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1. Nano SUS (Ultra Fine Grained Stainless-Steel) for Orthopedic Implants

   Shaunak Kelkar, Bahram Saleh (November 2020, American Institute of Chemical Engineers Conference)

   null (Ed.)

   Musculoskeletal conditions such as low back pain, arthritis and other diseases of the joints affect millions of people around the world and are one the leading causes of disability (1). These diseases often require surgery, including total joint replacement in cases of deterioration of the natural joint (2). Serious concern regarding such procedure is the bacteria adhesion and proliferate on the surfaces of these orthopedic implants. Moreover, bacteria have shown the ability to generate resistance against drugs that once could kill them, hence, being more difficult or even impossible to eliminate them. These pathogens are the principal causative agents of two major types of infection in bone: septic arthritis and osteomyelitis, which involve the inflammatory destruction of joint and bone (3). Therefore, there is an unmet need to generate materials capable of showing reduced bacterial adhesion as well as bactericidal effect in order to avoid further health complications. nanoSUS Bio-Tech was founded based on a collaboration between Komatsuseiki Kosakusho Co., Ltd (KSJ:Japan) and Northeastern University (NEU) in 2019. KSJ has been developing ultra-fine-grained stainless steel since 2002 (4, 5). Using this technology, we are able to control the grain size without any changes in the chemical composition of commercially available FDA approved stainless steel. On the other hand, Thomas J. Webster’s lab has achieved the ability to decrease bacteria adhesion and growth with and without the use of antibiotics, for nanostructured surfaces. As an outcome of this collaboration, we were able to manufacture high strength ultra-fine-grained stainless steel with antimicrobial surface. The global orthopedic implants market was estimated at $45.90 billion in 2017 and is expected to reach at $66.63 billion by 2025, registering a CAGR of 4.7% from 2018 to 2025 (6), due to the growing demand by increasing geriatric population, rising incidence of spine illness and technological advancements in this field. Based on geography, North America accounted for nearly half of the total market revenue in 2017 and is anticipated to retain its top status till 2025. At the same time, the Asia-Pacific region would cite the fastest CAGR of 6.4% throughout the study period. Based on current market trends, companies such as Zimmer, Stryker, S&N, Depuy, J&J, and Medtronic are our target customers. Currently, we are expanding our network in the US by becoming member of Center for Disruptive Musculoskeletal Innovations (CDMI). Moreover, this project is funded through CDMI NSF program that will aid to expand the collaboration between KSJ and NEU. The company will be established by financing from KSJ, in Boston, MA. It will manage the collaborations between academia, marketing consultants and lawyers in the US, and directors and researchers in Japan and the US. We are expecting to start our sales from the beginning of 2021. 

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2. NanoSUS (Ultra Fine Grained Stainless-Steel) for Orthopedic Implants

   Bahram Saleh, Ada Vernet-Crua (February 2021, Orthopaedic Research Society)

   Statement of Purpose: Orthopedic implants are important therapeutic devices for the management of a wide range of orthopedic conditions. However, bacterial infections of orthopedic implants remain a major problem, and not an uncommon one, leading to an increased rate of osteomyelitis, sepsis, implant failure and dysfunction, etc. Treating these infections is more challenging as the causative organism protects itself by the production of a biofilm over the implant’s surface (1). Infections start by the adhesion and colonization of pathogenic bacteria such as Staphylococcus aureus (SA), Staphylococcus epidermidis (SE), Escherichia coli (E. coli), Methicillin-Resistant Staphylococcus aureus (MRSA), and Multi-Drug Resistant Escherichia coli (MDR E. coli) on the implant’s surfaces. Specifically, Staphylococcus comprises up to two-thirds of all pathogens involved in orthopedic implant infections (2). However, bacterial surface adhesion is a complex process influenced by several factors such as chemical composition, hydrophobicity, magnetization, surface charge, and surface roughness of the implant (3). Considering the intimate association between bacteria and the implant surface, we measured the effect of stainless-steel surface properties on bacterial surface attachment and subsequent formation of biofilms controlling above mentioned factors. Method: The prominent bacteria responsible for orthopedic implant infections (SA, SE, E. coli, MRSA, and MDR E. coli) were used in this study. We were able to control the grain size of medical grade 304 and 316L stainless steel without altering their chemical composition (grain size range= 20μm-200nm) (4). Grain size control affected the nano-topography of the material surfaces which was measured by an Atomic Force Microscope (AFM). Grain sizes, such as 0.2, 0.5, 1, 2, 3, 9, and 10 μm, were used both polished and non-polished. All the stainless-steel samples were cleaned by treating with acetone and ethanol under sonication. Triplicates of all polished and non-polished samples with different grain sizes were subjected to magnetization of DM, 0.1T, 0.5T, and 1T, before seeding them with the bacteria. Controls were used in the form of untreated samples. Bacterial were grown in Tryptic Soy Broth (TSB). An actively growing bacterial suspension was seeded onto the stainless-steel discs into 24-well micro-titer plates and kept for incubation. After 24 hours of incubation, the stainless-steel discs were washed with Phosphate Buffer Saline (PBS) to remove the plankton bacteria and allow the sessile bacteria in the biofilm to remain. The degree of development of the bacterial biofilms on the stainless-steel discs were measured using spectrophotometric analysis. For this, the bacterial biofilm was removed from the stainless steel by sonication. The formation of biofilms was also determined by performing a biofilm staining method using Safranin. Results: AFM results revealed a slight decrease in roughness by decreasing the grain size of the material. Moreover, the samples were segregated into two categories of polished and non-polished samples, in which polishing decreased roughness significantly. After careful analysis we found out that polished surfaces showed a higher degree for biofilm formation in comparison to the non-polished ones. We also observed that bacteria showed a higher rate for biofilm formation for the demagnetized samples, whereas 0.5T magnetization showed the least amount of biofilm formation. After 0.5T, there was no significant change in the rate of biofilm formation on the stainless-steel samples. Altogether, stainless steel samples containing 0.5 μm and less grainsize, and magnetized with 0.5 tesla and stronger magnets demonstrated the least degree of biofilm formation. Conclusion: In summary, the results demonstrate that controlling the grain size of medical grade stainless steel can control and mitigate bacterial responses on, and thus possibly infections of, orthopedic implants or other implantable devices. The research was funded by Komatsuseiki Kosakusho Co., Ltd (KSJ: Japan) 

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3. Developing Bioactive-Nanograined Metals With Bacterial Biofilm Inhibition Properties For Orthopedic Devices

   Kelkar, Shaunak; Saleh, Bahram; Yusa, Fumie; Suzuki, Yohei; Komatsu, Takafumi; Webster, Thomas (January 2021, Orthopaedic Research Society)

   null (Ed.)

   INTRODUCTION: Orthopedic implants are important therapeutic devices for the management of a wide range of orthopedic conditions. However, bacterial infections of orthopedic implants remain a major problem, and not an uncommon one, leading to an increased rate of osteomyelitis, sepsis, implant failure and dysfunction, etc. Treating these infections is more challenging as the causative organism protects itself by the production of a biofilm over the implant’s surface (1). Infections start by the adhesion and colonization of pathogenic bacteria such as Staphylococcus aureus (SA), Staphylococcus epidermidis (SE), Escherichia coli (E. coli), Methicillin-Resistant Staphylococcus aureus (MRSA), and Multi-Drug Resistant Escherichia coli (MDR E. coli) on the implant’s surfaces. Specifically, Staphylococcus comprises up to two-thirds of all pathogens involved in orthopedic implant infections (2). However, bacterial surface adhesion is a complex process influenced by several factors such as chemical composition, hydrophobicity, magnetization, surface charge, and surface roughness of the implant (3). Considering the intimate association between bacteria and the implant surface, we measured the effect of stainless-steel surface properties on bacterial surface attachment and subsequent formation of biofilms controlling above mentioned factors. METHODS: The prominent bacteria responsible for orthopedic implant infections (SA, SE, E. coli, MRSA, and MDR E. coli) were used in this study. We were able to control the grain size of medical grade 304 and 316L stainless steel without altering their chemical composition (grain size range= 20μm-200nm) (4). Grain size control affected the nano-topography of the material surfaces which was measured by an Atomic Force Microscope (AFM). Grain sizes, such as 0.2, 0.5, 1, 2, 3, 9, and 10 μm, were used both polished and non-polished. All the stainless-steel samples were cleaned by treating with acetone and ethanol under sonication. Triplicates of all polished and non-polished samples with different grain sizes were subjected to magnetization of DM, 0.1T, 0.5T, and 1T, before seeding them with the bacteria. Controls were used in the form of untreated samples. Bacterial were grown in Tryptic Soy Broth (TSB). An actively growing bacterial suspension was seeded onto the stainless-steel discs into 24-well micro-titer plates and kept for incubation. After 24 hours of incubation, the stainless-steel discs were washed with Phosphate Buffer Saline (PBS) to remove the plankton bacteria and allow the sessile bacteria in the biofilm to remain. The degree of development of the bacterial biofilms on the stainless-steel discs were measured using spectrophotometric analysis. For this, the bacterial biofilm was removed from the stainless steel by sonication. The formation of biofilms was also determined by performing a biofilm staining method using Safranin. RESULTS SECTION: AFM results revealed a slight decrease in roughness by decreasing the grain size of the material. Moreover, the samples were segregated into two categories of polished and non-polished samples, in which polishing decreased roughness significantly. After careful analysis we found out that polished surfaces showed a higher degree for biofilm formation in comparison to the non-polished ones. We also observed that bacteria showed a higher rate for biofilm formation for the demagnetized samples, whereas 0.5T magnetization showed the least amount of biofilm formation. After 0.5T, there was no significant change in the rate of biofilm formation on the stainless-steel samples. Altogether, stainless steel samples containing 0.5 μm and less grainsize, and magnetized with 0.5 tesla and stronger magnets demonstrated the least degree of biofilm formation. DISCUSSION: In summary, the results demonstrate that controlling the grain size of medical grade stainless steel can control and mitigate bacterial responses on, and thus possibly infections of, orthopedic implants or other implantable devices. The research was funded by Komatsuseiki Kosakusho Co., Ltd (KSJ: Japan) SIGNIFICANCE/CLINICAL RELEVANCE: Orthopedic implants that more than 70% of them are made of metals (i.e., stainless steel, titanium, and cobalt-chromium alloys) are failing through loosening and breakage due to their limited mechanical properties. On the other hand, the risk of infection for these implants and its financial burden on our society is undeniable. We have seen that our uniformly nanograined stainless steel shows improved mechanical properties (i.e., higher stiffness, hardness, fatigue) as compared to conventional stainless steel along with the reduction of biofilm formation on its surface. These promising results made us to peruse the development of nanograined titanium and cobalt-chromium alloys for resolving the complications of orthopedic implants. 

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4. Biomechanical Properties of Various Surgical Suture Needles in a Cadaveric Quadriceps Tendon Model

   Diaz, Miguel A.; Branch, Eric A.; Dunn, Jake; Brothers, Anthony; Jordan, Steve (February 2023, Transactions of the annual meeting of the Orthopaedic Research Society)

   INTRODUCTION: Quadriceps tendon autografts have experienced a rapid rise in popularity for anterior cruciate ligament (ACL) reconstruction due to advantages in graft sizing and potential improvement in biomechanics. While there is a growing body of literature on use of quadriceps tendon grafts, deeper investigation into the biomechanical properties of stitch techniques in this construct has been limited. The purpose of this study was to evaluate the performance of a novel suture needle against different conventional suture needles by comparing the biomechanical properties of two commonly used stitch methods, a whip stitch, and a locking stitch in quadriceps tendon. It was hypothesized that the new device would be capable of creating both whip stitches and locking stitches that are biomechanically equivalent to similar stitch techniques performed with conventional needle products. METHODS: This was a controlled biomechanical study. A total of 24 matched pair cadaveric knees were dissected and a total of 48 quadriceps tendons were harvested and tested. All tendon grafts were standardized to the same size. Samples were then randomized into the following groups, keeping the matched pairs together: (Group 1, n=16) consisted of Company W’s novel two-part suture needle design, (Group 2, n=16) consisted of Company A suture, and (Group 3, n=16) consisted of Company B suture. For each group, the matched pairs were categorized into subgroups to be instrumented with either a whip stitch or a locking stitch. Two fellowship-trained surgeons performed all stitching, where they each instrumented 8 tendon grafts per group. For instrumentation, the grafts were clamped to a preparation stand in accordance with the manufacturer’s recommendations for passing each suture needle. A skin marker was used to identify and mark five evenly spaced points, 0.5 cm apart, as a guide to create a 5-stitch series. For Group 1, the whip stitch as well as the locking whip stitch were performed with a novel 2-part needle. For Group 2, the whip stitch was performed with loop suture needle and the locking stitch was krackow with a curved needle. Similarly, for Group 3, the whip stitch was performed with loop suture needle and the locking stitch was krackow with a curved needle (Figure 1). Cyclical testing was performed using a servohydraulic testing machine (MTS Bionix) equipped with a 5kN load cell. A standardized length of tendon, 7 cm, was coupled to the MTS actuator by passing it through a cryoclamp cooled by dry ice to a temperature of -5°C (Figure 2). All testing samples were then pre-conditioned to normalize viscoelastic effects and testing variability through application of cyclical loading to 25-100 N for three cycles. The samples were then held at 89 N for 15 minutes. Thereafter, the samples were loaded to 50-200 N for 500 cycles at 1 Hz. If samples survived, they were ramped to failure at 20 mm/min. Displacement and force data was collected throughout testing. Metrics of interest were total elongation (mm), stiffness (N/mm), ultimate failure load (N) and failure mode. Data are presented as averages plus/minus standard deviation. A one-way analysis of variance (ANOVA) with a Tukey pairwise comparison post hoc analysis was used to evaluate differences between the various stitching methods. Statistical significance was set at P = .05. RESULTS SECTION: For the whip stitch methods, the total elongation was found to be equivalent across all methods (W: 36 ± 10 mm; A: 32 ± 18 mm; B: 33 ± 8 mm). The stiffness of Company A (103 ± 11 N/mm) method was significantly larger than Company W (64 ± 8 N/mm; p=.001), whereas stiffness of whip stitch by Company W was equivalent to Company B (80 ± 32 N/mm). The ultimate failure load was equivalent across all whip stitch methods (W: 379 ± 31 mm; A: 412 ± 103 mm; B: 438 ± 63 mm). For the locking stitch method, the total elongation (W: 26 ± 10 mm; A: 14 ± 2 mm; B: 29 ± 5 mm), stiffness (W: 75 ± 11 N/mm; A: 104 ± 23 N/mm; B: 79 ± 10 N/mm) and ultimate load (W: 343 ± 22 N; A: 369 ± 30 N; B: 438 ± 63 N) were found to be equivalent across all methods. The failure mode for all groups is in Table 1. The common mode of failure across study groups and stitch configuration was suture breakage. However, the whip stitch from Company A and Company B had varied failure modes. DISCUSSION: Products from the three manufacturers were found to produce biomechanically equivalent whip stitches and locking stitches with respect to elongation and ultimate failure load. The only significant difference observed was that the whip stitch created with Company A’s product had a higher stiffness than Company W’s product, which could have been due to differences in the suture material. In this cadaveric quadriceps tendon model, it was shown that when using Company W’s novel two-part suture needle, users were capable of creating whip stitches and locking stitches that achieved equivalent biomechanical performance compared to similar stitch techniques performed with conventional needle products. A failure mode limited solely to suture breakage for methods completed with Company W’s needle product suggest a reliable suture construct with limited tissue damage. SIGNIFICANCE/CLINICAL RELEVANCE: Having a suture needle device with the versatility to easily perform different stitching constructs may provide surgeons an advantage needed to improve clinical outcomes. The data presented illustrates a strong new suture technique that has equivalent performance when compared to conventional needle devices and has promising applications in graft preparation for ligament and tendon reconstruction. 

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5. Modeling Fretting Wear Resistance and Shakedown of Metallic Materials with Graded Nanostructured Surfaces

   https://doi.org/10.3390/nano13101584  

   Yang, Ting; Venkatesh, T. A.; Dao, Ming (May 2023, Nanomaterials)

   In applications involving fretting wear damage, surfaces with high yield strength and wear resistance are required. In this study, the mechanical responses of materials with graded nanostructured surfaces during fretting sliding are investigated and compared to homogeneous materials through a systematic computational study. A three-dimensional finite element model is developed to characterize the fretting sliding characteristics and shakedown behavior with varying degrees of contact friction and gradient layer thicknesses. Results obtained using a representative model material (i.e., 304 stainless steel) demonstrate that metallic materials with a graded nanostructured surface could exhibit a more than 80% reduction in plastically deformed surface areas and volumes, resulting in superior fretting damage resistance in comparison to homogeneous coarse-grained metals. In particular, a graded nanostructured material can exhibit elastic or plastic shakedown, depending on the contact friction coefficient. Optimal fretting resistance can be achieved for the graded nanostructured material by decreasing the friction coefficient (e.g., from 0.6 to 0.4 in 304 stainless steel), resulting in an elastic shakedown behavior, where the plastically deformed volume and area exhibit zero increment in the accumulated plastic strain during further sliding. These findings in the graded nanostructured materials using 304 stainless steel as a model system can be further tailored for engineering optimal fretting damage resistance. 

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