The influence of prefreezing temperature on pore structure in freeze-dried beta-TCP scaffolds

Poly(propylene fumarate)/magnesium calcium phosphate injectable bone composite: Effect of filler size and its weight fraction on mechanical properties

This study aimed to produce a composite of poly(propylene fumarate)/magnesium calcium phosphate as a substitutional implant in the treatment of trabecular bone defects. So, the effect of magnesium calcium phosphate particle size, magnesium calcium phosphate:poly(propylene fumarate) weight ratio on compressive strength, Young's modulus, and toughness was assessed by considering effective fracture mechanisms. Micro-sized (∼30 µm) and nano-sized (∼50 nm) magnesium calcium phosphate particles were synthesized via emulsion precipitation and planetary milling methods, respectively, and added to poly(propylene fumarate) up to 20 wt.%. Compressive strength, Young's modulus, and toughness of the composites were measured by compressive test, and effective fracture mechanisms were evaluated by imaging fracture surface. In both micro- and nano-composites, the highest compressive strength was obtained by adding 10 wt.% magnesium calcium phosphate particles, and the enhancement in nano-composite was superior to micro-one. The micrographs of fracture surface revealed different mechanisms such as crack pinning, void plastic growth, and particle cleavage. According to the results, the produced composite can be considered as a candidate for substituting hard tissue.

3D-printing porosity: A new approach to creating elevated porosity materials and structures

We introduce a new process that enables the ability to 3D-print high porosity materials and structures by combining the newly introduced 3D-Painting process with traditional salt-leaching. The synthesis and resulting properties of three 3D-printable inks comprised of varying volume ratios (25:75, 50:50, 70:30) of CuSO₄ salt and polylactide-co-glycolide (PLGA), as well as their as-printed and salt-leached counterparts, are discussed. The resulting materials are comprised entirely of PLGA (F-PLGA), but exhibit porosities proportional to the original CuSO₄ content. The three distinct F-PLGA materials exhibit average porosities of 66.6-94.4%, elastic moduli of 112.6-2.7 MPa, and absorbency of 195.7-742.2%. Studies with adult human mesenchymal stem cells (hMSCs) demonstrated that elevated porosity substantially promotes cell adhesion, viability, and proliferation. F-PLGA can also act as carriers for weak, naturally or synthetically-derived hydrogels. Finally, we show that this process can be extended to other materials including graphene, metals, and ceramics.

STATEMENT OF SIGNIFICANCE

Porosity plays an essential role in the performance and function of biomaterials, tissue engineering, and clinical medicine. For the same material chemistry, the level of porosity can dictate if it is cell, tissue, or organ friendly; with low porosity materials being far less favorable than high porosity materials. Despite its importance, it has been difficult to create three-dimensionally printed structures that are comprised of materials that have extremely high levels of internal porosity yet are surgically friendly (able to handle and utilize during surgical operations). In this work, we extend a new materials-centric approach to 3D-printing, 3D-Painting, to 3D-printing structures made almost entirely out of water-soluble salt. The structures are then washed in a specific way that not only extracts the salt but causes the structures to increase in size. With the salt removed, the resulting medical polymer structures are almost entirely porous and contain very little solid material, but the maintain their 3D-printed form and are highly compatible with adult human stem cells, are mechanically robust enough to use in surgical manipulations, and can be filled with and act as carriers for biologically active liquids and gels. We can also extend this process to three-dimensionally printing other porous materials, such as graphene, metals, and even ceramics.

Physical Properties of Implanted Porous Bioscaffolds Regulate Skin Repair: Focusing on Mechanical and Structural Features

Porous bioscaffolds are applied to facilitate skin repair since the early 1990s, but a perfect regeneration outcome has yet to be achieved. Until now, most efforts have focused on modulating the chemical properties of bioscaffolds, while physical properties are traditionally overlooked. Recent advances in mechanobiology and mechanotherapy have highlighted the importance of biomaterials' physical properties in the regulation of cellular behaviors and regenerative processes. In skin repair, the mechanical and structural features of porous bioscaffolds are two major physical properties that determine therapeutic efficacy. Here, first an overview of natural skin repair with an emphasis on the major biophysically sensitive cell types involved in this multistage process is provided, followed by an introduction of the four roles of bioscaffolds as skin implants. Then, how the mechanical and structural features of bioscaffolds influence these four roles is discussed. The mechanical and structural features of porous bioscaffolds should be tailored to balance the acceleration of wound closure and functional improvements of the repaired skin. This study emphasizes that decoupling and precise control of the mechanical and structural features of bioscaffolds are significant aspects that should be considered in future biomaterial optimization, which can build a foundation to ultimately achieve perfect skin regeneration outcomes.

The effects of different amounts of drug microspheres on the vivo and vitro performance of the PLGA/β-TCP scaffold

OIC-A006 (BMPs osteogenesis compounds), can stimulate bone marrow mesenchymal stem cells ALP, OPN, OC, Cbfal expression. To stimulate new bone formation in the body. We postulate different amounts of drug microspheres on the PLGA/β-CPT scaffold can produce the effects on performance and sustained release characteristics. In this paper, through adding different amount of carrier drug microsphere, three concentrations scaffolds which are 12.5, 18.75 and 25 μmol/L are prepared by adding different amounts of drug-loaded microspheres. Hereafter called OICM/CPT-200, OICM/CPT-300, OICM/CPT-400. We implant them in rat femur diameter 3 mm depth of 3 mm hole for eight weeks. The degradation, microsphere, delivery properties, with X-ray, micro-CT and histology are tested. Results show that the contain carrier drug microsphere scaffolds become radiopaque, and the gaps between the scaffold and radial cut ends are often invisible. This preliminary study reveals that different carrier drug microsphere has a corresponding effect the performance of stent body, OICM/CPT – 200 scaffolds induction effect is best. Illustrates that the low concentration load OIC-A006 microspheres can promote bone healing, and high concentration of OIC-A006 micro ball is played a inhibitory effect on bone healing process.

Harnessing Hierarchical Nano- and Micro-Fabrication Technologies for Musculoskeletal Tissue Engineering

Cells within a tissue are able to perceive, interpret and respond to the biophysical, biomechanical, and biochemical properties of the 3D extracellular matrix environment in which they reside. Such stimuli regulate cell adhesion, metabolic state, proliferation, migration, fate and lineage commitment, and ultimately, tissue morphogenesis and function. Current scaffold fabrication strategies in musculoskeletal tissue engineering seek to mimic the sophistication and comprehensiveness of nature to develop hierarchically assembled 3D implantable devices of different geometric dimensions (nano- to macrometric scales) that will offer control over cellular functions and ultimately achieve functional regeneration. Herein, advances and shortfalls of bottom-up (self-assembly, freeze-drying, rapid prototype, electrospinning) and top-down (imprinting) scaffold fabrication approaches, specific to musculoskeletal tissue engineering, are discussed and critically assessed.

Bone regeneration using a freeze-dried 3D gradient-structured scaffold incorporating OIC-A006-loaded PLGA microspheres based on β-TCP/PLGA

To reveal the latent capacity of the growth factor-like low-molecular-weight material OIC-A006 in tissue regeneration, it is essential to design a porous scaffold in order to concurrently accommodate cells and drug release in a controlled manner. Consequently, we fabricated poly (L-lactide-co-glycolide) (PLGA)-based microspheres with an OIC-A006-loaded gradient-structured β-TCP/PLGA scaffold by freeze-drying which could then be used for drug delivery and bone regeneration. The OIC-A006-loaded β-TCP/PLGA scaffold consisted of two parts which loaded different doses of OIC-A006 (6.25 μM, outside; 12.5 μM, inside). The porosity, compressive strength, SEM, degradation, and cumulative amount of drug release in vitro were characterized. Furthermore, we confirmed the incorporation of OIC-A006 into the PLGA-based microspheres within the scaffolds using UV-spectrophotometry, and the amount of drug remaining in the scaffold was maintained by 10 % for up to 28 days. The drug release was slower in the normal-structured drug-loaded scaffold. The OIC-A006 released action from the OIC-A006-loaded β-TCP/PLGA scaffold with ideal therapeutic prospects in tissue regeneration. In vitro cell culture results showed that this gradient-structured composite scaffold can induce the adhesion and proliferation of rat bone marrow stromal cells towards osteoblasts. These results showed that the newly developed OIC-A006-loaded scaffolds with gradient structure can be potentially applied to bone regeneration in clinical applications.

Silk as a biocohesive sacrificial binder in the fabrication of hydroxyapatite load bearing scaffolds

Limitations of current clinical methods for bone repair continue to fuel the demand for a high strength, bioactive bone replacement material. Recent attempts to produce porous scaffolds for bone regeneration have been limited by the intrinsic weakness associated with high porosity materials. In this study, ceramic scaffold fabrication techniques for potential use in load-bearing bone repairs have been developed using naturally derived silk from Bombyx mori. Silk was first employed for ceramic grain consolidation during green body formation, and later as a sacrificial polymer to impart porosity during sintering. These techniques allowed preparation of hydroxyapatite (HA) scaffolds that exhibited a wide range of mechanical and porosity profiles, with some displaying unusually high compressive strength up to 152.4 ± 9.1 MPa. Results showed that the scaffolds exhibited a wide range of compressive strengths and moduli (8.7 ± 2.7 MPa to 152.4 ± 9.1 MPa and 0.3 ± 0.1 GPa to 8.6 ± 0.3 GPa) with total porosities of up to 62.9 ± 2.7% depending on the parameters used for fabrication. Moreover, HA-silk scaffolds could be molded into large, complex shapes, and further machined post-sinter to generate specific three-dimensional geometries. Scaffolds supported bone marrow-derived mesenchymal stem cell attachment and proliferation, with no signs of cytotoxicity. Therefore, silk-fabricated HA scaffolds show promise for load bearing bone repair and regeneration needs.