Mechanical properties of collagen membranes: are they sufficient for orbital floor reconstructions?

The impact of polydioxanone (PDS) foil thickness on reconstruction of the orbital geometry after isolated orbital floor fractures

PURPOSE

The orbital floor is frequently involved in head trauma. Current evidence on the use of reconstruction materials for orbital floor repair is inconclusive. Accordingly, this study aimed to compare the impact of polydioxanone (PDS) foil thickness on reconstruction of the orbital geometry after isolated orbital floor fractures.

METHODS

Standardized isolated orbital floor fractures were symmetrically created in 11 cadaver heads that provided 22 orbits. PDS foils with thicknesses of 0.25-0.5 mm were inserted. Computed tomography (CT) scans of the native, fractured, and reconstructed orbits were obtained, and orbital volume, orbital height, and foil bending were measured.

RESULTS

Orbital volume and height significantly (p < 0.01) increased after the creation of isolated orbital floor fractures and significantly (p = 0.001) decreased with overcorrection of the orbital geometry after orbital floor reconstruction with PDS 0.25 mm or PDS 0.5 mm. The orbital geometry reconstruction rate did not differ significantly with respect to foil thickness. However, compared to PDS 0.5 mm, the use of PDS 0.25 mm resulted in quantitatively higher reconstructive accuracy and a restored orbital volume that did not significantly differ from the initial volume.

CONCLUSION

Orbital floors subjected to isolated fractures were successfully reconstructed using PDS regardless of foil thickness, with overcorrection of the orbital geometry. Due to its lower flexural stiffness, PDS 0.25 mm appeared to provide more accurate orbital geometry reconstruction than PDS 0.5 mm, although no significant difference in reconstructive accuracy between PDS 0.25 mm and PDS 0.5 mm was observed in this cadaveric study.

Newly Developed Resorbable Magnesium Biomaterials for Orbital Floor Reconstruction in Caprine and Ovine Animal Models-A Prototype Design and Proof-of-Principle Study

BACKGROUND

orbital floor fractures have not been reconstructed using magnesium biomaterials.

METHODS

To test technical feasibility, ex vivo caprine and ovine heads (n = 5) were used. Head tissues were harvested from pubescent animals (n = 5; mean age: 3.2 years; mean mass: 26.3 kg) and stored below 11 degrees for 7-10 days. All procedures were performed in a university animal resource facility. Two experienced maxillofacial surgeons performed orbital floor procedures in both orbits of all animals in a step-by-step preplanned dissection. A transconjunctival approach was chosen to repair the orbital floor with three different implants (i.e., magnesium implants; titanium mesh; and polydioxanone or PDO sheets). The position of each implant was evaluated by Cone-beam computed tomography (CBCT).

RESULTS

Axial, coronal, and sagittal plane images showed good positioning of the magnesium plates. The magnesium plates had a radiographic visibility similar to that of the PDO sheets but lower than that of the titanium mesh.

CONCLUSIONS

The prototype design study showed a novel indication for magnesium biomaterials. Further testing of this new biomaterial may lead to the first resorbable biomaterial with good mechanical properties for extensive orbital wall defects.

Mechanical behavior of 3D-printed PEEK and its application for personalized orbital implants with various infill patterns and densities

This study proposed a 3D-printed PEEK with a specific design to restore the damaged orbit shape. Such printed personalized implants are greatly affected by the process parameters, wherefore the effects of the nozzle temperatures, printing speed and layer thickness on the tensile properties were investigated based on the Taguchi approach. The optimal mechanical properties, i.e., the tensile strength and Young's modulus, were found to be 54.97 MPa and 2.67 GPa, respectively. These properties were obtained by adjusting the nozzle temperature to its high level (450 °C), while the layer thickness (0.1 mm) and printing speed (20 mm/s) were set to their low levels. Secondly, the mechanical behavior of a personalized orbital implant with these optimized properties was evaluated via finite elements analysis with various infill patterns and densities, at three thicknesses: 0.3, 0.5 and 0.7 mm. It was found that all thicknesses were acceptable for the 100% filling. For the honeycomb pattern, the thicknesses 0.5 and 0.7 mm were satisfactory with a fill rate of 70% and 55% whereas only the thickness of 0.7 mm was suitable for the 40% filling. The honeycomb pattern with 40% filling and a maximum stress (7.186 MPa) and strain (0.00627 mm) should be beneficial for light-weight orbital implants.

Ultrastructural and Physicochemical Characterization of a Non-Crosslinked Type 1 Bovine Derived Collagen Membrane

In this work, in vitro testing was used to study the properties of non-crosslinked type 1 bovine derived collagen membranes used in bone regeneration surgery. Collagen membranes were prepared, their surface roughness was quantified by interferometry, their morphology was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), their wettability was measured by the contact angle technique, their mechanical properties were investigated by tensile testing, their phase transformation temperatures were measured by Differential Scanning Calorimetry (DSC), and their biocompatibility was evaluated by immunological testing. The calorimetry tests showed that the membrane is formed only by type 1 collagen. The SEM observations showed that the morphology consists of layers of highly organized collagen fibers and patterns of striated fibrils typical of type 1 collagen. The small contact angle showed that the membrane is hydrophilic, with the possibility of rapid absorption of body fluids. The tensile tests showed that the membrane has enough elasticity, ductility, and mechanical strength for use in tissue regeneration. With the immunostaining technique, it was possible to confirm the membrane biocompatibility.

A Multi-Criteria Assessment Strategy for 3D Printed Porous Polyetheretherketone (PEEK) Patient-Specific Implants for Orbital Wall Reconstruction

Pure orbital blowout fractures occur within the confines of the internal orbital wall. Restoration of orbital form and volume is paramount to prevent functional and esthetic impairment. The anatomical peculiarity of the orbit has encouraged surgeons to develop implants with customized features to restore its architecture. This has resulted in worldwide clinical demand for patient-specific implants (PSIs) designed to fit precisely in the patient's unique anatomy. Material extrusion or Fused filament fabrication (FFF) three-dimensional (3D) printing technology has enabled the fabrication of implant-grade polymers such as Polyetheretherketone (PEEK), paving the way for a more sophisticated generation of biomaterials. This study evaluates the FFF 3D printed PEEK orbital mesh customized implants with a metric considering the relevant design, biomechanical, and morphological parameters. The performance of the implants is studied as a function of varying thicknesses and porous design constructs through a finite element (FE) based computational model and a decision matrix based statistical approach. The maximum stress values achieved in our results predict the high durability of the implants, and the maximum deformation values were under one-tenth of a millimeter (mm) domain in all the implant profile configurations. The circular patterned implant (0.9 mm) had the best performance score. The study demonstrates that compounding multi-design computational analysis with 3D printing can be beneficial for the optimal restoration of the orbital floor.

Polydioxanone-Based Membranes for Bone Regeneration

Resorbable synthetic and natural polymer-based membranes have been extensively studied for guided tissue regeneration. Alloplastic biomaterials are often used for tissue regeneration due to their lower immunoreactivity when compared with allogeneic and xenogeneic materials. Plenum^® Guide is a synthetic membrane material based on polydioxanone (PDO), whose surface morphology closely mimics the extracellular matrix. In this study, Plenum^® Guide was compared with collagen membranes as a barrier material for bone-tissue regeneration in terms of acute and subchronic systemic toxicity. Moreover, characterizations such as morphology, thermal analysis (Tm = 107.35 °C and crystallinity degree = 52.86 ± 2.97 %, final product), swelling (thickness: 0.25 mm ≅ 436% and 0.5 mm ≅ 425% within 24 h), and mechanical tests (E = 30.1 ± 6.25 MPa; σ = 3.92 ± 0.28 MPa; ε = 287.96 ± 34.68%, final product) were performed. The in vivo results revealed that the PDO membranes induced a slightly higher quantity of newly formed bone tissue than the control group (score: treated group = 15, control group = 13) without detectable systemic toxicity (clinical signs and evaluation of the membranes after necropsy did not result in differences between groups, i.e., non-reaction -> tissue-reaction index = 1.3), showing that these synthetic membranes have the essential characteristics for an effective tissue regeneration. Human adipose-derived stem cells (hASCs) were seeded on PDO membranes; results demonstrated efficient cell migration, adhesion, spread, and proliferation, such that there was a slightly better hASC osteogenic differentiation on PDO than on collagen membranes. Hence, Plenum^® Guide membranes are a safe and efficient alternative for resorbable membranes for tissue regeneration.

Orbital floor repair using patient specific osteoinductive implant made by stereolithography

The orbital floor (OF) is an anatomical location in the craniomaxillofacial (CMF) region known to be highly variable in shape and size. When fractured, implants commonly consisting of titanium meshes are customized by plying and crude hand-shaping. Nevertheless, more precise customized synthetic grafts are needed to meticulously reconstruct the patients' OF anatomy with better fidelity. As alternative to titanium mesh implants dedicated to OF repair, we propose a flexible patient-specific implant (PSI) made by stereolithography (SLA), offering a high degree of control over its geometry and architecture. The PSI is made of biodegradable poly(trimethylene carbonate) (PTMC) loaded with 40 wt % of hydroxyapatite (called Osteo-PTMC). In this work, we developed a complete work-flow for the additive manufacturing of PSIs to be used to repair the fractured OF, which is clinically relevant for individualized medicine. This work-flow consists of (i) the surgical planning, (ii) the design of virtual PSIs and (iii) their fabrication by SLA, (iv) the monitoring and (v) the biological evaluation in a preclinical large-animal model. We have found that once implanted, titanium meshes resulted in fibrous tissue encapsulation, whereas Osteo-PMTC resulted in rapid neovascularization and bone morphogenesis, both ectopically and in the OF region, and without the need of additional biotherapeutics such as bone morphogenic proteins. Our study supports the hypothesis that the composite osteoinductive Osteo-PTMC brings advantages compared to standard titanium mesh, by stimulating bone neoformation in the OF defects. PSIs made of Osteo-PTMC represent a significant advancement for patients whereby the anatomical characteristics of the OF defect restrict the utilization of traditional hand-shaped titanium mesh.

Supercritical carbon dioxide decellularised pericardium: Mechanical and structural characterisation for applications in cardio-thoracic surgery

INTRODUCTION

Many biomaterials are used in cardio-thoracic surgery with good short-term results. However, calcification, dehiscence, and formation of scar tissue are reported. The aim of this research is to characterise decellularised pericardium after supercritical carbon dioxide (scCO₂) processing as an alternative biological material for uses in cardio-thoracic surgery.

METHODS

Porcine and bovine pericardium were decellularised using scCO₂. Mechanical properties such as tensile strength, elastic modulus, fracture toughness and suture retention strength were determined. Ultrastructure was visualised using Scanning Electron Microscopy. Water uptake and swelling was experimentally determined. Commercially available glutaraldehyde treated bovine pericardium was used as gold standard for comparison.

RESULTS

scCO₂ decellularised porcine (and bovine pericardium) maintained their tensile strength compared to untreated native pericardium (13.3 ± 2.4MPa vs 14.0 ± 4.1MPa, p = 0.73). Tensile strength of glutaraldehyde treated pericardium was significantly higher compared to untreated pericardium (19.4 ± 7.3MPa vs 10.2 ± 2.2MPa, p = 0.02). Suture retention strength of scCO₂ treated pericardium was significantly higher than glutaraldehyde treated pericardium (p = 0.01). We found no anisotropy of scCO₂ or glutaraldehyde treated pericardium based on a trouser tear test. Ultrastructure was uncompromised in scCO₂ treated pericardium, while glutaraldehyde treated pericardium showed deterioration of extracellular matrix.

CONCLUSION

scCO₂ processing preserves initial mechanical and structural properties of porcine and bovine pericardium, while glutaraldehyde processing damages the extracellular matrix of bovine pericardium. Decellularisation of tissue using scCO₂ might give long-term solutions for cardio-thoracic surgery without compromising initial good mechanical properties.

Mechanical resistance of the periorbita and the orbital floor complex--are isolated orbital floor fractures only a soft tissue problem?

The primary aims of orbital floor reconstruction are to prevent enophthalmos and herniation of the orbital contents in order to achieve correct globe position. Theoretically, the mechanical load of the orbital floor is approximately 0.0005N/mm(2) (30g orbital content onto 600mm(2) of orbital floor area). Therefore, low mechanical stress from orbital floor reconstruction materials is expected. The periorbita and orbital floor complex (bony orbital floor with periorbita) of 12 human cadavers were investigated for their mechanical resistance to distortion and compared to different absorbable pliable reconstruction materials after modification with pores (Bio-Gide, Creos, and PDS). The human periorbita resistance (approximately 1.4N/mm(2)) was comparable to that of the absorbable membranes (Creos, Bio-Gide), and the resistance of PDS (approximately 2.3N/mm(2)) was comparable to that of the orbital floor complex. The periorbita has a higher stability than the bony orbital floor. Therefore, in isolated orbital floor fractures with a traumatized bony orbital floor and periorbita, reconstruction of the soft tissue as a periorbita equivalent with a resorbable membrane appears to be adequate to prevent enophthalmos and herniation of the orbital contents.

Mechanical properties of collagen membranes modified with pores--are they still sufficient for orbital floor reconstruction?

Adequate mechanical strength is essential for materials used to reconstruct the orbital floor, and collagen membranes have recently been suggested for the repair of isolated fractures of the orbital floor. However, their mechanical properties after modification with pores for increased drainage of blood into the sinus have not been sufficiently investigated. We have tested the mechanical resistance of polydioxanone foils (PDS) to distortion and compared it with that of 3 resorbable collagen membranes (Smartbrane(®), Bio-Gide(®), and Creos(®)) in mint condition and when artificially aged (3 weeks, 6 weeks, and 8 weeks) after modification with pores (diameter 2mm) in a standard configuration (n=12 in each group). PDS and Creos(®) had comparable initial values for mechanical resistance of about 2.3N/mm(2), and Bio-Gide(®) and Smartbrane(®) had about 20% and 80% lower initial mechanical resistance, respectively. All materials tested had lower values after artificial ageing. After eight weeks of ageing, PDS lost about 99% of its initial mechanical resistance, Creos(®) about 66%, Bio-Gide(®) about 30%, and Smartbrane(®) about 95%. After 3 weeks the mechanical resistance in all groups was significantly less than the initial values (p=0.05), but there was no difference between samples aged artificially for 6 compared with 8 weeks. The mechanical resistance of the tested materials was not influenced by the presence of pores in a standard configuration and was in the appropriate range for moderate fractures of the orbital floor. We recommend further clinical investigations of collagen membranes modified with pores.

The use of anatomically drop-shaped bioactive glass S53P4 implants in the reconstruction of orbital floor fractures--A prospective long-term follow-up study

An isolated fracture of the orbital floor needs reconstruction if there is a clear herniation of adipose tissue or of the rectus inferior muscle into the maxillary sinus. A prospective study was carried out treating 20 patients with an isolated blow-out fracture of the orbital floor or with a combined zygomatico-orbito-maxillary complex fracture, using a newly designed anatomically drop-shaped implants made of bioactive glass (BAG) S53P4. Computed tomography (CT) was performed immediately postoperatively to confirm the correct position of the plate. The patients were followed up for an average of 32 months clinically and radiologically with magnetic resonance imaging (MRI) for an average of 31 months. None of the patients had any signs of complications related to the implant and the clinical outcome was very good. None of the patients had persisting diplopia. The level of the pupillas was normal in 15 of 20 patients. Minor hypo-ophthalmos ranging from 0.5 to 1.0 mm was observed in three patients, and moderate hypo-ophthalmos of 2.0 mm was seen in one patient. Hyperophthalmos of 1.0 mm was seen in one patient. Minor enophthalmos on the operated side ranging from 0.5 to 1.0 mm was seen in eight patients. Mild to moderate paraesthesia of the infraorbital nerve was observed in six patients. The immediate postoperative CT and the long term follow-up MRI revealed that the drop-shaped BAG implants retained their correct position in the orbital floor and did not show any evidence of losing their original shape or material resorption. No adverse tissue reaction was associated with the material. Due to the anatomical drop shape, the implants could successfully maintain the orbital volume and compensate for the retrobulbar adipose tissue atrophy.