The Role of Microsphere Structures in Bottom-Up Bone Tissue Engineering

Bone defects have caused immense healthcare concerns and economic burdens throughout the world. Traditional autologous allogeneic bone grafts have many drawbacks, so the emergence of bone tissue engineering brings new hope. Bone tissue engineering is an interdisciplinary biomedical engineering method that involves scaffold materials, seed cells, and "growth factors". However, the traditional construction approach is not flexible and is unable to adapt to the specific shape of the defect, causing the cells inside the bone to be unable to receive adequate nourishment. Therefore, a simple but effective solution using the "bottom-up" method is proposed. Microspheres are structures with diameters ranging from 1 to 1000 µm that can be used as supports for cell growth, either in the form of a scaffold or in the form of a drug delivery system. Herein, we address a variety of strategies for the production of microspheres, the classification of raw materials, and drug loading, as well as analyze new strategies for the use of microspheres in bone tissue engineering. We also consider new perspectives and possible directions for future development.

Nervous System-Driven Osseointegration

Implants are essential therapeutic tools for treating bone fractures and joint replacements. Despite the in-depth study of osseointegration for more than fifty years, poor osseointegration caused by aseptic loosening remains one of the leading causes of late implant failures. Osseointegration is a highly sophisticated and spatiotemporal process in vivo involving the immune response, angiogenesis, and osteogenesis. It has been unraveled that the nervous system plays a pivotal role in skeletal health via manipulating neurotrophins, neuropeptides, and nerve cells. Herein, the research related to nervous system-driven osseointegration was systematically analyzed and reviewed, aiming to demonstrate the prominent role of neuromodulation in osseointegration. Additionally, it is indicated that the implant design considering the role of neuromodulation might be a promising way to prevent aseptic loosening.

An overview of the production methods for core-shell microspheres for parenteral controlled drug delivery

Core-shell microspheres hold great promise as a drug delivery system because they offer several benefits over monolithic microspheres in terms of release kinetics, for instance a reduced initial burst release, the possibility of delayed (pulsatile) release, and the possibility of dual-drug release. Also, the encapsulation efficiency can significantly be improved. Various methods have proven to be successful in producing these core-shell microspheres, both the conventional bulk emulsion solvent evaporation method and methods in which the microspheres are produced drop by drop. The latter have become increasingly popular because they provide improved control over the particle characteristics. This review assesses various production methods for core-shell microspheres and summarizes the characteristics of formulations prepared by the different methods, with a focus on their release kinetics.

An MSC bone-homing compound, Rab001, increases bone mass and reduces the incidence of osteonecrosis in a glucocorticoid-induced osteonecrosis mouse model

Currently, there are no effective medications to either prevent or slow the progression of atraumatic osteonecrosis (ON). The objective of this study is to determine the effects of bone-targeted delivery of mesenchymal stem cells on the prevalence of ON in a glucocorticoid (GC)-induced mouse model. Eight-week-old male BALB/c mice were randomized into groups that received placebo (PL), prednisolone (GC), or concurrent treatments with GC + mesenchymal stromal cells (MSCs), Rab001 or GC + Rab001 + MSCs. Human parathyroid hormone (hPTH) was used as a positive control for bone anabolism. Mice were killed after 30 days, and quantitative measurements of bone mass, bone strength, prevalent ON at the distal femoral epiphysis (DFE) were performed. Angiogenesis was accessed by RNA-Seq, the circulating angiogenic markers, as well as by immunohistochemical staining. We have showed that a novel agent, Rab001 that can noncovalently bind to mesenchymal stem cells (MSC) and direct them to the bone, prevents the incidence of glucocorticoid-induced osteonecrosis in the mouse. In contrast, PTH, a bone anabolic treatment, preserves bone mass but sustains higher ON incidence than Rab001+/- MSC-treated mice. The results of these experiments reveal that glucocorticoids increase the prevalence of ON, and agents that prevent loss of bone vascularity appear to prevent the development of ON. This intervention might be useful in patients with early stages of atraumatic ON.

Electrospray for generation of drug delivery and vaccine particles applied in vitro and in vivo

Also known as electrospray, electrohydrodynamic atomization has been used extensively in the last 15 years to develop polymer-based particles for drug delivery in cell and animal models. More recently, novel core-shell, multi-axial, and other electrospray particles have been developed from an array of polymers for a variety of biomedical applications. This review focuses on electrospray as a novel method of particle fabrication for drug delivery, specifically highlighting the applications of these particle systems in cell culture and animal models while also discussing polymers used for particle fabrication. Applications of electrospray particles to treat glioma, ovarian cancer, and breast cancer are reviewed. Additionally, delivery of antibiotics, gene therapy, and bacterial cells formulated in electrospray particles is discussed. Finally, vaccines as well as drug eluting particles for differentiation of stem cells and tissue engineering are highlighted. The article concludes with a discussion of where the future of electrospray technology can go to strengthen its foothold in the biomedical field.

Scaffolds as Structural Tools for Bone-Targeted Drug Delivery

Although bone has a high potential to regenerate itself after damage and injury, the efficacious repair of large bone defects resulting from resection, trauma or non-union fractures still requires the implantation of bone grafts. Materials science, in conjunction with biotechnology, can satisfy these needs by developing artificial bones, synthetic substitutes and organ implants. In particular, recent advances in materials science have provided several innovations, underlying the increasing importance of biomaterials in this field. To address the increasing need for improved bone substitutes, tissue engineering seeks to create synthetic, three-dimensional scaffolds made from organic or inorganic materials, incorporating drugs and growth factors, to induce new bone tissue formation. This review emphasizes recent progress in materials science that allows reliable scaffolds to be synthesized for targeted drug delivery in bone regeneration, also with respect to past directions no longer considered promising. A general overview concerning modeling approaches suitable for the discussed systems is also provided.

Role of Simvastatin on fracture healing and osteoporosis: a systematic review on in vivo investigations

Simvastatin is a lipid lowering drug whose beneficial role on bone metabolism was discovered in 1999. Several in vivo studies evaluated its role on osteoporosis and fracture healing, however, controversial results are seen in the literature. For this reason, Simvastatin has not been the focus of any clinical trials as yet. This systematic review clears the mechanisms of action of Simvastatin on bone metabolism and focuses on in vivo investigations that have evaluated its role on osteoporosis and fracture repair to find out (i) whether Simvastatin is effective on treatment of osteoporosis and fracture repair, and (ii) which of the many available protocols may have the ability to be translated in the clinical setting. Simvastatin induces osteoinduction by increasing osteoblast activity and differentiation and inhibiting their apoptosis. It also reduces osteoclastogenesis by decreasing both the number and activity of osteoclasts and their differentiation. Controversial results between the in vivo studies are mostly due to the differences in the route of administration, dose, dosage and carrier type. Local delivery of Simvastatin through controlled drug delivery systems with much lower doses and dosages than the systemic route seems to be the most valuable option in fracture healing. However, systemic delivery of Simvastatin with much higher doses and dosages than the clinical ones seems to be effective in managing osteoporosis. Simvastatin, in a particular range of doses and dosages, may be beneficial in managing osteoporosis and fracture injuries. This review showed that Simvastatin is effective in the treatment of osteoporosis and fracture healing.

Radiolucent inflammatory implant periapical lesions: a review of the literature

PURPOSE

To discuss the terminology, etiopathogenesis, and treatment of radiolucent inflammatory implant periapical lesions.

MATERIALS AND METHODS

An electronic search for relevant articles published in the English literature in the PubMed database.

RESULTS

Bacterial contamination of the apical portion of the implant either from a preexisting dental periapical infection or from a periapical lesion of endodontic origin of an adjacent tooth is the probable causative factor. Aseptic bone necrosis owing to overheating of the bone during preparation of osteotomies, or compression of the bone at the apex of the implant owing to excessive tightening, may also play a role. The histopathological features are of a mixed inflammatory cell infiltrate on a background of granulation tissue consistent with either a granuloma or an abscess as may be found at the apex of a nonvital tooth. Treatment consists of immediate and aggressive surgical debridement, chemical detoxification of the apical portion of the exposed implant surface, and systemic antibiotics with or without a bone regenerative procedure.

CONCLUSION

A radiolucent inflammatory implant periapical lesion is analogous to either a granuloma or an abscess as may be found at the apex of a nonvital tooth.

Influence of simvastatin-loaded implants on osseointegration in an ovariectomized animal model

The success of bone implants in the presence of osteoporosis is limited by lack of osseointegration between the implant and the natural bone. This study applied an electrochemical process to deposit simvastatin-nanohydroxyapatite (HA) coatings on porous implant surfaces and investigated the effects of these simvastatin-HA coatings on implant surfaces in an animal model of osteoporosis. In this study, simvastatin-HA coated implants were inserted into the tibia of osteoporotic rats. After 2, 4, and 12 weeks, tissue was retrieved for histomorphometric evaluation. The results indicated that the simvastatin-HA coatings increased bone-implant contact and new bone formation around implant surfaces. In conclusion, implants loaded with simvastatin by an electrochemical process improved implant osseointegration in osteoporotic rats. Furthermore, the increased concentration of simvastatin could affect the osseointegration, but the dose-effects also need further investigation.

Sequential platelet-derived growth factor-simvastatin release promotes dentoalveolar regeneration

OBJECTIVES

Timely augmentation of the physiological events of dentoalveolar repair is a prerequisite for the optimization of the outcome of regeneration. This study aimed to develop a treatment strategy to promote dentoalveolar regeneration by the combined delivery of the early mitogenic factor platelet-derived growth factor (PDGF) and the late osteogenic differentiation factor simvastatin.

MATERIALS AND METHODS

By using the coaxial electrohydrodynamic atomization technique, PDGF and simvastatin were encapsulated in a double-walled poly(D,L-lactide) and poly(D,L-lactide-co-glycolide) (PDLLA-PLGA) microspheres in five different modes: microspheres encapsulating bovine serum albumin (BB), PDGF alone (XP), simvastatin alone (SB), PDGF-in-core and simvastatin-in-shell (PS), and simvastatin-in-core and PDGF-in-shell (SP). The microspheres were characterized using scanning electronic microscopy, and the in vitro release profile was evaluated. Microspheres were delivered to fill large osteotomy sites on rat maxillae for 14 and 28 days, and the outcome of regeneration was evaluated by microcomputed tomography and histological assessments.

RESULTS

Uniform 20-μm controlled release microspheres were successfully fabricated. Parallel PDGF-simvastatin release was noted in the PS group, and the fast release of PDGF followed by the slow release of simvastatin was noted in the SP group. The promotion of osteogenesis was observed in XP, PS, and SP groups at day 14, whereas the SP group demonstrated the greatest bone fill, trabecular numbers, and thickest trabeculae. Bone bridging was evident in the PS and SP group, with significantly increased osteoblasts in the SP group, and osteoclastic cell recruitment was promoted in all bioactive molecule-treated groups. At day 28, osteogenesis was promoted in all bioactive molecule-treated groups. Initial corticalization was noted in the XP, PS, and SP groups. Osteoblasts appeared to be decreased in all groups, and significantly, a greater osteoclastic cell recruitment was noted in the SB and SP groups.

CONCLUSIONS

Both PDGF and simvastatin facilitate dentoalveolar regeneration, and sequential PDGF-simvastatin release (SP group) further accelerated the regeneration process through the enhancement of osteoblastogenesis and the promotion of bone maturation.

Platelet-rich plasma, plasma rich in growth factors and simvastatin in the regeneration and repair of alveolar bone

Platelet preparations promote bone regeneration by inducing cell migration, proliferation and differentiation in the area of the injury, which are essential processes for regeneration. In addition, several studies have indicated that simvastatin (SIMV), widely used for the treatment of hypercholesterolemia, stimulates osteogenesis. The objective of this study was to evaluate the effects of treatment with either platelet-rich plasma (PRP) or plasma rich in growth factors (PRGF) in combination with SIMV in the regeneration and repair of alveolar bone. The jaws of Sprague Dawley rats (n=18) were subjected to rotary instrument-induced bone damage (BD). Animals were divided into six groups: BD/H₂O (n=3), distilled water without the drug and alveolar bone damage; BD/H₂O/PRP (n=3), BD and PRP; BD/H₂O/PRGF (n=3), BD and PRGF; BD/SIMV (n=3), BD and water with SIMV; BD/SIMV/PRP (n=3), BD, PRP and SIMV; and BD/SIMV/PRGF (n=3), BD, PRGF and SIMV. Conventional histological analysis (hematoxylin and eosin staining) revealed that the BD/SIMV group showed indicators for mature bone tissue, while the BD/SIMV/PRP and BD/SIMV/PRGF groups showed the coexistence of indicators for mature and immature bone tissue, with no statistical differences between the platelet preparations. Simvastatin did not improve the effect of platelet-rich plasma and plasma rich in growth factors. It was not possible to determine which platelet preparation produced superior effects.