Biodegradable hollow microfibres for tissue engineering and drug delivery applications

Tissue engineering represents one of the most important areas of application of polymeric biomaterials. Synthetic and biological polymers are employed to produce tissue–engineering scaffolds. Several techniques are currently used to construct highly porous three–dimensional scaffolds able to aid cell organisation and to guide tissue regeneration. Among these techniques, fibre bonding was used in this study to produce non–woven meshes based on polymer hollow microfibres. The development of hollow fibres allows for creating bioactive scaffolds whereby biological components such as growth factors and particle systems loaded with specific drugs can be introduced into the cavity of the fibres. In order to create scaffolds for human tissue replacement, polycaprolactone (PCL) fibres, poly(L–lactic acid) (PLLA) fibres and bioartificial fibres based on PLLA and polysaccharides were developed. An apparatus able to produce this kind of fibres was designed and created in collaboration with GIMAC (Castronno, Italy). Preliminary in vitro experiments were performed by using ovine fibroblasts and human osteosarcoma cells. SEM (Scanning Electron Microscopy) images obtained after 8 and 6 weeks culture, respectively, showed a very large number of cells well adherent and spread onto the fibre surface. These results were also confirmed by staining with haematoxylin and also by Alamar Blue, MTT and Neutral red tests. During the last year the project focused on the replacement of human cartilage in vitro. The idea was to use hollow microfibres based on PLLA and dextran or chitosan in order to create a favourable substrate for chondrocytes. Porous fibres were created to enhance nutrients (polysaccharides) to the chondrocytes and also for the delivery of incorporated factors. Bovine chondrocytes, isolated from articular knee cartilage were seeded on PCL and PDM1 (PLLA–dextran with low wall–porosity) meshes and cultured for two–weeks. Histological analysis confirmed the presence of chondrocytes inside the scaffolds. Studies were performed in order to test the potential of the investigated materials for chondrogenic differentiation of human bone marrow stem cell (HBMSC) by recombinant human transforming growth factor–B1 (TGF–B1). This work involved investigation of cell activity and viability (Alamar Blue™, Live–Dead Stain), cell morphology studies by SEM, and glycosaminoglycan (GAG) analysis. These in vitro tests were carried out for 28 days, the Alamar Blue test and Live–Dead stain showed adequate stem cell adhesion and proliferation, but GAG analysis resulted not enough sensible. Degradation studies of these scaffolds were performed at 37°C in simulated body fluid (SBF). The results collected by gravimetric analysis, pH measurements and FTIR spectroscopy showed that PLLA–based scaffolds are completely degraded after five–months whereas PCL–based supports just started the process

Bovine bone matrix/poly(l-lactic-co-ε-caprolactone)/gelatin hybrid scaffold (SmartBone®) for maxillary sinus augmentation: A histologic study on bone regeneration

The ideal scaffold for bone regeneration is required to be highly porous, non-immunogenic, biostable until the new tissue formation, bioresorbable and osteoconductive. This study aimed at investigating the process of new bone formation in patients treated with granular SmartBone® for sinus augmentation, providing an extensive histologic analysis. Five biopsies were collected at 4-9 months post SmartBone® implantation and processed for histochemistry and immunohistochemistry. Histomorphometric analysis was performed. Bone-particle conductivity index (BPCi) was used to assess SmartBone® osteoconductivity.At 4 months, SmartBone® (12%) and new bone (43.9%) were both present and surrounded by vascularized connective tissue (37.2%). New bone was grown on SmartBone® (BPCi=0.22). At 6 months, SmartBone® was almost completely resorbed (0.5%) and new bone was massively present (80.8%). At 7 and 9 months, new bone accounted for a large volume fraction (79.3% and 67.4%, respectively) and SmartBone® was resorbed (0.5% and 0%, respectively). Well-oriented lamellae and bone scars, typical of mature bone, were observed. In all the biopsies, bone matrix biomolecules and active osteoblasts were visible. The absence of inflammatory cells confirmed SmartBone® biocompatibility and non-immunogenicity. These data indicate that SmartBone® is osteoconductive, promotes fast bone regeneration, leading to mature bone formation in about 7 months

Boron nitride nanotube-functionalised myoblast/microfibre constructs: a nanotech-assisted tissue-engineered platform for muscle stimulation

In this communication, we introduce boron nitride nanotube (BNNT)-functionalised muscle cell/microfibre mesh constructs, obtained via tissue engineering, as a three-dimensional (3D) platform to study a wireless stimulation system for electrically responsive cells and tissues. Our stimulation strategy exploits the piezoelectric behaviour of some classes of ceramic nanoparticles, such as BNNTs, able to polarize under mechanical stress, e.g. using low-frequency ultrasound (US). In the microfibre scaffolds, C2C12 myoblasts were able to differentiate into viable myotubes and to internalize BNNTs, also upon US irradiation, so as to obtain a nanotech-assisted 3D in vitro model. We then tested our stimulatory system on 2D and 3D cellular models by investigating the expression of connexin 43 (Cx43), as a molecule involved in cell crosstalk and mechanotransduction, and myosin, as a myogenic differentiation marker. Cx43 gene expression revealed a marked model dependency. In control samples (without US and/or BNNTs), Cx43 was upregulated under 2D culture conditions (10.78 ± 1.05-fold difference). Interactions with BNNTs increased Cx43 expression in 3D samples. Cx43 mRNA dropped in 2D under the 'BNNTs + US' regimen, while it was best enhanced in 3D samples (3.58 ± 1.05 vs 13.74 ± 1.42-fold difference, p = 0.0001). At the protein level, the maximal expressions of Cx43 and myosin were detected in the 3D model. In contrast with the 3D model, in 2D cultures, BNNTs and US exerted a synergistic depletive effect upon myosin synthesis. These findings indicate that model dimensionality and stimulatory regimens can strongly affect the responses of signalling and differentiation molecules, proving the importance of developing proper in vitro platforms for biological modellin

Investigating the microenvironmental effects of scaffold chemistry and topology in human mesenchymal stromal cell/polymeric hollow microfiber constructs

Tissue engineering scaffolds have shown an intrinsic ability to provide cellular stimulation, thus behaving as physically active microenvironments. This study reports on the interaction between human mesenchymal stromal cells (hMSCs) and dry-wet spun polymer microfiber meshes. The following scaffolding parameters were tested: i) polymer type: poly-L-lactide (PLLA) vs poly-ε-caprolactone (PCL); ii) non-solvent type: ethanol (Et-OH) vs isopropanol/ gelatin; iii) scaffold layout: patterned vs random microfiber fabrics. After two culture weeks, the effects on metabolic activity, scaffold colonization and function of undifferentiated hMSCs were assayed. In our study, the polymer type affected the hMSC metabolic activity timeline, and the metabolic picks occurred earlier in PLLA (day 6) than in PCL (day 9) scaffolds. Instead, PLLA vs PCL had no endpoint effect on alkaline phosphatase (ALP) activity expression. On average, the hMSCs grown on all the random microfiber fabrics showed an ALP activity statistically superior to that detected on patterned microfiber fabrics, with the highest in Et-OH random subtypes. Such findings are suggestive of enhanced osteogenic potential. The understanding of scaffold-driven stimulation could enable environmental hMSC commitment, paving the way for new regenerative strategies

COMPOSITE POLYMER-COATED MINERAL SCAFFOLDS FOR BONE REGENERATION: FROM MATERIAL CHARACTERIZATION TO HUMAN STUDIES

Bovine bone xenografts, made of hydroxyapatite (HA), were coated with poly(L-lactide-co-ε- caprolactone) (PLCL) and RGD-containing collagen fragments in order to increase mechanical properties, hydrophilicity, cell adhesion and osteogenicity. In vitro the scaffold microstructure was investigated with Environmental Scanning Electronic Microscopy (ESEM) analysis and micro tomography, while mechanical properties were investigated by means compression tests. In addition, cell attachment and growth within the three-dimensional scaffold inner structure were validated using human osteosarcoma cell lines (SAOS-2 and MG-63). Standard ISO in vivo biocompatibility studies were carried out on model animals, while bone regenerations in humans were performed to assess the efficacy of the product. All results from in vitro to in vivo investigations are here reported, underlining that this scaffold promotes bone regeneration and has good clinical outcome

Adipose-Derived Stromal Vascular Fraction/Xenohybrid Bone Scaffold: An Alternative Source for Bone Regeneration

Adipose tissue-derived stem cells (ASCs) are a promising tool for the treatment of bone diseases or skeletal lesions, thanks to their ability to potentially repair damaged tissue. One of the major limitations of ASCs is represented by the necessity to be isolated and expanded through in vitro culture; thus, a strong interest was generated by the adipose stromal vascular fraction (SVF), the noncultured fraction of ASCs. SVF is a heterogeneous cell population, directly obtained after collagenase treatment of adipose tissue. In order to investigate and compare the bone-regenerative potential of SVF and ASCs, they were plated on SmartBone®, a xenohybrid bone scaffold, already used in clinical practice with successful results. We showed that SVF plated on SmartBone, in the presence of osteogenic factors, had better osteoinductive capabilities than ASCs, in terms of differentiation into bone cells, mineralization, and secretion of soluble factors stimulating osteoblasts. Indeed, we observed an increasing area of new tissue over time, with and without OM. These data strongly support an innovative idea for the use of adipose SVF and bone scaffolds to promote tissue regeneration and repair, also thanks to an easier cell management preparation that allows a potentially larger use in clinical applications

The Few Who Made It : Commercially and Clinically Successful Innovative Bone Grafts

Bone reconstruction techniques are mainly based on the use of tissue grafts and artificial scaffolds. The former presents well-known limitations, such as restricted graft availability and donor site morbidity, while the latter commonly results in poor graft integration and fixation in the bone, which leads to the unbalanced distribution of loads, impaired bone formation, increased pain perception, and risk of fracture, ultimately leading to recurrent surgeries. In the past decade, research efforts have been focused on the development of innovative bone substitutes that not only provide immediate mechanical support, but also ensure appropriate graft anchoring by, for example, promotingde novobone tissue formation. From the countless studies that aimed in this direction, only few have made the big jump from the benchtop to the bedside, whilst most have perished along the challenging path of clinical translation. Herein, we describe some clinically successful cases of bone device development, including biological glues, stem cell-seeded scaffolds, and gene-functionalized bone substitutes. We also discuss the ventures that these technologies went through, the hindrances they faced and the common grounds among them, which might have been key for their success. The ultimate objective of this perspective article is to highlight the important aspects of the clinical translation of an innovative idea in the field of bone grafting, with the aim of commercially and clinically informing new research approaches in the sector