Rotary-jet spun polycaprolactone/nano-hydroxyapatite scaffolds modified by simulated body fluid influenced the flexural mode of the neoformed bone

Toward osteomimetic formation of calcium phosphate coatings with carbonated hydroxyapatite

Biomimetic production of coatings on various types of scaffolds is based mainly on simulated body fluid precipitation (SBF) of apatites, or, if the HCO₃^- is present, carbonated apatites. Recently, we proposed formation of calcium phosphates (CaP) precipitates by alkaline phosphatase (ALP) hydrolysing glycerophosphate in presence of calcium ions as an alternative to SBF. Since apatites synthesized in bone by the ALP activity contain carbonate anions, it was tempting to investigate whether the phosphatase method could be advanced into osteomimetic one. Therefore, taking example from the SBF studies, phosphatase incubation medium was enriched with carbonate ions at 4.2 and 27 mM concentration. X-ray diffraction of the precipitates disclosed peaks typical for hydroxyapatite (HAP). FTIR analysis showed that at both concentration of carbonate ions, apatites underwent both B and A substitution, more extensive at higher concentration. Thus, osteomimetic approach produced carbonated hydroxyapatites of the type encountered in bone tissue even at HCO₃^- concentration as low as 4.2 mM. Composite plates made of poly(ε-caprolactone) and mixture of β-tricalcium phosphate and hydroxyapatite at mass ratio of 1:0.5:0.5, respectively, were covered by CaP coatings, i.e., CaP-0, CaP-4.2, CaP-27, by incubation in phosphatase medium containing 0, 4.2 or 27 mM of NaHCO₃, respectively. Pristine or coated PCL50 plates were used to study release of calcium and adsorption/desorption of proteins, or seeded with human bone marrow mesenchymal stem cells (hMSC) for study of cell adhesion, spreading and osteogenic differentiation. Introduction of carbonate into the CaP coatings significantly increased release of Ca²⁺ in a carbonate concentration-dependent manner; the release was up to 4 times higher, when compared to CaP-0 coating, and reached 0.41 ± 0.01 mM for CaP-27 after first 24 h. Coating CaP-4.2 yielded significantly higher adsorption of bovine serum albumin and cytochrome C than CaP-0. All of the CaP coatings improved significantly hMSC adhesion, however, only CaP-4.2 provided 2 times higher cell number than PCL50 after 2 weeks of culture. Interestingly, ALP activity calculated per cell number was the highest on pristine plates, presumably because hMSC differentiate preferentially into osteoblasts at lower seeding densities. It appears, therefore, that the osteomimetic approach may be useful for production of carbonated hydroxyapatite coatings, but requires further studies and replacing intestinal phosphatase used in this work with one originating from bone.

Boron nitride nanofiber/Zn-doped hydroxyapatite/polycaprolactone scaffolds for bone tissue engineering applications

In this study, Zn doped hydroxyapatite (Zn HA)/boron nitride nanofiber (BNNF)/poly-ε-caprolactone (PCL) composite aligned fibrous scaffolds are produced with rotary jet spinning (RJS) for bone tissue engineering applications. It is hypothesized that addition of Zn HA and BNNF will contribute to cell viability as well as mechanical and osteogenic properties of the PCL scaffolds. Zn HA was synthesized by mixing Ca and P sources followed by sonication and aging whereas BNNF was obtained by the reaction of melamine with boric acid followed by freeze-drying for annealing of fibers. It is found that incorporation of both Zn HA and BNNF in PCL fibers resulted in higher calcium phosphate (CaP) precipitation on the scaffolds. Also, in vitro cell culture studies showed that presence of both Zn HA and BNNF also had synergistic effect for enhanced proliferation and osteogenic activity of Saos-2 cells. Mechanical properties of PCL-Zn HA-BNNF were found similar to that of non-load bearing bones. Furthermore, the presence of Zn HA and BNNF had synergistic effects to cell attachment, proliferation and spreading without causing cytotoxic effect on cells. The highest ALP activity was obtained in the PCL-Zn HA- BNNF group at days 7 and 14 due to release of zinc, calcium, phosphate and boron. Considering its mechanical and bioactivity properties, PCL-Zn HA-BNNF composite scaffolds hold promise as non-load bearing bone substitutes.

Nano-Hydroxyapatite Composite Scaffolds Loaded with Bioactive Factors and Drugs for Bone Tissue Engineering

Nano-hydroxyapatite (n-HAp) is similar to human bone mineral in structure and biochemistry and is, therefore, widely used as bone biomaterial and a drug carrier. Further, n-HAp composite scaffolds have a great potential role in bone regeneration. Loading bioactive factors and drugs onto n-HAp composites has emerged as a promising strategy for bone defect repair in bone tissue engineering. With local delivery of bioactive agents and drugs, biological materials may be provided with the biological activity they lack to improve bone regeneration. This review summarizes classification of n-HAp composites, application of n-HAp composite scaffolds loaded with bioactive factors and drugs in bone tissue engineering and the drug loading methods of n-HAp composite scaffolds, and the research direction of n-HAp composite scaffolds in the future is prospected.

Rotary Jet Spinning (RJS): A Key Process to Produce Biopolymeric Wound Dressings

Wounds result from different causes (e.g., trauma, surgeries, and diabetic ulcers), requiring even extended periods of intensive care for healing, according to the patient's organism and treatment. Currently, wound dressings generated by polymeric fibers at micro and nanometric scales are promising for healing the injured area. They offer great surface area and porosity, mimicking the fibrous extracellular matrix structure, facilitating cell adhesion, migration, and proliferation, and accelerating the wound healing process. Such properties resulted in countless applications of these materials in biomedical and tissue engineering, also as drug delivery systems for bioactive molecules to help tissue regeneration. The techniques used to engineer these fibers include spinning methods (electro-, rotary jet-), airbrushing, and 3D printing. These techniques have important advantages, such as easy-handle procedure and process parameters variability (type of polymer), but encounter some scalability problems. RJS is described as a simple and low-cost technique resulting in high efficiency and yield for fiber production, also capable of bioactive agents' incorporation to improve the healing potential of RJS wound dressings. This review addresses the use of RJS to produce polymeric fibers, describing the concept, type of configuration, comparison to other spinning techniques, most commonly used polymers, and the relevant parameters that influence the manufacture of the fibers, for the ultimate use in the development of wound dressings.

Smart Mushroom-Inspired Imprintable and Lightly Detachable (MILD) Microneedle Patterns for Effective COVID-19 Vaccination and Decentralized Information Storage

The key to controlling the spread of the coronavirus disease 2019 (COVID-19) and reducing mortality is highly dependent on the safe and effective use of vaccines for the general population. Current COVID-19 vaccination practices (intramuscular injection of solution-based vaccines) are limited by heavy reliance on medical professionals, poor compliance, and laborious vaccination recording procedures, resulting in a waste of health resources and low vaccination coverage, etc. In this study, we developed a smart mushroom-inspired imprintable and lightly detachable (MILD) microneedle platform for the effective and convenient delivery of multidose COVID-19 vaccines and decentralized vaccine information storage. The mushroom-like structure allows the MILD system to be easily pressed into the skin and detached from the patch base, acting as a "tattoo" to record the vaccine counts in situ without any storage equipment, offering quick accessibility and effortless readout, saving a great deal of valuable time and energy for both patients and health professionals. After loading inactivated SARS-CoV-2 virus-based vaccines, MILD system induced a high level of antibodies against the SARS-CoV-2 receptor-binding domain (RBD) in vivo without eliciting systemic toxicity and local damage. Collectively, this smart delivery platform serves as a promising carrier to improve COVID-19 vaccination efficacy through its dual capabilities of vaccine delivery and in situ data storage, thus exhibiting great potential for helping to contain the COVID-19 pandemic or a resurgence.

Fabrication of Biomedical Scaffolds Using Biodegradable Polymers

Degradable polymers are used widely in tissue engineering and regenerative medicine. Maturing capabilities in additive manufacturing coupled with advances in orthogonal chemical functionalization methodologies have enabled a rapid evolution of defect-specific form factors and strategies for designing and creating bioactive scaffolds. However, these defect-specific scaffolds, especially when utilizing degradable polymers as the base material, present processing challenges that are distinct and unique from other classes of materials. The goal of this review is to provide a guide for the fabrication of biodegradable polymer-based scaffolds that includes the complete pathway starting from selecting materials, choosing the correct fabrication method, and considering the requirements for tissue specific applications of the scaffold.

Electrospun Poly(butylene-adipate-co-terephthalate)/Nano-hyDroxyapatite/Graphene Nanoribbon Scaffolds Improved the In Vivo Osteogenesis of the Neoformed Bone

Electrospun ultrathin fibrous scaffold filed with synthetic nanohydroxyapatite (nHAp) and graphene nanoribbons (GNR) has bioactive and osteoconductive properties and is a plausible strategy to improve bone regeneration. Poly(butylene-adipate-co-terephthalate) (PBAT) has been studied as fibrous scaffolds due to its low crystallinity, faster biodegradability, and good mechanical properties; however, its potential for in vivo applications remains underexplored. We proposed the application of electrospun PBAT with high contents of incorporated nHAp and nHAp/GNR nanoparticles as bone grafts. Ultrathin PBAT, PBAT/nHAp, and PBAT/nHAp/GNR fibers were produced using an electrospinning apparatus. The produced fibers were characterized morphologically and structurally using scanning electron (SEM) and high-resolution transmission electron (TEM) microscopies, respectively. Mechanical properties were analyzed using a texturometer. All scaffolds were implanted into critical tibia defects in rats and analyzed after two weeks using radiography, microcomputed tomography, histological, histomorphometric, and biomechanical analyses. The results showed through SEM and high-resolution TEM characterized the average diameters of the fibers (ranged from 0.208 µm ± 0.035 to 0.388 µm ± 0.087) and nHAp (crystallite around 0.28, 0.34, and 0.69 nm) and nHAp/GNR (200–300 nm) nanoparticles distribution into PBAT matrices. Ultrathin fibers were obtained, and the incorporated nHAp and nHAp/GNR nanoparticles were well distributed into PBAT matrices. The addition of nHAp and nHAp/GNR nanoparticles improved the elastic modulus of the ultrathin fibers compared to neat PBAT. High loads of nHAp/GNR (PBATnH5G group) improved the in vivo lamellar bone formation promoting greater radiographic density, trabecular number and stiffness in the defect area 2 weeks after implantation than control and PBAT groups.