Artificial Implants Research Articles

Construction of polyacrylamide/graphene oxide/gelatin/sodium alginate composite hydrogel with bioactivity for promoting Schwann cells growth.

Various hydrogels made from natural or synthetic polymers have been widely used in biologic tissues, drug delivery, and artificial implants due to their good biocompatibility, indicating a promising perspective in regenerative medicine. In the present study, a composite hydrogel named polyacrylamide/graphene oxide/gelatin/sodium alginate (PAM/GO/Gel/SA) for accelerating peripheral nerve regeneration was fabricated through in situ free radical polymerization for the first time. A series of physicochemical properties including morphology, porosity, swelling behaviors, component, mechanical properties, and in vitro degradation behavior of the prepared composite hydrogel were characterized. The effects of the composite hydrogel on Schwann cells growth were evaluated and the related molecular mechanism was further penetrated. The results showed that the prepared PAM/GO/Gel/SA composite hydrogels displayed different color appearance as the function of component variations. The surface morphology, components, swelling ratio, mechanical properties, and porosity were all changed with the concentration alteration of each ingredient, while no obvious degradation behavior was observed, indicating a controllable physicochemical property. The culture of cells exhibited that the composite hydrogels could well support the attachment and proliferation of Schwann cells. The gene expression levels of Sox10, GAP43, and myelin basic protein (MBP) in PGG0.5 SYR1 and PGG1 SYR0.5 were higher than those of NC. This study may provide important theoretical and experimental basis for the design and development of hydrogel scaffolds for nerve tissue engineering application. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1951-1964, 2018.

Senescent cells and osteoarthritis: a painful connection.

Senescent cells (SnCs) are associated with age-related pathologies. Osteoarthritis is a chronic disease characterized by pain, loss of cartilage, and joint inflammation, and its incidence increases with age. For years, the presence of SnCs in cartilage isolated from patients undergoing total knee artificial implants has been noted, but these cells' relevance to disease was unclear. In this Review, we summarize current knowledge of SnCs in the multiple tissues that constitute the articular joint. New evidence for the causative role of SnCs in the development of posttraumatic and age-related arthritis is reviewed along with the therapeutic benefit of SnC clearance. As part of their senescence-associated secretory phenotype, SnCs secrete cytokines that impact the immune system and its response to joint tissue trauma. We present concepts of the immune response to tissue trauma as well as the interactions with SnCs and the local tissue environment. Finally, we discuss therapeutic implications of targeting SnCs in treating osteoarthritis.

Abstract 77: Outcomes Analysis of Goldilocks Mastectomy and Breast Reconstruction: The Mayo Clinic Experience

PURPOSE: The Goldilocks mastectomy procedure involves local contouring of completely autologous breast tissue created by preserving and de-epithelializing the residual mastectomy flap. This technique provides patients with an option for post-mastectomy breast reconstruction alternative to simple mastectomy without reconstruction, complex autologous flap harvesting techniques, or the use of artificial implants. The purpose of this study was to provide outcomes data for 172 Goldilocks mastectomy procedures performed at a single tertiary academic center analyzing complication rate, relevant comorbidities, and adjuvant cancer treatment impacting functional and aesthetic outcomes. This is the largest series of Goldilocks mastectomy procedures to be reported to date. METHODS: Relevant comorbidities and complication data were collected. Patients who had prior surgical procedures before presenting to our institution were designated as such. Specific breast cancer pathology and previous breast therapy were indicated. Data relevant to the Goldilocks reconstruction at our institution were collected, including laterality of procedure(s), indication (i.e. prophylactic or therapeutic), whether a tissue expander or an implant was placed at the time of the Goldilocks procedure or at any point following the procedure, the number of procedures needed for the entire reconstructive regimen, and any specific revision procedures, if needed (i.e. fat grafting, mastopexy, augmentation, or scar revision). RESULTS: A total of 95 patients underwent reconstruction with Goldilocks procedure. 82.1% (78) of cases were bilateral, and 17.8% (17) were unilateral reconstructions. Breast cancer pathology results included: DCIS 27.3% (26), LCIS 5.26% (5), stage I 11.57 (11), stage II 23.1% (22), stage III 23.1% (22), inflammatory 5.3% (5), BRCA prophylactic 11.5% (11), other 2.1% (2), and recurrent cancer 6.3% (6). Pre-operative radiation therapy was given in 7.4% (7) of patients, while post-operative radiation therapy was given to 6.31% (6) of patients. 22.1% (21) of patients received chemotherapy and 17.8% (17) received hormone therapy. Previous breast reconstruction history included implant-based reconstruction in 3.15% (3), autologous 1% (1), multiple attempts 1% (1), and failed reconstruction 1% (1). Reconstruction types included Goldilocks-only in 58% (53) of patients, Goldilocks + tissue expander in 35.8% (34), and Goldilocks with implant in 10.5% (10). 45.3% (43) of patients underwent adjuvant fat grafting, 7.3% (7) underwent concurrent mastopexy, 5.2% (5) underwent concurrent breast augmentation, and 14.7% (14) had scar revision procedures performed at the time of Goldilocks procedure. Complications included: seroma 6.3% (6), hematoma 4.2% (4), cellulitis 4.2% (4), wound dehiscence 4.2% (4), DVT/PE 1% (1), readmission 1% (1), needed take back to OR 9.5% (9), needed explant 7.4 %(7), or other complications 3.1% (3). CONCLUSION: Goldilocks mastectomy procedures are a useful adjunct in reconstruction, and can also be used in implant-based reconstruction, providing a dermal sling to build an internal bra and scaffold for the implant. Patients who have relevant medical comorbidities or who decline traditional methods of reconstruction can greatly benefit from Goldilocks mastectomy. There may be substantial utility in considering Goldilocks procedures during pre-operative planning in patient-centered care along the reconstructive ladder, as this approach has the ability of being modified with additional procedures such as fat grafting or implant placement. J. Oliver: None. A. Chaudhry: None. S. Alsubaie: None. J. Martinez-Jorge: None.

Polydimethylsiloxane films engineered for smart nanostructures

Herein, we present organic molecular beam deposition to fabricate (sub-)micrometer-thin polydimethylsiloxane (PDMS) substrate-fixed films with a thickness homogeneity better than 2% on square centimeters. Their surface roughness and wrinkle morphology is controlled by the evaporation temperature, the growth rate, and the ultraviolet-light irradiation. The tailoring of the elastic modulus for the selected vinyl-functionalized PDMS nano-membranes is demonstrated. Both the surface morphology and mechanics are key parameters, which crucially determine the tissue-to-implant interactions for applications in bioelectronics. The cross-linked PDMS nano-membranes with elastic moduli of only a few hundred kPa are realized – a compliance similar to human soft tissues. The in situ characterization of their mechanical properties is presented based on their temperature sensitivity by spectroscopic ellipsometry and correlated to subsequently performed nano-indentation using a sophisticated atomic force microscopy instrument. Such soft sub-micrometer-thin elastomer membranes will become an essential component of dielectric elastomer transducers with strains comparable to human muscles, operated at the conventional battery voltages for future artificial muscles or skin implants.

Technical note: Comparison of metal-on-metal hip simulator wear measured by gravimetric, CMM and optical profiling methods

Simulation of wear in artificial joint implants is critical for evaluating implant designs and materials. Traditional protocols employ the gravimetric method to determine the loss of material by measuring the weight of the implant components before and after various test intervals and after the completed test. However, the gravimetric method cannot identify the location, area coverage or maximum depth of the wear and it has difficulties with proportionally small weight changes in relatively heavy implants. In this study, we compare the gravimetric method with two geometric surface methods; an optical light method (RedLux) and a coordinate measuring method (CMM). We tested ten Adept hips in a simulator for 2 million cycles (MC). Gravimetric and optical methods were performed at 0.33, 0.66, 1.00, 1.33 and 2 MC. CMM measurements were done before and after the test. A high correlation was found between the gravimetric and optical methods for both heads (R2 = 0.997) and for cups (R2 = 0.96). Both geometric methods (optical and CMM) measured more volume loss than the gravimetric method (for the heads, p = 0.004 (optical) and p = 0.08 (CMM); for the cups p = 0.01 (optical) and p = 0.003 (CMM)). Two cups recorded negative wear at 2 MC by the gravimetric method but none did by either the optical method or by CMM. The geometric methods were prone to confounding factors such as surface deformation and the gravimetric method could be confounded by protein absorption and backside wear. Both of the geometric methods were able to show the location, area covered and depth of the wear on the bearing surfaces, and track their changes during the test run; providing significant advantages to solely using the gravimetric method.

Design and Compressive Behavior of Controllable Irregular Porous Scaffolds: Based on Voronoi-Tessellation and for Additive Manufacturing.

Adjustment of the mechanical properties (apparent elastic modulus and compressive strength) in porous scaffolds is important for artificial implants and bone tissue engineering. In this study, a top-down design method based on Voronoi-Tessellation was proposed. This method was successful in obtaining the porous structures with specified and functionally graded porosity. The porous specimens were prepared by selective laser melting technology. Quasi-static compressive tests were conducted as well. The experiment results revealed that the mechanical properties were affected by both porosity and irregularity. The irregularity coefficient proposed in this study can achieve good accommodation and balance of "irregularity" and "controllability". The method proposed in this study provides an efficient approach for the bionic design and topological optimization of scaffolds.

Effect of stereoisomerism of poly(lactic acid) during neural guide conduit membrane synthesis

ABSTRACTPoly(lactic acid) membranes are being developed as biomaterials for several purposes such as artificial implants for peripheral nerve injury, also known as neural guide conduits (NGC). These membranes need to meet standards of mechanical, degradability, and permeability properties, besides dimensional and structural requirements. Among the stereoisomers of polylactides, poly(l‐lactic acid), and poly(d,l‐lactic acid) are the most used as biomaterials, having significant differences in solubility, crystallinity thermal, and mechanical properties. In this work, PLLA and PDLLA were compared for hollow fiber membrane synthesis by liquid induced phase separation. PLLA samples presented 18% of crystallinity, while PDLLA is amorphous. PDLLA and PLLA polymer solutions on N‐methyl‐pyrrolidone presented values of 3428 and 320.2 cP, respectively. In immersion of PLA‐NMP solutions in water, PLLA solution presented instantaneous demixing, while PDLLA showed a 28 s delay on precipitation. The PLLA–NMP–water has a larger demixing region compared to PDLLA–NMP–water system. Hollow fibers of both polymers presented closed external surface with finger‐like macropores morphology in their cross‐sections. PDLLA presented typical liquid–liquid demixing pores while PLLA presented spherulitical crystalline solid–liquid separation structures, which deeply compromised its mechanical properties. PDLLA presented as a good candidate for hollow fiber NGC material, as presented good mechanical resistance in tensile and suture simulating tests. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46190.

Automatic Artificial Hair Implant: Safety and Efficacy in Androgenetic Alopecia. A Prospective Study with a Highly Biocompatible Fiber

AIM:A multi - centre two years the long prospective open clinical study was conducted in five countries located in four different continents from May 2015 to evaluate the clinical safety and efficacy of Automatic Biofibre hair implant in male and female androgenetic alopecia. Biofibre®is a CE/TGA certified medical grade polyamide fibre suitable for implantation.MATERIAL AND METHODS:A total of 213 patients were enrolled in the study. Patients were assessed pre -operatively by Hamilton scale grading and the percentage of scalp covered by hair. All the patients underwent Biofibre hair implantation by a standardised surgical technique followed by adequate post-operative care. Efficacy of the implant was evaluated by surgeons and patients bimonthly for the first year and trimonthly during the second year. Any adverse effects were recorded during these visits.RESULTS:At the completion of the study period, a total of 194 patients concluded the trial and the results were statistically evaluated. Both Hamilton scale grading and covered area percent improved at the end of the study, and subjective and objective evaluations revealed satisfactory results. Side effects were reported in only 18 cases (9.27%) which were easily controlled by either topical or systemic treatment in 8 to 10 days.CONCLUSION:Overall a successful result was noticed in 97.94% of patients with great psychological satisfaction.

3D printing of hydroxyapatite scaffolds with good mechanical and biocompatible properties by digital light processing

Hydroxyapatite is a scaffold material widely used in clinical repair of bone defects, but it is difficult for traditional methods to make customized artificial bone implants with complicated shapes. 3D printing biomaterials used as personalized tissue substitutes have the ability to promote and enhance regeneration in areas of defected tissue. The present study aimed at demonstrating the capacity of one 3D printing technique, digital light processing (DLP), to produce HA scaffold. Using HA powder and photopolymer as raw materials, a mixture of HA mass ratio of 30 wt% was prepared by viscosity test. It was used for forming ceramic sample by DLP technology. According to differential scanning calorimetry and thermal gravity analysis, it was revealed that the main temperature range for the decomposition of photopolymer was from 300 to 500 °C. Thus, the two-step sintering process parameters were determined, including sintering temperature range and heating rate. XRD analysis showed that the phase of HA did not change after sintering. SEM results showed that the grain of the sintered ceramic was compact. The compression model was designed by finite element analysis. The mechanical test results showed that the sample had good compression performance. The biological properties of the scaffold were determined by cell culture in vitro. According to the proliferation of cells, it was concluded that the HA scaffold was biocompatible and suitable for cell growth and proliferation. The experimental results show that the DLP technology can be used to form the ceramic scaffold, and the photopolymer in the as-printed sample can be removed by proper high-temperature sintering. The ceramic parts with good compression performance and biocompatibility could be obtained.

Role of different orthopedic biomaterials on wear of hip joint prosthesis: A review

The wear of the bearing surfaces of hip joint prostheses is a key problem causing their primary failure. Hard-on-soft bearings have suffered long term failure due to polyethylene wear debris induced Osteolysis. This is dependent on the wear volumes and size and shape of the wear debris produced. Small submicron polyethylene wear particles elicit more powerful biological activities than larger particles. This detailed study of wear analysis of hip joint is carried out by highlighting anatomy of hip joint, different materials used in prosthesis, wear and artificial implants such as hard on hard and hard on soft implants for hip joint. It aims to obtain in depth understanding of wear of bearing couples of artificial hip joint due to different parameters.

Construction of perfluorohexane/IR780@liposome coating on Ti for rapid bacteria killing under permeable near infrared light.

Near infrared (NIR) light induced photodynamic antibacterial therapy (PDAT) is a promising antibacterial technique in rapid in situ disinfection of bacterially infected artificial implants due to its penetration ability into tissues. However, the lower oxygen content in vivo may restrict the yields of reactive oxygen species (ROS), thus reducing the antibacterial efficacy of PADT significantly. Herein, liposome encapsulated photosensitizers (PS), IR780 and perfluorohexane (PFH), have been constructed on the surface of Ti implants via a covalent linkage to overcome this issue. Thanks to the high oxygen capacity of PFH, more ROS can be generated during NIR irradiation regardless of the low content of oxygen in vivo. As a result, in vitro tests demonstrated that 15 minutes of 808 nm near-infrared irradiation could achieve a high antibacterial efficacy of 99.62% and 99.63% on the implant surface against Escherichia coli and Staphylococcus aureus, respectively. By contrast, the PDAT system without PFH modification shows a lower antibacterial efficacy (only 66.54% and 48.04%, respectively). In addition, this enhanced PDAT system also possesses great biocompatibility based on the in vitro and in vivo subcutaneous assays. This surface system makes it possible for rapid bacteria-killing in artificial implants that have been implanted in vivo under local conditions with lower oxygen content.

A classification of implants for reconstruction of the anterior and middle supporting columns of the spine

The study objective was to classify implants for anterior interbody fusion, depending on their design features and functional capabilities, to optimize the choice of endoprosthesis designs for reconstructive surgery of the spin. We analyzed information provided in advertising brochures, annotations, and communications describing the designs of vertebral body endoprostheses. To study the design features of various implants, we selected 25 implant types with the structural designs of major units typical of vertebral body replacement systems. We performed static tests of mechanical features of anterior interbody fusion systems using special equipment and mathematical modeling based on the finite element technique to determine features of the stressed-deformed state in replacement of the vertebral bodies with artificial implants of various designs. The analysis results define the prerogative of combined telescopic designs with axisymmetric accommodation of compression stresses, which enable reconstruction and stabilization of the spinal motion segment without additional fixation by a ventral plate. The classification of endoprostheses enables evaluation of advantages and disadvantages of various implants to objectively assess the mechanisms of potential postoperative complications and to prevent them. The presented data may facilitate the optimal choice of an implant with allowance for the peculiarities of a clinical situation in each particular case.

Nano Ag/ZnO-Incorporated Hydroxyapatite Composite Coatings: Highly Effective Infection Prevention and Excellent Osteointegration.

Interfacial characteristics play an important role in infection prevention and osteointegration of artificial bone implants. In this work, both Ag nanoparticles (AgNPs) and ZnO NPs are incorporated into hydroxyapatite (HA) nanopowders and deposited onto Ti6Al4V (Ti6) implants by laser cladding. The composite coatings possess a hierarchical surface structure with homogeneous distributions of Ag and ZnO. The Ag and ZnO NPs that are immobilized by laser cladding ensure long-term and gradual release of Ag and Zn ions at low cumulative concentrations of 36.2 and 56.4 μg/L after immersion for 21 days. A large concentration of Ag released initially increases the cytotoxicity but the large initial ZnO content enhances the cell viability and osteogenetic ability. The nano Ag/ZnO-embedded HA coating (Ag/ZnO/HA = 7:3:90 wt %, namely Ag7ZnO3HA) exhibits optimal antibacterial efficacy and osteogenetic capability, as exemplified by the broad spectrum antibacterial efficacy of 96.5 and 85.8% against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), respectively, together with enhanced osteoinductivity with higher alkaline phosphatase (ALP) activity of 134.60 U/g protein compared to 70.79 U/g protein for the untreated implants after culturing for 7 days. The rabbit femoral implant model further confirms that the optimized composite coating accelerates the formation of new bone tissues indicating 87.15% of the newly formed bone area and osteointegration showing 83.75% of the bone-implant contact area even in the presence of injected S. aureus. The laser-cladded Ag7ZnO3HA composite coatings are promising metallic implants with excellent intrinsic antibacterial activity and osteointegration ability.

The Role of Nanomechanics in Healthcare.

Nanomechanics has played a vital role in pushing our capability to detect, probe, and manipulate the biological species, such as proteins, cells, and tissues, paving way to a deeper knowledge and superior strategies for healthcare. Nanomechanical characterization techniques, such as atomic force microscopy, nanoindentation, nanotribology, optical tweezers, and other hybrid techniques have been utilized to understand the mechanics and kinetics of biospecies. Investigation of the mechanics of cells and tissues has provided critical information about mechanical characteristics of host body environments. This information has been utilized for developing biomimetic materials and structures for tissue engineering and artificial implants. This review summarizes nanomechanical characterization techniques and their potential applications in healthcare research. The principles and examples of label-free detection of cancers and myocardial infarction by nanomechanical cantilevers are discussed. The vital importance of nanomechanics in regenerative medicine is highlighted from the perspective of material selection and design for developing biocompatible scaffolds. This review interconnects the advancements made in fundamental materials science research and biomedical technology, and therefore provides scientific insight that is of common interest to the researchers working in different disciplines of healthcare science and technology.

The Effect of Solution Treatment Temperature on Plastic Deformation and Fracture Mechanisms of Beta-Titanium Alloy

The beta-titanium alloys are used mainly in bioapplications for artificial joints and other implants. They posses interesting properties such as, high corrosion resistance, low Young’s modulus, good plasticity or superelasticity etc. In this work the effect of solution treatment temperature on deformation and fracture properties has been studied. The alloy Ti-35Nb-2Zr was processed via powder metallurgy process (cold isostatic pressing, sintering and subsequent swaging). Swaged alloy was annealed at 800, 850, 900, 950 and 1000 °C. Tensile tests have been performed on such heat treated specimens and the fracture surface has been studied in correlation with microstructure. With increasing annealing temperature both tensile strength (from 925 MPa to 990 MPa) and elongation (from 13 to 25 %) increased where the maximum values were obtained for 900 °C annealed specimens and subsequently slight decrease has been observed. The simultaneous increase of strength and elongation was attached to change of deformation mechanisms which was described by studying fracture surfaces and microstructure of deformed (tensile tested) specimens.

Custom Repair of Mandibular Bone Defects with 3D Printed Bioceramic Scaffolds

Implanting artificial biomaterial implants into alveolar bone defects with individual shape and appropriate mechanical strength is still a challenge. In this study, bioceramic scaffolds, which can precisely match the mandibular defects in macro and micro, were manufactured by the 3-dimensional (3D) printing technique according to the computed tomography (CT) image. To evaluate the stimulatory effect of the material substrate on bone tissue regeneration in situ in a rabbit mandibular alveolar bone defect model, implants made with the newly developed, mechanically strong ~10% Mg-substituted wollastonite (Ca90%Mg10%SiO3; CSi-Mg10) were fabricated, implanted into the bone defects, and compared with implants made with the typical Ca-phosphate and Ca-silicate porous bioceramics, such as β-tricalcium phosphate (TCP), wollastonite (CaSiO3; CSi), and bredigite (Bred). The initial physicochemical tests indicated that although the CSi-Mg10 scaffolds had the largest pore dimension, they had the lowest porosity mainly due to the significant linear shrinkage of the scaffolds during sintering. Compared with the sparingly dissolvable TCP scaffolds (~2% weight loss) and superfast dissolvable (in Tris buffer within 6 wk) pure CSi and Bred scaffolds (~12% and ~14% weight loss, respectively), the CSi-Mg10 exhibited a mild in vitro biodissolution and moderate weight loss of ~7%. In addition, the CSi-Mg10 scaffolds showed a considerable initial flexural strength (31 MPa) and maintained very high flexural resistance during soaking in Tris buffer. The in vivo results revealed that the CSi-Mg10 scaffolds have markedly higher osteogenic capability than those on the TCP, CSi, and Bred scaffolds after 16 wk. These results suggest a promising potential application of customized CSi-Mg10 3D robocast scaffolds in the clinic, especially for repair of alveolar bone defects.

Thermoresponsive Mobile Interfaces with Switchable Wettability, Optical Properties, and Penetrability.

Liquid-based mobile interfaces, in which liquids are being utilized as structural long-term components, have shown their multifunctionality in materials science, such as the hydration layer of polyelectrolyte brushes used for artificial implants, stabilized lubricants for antibiofouling, anti-icing, self-cleaning, optical control, and so forth. However, these currently available systems do not usually show a response to environmental stimuli. Here, we describe a strategy for preparing thermoresponsive mobile interfaces made from novel silicone-based lubricants that display lower critical solution temperature and demonstrate their capabilities on controlling in situ water wetting and dewetting, thermo-gating penetration, and optical properties. These properties allow the mobile films to form a kind of erasable recording platforms. We foresee diverse applications in liquid transport, wetting and adhesion control, and transport switching.

A Novel Rhinoplasty Sculpture Technique Using Ancient Chinese Architectural Technology.

Rhinoplasty is one of the most delicate procedures in plastic and reconstructive surgery. Precision in every millimeter is vital in ensuring a better quality of surgical outcome. Many methods have been developed to fulfill this requirement. One such method is an implant, whether autogenous or artificial. Artificial implants involve several surgical complications, such as recipient rejection of implant material, infections, and rigid feel of the nasal tip. Hence, autogenous implants were eventually more widely applied, with material being obtained from the septum, concha, or rib cartilages. Therefore, the authors developed a new technique of rhinoplasty, using the osteochondral rib as an autogenous implant based on the ancient Chinese architectural technology called the DouGong method. The authors hereby present the results of 288 patients treated in our faculty wherein the data from the patients and the preoperative and postoperative 3-dimensional computed tomography scans were processed using Mimics software. The uniqueness of these implants is that the joint between the nasal dorsum and the columella strut is fixated without any screw, stitches, or K-wire. This procedure proved to be very useful as this technique not only minimized the application of fixation techniques, but also helped achieve a better nasofrontal angle, nasolabial angle, and columella length. After monitoring follow-ups of our patients, the authors hereby propose the use of this DouGong-based novel technique to improve the overall quality and outcome of corrective rhinoplasty.

Fractal Electrodes as a Generic Interface for Stimulating Neurons

The prospect of replacing damaged body parts with artificial implants is being transformed from science fiction to science fact through the increasing application of electronics to interface with human neurons in the limbs, the brain, and the retina. We propose bio-inspired electronics which adopt the fractal geometry of the neurons they interface with. Our focus is on retinal implants, although performance improvements will be generic to many neuronal types. The key component is a multifunctional electrode; light passes through this electrode into a photodiode which charges the electrode. Its electric field then stimulates the neurons. A fractal electrode might increase both light transmission and neuron proximity compared to conventional Euclidean electrodes. These advantages are negated if the fractal’s field is less effective at stimulating neurons. We present simulations demonstrating how an interplay of fractal properties generates enhanced stimulation; the electrode voltage necessary to stimulate all neighboring neurons is over 50% less for fractal than Euclidean electrodes. This smaller voltage can be achieved by a single diode compared to three diodes required for the Euclidean electrode’s higher voltage. This will allow patients, for the first time, to see with the visual acuity necessary for navigating rooms and streets.

Evaluating the effects of material properties of artificial meniscal implant in the human knee joint using finite element analysis

Artificial meniscal implants may replace severely injured meniscus and restore the normal functionality of the knee joint. Implant material stiffness and shape influence the longevity of implantations. This study, using 3D finite element analysis, aimed to evaluate the effects of material stiffness variations of anatomically shaped artificial meniscal implant in the knee joint. Finite element simulations were conducted on five different cases including intact knee, medial meniscectomized knee, and the knee joint with the meniscal implant with three distinct material stiffness. Cartilage contact pressures, compression stresses, shear stresses, and implant kinematics (medial-lateral and posterior-anterior displacement) were evaluated for an axial compressive load of 1150 N at full extension. Compared to the meniscectomized knee, the knee joint with the meniscal implant induced lower peak cartilage contact pressure and reduced the cartilage regions loaded with contact pressures greater than the peak cartilage contact pressure induced by the intact knee. Results of the current study also demonstrate that cartilage contact pressures and implant displacement are sensitive to the implant material stiffness. The meniscal implant with a stiffness of 11 MPa restores the intact knee contact mechanics, thereby reducing the risk of physiological damage to the articular cartilage.