Hydrolytic degradation of porous poly(hydroxybutyrate-co-hydroxyvalerate) scaffolds manufactured using selective laser sintering

Degradation behaviour of porous poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) scaffolds in cell culture

Exploring the degradation behaviour of biomaterials in a complex in vitro physiological environment can assist in predicting their performance in vivo, yet this aspect remains largely unexplored. In this study, the in vitro degradation over 12 weeks of porous poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) bone scaffolds in human osteoblast (hOB) culture was investigated. The objective was to evaluate how the presence of cells influenced both the degradation behaviour and mechanical stability of these scaffolds. The molecular weight (Mw) of the scaffolds decreased with increasing incubation time and the Mw reduction rate (6.2 ± 0.4 kg mol-1 week-1) was similar to that observed when incubated in phosphate buffered saline (PBS) solution, implying that the scaffolds underwent hydrolytic degradation in hOB culture. The mass of the scaffolds increased by 0.8 ± 0.2 % in the first 4 weeks, attributed to cells attachment and extracellular matrix (ECM) deposition including biomineralisation. During the first 8 weeks, the nominal compressive modulus, E⁎, of the scaffolds remained constant. However, it increased significantly from Week 8 to 12, with increments of 55 % and 42 % in normal and lateral directions, respectively, attributed to the reinforcement effect of cells, ECM and minerals attached on the surface of the scaffold. This study has highlighted, that while the use of PBS in degradation studies is suitable for evaluating Mw changes it cannot predict changes in mechanical properties to PHBV scaffolds in the presence of cells and culture media. Furthermore, the PHBV scaffolds had mechanical stability in cell culture for 12 weeks validating their suitability for tissue engineering applications.

Additive manufacturing of sustainable biomaterials for biomedical applications

Biopolymers are promising environmentally benign materials applicable in multifarious applications. They are especially favorable in implantable biomedical devices thanks to their excellent unique properties, including bioactivity, renewability, bioresorbability, biocompatibility, biodegradability and hydrophilicity. Additive manufacturing (AM) is a flexible and intricate manufacturing technology, which is widely used to fabricate biopolymer-based customized products and structures for advanced healthcare systems. Three-dimensional (3D) printing of these sustainable materials is applied in functional clinical settings including wound dressing, drug delivery systems, medical implants and tissue engineering. The present review highlights recent advancements in different types of biopolymers, such as proteins and polysaccharides, which are employed to develop different biomedical products by using extrusion, vat polymerization, laser and inkjet 3D printing techniques in addition to normal bioprinting and four-dimensional (4D) bioprinting techniques. This review also incorporates the influence of nanoparticles on the biological and mechanical performances of 3D-printed tissue scaffolds. This work also addresses current challenges as well as future developments of environmentally friendly polymeric materials manufactured through the AM techniques. Ideally, there is a need for more focused research on the adequate blending of these biodegradable biopolymers for achieving useful results in targeted biomedical areas. We envision that biopolymer-based 3D-printed composites have the potential to revolutionize the biomedical sector in the near future.

Review on Porous Scaffolds Generation Process: A Tissue Engineering Approach

Porous scaffolds have been widely explored for tissue regeneration and engineering in vitro three-dimensional models. In this review, a comprehensive literature analysis is conducted to identify the steps involved in their generation. The advantages and disadvantages of the available techniques are discussed, highlighting the importance of considering pore geometrical parameters such as curvature and size, and summarizing the requirements to generate the porous scaffold according to the desired application. This paper considers the available design tools, mathematical models, materials, fabrication techniques, cell seeding methodologies, assessment methods, and the status of pore scaffolds in clinical applications. This review compiles the relevant research in the field in the past years. The trends, challenges, and future research directions are discussed in the search for the generation of a porous scaffold with improved mechanical and biological properties that can be reproducible, viable for long-term studies, and closer to being used in the clinical field.

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV))/Bacterial Cellulose (BC) Biocomposites for Potential Use in Biomedical Applications

The aim of this study was to obtain biocomposites consisting of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), bacterial cellulose (BC) and α-tocopherol by a melt processing technique for potential use in biomedical applications. The melt processing and roughness of biocomposites were evaluated and compared to sample without BC. The degradation rate of PHBV/BC biocomposites was measured in phosphate buffer saline (PBS) by determining the mass variation and evidencing of thermal and structural changes by differential scanning calorimetry (DSC) and attenuated total reflectance-Fourier transformed infrared spectrometry (ATR-FTIR). The cell viability, cell morphology, cell cycle distribution and total collagen content were investigated on murine NCTC fibroblasts. Overall, the adding of BC to polyester matrix led to an adequate melt processing of biocomposites and increased surface roughness and cytocompatibility, allowing the cells to secrete the extracellular matrix (collagen) and stimulate cell proliferation. Results showed that the PHBV/BC biocomposites were favorable for long-term degradation and could be used for the design of medical devices with controlled degradability.

Electrically Conductive Biocomposites Based on Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and Wood-Derived Carbon Fillers

In this paper, biobased carbons were used as fillers in poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). The mechanical and electrical properties of these 100% biocomposites were analyzed. First, biocarbons were prepared from wood dust and cellulose fibers using carbonization temperatures ranging 900–2300 °C. XRD revealed significant improvements of the graphitic structure with increasing temperatures for both precursors, with slightly higher ordering in wood-dust-based carbons. An increase of the carbon content with continuous removal of other elements was observed with increasing temperature. The carbonized cellulose fiber showed an accumulation of Na and O on the fiber surface at a carbonization temperature of 1500 °C. Significant degradation of PHBV was observed when mixed with this specific filler, which can, most probably, be attributed to this exceptional surface chemistry. With any other fillers, the preparation of injection-molded PHBV composites was possible without any difficulties. Small improvements in the mechanical performance were observed, with carbonized fibers being slightly superior to the wood dust analogues. Improvements at higher filler content were observed. These effects were even more pronounced in the electrical conductivity. In the range of 15–20 vol.% carbonized fibers, the percolation threshold could be reached, resulting in an electrical conductivity of 0.7 S/cm. For comparison, polypropylene composites were prepared using cellulose fibers carbonized at 2000 °C. Due to longer fibers retained in the composites, percolation could be reached in the range of 5–10 vol.%. The electrical conductivity was even higher compared to that of composites using commercial carbon fibers, showing a great potential for carbonized cellulose fibers in electrical applications.

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.

Selective Laser Melting of PA 2200 for Hip Implant Applications: Finite Element Analysis, Process Optimization, and Morphological and Mechanical Characterization

Polyamide 12 (PA 22000) is a well-known material and one of the most biocompatible materials tested and used to manufacture customized medical implants by selective laser sintering technology. To optimize the implants, several research activities were considered, starting with the design and manufacture of test samples made of PA 2200 by selective laser sintering (SLS) technology, with different processing parameters and part orientations. The obtained samples were subjected to compression tests and later to SEM analyses of the fractured zones, in which we determined the microstructural properties of the analyzed samples. Finally, an evaluation of the surface roughness of the material and the possibility of improving the surface roughness of the realized parts using finite element analysis to determine the optimum contact pressure between the component made of PA 2200 by SLS and the component made of TiAl6V4 by SLM was performed.

Two-Photon Polymerization: Functionalized Microstructures, Micro-Resonators, and Bio-Scaffolds

The direct laser writing technique based on two-photon polymerization (TPP) has evolved considerably over the past two decades. Its remarkable characteristics, such as 3D capability, sub-diffraction resolution, material flexibility, and gentle processing conditions, have made it suitable for several applications in photonics and biosciences. In this review, we present an overview of the progress of TPP towards the fabrication of functionalized microstructures, whispering gallery mode (WGM) microresonators, and microenvironments for culturing microorganisms. We also describe the key physical-chemical fundamentals underlying the technique, the typical experimental setups, and the different materials employed for TPP.