Computational design and fabrication of a novel bioresorbable cage for tibial tuberosity advancement application

In Vivo Investigation of 3D-Printed Calcium Magnesium Phosphate Wedges in Partial Load Defects

Bone substitutes are ideally biocompatible, osteoconductive, degradable and defect-specific and provide mechanical stability. Magnesium phosphate cements (MPCs) offer high initial stability and faster degradation compared to the well-researched calcium phosphate cements (CPCs). Calcium magnesium phosphate cements (CMPCs) should combine the properties of both and have so far shown promising results. The present study aimed to investigate and compare the degradation and osseointegration behavior of 3D powder-printed wedges of CMPC and MPC in vivo. The wedges were post-treated with phosphoric acid (CMPC) and diammonium hydrogen phosphate (MPC) and implanted in a partially loaded defect model in the proximal rabbit tibia. The evaluation included clinical, in vivo µ-CT and X-ray examinations, histology, energy dispersive X-ray analysis (EDX) and scanning electron microscopy (SEM) for up to 30 weeks. SEM analysis revealed a zone of unreacted material in the MPC, indicating the need to optimize the manufacturing and post-treatment process. However, all materials showed excellent biocompatibility and mechanical stability. After 24 weeks, they were almost completely degraded. The slower degradation rate of the CMPC corresponded more favorably to the bone growth rate compared to the MPC. Due to the promising results of the CMPC in this study, it should be further investigated, for example in defect models with higher load.

Enhanced bone formation in locally-optimised, low-stiffness additive manufactured titanium implants: An in silico and in vivo tibial advancement study

A tibial tuberosity advancement (TTA), used to treat lameness in the canine stifle, provides a framework to investigate implant performance within an uneven loading environment due to the dominating patellar tendon. The purpose of this study was to reassess how we design orthopaedic implants in a load-bearing model to investigate potential for improved osseointegration capacity of fully-scaffolded mechanically-matched additive manufactured (AM) implants. While the mechanobiological nature of bone is well known, we have identified a lower limit in the literature where investigation into exceedingly soft scaffolds relative to trabecular bone ceases due to the trade-off in mechanical strength. We developed a finite element model of the sheep stifle to assess the stresses and strains of homogeneous and locally-optimised TTA implant designs. Using additive manufacturing, we printed three different low-stiffness Ti-6Al-4 V TTA implants: 0.8 GPa (Ti1), 0.6 GPa (Ti2) and an optimised design with a 0.3 GPa cortex and 0.1 GPa centre (Ti3), for implantation in a 12-week in vivo ovine pilot study. Static histomorphometry demonstrated uniform bone ingrowth in optimised low-modulus Ti3 samples compared to homogeneous designs (Ti1 and Ti2), and greater bone-implant contact. Mineralising surfaces were apparent in all implants, though mineral apposition rate was only consistent throughout Ti3. The greatest bone formation scores were seen in Ti3, followed by Ti2 and Ti1. Results from our study suggest lower stiffnesses and higher strain ranges improve early bone formation, and that by accounting for loading environments through rational design, implants can be optimised to improve uniform osseointegration. STATEMENT OF SIGNIFICANCE: The effect of different strain ranges on bone healing has been traditionally investigated and characterised through computational models, with much of the literature suggesting higher strain ranges being favourable. However, little has been done to incorporate strain-optimisation into porous orthopaedic implants due to the trade-off in mechanical strength required to induce these microenvironments. In this study, we used finite element analysis to optimise the design of additive manufactured (AM) titanium orthopaedic implants for different strain ranges, using a clinically-relevant surgical model. Our research suggests that there is potential for locally-optimised AM scaffolds in the use of orthopaedic devices to induce higher strains, which in turn encourages de novo bone formation and uniform osseointegration.

Physicochemical degradation of calcium magnesium phosphate (stanfieldite) based bone replacement materials and the effect on their cytocompatibility

Regenerative bone implants should be completely replaced by new bone within a period of time corresponding to the growth rate of native bone. To meet this requirement, suitable biomaterials must be biodegradable and promote osteogenesis. The combination of slowly degrading but osteoconductive calcium phosphates (CPs) with rapidly degrading and mechanically more resilient magnesium phosphates represents a promising material class for this purpose. In order to create the best possible conditions for optimal implant integration, microporous calcium magnesium phosphate (CMP) cements were processed using 3D powder printing. This technique enables the production of a defect-adapted implant with an optimal fit and a high degree of open porosity to promote bone ingrowth. Four different compositions of 3D printed CMP ceramics were investigated with regard to essential properties of bone implants, including chemical composition, porosity, microstructure, mechanical strength, and cytocompatibility. The ceramics consisted of farringtonite (Mg₃(PO₄)₂) and stanfieldite (Ca₄Mg₅(PO₄)₆), with either struvite (NH₄MgPO₄·6H₂O) or newberyite (MgHPO₄·3H₂O) and brushite (CaHPO₄·2H₂O) as additional phases. The CMP materials showed open porosities between 13 and 28% and compressive strengths between 11 and 17 MPa, which was significantly higher, as compared with clinically established CP. The cytocompatibility was evaluated with the human fetal osteoblast cell line hFOB 1.19 and was proven to be equal or to even exceed that of tricalcium phosphate. Furthermore, a release of 4-8 mg magnesium and phosphate ions per mg scaffold material could be determined for CMPs over a period of 21 d. In the case of struvite containing CMPs the chemical dissolution of the cement matrix was combined with a physical degradation, which resulted in a mass loss of up to 3.1 wt%. In addition to its beneficial physical and biological properties, the proven continuous chemical degradation and bioactivity in the form of CP precipitation indicate an enhanced bone regeneration potential of CMPs.

Application of Patient-Specific Instrumentation in a Dog Model with Antebrachial Growth Deformity Using a 3-D Phantom Bone Model

One of the most frequent bone deformities in dogs is antebrachial growth deformity (AGD), which results from malunion of the distal growth plates. The objective of the present study was to re-align the limbs, which can correct the length mismatch and reset the coherence of the joint with the aid of a 3-D phantom model for surgical preplanning. A 14-month-old, intact female Golden Retriever with an angular deformity of the left radius and ulna was selected for the study. The diagnosis was confirmed by orthogonal radiographs. Moreover, computed tomography (CT) scans revealed a multiplane deformity with valgus, procurator, and external rotation of the left radius. The pre-surgical planning started with the quantification of the angular deformity, followed by a simulated virtual osteotomy, and concluded with an in vitro rehearsal surgery on 3-D printed phantom bone models. In the operating room, prefabricated patient-specific instrumentation (PSI) was attached at the planned site of the radial bone surface for a precise closing wedge osteotomy. Then two locking plates were fixed routinely. Post-operative radiographs showed accurate correction of the deformity as we had planned. At 12 weeks post-operatively, the follow-up surveys revealed improved gait, weight-bearing, and progression of bone healing. Our PSI design, based on novel surgical planning, was steady yet straightforward during the osteotomy. The osteotomy was performed without difficulty since the PSI that pre-determined the sites and angles let the surgeon perform the antebrachial malformation surgery. This method of operation reduces stress on the operator and helps to improve accuracy, repeatability, and surgery time.

Applications of 3-dimensional printing in small-animal surgery: A review of current practices

Three-dimensional (3D) printing, also called rapid prototyping or additive manufacturing, transforms digital images into 3D printed objects, typically by layering consecutive thin films of material. This technology has become increasingly accessible to the public, prompting applications in veterinary surgery. Three-dimensional prints provide direct visualization of complex 3D structures and also haptic feedback relevant to surgery. The main objective of this review is to report current applications of 3D printing in small-animal surgery, including surgical education, preoperative planning, and treatment of tissue defects. The reported uses of 3D prints, their proposed advantages, and current limitations are discussed considering published evidence. Aspects of the manufacturing process specific to each application are described, along with current practices in veterinary surgery.

Does PRGF Work? A Prospective Clinical Study in Dogs with A Novel Polylactic Acid Scaffold Injected with PRGF Using the Modified Maquet Technique

Simple Summary

PRGF is a concentration of autologous platelets in a small volume of plasma, which is performed in a specific way and is an accessible resource in veterinary medicine. The PRGF has multiple demonstrated properties as antimicrobial, analgesic and anti-inflammatory but their osteoinductivity potential is controversial. We decided to use PRGF in combination with a PLA bioresorbable scaffold (a specific type of implant with osteoconduction properties) performed by 3D printing, and personalized for each patient, to determinate if the PRGF can produce osteoinduction and as a result, a faster bone healing and a faster patient recovery. Furthermore, in this study PLA scaffolds are proposed as an alternative for metallic implants to avoid the problems that those can cause. The MMT was the technique selected for solving the RCrCL as it is a variant of TTA that follows the same principle for the correction of the patellar tendon angle to neutralize distractive forces; however, this technique needs a lower amount of metallic implants for the scaffold fixation.

Abstract

Tibial tuberosity advancement is a surgical technique to restore the dynamical stability in the knee by advancing the insertion of the patellar ligament, for which it is necessary to advance the tibial crest, being maintained in the desired position usually by a cage and metallic implants. The purpose of this study was to replace the cage with a polylactic acid biodegradable scaffold designed for each patient by 3D printing, inserting platelet-rich in growth factors (PRGF) to demonstrate its osteoinductive properties. To this end, we used the modified Maquet technique to reduce the amount of metal to a minimum. Fifty-three dogs finished the study. The control and PRGF groups did not present any statistically significant differences in terms of ossification degree (p > 0.001) but they demonstrated satisfactory ossification compared to previous publications, although in the PRGF group three of the scaffolds suffered complete reabsorption. The PRGF and control groups did not show any statistically significant differences in terms of lameness degree (p > 0.001). However, the PRGF group showed at the first control some analgesic and anti-inflammatory properties but they were not enough for reducing the functional recovery time in a significant way. The PRGF group did not show any complications or negative results associated with their use.

Prospective Evaluation of a Citrate-Based Biomaterial Wedge for a Modified Maquet Procedure in the Treatment of Cranial Cruciate Ligament Rupture in Dogs

OBJECTIVE

 The aim of this study was to describe short- and mid-term outcomes, complications, implant bioabsorption and owner satisfaction for a modified Maquet procedure (MMP) in which a novel bioabsorbable citrate-based implant is used as the wedge component to treat cranial cruciate ligament rupture in client-owned dogs.

STUDY DESIGN

 Prospective clinical study of dogs (n = 13) undergoing MMP (n = 15). Intraoperative complications, postoperative complications, clinical follow-up using a 5-point lameness score and radiographs at 8 weeks and 6 months postoperatively were obtained. Mid-term outcome was assessed via physical examination, radiographs, canine orthopaedic index and owner satisfaction questionnaires.

RESULTS

 No catastrophic complications occurred. Major complications occurred in 3/15 stifles. All were surgical site infections and one case required implant removal. Minor complications occurred in 9/15 stifles. Non-displaced cortical hinge fractures were the most common minor complication, and these occurred intraoperatively (4/15) or postoperatively (2/15). Three dogs achieved full function, eight dogs acceptable function and the outcome was unacceptable in two dogs. Most owners were satisfied with the procedure (11/13). Complete implant bioabsorption was not confirmed on mid-term radiographs.

CONCLUSION

 The described MMP with a citrate-based implant can produce satisfactory mid-term results. However, the long-term outcome of this procedure must be evaluated and technical modifications need to be implemented prior to larger-scale use of this implant.

An Easy and Economical Way to Produce a Three-Dimensional Bone Phantom in a Dog with Antebrachial Deformities

Simple Summary

Accurate planning, for corrective surgeries in case of bone cutting, is necessary to obtain a precise coordination of the skeleton and to achieve the owner’s satisfaction. The present experiment displays a simple and cost-effective technique for surgical planning, utilizing a 3-D bone phantom model in a dog with foreleg deformity.

Abstract

3-D surgical planning for restorative osteotomy is costly and time-consuming because surgeons need to be helped from commercial companies to get 3-D printed bones. However, practitioners can save time and keep the cost to a minimum by utilizing free software and establishing their 3-D printers locally. Surgical planning for the corrective osteotomy of antebrachial growth deformities (AGD) is challenging for several reasons (the nature of the biapical or multiapical conformational abnormalities and lack of a reference value for the specific breed). Pre-operative planning challenges include: a definite description of the position of the center of rotation of angulation (CORA) and proper positioning of the osteotomies applicable to the CORA. In the present study, we demonstrated an accurate and reproducible bone-cutting technique using patient-specific instrumentations (PSI) 3-D technology. The results of the location precision showed that, by using PSIs, the surgeons were able to accurately replicate preoperative resection planning. PSI results also indicate that PSI technology provides a smaller standard deviation than the freehand method. PSI technology performed in the distal radial angular deformity may provide good cutting accuracy. In conclusion, the PSI technology may improve bone-cutting accuracy during corrective osteotomy by providing clinically acceptable margins.

Multitechnology Biofabrication: A New Approach for the Manufacturing of Functional Tissue Structures?

Most available 3D biofabrication technologies rely on single-component deposition methods, such as inkjet, extrusion, or light-assisted printing. It is unlikely that any of these technologies used individually would be able to replicate the complexity and functionality of living tissues. Recently, new biofabrication approaches have emerged that integrate multiple manufacturing technologies into a single biofabrication platform. This has led to fabricated structures with improved functionality. In this review, we provide a comprehensive overview of recent advances in the integration of different manufacturing technologies with the aim to fabricate more functional tissue structures. We provide our vision on the future of additive manufacturing (AM) technology, digital design, and the use of artificial intelligence (AI) in the field of biofabrication.

Biological response to an experimental implant for tibial tuberosity advancement in dogs: A pre-clinical study

In this study, we propose a novel bioresorbable bioactive implant for tibial tuberosity advancement (TTA). The implant consists of a gradually resorbing load-bearing shell which encompasses rapidly resorbing small casings loaded with silica-based bioactive glass (BG) particulates which promote bone formation and reduce the risk of infection. The shell and the casings are manufactured by 3D printing from two medical grade bioresorbable polymers (a polyglycolide/lactide based and a polydioxanone based) that have different degradation rates. The casings are expected to resorb within days after surgery to expose the BG particulates while the shell would retain the load-bearing properties of the implant for the time required by bone healing. Unlike the currently used metallic devices, the novel implant is resorbed and excreted from the body once its purpose is fulfilled. This study presents a logical progression from the in vitro characterisation of the materials and implants to the in vivo investigation of the experimental implants. This included mechanical testing of the materials, finite element analysis of a preliminary design of the novel TTA implant, assessment of the degradation behaviour of the polymers and the ion exchange of BG in simulated body fluid, and investigation of the biological response to the novel implants after implantation in rabbits. The osteointegration of the novel implants was comparable to the osteointegration of Ti6Al4V implants in the control group; the biological efficacy and safety were confirmed. The biological response was in line with the expectations. The proof of concept for the novel TTA implants was demonstrated.

The anisotropic elastic behavior of the widely-used triply-periodic minimal surface based scaffolds

The Triple Periodic Minimal Surface (TPMS) has emerged as a new approach for producing open cell porous scaffolds for biomedical applications. However, different from the traditional scaffolds, the TPMS scaffolds always exhibit anisotropic elastic behaviors and consequently the simple mechanical testing is not capable to provide a full characterization of their mechanical behaviors. Additionally, it is still unclear if the TPMS scaffolds possess the similar anisotropic behaviors as the natural bones. The aim of the present study was to analyze the anisotropic elastic behaviors of TPMS based scaffolds using the numerical homogenization method and the analytical analysis approach. Five widely-used TPMS scaffold topologies (Diamond, Gyroid, Fischer-Koch S, Schwarz P and F-RD) were investigated. The independent elastic constants were determined from the analytical analysis and then, the values for these independent constants were determined using the finite element (FE) unit cell models of the scaffolds combined with the periodic boundary condition. The analytical analysis revealed that the Diamond, Gyroid and Fischer-Koch S topologies are threefold rotational symmetric and consequently have seven independent elastic constants. The Schwarz P and F-RD topologies are cubic symmetric and have three independent elastic constants. The FE analysis showed that the Diamond, Gyroid and Fischer-Koch S based scaffolds have only three non-zero independent elastic constants, implying the cubic symmetric property of these scaffolds. All the independent elastic constants decreased quadratically with the increase of scaffold porosity. The absolute difference between the Zener anisotropic factor and one increased the most for the Gyroid based scaffold, while the value for the Fischer-Koch S based scaffold increased the least. The present study revealed that all the five TPMS scaffolds possess cubic symmetry, limiting their anisotropic behaviors. The information on the Zener anisotropic factor and the relationship between the scaffold elastic constants and the porosity can facilitate the selection and design of scaffolds in biomedicine and relevant fields.

The accuracy of computed tomography scans for rapid prototyping of canine skulls

This study’s objective was to determine the accuracy of using current computed tomography (CT) scan and software techniques for rapid prototyping by quantifying the margin of error between CT models and laser scans of canine skull specimens. Twenty canine skulls of varying morphology were selected from an anatomy collection at a veterinary school. CT scans (bone and standard algorithms) were performed for each skull, and data segmented (testing two lower threshold settings of 226HU and -650HU) into 3-D CT models. Laser scans were then performed on each skull. The CT models were compared to the corresponding laser scan to determine the error generated from the different types of CT model parameters. This error was then compared between the different types of CT models to determine the most accurate parameters. The mean errors for the 226HU CT models, both bone and standard algorithms, were not significant from zero error (p = 0.1076 and p = 0.0580, respectively). The mean errors for both -650HU CT models were significant from zero error (p < 0.001). Significant differences were detected between CT models for 3 CT model comparisons: Bone (p < 0.0001); Standard (p < 0.0001); and -650HU (p < 0.0001). For 226HU CT models, a significant difference was not detected between CT models (p = 0.2268). Independent of the parameters tested, the 3-D models derived from CT imaging accurately represent the real skull dimensions, with CT models differing less than 0.42 mm from the real skull dimensions. The 226HU threshold was more accurate than the -650HU threshold. For the 226HU CT models, accuracy was not dependent on the CT algorithm. For the -650 CT models, bone was more accurate than standard algorithms. Knowing the inherent error of this procedure is important for use in 3-D printing for surgical planning and medical education.

3D printed porous ceramic scaffolds for bone tissue engineering: a review

This study summarizes the recent research status and development of three-dimensional (3D)-printed porous ceramic scaffolds in bone tissue engineering. Recent literature on 3D-printed porous ceramic scaffolds was reviewed. Compared with traditional processing and manufacturing technologies, 3D-printed porous ceramic scaffolds have obvious advantages, such as enhancement of the controllability of the structure or improvement of the production efficiency. More sophisticated scaffolds were fabricated by 3D printing technology. 3D printed bioceramics have broad application prospects in bone tissue engineering. Through understanding the advantages and limitations of different 3D-printing approaches, new classes of bone graft substitutes can be developed.