Fellowship programs in critical care medicine: 1990/1991

In vitro evaluation of porous poly(hydroxybutyrate-co-hydroxyvalerate)/akermanite composite scaffolds manufactured using selective laser sintering

Incorporation of a bioactive mineral filler in a biodegradable polyester scaffold is a promising strategy for scaffold assisted bone tissue engineering (TE). The current study evaluates the in vitro behavior of poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV)/Akermanite (AKM) composite scaffolds manufactured using selective laser sintering (SLS). Exposure of the mineral filler on the surface of the scaffold skeleton was evident from in vitro mineralization in PBS. PHBV scaffolds and solvent cast films served as control samples and all materials showed preferential adsorption of fibronectin compared to serum albumin as well as non-cytotoxic response in human osteoblasts (hOB) at 24 h. hOB culture for up to 21 days revealed that the metabolic activity in PHBV films and scaffolds was significantly higher than that of PHBV/AKM scaffolds within the first two weeks of incubation. Afterwards, the metabolic activity in PHBV/AKM scaffolds exceeded that of the control samples. Confocal imaging showed cell penetration into the porous scaffolds. Significantly higher ALP activity was observed in PHBV/AKM scaffolds at all time points in both basal and osteogenic media. Mineralization during cell culture was observed on all samples with PHBV/AKM scaffolds exhibiting distinctly different mineral morphology. This study has demonstrated that the bioactivity of PHBV SLS scaffolds can be enhanced by incorporating AKM, making this an attractive candidate for bone TE application.

Graphene Oxide versus Carbon Nanofibers in Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Films: Degradation in Simulated Intestinal Environments

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a microbial biodegradable polymer with a broad range of promising industrial applications. The effect of incorporation of low amounts (1% w/w) of carbon nanomaterials (CBNs) such as 1D carbon nanofibers (CNFs) or 2D graphene oxide (GO) nanosheets into the PHBV polymer matrix affects its degradation properties, as it is reported here for the first time. The study was performed in simulated gut conditions using two different media: an acidic aqueous medium (pH 6) and Gifu anaerobic medium. The results of this study showed that the incorporation of low amounts of filamentous 1D hydrophobic CNFs significantly increased the degradability of the hydrophobic PHBV after 3 months in simulated intestinal conditions as confirmed by weight loss (~20.5% w/w in acidic medium) and electron microscopy. We can attribute these results to the fact that the long hydrophobic carbon nanochannels created in the PHBV matrix with the incorporation of the CNFs allowed the degradation medium to penetrate at ultrafast diffusion speed increasing the area exposed to degradation. However, the hydrogen bonds formed between the 2D hydrophilic GO nanosheets and the hydrophobic PHBV polymer chains produced a homogeneous composite structure that exhibits lower degradation (weight loss of ~4.5% w/w after three months in acidic aqueous medium). Moreover, the water molecules present in both degradation media can be linked to the hydroxyl (-OH) and carboxyl (-COOH) groups present on the basal planes and at the edges of the GO nanosheets, reducing their degradation potential.

Piezoelectric Signals in Vascularized Bone Regeneration

The demand for bone substitutes is increasing in Western countries. Bone graft substitutes aim to provide reconstructive surgeons with off-the-shelf alternatives to the natural bone taken from humans or animal species. Under the tissue engineering paradigm, biomaterial scaffolds can be designed by incorporating bone stem cells to decrease the disadvantages of traditional tissue grafts. However, the effective clinical application of tissue-engineered bone is limited by insufficient neovascularization. As bone is a highly vascularized tissue, new strategies to promote both osteogenesis and vasculogenesis within the scaffolds need to be considered for a successful regeneration. It has been demonstrated that bone and blood vases are piezoelectric, namely, electric signals are locally produced upon mechanical stimulation of these tissues. The specific effects of electric charge generation on different cells are not fully understood, but a substantial amount of evidence has suggested their functional and physiological roles. This review summarizes the special contribution of piezoelectricity as a stimulatory signal for bone and vascular tissue regeneration, including osteogenesis, angiogenesis, vascular repair, and tissue engineering, by considering different stem cell sources entailed with osteogenic and angiogenic potential, aimed at collecting the key findings that may enable the development of successful vascularized bone replacements useful in orthopedic and otologic surgery.

Review of Hybrid Materials Based on Polyhydroxyalkanoates for Tissue Engineering Applications

This review is focused on hybrid polyhydroxyalkanoate-based (PHA) biomaterials with improved physico-mechanical, chemical, and piezoelectric properties and controlled biodegradation rate for applications in bone, cartilage, nerve and skin tissue engineering. PHAs are polyesters produced by a wide range of bacteria under unbalanced growth conditions. They are biodegradable, biocompatible, and piezoelectric polymers, which make them very attractive biomaterials for various biomedical applications. As naturally derived materials, PHAs have been used for multiple cell and tissue engineering applications; however, their widespread biomedical applications are limited due to their lack of toughness, elasticity, hydrophilicity and bioactivity. The chemical structure of PHAs allows them to combine with other polymers or inorganic materials to form hybrid composites with improved structural and functional properties. Their type (films, fibers, and 3D printed scaffolds) and properties can be tailored with fabrication methods and materials used as fillers. Here, we are aiming to fill in a gap in literature, revealing an up-to-date overview of ongoing research strategies that make use of PHAs as versatile and prospective biomaterials. In this work, a systematic and detailed review of works investigating PHA-based hybrid materials with tailored properties and performance for use in tissue engineering applications is carried out. A literature survey revealed that PHA-based composites have better performance for use in tissue regeneration applications than pure PHA.

Effects of a novel biodegredable implant system on a rat tibia fracture model

OBJECTIVE

This study aimed to determine the effects of a novel biodegradable implant releasing platelet-derived growth factor (PDGF) at the fracture site on fracture healing in a rat tibia fracture model.

METHODS

In this study, 35 male Sprague-Dawley rats weighing between 300 and 350 g were used. The rats were divided into four groups: Group A (control group without any treatment, n=10), Group B (spacer without PDGF Group, n=10), Group C (spacer with PDGF group, n=10), and Group D (healthy rat Group, n=5). Standardized fractures were created in the right tibias of rats, and then biodegradable implants made of poly-β-hydroxybutyrate-co-3-hydroxy valerate were implanted at the fracture sites in Groups B and C. In Group C, implants were loaded with 600 ng of PDGF. Animals were sacrificed 30 days after the operation, and fracture healing in each group was assessed radiologically based on the Goldberg score. Furthermore, the anteroposterior (AP) and mediolateral (ML) callus diameters were measured macroscopically, and fracture sites were mechanically tested.

RESULTS

In the radiological assessment, Group C showed higher fracture healing rate than Groups A and B (p=0.001), whereas no significant difference was found between group C and Group D (p>0.05). In the macroscopic assessment, while Group C exhibited the thickest AP callus diameter (p=0.02), no significant differences in ML callus diameters existed among the groups (p>0.05). Mechanical testing revealed that Group C had higher torsional strength (p=0.001) and stiffness than Groups A and B (p=0.001) while there was no significant difference between Groups C and D (p>0.05).

CONCLUSION

Biodegradable implant releasing PDGF may have positive effects on fracture healing.

The comparison of biocompatibility and osteoinductivity between multi-walled and single-walled carbon nanotube/PHBV composites

The applications of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) in tissue engineering have been widely studied. This study aimed to compare the biocompatibility and osteoinductivity of single-walled carbon nanotubes (SWCNTs)/PHBV composites with multi-walled CNTs (MWCNTs)/PHBV composites. CNTs were dispersed in PHBV by ultrasonication and composites were created using thermal injection moulding. In order to test their biocompatibility and osteoinductivity. Rat osteoblasts (rOBs) were then cultured and seeded on the composites. The composites were implanted in rat femoral bone defects. Our results showed that lower weight percentages of SWCNTs and MWCNTs (2-4%) improved both their mechanical and thermal decomposition properties. However, further reduction of rOBs cell death was observed in MWCNTs/PHBV. SWCNTs were shown to upregulate the expression of Runx-2 and Bmp-2 in early stage significantly, while MWCNTs showed a stronger long-term effect on Opn and Ocn. The in vivo result was that MWCNTs/PHBV composites induced intact rounding new bone, increased integration with new bone, and earlier completed bone remodeling when compared with SWCNTs. Immunohistochemistry also detected higher expression of RUNX-2 around MWCNTs/PHBV composites. In conclusion, there were no differences observed between SWCNTs and MWCNTs in the reinforcement of PHBV, while MWCNTs/PHBV composites showed better biocompatibility and osteoinductivity both in vitro and in vivo.

Poly (3-hydroxybutyrate-co-3-hydroxyvalerate) improved osteogenic differentiation of the human induced pluripotent stem cells while considered as an artificial extracellular matrix

Cocell polymers can be the best implants for replacing bone defects in patients. The pluripotent stem cells produced from the patient and the nanofibrous polymeric scaffold that can be completely degraded in the body and its produced monomers could be also usable are the best options for this implant. In this study, electrospun poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) nanofibers were fabricated and characterized and then osteogenic differentiation of the human-induced pluripotent stem cells (iPSCs) was investigated while cultured on PHBV scaffold. MTT results showed that cultured iPSCs on PHBV proliferation were increased compared to those cultured on tissue culture polystyrene (TCPS) as the control. Alkaline phosphatase (ALP) activity and calcium content were also significantly increased in iPSCs cultured on PHBV compared to the cultured on TCPS under osteogenic medium. Gene expression evaluation demonstrated that Runx2, collagen type I, ALP, osteonectin, and osteocalcin were upregulated in iPSCs cultured on PHBV scaffold in comparison with those cultured on TCPS for 2 weeks. Western blot analysis have shown that osteocalcin and osteopontin expression as two major osteogenic markers were increased in iPSCs cultured on PHBV scaffold. According to the results, nanofiber-based PHBV has a promising potential to increase osteogenic differentiation of the stem cells and iPSCs-PHBV as a cell-co-polymer construct demonstrated that has a great efficiency for use as a bone tissue engineered bioimplant.

In vitro degradation of a unique porous PHBV scaffold manufactured using selective laser sintering

Biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) scaffolds have shown great promise for bone tissue engineering applications. The investigation of their hydrolytic degradation is thus essential to understand the effect of hydrolysis on the complex biodegradation behavior of PHBV scaffolds. In this study, we investigated the degradation behavior of high molecular weight PHBV scaffolds manufactured using selective laser sintering (SLS) without using predesigned porous architectures. The manufactured scaffolds have high specific surface areas with great water-uptake abilities. After an incubation of 6 weeks in phosphate-buffered saline solution, the structural integrity of the scaffolds was unaffected. However, a significant decrease in molecular weight ranging from 39% to 46% was found. The measured weight loss was negligible, but their compressive modulus and strength both decreased, likely due to water plasticization. These findings suggest that hydrolytic degradation of PHBV by means of bulk degradation was the predominant mechanism, attributed to their excellent water absorptivity. Overall, the PHBV scaffolds manufactured using SLS exhibited adequate mechanical properties and satisfactory structural integrity after incubation. As a result, the scaffolds have great potential as candidates for bone repair in clinical practice. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 154-162, 2019.

Fabrication of polycaprolactone-silanated β-tricalcium phosphate-heparan sulfate scaffolds for spinal fusion applications

BACKGROUND CONTEXT

Interbody spinal fusion relies on the use of external fixation and the placement of a fusion cage filled with graft materials (scaffolds) without regard for their mechanical performance. Stability at the fusion site is instead reliant on fixation hardware combined with a selected cage. Ideally, scaffolds placed into the cage should both support the formation of new bone and contribute to the mechanical stability at the fusion site.

PURPOSE

We recently developed a scaffold consisting of silane-modified PCL-TCP (PCL-siTCP) with mechanical properties that can withstand the higher loads generated in the spine. To ensure the scaffold more closely mimicked the bone matrix, we incorporated collagen (Col) and a heparan sulfate glycosaminoglycan sugar (HS3) with increased affinity for heparin-binding proteins such as bone morphogenetic protein-2 (BMP-2). The osteostimulatory characteristic of this novel device delivering exogenous BMP2 was assessed in vitro and in vivo as a prelude to future spinal fusion studies with this device.

STUDY DESIGN/SETTING

A combination of cell-free assays (BMP2 release), progenitor cell-based assays (BMP2 bioactivity, cell proliferation and differentiation), and rodent ectopic bone formation assays was used to assess the osteostimulatory characteristics of the PCL-siTCP-based scaffolds.

MATERIALS AND METHODS

Freshly prepared rat mesenchymal stem cells were used to determine reparative cell proliferation and differentiation on the PCL-siTCP-based scaffolds over a 28-day period in vitro. The bioactivity of BMP2 released from the scaffolds was assessed on progenitor cells over a 28-day period using ALP activity assays and release kinetics as determined by enzyme-linked immunosorbent assay. For ectopic bone formation, intramuscular placement of scaffolds into Sprague Dawley rats (female, 4 weeks old, 120-150 g) was achieved in five animals, each receiving four treatments randomized for location along the limb. The four groups tested were (1) PCL-siTCP/Col (5-mm diameter×1-mm thickness), PCL-siTCP/Col/BMP2 (5 µg), (3) PCL-siTCP/Col/HS3 (25 µg), and (4) PCL-siTCP/Col/HS3/BMP2 (25 and 5 µg, respectively). Bone formation was evaluated at 8 weeks post implantation by microcomputed tomography (µCT) and histology.

RESULTS

Progenitor cell-based assays (proliferation, mRNA transcripts, and ALP activity) confirmed that BMP2 released from PCL-siTCP/Col/HS3 scaffolds increased ALP expression and mRNA levels of the osteogenic biomarkers Runx2, Col1a2, ALP, and bone gla protein-osteocalcin compared with devices without HS3. When the PCL-siTCP/Col/HS3/BMP2 scaffolds were implanted into rat hamstring muscle, increased bone formation (as determined by two-dimensional and three-dimensional µCTs and histologic analyses) was observed compared with scaffolds lacking BMP2. More consistent increases in the amount of ectopic bone were observed for the PCL-siTCP/Col/HS3/BMP2 implants compared with PCL-siTCP/Col/BMP2. Also, increased mineralizing tissue within the pores of the scaffold was seen with modified-tetrachrome histology, a result confirmed by µCT, and a modest but detectable increase in both the number and the thickness of ectopic bone structures were observed with the PCL-siTCP/Col/HS3/BMP2 implants.

CONCLUSIONS

The combination of PCL-siTCP/Col/HS3/BMP2 thus represents a promising avenue for further development as a bone graft alternative for spinal fusion surgery.

* Engineering Membranes for Bone Regeneration

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

Third generation poly(hydroxyacid) composite scaffolds for tissue engineering

Bone tissue engineering based on scaffolds is quite a complex process as a whole gamut of criteria needs to be satisfied to promote cellular attachment, proliferation and differentiation: biocompatibility, right surface properties, adequate mechanical performance, controlled bioresorbability, osteoconductivity, angiogenic cues, and vascularization. Third generation scaffolds are more of composite types to maximize biological-mechanical-chemical properties. In the present review, our focus is on the performance of micro-organism-derived polyhydroxyalkanoates (PHAs)-polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-valerate (PHBV)-composite scaffolds with ceramics and natural polymers for tissue engineering applications with emphasis on bone tissue. We particularly emphasize on how material properties of the composites affect scaffold performance. PHA-based composites have demonstrated their biocompatibility with a range of tissues and their capacity to induce osteogenesis due to their piezoelectric properties. Electrospun PHB/PHBV fiber mesh in combination with human adipose tissue-derived stem cells (hASCs) were shown to improve vascularization in engineered bone tissues. For nerve and skin tissue engineering applications, natural polymers such as collagen and chitosan remain the gold standard but there is scope for development of scaffolds combining PHAs with other natural polymers which can address some of the limitations such as brittleness, lack of bioactivity and slow degradation rate presented by the latter. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1667-1684, 2017.

PHBV/PAM scaffolds with local oriented structure through UV polymerization for tissue engineering

Locally oriented tissue engineering scaffolds can provoke cellular orientation and direct cell spread and migration, offering an exciting potential way for the regeneration of the complex tissue. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) scaffolds with locally oriented hydrophilic polyacrylamide (PAM) inside the macropores of the scaffolds were achieved through UV graft polymerization. The interpenetrating PAM chains enabled good interconnectivity of PHBV/PAM scaffolds that presented a lower porosity and minor diameter of pores than PHBV scaffolds. The pores with diameter below 100 μm increased to 82.15% of PHBV/PAM scaffolds compared with 31.5% of PHBV scaffolds. PHBV/PAM scaffold showed a much higher compressive elastic modulus than PHBV scaffold due to PAM stuffing. At 5 days of culturing, sheep chondrocytes spread along the similar direction in the macropores of PHBV/PAM scaffolds. The locally oriented PAM chains might guide the attachment and spreading of chondrocytes and direct the formation of microfilaments via contact guidance.

Human serum is a suitable supplement for the osteogenic differentiation of human adipose-derived stem cells seeded on poly-3-hydroxibutyrate-co-3-hydroxyvalerate scaffolds

Human adipose-derived stem cells (hASCs) are currently a point of focus for bone tissue engineering applications. However, the ex vivo expansion of stem cells before clinical application remains a challenge. Fetal bovine serum (FBS) is largely used as a medium supplement and exposes the recipient to infections and immunological reactions. In this study, we evaluated the osteogenic differentiation process of hASCs in poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHB-HV) scaffolds with the osteogenic medium supplemented with pooled allogeneic human serum (aHS). The hASCs grown in the presence of FBS or aHS did not show remarkable differences in morphology or immunophenotype. The PHB-HV scaffolds, which were developed by the freeze-drying technique, showed an adequate porous structure and mechanical performance as observed by micro-computed tomography, scanning electron microscopy (SEM), and compression test. The three-dimensional structure was suitable for allowing cell colonization, which was revealed by SEM micrographs. Moreover, these scaffolds were not toxic to cells as shown by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The differentiation capacity of hASCs seeded on scaffolds was confirmed by the reduction of the proliferation, the alkaline phosphatase (AP) activity, expression of osteogenic gene markers (AP, collagen type I, Runx2, and osteocalcin), and the expression of bone markers, such as osteopontin, osteocalcin, and collagen type I. The osteogenic capacity of hASCs seeded on PHB-HV scaffolds indicates that this scaffold is adequate for cell growth and differentiation and that aHS is a promising supplement for the in vitro expansion of hASCs. In conclusion, this strategy seems to be useful and safe for application in bone tissue engineering.

Evaluation of the ability of collagen-glycosaminoglycan scaffolds with or without mesenchymal stem cells to heal bone defects in Wistar rats

PURPOSE

The aim of this experiment was to examine the capacity of collagen-glycosaminoglycan scaffolds, with or without mesenchymal stem cells, to satisfactorily repair a 5-mm rat calvarial defect.

METHODS

Fifty-five Wistar rats were used in the study. The defects were either left empty to serve as controls (n = 7) or filled with cell-free scaffolds (n = 11), cell-seeded scaffolds that were pre-cultured in standard culture medium (n = 13), cell-seeded scaffolds that were pre-cultured in osteoinductive factor-supplemented medium (n = 12) or particulate autogenous bone (n = 12). The animals were sacrificed at 12 weeks after surgery, and specimens were prepared for histomorphometric analysis. The linear bone healing and the bone area within the defect were measured.

RESULTS

Comparable results were obtained using cell-free collagen-glycosaminoglycan scaffolds and autogenous bone both in terms of linear bone healing (P < 0.986) and area of new bone (P < 0.846). While the test groups showed significantly more bone formation compared to the empty defect control group, the linear bone healing and area of new bone within the defect were significantly lower in the cell-seeded scaffolds than in the cell-free scaffolds. The results have demonstrated that a cell-free collagen-glycosaminoglycan scaffold is capable of repairing a 5-mm rat calvarial defect as effectively as autogenous bone and that seeding the scaffold with pre-cultured mesenchymal stem cells prior to implantation offered no beneficial effect and resulted in incomplete healing of the defect.

CONCLUSIONS

The results thus suggest that the scaffold has immense potential for tissue repair showing favorable osteoconductive properties, biocompatibility and degradability.

Poly(3-hydroxybutyrate) multifunctional composite scaffolds for tissue engineering applications

Poly(3-hydroxybutyrate) (P(3HB)) foams exhibiting highly interconnected porosity (85% porosity) were prepared using a unique combination of solvent casting and particulate leaching techniques by employing commercially available sugar cubes as porogen. Bioactive glass (BG) particles of 45S5 Bioglass grade were introduced in the scaffold microstructure, both in micrometer ((m-BG), <5 microm) and nanometer ((n-BG), 30 nm) sizes. The in vitro bioactivity of the P(3HB)/BG foams was confirmed within 10 days of immersion in simulated body fluid and the foams showed high level of protein adsorption. The foams interconnected porous microstructure proved to be suitable for MG-63 osteoblast cell attachment and proliferation. The foams implanted in rats as subcutaneous implants resulted in a non-toxic and foreign body response after one week of implantation. In addition to showing bioactivity and biocompatibility, the P(3HB)/BG composite foams also exhibited bactericidal properties, which was tested on the growth of Staphylococcus aureus. An attempt was made at developing multifunctional scaffolds by incorporating, in addition to BG, selected concentrations of Vitamin E or/and carbon nanotubes. P(3HB) scaffolds with multifunctionalities (viz. bactericidal, bioactive, electrically conductive, antioxidative behaviour) were thus produced, which paves the way for next generation of advanced scaffolds for bone tissue engineering.

Fabrication of HA/PHBV composite scaffolds through the emulsion freezing/freeze-drying process and characterisation of the scaffolds

Biodegradable polymer-based scaffolds containing osteoconductive hydroxyapatite (HA) particles can be very useful for bone tissue engineering. In this investigation, HA nanoparticles were incorporated in poly(hydroxybutyrate-co-valerate) (PHBV) polymer to fabricate osteoconductive composite scaffolds. PHBV and HA/PHBV scaffolds were made using an emulsion freezing/freeze-drying technique. The scaffolds produced were subsequently characterized using several techniques. It was found that the scaffolds were highly porous and had interconnected porous structures. The pore size ranged from several microns to around 300 microm. The spherical HA nanoparticles which were produced in-house through a nanoemulsion process could be incorporated into composite scaffolds although some of these nanoparticles existed on the surface of pore walls when a relatively large amount of HA was used for composite scaffolds. The incorporation of HA nanoparticles also enhanced compressive mechanical properties of the scaffolds.

Increased response of Vero cells to PHBV matrices treated by plasma

The copolymers poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) (PHBV) are being intensely studied as a tissue engineering substrate. It is known that poly 3-hydroxybutyric acids (PHBs) and their copolymers are quite hydrophobic polyesters. Plasma-surface modification is an effective and economical surface treatment technique for many materials and of growing interest in biomedical engineering. In this study we investigate the advantages of oxygen and nitrogen plasma treatment to modify the PHBV surface to enable the acceleration of Vero cell adhesion and proliferation. PHBV was dissolved in methylene chloride at room temperature. The PHBV membranes were modified by oxygen or nitrogen-plasma treatments using a plasma generator. The membranes were sterilized by UV irradiation for 30 min and placed in 96-well plates. Vero cells were seeded onto the membranes and their proliferation onto the matrices was also determined by cytotoxicity and cell adhesion assay. After 2, 24, 48 and 120 h of incubation, growth of fibroblasts on matrices was observed by scanning electron microscopy (SEM). The analyses of the membranes indicated that the plasma treatment decreased the contact angle and increased the surface roughness; it also changed surface morphology, and consequently, enhanced the hydrophilic behavior of PHBV polymers. SEM analysis of Vero cells adhered to PHBV treated by plasma showed that the modified surface had allowed better cell attachment, spreading and growth than the untreated membrane. This combination of surface treatment and polymer chemistry is a valuable guide to prepare an appropriate surface for tissue engineering application.

Chemical and topographical modification of PHBV surface to promote osteoblast alignment and confinement

Proper cell attachment and distribution, and thus stronger association in vivo between a bone implant and native tissue will improve the success of the implant. In this study, the aim was to achieve promotion of attachment and uniform distribution of rat mesenchymal stem cell-derived osteoblasts by introducing chemical and topographical cues on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) film surfaces. As the chemical cues, either alkaline phosphatase was covalently immobilized on the film surface to induce deposition of calcium phosphate minerals or fibrinogen was adsorbed to improve cell adhesion. Microgrooves and micropits were introduced on the film surface by negative replication of micropatterned Si wafers. Both chemical cues improved cell attachment and even distribution on the PHBV films, but Fb was more effective especially when combined with the micropatterns. Cell alignment (<10 degrees deviation angle) parallel to chemically modified microgrooves (1, 3, or 8 microm groove width) and on 10 microm-thick Fb lines printed on the unpatterned films was achieved. The cells on unpatterned and 5 microm-deep micropitted films were distributed and oriented randomly. Results of this study proved that microtopographies on PHBV can improve osseointegration when combined with chemical cues, and that microgrooves and cell adhesive protein lines on PHBV can guide selective osteoblast adhesion and alignment.

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) composite biomaterials for bone tissue regeneration: in vitro performance assessed by osteoblast proliferation, osteoclast adhesion and resorption, and macrophage proinflammatory response

The efficacy of composite materials for bone tissue engineering is dependent on the materials' ability to support bone regeneration whilst inducing a minimal inflammatory response. In this study we examined the in vitro osteogenic and inflammatory properties of poly(3-hydroxybutyrate-co-3-valerate) (PHBV) with various calcium phosphate-reinforcing phases: nano-sized hydroxyapatite (HA); submicron-sized calcined hydroxyapatite (cHA); and submicron-sized beta-tricalcium phosphate (beta-TCP), using bioassays of cultured osteoblasts, osteoclasts, and macrophages. Our study showed that the addition of a nano-sized reinforcing phase to PHBV, whilst improving osteogenic properties, also reduces the proinflammatory response. Proinflammatory responses of RAW264.7/ELAM-eGFP macrophages to PHBV were shown to be markedly reduced by the introduction of a reinforcing phase, with HA/PHBV composites having the lowest inflammatory response. Osteoclasts, whilst able to attach to all the materials, failed to form functional actin rings or resorption pits on any of the materials under investigation. Cultures of osteoblasts (MC3T3-E1) readily attached and mineralised on all the materials, with HA/PHBV inducing the highest levels of mineralization. The improved biological performance of HA/PHBV composites when compared with cHA/PHBV and beta-TCP/PHBV composites is most likely a result of the nano-sized reinforcing phase of HA/PHBV and the greater surface presentation of mineral in these composites. Our results provide a new strategy for improving the suitability of PHBV-based materials for bone tissue regeneration.

Bioluminescence imaging of calvarial bone repair using bone marrow and adipose tissue-derived mesenchymal stem cells

A combined strategy using bioluminescence imaging, bone densitometry and histology was used to analyze the bone regeneration capacity of human bone marrow (hBMSC) and adipose tissue (hAMSC) mesenchymal stem cells, seeded in an osteoconductive arginine-glycine-aspartate (RGD) crosslinked hydrogel scaffold, implanted in a mouse calvarial bone defect. We show that firefly luciferase labeled stem cells can be monitored in vivo through a prolonged 90 days period, during which hBMSCs survive better than hAMSCs and that the density of scaffold bearing defects increased significantly more than that of defects without scaffolds.

Polyhydroxyalkanoate (PHA)/inorganic phase composites for tissue engineering applications

Polyhydroxyalkanoates are emerging as a class of biodegradable polymers for applications in tissue engineering. Members of the polyhydroxyalkanoates family encompass a wide variety of materials, from hard and brittle materials to soft and elastomeric. Over the years, efforts have been made to extend the group of polyhydroxyalkanoates and to investigate their use in numerous biomedical applications, such as sutures, cardiovascular patches, wound dressings, guided tissue repair/regeneration devices, and tissue engineering scaffolds. Along with the development of polyhydroxyalkanoates, researchers have looked into the possibility of designing composites in combination with inorganic phases to further improve the mechanical properties, rate of degradation, and also impart bioactivity. Poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) are some of the polymers which have been studied extensively to fabricate composites in combination with hydroxyapatite, bioactive glass, and glass-ceramic fillers or coatings. This paper reviews international research carried out toward development of polyhydroxyalkanoates/inorganic phase composites in terms of systems investigated, microstructures, properties achieved, and applications, with special focus on tissue engineering scaffolds. A comparison between different composite systems developed in the past few years is presented. The paper also addresses the prospect of potential further development of polyhydroxyalkanoates/inorganic phase composites with optimized microstructure and properties for improved tissue engineering scaffolds.

Effect of 3-hydroxyhexanoate content in poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) on in vitro growth and differentiation of smooth muscle cells

In this paper, comprehensive characteristics including cell attachment, cell proliferation status, cell cycle progression and phenotypic changes of smooth muscle cells from rabbit aorta (RaSMCs) were studied on poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) containing 0-20% HHx (mol%) in comparison with tissue culture plates (TCPs). Results demonstrated that RaSMCs adhered better on PHBHHx containing 12% HHx (12%HHx) although they proliferated better on 20%HHx-containing PHBHHx films (20%HHx). This was explained by the difference in cell cycle progression observed using flow cytometry, as it was found that only 20%HHx-containing polymer could maintain the normal cell cycle evolution as TCPs did after 3 d incubation. The highest expression level and typical spindle-like distribution of alpha-actin on 20%HHx-containing polymer were characterized as the contractile-like phenotype, suggesting that RaSMCs tended to differentiate rather than proliferate compared to the cells grown on 12%HHx polymer. Results obtained above suggested that 20%HHx was suitable for RaSMCs proliferation, leading to its change to contractile phenotype. This study extends the potential applications of PHBHHx in SMCs-related graft scaffold fabrication for tissue engineering.