Polymeric Implants Research Articles

Influence of different polymeric materials of implant and attachment on stress distribution in implant-supported overdentures: a three-dimensional finite element study

PurposeInvestigating high performance thermoplastic polymers as substitutes to titanium alloy, in fabrication of implants and attachments to support mandibular overdenture, aiming to overcome stress shielding effect of titanium alloy implants.Aim of studyAssessment of stress distribution in polymeric prosthetic components and bone around polymeric implants, in case of implant-supported mandibular overdenture.Materials and methods3D finite element model was established for mandibular overdenture, supported bilaterally by two implants at canine region, and retained by two ball attachments. Linear static stress analysis was carried out by ANSYS 2020 R1. Three identical models were created with different materials for modeling of prosthetic components (implant body, gingival former, ball attachment and matrix). The Monolithic principle was applied as the same material was used in modelling all the prosthetic components in each model (Titanium alloy grade V, poly-ether-ether-ketone (PEEK) and poly-ether-ketone-ketone (PEKK)). Simultaneous Force application of 60 N was carried out bilaterally at the first molar occlusal surface area using 3 runs (vertical, lateral and oblique).ResultsPEEK and PEKK prosthetic components exhibited the highest total deformation and critical Maximum von Mises stresses values in implant body and gingival former under lateral and oblique loads. The stress values approached the fatigue limit of both polymeric materials presenting low factor of safety (< 1.5). The Peri-implant cortical bone in case of PEEK and PEKK showed nearly double maximum principal stresses compared with the titanium model. Conversely, Maximum von Mises stresses in spongy bone were lower in polymeric models than those of titanium ones. Additionally maximum equivalent strain values in spongy peri-implant bone of polymeric models were also lower than those of titanium model.ConclusionCritical high stresses were induced in implant body and gingival former under oblique or lateral loadings, accordingly, fatigue failure of both PEEK and PEKK polymer prosthetic elements was estimated due to low factor of safety. Both PEEK and PEKK Polymer models offered no advantage over titanium one regarding stress shielding effect, due to low stress and strain values generated at spongy peri-implant bone in polymer models.

Radiotherapy and surgery: can this combination be further optimized for patients with metastatic spine disease?

This narrative review provides a comprehensive overview of the current status, recent advancements, and future directions in the management of metastatic spine disease using both radiotherapy and surgery. Emphasis has been put on the integrated use of radiotherapy and surgery, incorporating recent developments such as separation surgery, active dose sparing of the surgical field, and the implementation of carbon fiber-reinforced polymer implants. Future studies should explore the effects of minimizing the time between radiotherapy and surgery and investigate the potential of vertebral re-ossification after radiotherapy to obviate the need for stabilization surgery. Concerted efforts should be directed toward fostering multidisciplinary collaboration among radiation oncologists, spine surgeons, and medical oncologists.

Finite element investigation for improving chest wall reconstruction process using ceramic and polymeric implants

Car accidents, infections caused by bacteria or viruses, metastatic lesions, tumors, and malignancies are the most frequent causes of chest wall damage, leading to the removal of the affected area. After excision, artificial bone or synthetic materials are used in chest wall reconstruction to restore the skeletal structure of the chest. Chest implants have traditionally been made from metallic materials like titanium alloys due to their biocompatibility and durability. However, the drawbacks of these materials have prompted researchers to seek alternative materials for use in the reconstruction process. This research aims to explore alternatives to metallic implants in order to overcome their drawbacks and enhance the performance of chest wall reconstruction using the finite element method. In this research, customized implants for the ribs and cartilages are used to repair the defective portion of the chest wall. The implants are made from various materials, including stiff bioceramics (alumina and zirconia), soft polymers (polyether ether ketone (PEEK) and polyethylene (PE)), and polymeric composites (carbon fiber-reinforced PEEK 30 and 60% (CFP 30 and 60%)) as alternatives for titanium. They are tested under normal breathing and impact loading conditions. The null hypothesis suggests that stiff implants will provide optimal results. The results illustrate that when using alumina implants, under normal breathing, the maximum tensile and compressive stresses increased to 11.41 and 15.86 MPa on ribs, while decreasing to 0.32 and 0.324 MPa, and 0.96 and 0.56 Pa on cartilages and lung respectively, compared to titanium. Conversely, when using PE implants, the maximum tensile and compressive stresses decreased to 5.69 and 8.2 MPa on ribs and increased to 0.4 and 0.42 MPa, and 1.71 and 1.1 MPa on cartilages and lung respectively. Under impact force, compared to titanium, the maximum tensile and compressive stresses increased to 47.5 and 49.8 MPa on ribs, and decreased to 1.91 and 6.15 MPa, and 4.56 and 7.7 Pa on cartilages and lung respectively, when using alumina implants. On the other hand, the maximum tensile and compressive stresses decreased to 31 and 23 MPa on ribs and increased to 2.52 and 7.83 MPa, and 5.8 and 9.3 MPa on cartilages and lung respectively, when using PE implants. The highest tensile and compressive strains on ribs were 6,162 and 6,235 µε when using alumina implants under impact force. Additionally, the highest tensile and compressive strains on cartilages and lung were 11,192 and 20,918 µε and 5,836 and 9,335 µε, respectively, when using PE implants. For screws, the peak values of von Mises stress were 61.6 MPa and 433.4 MPa under normal breathing and impact force respectively, when using PE implants. In fatigue analysis, alumina, PEEK, and PE implants failed under impact force as the maximum equivalent alternating stresses exceeded their fatigue limits, resulting in safety factors of less than one. It was concluded that stiff bioceramic implants (alumina and zirconia) produced the lowest stresses and strains on the surrounding cartilages and underlying lung, and the highest stresses and strains on the surrounding ribs, unlike soft PEEK and PE implants. Additionally, CFP 30% and 60% implants distributed stresses on the ribs, cartilages, and lungs similarly to titanium implants. Furthermore, the tensile and compressive stresses and strains on the ribs, cartilages, and lungs did not exceed allowable limits for all used implants. Finally, Zirconia, CFP 30%, and CFP 60% implants can be used as substitutes for titanium in chest wall reconstruction to restore damaged portions of the ribs and cartilage. However, stiff alumina implants and soft PEEK & PE implants were not recommended for use as they were susceptible to fracture under impact force.

Towards cell-adhesive, 4D printable PCL networks through dynamic covalent chemistry.

In recent years, the development of biodegradable, cell-adhesive polymeric implants and minimally invasive surgery has significantly advanced healthcare. These materials exhibit multifunctional properties like self-healing, shape-memory, and cell adhesion, which can be achieved through novel chemical approaches. Engineering of such materials and their scalability using a classical polymer network without complex chemical synthesis and modification has been a great challenge, which potentially can be resolved using biobased dynamic covalent chemistry (DCC). Here, we report a scalable, self-healable, biodegradable, and cell-adhesive poly(ε-caprolactone) (PCL)-based vitrimer scaffold, using imine exchange, free from the limitations of melting transitions and supramolecular interactions in 4D-printed PCL. PCL's typical hydrophobicity hinders cell adhesion; however, our design, based on photopolymerization of PCL-dimethacrylate and methacrylate-terminated vanillin-based imine, achieves a water contact angle of 64°. The polymer network, fabricated in varying proportions, exhibited a co-continuous phase morphology, achieving optimal shape fixity (91 ± 1.7%) and shape recovery (92.5 ± 0.1%) at physiological temperature (37 °C). Additionally, the scaffold promoted cell adhesion and proliferation and reduced oxidative stress at the defect site. This multifunctional material shows the potential of DCC-based research in developing smart biomedical devices with complex geometries, paving the way for novel applications in regenerative medicine and implant design.

Cranial reconstruction utilizing polymeric implants in two different designs: finite element investigation

IntroductionImpact loads applied to the human head can result in skull fractures or other injuries that require a craniectomy. The removed portion is replaced with biological or synthetic materials using cranioplasty surgery. Titanium has been the material of choice for cranial implants due to its superior properties and biocompatibility; however, its issues have prompted the search for substitute materials (e.g., polymers). The issues are related to the requirement for surface modification, casting, radiologic incompatibility and potential allergy risks. Recently, polymeric materials have been used in many fields as alternatives to titanium.ObjectiveThis research aims to conduct a finite element study to evaluate the skull reconstruction process by using PEEK and carbon fiber reinforced PEEK 30 and 60% in the production of cranial implants as alternatives to conventional titanium implants.Materials and methodsA three-dimensional model of a defective skull was rehabilitated with a custom-made cranial implant. The implants were stimulated using two designs (plate and mesh), and different polymeric materials (PEEK and carbon fiber reinforced PEEK 30 and 60%) as titanium substitutes, under 2000 N impact force.ResultsThe results illustrated that plate implants reduced the stresses on the skull and increased the stresses on brain tissues compared to mesh implants. Titanium, CFR-PEEK 30 & 60% implants (whether mesh or flat) were not prone to fracture, unlike mesh PEEK implants. In addition, CFR-PEEK 60% implants produced the lowest values of stress, strain, and total deformation on the skull and brain compared to titanium implants, unlike PEEK implants. By using the titanium plate implant, the peak tensile and compressive stresses on the skull were 24.99 and 25.88 MPa, respectively. These stresses decreased to 21.6 and 24.24 MPa when using CFR-PEEK 60%, increased to 26.07 and 28.99 MPa with CFR-PEEK 30%, and significantly increased to 41.68 and 87.61 MPa with PEEK. When the titanium mesh implant was used, the peak tensile and compressive stresses on the skull were 29.83 and 33.86 MPa. With CFR-PEEK 60%, these stresses decreased to 27.77 and 30.57 MPa, and with CFR-PEEK 30% and PEEK, the stresses increased to 34.04 and 38.43 MPa, and 44.65 and 125.67 MPa, respectively. For the brain, using the titanium plate implant resulted in peak tensile and compressive stresses of 14.9 and 16.6 Pa. These stresses decreased to 13.7 and 15.2 Pa with CFR-PEEK 60%, and increased to 16.3 and 18.1 Pa, and 73.5 and 80 Pa, with CFR-PEEK 30% and PEEK, respectively. With the titanium mesh implant, the peak tensile and compressive stresses were 12.3 and 13.5 Pa. Using CFR-PEEK 60%, these stresses decreased to 11.2 and 12.4 Pa on the brain, and increased with CFR-PEEK 30% and PEEK to 14.1 and 15.5 Pa, and 53.7 and 62 Pa, respectively. Additionally, the contact area between the PEEK implant (whether mesh or plate design) and the left parietal bone of the skull was expected to be damaged due to excessive strains. Importantly, all implants tested did not exceed permissible limits for tensile and compressive stresses and strains on the brain.ConclusionIt was concluded that carbon fiber-reinforced PEEK implants, with 30% and 60% reinforcements, can be used as alternatives to titanium for cranial reconstruction. The addition of carbon fibers to the PEEK matrix in these percentages enhances the mechanical, chemical, and thermal properties of the implants. Additionally, these composites are characterized by their low weight, biocompatibility, lack of clinical issues, and ease of fabrication. They can also help preserve the skull, protect the brain, and are not susceptible to damage.Clinical significanceOvercoming the drawbacks of titanium cranial implants and increasing the effectiveness of the cranioplasty process by utilizing PEEK and carbon fiber reinforced PEEK materials in the reconstruction of the damaged portion of skull.

Study of Physicochemical and Biological Properties of UHMWPE Joint Implant With Ti, Ta, and Zr Thin Films

ABSTRACTThis study aimed to improve the surface of polymer implants by examining the physicochemical and biological properties of UHMWPE coated with titanium, tantalum, and zirconium thin films. The coatings exhibited enhancements in wettability alongside diminished roughness. The Zr film exhibited a contact angle of 16°, a significant improvement compared to the UHMWPE sample, which has an angle of 102°. Moreover, the roughness of the pristine sample (0.958 μm) was substantially reduced to 0.403 μm with the Ta film. These characteristics prevented the adhesion of fibroblasts, minimizing the risk of fibrous encapsulation surrounding the implant [2]. Micro‐abrasion tests demonstrated that the coatings reduced the wear coefficient, making them ideal for increasing the longevity of the implant in the human body. Transitioning from a wear coefficient of 0.47 × 10–12 m2/N for UHMWPE, values as low as 0.21 × 10–12 m2/N were attained, particularly in the sample with the Ti film. Therefore, the coatings exhibit favorable characteristics for the intended biomedical application.

In Vivo Study of Organ and Tissue Stability According to the Types of Bioresorbable Bone Screws.

Biodegradable material, such as magnesium alloy or polylactic acid (PLA), is a promising candidate for orthopedic surgery. The alloying of metals and the addition of rare earths to increase mechanical strength are still questionable in terms of biosafety as absorbent materials. Therefore, the purpose of this study is to understand the effect of substances due to the degradation of various biodegradable substances on organs in the body or surrounding tissues. A total of eighty male Sprague-Dawley rats were selected for this study, and the animals were divided into four groups. Each of the three experimental groups was implanted with magnesium alloy, polymer, and titanium implants; the control group only drilled into the cortical bone. Serum assay, micro-CT, hematoxylin and eosin staining, immunoblotting, and real-time PCR were evaluated. There was no significant difference between the two groups of magnesium alloy and polymer in serum assay, but micro-CT analysis confirmed that magnesium alloy degrades faster than polymer, and histological examination showed a strong inflammatory response in the early stages, which was similarly observed in immunoblotting and real-time PCR. Our findings show that there was no toxicity due to the degradation of the biodegradable material, and the difference in each inflammatory response is thought to be determined by the rate of degradation in the body.

Multi-Layered Implant Approach for Hemilaryngectomy Reconstruction in a Porcine Model.

Partial laryngectomies result in voice, swallowing, and airway impairment for thousands of patients in the United States each year. Treatment options for dynamic restoration of laryngeal function are limited. Thus, there is a need for new reconstructive approaches. Here, we evaluated early (4 week) outcomes of multi-layered mucosal-myochondral (MMC) implants when used to restore laryngeal form and function after hemilaryngectomy in a porcine model. Six Yucatan minipigs underwent transmural hemilaryngectomies followed by reconstruction with customized MMC implants aiming to provide site-appropriate localization of regenerated laryngeal tissues, while supporting laryngeal function. All implants were fabricated from polymeric collagen, with a subset of muscle and cartilage implants containing motor endplate-expressing muscle progenitor cells or cartilage-like cells differentiated from adipose stem cells, respectively. Vocalization and laryngeal electromyography (L-EMG) measurements with nerve conduction studies were performed post-operatively and compared with baseline along with gross and histological analyses of the healing response. All animals (n = 6) survived and maintained airway patency, safe swallowing, and phonation, without the use of tracheostomy and/or gastrostomy tubes. Histological evaluation indicated no adverse tissue reaction or implant degradation, showing progressive regenerative remodeling with mucosa reformation and ingrowth of new muscle and cartilage. Preliminary L-EMG suggested weak but detectable motor unit action potentials. Although vocalization duration, frequency, and intensity decreased post-operatively, all animals retained vocal capacity and parameter recovery was evident over the study duration. Engineered collagen polymeric implants in the presence or absence of autologous cell populations may serve as a feasible reconstructive option to restore dynamic function after hemilaryngectomy. Long-term follow-up is needed to further assess functional outcomes. NA Laryngoscope, 2024.

“Janus” PEEK implant with sandwich Mg-containing coating for infected tissue repair

Having good antibacterial properties and promoting soft and hard tissue repair are the keys to successful implantation of intraosseous transcutaneous. Polyether ether ketone (PEEK) is a class of FDA-approved polymer implants. However, the surface of PEEK is bioinert, which is easy to cause postoperative infection and poor tissue integration. In this study, polypyrrole (Ppy) was polymerized on sulfonated PEEK, Mg3(PO4)2 nanosheets were grown in situ on one side, and polycaprolactone (PCL) was then spun on the surface to form a Janus-like surface on PEEK. The Ppy/Mg3(PO4)2/PCL composite coating could inhibit bacterial adhesion, and the excellent photothermal properties of Ppy/Mg3(PO4)2/PCL and Ppy coatings further promote the removal of bacteria due to the accumulated heat. After the infection was eliminated, the Janus-like surface of modified PEEK switched macrophages to anti-proinflammatory response and promoted both soft and hard tissue repair. The Ppy modified sulfonated PEEK could promote collagen secretion in the soft tissue, while the PCL films on Ppy/Mg3(PO4)2/PCL was densified by temperature response under near-infrared light treatment to close the exposed interface of Mg3(PO4)2 nanosheets that was more conducive to bone repair. In summary, PEEK with Janus-like surface consisting of Ppy/Mg3(PO4)2/PCL and Ppy has multiple biological functions of sequential antibacterial and soft and hard tissue repair, and is a promising candidate material for intraosseous transcutaneous implants.

A Systematic Review of the Contribution of Additive Manufacturing toward Orthopedic Applications.

Human bone holds an inherent capacity for repairing itself from trauma and damage, but concerning the severity of the defect, the choice of implant placement is a must. Additive manufacturing has become an elite option due to its various specifications such as patient-specific custom development of implants and its easy fabrication rather than the conventional methods used over the years. Additive manufacturing allows customization of the pore size, porosity, various mechanical properties, and complex structure design and formulation. Selective laser melting, powder bed fusion, electron beam melting, and fused deposition modeling are the various AM methods used extensively for implant fabrication. Metals, polymers, biocrystals, composites, and bio-HEA materials are used for implant fabrication for various applications. A wide variety of polymer implants are fabricated using additive manufacturing for nonload-bearing applications, and β-tricalcium phosphate, hydroxyapatite, bioactive glass, etc. are mainly used as ceramic materials in additive manufacturing due to the biological properties that could be imparted by the latter. For decades metals have played a major role in implant fabrication, and additive manufacturing of metals provides an easy approach to implant fabrication with augmented qualities. Various challenges and setbacks faced in the fabrication need postprocessing such as sintering, coating, surface polishing, etc. The emergence of bio-HEA materials, printing of shape memory implants, and five-dimensional printing are the trends of the era in additive manufacturing.

Application of hs-CRP in Assessment of Tissue Inflammation Following Implantation of Biodegradable Polymer in Experiment.

Implants made of biodegradable polymers are replaced by regenerating tissues through inflammation. The changes occurring in tissues and the organism are of practical interest for studying the biocompatibility of the material and searching for systemic markers in the blood that reflect inflammation in peri-implantation tissues. The highly sensitive C-reactive protein (hs-CRP) measurements in blood and morphometric studies of tissue surrounding the implant were carried out in the experiment within three months of implantation of a biopolymer consisting of polycaprolactone (PCL) and polytrimethylene carbonate (PTMC). During the first month, tissue inflammation decreased, and the blood level of hs-CRP did not increase. The polymer biotransformation began in the tissues after a month of implantation and was accompanied by inflammation moving deeper into the matrix. Proliferation of inflammatory cells in tissues was reflected in an increase in the hs-CRP level three months after polymer installation. The result achieved confirmed the polymer's bioinertness. The level of hs-CRP in the blood of the animals correlated with the level of inflammation in peri-implantation tissues, reflecting the activity of inflammation in the process of polymer biotransformation. This inflammation protein can be recommended for assessing tissue processes following implantation of biopolymers and their biocompatibility.

A 3D printing-based hybrid manufacturing method for high-strength polymeric medical implant fabrication

This paper presents a novel 3D printing-based hybrid manufacturing method to fabricate high-strength polymeric medical implants. Poly-ether-ether-ketone (PEEK) and polyether sulfone (PES) are blended to make filament for use with the fused filament fabrication technique to print custom designed implants. After printing and annealing, PES is removed by leaching to create interconnected porous PEEK structure with suitable pore size and porosity for bone tissue ingrowth. The proposed method provides a versatile approach to fabricating medical implants that are both mechanically strong and microstructurally inducive to osseointegration. The polymeric implants are also X-ray transparent to allow post-surgery evaluations using an imaging method. An intervertebral spacer implant example is used to demonstrate the proposed fabrication method.

Determination of biodegradation performance for fabricated by MEW Chitosan/PCL composite stents with in vitro tests

Today, biodegradable implants have begun to become a serious alternative to permanent implant groups. Especially the development of polymer material technology can be an alternative to metallic medical instruments. An innovative manufacturing method for the fabricated of these polymeric implants is melt electrowriting (MEW). This innovative method, which emerged as a result of studies on the production quality of additive manufacturing technology, is used in products with smaller and more complex geometries, such as stents. It is anticipated that this method, which is particularly convenient for patient-specific implant models, will have an important place in the implant production market in the future. Within the framework of this perspective, in this study, a study was conducted on the polycarbolactone group using the MEW method. In order to improve the biodegradability character, biodegradability experiments of chitosan-doped stents were conducted in vitro. The degradation character of the samples subjected to immersion corrosion in two different media for 1, 7, 14 and 21 days was examined based on residual mass. It has been determined that chitosan reinforcement has a buffering effect and plays a retarding role on the degradation time.

Influence of Conditions for Obtaining Polylactide-Based Materials on Their Physico-Mechanical and Rheological Characteristics

The work is devoted to the study of the influence of the conditions for obtaining materials based on the synthetic polymer polylactide on their physico-mechanical and rheological characteristics. These materials are promising for the creation of biodegradable polymer implants of temporary action to maintain the mechanical properties of broken bones during the healing period. They are designed to replace the titanium fixators currently used for these purposes, which is due not only to the need for repeated surgery to extract them, but also to the fact that the strength and modulus of elasticity of titanium fixators exceed the values of bone strength indicators by an order of magnitude, which can cause the phenomenon of bone resorption and a decrease in its strength. It has been established that with an increase in temperature in the plasticization and pressing zone, as well as with an increase in pressure in the press, there is a natural decrease in the viscosity of the polylactide melt, as well as the values of the elastic modulus and breaking stress of solid samples. Varying the cooling rate of the material during the pressing process affects the degree of its crystallinity. At the same time, the lower the cooling rate, the greater the degree of crystallinity of the polylactide and the greater the values of the elastic modulus and breaking stress.

Novel dissolution methods for drug release testing of Long-Acting injectables

Long-acting parenteral drug products are a popular choice for therapeutic areas requiring long term treatment. These products range from dispersed systems such as drug suspensions and polymeric microspheres to in situ forming polymeric implants. The lack of reliable drug release testing methods for these drug products not only impedes the development of new drug products but also affects generic drug development. Current release methods suffer from a range of problems such as high variability, poor reproducibility, poor discriminatory ability, lack of depot-like structure formation (that could mimic the in vivo situation). Moreover, shorter duration (less than a week) of release renders them unsuitable for in vitro-in vivo correlations (IVIVCs). To overcome these issues, novel adapters were developed for both USP-type-II & IV apparatus. These adapters were validated and assessed using the long-acting injectable (LAI) suspension drug product Depo Provera 150® as well as its Q1/Q2 equivalents. For USP-type-IV apparatus, two open adapter designs (conical and ellipsoidal shaped cavity with volume capacities of 50 µl and 1 ml, respectively) were developed. A closed conical adapter design with a volume capacity of 0.05 ml was developed for USP apparatus type-II. All three novel adapter designs effectively retained the suspensions, achieved release durations of 3–6 weeks with good reproducibility, minimal variability (RSD≤5%) and had good discriminatory ability. Based on this, the adapter-based dissolution methods were deemed suitable for IVIVC development of long-acting injectables. A successful Level A IVIVC was developed for Depo SubQ Provera 104® and its Q1Q2 equivalents using USP apparatus type IV with a conical adapter design. The closed adapter design for apparatus type-II was also investigated for suitability with risperidone in situ forming implants. The adapter was able to securely retain and maintain the shape of the in situ forming implants and resulted in release profiles of up to one month with good discriminatory ability and low standard error (RSD≤5%). These novel adapters hold promise of wide use for in vitro release testing of different long-acting parenteral drug products.

Design and evaluation of mechanical strength of multi-material polymeric implants for mandibular reconstruction.

Reconstruction of mandible implants to address segmental abnormalities is still a challenging task, both in vitro and in vivo. The mechanical strength of the materials used is a critical factor that determines how well bone is regenerated. The reconstruction technique of mandibular abnormalities widely uses polymeric implants. It is critical to evaluate the mechanical resilience under different load cases, including axial, combined, and flexural loading conditions. This study developed implants for mandibular defects using a combination of four materials: polylactic acid (PLA), polyethylene terephthalate glycol (PETG), thermoplastic polyurethane (TPU), and polycaprolactone (PCL), with the aim of mimicking the inherent characteristics of cortical and cancellous bone structures and evaluating their mechanical properties to support bone Osseo integration. The eleven of these combinations of structures result below the micro strain threshold level of <3000 µε, and the five combinations of the structures result in micro strain above the threshold value. The intact bone study results show that the stress under axial, combined, and flexural loading conditions is 27.6, 38.9, and 64.9 MPa, respectively. This study's stress results are lower than those from the intact bone study. The study found that the combinations of PLA and TPU material were most preferred for the cortical and cancellous bone regions of polymeric implants. These materials are also compatible with 3D printing. The results of this study can be used to find multi-material combinations that are strong and flexible.

Customizable, biocompatible implants for dorsal nasal augmentation: An in vivo pilot study of eight polylactic acid scaffold designs.

Augmentation of the nasal dorsum often requires implantation of structural material. Existing methods include autologous, cadaveric or alloplastic materials and injectable hydrogels. Each of these options is associated with considerable limitations. There is an ongoing need for precise and versatile implants that produce long-lasting craniofacial augmentation. Four separate polylactic acid (PLA) dorsal nasal implant designs were 3D-printed. Two implants had internal PLA rebar of differing porosities and two were designed as "shells" of differing porosities. Shell designs were implanted without infill or with either minced or zested processed decellularized ovine cartilage infill to serve as a "biologic rebar", yielding eight total treatment groups. Scaffolds were implanted heterotopically on rat dorsa (N = 4 implants per rat) for explant after 3, 6, and 12 months followed by volumetric, histopathologic, and biomechanical analysis. Low porosity implants with either minced cartilage or PLA rebar infill had superior volume retention across all timepoints. Overall, histopathologic and immunohistochemical analysis showed a resolving inflammatory response with an M1/M2 ratio consistently favoring tissue regeneration over the study course. However, xenograft cartilage showed areas of degradation and pro-inflammatory infiltrate contributing to volume and contour loss over time. Biomechanical analysis revealed all constructs had equilibrium and instantaneous moduli higher than human septal cartilage controls. Biocompatible, degradable polymer implants can induce healthy neotissue ingrowth resulting in guided soft tissue augmentation and offer a simple, customizable and clinically-translatable alternative to existing craniofacial soft tissue augmentation materials. PLA-only implants may be superior to combination PLA and xenograft implants due to contour irregularities associated with cartilage degradation.

A comprehensive analysis of high-temperature material extrusion 3D printing parameters on fracture patterns and strength of polyetheretherketone cranial implants

A polyetheretherketone (PEEK) cranial implant is one of the most well-known polymeric implants used in cranioplasty. However, most off-the-shelf PEEK cranial implants are developed by molding and then sized into the patient's defect anatomy by machining, which is time-consuming and capital-intensive. On the contrary, 3D printing, specifically material extrusion, can develop patient-specific cranial implants that precisely fit the defect anatomy, ensuring stable fixation and restoring esthetic cranial symmetry. However, 3D printing high-quality, mechanically robust PEEK implants are challenging due to the high thermal processing conditions required for PEEK printing, its high melt viscosity, and its susceptibility to incomplete crystallization. If appropriately attuned, an optimized set of 3D printing conditions can yield high-quality patient-specific PEEK cranial implants with clinically relevant mechanical properties. Hence, in this study, we comprehensively analyzed the effect of essential 3D printing conditions on cranial implants' material and mechanical properties. Specifically, we varied critical 3D printing material extrusion parameters, such as build orientation, nozzle, bedplate, chamber temperature, and print speed, and analyzed their effect on the implants' impact strength. We also used microscopy and Finite Element Analysis to understand the implants' fracture patterns with the impact indentor's impact. Based on our research, we determined an optimized set of 3D printing conditions to yield cranial implants with appropriate impact strength. Our results revealed that specimens printed at 0° build orientation, i.e., parallel to the bedplate, with optimum printing parameters, such as nozzle, bedplate, chamber temperature, and print speed, sustained a peak force of 2034 N. We envision that this study will help implant manufacturers utilize high-temperature material extrusion 3D printing to develop patient-specific PEEK cranial implants with clinically viable mechanical properties.

Computed tomography technologies to measure key structural features of polymeric biomedical implants from bench to bedside.

Implanted polymeric devices, designed to encourage tissue regeneration, require porosity. However, characterizing porosity, which affects many functional device properties, is non-trivial. Computed tomography (CT) is a quick, versatile, and non-destructive way to gain 3D structural information, yet various CT technologies, such as benchtop, preclinical and clinical systems, all have different capabilities. As system capabilities determine the structural information that can be obtained, seamless monitoring of key device features through all stages of clinical translation must be engineered intentionally. Therefore, in this study we tested feasibility of obtaining structural information in pre-clinical systems and high-resolution micro-CT (μCT) under physiological conditions. To overcome the low CT contrast of polymers in hydrated environments, radiopaque nanoparticle contrast agent was incorporated into porous devices. The size of resolved features in porous structures is highly dependent on the resolution (voxel size) of the scan. As the voxel size of the CT scan increased (lower resolution) from 5 to 50 μm, the measured pore size was overestimated, and percentage porosity was underestimated by nearly 50%. With the homogeneous introduction of nanoparticles, changes to device structure could be quantified in the hydrated state, including at high-resolution. Biopolymers had significant structural changes post-hydration, including a mean increase of 130% in pore wall thickness that could potentially impact biological response. By incorporating imaging capabilities into polymeric devices, CT can be a facile way to monitor devices from initial design stages through to clinical translation.

A Preclinical Trial Protocol Using an Ovine Model to Assess Scaffold Implant Biomaterials for Repair of Critical-Sized Mandibular Defects.

The present work describes a preclinical trial (in silico, in vivo and in vitro) protocol to assess the biomechanical performance and osteogenic capability of 3D-printed polymeric scaffolds implants used to repair partial defects in a sheep mandible. The protocol spans multiple steps of the medical device development pipeline, including initial concept design of the scaffold implant, digital twin in silico finite element modeling, manufacturing of the device prototype, in vivo device implantation, and in vitro laboratory mechanical testing. First, a patient-specific one-body scaffold implant used for reconstructing a critical-sized defect along the lower border of the sheep mandible ramus was designed using on computed-tomographic (CT) imagery and computer-aided design software. Next, the biomechanical performance of the implant was predicted numerically by simulating physiological load conditions in a digital twin in silico finite element model of the sheep mandible. This allowed for possible redesigning of the implant prior to commencing in vivo experimentation. Then, two types of polymeric biomaterials were used to manufacture the mandibular scaffold implants: poly ether ether ketone (PEEK) and poly ether ketone (PEK) printed with fused deposition modeling (FDM) and selective laser sintering (SLS), respectively. Then, after being implanted for 13 weeks in vivo, the implant and surrounding bone tissue was harvested and microCT scanned to visualize and quantify neo-tissue formation in the porous space of the scaffold. Finally, the implant and local bone tissue was assessed by in vitro laboratory mechanical testing to quantify the osteointegration. The protocol consists of six component procedures: (i) scaffold design and finite element analysis to predict its biomechanical response, (ii) scaffold fabrication with FDM and SLS 3D printing, (iii) surface treatment of the scaffold with plasma immersion ion implantation (PIII) techniques, (iv) ovine mandibular implantation, (v) postoperative sheep recovery, euthanasia, and harvesting of the scaffold and surrounding host bone, microCT scanning, and (vi) in vitro laboratory mechanical tests of the harvested scaffolds. The results of microCT imagery and 3-point mechanical bend testing demonstrate that PIII-SLS-PEK is a promising biomaterial for the manufacturing of scaffold implants to enhance the bone-scaffold contact and bone ingrowth in porous scaffold implants. MicroCT images of the harvested implant and surrounding bone tissue showed encouraging new bone growth at the scaffold-bone interface and inside the porous network of the lattice structure of the SLS-PEK scaffolds.