H₂ O, quadrupolar molecules such as CO₂ , and metal ions. However, the main challenges of poly(ethylene oxide) (PEO) membranes are their weak mechanical properties and high crystallinity nature. The amphiphilic copolymer made from PEO terephthalate and poly(butylene terephthalate) (PEOT/PBT) comprises both hydrophilic and hydrophobic segments. The hydrophilic PEOT segment is thermosensitive, which facilities gas transports whereas the hydrophobic PBT segment is rigid, which provides mechanical robustness. This work demonstrates a new strategy to design amphiphilic mixed matrix membranes (MMMs) by incorporating zeolitic imidazolate framework, ZIF-71, into the PEOT/PBT copolymer. The resultant membrane shows an enhanced CO₂ permeability with an ideal CO₂ /N₂ selectivity surpassing the original PEOT/PBT and Robeson's Upper bound line. The nanoparticles-embedded amphiphilic membranes exhibit characteristics of high transparency and mechanical robustness. Mechanically strong composite hollow fiber membranes consisting of PEOT/PBT/ZIF-71 as the selective layer were also prepared. The resultant hollow fibers possess an excellent CO₂ permeance of 131 GPU (gas permeation units), CO₂ /N₂ selectivity of 52.6, H₂ O permeance of 9300 GPU and H₂ O/N₂ selectivity of 3700, showing great potential for industrial CO₂ capture and dehumidification.

Colloidal Gold Nanoclusters Spiked Silica Fillers in Mixed Matrix Coatings: Simultaneous Detection and Inhibition of Healthcare-Associated Infections

Healthcare-associated infections (HAIs) are the infections that patients get while receiving medical treatment in a medical facility with bacterial HAIs being the most common. Silver and gold nanoparticles (NPs) have been successfully employed as antibacterial motifs; however, NPs leaching in addition to poor dispersion and overall reproducibility are major hurdles to further product development. In this study, the authors design and fabricate a smart antibacterial mixed-matrix membrane coating comprising colloidal lysozyme-templated gold nanoclusters as nanofillers in poly(ethylene oxide)/poly(butylene terephthalate) amphiphilic polymer matrix. Mesoporous silica nanoparticles-lysozyme functionalized gold nanoclusters disperse homogenously within the polymer matrix with no phase separation and zero NPs leaching. This mixed-matrix coating can successfully sense and inhibit bacterial contamination via a controlled release mechanism that is only triggered by bacteria. The system is coated on a common radiographic dental imaging device (photostimulable phosphor plate) that is prone to oral bacteria contamination. Variation and eventually disappearance of the red fluorescence surface under UV light signals bacterial infection. Kanamycin, an antimicrobial agent, is controllably released to instantly inhibit bacterial growth. Interestingly, the quality of the images obtained with these coated surfaces is the same as uncoated surfaces and thus the safe application of such smart coatings can be expanded to include other medical devices without compromising their utility.

Interfacing polymeric scaffolds with primary pancreatic ductal adenocarcinoma cells to develop 3D cancer models

We analyzed the interactions between human primary cells from pancreatic ductal adenocarcinoma (PDAC) and polymeric scaffolds to develop 3D cancer models useful for mimicking the biology of this tumor. Three scaffold types based on two biocompatible polymeric formulations, such as poly(vinyl alcohol)/gelatin (PVA/G) mixture and poly(ethylene oxide terephthalate)/poly(butylene terephthalate) (PEOT/PBT) copolymer, were obtained via different techniques, namely, emulsion and freeze-drying, compression molding followed by salt leaching, and electrospinning. In this way, primary PDAC cells interfaced with different pore topographies, such as sponge-like pores of different shape and size or nanofiber interspaces. The aim of this study was to investigate the influence played by the scaffold architecture over cancerous cell growth and function. In all scaffolds, primary PDAC cells showed good viability and synthesized tumor-specific metalloproteinases (MMPs) such as MMP-2, and MMP-9. However, only sponge-like pores, obtained via emulsion-based and salt leaching-based techniques allowed for an organized cellular aggregation very similar to the native PDAC morphological structure. Differently, these cell clusters were not observed on PEOT/PBT electrospun scaffolds. MMP-2 and MMP-9, as active enzymes, resulted to be increased in PVA/G and PEOT/PBT sponges, respectively. These findings suggested that spongy scaffolds supported the generation of pancreatic tumor models with enhanced aggressiveness. In conclusion, primary PDAC cells showed diverse behaviors while interacting with different scaffold types that can be potentially exploited to create stage-specific pancreatic cancer models likely to provide new knowledge on the modulation and drug susceptibility of MMPs.

Adipose-derived stem cells and BMP-2 delivery in chitosan-based 3D constructs to enhance bone regeneration in a rat mandibular defect model

Reconstructing segmental mandiblular defects remains a challenge in the clinic. Tissue engineering strategies provide an alternative option to resolve this problem. The objective of the present study was to determine the effects of adipose-derived stem cells (ASCs) and bone morphogenetic proteins-2 (BMP-2) in three-dimensional (3D) scaffolds on mandibular repair in a small animal model. Noggin expression levels in ASCs were downregulated by a lentiviral short hairpin RNA strategy to enhance ASC osteogenesis (ASCs(Nog-)). Chitosan (CH) and chondroitin sulfate (CS), natural polysaccharides, were fabricated into 3D porous scaffolds, which were further modified with apatite coatings for enhanced cellular responses and efficient delivery of BMP-2. The efficacy of 3D apatite-coated CH/CS scaffolds supplemented with ASCs(Nog-) and BMP-2 were evaluated in a rat critical-sized mandibular defect model. After 8 weeks postimplantation, the scaffolds treated with ASCs(Nog-) and BMP-2 significantly promoted rat mandibular regeneration as demonstrated by micro-computerized tomography, histology, and immunohistochemistry, compared with the groups treated with ASCs(Nog-) or BMP-2 alone. These results suggest that our combinatorial strategy of ASCs(Nog-)+BMP-2 in 3D apatite microenvironments can significantly promote mandibular regeneration, and these may provide a potential tissue engineering approach to repair large bony defects.

The use of physiological solutions or media in calcium phosphate synthesis and processing

This review examined the literature to spot uses, if any, of physiological solutions/media for the in situ synthesis of calcium phosphates (CaP) under processing conditions (i.e. temperature, pH, concentration of inorganic ions present in media) mimicking those prevalent in the human hard tissue environments. There happens to be a variety of aqueous solutions or media developed for different purposes; sometimes they have been named as physiological saline, isotonic solution, cell culture solution, metastable CaP solution, supersaturated calcification solution, simulated body fluid or even dialysate solution (for dialysis patients). Most of the time such solutions were not used as the aqueous medium to perform the biomimetic synthesis of calcium phosphates, and their use was usually limited to the in vitro testing of synthetic biomaterials. This review illustrates that only a limited number of research studies used physiological solutions or media such as Earle's balanced salt solution, Bachra et al. solutions or Tris-buffered simulated body fluid solution containing 27mM HCO3(-) for synthesizing CaP, and these studies have consistently reported the formation of X-ray-amorphous CaP nanopowders instead of Ap-CaP or stoichiometric hydroxyapatite (HA, Ca10(PO4)6(OH)2) at 37°C and pH 7.4. By relying on the published articles, this review highlights the significance of the use of aqueous solutions containing 0.8-1.5 mMMg(2+), 22-27mM HCO3(-), 142-145mM Na(+), 5-5.8mM K(+), 103-133mM Cl(-), 1.8-3.75mM Ca(2+), and 0.8-1.67mM HPO4(2-), which essentially mimic the composition and the overall ionic strength of the human extracellular fluid (ECF), in forming the nanospheres of X-ray-amorphous CaP.

Inorganic coatings for optimized non-viral transfection of stem cells

“Biomimetic” approaches for heterogeneous growth of inorganic coatings have become particularly widespread in biomedical applications, where calcium phosphate (CaP) mineral coatings are used to improve biomedical implants. Changes in coating properties can influence the effects of mineral coatings on adjacent cells, but to date it has not been practical to systematically vary inorganic coating properties to optimize specific cell behaviors. Here, we present an approach to grow CaP mineral coatings in an enhanced throughput format to identify unprecedented capabilities in non-viral gene delivery. Subtle changes in coating properties resulted in widely variable transfection, and optimized coatings led to greater than 10-fold increases in transgene expression by multiple target cell types when compared to standard techniques. The enhanced transfection observed here is substrate-mediated, and related to the characteristics of the local environment near the surface of dissolving mineral coatings. These findings may be particularly translatable to medical device applications.

Plug and play: combining materials and technologies to improve bone regenerative strategies

Despite recent advances in the development of biomaterials intended to replace natural bone grafts for the regeneration of large, clinically relevant defects, most synthetic solutions that are currently applied in the clinic are still inferior to natural bone grafts with regard to regenerative potential and are limited to non-weight-bearing applications. From a materials science perspective, we always face the conundrum of the preservation of bioactivity of calcium phosphate ceramics in spite of better mechanical and handling properties and processability of polymers. Composites have long been investigated as a method to marry these critical properties for the successful regeneration of bone and, indeed, have shown a significant improvement when used in combination with cells or growth factors. However, when looking at this approach from a clinical and regulatory perspective, the use of cells or biologicals prolongs the path of new treatments from the bench to the bedside. Applying 'smart' synthetic materials alone poses the fascinating challenge of instructing tissue regeneration in situ, thereby tremendously facilitating clinical translation. In the journey to make this possible, and with the aim of adding up the advantages of different biomaterials, combinations of fabrication technologies arise as a new strategy for generating instructive three-dimensional (3D) constructs for bone regeneration. Here we provide a review of recent technologies and approaches to create such constructs and give our perspective on how combinations of technologies and materials can help in obtaining more functional bone regeneration.

Microstructure and chemistry affects apatite nucleation on calcium phosphate bone graft substitutes

The bioactivity of calcium phosphate bone grafts of varying chemistry and strut-porosity was compared by determining the rate of formation of hydroxycarbonate apatite crystals on the material surface after being soaked in simulated body fluid for up to 30 days. Three groups of silicate-substituted hydroxyapatite material were tested, with each group comprising a different quantity of strut-porosity (23, 32, and 46 % volume). A commercially available porous β-tricalcium phosphate bone graft substitute was tested for comparison. Results indicate that strut-porosity of a material affects the potential for formation of a precursor to bone-like apatite and further confirms previous findings that β-tricalcium phosphate is less bioactive than hydroxyapatite.

The design and features of apatite-coated chitosan microspheres as injectable scaffold for bone tissue engineering

In this paper we developed two types of chitosan-based microspheres with and without biomimetic apatite coatings and compared their potential as injectable scaffolds for bone regeneration. The microspheres were obtained by emulsion cross-linking (E0) and coacervate precipitation (C0), respectively. They were then biomimetically coated with apatite to become E1 and C1 microspheres. The physicochemical properties and biocompatibility of the microspheres were characterized. Both E0 and C0 microspheres presented favorable ranges of diameter, density and Rockwell hardness. However, there were differences in the degree of cross-linking, shape, morphology, degradation rate, swelling rate, pH value after PBS immersion and the biocompatibility between E0 and C0. The apatite coating was successfully prepared for both C0 and E0, which enhanced the attachment, proliferation and differentiation of MC3T3-E1 cells. In conclusion, our results suggest the feasibility of using chitosan microspheres as a potential injectable scaffold. Both the preparation method and the biomimetic apatite coating contribute to their biological properties.

Combining technologies to create bioactive hybrid scaffolds for bone tissue engineering

Combining technologies to engineer scaffolds that can offer physical and chemical cues to cells is an attractive approach in tissue engineering and regenerative medicine. In this study, we have fabricated polymer-ceramic hybrid scaffolds for bone regeneration by combining rapid prototyping (RP), electrospinning (ESP) and a biomimetic coating method in order to provide mechanical support and a physico-chemical environment mimicking both the organic and inorganic phases of bone extracellular matrix (ECM). Poly(ethylene oxide terephthalate)-poly(buthylene terephthalate) (PEOT/PBT) block copolymer was used to produce three dimensional scaffolds by combining 3D fiber (3DF) deposition, and ESP, and these constructs were then coated with a Ca-P layer in a simulated physiological solution. Scaffold morphology and composition were studied using scanning electron microscopy (SEM) coupled to energy dispersive X-ray analyzer (EDX) and Fourier Tranform Infrared Spectroscopy (FTIR). Bone marrow derived human mesenchymal stromal cells (hMSCs) were cultured on coated and uncoated 3DF and 3DF + ESP scaffolds for up to 21 d in basic and mineralization medium and cell attachment, proliferation, and expression of genes related to osteogenesis were assessed. Cells attached, proliferated and secreted ECM on all the scaffolds. There were no significant differences in metabolic activity among the different groups on days 7 and 21. Coated 3DF scaffolds showed a significantly higher DNA amount in basic medium at 21 d compared with the coated 3DF + ESP scaffolds, whereas in mineralization medium, the presence of coating in 3DF+ESP scaffolds led to a significant decrease in the amount of DNA. An effect of combining different scaffolding technologies and material types on expression of a number of osteogenic markers (cbfa1, BMP-2, OP, OC and ON) was observed, suggesting the potential use of this approach in bone tissue engineering.

Biomimetic calcium phosphate coatings on recombinant spider silk fibres

Calcium phosphate ceramic coatings, applied on surfaces of metallic and polymeric biomaterials, can improve their performance in bone repair and regeneration. Spider silk is biocompatible, strong and elastic, and hence an attractive biomaterial for applications in connective tissue repair. Recently, artificial spider silk, with mechanical and structural characteristics similar to those of native spider silk, has been produced from recombinant minispidroins. In the present study, supersaturated simulated body fluid was used to deposit calcium phosphate coatings on recombinant spider silk fibres. The mineralization process was followed in time using scanning electron microscopy equipped with an energy dispersive x-ray (EDX) detector and Raman spectroscope. Focused ion beam technology was used to produce a cross section of a coated fibre, which was further analysed by EDX. Preliminary in vitro experiments using a culture of bone marrow-derived human mesenchymal stem cells (hMSCs) on coated fibres were also performed. This study showed that recombinant spider silk fibres were successfully coated with a homogeneous and thick crystalline calcium phosphate layer. In the course of the mineralization process from modified simulated body fluid, sodium chloride crystals were first deposited on the silk surface, followed by the deposition of a calcium phosphate layer. The coated silk fibres supported the attachment and growth of hMSCs.

Biomimetic coating of organic polymers with a protein-functionalized layer of calcium phosphate: the surface properties of the carrier influence neither the coating characteristics nor the incorporation mechanism or release kinetics of the protein

Polymers that are used in clinical practice as bone-defect-filling materials possess many essential qualities, such as moldability, mechanical strength and biodegradability, but they are neither osteoconductive nor osteoinductive. Osteoconductivity can be conferred by coating the material with a layer of calcium phosphate, which can be rendered osteoinductive by functionalizing it with an osteogenic agent. We wished to ascertain whether the morphological and physicochemical characteristics of unfunctionalized and bovine-serum-albumin (BSA)-functionalized calcium-phosphate coatings were influenced by the surface properties of polymeric carriers. The release kinetics of the protein were also investigated. Two sponge-like materials (Helistat® and Polyactive®) and two fibrous ones (Ethisorb™ and poly[lactic-co-glycolic acid]) were tested. The coating characteristics were evaluated using state-of-the-art methodologies. The release kinetics of BSA were monitored spectrophotometrically. The characteristics of the amorphous and the crystalline phases of the coatings were not influenced by either the surface chemistry or the surface geometry of the underlying polymer. The mechanism whereby BSA was incorporated into the crystalline layer and the rate of release of the truly incorporated depot were likewise unaffected by the nature of the polymeric carrier. Our biomimetic coating technique could be applied to either spongy or fibrous bone-defect-filling organic polymers, with a view to rendering them osteoconductive and osteoinductive.

Rapid prototyping of anatomically shaped, tissue-engineered implants for restoring congruent articulating surfaces in small joints

BACKGROUND

Preliminary studies investigated advanced scaffold design and tissue engineering approaches towards restoring congruent articulating surfaces in small joints.

MATERIALS AND METHODS

Anatomical femoral and tibial cartilage constructs, fabricated by three-dimensional fibre deposition (3DF) or compression moulding/particulate leaching (CM), were evaluated in vitro and in vivo in an autologous rabbit model. Effects of scaffold pore architecture on rabbit chondrocyte differentiation and mechanical properties were evaluated following in vitro culture and subcutaneous implantation in nude mice. After femoral and tibial osteotomy and autologous implantation of tissue-engineered constructs in rabbit knee joints, implant fixation and joint articulation were evaluated.

RESULTS

Rapid prototyping of 3DF architectures with 100% interconnecting pores promoted homogeneous distribution of viable cells, glycosaminoglycan (GAG) and collagen type II; significantly greater GAG content and differentiation capacity (GAG/DNA) in vitro compared to CM architectures; and higher mechanical equilibrium modulus and dynamic stiffness (at 0.1 Hz). Six weeks after implantation, femoral and tibial constructs had integrated with rabbit bone and knee flexion/extension and partial load bearing were regained. Histology demonstrated articulating surfaces between femoral and tibial constructs for CM and 3DF architectures; however, repair tissue appeared fibrocartilage-like and did not resemble implanted cartilage.

CONCLUSIONS

Anatomically shaped, tissue-engineered constructs with designed mechanical properties and internal pore architectures may offer alternatives for reconstruction or restoration of congruent articulating surfaces in small joints.

Encapsulation and release of a hydrophobic drug from hydroxyapatite coated liposomes

Hydroxyapatite (HA) coated liposomes (HACL) have been successfully manufactured and filled with a model hydrophobic (lipophilic) drug, indomethacin (IMC). These HACL particles have been characterized in terms of particle size and zeta-potential. The liposomes are formed from 1,2-dimyristoyl-sn-glycero-3-phosphate (DMPA) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). Altering their relative proportions caused the zeta-potential to change from -38.8 to -67.0 mV, with a concomitant change in phase transition temperature from 36.4 to 53.3 degrees C. These changes also affect the drug loading efficiency. The release profiles of IMC have been measured. HA coating of the liposome reduces the release rate of IMC over uncoated liposomes. Under the present experimental conditions 70% of the drug is released after approximately 5h from the liposome, but coating with HA changes this time to over 20 h. Perhaps most importantly, it has been observed that for uncoated liposomes, IMC is released at a greater rate at pH=7.4 than at pH=4. However, coating with HA reduced the rate at pH=7.4 compared to pH=4. This behaviour arises because IMC is more soluble under basic conditions, but HA is more soluble under acidic conditions. This behaviour shows that it is now possible to have environmental control over the release of drugs from HA-coated liposomes.

Improved Neovascularization of PEGT/PBT Copolymer Matrices in Response to Surface Modification by Biomimetic Coating

PEGT/PBT (polyethylene glycol terephthalate/polybutylene terephthalate) copolymer matrices with three different surface coatings [calcium-phosphate (Ca-P), collagen, and gas plasma] were placed into dorsal skinfold chambers of 24 balb/c mice. Untreated PEGT/PBT matrices served as the controls. The basal surfaces of the implants directly contacted the striated skin muscle. Neovascularization of the implants was analyzed by intravital fluorescence microscopy. Microcirculatory observations were performed in the surrounding skin muscle, at the border zone of the implant, and in the center of the implant. The functional vessel density (FVD; mm/mm2), as the length of perfused microvessels per observation area, was measured by computer-assisted analysis. The FVD served as the parameter of neovascularization. At the end of the protocol, histological observation of hematoxylin/eosin-standard-stained sections was performed by light microscopy. The FVD in the center of the implant on day 8 was only observed in gas-plasma-coated (8.8 +/- 10.2 mm/mm2) and Ca-P-coated implants (0.8 +/- 2.0 mm/mm2). None of the other groups showed perfused microvessels in the center of the implant on day 8 (p < 0.05). The FVD values in the center of the gas-plasma-coated and the Ca-P-coated implants were 20.7 +/- 8.2 and 19.2 +/- 15.5 mm/mm2 as compared with 7.1 +/- 17.4 and 7.7 +/- 5.9 mm/mm2 for collagen-coated and untreated implants on day 16. The histological examination confirmed the profound microvascular ingrowth into the matrix pores of the gas-plasma-treated and the Ca-P-coated copolymer matrices in the center of the implants. The study showed that the ingrowth of microvessels into PEGT/PBT matrices can be accelerated by Ca-P coating and gas plasma treatment in the dorsal skinfold chamber in mice.

Transfer of apatite coating from porogens to scaffolds: Uniform apatite coating within porous poly(DL-lactic-co-glycolic acid) scaffoldin vitro

Strategies to bone tissue engineering have focused on the use of synthetic or natural degradable materials as scaffolds for cell transplantation to guide bone regeneration. Biocompatibility, biodegradability, biomechanical integrity, and osteoconductivity are important requirements for the scaffold materials. This study explored a new approach of apatite coating to enhance the osteoconductivity of a synthetic degradable poly(DL-lactic-co-glycolic acid) (PLGA) scaffold. The new approach was developed to ensure a relatively uniform apatite coating on the interior pore surfaces deep inside a scaffold, even for a relatively thick scaffold with small pores. Apatite was first coated on the surface of paraffin spheres of the desirable sizes. The paraffin spheres were then molded to form a foam. PLGA/pyridine solution was cast into the interspaces among the paraffin spheres. After the paraffin spheres were dissolved and removed by cyclohexane, PLGA scaffold with controlled pore size, good interconnectivity and high porosity was obtained with apatite left on the pore surface uniformly throughout the whole scaffold. The scaffold and apatite coating were characterized using thermogravimetry analysis, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffractometry.

3D fiber-deposited scaffolds for tissue engineering: influence of pores geometry and architecture on dynamic mechanical properties

One of the main issues in tissue engineering is the fabrication of scaffolds that closely mimic the biomechanical properties of the tissues to be regenerated. Conventional fabrication techniques are not sufficiently suitable to control scaffold structure to modulate mechanical properties. Within novel scaffold fabrication processes 3D fiber deposition (3DF) showed great potential for tissue engineering applications because of the precision in making reproducible 3D scaffolds, characterized by 100% interconnected pores with different shapes and sizes. Evidently, these features also affect mechanical properties. Therefore, in this study we considered the influence of different structures on dynamic mechanical properties of 3DF scaffolds. Pores were varied in size and shape, by changing fibre diameter, spacing and orientation, and layer thickness. With increasing porosity, dynamic mechanical analysis (DMA) revealed a decrease in elastic properties such as dynamic stiffness and equilibrium modulus, and an increase of the viscous parameters like damping factor and creep unrecovered strain. Furthermore, the Poisson's ratio was measured, and the shear modulus computed from it. Scaffolds showed an adaptable degree of compressibility between sponges and incompressible materials. As comparison, bovine cartilage was tested and its properties fell in the fabricated scaffolds range. This investigation showed that viscoelastic properties of 3DF scaffolds could be modulated to accomplish mechanical requirements for tailored tissue engineered applications.

Fabrication of hybrid nanocapsules by calcium phosphate mineralization of shell cross-linked polymer micelles and nanocages

Self-assembled shell cross-linked poly(acrylic acid-b-isoprene) (PAA78-b-PI97) micelles or cross-linked PAA nanocages in aqueous solution were used as templates for the preparation of novel polymer-inorganic nanocapsules. The hybrid nanostructures were typically 50-70 nm in diameter and consisted of spherical polymer nanoparticles or nanocages enclosed within a continuous 10-20 nm thick surface layer of amorphous calcium phosphate. Nucleation of calcium phosphate specifically in association with the polymer nanoparticles was facilitated by low supersaturation levels and by sequestration of Ca2+ ions within the carboxylate-rich PAA domains prior to addition of HPO4(2-). Modifications in ionic concentrations were used to control the calcium phosphate surface layer thickness and prepare mineralized cross-linked PAA-b-PI micelles with variable shell permeability. The permeability of beta-carotene into the hydrophobic PI core of mineralized shell cross-linked PAA-b-PI micelles was reduced by approximately 50 or 100% respectively for hybrid nanostructures enclosed within 10 or 20 nm thick calcium phosphate layers. Our results suggest that calcium phosphate-polymer cross-linked nanocapsules could have potential applications as pH-responsive biocompatible hybrid nanostructures for use in applications such as drug delivery, bioimaging, and therapeutics.

The effect of PEGT/PBT scaffold architecture on the composition of tissue engineered cartilage

A highly interconnecting and accessible pore network has been suggested as one of a number of prerequisites in the design of scaffolds for tissue engineering. In the present study, two processing techniques, compression-molding/particulate-leaching (CM), and 3D fiber deposition (3DF), were used to develop porous scaffolds from biodegradable poly(ethylene glycol)-terephthalate/poly(butylene terephthalate) (PEGT/PBT) co-polymers with varying pore architectures. Three-dimensional micro-computed tomography (microCT) was used to characterize scaffold architectures and scaffolds were seeded with articular chondrocytes to evaluate tissue formation. Scaffold porosity ranged between 75% and 80%. Average pore size of tortuous CM scaffolds (182 microm) was lower than those of organized 3DF scaffolds (525 microm). The weight ratio of glycosaminoglycans (GAG)/DNA, as a measure of cartilage-like tissue formation, did not change after 14 days of culture whereas, following subcutaneous implantation, GAG/DNA increased significantly and was significantly higher in 3DF constructs than in CM constructs, whilst collagen type II was present within both constructs. In conclusion, 3DF PEGT/PBT scaffolds create an environment in vivo that enhances cartilaginous matrix deposition and hold particular promise for treatment of articular cartilage defects.

The effect of PEGT/PBT scaffold architecture on oxygen gradients in tissue engineered cartilaginous constructs

Repair of articular cartilage defects using tissue engineered constructs composed of a scaffold and cultured autologous cells holds promise for future treatments. However, nutrient limitation (e.g. oxygen) has been suggested as a cause of the onset of chondrogenesis solely within the peripheral boundaries of larger constructs. In the present study, oxygen gradients were evaluated by microelectrode measurements in two porous polyethylene glycol terephthalate/polybutylene terephthalate (PEGT/PBT) scaffold architectures, a compression-molded and particle-leached sponge (CM) and a 3D-deposited fiber (3DF) scaffold. During the first 14 days in vitro, gradients intensified, after which a gradual decrease of the gradients was observed in vitro. In vivo, however, gradients changed instantly and became less pronounced. Although similar gradients were observed regardless of scaffold type, significantly more cells were present in the center of 3DF constructs after 2 weeks of in vivo culture. Our results stress the importance of a rationally designed scaffold for tissue-engineering applications. Organized structures, such as the 3DF PEGT/PBT polymer scaffolds, offer possibilities for regulation of nutrient supply and, therefore, hold promise for clinical approaches for cartilage repair.

Expansion of human nasal chondrocytes on macroporous microcarriers enhances redifferentiation

Articular cartilage has a limited capacity for self-repair. To overcome this problem, it is expected that functional cartilage replacements can be created from expanded chondrocytes seeded in biodegradable scaffolds. Expansion of chondrocytes in two-dimensional culture systems often results in dedifferentiation. This investigation focuses on the post-expansion phenotype of human nasal chondrocytes expanded on macroporous gelatin CultiSpher G microcarriers. Redifferentiation was evaluated in vitro via pellet cultures in three different culture media. Furthermore, the chondrogenic potential of expanded cells seeded in polyethylene glycol terephthalate/ polybuthylene terephthalate (PEGT/PBT) scaffolds, cultured for 14 days in vitro, and subsequently implanted subcutaneously in nude mice, was assessed. Chondrocytes remained viable during microcarrier culture and yielded doubling times (1.07+/-0.14 days) comparable to T-flask expansion (1.20+/-0.36 days). Safranin-O staining from pellet culture in different media demonstrated that production of GAG per cell was enhanced by microcarrier expansion. Chondrocyte-polymer constructs with cells expanded on microcarriers contained significantly more proteoglycans after subcutaneous implantation (288.5+/-29.2 microg) than those with T-flask-expanded cells (164.0+/-28.7 microg). Total collagen content was similar between the two groups. This study suggests that macroporous gelatin microcarriers are effective matrices for nasal chondrocyte expansion, while maintaining the ability of chondrocyte differentiation. Although the exact mechanism by which chondrocyte redifferentiation is induced through microcarrier expansion has not yet been elucidated, this technique shows promise for cartilage tissue engineering approaches.

Effect of wollastonite ceramics and bioactive glass on the formation of a bonelike apatite layer on a cobalt base alloy

A biomimetic method was used to promote a bioactive surface on a cobalt base alloy (ASTM F-75). The metallic substrates were alkali treated and some of the samples were subsequently heat treated. The treated samples were immersed in simulated body fluid (SBF) on granular particles of either bioactive glass or wollastonite. For comparative purposes, no bioactive system was used in some tests. Three different methods were used for the immersion of the samples in SBF: 1) 21 days in SBF, 2) 21 days in 1.5 SBF, and 3) 7 days in SBF followed by 14 days in 1.5 SBF (re-immersion method). A bonelike apatite layer was formed on all the samples placed on wollastonite and bioactive glass particles. The morphology of the apatite layer formed by using the re-immersion method and wollastonite closely resembled the existing bioactive systems. No apatite layer was observed on the samples treated without bioactive material and soaked for 21 days in SBF or 1.5 SBF, apart from the substrates treated by using the re-immersion method. The heat treatment delayed the apatite formation in all the cases studied.

Oxygen gradients in tissue-engineered Pegt/Pbt cartilaginous constructs: Measurement and modeling

The supply of oxygen within three-dimensional tissue-engineered (TE) cartilage polymer constructs is mainly by diffusion. Oxygen consumption by cells results in gradients in the oxygen concentration. The aims of this study were, firstly, to identify the gradients within TE cartilage polymer constructs and, secondly, to predict the profiles during in vitro culture. A glass microelectrode system was adapted and used to penetrate cartilage and TE cartilaginous constructs, yielding reproducible measurements with high spatial resolution. Cartilage polymer constructs were cultured for up to 41 days in vitro. Oxygen concentrations, as low as 2-5%, were measured within the center of these constructs. At the beginning of in vitro culture, the oxygen gradients were steeper in TE constructs in comparison to native tissue. Nevertheless, during the course of culture, oxygen concentrations approached the values measured in native tissue. A mathematical model was developed which yields oxygen profiles within cartilage explants and TE constructs. Model input parameters were assessed, including the diffusion coefficient of cartilage (2.2 x 10(-9)) + (0.4 x 10(-9) m(2) s(-1)), 70% of the diffusion coefficient of water and the diffusion coefficient of constructs (3.8 x 10(-10) m(2) s(-1)). The model confirmed that chondrocytes in polymer constructs cultured for 27 days have low oxygen requirements (0.8 x 10(-19) mol m(-3) s(-1)), even lower than chondrocytes in native cartilage. The ability to measure and predict local oxygen tensions offers new opportunities to obtain more insight in the relation between oxygen tension and chondrogenesis.

Bone growth in biomimetic apatite coated porous Polyactive 1000PEGT70PBT30 implants

We recently, developed a simple one-day one-step incubation method to obtain bone-like apatite coating on flexible and biodegradable Polyactive 1000PEGT70PBT30. The present study reports a preliminary biological evaluation on the coated polymer after implantation in rabbit femurs. The porous cylindrical implants were produced from a block fabricated by injection molding and salt leaching. This technique provided the block necessary mechanical integrity to make small cylinders (diameter 3.5 x 5 mm2) that were suitable for implantation in rabbits. The coating continuously covered the surface of the polymer, preserving the porous architecture of outer contour of the cylinders. Two defects with a diameter of 3.5 or 4 mm were drilled in the proximal and distal part of femur diaphysis. The implants were inserted as press-fit or undersized into the cortex as well as in the marrow cavity. The polymer swelled after implantation due to hydration, leading to a tight contact with the surrounding bone in both defects. The adherence of the coating on the polymer proved to be sufficient to endure a steam sterilization process as well as the 15% swelling of the polymer in vivo. The coated Polyactive 1000PEGT70PBT30 has a good osteoconductive property, as manifested by abundant bone growth into marrow cavity along the implant surface during 4-week implantation. A favorable bioactive effect of the coating with an intimate bone contact and extensive bone bonding with this polymer was qualitatively confirmed. Concerning the bone ingrowth into the porous implant in the defect of 4 mm diameter, only marginal bone formation was observed up to 8 weeks with a maximal penetration depth of about 1 mm. The pore interconnectivity is important not only for producing a coating inside the porous structure but also for bone ingrowth into this biodegradable material. This preliminary study provided promising evidence for a further study using a bigger animal model.