Bone Tissue Engineering Using Porous Carbonate Apatite and Bone Marrow Cells

Biological Properties and Medical Applications of Carbonate Apatite: A Systematic Review

Bone defects represent an everyday challenge for clinicians who work in the fields of orthopedic surgery, maxillofacial and oral surgery, otorhinolaryngology, and dental implantology. Various bone substitutes have been developed and utilized, according to the needs of bone reconstructive surgery. Carbonate apatite has gained popularity in recent years, due to its excellent tissue behavior and osteoconductive potential. This systematic review aims to evaluate the role of carbonate apatite in bone reconstructive surgery and tissue engineering, analyze its advantages and limitations, and suggest further directions for research and development. The Web of Science, PubMed, and Scopus electronic databases were searched for relevant review articles, published from January 2014 to 21 July 2023. The study was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Eighteen studies were included in the present review. The biological properties and medical applications of carbonate apatite (CO3Ap) are discussed and evaluated. The majority of articles demonstrated that CO3Ap has excellent biocompatibility, resorbability, and osteoconductivity. Furthermore, it resembles bone tissue and causes minimal immunological reactions. Therefore, it may be successfully utilized in various medical applications, such as bone substitution, scaffolding, implant coating, drug delivery, and tissue engineering.

Calcium Orthophosphate (CaPO4)-Based Bioceramics: Preparation, Properties, and Applications

Various types of materials have been traditionally used to restore damaged bones. In the late 1960s, a strong interest was raised in studying ceramics as potential bone grafts due to their biomechanical properties. A short time later, such synthetic biomaterials were called bioceramics. Bioceramics can be prepared from diverse inorganic substances, but this review is limited to calcium orthophosphate (CaPO4)-based formulations only, due to its chemical similarity to mammalian bones and teeth. During the past 50 years, there have been a number of important achievements in this field. Namely, after the initial development of bioceramics that was just tolerated in the physiological environment, an emphasis was shifted towards the formulations able to form direct chemical bonds with the adjacent bones. Afterwards, by the structural and compositional controls, it became possible to choose whether the CaPO4-based implants would remain biologically stable once incorporated into the skeletal structure or whether they would be resorbed over time. At the turn of the millennium, a new concept of regenerative bioceramics was developed, and such formulations became an integrated part of the tissue engineering approach. Now, CaPO4-based scaffolds are designed to induce bone formation and vascularization. These scaffolds are usually porous and harbor various biomolecules and/or cells. Therefore, current biomedical applications of CaPO4-based bioceramics include artificial bone grafts, bone augmentations, maxillofacial reconstruction, spinal fusion, and periodontal disease repairs, as well as bone fillers after tumor surgery. Prospective future applications comprise drug delivery and tissue engineering purposes because CaPO4 appear to be promising carriers of growth factors, bioactive peptides, and various types of cells.

The potential of carbonate apatite as an alternative bone substitute material

Bone reconstructive surgery has become a common procedure, and bone transplantation has become the second most frequently performed tissue transplantation procedure worldwide. Therefore, the need for bone substitute materials has increased. Artificial bone substitutes exhibit osteoconductive properties and feature several advantages, including abundant resources, low cost, and low donor site morbidity. Carbonate apatite (CO3Ap) is a calcium phosphate ceramic that can be used as a synthetic bone graft. The carbonate content of this ceramic is similar to that of bone apatite. In this review, we show that carbonate apatite can be degraded given its chemical reactivity in a weakly acidic environment and through osteoclast resorption. Moreover, it is osteoconductive and promotes bone tissue formation without fibrotic tissue formation. Additionally, microstructural analysis revealed that new bone tissue is formed within the bone graft itself.

Impact of Biomimicry in the Design of Osteoinductive Bone Substitutes: Nanoscale Matters

Bone apatite consists of carbonated calcium-deficient hydroxyapatite (CDHA) nanocrystals. Biomimetic routes allow fabricating synthetic bone grafts that mimic biological apatite. In this work, we explored the role of two distinctive features of biomimetic apatites, namely, nanocrystal morphology (plate vs needle-like crystals) and carbonate content, on the bone regeneration potential of CDHA scaffolds in an in vivo canine model. Both ectopic bone formation and scaffold degradation were drastically affected by the nanocrystal morphology after intramuscular implantation. Fine-CDHA foams with needle-like nanocrystals, comparable in size to bone mineral, showed a markedly higher osteoinductive potential and a superior degradation than chemically identical coarse-CDHA foams with larger plate-shaped crystals. These findings correlated well with the superior bone-healing capacity showed by the fine-CDHA scaffolds when implanted intraosseously. Moreover, carbonate doping of CDHA, which resulted in small plate-shaped nanocrystals, accelerated both the intrinsic osteoinduction and the bone healing capacity, and significantly increased the cell-mediated resorption. These results suggest that tuning the chemical composition and the nanostructural features may allow the material to enter the physiological bone remodeling cycle, promoting a tight synchronization between scaffold degradation and bone formation.

Calcium Orthophosphate-Based Bioceramics

Various types of grafts have been traditionally used to restore damaged bones. In the late 1960s, a strong interest was raised in studying ceramics as potential bone grafts due to their biomechanical properties. A bit later, such synthetic biomaterials were called bioceramics. In principle, bioceramics can be prepared from diverse materials but this review is limited to calcium orthophosphate-based formulations only, which possess the specific advantages due to the chemical similarity to mammalian bones and teeth. During the past 40 years, there have been a number of important achievements in this field. Namely, after the initial development of bioceramics that was just tolerated in the physiological environment, an emphasis was shifted towards the formulations able to form direct chemical bonds with the adjacent bones. Afterwards, by the structural and compositional controls, it became possible to choose whether the calcium orthophosphate-based implants remain biologically stable once incorporated into the skeletal structure or whether they were resorbed over time. At the turn of the millennium, a new concept of regenerative bioceramics was developed and such formulations became an integrated part of the tissue engineering approach. Now calcium orthophosphate scaffolds are designed to induce bone formation and vascularization. These scaffolds are often porous and harbor different biomolecules and/or cells. Therefore, current biomedical applications of calcium orthophosphate bioceramics include bone augmentations, artificial bone grafts, maxillofacial reconstruction, spinal fusion, periodontal disease repairs and bone fillers after tumor surgery. Perspective future applications comprise drug delivery and tissue engineering purposes because calcium orthophosphates appear to be promising carriers of growth factors, bioactive peptides and various types of cells.

Osteoblast activity on carbonated hydroxyapatite

Hydroxyapatite (HA), has been used commonly as a bone substitute and as a scaffold in bone tissue engineering. However it has certain drawbacks such as limited biodegradability and osteointegration properties. Other forms of HA, for example, carbonated hydroxyapatite (CHA) could prove to have enhanced bioactivity as they more closely mimic the chemical composition of the apatite found in human bone. The aim of this study was to test the efficacy of CHA in comparison to HA used as a control. The CHA (4.9 wt %) and the HA discs were seeded with MC3T3-E1 osteoblastic cells. Results revealed a trend of increased cell attachment on the HA discs at day 0, however, the cell proliferation on the CHA discs at 7 and 28 days showed no significant difference in comparison to the HA control. SEM of the CHA discs showed surface irregularities at 7 days indicating dissolution. Also at 7 days, SEM demonstrated cell attachment and extracellular matrix production on both the CHA and HA samples. There was no significant difference in the total amount of collagen produced in the CHA samples relative to the HA control samples at 28 days as evaluated by the hydroxyproline assay. Real time PCR revealed mRNA increase by 2.08, 7.62, and 9.86 fold for collagen I a1, collagen III a1, and osteocalcin respectively on the CHA as compared to the HA discs. This study demonstrates the use of CHA as a biocompatible material that has potentially increased biodegradation properties and osteogenic capability in comparison to HA.