The importance of the dura in craniofacial surgery

In vivo validation of highly customized cranial Ti-6AL-4V ELI prostheses fabricated through incremental forming and superplastic forming: an ovine model study

Cranial reconstructions are essential for restoring both function and aesthetics in patients with craniofacial deformities or traumatic injuries. Titanium prostheses have gained popularity due to their biocompatibility, strength, and corrosion resistance. The use of Superplastic Forming (SPF) and Single Point Incremental Forming (SPIF) techniques to create titanium prostheses, specifically designed for cranial reconstructions was investigated in an ovine model through microtomographic and histomorphometric analyses. The results obtained from the explanted specimens revealed significant variations in bone volume, trabecular thickness, spacing, and number across different regions of interest (VOIs or ROIs). Those regions next to the center of the cranial defect exhibited the most immature bone, characterized by higher porosity, decreased trabecular thickness, and wider trabecular spacing. Dynamic histomorphometry demonstrated differences in the mineralizing surface to bone surface ratio (MS/BS) and mineral apposition rate (MAR) depending on the timing of fluorochrome administration. A layer of connective tissue separated the prosthesis and the bone tissue. Overall, the study provided validation for the use of cranial prostheses made using SPF and SPIF techniques, offering insights into the processes of bone formation and remodeling in the implanted ovine model.

Perioperative Comparison Between Open Cranial Vault Remodeling and Distraction Osteogenesis for Unilateral Lambdoid Craniosynostosis

There are multiple treatment options for unilateral lambdoid craniosynostosis (ULS) including open posterior cranial vault remodeling (OCVR) and distraction osteogenesis (DO). There is a paucity of data comparing these techniques in the treatment of ULS. This study compared the perioperative characteristics of these interventions for patients with ULS. An IRB-approved chart review was performed from January 1999 to November 2018 at a single institution. Inclusion criteria included the diagnosis of ULS, treatment with either OCVR or DO using a posterior rotational flap technique, and a minimum 1-year follow-up. Seventeen patients met the inclusion criteria (12 OCVR and 5 DO). Patients in each cohort were found to have a similar distribution in sex, age at the time of surgery, synostosis laterality, weight, and length of follow-up. There was no significant difference in mean estimated blood loss/kg, surgical time, or transfusion requirements between cohorts. Distraction osteogenesis patients had a longer mean hospital length of stay (3.4 +/- 0.6 d versus 2.0 +/- 0.6 d, P = 0.0004). All patients were admitted to the surgical ward postoperatively. In the OCVR cohort, complications included 1 dural tear, 1 surgical site infection, and 2 reoperations. In the DO cohort, 1 patient had a distraction site infection, treated with antibiotics. There was no significant difference in estimated blood loss, volume of blood transfusion, or surgical time between OCVR and DO. Patients who underwent OCVR had a higher incidence of postoperative complications and the need for reoperation. This data provides insight into the perioperative differences between OCVR and DO in patients with ULS.

Spontaneous Closure of Congenital Cranial Defect: Is Early Surgical Intervention Warranted?

Infantile cranial development typically occurs in a predictable sequence of events; however, less is known about how the development occurs in isolated, nonsyndromic congenital craniofacial anomalies. Furthermore, the timing of pediatric cranioplasty has been extrapolated from adult studies. Thus, the management of nonsyndromic congenital craniofacial anomalies presents with unique challenges to the craniofacial surgeon. The authors describe the case of a baby girl who was born with right Tessier 3 cleft, cleft palate, anophthalmos, and severe left craniofacial microsomia with Pruzansky grade III left mandibular anomaly. By analyzing 3-dimensional chronological models of the patient, the authors found that her abnormal fontanelle initially increased in size until 22 weeks of age, with subsequent spontaneous closure at a rate of 60.53 mm2/y. Although similar cranial anomalies are typically surgically corrected early in life, delaying treatment until after 2 years of age may be appropriate in some patients, obviating surgical morbidity in the newborn period.

One-piece fronto-orbital distraction osteogenesis without bandeau in patients with coronal craniosynostosis: A five-year follow-up retrospective study of 45 consecutive patients

This study aimed to review the surgical outcomes, complications, and long-term relapses in patients with unilateral or bilateral coronal craniosynostosis, who underwent one-piece fronto-orbital distraction osteogenesis (FODO) without bandeau. The cephalic index, frontal angle, and supraorbital symmetry ratio were measured on the initial and follow-up computed tomography images. Esthetic outcomes were evaluated using the Whitaker classification. 45 patients were included in this study. The average follow-up interval was 5.4 ± 1.1 years (range 2.5-8.5 years). In patients with bilateral coronal craniosynostosis, the frontal angle decreased with a relapse ratio of -2.8 ± 4.3% during long-term follow-up compared with that during short-term follow-up (p = 0.028). In patients with unilateral coronal craniosynostosis, the supraorbital symmetry ratio decreased slightly, with a relapse ratio of -3.8 ± 2.6% during long-term follow-up (p = 0.017). Complications included dural tears during osteotomy (n = 2), early distractor removal (n = 2), and wound problems (n = 3). Within the limitations of the study it seems that one-piece fronto-orbital distraction osteogenesis (FODO) generates successful and sustainable results even in the long term. Therefore, this treatment option should be considered for patients with unilateral and bilateral coronal craniosynostoses whenever appropriate.

Middle meningeal artery embolization in pediatric patient

PURPOSE

There is paucity of data in management of recurrent and expanding subdural hematomas (SDH) within the pediatric population, who are otherwise not surgical candidates. Middle meningeal artery (MMA) embolization has been utilized minimally in this population and here, we explore the utility of this procedure in a 15-month-old-child, along with review of the literature.

METHODS

A case report of a 15-month-old child who underwent MMA embolization for recurrent and expanding SDH in the setting of anticoagulation for cardiac condition. A literature review of MMA embolization in pediatric patients was conducted.

RESULTS

Initially stabilization of SDH was noted on serial imaging; however, recurrent hemorrhages were noted with subsequent boluses of antiplatelet and anticoagulating agents. There are only 5 total reported cases, included ours, of MMA embolization in pediatrics with an overall success rate of 80%.

CONCLUSION

Treatment of chronic or recurrent subdural hematoma by MMA embolization in the pediatric population is understudied. Our case notes limitation of this procedure and impact on long-term success, specifically in patients with systemic illness and ongoing anticoagulation.

Treatment options for critical size defects - Comparison of different materials in a calvaria split model in sheep

Bone defects of the craniofacial skeleton are often associated with aesthetic and functional impairment as well as loss of protection to intra- and extracranial structures. Solid titanium plates and individually adapted bone cements have been the materials of choice, but may lead to foreign-body reactions and insufficient osseointegration. In contrast, porous scaffolds are thought to exhibit osteoconductive properties to support bone ingrowth. Here, we analyse in critical size defects of the calvaria in sheep whether different bone replacement materials may overcome those remaining challenges. In a critical size defect model, bilateral 20 × 20 × 5-mm craniectomies were performed on either side of the sagittal sinus in 24 adult female blackheaded sheep. Bony defects were randomised to one of five different bone replacement materials (BRMs): titanium scaffold, biodegradable poly(d,l-lactic acid) calcium carbonate scaffold (PDLLA/CC), polyethylene 1 (0.71 mm mean pore size) or 2 (0.515 mm mean pore size) scaffolds and polymethyl methacrylate (PMMA)-based bone cement block. Empty controls (n = 3) served as references. To evaluate bone growth over time, three different fluorochromes were administered at different time points. At 3, 6 and 12 months after surgery, animals were sacrificed and the BRMs and surrounding bone analysed by micro-CT and histomorphometry. The empty control group verified that the calvaria defect in this study was a reliable critical size defect model. Bone formation in vivo was detectable in all BRMs after 12 months by micro-CT and histomorphometric analysis, except for the non-porous PMMA group. A maximum of bone formation was detected in the 12-months group for titanium and PDLLA/CC. Bone formation in PDLLA/CC starts to increase rapidly between 6 and 12 months, as the BRM resorbs over time. Contact between bone and BRM influenced bone formation inside the BRM. Empty controls exhibited bone formation solely at the periphery. Overall, porous BRMs offered bone integration to different extent over 12 months in the tested calvaria defect model. Titanium and PDLLA/CC scaffolds showed remarkable osseointegration properties by micro-CT and histomorphometric analysis. PDLLA/CC scaffolds degraded over time without major residues. Pore size influenced bone ingrowth in polyethylene, emphasising the importance of porous scaffold structure.

Titanium reinforced calcium phosphate improves bone formation and osteointegration in ovine calvaria defects: a comparative 52-weeks study

In a 52-week ovine calvaria implantation model, the restoration of cranial defects with a bare titanium mesh (Ti-mesh) and a titanium mesh embedded in a calcium phosphate (CaP-Ti) were evaluated in seven animals. During the study, no major clinical abnormalities were observed, and all sheep presented a normal neurologic assessment. Blood and CSF analysis, made at termination, did not show any abnormalities. No indentation of the soft tissue was observed for either test article; however, the Ti-mesh burr-hole covers were associated with filling of the calvarial defect by fibrous tissue mainly. Some bone formation was observed at the bottom of the created defect, but no significant bone was formed in the proximity of the implant. The defect sites implanted with CaP-Ti were characterized by a moderate degradation of the calcium phosphate that was replaced by mature bone tissue. Calcium-phosphate-filled macrophages were observed in all animals, indicating that they might play a vital role in osteogenesis. The newly formed bone was present, especially at the bony edges of the defect and on the dura side. Integration of the titanium mesh in a calcium phosphate improved bone formation and osteointegration in comparison to a bare titanium mesh.

In vivo evaluation of bilayer ORC/PCL composites in a rabbit model for using as a dural substitute

OBJECTIVE

After a neurosurgical procedure, dural closure is commonly needed to prevent cerebrospinal fluids (CSF) leakage and to reduce the risk of complications, including infections and chronic inflammatory reactions. Although several dural substitutes have been developed, their manufacturing processes are complicated and costly and that many of them have been implicated in causing postoperative complications. This study aimed to assess the effectiveness and safety of new bilayer ORC/PCL composites in a rabbit model.

METHODS

Two formulations of bilayer oxidized regenerated cellulose (ORC)/poly ε-caprolactone (PCL) knitted fabric-reinforced composites and an autologous graft (pericranium) were employed for dural closure in forty-five male rabbits. Systemic reaction and the local reaction of the samples were assessed and compared at one-, three- and six-months post-implantation by blood chemistry and gross, and microscopic assessment using hematoxylin-eosin and Masson's trichrome stains.

RESULTS

No signs of CSF leakage or systemic infection were seen for all samples. All samples demonstrated minimal adhesion to adjacent tissues. The degree of host fibrous connective tissue ingrowth into both composites was comparable to that of the autologous group, but bone formation and osteoclast activities were significantly greater. Both composites progressively degraded over times and the residual thickness of the nonporous layer was 50% of the initial thickness at six months post-implantation.

DISCUSSION

Bilayer ORC/PCL composites were successfully employed for dural closure in the rabbit model. They were biocompatible and could support dural regeneration comparable to that of the autologous group, but induced greater osteogenesis.

Introduction of the Anspach drill as a novel surgical driller for creating calvarial defects in animal models

Standardized and reproducible animal models are required for the assessment of bone healing mediated by biomaterials, cells, and drugs. Among the available bone-fractured models, calvarial defect is a simple and adequate option when researchers investigate intra-membranous bone formation and the influence of their regenerative solutions. However, the conventional surgical tools required to perform calvaria osteotomies (i.e., trephine bur mounted on a dental handpiece, DS) can affect the subjacent tissues of the skull, which are the dura mater and the brain. We hypothesized that the quality of the calvaria defect and the preservation of underlying tissues can be improved using a novel Anspach high-speed drill with a Codman Neuro Disposable Perforator handheld (ACP). Using a rabbit cadaveric models, we performed calvarial defects with either conventional DS or the ACP system, and showed that both techniques allowed to create standardized defects with circular geometry. We demonstrated that the ACP had clear benefices in terms of DM preservation and absence of exothermic reaction upon drilling. Even though this comparative work was conducted on cadaver, it is of substantial importance as it introduces a novel technique, easily applicable to investigate calvaria bone healing, which brings clear advantages compared to the conventional dental station. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 9999:1-9, 2019.

Developmental biology of the meninges

The meninges are membranous layers surrounding the central nervous system. In the head, the meninges lie between the brain and the skull, and interact closely with both during development. The cranial meninges originate from a mesenchymal sheath on the surface of the developing brain, called primary meninx, and undergo differentiation into three layers with distinct histological characteristics: the dura mater, the arachnoid mater, and the pia mater. While genetic regulation of meningeal development is still poorly understood, mouse mutants and other models with meningeal defects have demonstrated the importance of the meninges to normal development of the calvaria and the brain. For the calvaria, the interactions with the meninges are necessary for the progression of calvarial osteogenesis during early development. In later stages, the meninges control the patterning of the skull and the fate of the sutures. For the brain, the meninges regulate diverse processes including cell survival, cell migration, generation of neurons from progenitors, and vascularization. Also, the meninges serve as a stem cell niche for the brain in the postnatal life. Given these important roles of the meninges, further investigation into the molecular mechanisms underlying meningeal development can provide novel insights into the coordinated development of the head.

Histopathological Evaluation of Orthopedic Medical Devices: The State-of-the-art in Animal Models, Imaging, and Histomorphometry Techniques

Orthopedic medical devices are continuously evolving for the latest clinical indications in craniomaxillofacial, spine, trauma, joint arthroplasty, sports medicine, and soft tissue regeneration fields, with a variety of materials from new metallic alloys and ceramics to composite polymers, bioresorbables, or surface-treated implants. There is great need for qualified medical device pathologists to evaluate these next generation biomaterials, with improved biocompatibility and bioactivity for orthopedic applications, and a broad range of knowledge is required to stay abreast of this ever-changing field. Orthopedic implants require specialized imaging and processing techniques to fully evaluate the bone-implant interface, and the pathologist plays an important role in determining the proper combination of histologic processing and staining for quality slide production based on research and development trials and validation. Additionally, histomorphometry is an essential part of the analysis to quantify tissue integration and residual biomaterials. In this article, an overview of orthopedic implants and animal models, as well as pertinent insights for tissue collection, imaging, processing, and slide generation will be provided with a special focus on histopathology and histomorphometry evaluation.

The Efficacy of Cyclic Injection of Bone Morphogenetic Protein-2 in Large-Scale Calvarial Bone Defects

Bone morphogenetic protein-2 (BMP-2) appears to be one of the most potent growth factors thus far studied. However, recent publications on the clinical application of BMP-2 revealed that its correct control is the paramount issue in clinical practice. For improving BMP-2 delivery, the cyclic administration might be an alternative. Accordingly, the authors cyclically injected BMP-2 in a cyclic injection model of large cranial defects to maintain the proper dosage during the bone healing process. A 10-mm diameter calvarial bone defect was produced using a round drill in 8-week-old Sprague-Dawley rats. Silk-hydroxyapatite scaffolds soaked in the appropriate concentration of BMP-2 were implanted into the defect. The animals were split into 4 single-injection groups and 3 multiple-injection groups; the latter groups received weekly subcutaneous injections of BMP-2 solution (1, 5, and 10 μg/mL) for 4 weeks, whereas the former groups received a single injection of BMP-2 at these concentrations. Each rat underwent computed tomography at 8 weeks. In terms of total volumes of the new bone, the 5 μg/mL multiple-injection BMP-2 group had significantly greater increases in bone volume than the single-injection groups. In terms of bone thickness, the multiple-injection groups had better outcomes than the single-injection groups. Thus, the cyclic injection protocol restored the original thickness without overgrowth. Cyclic injection of BMP-2 permits more accurate dosage control than single injection and improves thickness and dense bone regeneration. Therefore, it may represent a promising approach for future clinical trials. Further investigation using a greater number of animals is required.

Infantile cranial fasciitis: case-based review and operative technique

BACKGROUND

Cranial fasciitis (CF) is an uncommon benign primary lesion of the skull that typically affects the pediatric age group. Due to the rarity of CF, no prospective studies exist. Earliest description of this condition dates to 1980. The limited scientific and clinical literature regarding CF is dominated by case reports. For these reasons, questions pertaining to the true incidence, genetic risk factors, prognosis, and long-term outcome remain unanswered.

DISCUSSION

Clinically, CF presents as a firm, painless, growing scalp mass that is typically not considered in the differential diagnosis. Preoperative pathognomonic signs and symptoms are absent, and imaging features are often nonspecific. Treatment is typically through complete surgical resection, at which time histopathological examination confirms the diagnosis of CF. Reconstruction of the skull defect in the child is critical. Autograft techniques help maintain a rigid construct that integrates with the native skull while preserving its continued ability to grow. Generally, a good outcome is observed with complete resection.

EXEMPLARY CASE

We report a case of CF in an infant with emphasis on operative nuances and early follow-up results.

CONCLUSION

CF is a rare fibroproliferative disease that has a poorly defined incidence and long-term follow-up. Due to its locally invasive nature and nonspecific presentation, CF is often difficult to differentiate from malignancies and infections. Complete surgical resection is the best approach for diagnosis and cure. Its occult clinical presentation often allows it to achieve considerable growth, leaving a sizeable skull defect following resection. Since CF presents in the pediatric population, allograft reconstruction is preferred over titanium mesh or other synthetic materials to allow osseous integration and continued uninterrupted skull growth.

Histological assessment of porous custom-made hydroxyapatite implants 6 months and 2.5 years after cranioplasty

Background:

In cranial reconstruction, the features of artificial bone differ. Custom-made porous hydroxyapatite (HAp) implants for cranioplasty have been used all over the world because of their good cosmetic, biocompatibility, and osteoconductive properties. Surgical techniques were analyzed, and histological assessment of new bone formation in the hydroxyapatite was performed.

Methods:

Over a 6-year time period, 41 patients underwent cranioplasty using a custom-made three-dimensional hybrid pore structured hydroxyapatite (3DHPoHAp) implant. The surgical techniques and histological evaluations of 3DHPoHAp in 2 cases, removed 6 months and 2.5 years after cranioplasty, are described.

Results:

Using 3DHPoHAp, cranioplasty was successfully performed for all patients. The implant fit the bone defect exactly, and surgical manoeuvres were simple and easy. All implants were firmly fixed using a titanium plate, and postoperative infection occurred in 1 patient (2.4%). New bone formation was seen in 2 cases 6 months and 2.5 years after cranioplasty. Osteoblasts were progressing to the stoma at various depths, and bone tissue had ripened. Furthermore, lamellar structure was observed in the case at 2.5 years.

Conclusions:

In this study, there was a low infection rate, and new bone formation was seen in vivo after cranioplasty. This study also demonstrated that the 3DHPoHAp implant is a good candidate for cranial bone implants because its good osteoconductivity and biocompatibility.

Surface guidance of stem cell behavior: Chemically tailored co-presentation of integrin-binding peptides stimulates osteogenic differentiation in vitro and bone formation in vivo

Surface modification stands out as a versatile technique to create instructive biomaterials that are able to actively direct stem cell fate. Chemical functionalization of titanium has been used in this work to stimulate the differentiation of human mesenchymal stem cells (hMSCs) into the osteoblastic lineage, by covalently anchoring a synthetic double-branched molecule (PTF) to the metal that allows a finely controlled presentation of peptidic motifs. In detail, the effect of the RGD adhesive peptide and its synergy motif PHSRN is studied, comparing a random distribution of the two peptides with the chemically-tailored disposition within the custom made synthetic platform, which mimics the interspacing between the motifs observed in fibronectin. Contact angle measurement and XPS analysis are used to prove the efficiency of functionalization. We demonstrate that, by rationally designing ligands, stem cell response can be efficiently guided towards the osteogenic phenotype: In vitro, PTF-functionalized surfaces support hMSCs adhesion, with higher cell area and formation of focal contacts, expression of the integrin receptor α5β1 and the osteogenic marker Runx2, and deposition a highly mineralized matrix, reaching values of mineralization comparable to fibronectin. Our strategy is also demonstrated to be efficient in promoting new bone growth in vivo in a rat calvarial defect. These results highlight the efficacy of chemical control over the presentation of bioactive peptides; such systems may be used to engineer bioactive surfaces with improved osseointegrative properties, or can be easily tuned to generate multi-functional coatings requiring a tailored disposition of the peptidic motifs.

STATEMENT OF SIGNIFICANCE

Organic coatings have been proposed as a solution to foster osseointegration of orthopedic implants. Among them, extracellular matrix-derived peptide motifs are an interesting biomimetic strategy to harness cell-surface interactions. Nonetheless, the combination of multiple peptide motifs in a controlled manner is essential to achieve receptor specificity and fully exploit the potentiality of synthetic peptides. Herein, we covalently graft to titanium a double branched molecule to guide stem cell fate in vitro and generate an osseoinductive titanium surface in vivo. Such synthetic ligand allows for the simultaneous presentation of two bioactive motifs, thus is ideal to test the effect of synergic sequences, such as RGD and PHSRN, and is a clear example of the versatility and feasibility of rationally designed biomolecules.

The Recent Revolution in the Design and Manufacture of Cranial Implants: Modern Advancements and Future Directions

Large format (i.e., >25 cm) cranioplasty is a challenging procedure not only from a cosmesis standpoint, but also in terms of ensuring that the patient's brain will be well-protected from direct trauma. Until recently, when a patient's own cranial flap was unavailable, these goals were unattainable. Recent advances in implant computer-aided design and 3-dimensional (3-D) printing are leveraging other advances in regenerative medicine. It is now possible to 3-D-print patient-specific implants from a variety of polymer, ceramic, or metal components. A skull template may be used to design the external shape of an implant that will become well integrated in the skull, while also providing beneficial distribution of mechanical force in the event of trauma. Furthermore, an internal pore geometry can be utilized to facilitate the seeding of banked allograft cells. Implants may be cultured in a bioreactor along with recombinant growth factors to produce implants coated with bone progenitor cells and extracellular matrix that appear to the body as a graft, albeit a tissue-engineered graft. The growth factors would be left behind in the bioreactor and the graft would resorb as new host bone invades the space and is remodeled into strong bone. As we describe in this review, such advancements will lead to optimal replacement of cranial defects that are both patient-specific and regenerative.

Cranial sutures: a multidisciplinary review

INTRODUCTION

Progress in cranial suture research is shaping our current understanding of the topic; however, emphasis has been placed on individual contributing components rather than the cranial sutural system as a whole. Improving our holistic view helps further guide clinicians who treat cranial sutural abnormalities as well as researchers who study them.

MATERIALS AND METHODS

Information from anatomy, anthropology, surgery, and computed modeling was integrated to provide a perspective to interpret suture formation and variability within the cranial functional and structural system.

RESULTS

Evidence from experimental settings, simulations, and evolution suggest a multifactorial morphogenetic process associated with functions and morphology of the sutures. Despite molecular influences, the biomechanical cranial environment has a main role in both the ontogenetic and phylogenetic suture dynamics.

CONCLUSIONS

Furthering our holistic understanding of the intricate cranial sutural system promises to expand our knowledge and enhance our ability to treat associated anomalies.

Negative pressure therapy stimulates healing of critical-size calvarial defects in rabbits

Negative pressure therapy (NPT) is the controlled application of subatmospheric pressure to wounds. It has been shown to stimulate healing across a broad spectrum of soft-tissue wounds, at least in part from the application of mechanical stress on cells and tissues in the wound environment. This study tests the hypothesis that application of NPT to cranial critical-size defects (CSD) in skeletally mature rabbits leads to osseous healing. NPT was delivered 1, 4, 6 or 10 days over CSD-containing calcium phosphate scaffolds placed in contact with intact dura. At 12 weeks after defect creation, NPT groups exhibited significantly greater defect bridging and bone within the scaffolds (P<0.01). Increasing duration of NPT did not result in a greater amount of bone within the scaffolds, but did increase the amount of bone distributed in the upper half of the scaffolds. Appearance of tissue within defects immediately following the removal of NPT at day 6 suggests alternating regions of dural compression and distention indicative of cell stretching. Dura and adjacent tissue were composed of multiple cell layers that extended up into the scaffolds, lining struts and populating pore spaces. An extracellular matrix densely populated with cells and capillaries, as well as larger vessels, infiltrated pores of NPT-treated scaffolds, while scattered spindle-shaped cells and sparse stroma are present within pores of control scaffolds. This rabbit model data suggest that NPT activates within mature dura a natural healing cascade that results in osseous tissue formation without the addition of exogenous factors or progenitor cells.

Hand in glove: brain and skull in development and dysmorphogenesis

The brain originates relatively early in development from differentiated ectoderm that forms a hollow tube and takes on an exceedingly complex shape with development. The skull is made up of individual bony elements that form from neural crest- and mesoderm-derived mesenchyme that unite to provide support and protection for soft tissues and spaces of the head. The meninges provide a protective and permeable membrane between brain and skull. Across evolutionary and developmental time, dynamic changes in brain and skull shape track one another so that their integration is evidenced in two structures that fit soundly regardless of changes in biomechanical and physiologic functions. Evidence for this tight correspondence is also seen in diseases of the craniofacial complex that are often classified as diseases of the skull (e.g., craniosynostosis) or diseases of the brain (e.g., holoprosencephaly) even when both tissues are affected. Our review suggests a model that links brain and skull morphogenesis through coordinated integration of signaling pathways (e.g., FGF, TGFβ, Wnt) via processes that are not currently understood, perhaps involving the meninges. Differences in the earliest signaling of biological structure establish divergent designs that will be enhanced during morphogenesis. Signaling systems that pattern the developing brain are also active in patterning required for growth and assembly of the skull and some members of these signaling families have been indicated as causal for craniofacial diseases. Because cells of early brain and skull are sensitive to similar signaling families, variation in the strength or timing of signals or shifts in patterning boundaries that affect one system (neural or skull) could also affect the other system and appropriate co-adjustments in development would be made. Interactions of these signaling systems and of the tissues that they pattern are fundamental to the consistent but labile functional and structural association of brain and skull conserved over evolutionary time obvious in the study of development and disease.

Evaluation of bone regeneration using the rat critical size calvarial defect

Animal models that are reliably reproducible, appropriate analogs to the clinical condition they are used to investigate, and that offer minimal morbidity and periprocedural mortality to the subject, are the keystone to the preclinical development of translational technologies. For bone tissue engineering, a number of small animal models exist. Here we describe the protocol for one such model, the rat calvarial defect. This versatile model allows for evaluation of biomaterials and bone tissue engineering approaches within a reproducible, non-load-bearing orthotopic site. Crucial steps for ensuring appropriate experimental control and troubleshooting tips learned through extensive experience with this model are provided. The surgical procedure itself takes ∼30 min to complete, with ∼2 h of perioperative care, and tissue collection is generally performed 4-12 weeks postoperatively. Several analytical techniques are presented, which evaluate the cellular and extracellular matrix components, functionality and mineralization, including histological, mechanical and radiographic methods.

Biological Principles and Physiology of Bone Regeneration under the Schneiderian Membrane after Sinus Lift Surgery: A Radiological Study in 14 Patients Treated with the Transcrestal Hydrodynamic Ultrasonic Cavitational Sinus Lift (Intralift)

Introduction. Sinus lift procedures are a commonly accepted method of bone augmentation in the lateral maxilla with clinically good results. Nevertheless the role of the Schneiderian membrane in the bone-reformation process is discussed controversially. Aim of this study was to prove the key role of the sinus membrane in bone reformation in vivo. Material and Methods. 14 patients were treated with the minimal invasive tHUCSL-Intralift, and 2 ccm collagenous sponges were inserted subantrally and the calcification process followed up with CBCT scans 4 and 7 months after surgery. Results. An even and circular centripetal calcification under the sinus membrane and the antral floor was detected 4 months after surgery covering 30% of the entire augmentation width/height/depth at each wall. The calcification process was completed in the entire augmentation volume after 7 months. A loss of approximately 13% of absolute augmentation height was detected between the 4th and 7th month. Discussion. The results of this paper prove the key role of the sinus membrane as the main carrier of bone reformation after sinus lift procedures as multiple experimental studies suggested. Thus the importance of minimal invasive and rupture free sinuslift procedures is underlined and does not depend on the type of grafting material used.

Resveratrol-conjugated poly-ε-caprolactone facilitates in vitro mineralization and in vivo bone regeneration

Incorporation of osteoinductive factors in a suitable scaffold is considered a promising strategy for generating osteogenic biomaterials. Resveratrol is a polyphenol found in parts of certain plants, including nuts, berries and grapes. It is known to increase DNA synthesis and alkaline phosphatase (ALP) activity in osteoblasts and to prevent femoral bone loss in ovariectomized (OVX) rats. In the present study resveratrol was coupled through a hydrolysable covalent bond with the carboxylic acid groups in porous poly-ε-caprolactone (PCL) surface grafted with acrylic acid (AA). The osteogenic effect of this new scaffold was evaluated in mesenchymal cell culture and in the rat calvarial defect model. We found that the incorporation of resveratrol caused increased ALP activity of rat bone marrow stromal cells and enhanced mineralization of the cell-scaffold composites in vitro. After 8 weeks the calvarial defects implanted with resveratrol-conjugated PCL displayed a higher X-ray density than the defects implanted with control PCL. Bone-like structures, positively immunostained for bone sialoprotein, were shown to be more extensively formed in the resveratrol-conjugated PCL. These results show that incorporation of resveratrol into the AA-functionalized porous PCL scaffold led to a significant increase in osteogenesis.

Molecular and tissue responses in the healing of rat calvarial defects after local application of simvastatin combined with alpha tricalcium phosphate

We have previously reported that healing of rat calvarial defects was enhanced by application of alpha tricalcium phosphate (alphaTCP) combined with simvastatin, a cholesterol synthesis inhibitor. The purpose of the present study was to investigate the cellular and molecular mechanisms in this phenomenon. Rat calvarial defects were grafted with alphaTCP with or without simvastatin or left untreated. Animals were sacrificed on 3, 7, 10, 14, and 21 days postoperatively and histological changes in the defect region were assessed. Gene expression patterns were examined by RT-PCR. Proliferation and migration of osteoprogenitor cells from the dura mater were increased in simvastatin group from day 3 to day 10 (p < 0.01). New bone formation was significantly increased in simvastatin group on day 14 and day 21 (p < 0.01). BMP-2 expression was significantly higher in simvastatin group on day 3 and day 14 (p < 0.05) and maintained until day 21. Increased upregulation of TGF-beta1 was also observed in the simvastatin group on day 7 (p < 0.05) which was maintained until day 14. These findings suggest that the proliferation and recruitment of osteoprogenitor cells were critical steps in early stage of bone healing and that these steps were enhanced by TGF-beta1 and BMP-2, which were stimulated by simvastatin.

Effect of recombinant human bone morphogenetic protein-2 on bone regeneration in large defects of the growing canine skull after dura mater replacement with a dura mater substitute

OBJECT

This study was designed to evaluate the bone regeneration potential of the dura mater and dura mater substitute (Durepair) in the presence of recombinant human bone morphogenetic protein-2 (rhBMP-2) delivered in a collagen sponge-collagen-ceramic matrix (CCM; MasterGraft Matrix) in a large skull defect in growing canines.

METHODS

Forty immature male beagles were used to create two 2.5 x 4-cm cranial defects on each side of the sagittal suture. The dura mater on the left side was cut to make a 1 x 3-cm defect and replaced with bovine skin collagen (Durepair). The dura mater on the right side remained intact. Different doses of rhBMP-2 (none [8 animals], 0.11 mg/ml [4 animals], 0.21 mg/ml [4 animals], and 0.43 mg/ml [8 animals]) were infused on 2 Type I bovine absorbable collagen sponge (ACS) strips. The strips were layered with the CCM (15% hydroxyapatite [HA]/85% tricalcium phosphate [TCP]) to reconstruct both cranial defects. In a fifth group (8 animals), 0.43 mg/ml rhBMP-2 was directly infused into the CCM. Demineralized canine cancellous freeze-dried demineralized bone matrix (DBM; 8 animals) was used as a control in a sixth group. All materials were fixed under 2 resorbable protective sheets (MacroPore). Skulls were resected 16 weeks after operation. Histological and histomorphometric analyses on the percentage of the defect spanned by bone, and the percentage of residual HA-TCP granules and collagen were analyzed.

RESULTS

Calcified seroma was the only complication observed and only occurred in the 0.43-mg/ml rhBMP-2 groups (Groups 4 and 5). Dura mater repair appeared complete at 4 months in all animals. New bone was formed sporadically throughout the skull defect in the ACS+CCM and DBM groups without rhBMP-2. In all rhBMP-2 groups, mature new bone (compact and trabecular) was uniformly formed across the defect on both the repaired and intact dura mater sides. There was significant new compact bone formation on top of the repaired dura mater, which did not appear in the ACS+CCM and DBM groups lacking rhBMP-2. Greater HA-TCP and collagen scaffold resorption was noted in rhBMP-2 groups compared with non-rhBMP-2 groups. Statistical analysis showed there was a significantly lower percentage of bone spanning the defect in the ACS+CCM group compared with groups with rhBMP-2, with more residual HA-TCP and collagen on the repaired dura mater side than the intact dura mater side (p < 0.05). In all rhBMP-2 groups, there were no significant differences in new bone formation between the repaired and intact dura mater sides (p > 0.05).

CONCLUSIONS

The ACS+CCM combination had an effect similar to demineralized bone-on-bone regeneration in craniofacial reconstruction. The addition of rhBMP-2 to CCM directly or with ACS induces mature new bone formation in large cranial defects both in the presence of intact dura mater and repaired dura mater.

Comparative effects of scaffold pore size, pore volume, and total void volume on cranial bone healing patterns using microsphere-based scaffolds

Bony craniofacial deficits resulting from injury, disease, or birth defects remain a considerable clinical challenge. In this study, microsphere-based scaffold fabrication methods were use to study the respective effects of scaffold pore size, open pore volume, and total void volume fraction on osseous tissue infiltration and bone regeneration in a critical size rat cranial defect. To compare the healing effects of these parameters, three different scaffolds types were fabricated: solid 100 microm spheres, solid 500 microm spheres, and hollow 500 microm spheres. These constructs were implanted into surgically created rat calvarial defects. By 90-days post op, results of micro computed tomography (CT) analysis showed that all scaffolds generated similar amounts of new bone which was significantly greater than untreated controls. Interestingly, the spatial distribution of new bone within the defect area varied by scaffold group. MicroCT and histological analysis demonstrated healing restricted to the dural side in the hollow 500 microm group, whereas the solid 500 microm group demonstrated healing along the dural side and within the center of the defect. Solid 100 microm groups demonstrated healing along the dural layer, periosteal layer, and within the center of the defect. These results suggest that pore size and closed void volume may both play important roles in scaffold degradation patterns and associated bone healing.

Osteogenic differentiation of dura mater stem cells cultured in vitro on three-dimensional porous scaffolds of poly(epsilon-caprolactone) fabricated via co-extrusion and gas foaming

A novel scaffold fabrication method utilizing both polymer blend extrusion and gas foaming techniques to control pore size distribution is presented. Seventy-five per cent of all pores produced using polymer blend extrusion alone were less than 50microm. Introducing a gas technique provided better control of pore size distribution, expanding the range from 0-50 to 0-350microm. Varying sintering time, annealing temperature and foaming pressure also helped to reduce the percentage of pore sizes below 50microm. Scaffolds chosen for in vitro cellular studies had a pore size distribution of 0-300microm, average pore size 66+/-17microm, 0.54+/-0.02% porosity and 98% interconnectivity, measured by micro-computed tomography (microCT) analysis. The ability of the scaffolds to support osteogenic differentiation for subsequent cranial defect repair was evaluated by static and dynamic (0.035+/-0.006ms(-1) terminal velocity) cultivation with dura mater stem cells (DSCs). In vitro studies showed minimal increases in proliferation over 28 days in culture in osteogenic media. Alkaline phosphatase expression remained constant throughout the study. Moderate increases in matrix deposition, as assessed by histochemical staining and microCT analysis, occurred at later time points, days 21 and 28. Although constructs cultured dynamically showed greater mineralization than static conditions, these trends were not significant. It remains unclear whether bioreactor culture of DSCs is advantageous for bone tissue engineering applications. However, these studies show that polycaprolactone (PCL) scaffolds alone, without the addition of other co-polymers or ceramics, support long-term attachment and mineralization of DSCs throughout the entire porous scaffold.

Operative management of growing skull fractures: a technical note

OBJECTS

Growing skull fractures can be a challenging surgical problem facing the pediatric neurosurgeon. The goal of this manuscript is to clarify effective surgical methods and to provide the rationale for these techniques.

METHODS

We describe the surgical techniques for treatment of growing skull fractures. We clarify the underlying concepts, with respect to dural closure and repair of bony defects, that have led to these techniques.

CONCLUSIONS

With effective surgical technique, the pediatric neurosurgeon can effectively treat growing skull fractures, with excellent outcomes in terms of bony coverage and cosmesis.

Proliferative capacity and osteogenic potential of novel dura mater stem cells on poly-lactic-co-glycolic acid

The rational design of biomimetic structures for the regeneration of damaged or missing tissue is a fundamental principle of tissue engineering. Multiple variables must be optimized, ranging from the scaffold type to the selection and properties of implanted cell(s). In this study, the osteogenic potential of a novel stem cell was analyzed on biodegradable poly(lactic-co-glycolic acid) (PLGA) biomaterials as a step toward creating new cell-materials constructs for bony regeneration. Dura mater stem cells (DSCs), isolated from rat dura mater, were evaluated and compared to bone marrow stem cells (BMSCs) for proliferative and differentiative properties in vitro. Experiments were carried out on both tissue culture plastic (TCP) and 2D planar films of PLGA. Proliferation of DSCs on both TCP and PLGA films increased over 21 days. Positive fold inductions in all five bone marker genes were observed at days 7, 14, 21 in all experimental samples compared with day 0 controls. DSCs demonstrated greater cell coverage and enhanced matrix staining on 2D PLGA films when compared with BMSCs. These cells can be isolated and expanded in culture and can subsequently attach, proliferate, and differentiate on both TCP and PLGA films to a greater extent than BMSCs. This suggests that DSCs are promising for cell-based bone tissue engineering therapies, particularly those applications involving regeneration of cranial bones.

Enhanced Bone Regeneration by Electrical Polarization of Hydroxyapatite

We examined osteogenic cell responses and new bone formation on electrically polarized hydroxyapatite (HAp) plates implanted into calvarial bone defects in rats. In the first group of rats, test pieces were placed with their positively charged surfaces face down on the dura mater. In a second group, test pieces were placed with their negatively charged surfaces facedown on the dura mater. A third group received noncharged test pieces. Histological examination was carried out to characterize the newly formed bone as well as quantification. Enzyme histochemistry involving the detection of alkaline phosphatase and tartrate-resistant acid phosphatase was performed to quantify osteogenic cell activity. Bone growth was enhanced in the groups that received polarized HAp plates, both at the negatively and positively charged surfaces. In addition to the electrostatic force that attracts Ca2+ to the negatively charged surfaces, the suppressive effects on osteoclasts proliferation on the positively charged surfaces may enhance bone formation.

Differential gene expression between juvenile and adult dura mater: a window into what genes play a role in the regeneration of membranous bone

BACKGROUND

Although reossification of large calvarial defects is possible in children, adults lack this tissue engineering capacity. In this study, the authors compared the differences in gene expression between juvenile and adult dura mater using a mouse cDNA microarray with 42,000 unique elements.

METHODS

Non-suture-associated parietal bone was harvested from 6-day-old and 60-day-old mice. The dura mater was carefully dissected from the calvarial disk and snap-frozen. RNA was extracted from pooled dura mater for microarray analysis. The 25 most differentially expressed genes were listed, as were selected bone-related genes. In addition, quantitative real-time reverse-transcriptase polymerase chain reaction confirmation of selected genes-BMP-2, BMP-4, and BMP-7; and osteopontin (OP), osteocalcin (OC), and FGFR-1-was performed.

RESULTS

Juvenile dura mater expressed significantly greater amounts of BMP-2 and OP. Minimal difference in OC expression was observed between juvenile and adult dura mater. Extracellular matrix proteins (Col3a1, 5a1, 6a1, and fibronectin 1), osteoblast differentiation markers (Runx2/Cbfa1, Itm2a, and FGFR-1), and the growth factor Ptn were among other genes with greater expression in juvenile dura mater. Markers of osteoclasts (Acp5, MMP9, Ctsk) and the multiple candidate gene Ntrk2 were also expressed at higher levels in the juvenile dura mater.

CONCLUSIONS

These findings suggest a more differentiated osteoprogenitor population to exist along with a greater presence of osteoclasts in the juvenile dura mater relative to adults. In addition to establishing a baseline difference in gene expression between juvenile and adult dura mater, new genes potentially critical to the regenerative potential of juvenile calvaria were identified.

Performance of functionally graded implants of polylactides and calcium phosphate/calcium carbonate in an ovine model for computer assisted craniectomy and cranioplasty

Biodegradable functionally graded skull implants on the basis of polylactides and calcium phosphate/calcium carbonate were prepared in an individual mould using a combination of different processing techniques. A geometrically corresponding resection template was designed to enable a craniectomy and cranioplasty with the prepared implant in the same operation. After various preliminary experiments concerning degradation kinetics, pH evolution during degradation, micromorphology, biocompatibility tests in human osteoblast cell cultures and surgery of cadaver heads, a new large-animal model was developed for long-term in vivo studies. In eight 12-months-old sheep, the surgical templates were used to create 4.5 x 5 cm(2) calvarial defects which were then filled with the corresponding degradable implants in the same operation. The animals were sacrificed after 2, 9, 12 and 18 months, and the implants and the surrounding tissues were analysed by computer tomography (CT), macroscopic examination and microscopy. The new animal model proved to be reliable and very suitable for large individual craniectomies and cranioplasties. The formation of new bone from the dural layer of the meninges corresponded well to the degradation of the porous inner layer of the implants whereas the skull contour was stabilised by the compact outer layer over the follow-up period.

Age-dependent residual tensile strains are present in the dura mater of rats

The objectives of this study were to determine whether residual tensile strains exist in the dura mater of mammals in vivo, and whether the strains are age-dependent. We made incisions in the parietal dura mater of immature and mature rats, and measured the retraction of the dura mater from each incision. We then used a finite-element model to calculate the strain present in the parietal dura mater of each rat. We found that age-dependent residual tensile strains are present in the dura mater of rats. The mean average residual strain of the immature rats was significantly larger than that of the mature rats (4.96+/-1.54% (s.d.) versus 0.39+/-0.13%, p<0.0001), with the mean strain calculated in the mature rats of the order of the minimum measurement that could be made using our experimental approach. In addition, in the immature rats mean residual strain in the longitudinal direction was significantly larger than mean residual strain in the transverse direction (6.11+/-3.62% versus 3.82+/-2.64%, p=0.0218). Our findings show that age-dependent residual tensile strains exist in the dura mater of rats. We speculate that these strains may reflect the rate and direction of cranial growth and may also influence cranial healing.

Differential transcriptional expression profiles of juvenile and adult calvarial bone

BACKGROUND

It has widely been observed that young children are capable of reossifying large calvarial defects, while adults lack this endogenous tissue-engineering capacity. The ability of juvenile animals to regenerate calvarial defects has been investigated in multiple animal models, including mice. In this study, the authors used cDNA microarrays to investigate the expression of osteogenesis-associated genes upstream and downstream of Runx2 in juvenile and adult mouse calvaria.

METHODS

Nonsuture-associated parietal bone discs were harvested from 6-day-old (n = 50) and 60-day-old (n = 35) male CD-1 mice. After separation of the underlying dura mater and overlying pericranium, the calvarial discs were snap-frozen and RNA was extracted from pooled samples of calvaria for microarray analysis. Genes analyzed included cytokines, receptors, and cell-surface and matrix proteins both upstream and downstream of Runx2.

RESULTS

Genes associated with the Runx2 pathway had notably higher levels in the juvenile versus adult calvaria. All genes except for osteocalcin were expressed at least twofold higher in the juvenile calvaria. This pattern was validated with quantitative real-time polymerase chain reaction. In addition, mRNA for potent osteoinductive growth factors was present at higher levels in the juvenile compared with the adult calvaria.

CONCLUSIONS

These findings reflect a genomic environment of active osteoblast differentiation and ossification in the juvenile calvaria compared with the adult "quiescent" calvarial tissue. These data suggest that a decreased osteogenic potential of adult calvarial osteoblasts may, in part, explain the inability of adult animals to heal calvarial defects.

Early dural reaction to polylactide in cranial defects in rabbits

Restoring the bone integrity to injured calvariae remains a challenge to surgeons. In this study, the dural biocompatibility of biodegradable poly-L/DL-lactide 80/20 and 70/30 defect covers, designed for guided bone regeneration, was assessed. In each of the 16 test rabbits, bilateral (8.3 mm) cranial defects were created. The different covers were applied to one defect each in every rabbit and consisted of three parts: an epicranial cover, a spacer, and a dural cover. All defects had closed after 8 weeks due to new bone formation. A few giant cells were found at the cover-to-dura interface in equal numbers for both covers. Dural bone formation was present in 15 of 16 rabbits and progressed unhindered by the defect cover or its early degradation products.

Additional Distraction Osteogenesis After Conventional Fronto-Orbital Advancement

In the conventional fronto-orbital advancement method, there is a limit to advancement because of scalp skin tension and an absence of a supraorbital bar fixating point. In a case of insufficient advancement after the primary operation, a secondary re-advancement must be performed. In such a condition, additional fronto-orbital advancement by distraction osteogenesis has proved to be very useful. The authors used additional distraction osteogenesis in three infant cases: two of nonsyndromic craniosynostosis and one of Apert's syndrome. They were able to perform these operations safely using their original internal devices. Distraction was started 3 days after the operation. The rate of advancement was 0.5 to 1.0 mm per day. The distraction distances ranged from 16 to 22 mm. They were able to gain enough advancement in all three cases. A reoperation of a fronto-orbital advancement is more difficult than the primary operation because of possible infection, much loss of blood, low blood supply to advanced bones, a tendency of advanced bones to relapse, increased scalp skin tension, and the existence of bone defects. In these poor conditions, distraction osteogenesis has many advantages: good vascularization, no relapsing, a low infection rate, and no need for bony fixating points in the bone defects. Although it is necessary to have a secondary operation to remove the devices and prolonged hospitalization is required, the disadvantages are far outweighed by the many advantages when performing additional fronto-orbital advancement.

Distraction Osteogenesis of the Cranial Vault for the Treatment of Craniofacial Synostosis

From January 2000 to December 2001, six patients with craniosynostosis were treated. Involved sutures were coronal sutures in three patients, coronal and metopic sutures in one patient, multiple sutures (brachycephaly and oxycephaly) in one patient, and multiple sutures with a cloverleaf skull deformity in one patient. The age distribution of the patients was 4 months to 3 years. Four were male, and two were female. A frontal craniotomy was performed in four patients with brachycephaly. In one patient with brachycephaly, the osteotomies were made across the nasofrontal junction, across the roof of the orbit, and along the lateral orbital wall. In one patient with a cloverleaf skull deformity, a frontal bone osteotomy was first performed 1 cm above the roof of the orbit. A supraorbital frontal bar was then made across the nasofrontal junction, across the roof of the orbit, and down to the lateral orbital wall. The frontal bone flap was repositioned to the supraorbital bar using absorbable miniplates and screws. Distraction was started 3 to 7 days after the operation at a distraction rate of 1 mm/d. The real duration of the first operation was 90 to 120 minutes, and the second operation to remove the device took 40 to 50 minutes to perform. The distracted length was 15 to 25 mm. The consolidation period was 3 to 5 weeks. The follow-up period was 6 months to 1 year. Postoperative three-dimensional computed tomography demonstrated reossification at the bone flap and advancement of the fronto-orbital area. After surgery, the cranial volume increased 22.7% on average compared with before surgery. The mean ratio of the anteroposterior length to the transverse length of the cranial vault was changed from 0.96 before surgery to 1.04 after surgery. In conclusion, the advantages of distraction osteogenesis of the cranial vault are that it offers a less invasive technique, a shorter operation time, easy care, and postoperative safety as a result of minimal dissection of the dura. Disadvantages are the limited possibility of initial reshaping and the necessity of one more operation for device removal.

Osteogenesis in calvarial defects: contribution of the dura, the pericranium, and the surrounding bone in adult versus infant animals

Guided bone regeneration is a promising means for reconstructing bone defects in the cranium. The present study was performed to better define those factors that affect osteogenesis in the cranium. The authors studied a single animal model, investigating the contribution of the dura, the pericranium, and the adjacent calvarial bone in the process of calvarial regeneration in both mature and immature animals. Bilateral, 100-mm2, parietal calvariectomies were performed in immature (n = 16) and mature (n = 16) rabbits. Parietal defects were randomized to one of four groups depending on the differential blockade of the dura and/or the pericranium by expanded polytetrafluoroethylene membranes. Animals were humanely killed after 12 weeks, and histometric analysis was performed to quantitate the area of the original bone defect, new bone formation, and new bone density. Bone formation was quantified separately both at the periphery and in the center of the defects. Extrasite bone formation was also quantified both on the dural and on the pericranial sides of the barriers. Bone regeneration was incomplete in all groups over the 12-week study period, indicating that complete bone healing was not observed in any group. The dura was more osteogenic than the pericranium in mature and immature animals, as there was significantly more extrasite bone formed on the dural side in the double expanded polytetrafluoroethylene barrier groups. In both the dural and the double expanded polytetrafluoroethylene barrier groups, dural bone production was significantly greater in immature compared with mature animals. The dura appeared to be the source of central new bone, because dural blockade in the dural and double expanded polytetrafluoroethylene groups resulted in a significant decrease in central bone density in both mature and immature animals. Paradoxically, isolation of the pericranium in mature animals resulted in a significant reduction in total new bone area, whereas pericranial contact appeared to enhance peripheral new bone formation, with the control group having the greatest total new bone area. The present study establishes a model to quantitatively study the process of bone regeneration in calvarial defects and highlights differences in the contribution of the dura and pericranium to calvarial bone regeneration between infant and adult animals. On the basis of these findings, the authors propose that subsequent studies in which permeability of the expanded polytetrafluoroethylene membranes is altered to permit migration of osteoinductive proteins into the defect while blocking prolapse of adjacent soft tissues may help to make guided bone regeneration a realistic alternative for the repair of cranial defects.

New strategies for craniofacial repair and replacement: a brief review

Craniofacial anomalies can severely affect the appearance, function, and psychosocial well being of patients; thus, tissue engineers are developing new techniques to functionally and aesthetically rebuild craniofacial structures. In the past decade, there have been tremendous advances in the field of tissue engineering that will substantially alter how surgeons approach craniofacial reconstruction. In this brief review, we highlight some of the preclinical recombinant protein, gene transfer, and cell-based strategies currently being developed to augment endogenous tissue repair or create structures for replacement. In addition, we discuss the importance of studying endogenous models of tissue induction and present some of the current in vitro and in vivo approaches to growing complex tissues/organs for craniofacial reconstruction.