Histologic study of incorporation and resorption of a bone cement–collagen composite: an in vivo study in the minipig

Calcium Orthophosphate (CaPO4) Containing Composites for Biomedical Applications: Formulations, Properties, and Applications

The goal of this review is to present a wide range of hybrid formulations and composites containing calcium orthophosphates (abbreviated as CaPO4) that are suitable for use in biomedical applications and currently on the market. The bioactive, biocompatible, and osteoconductive properties of various CaPO4-based formulations make them valuable in the rapidly developing field of biomedical research, both in vitro and in vivo. Due to the brittleness of CaPO4, it is essential to combine the desired osteologic properties of ceramic CaPO4 with those of other compounds to create novel, multifunctional bone graft biomaterials. Consequently, this analysis offers a thorough overview of the hybrid formulations and CaPO4-based composites that are currently known. To do this, a comprehensive search of the literature on the subject was carried out in all significant databases to extract pertinent papers. There have been many formulations found with different material compositions, production methods, structural and bioactive features, and in vitro and in vivo properties. When these formulations contain additional biofunctional ingredients, such as drugs, proteins, enzymes, or antibacterial agents, they offer improved biomedical applications. Moreover, a lot of these formulations allow cell loading and promote the development of smart formulations based on CaPO4. This evaluation also discusses basic problems and scientific difficulties that call for more investigation and advancements. It also indicates perspectives for the future.

Regeneration of alveolar bone defects in the experimental pig model: A systematic review and meta-analysis

OBJECTIVE

Pigs are emerging as a preferred experimental in vivo model for bone regeneration. The study objective was to answer the focused PEO question: in the pig model (P), what is the capacity of experimental alveolar bone defects (E) for spontaneous regeneration in terms of new bone formation (O)?

METHODS

Following PRISMA guidelines, electronic databases were searched for studies reporting experimental bone defects or extraction socket healing in the maxillae or mandibles of pigs. The main inclusion criteria were the presence of a control group of untreated defects/sockets and the assessment of regeneration via 3D tomography [radiographic defect fill (RDF)] or 2D histomorphometry [new bone formation (NBF)]. Random effects meta-analyses were performed for the outcomes RDF and NBF.

RESULTS

Overall, 45 studies were included reporting on alveolar bone defects or extraction sockets, most frequently in the mandibles of minipigs. Based on morphology, defects were broadly classified as 'box-defects' (BD) or 'cylinder-defects' (CD) with a wide range of healing times (10 days to 52 weeks). Meta-analyses revealed pooled estimates (with 95% confidence intervals) of 50% RDF (36.87%-63.15%) and 43.74% NBF (30.47%-57%) in BD, and 44% RDF (16.48%-71.61%) and 39.67% NBF (31.53%-47.81%) in CD, which were similar to estimates of socket-healing [48.74% RDF (40.35%-57.13%) and 38.73% NBF (28.57%-48.89%)]. Heterogeneity in the meta-analysis was high (I2 > 90%).

CONCLUSION

A substantial body of literature revealed a high capacity for spontaneous regeneration in experimental alveolar bone defects of (mini)pigs, which should be considered in future studies of bone regeneration in this animal model.

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.

Regenerative Potential of Hydroxyapatite-Based Ceramic Biomaterial on Mandibular Cortical Bone: An In Vivo Study

Reconstruction of bone defects and maintaining the continuity of the mandible is still a challenge in the maxillofacial surgery. Nowadays, the biomedical research within bone defect treatment is focussed on the therapy of using innovative biomaterials with specific characteristics consisting of the body’s own substances. Hydroxyapatite ceramic scaffolds have fully acceptable phase compositions, microstructures and compressive strengths for their use in regenerative medicine. The innovative hydroxyapatite ceramics used by us were prepared using the tape-casting method, which allows variation in the shape of samples after packing hydroxyapatite paste to 3D-printed plastic form. The purpose of our qualitative study was to evaluate the regenerative potential of the innovative ceramic biomaterial prepared using this method in the therapy of the cortical bone of the lower jaw in four mature pigs. The mandible bone defects were evaluated after different periods of time (after 3, 4, 5 and 6 months) and compared with the control sample (healthy cortical bone from the opposite side of the mandible). The results of the morphological, clinical and radiological investigation and hardness examination confirmed the positive regenerative potential of ceramic implants after treatment of the mandible bone defects in the porcine mandible model.

Computed tomography and histological evaluation of xenogenic and biomimetic bone grafts in three-wall alveolar defects in minipigs

OBJECTIVES

This study aimed to compare the performance of a xenograft (XG) and a biomimetic synthetic graft (SG) in three-wall alveolar defects in minipigs by means of 3D computerised tomography and histology.

MATERIALS AND METHODS

Eight minipigs were used. A total of eight defects were created in the jaw of each animal, three of which were grafted with XGs, three with SGs, and two were left empty as a negative control. The allocation of the different grafts was randomised. Four animals were euthanised at 6 weeks and four at 12 weeks. The grafted volume was then measured by spiral computed tomography to assess volume preservation. Additionally, a histological analysis was performed in undecalcified samples by backscattered scanning electron microscopy and optical microscopy after Masson's trichrome staining.

RESULTS

A linear mixed-effects model was applied considering four fixed factors (bone graft type, regeneration time, anatomic position, and maxilla/mandible) and one random factor (animal). The SG exhibited significantly larger grafted volume (19%) than the XG. The anterior sites preserved better the grafted volume than the posterior ones. Finally, regeneration time had a positive effect on the grafted volume. Histological observations revealed excellent osseointegration and osteoconductive properties for both biomaterials. Some concavities found in the spheroidal morphologies of SGs were associated with osteoclastic resorption.

CONCLUSIONS

Both biomaterials met the requirements for bone grafting, i.e. biocompatibility, osseointegration, and osteoconduction. Granule morphology was identified as an important factor to ensure a good volume preservation.

CLINICAL RELEVANCE

Whereas both biomaterials showed excellent osteoconduction, SGs resulted in better volume preservation.

Cytocompatibility of Bone Substitute Materials and Membranes

BACKGROUND/AIM

With the demographic change and associated chronic bone loss, the need for cytocompatible bone replacement materials arise in modern medicine. The aim of this in vitro study was to investigate the cytocompatibility of eleven different bone substitute materials and membranes.

MATERIALS AND METHODS

Seven bone substitute materials and four membranes were assessed in vitro. The specimens were tested based on their interaction with MC3T3 pre-osteoblasts, through the utilization of viability, proliferation, and cytotoxicity assays. Cell vitality was evaluated using live-dead staining.

RESULTS

Although we found minor differences in cytocompatibility among the assessed materials, all tested materials can be considered as cytocompatible with a viability of more than 70% of the negative control, which indicates the non-toxic range as defined in current, international standards (DIN EN ISO 10993-5:2009, German Institute for Standardization, Berlin, Germany). Direct live-dead staining assays confirmed satisfactory cytocompatibility of all tested membranes.

CONCLUSION

All examined bone substitute materials and membranes were found to be cytocompatible. In order to assess whether the observed minor differences can impact regenerative processes, further in vivo studies need to be conducted.

Adhesive Cements That Bond Soft Tissue Ex Vivo

The aim of the present study was to evaluate the soft tissue bond strength of a newly developed, monomeric, biomimetic, tissue adhesive called phosphoserine modified cement (PMC). Two types of PMCs were evaluated using lap shear strength (LSS) testing, on porcine skin: a calcium metasilicate (CS1), and alpha tricalcium phosphate (αTCP) PMC. CS1 PCM bonded strongly to skin, reaching a peak LSS of 84, 132, and 154 KPa after curing for 0.5, 1.5, and 4 h, respectively. Cyanoacrylate and fibrin glues reached an LSS of 207 kPa and 33 kPa, respectively. αTCP PMCs reached a final LSS of ≈110 kPa. In soft tissues, stronger bond strengths were obtained with αTCP PMCs containing large amounts of amino acid (70-90 mol%), in contrast to prior studies in calcified tissues (30-50 mol%). When αTCP particle size was reduced by wet milling, and for CS1 PMCs, the strongest bonding was obtained with mole ratios of 30-50% phosphoserine. While PM-CPCs behave like stiff ceramics after setting, they bond to soft tissues, and warrant further investigation as tissue adhesives, particularly at the interface between hard and soft tissues.

Investigations of silk fiber/calcium phosphate cement biocomposite for radial bone defect repair in rabbits

Background

This study aimed to investigate the effects of silk fiber (SF)/calcium phosphate cement (CPC) biocomposite on repairing radial bone defects in rabbits.

Methods

Four-month-old New Zealand rabbits were selected to create a bilateral radial bone defect model and divided into four groups according to implanted material: SF/CPC, SF/CPC/particulate bone (PB), PB, and control (C). The specimens were removed at four and eight postoperative weeks for general observation, X-ray examination, tissue slicing, scanning electron microscopy (SEM), and biomechanical testing.

Results

Postoperative X-ray showed no bone defect repair in group C and different degrees of bone defect repair in the other three groups. Imaging, histology, and SEM showed the following: group SF/CPC formed fine trabecular bone in week 4, while the maximum bending load in group SF/CPC in week 4 was significantly different from those in the other groups (P < 0.05).

Conclusions

SF/CPC has good biocompatibility and bone-inducing ability, demonstrating its bone defect-repairing ability.

Biocompatibility of calcium phosphate bone cement with optimised mechanical properties: an in vivo study

This work establishes the in vivo performance of modified calcium phosphate bone cements for vertebroplasty of spinal fractures using a lapine model. A non-modified calcium phosphate bone cement and collagen-calcium phosphate bone cements composites with enhanced mechanical properties, utilising either bovine collagen or collagen from a marine sponge, were compared to a commercial poly(methyl methacrylate) cement. Conical cement samples (8 mm height × 4 mm base diameter) were press-fit into distal femoral condyle defects in New Zealand White rabbits and assessed after 5 and 10 weeks. Bone apposition and tartrate-resistant acid phosphatase activity around cements were assessed. All implants were well tolerated, but bone apposition was higher on calcium phosphate bone cements than on poly(methyl methacrylate) cement. Incorporation of collagen showed no evidence of inflammatory or immune reactions. Presence of positive tartrate-resistant acid phosphatase staining within cracks formed in calcium phosphate bone cements suggested active osteoclasts were present within the implants and were actively remodelling within the cements. Bone growth was also observed within these cracks. These findings confirm the biological advantages of calcium phosphate bone cements over poly(methyl methacrylate) and, coupled with previous work on enhancement of mechanical properties through collagen incorporation, suggest collagen-calcium phosphate bone cement composite may offer an alternative to calcium phosphate bone cements in applications where low setting times and higher mechanical stability are important.

Calcium Orthophosphate-Containing Biocomposites and Hybrid Biomaterials for Biomedical Applications

The state-of-the-art on calcium orthophosphate (CaPO4)-containing biocomposites and hybrid biomaterials suitable for biomedical applications is presented. Since these types of biomaterials offer many significant and exciting possibilities for hard tissue regeneration, this subject belongs to a rapidly expanding area of biomedical research. Through the successful combinations of the desired properties of matrix materials with those of fillers (in such systems, CaPO4 might play either role), innovative bone graft biomaterials can be designed. Various types of CaPO4-based biocomposites and hybrid biomaterials those are either already in use or being investigated for biomedical applications are extensively discussed. Many different formulations in terms of the material constituents, fabrication technologies, structural and bioactive properties, as well as both in vitro and in vivo characteristics have been already proposed. Among the others, the nano-structurally controlled biocomposites, those containing nanodimensional compounds, biomimetically fabricated formulations with collagen, chitin and/or gelatin, as well as various functionally graded structures seem to be the most promising candidates for clinical applications. The specific advantages of using CaPO4-based biocomposites and hybrid biomaterials in the selected applications are highlighted. As the way from a laboratory to a hospital is a long one and the prospective biomedical candidates have to meet many different necessities, the critical issues and scientific challenges that require further research and development are also examined.

Biocompatibility of calcium phosphate bone cement with optimized mechanical properties

The broad aim of this work was to investigate and optimize the properties of calcium phosphate bone cements (CPCs) for use in vertebroplasty to achieve effective primary fixation of spinal fractures. The incorporation of collagen, both bovine and from a marine sponge (Chondrosia reniformis), into a CPC was investigated. The biological properties of the CPC and collagen–CPC composites were assessed in vitro through the use of human bone marrow stromal cells. Cytotoxicity, proliferation, and osteoblastic differentiation were evaluated using lactate dehydrogenase, PicoGreen, and alkaline phosphatase activity assays, respectively. The addition of both types of collagen resulted in an increase in cytotoxicity, albeit not to a clinically relevant level. Cellular proliferation after 1, 7, and 14 days was unchanged. The osteogenic potential of the CPC was reduced through the addition of bovine collagen but remained unchanged in the case of the marine collagen. These findings, coupled with previous work showing that incorporation of marine collagen in this way can improve the physical properties of CPCs, suggest that such a composite may offer an alternative to CPCs in applications where low setting times and higher mechanical stability are important. © 2015 The Authors. Journal of Biomedical Materials Research Part B: Applied Biomaterials Published by Wiley Periodicals, Inc. 104B:308–315, 2015.

Engineering of bone using porous calcium phosphate cement and bone marrow stromal cells for maxillary sinus augmentation with simultaneous implant placement in goats

The aim of this study was to explore the effects of maxillary sinus floor elevation and simultaneous dental implantation with a tissue-engineered bone complex of calcium phosphate cement (CPC) scaffolds combined with bone marrow stromal cells (BMSCs). A large animal goat model is used with the tissue engineering method. Eighteen bilateral maxillary sinus of nine goats were randomly allocated into three groups; the CPC/BMSC complex (n=6) was used to elevate maxillary sinus floor with a simultaneous implant placement; the effects were compared with those treated with CPC alone (n=6) or autogenous bone (n=6). After a healing period of 3 months, sequential triad-color fluorescence labeling, micro-CT, as well as histological and histomorphometric analyses indicated that the tissue-engineered BMSC/CPC complex could promote earlier bone formation and mineralization, and maximally maintain the volume and height of the augmented maxillary sinus. By comparison, CPC-alone or autogenous bone achieved less bone formation and later mineralization. Besides, the average bone-implant contact value reflecting the osseointegration was 35.63%±9.42% in the BMSCs/CPC group, significantly higher than 22.47%±4.28% in the CPC-alone group or 28.26%±8.03% in the autogenous bone group. In conclusion, CPC serves as a potential substrate for BMSCs for the maxillary sinus floor augmentation and simultaneous implantation. The tissue-engineered bone might enhance the stability of implants and thus be of great significance to achieve improved quality to restore the oral function in clinic.

Collagen-calcium phosphate cement scaffolds seeded with umbilical cord stem cells for bone tissue engineering

Human umbilical cord mesenchymal stem cells (hUCMSCs) avoid the invasive procedure required to harvest bone marrow MSCs. The addition of collagen fibers into self-setting calcium phosphate cement (CPC) may increase the scaffold strength, and enhance cell attachment and differentiation. The objectives of this study were to develop a novel class of collagen-CPC composite scaffolds, and to investigate hUCMSC attachment, proliferation, and osteogenic differentiation on collagen-CPC scaffolds for the first time. Collagen fibers in CPC improved the load-bearing capability. Flow cytometry showed that the hUCMSCs expressed cell surface markers characteristic of MSCs, and were negative for hematopoietic and endothelial cell markers. hUCMSCs proliferated rapidly in all CPC composite scaffolds, with cell number increasing by sevenfold in 8 days. Cellular function was enhanced with collagen fibers in CPC scaffolds. Cell density increased from (645±60) cells/mm(2) on CPC with 0% collagen, to (1056±65) cells/mm(2) on CPC with 8% collagen (p<0.05). The actin stress fibers inside the hUCMSCs were stained, and the fluorescence intensity was doubled when the collagen in CPC was increased by 0% to 8%. RT-PCR showed that hUCMSCs on CPC with collagen had higher osteogenic expression than those on CPC without collagen. Alizarin Red S staining revealed a great increase in mineralization by hUCMSCs on CPC with collagen than that without collagen. In conclusion, hUCMSCs showed excellent proliferation, differentiation, and synthesis of bone minerals in collagen-CPC composite scaffolds for the first time. The novel hUCMSC-seeded collagen-CPC construct with superior cell function and load-bearing capability is promising to enhance bone regeneration in a wide range of orthopedic and craniofacial applications.

Biocomposites and hybrid biomaterials based on calcium orthophosphates

The state-of-the-art of biocomposites and hybrid biomaterials based on calcium orthophosphates that are suitable for biomedical applications is presented in this review. Since these types of biomaterials offer many significant and exciting possibilities for hard tissue regeneration, this subject belongs to a rapidly expanding area of biomedical research. Through successful combinations of the desired properties of matrix materials with those of fillers (in such systems, calcium orthophosphates might play either role), innovative bone graft biomaterials can be designed. Various types of biocomposites and hybrid biomaterials based on calcium orthophosphates, either those already in use or being investigated for biomedical applications, are extensively discussed. Many different formulations, in terms of the material constituents, fabrication technologies, structural and bioactive properties as well as both in vitro and in vivo characteristics, have already been proposed. Among the others, the nanostructurally controlled biocomposites, those containing nanodimensional compounds, biomimetically fabricated formulations with collagen, chitin and/or gelatin as well as various functionally graded structures seem to be the most promising candidates for clinical applications. The specific advantages of using biocomposites and hybrid biomaterials based on calcium orthophosphates in the selected applications are highlighted. As the way from the laboratory to the hospital is a long one, and the prospective biomedical candidates have to meet many different necessities, this review also examines the critical issues and scientific challenges that require further research and development.

Miniature pigs as an animal model for implant research: bone regeneration in critical-size defects

OBJECTIVE

Standardized experimental investigations determining the critical-size defect (CSD) in the mandible of miniature pigs are still lacking. The aim of the present study was to obtain information about the new bone formation in created defects of varying sizes.

STUDY DESIGN

Marginal resection of the alveolar crest of the lower jaw was performed in 3 female miniature pigs. The animals used in the study were 3 years of age and weighed approximately 55 kg. For histologic evaluation the dental implants were harvested with the surrounding bone tissue 10 weeks after implant placement. For this, bone segments including the implants were removed from each side of the mandible. The sizes of the resected bone blocks varied, showing the following volumes: 10.1 cm(3), 4.2 cm(3), and 1.9 cm(3). Periosteal coverage of the defects was performed. Computerized tomography (CT) of the skull of the miniature pig was performed immediately after the surgical procedure as well as 6 weeks later using a 64-channel mult-slice scanner.

RESULTS

The CT showed that 6 weeks after obtaining the biopsies, the filling of the defects with new bone varied. The percentage of newly formed bone in relation to the size of the original defect was 57.4% for the small- and 87.2% for the middle-sized defect. The large-sized defect showed 75.5% newly formed bone compared with baseline.

CONCLUSION

Considering the amount of new bone formation found within this study, it is questionable if the critical defect size of 5 cm(3) stated in the literature is valid. Further research concerning the mandibular model in minipigs is required and more refinement needed to assure a standardized CSD, allowing qualitative and quantitative evaluation of bone grafts and bone graft substitutes.