Osseointegration of preformed polymethylmethacrylate craniofacial prostheses coated with bone marrow-impregnated poly (DL-lactic-co-glycolic acid) foam

Conditioning of 3D Printed Nanoengineered Ionic-Covalent Entanglement Scaffolds with iP-hMSCs Derived Matrix

Additive manufacturing is a promising method for producing customized 3D bioactive constructs for regenerative medicine. Here, 3D printed highly osteogenic scaffolds using nanoengineered ionic-covalent entanglement ink (NICE) for bone tissue engineering are reported. This NICE ink consists of ionic-covalent entanglement reinforced with Laponite, a 2D nanosilicate (nSi) clay, allowing for the printing of anatomic-sized constructs with high accuracy. The 3D printed structure is able to maintain high structural stability in physiological conditions without any significant swelling or deswelling. The presence of nSi imparts osteoinductive characteristics to the NICE scaffolds, which is further augmented by depositing pluripotent stem cell-derived extracellular matrix (ECM) on the scaffolds. This is achieved by stimulating human induced pluripotent stem cell-derived mesenchymal stem cells (iP-hMSCs) with 2-chloro-5-nitrobenzanilide, a PPARγ inhibitor that enhances Wnt pathway, resulting in the deposition of an ECM characterized by high levels of collagens VI and XII found in anabolic bone. The osteoinductive characteristics of these bioconditioned NICE (bNICE) scaffolds is demonstrated through osteogenic differentiation of bone marrow derived human mesenchymal stem cells. A significant increase in the expression of osteogenic gene markers as well as mineralized ECM are observed on bioconditioned NICE (bNICE) scaffolds compared to bare scaffolds (NICE). The bioconditioned 3D printed scaffolds provide a unique strategy to design personalized bone grafts for in situ bone regeneration.

Xeno-Free In Vitro Cultivation and Osteogenic Differentiation of hAD-MSCs on Resorbable 3D Printed RESOMER®

The development of alloplastic resorbable materials can revolutionize the field of implantation technology in regenerative medicine. Additional opportunities to colonize the three-dimensionally (3D) printed constructs with the patient’s own cells prior to implantation can improve the regeneration process but requires optimization of cultivation protocols. Human platelet lysate (hPL) has already proven to be a suitable replacement for fetal calf serum (FCS) in 2D and 3D cell cultures. In this study, we investigated the in vitro biocompatibility of the printed RESOMER^® Filament LG D1.75 materials as well as the osteogenic differentiation of human mesenchymal stem cells (hMSCs) cultivated on 3D printed constructs under the influence of different medium supplements (FCS, human serum (HS) and hPL). Additionally, the in vitro degradation of the material was studied over six months. We demonstrated that LG D1.75 is biocompatible and has no in vitro cytotoxic effects on hMSCs. Furthermore, hMSCs grown on the constructs could be differentiated into osteoblasts, especially supported by supplementation with hPL. Over six months under physiological in vitro conditions, a distinct degradation was observed, which, however, had no influence on the biocompatibility of the material. Thus, the overall suitability of the material LG D1.75 to produce 3D printed, resorbable bone implants and the promising use of hPL in the xeno-free cultivation of human MSCs on such implants for autologous transplantation have been demonstrated.

Fronto-orbital reconstruction using polymethyl methacrylate implant

The objective of this article is to show a case of fronto-orbital reconstruction with prefabricated polymethyl methacrylate prosthesis. A 35-year-old male with alleged history of trauma following road traffic accident 3 months back reported with unaesthetic scar and deformity in right supraorbital region to us. As there was no functional deformity, the management was aimed at correcting the contour and esthetic only. The correction was achieved by overlaying the defect with a polymethyl methacrylate implant fabricated over a three-dimensional stereolithographically printed rapidly prototyped model. Postoperative phase was uneventful and esthetic outcome was satisfactory. The patient after 4-year follow-up reported with no discomfort and definite improvement in facial contour.

Multiple Delayed Scalp Reconstruction for Complicated Cranial Defects

In cases of skull trauma, emergency surgery for cranial decompression typically involves the shortest approach, with the incision lying directly on or immediately near the bony defect. Subsequent reconstructive plastic surgery for the skull is difficult in such cases because incisions taken on the previous scar overlying the bony defect are prone to dehiscence and infection. Herein, we describe a technique for creating a well-vascularized delayed skin flap via multistaged operation before the actual skull reconstruction. Four patients (age range, 10-25 y) were prepared for skull reconstruction using this technique. Flap elevation was performed in 3 stages, with adequate time intervals (4 wk between each stage) to allow for adequate delay. Dissection under the galea aponeurotica was performed only after initial flap elevation allowing for adequate vascularization. Skull reconstruction was then performed using custom-made implants. The patients were followed up for 6 to 12 months. No complications, including infections, exposure of the artificial bone, or flap necrosis, were observed. All the patients were satisfied with the cosmetic results. Despite the multiple stages required, we consider that our technique of using a delayed, well-vascularized bipedicled skin flap can be successfully used in the skull reconstruction of patients in whom the initial scar lies close to the bone defect. We recommend scalp incision be shifted outside of the foreseen bony flap to limit infectious risks during primary or subsequent cranial reconstruction.

A review of reconstructive materials for use in craniofacial surgery bone fixation materials, bone substitutes, and distractors

Over the last 40 years, craniofacial surgery, in general, and surgery for craniosynostosis, in particular, has witnessed the introduction of a number of new materials for use in operations involving the cranial vault. Some of these materials have proven quite useful over time, while others have failed to meet their stated objectives. In this review, the more popular implant materials are analyzed, and their relative merits and drawbacks are discussed. Craniofacial surgery in the pediatric population has its own unique limitations, quite different from the adult population and those issues are reviewed as well.

Surface characteristics of biomaterials used for space maintenance in a mandibular defect: a pilot animal study

PURPOSE

The purpose of the present study was to evaluate the effect of implant porosity on wound healing between solid and porous implants placed within a bony mandibular defect with intraoral exposure.

MATERIALS AND METHODS

Solid poly(methyl methacrylate) (PMMA) implants similar to those used currently in clinical space maintenance applications in maxillofacial surgery were compared with poly(propylene fumarate) implants that contained a porous outer surface surrounding a solid core. A 10-mm diameter nonhealing bicortical defect with open communication into the oral cavity was created in the molar mandibular region of 12 adult male New Zealand white rabbits. Of the 12 rabbits, 6 received the hybrid poly(propylene fumarate) implants and 6 received the solid PMMA implants. At 12 weeks, the rabbit mandibles were harvested and sent for histologic staining and sectioning.

RESULTS

Gross inspection and histologic examination showed all 6 poly(propylene fumarate) implants to be intact within the defect site at the termination of the study period, with 3 of the 6 specimens exhibiting a continuous circumferential soft tissue margin. In contrast, 5 of the 6 PMMA-implanted specimens were exposed intraorally with an incomplete cuff of soft tissue around the implant. One of the PMMA-implanted specimens exhibited complete extrusion and subsequent loss of the implant. Fisher's exact test was used to compare the occurrence of oral cavity wound healing between the 2 groups (P = .09).

CONCLUSIONS

Although statistically significant differences between the 2 groups were not seen, our results have indicated that advantages might exist to using porous implants for space maintenance. Additional study is needed to evaluate these findings.

Craniofacial bone tissue engineering

Repair and reconstruction of the craniofacial skeleton represents a significant biomedical burden, with thousands of procedures per-formed annually secondary to injuries and congenital malformations. Given the multitude of current approaches, the need for more effective strategies to repair these bone deficits is apparent. This article explores two major modalities for craniofacial bone tissue engineering: distraction osteogenesis and cellular based therapies. Current understanding of the guiding principles for each of these modalities is elaborated on along with the knowledge gained from clinical and investigative studies. By laying this foundation, future directions for craniofacial distraction and cell-based bone engineering have emerged with great promise for the advancement of clinical practice.

Effect of transforming growth factor beta 2 on marrow-infused foam poly(propylene fumarate) tissue-engineered constructs for the repair of critical-size cranial defects in rabbits

This study investigates the osseointegration of poly(propylene fumarate) (PPF) with beta-tricalcium phosphate (beta-TCP) scaffolds in a critical-size (diameter, 1.6 cm), cranial defect in 4-month-old rabbits (n = 51), killed at 6 or 12 weeks. Two molecular weights of PPF were used to produce bilayer scaffolds with 0.5-mm solid external and 2.0-mm porous internal layers. The porous layer was infused with bone marrow aspirate, with half the animals receiving 0.8 microg of transforming growth factor beta2 (TGF-beta2). No foreign body or inflammatory response was observed externally or on histological examination of explants. Statistical analysis of histological areal and linear measures of new bone formation found significantly more bone at the later sacrifice time, followed by implants receiving TGF-beta2, followed by low molecular weight PPF implants. Approximately 40% of the explants were tested for incorporation strength with a one-point "push-in" test. Because no permanent fixation was used, implant strength (28.37-129.03 N; range, 6.4 to 29.0 lb of resistance) was due entirely to new bone formation. The strongest bone was seen in implants receiving TGF-beta2-infused marrow in animals killed at 12 weeks. These results support the use of PPF as an osteogenic substrate and future research into preoperative fabrication of critical size and supercritical-size cranial prosthetic implants.

Ovine model for engineering bone segments

We propose a large animal model for bone tissue engineering that yields quantitative data and simulates clinical methods and tissue needs. Skeletally mature domestic sheep (n = 20) were each implanted with three rectangular (1 x 1 x 4 cm), hollow tissue-molding chambers that were empty (control) or filled with equal weights (6.71-6.78 g) of particulate autologous bone graft (MBG) or bone graft that was autoclaved to denature stored growth factors (DeMBG). MBG provided scaffold and bioactive factors, and DeMBG provided only scaffold. The chambers were enclosed on five sides and securely implanted so that the open face was apposed to the osteogenic (i.e., cambium) layer of the rib periosteum for 3, 6, 9, 12, or 24 weeks, after which the chambers were harvested and the contents analyzed. Each chamber contained osseous and fibrovascular tissue. MBG-containing chambers had the best maintenance of tissue volume compared with DeMBG-containing or empty chambers, but it still decreased steadily over time. Despite this, the MBG-containing chambers showed continuous active bone formation. There was increasing calcified tissue with penetration of osteogenesis up to a mean of 0.75 +/- 0.15 cm from the periosteum by 9 weeks, and the osteogenic area peaked at 0.59 +/- 0.13 cm2 by 12 weeks. Using quantitative measures that reflect clinical needs (i.e., tissue volume, shape, and quality), it was possible to distinguish differences in performance associated with manipulation of implanted scaffold and bioactive factors. This ovine model may serve as a useful tool to develop clinical osseous tissue-engineering strategies.

New developments in pediatric plastic surgery research

Pediatric plastic surgery research is a rapidly expanding field. Unique in many ways, researchers in this field stand at the union of multiple scientific specialties, including biomedical engineering, tissue engineering, polymer science, molecular biology, developmental biology, and genetics. The goal of this scientific effort is to translate research advances into improved treatments for children with congenital and acquired defects. Although the last decade has seen a dramatic acceleration in research related to pediatric plastic surgery, the next 10 years will no doubt lead to novel treatment strategies with improved clinical outcomes.

Poly(propylene fumarate) and poly(DL-lactic-co-glycolic acid) as scaffold materials for solid and foam-coated composite tissue-engineered constructs for cranial reconstruction

This pilot study investigates the osseointegration of four types of critical-size (1.5-cm diameter) rabbit cranial defect (n = 35) bone graft scaffolds. The first is a solid poly(propylene fumarate)/beta-tricalcium phosphate(PPF/beta-TCP) disk; the three remaining constructs contain a PPF/beta-TCP core coated with a 1-mm resorptive porous foam layer of PPF or PLGA [poly(DL-lactic-co-glycolic acid)], and bone marrow. Animals were killed at 6, 12, and 20 weeks. There was no evidence of a foreign body inflammatory response at any time during the study. Histomorphometric analyses of new bone formation sorted lineal and areal measures of new bone into three cranial layers (i.e., external, middle, and internal). Statistical analyses revealed significantly more bone in the PLGA foam-coated constructs than in the PPF foam-coated constructs (p < 0.03). No implant fixation was used; there is no strength at time 0. Twenty percent of all explants were tested for incorporation strength with a one-point "push-in" test, and failure ranged from 8.3 to 34.7 lb. The results of this study support the use of PPF as a biocompatible material that provides both a structural and osteogenic substrate for the repair of cranial defects.

Clinical outcome in cranioplasty: critical review in long-term follow-up

Various materials have been proposed for cranial reconstruction. Bone autograft and alloplasts such as polymethylmethacrylate (PMMA) and hydroxyapatite (HA) cement are most commonly used at the present time. Patients submitted for cranioplasty were evaluated. The prognostic factors influencing the results and the outcome were analyzed. Three hundred twelve patients who had 449 procedures performed by a single surgeon to reconstruct a calvarial deformity between 1981 and 2001 were studied. Post-tumor resection deformity was the main reason for cranioplasty (32.4%). Bone graft was the material of choice (69.5%). The main surgical site was the frontal bone (53.2%). Complications were observed in 23.6% of cases and were responsible for the least satisfactory results (P > 0.001), with infection and material exposure being the most critical complications. The eventual outcome was considered good in 91.8% of cases. The use of HA cement was associated with the worst results (P > 0.001). Bone grafts showed a high grade of partial resorption and required further surgery for correction. Multiple surgical procedures were correlated with a high rate of complications and an unsatisfactory outcome. Bone graft and PMMA are still the best materials in calvarial reconstruction. Even though HA cement is an osteoconductive material, it seems to induce what appears to be an immunoguided delayed inflammatory reaction that leads to thinning of the skin and exposure of the material, making secondary repair difficult. Before deciding which reconstructive option to use, a careful evaluation of the patient in terms of diagnosis, number of previous surgeries, and surgical site should be undertaken. If this is adopted, good results and a satisfactory outcome can be achieved on long-term follow-up.

A procedure to average 3D anatomical structures

Creating a feature-preserving average of three dimensional anatomical surfaces extracted from volume image data is a complex task. Unlike individual images, averages present right-left symmetry and smooth surfaces which give insight into typical proportions. Averaging multiple biological surface images requires careful superimposition and sampling of homologous regions. Our approach to biological surface image averaging grows out of a wireframe surface tessellation approach by Cutting et al. (1993). The surface delineating wires represent high curvature crestlines. By adding tile boundaries in flatter areas the 3D image surface is parametrized into anatomically labeled (homology mapped) grids. We extend the Cutting et al. wireframe approach by encoding the entire surface as a series of B-spline space curves. The crestline averaging algorithm developed by Cutting et al. may then be used for the entire surface. Shape preserving averaging of multiple surfaces requires careful positioning of homologous surface regions such as these B-spline space curves. We test the precision of this new procedure and its ability to appropriately position groups of surfaces in order to produce a shape-preserving average. Our result provides an average that well represents the source images and may be useful clinically as a deformable model or for animation.