Reconstruction of mandibular bone defects using biphasic calcium phosphate bone substitutes with simultaneous implant placement in mini‐swine: A pilot in vivo study

Melatonin and calcium phosphate crystal-loaded poly(L-lactic acid) porous microspheres reprogram macrophages to improve bone repair

The bone immune microenvironment can influence the occurrence and progression of bone defects. To date, research on promoting macrophage M2 polarization to improve bone injury repair has been insufficient. In this study, we designed an injectable poly(L-lactic acid) (PLLA) porous microsphere that forms calcium phosphate crystals on its surface by binding to melatonin, followed by bionanomimetic mineralization in vitro. The microsphere is injectable and degradable, and its release of melatonin (MT) and calcium phosphate (CaP) crystals promotes macrophage M2 polarization, reprogramming of macrophages, and enhanced osteogenesis. After LPS stimulation, the proportion of M2-polarized macrophages in the MS@CaP@MT group was 39.2 ± 2.7%, significantly higher than that in other groups (P < 0.05). Further, in the MS@CaP@MT group, rats exhibited bone mineral densities of 129.4 ± 12.8 mg cc-1 at 2 weeks and 171.6 ± 13.6 mg cc-1 at 4 weeks in the defect area, which were significantly higher than those in other groups (P < 0.05). Using an animal model of femoral condylar defects, we demonstrated that MT PLLA porous microspheres loaded with calcium phosphate crystals can improve the immune microenvironment and form a microsphere-centered osteogenesis model. This significantly accelerates bone defect repair and provides a potential strategy for bone defect treatment.

Recent advancement in vascularized tissue-engineered bone based on materials design and modification

Bone is one of the most vascular network-rich tissues in the body and the vascular system is essential for the development, homeostasis, and regeneration of bone. When segmental irreversible damage occurs to the bone, restoring its vascular system by means other than autogenous bone grafts with vascular pedicles is a therapeutic challenge. By pre-generating the vascular network of the scaffold in vivo or in vitro, the pre-vascularization technique enables an abundant blood supply in the scaffold after implantation. However, pre-vascularization techniques are time-consuming, and in vivo pre-vascularization techniques can be damaging to the body. Critical bone deficiencies may be filled quickly with immediate implantation of a supporting bone tissue engineered scaffold. However, bone tissue engineered scaffolds generally lack vascularization, which requires modification of the scaffold to aid in enhancing internal vascularization. In this review, we summarize the relationship between the vascular system and osteogenesis and use it as a basis to further discuss surgical and cytotechnology-based pre-vascularization strategies and to describe the preparation of vascularized bone tissue engineered scaffolds that can be implanted immediately. We anticipate that this study will serve as inspiration for future vascularized bone tissue engineered scaffold construction and will aid in the achievement of clinical vascularized bone.

Role of periosteum during healing of alveolar critical size bone defects in the mandible: a pilot study

OBJECTIVES

Minipigs present advantages for studying oral bone regeneration; however, standardized critical size defects (CSD) for alveolar bone have not been validated yet. The objectives of this study are to develop a CSD in the mandibular alveolar bone in Aachen minipigs and to further investigate the specific role of periosteum.

MATERIALS AND METHODS

Three female Aachen minipigs aged 17, 24, and 84 months were used. For each minipig, a split-mouth design was performed: an osteotomy (2 cm height × 2.5 cm length) was performed; the periosteum was preserved on the left side and removed on the right side. Macroscopic, cone beam computed tomography (CBCT), microcomputed tomography (µCT), and histological analyses were performed to evaluate the bone defects and bone healing.

RESULTS

In both groups, spontaneous healing was insufficient to restore initial bone volume. The macroscopic pictures and the CBCT results showed a larger bone defect without periosteum. µCT results revealed that BMD, BV/TV, and Tb.Th were significantly lower without periosteum. The histological analyses showed (i) an increased osteoid apposition in the crestal area when periosteum was removed and (ii) an ossification process in the mandibular canal area in response to the surgical that seemed to increase when periosteum was removed.

CONCLUSIONS

A robust model of CSD model was developed in the alveolar bone of minipigs that mimics human mandibular bone defects. This model allows to further investigate the bone healing process and potential factors impacting healing such as periosteum.

CLINICAL RELEVANCE

This model may be relevant for testing different bone reconstruction strategies for preclinical investigations.

Calcium-to-phosphorus releasing ratio affects osteoinductivity and osteoconductivity of calcium phosphate bioceramics in bone tissue engineering

Calcium phosphate (Ca-P) bioceramics, including hydroxyapatite (HA), biphasic calcium phosphate (BCP), and beta-tricalcium phosphate (β-TCP), have been widely used in bone reconstruction. Many studies have focused on the osteoconductivity or osteoinductivity of Ca-P bioceramics, but the association between osteoconductivity and osteoinductivity is not well understood. In our study, the osteoconductivity of HA, BCP, and β-TCP was investigated based on the osteoblastic differentiation in vitro and in situ as well as calvarial defect repair in vivo, and osteoinductivity was evaluated by using pluripotent mesenchymal stem cells (MSCs) in vitro and heterotopic ossification in muscles in vivo. Our results showed that the cell viability, alkaline phosphatase activity, and expression of osteogenesis-related genes, including osteocalcin (Ocn), bone sialoprotein (Bsp), alpha-1 type I collagen (Col1a1), and runt-related transcription factor 2 (Runx2), of osteoblasts each ranked as BCP > β-TCP > HA, but the alkaline phosphatase activity and expression of osteogenic differentiation genes of MSCs each ranked as β-TCP > BCP > HA. Calvarial defect implantation of Ca-P bioceramics ranked as BCP > β-TCP ≥ HA, but intramuscular implantation ranked as β-TCP ≥ BCP > HA in vivo. Further investigation indicated that osteoconductivity and osteoinductivity are affected by the Ca/P ratio surrounding the Ca-P bioceramics. Thus, manipulating the appropriate calcium-to-phosphorus releasing ratio is a critical factor for determining the osteoinductivity of Ca-P bioceramics in bone tissue engineering.

Wnt signalling in oral and maxillofacial diseases

Wnts include more than 19 types of secreted glycoproteins that are involved in a wide range of pathological processes in oral and maxillofacial diseases. The transmission of Wnt signalling from the extracellular matrix into the nucleus includes canonical pathways and noncanonical pathways, which play an important role in tooth development, alveolar bone regeneration, and related diseases. In recent years, with the in-depth study of Wnt signalling in oral and maxillofacial-related diseases, many new conclusions and perspectives have been reached, and there are also some controversies. This article aims to summarise the roles of Wnt signalling in various oral diseases, including periodontitis, dental pulp disease, jaw disease, cleft palate, and abnormal tooth development, to provide researchers with a better and more comprehensive understanding of Wnts in oral and maxillofacial diseases.

Biomaterial Properties Modulating Bone Regeneration

Biomaterial scaffolds have been gaining momentum in the past several decades for their potential applications in the area of tissue engineering. They function as three-dimensional porous constructs to temporarily support the attachment of cells, subsequently influencing cell behaviors such as proliferation and differentiation to repair or regenerate defective tissues. In addition, scaffolds can also serve as delivery vehicles to achieve sustained release of encapsulated growth factors or therapeutic agents to further modulate the regeneration process. Given the limitations of current bone grafts used clinically in bone repair, alternatives such as biomaterial scaffolds have emerged as potential bone graft substitutes. This review summarizes how physicochemical properties of biomaterial scaffolds can influence cell behavior and its downstream effect, particularly in its application to bone regeneration.

Evolution of drug-eluting biomedical implants for sustained drug delivery

In the field of drug delivery, the most commonly used treatments have traditionally been systemically delivered using oral or intravenous administration. The problems associated with this type of delivery is that the drug concentration is controlled by first pass metabolism, and therefore may not always remain within the therapeutic window. Implantable drug delivery systems (IDDSs) are an excellent alternative to traditional delivery because they offer the ability to precisely control the drug release, deliver drugs locally to the target tissue, and avoid the toxic side effects often experienced with systemic administration. Since the creation of the first FDA-approved IDDS in 1990, there has been a surge in research devoted to fabricating and testing novel IDDS formulations. The versatility of these systems is evident when looking at the various biomedical applications that utilize IDDSs. This review provides an overview of the history of IDDSs, with examples of the different types of IDDS formulations, as well as looking at current and future biomedical applications for such systems. Though there are still obstacles that need to be overcome, ever-emerging new technologies are making the manufacturing of IDDSs a rewarding therapeutic endeavor with potential for further improvements.

Assessment of biphasic calcium phosphate 70/30 alginate scaffold on the tibia in pigs

Background and Aim:

Calcium phosphate bioceramics have been used for at least a decade, and many investigations have focused on the use of hydroxyapatite (HA) derivative in the regeneration of bone defects. Biphasic calcium phosphate (BCP) is a biomaterial composed of HA and beta-tricalcium phosphate (BCP), with a structure similar to bone. The aim of the study was to determine the influence of the BCP/alginate scaffold on tissue growth, blood, the lungs, and the electrical activity of the heart during bone healing in the tibia of pig.

Materials and Methods:

Three pigs were implanted with BCP/alginate scaffolds in the tibias. Pigs were acclimatized and treated with antibiotics and anthelminthic drugs 14 days before implantation. Each pig was implanted with a BCP/alginate scaffold in the right tibia and a defect without the implant was made in the left tibia as the control. Radiographic images of the tibia were captured 0, 7, 30, and 60 days after the operation. Erythrograms, radiography of the lungs, and electrocardiogram (ECG) recordings were done 0, 30, and 60 days after the operation.

Results:

Radiographic evaluations showed that the implant and peri-implant density of BCP decreased throughout the process of bone healing. The erythrogram profile indicated that a substantial amount of time (60 days) was required to adapt and return to pre-operative conditions. No significant differences in ECG recordings or pulmonary radiography were detected.

Conclusion:

The BCP/alginate scaffold did not induce a faster recovery rate from the bone defect compared to the control with no implant. However, the BCP/alginate scaffold was biodegradable, bioresorbable, and non-toxic.