Degradation and related changes in supermolecular structure of poly(caprolactone) in vivo conditions

Electrospun scaffolds based on a PCL/starch blend reinforced with CaO nanoparticles for bone tissue engineering

Electrospun nanocomposite scaffolds with improved bioactive and biological properties were fabricated from a blend of polycaprolactone (PCL) and starch, and then combined with 5 wt% of calcium oxide (CaO) nanoparticles sourced from eggshells. SEM analyses showed scaffolds with fibrillar morphology and a three-dimensional structure. The hydrophilicity of scaffolds was improved with starch and CaO nanoparticles, which was evidenced by enhanced water absorption (3500 %) for 7 days. In addition, PCL/Starch/CaO scaffolds exhibited major degradation, with a mass loss of approximately 60 % compared to PCL/Starch and PCL/CaO. The PCL/Starch/CaO scaffolds decreased in crystallinity as intermolecular interactions between the nanoparticles retarded the mobility of the polymeric chains, leading to a significant increase in Young's modulus (ca. 60 %) and a decrease in tensile strength and elongation at break, compared to neat PCL. SEM-EDS, FT-IR, and XRD analyses indicated that PCL/Starch/CaO scaffolds presented a higher biomineralization capacity due to the ability to form hydroxyapatite (HA) in their surface after 28 days. The PCL/Starch/CaO scaffolds showed attractive biological performance, allowing cell adhesion and viability of M3T3-E1 preosteoblastic cells. In vivo analysis using a subdermal dorsal model in Wistar rats showed superior biocompatibility and improved resorption process compared to a pure PCL matrix. This biological analysis suggested that the PCL/Starch/CaO electrospun mats are suitable scaffolds for guiding the regeneration of bone tissue.

Influence of Polymeric Microparticle Size and Loading Concentration on 3D Printing Accuracy and Degradation Behavior of Composite Scaffolds

Successful employment of 3D printing for delivery of therapeutic biomolecules requires protection of their bioactivity on exposure to potentially inactivating conditions. Although intermediary encapsulation of the biomolecules in polymeric particulate delivery vehicles is a promising strategy for this objective, the inclusion of such particles in 3D printing formulations may critically impact the accuracy or precision of 3D printed scaffolds relative to their intended designed architectures, as well as the degradation behavior of both the scaffolds and the included particles. The present work aimed to elucidate the effect of poly(d,l-lactic-co-glycolic acid) particle size and loading concentration on material accuracy, machine precision, and degradation of 3D printed poly(ɛ-caprolactone)-based scaffolds. Using a main effects analysis, the sizes and loading concentrations of particle delivery vehicles investigated were found to have neither a beneficial nor disadvantageous influence on the metrics of printing quality such as material accuracy and machine precision. Meanwhile, particle loading concentration was determined to influence degradation rate, whereas printing temperature affected the trends in composite weight-average molecular weight. Neither of the two particle-related parameters (concentration nor diameter) was found to exhibit a significant effect on intra-fiber nor inter-fiber porosity. These findings evidence the capacity for controlled loading of particulate delivery vehicles in 3D printed scaffolds while preserving construct accuracy and precision, and with predictable dictation of composite degradation behavior for potential controlled release of encapsulated biomolecules.

The Gradual Release of Alendronate for the Treatment of Critical Bone Defects in Osteoporotic and Control Rats

Purpose

Osteoporosis is a severe health problem with social and economic impacts on society. The standard treatment consists of the systemic administration of drugs such as bisphosphonates, with alendronate (ALN) being one of the most common. Nevertheless, complications of systemic administration occur with this drug. Therefore, it is necessary to develop new strategies, such as local administration.

Methods

In this study, emulsion/dispersion scaffolds based on W/O emulsion of PCL and PF68 with ALN, containing hydroxyapatite (HA) nanoparticles as the dispersion phase were prepared using electrospinning. Scaffolds with different release kinetics were tested in vitro on the co-cultures of osteoblasts and osteoclast-like cells, isolated from adult osteoporotic and control rats. Cell viability, proliferation, ALP, TRAP and CA II activity were examined. A scaffold with a gradual release of ALN was tested in vivo in the bone defects of osteoporotic and control rats.

Results

The release kinetics were dependent on the scaffold composition and the used system of the poloxamers. The ALN was released from the scaffolds for more than 22 days. The behavior of cells cultured in vitro on scaffolds with different release kinetics was comparable. The difference was evident between cell co-cultures isolated from osteoporotic and control animals. The PCL/HA scaffold show slow degradation in vivo and residual scaffold limited new bone formation inside the defects. Nevertheless, the released ALN supported bone formation in the areas surrounding the residual scaffold. Interestingly, a positive effect of systemic administration of ALN was not proved.

Conclusion

The prepared scaffolds enabled tunable control release of ALN. The effect of ALN was proved in vitro and in in vivo study supported peri-implant bone formation.

Advanced strategies for constructing interfacial tissues of bone and tendon/ligament

Enthesis, the interfacial tissue between a tendon/ligament and bone, exhibits a complex histological transition from soft to hard tissue, which significantly complicates its repair and regeneration after injury. Because traditional surgical treatments for enthesis injury are not satisfactory, tissue engineering has emerged as a strategy for improving treatment success. Rapid advances in enthesis tissue engineering have led to the development of several strategies for promoting enthesis tissue regeneration, including biological scaffolds, cells, growth factors, and biophysical modulation. In this review, we discuss recent advances in enthesis tissue engineering, particularly the use of biological scaffolds, as well as perspectives on the future directions in enthesis tissue engineering.

Modified Histopathological Protocol for Poly-ɛ-Caprolactone Scaffolds Preserving Their Trabecular, Honeycomb-like Structure

Poly-ɛ-caprolactone (PCL) is now widely studied in relation to the engineering of bone, cartilage, tendons, and other tissues. Standard histological protocols can destroy the carefully created trabecular and honeycomb-like architecture of PCL scaffolds, and could lead to scaffold fibers swelling, resulting in the displacement or compression of tissues inside the scaffold. The aim of this study was to modify a standard histopathological protocol for PCL scaffold preparation and evaluate it on porous cylindrical PCL scaffolds in a rat model. In 16 inbred Wag rats, 2 PCL scaffolds were implanted subcutaneously to both inguinal areas. Two months after implantation, harvested scaffolds were first subjected to μCT imaging, and then to histopathological analysis with standard (left inguinal area) and modified histopathological protocols (right inguinal area). To standardize the results, soft tissue percentages (STPs) were calculated on scaffold cross-sections obtained from both histopathological protocols and compared with corresponding µCT cross-sections. The modified protocol enabled the assessment of almost 10× more soft tissues on the scaffold cross-section than the standard procedure. Moreover, STP was only 1.5% lower than in the corresponding µCT cross-sections assessed before the histopathological procedure. The presented modification of the histopathological protocol is cheap, reproducible, and allows for a comprehensive evaluation of PCL scaffolds while maintaining their trabecular, honeycomb-like structure on cross-sections.

Synthesis of bio-based polyester elastomers and evaluation of the in vivo biocompatibility and biodegradability as biomedical materials

Biodegradable polyester elastomers have found wide applications in the tissue engineering field. In this study, all bio-based polyester elastomer (BPE) is synthesized from five bio-based monomers; and the in vivo...

Advances in 3D Printing for Tissue Engineering

Tissue engineering (TE) scaffolds have enormous significance for the possibility of regeneration of complex tissue structures or even whole organs. Three-dimensional (3D) printing techniques allow fabricating TE scaffolds, having an extremely complex structure, in a repeatable and precise manner. Moreover, they enable the easy application of computer-assisted methods to TE scaffold design. The latest additive manufacturing techniques open up opportunities not otherwise available. This study aimed to summarize the state-of-art field of 3D printing techniques in applications for tissue engineering with a focus on the latest advancements. The following topics are discussed: systematics of the available 3D printing techniques applied for TE scaffold fabrication; overview of 3D printable biomaterials and advancements in 3D-printing-assisted tissue engineering.

The effect of diameter of fibre on formation of hydrogen bonds and mechanical properties of 3D-printed PCL

Fused Deposition Modelling (FDM) technique has been widely utilized in fabrication of 3D porous scaffolds for tissue engineering (TE) applications. Surprisingly, although there are many publications devoted to the architectural features of the 3D scaffolds fabricated by the FDM, none of them give us evident information about the impact of the diameter of the fibres on material properties. Therefore, the aim of this study was to investigate, for the first time, the effect of the diameter of 3D-printed PCL fibres on variations in their microstructure and resulting mechanical behaviour. The fibres made of poly(ε-caprolactone) (PCL) were extruded through commonly used types of nozzles (inner diameter ranging from 0.18 mm to 1.07 mm) by means of FDM technique. Static tensile test and atomic force microscopy working in force spectroscopy mode revealed strong decrease in the Young's modulus and yield strength with increasing fibre diameter in the investigated range. To explain this phenomenon, we conducted differential scanning calorimetry, wide-angle X-ray-scattering, Fourier-transform infrared spectroscopy, infrared and polarized light microscopy imaging. The obtained results clearly showed that the most prominent effect on the obtained microstructures and mechanical properties had different cooling and shear rates during fabrication process causing changes in supramolecular interactions of PCL. The observed fibre size-dependent formation of hydrogen bonds affected the crystalline structure and its stability. Summarising, this study clearly demonstrates that the diameter of 3D-printed fibres has a strong effect on obtained microstructure and mechanical properties, therefore should be taken into consideration during design of the 3D TE scaffolds.

In-situ re-melting and re-solidification treatment of selective laser sintered polycaprolactone lattice scaffolds for improved filament quality and mechanical properties

Selective laser sintering (SLS) is a promising additive manufacturing technique that produces biodegradable tissue-engineered scaffolds with highly porous architectures without additional supporting. However, SLS process inherently results in partially melted microstructures which significantly impair the mechanical properties of the resultant scaffolds for potential applications in tissue engineering and regenerative medicine. Here, a novel post-treatment strategy was developed to endow the SLS-fabricated polycaprolactone (PCL) scaffolds with dense morphology and enhanced mechanical properties by embedding them in dense NaCl microparticles for in-situ re-melting and re-solidification. The effects of re-melting temperature and dwelling time on the microstructures of the SLS-fabricated filaments were studied. The results demonstrated that the minimum requirements of re-melting temperature and dwelling time for sufficient treatment were 65 °C and 5 min respectively and the size of the SLS-fabricated filaments was reduced from 683.3 ± 28.0 μm to 601.6 ± 17.4 μm. This method was also highly effective in treating three-dimensional (3D) PCL lattice scaffolds, which showed improved filament quality and mechanical properties after post-treatment. The treated PCL scaffolds with an initial compressive modulus and strength of 3027.8 ± 204.2 kPa and 208.8 ± 14.5 kPa can maintain their original shapes after implantation in vivo for 24 weeks. Extensive newly-grown tissues were found to gradually penetrate into the porous regions along the PCL filaments. Although degradation occurred, the mechanical properties of the implanted constructs stably maintained. The presented method provides an innovative, green and general post-treatment strategy to improve both the filament quality and mechanical properties of SLS-fabricated PCL scaffolds for various tissue engineering applications.

Internal nanocrystalline structure and stiffness alterations of electrospun polycaprolactone-based mats after six months of in vitro degradation. An atomic force microscopy assay

Biodegradable electrospun nanofibrous scaffolds for bone tissue engineering applications have been extensively studied as they can provide attractive open-worked architecture resembling natural extracellular matrix, with tunable physical and mechanical properties enhancing positive cellular response. For this purpose, electrospun mats were tested in terms of morphology, mechanical and physical properties, degradation kinetics and related phenomena occurring in micro- and nanoscale. However, detailed description of internal nanostructures of electrospun mats and their changes related to in vitro degradation is still missing. In this manuscript, we report qualitative and quantitative evaluation of internal lamellar nanostructure of electrospun fibrous scaffolds made of pristine polycaprolactone and composite with polymeric matrix and nanoceramic (hydroxyapatite) filler during in vitro degradation. Morphological and mechanical studies performed with an atomic force microscope were followed by scanning electron microscope imaging and X-Ray diffraction. The results suggest degradation-dependent alteration of both organization and thickness of nano-scaled lamellas recorded with atomic force microscope. Moreover, changes of the material's internal structure were followed by enhanced stiffness and higher crystallinity of electrospun fibers.

Alignment and bioactive molecule enrichment of bio-composite scaffolds towards peripheral nerve tissue engineering

Providing topographical cues along with chemical and biological factors is essential for biomimetic scaffolds applied in nerve tissue engineering.