Development and Characterization of a Rabbit Model of Compromised Maxillofacial Wound Healing

A novel micro-CT analysis for evaluating the regenerative potential of bone augmentation xenografts in rabbit calvarias

Guided Bone Regeneration is a common procedure, yet, as new grafting materials are being introduced into the market, a reliable evaluation method is required. Critical size defect in animal models provides an accurate simulation, followed by histological sections to evaluate the new bone formation. However, histology is destructive, two-dimensional and technique-sensitive. In this study we developed a novel volumetric Micro-CT analysis to quantify new bone formation characteristics. Eight adult female New Zealand white rabbits were subjected to calvarial critical-size defects. Four 8 mm in diameter circular defects were preformed in each animal, to allow random allocation of four treatment modalities. All calvarias were scanned using Micro-CT. Each defect was segmented into four equal parts: pristine bone, outer, middle, and inner. Amira software (v. 6.3, www.fei.com ) was used to calculate the new bone volume in each region and compare it to that of the pristine bone. All grafting materials demonstrated that new bone formation decreased as it moved inward. Only the inner region differed across grafting materials (p = 0.001). The new Micro-CT analysis allowed us to divide each defect into 3D regions providing better understanding of the bone formation process. Amongst the various advantages of the Micro-CT, it enables us to quantify the graft materials and the newly formed bone independently, and to describe the defect morphology in 3D (bi- vs. uni-cortical defects). Providing an insight into the inner region of the defect can better predict the regenerative potential of the bone augmentation graft material. Therefore, the suggested Micro-CT analysis is beneficial for further developing of clinical approaches.

3D Printing Applications for Craniomaxillofacial Reconstruction: A Sweeping Review

The field of craniomaxillofacial (CMF) surgery is rich in pathological diversity and broad in the ages that it treats. Moreover, the CMF skeleton is a complex confluence of sensory organs and hard and soft tissue with load-bearing demands that can change within millimeters. Computer-aided design (CAD) and additive manufacturing (AM) create extraordinary opportunities to repair the infinite array of craniomaxillofacial defects that exist because of the aforementioned circumstances. 3D printed scaffolds have the potential to serve as a comparable if not superior alternative to the "gold standard" autologous graft. In vitro and in vivo studies continue to investigate the optimal 3D printed scaffold design and composition to foster bone regeneration that is suited to the unique biological and mechanical environment of each CMF defect. Furthermore, 3D printed fixation devices serve as a patient-specific alternative to those that are available off-the-shelf with an opportunity to reduce operative time and optimize fit. Similar benefits have been found to apply to 3D printed anatomical models and surgical guides for preoperative or intraoperative use. Creation and implementation of these devices requires extensive preclinical and clinical research, novel manufacturing capabilities, and strict regulatory oversight. Researchers, manufacturers, CMF surgeons, and the United States Food and Drug Administration (FDA) are working in tandem to further the development of such technology within their respective domains, all with a mutual goal to deliver safe, effective, cost-efficient, and patient-specific CMF care. This manuscript reviews FDA regulatory status, 3D printing techniques, biomaterials, and sterilization procedures suitable for 3D printed devices of the craniomaxillofacial skeleton. It also seeks to discuss recent clinical applications, economic feasibility, and future directions of this novel technology. By reviewing the current state of 3D printing in CMF surgery, we hope to gain a better understanding of its impact and in turn identify opportunities to further the development of patient-specific surgical care.

Revolutionizing bone regeneration: advanced biomaterials for healing compromised bone defects

In this review, we explore the application of novel biomaterial-based therapies specifically targeted towards craniofacial bone defects. The repair and regeneration of critical sized bone defects in the craniofacial region requires the use of bioactive materials to stabilize and expedite the healing process. However, the existing clinical approaches face challenges in effectively treating complex craniofacial bone defects, including issues such as oxidative stress, inflammation, and soft tissue loss. Given that a significant portion of individuals affected by traumatic bone defects in the craniofacial area belong to the aging population, there is an urgent need for innovative biomaterials to address the declining rate of new bone formation associated with age-related changes in the skeletal system. This article emphasizes the importance of semiconductor industry-derived materials as a potential solution to combat oxidative stress and address the challenges associated with aging bone. Furthermore, we discuss various material and autologous treatment approaches, as well as in vitro and in vivo models used to investigate new therapeutic strategies in the context of craniofacial bone repair. By focusing on these aspects, we aim to shed light on the potential of advanced biomaterials to overcome the limitations of current treatments and pave the way for more effective and efficient therapeutic interventions for craniofacial bone defects.

Bilateral double site (calvarial and mandibular) critical-size bone defect model in rabbits for evaluation of a craniofacial tissue engineering constructs

Most existing preclinical models for evaluating the biosafety and bone-regeneration efficacy of innovative bone substitute materials (BSMs) or tissue engineering (TE) constructs only consisted of a single-site defect and the anatomical locations of defect varied drastically. While the compelling evidence showed that the bone healing pattern is location-dependent, owing to developmental, structural, and functional differences of anatomical locations, this is particularly true for the craniofacial region. Taking this into account, the bone healing efficiency of a BSM shown at one anatomical defect location cannot ensure the same impact at another. This prompted us to develop, for the first time, a model of bilateral critical-sized defect (CSD) at two distinctly different locations (non-load-bearing parietal calvaria and load-bearing mandibular body) co-existing in one rabbit to reduce the number of animals needed and avoid the influence of interindividual variability and evaluation bias on comparisons.

24 healthy adult male New Zealand White rabbits were randomly assigned to a group, either control, autograft (considered the “gold standard”) or a clinically relevant BSM (biphasic calcium phosphate granules) (BCPg, Mastergraft®, Medronics). The full-thickness cylindrical calvarial defect (ø10 mm) on frontoparietal region and mandibular composite defect (ø11 mm) on the body of the mandible were created bilaterally using low-speed drilling with saline irrigation. The defect on one side was filled with autograft debris or BCPg, and the other side was no graft (empty). Following the euthanasia of animals at the predetermined intervals (4w and 12w), the defect zones were examined macroscopically and then sampled and processed for microcomputed tomography (microCT) and histological analysis.

All surgeries went uneventfully, and all rabbits recovered slowly but steadily. No symptoms of infection or inflammation associated with the defect were observed during the experiment. At 4w and 12w, macroscopic views of all defect sites were clean without any signs of necrosis or abscess, and no intraoral communication was found. The analysis of microCT and histological findings showed the non-healing nature of the empty defect, thereby both calvaria and mandible CSDs can be validated. The study of the application of BCPg in this defect model highlighted good osteointegration and excellent osteoconductive properties but compromised the osteoinductive properties of this material (compared with autograft).

To conclude, this novel double-site CSD model holds great promise in the application for preclinical evaluation of BSMs, TE construct, etc. With a reduced number of animals in use, and lower interindividual variability and evaluation bias for comparisons.

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A novel rabbit model of bilateral critical-sized defect co-existing at two distinctly different locations was developed.

Three-Dimensional Printing for Craniofacial Bone Tissue Engineering

The basic concepts from the fields of biology and engineering are integrated into tissue engineering to develop constructs for the repair of damaged and/or absent tissues, respectively. The field has grown substantially over the past two decades, with particular interest in bone tissue engineering (BTE). Clinically, there are circumstances in which the quantity of bone that is necessary to restore form and function either exceeds the patient's healing capacity or bone's intrinsic regenerative capabilities. Vascularized osseous or osteocutaneous free flaps are the standard of care with autologous bone remaining the gold standard, but is commonly associated with donor site morbidity, graft resorption, increased operating time, and cost. Regardless of the size of a craniofacial defect, from trauma, pathology, and osteonecrosis, surgeons and engineers involved with reconstruction need to consider the complex three-dimensional (3D) geometry of the defect and its relationship to local structures. Three-dimensional printing has garnered significant attention and presents opportunities to use craniofacial BTE as a technology that offers a personalized approach to bony reconstruction. Clinicians and engineers are able to work together to produce patient-specific space-maintaining scaffolds tailored to site-specific defects, which are osteogenic, osseoconductive, osseoinductive, encourage angiogenesis/vasculogenesis, and mechanically stable upon implantation to prevent immediate failure. In this work, we review biological and engineering principles important in applying 3D printing technology to BTE for craniofacial reconstruction as well as present recent translational advancements in 3D printed bioactive ceramic scaffold technology.

Assessment of irradiated socket healing in the rabbit's mandible: Experimental study

As bone healing is altered after external radiation therapy, its evaluation is mandatory and lacks in clinical practice. The aim of the pilot study was to validate micro computed tomography (microCT) as a simple and reliable technique for assessing irradiated bone healing in the rabbit's mandible and compare with histologic findings. Nineteen rabbits (female New Zealand white) were used. The radiation protocol consisted of 5 sessions delivering 8.5 Gy each. MicroCT was performed at D0, D7, D14, D28 and D42 for the control group and D0, D28 and D42 for the irradiated group. A modified Perry's score was determined on histologic samples, and comparison between microCT and histological findings was performed. The main differences between irradiated and non-irradiated rabbits were observed at Day 28 and 42. There was a strong correlation between imaging and histologic findings. Radiation decreases bone quality and bone mineral density. As the correlation was strong between microCT and histologic findings, micro imaging could be considered as a simple and reliable technique to assess bone healing after radiation therapy and allows an easy comparison between samples, without invasive procedures. Great attention should be kept on the parameters and on the region of interest. The development of in-vivo microCT enlarges the perspectives of microCT use in experimental studies, avoiding invasive procedures, and preserving animal lives and well-being, and furthermore lead to clinical applications.

Effect of Radiation on DCE-MRI Pharmacokinetic Parameters in a Rabbit Model of Compromised Maxillofacial Wound Healing: A Pilot Study

PURPOSE

Osteoradionecrosis (ORN), a potentially debilitating complication of maxillofacial radiation, continues to present a challenging clinical scenario, with limited treatment options that often fail. Translational animal models that can accurately mimic the human characteristics of the condition are lacking. In the present pilot study, we aimed to characterize the effects of radiation on the dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) pharmacokinetic parameters in a rabbit model of compromised maxillofacial wound healing to determine its potential as a translational model of ORN.

MATERIALS AND METHODS

An experimental group underwent fractionated radiation of the mandible totaling 36 Gy. At 4 weeks after irradiation, the experimental and control groups (n = 8 rabbits each) underwent a surgical procedure to create a critical size defect in the mandibular bone. DCE-MRI scans were acquired 1 week after arrival (baseline; time point 1), 4 weeks after completion of irradiation in the experimental group (just before surgery, time point 2), and 4 weeks after surgery (time point 3).

RESULTS

No differences in the analyzed DCE-MRI parameters were noted within the experimental or control group between the baseline values (time point 1) and those after irradiation (time point 2). The whole blood volume fraction (v_b) in the experimental group was increased compared with that in the control group after irradiation (time point 2; P < .05). After surgery (time point 3), both the forward flux rate of contrast from blood plasma and the extracellular extravascular space and the v_b were increased in the control group compared with the experimental group (P < .05).

CONCLUSIONS

The results of the present study suggest that DCE-MRI of a rabbit model of compromised maxillofacial wound healing could reflect the DCE-MRI characteristics of human patients with ORN and those at risk of developing the condition. Future studies will focus on further characterization of this rabbit model as a translational preclinical model of ORN.