New materials for hip and knee joint replacement: What's hip and what's in kneed?

Over the last three decades there have been significant advancements in the knee and hip replacement technology that has been driven by an issue in the past concerning adverse local tissue reactions, aseptic and septic loosening. The implants and the materials we utilize have improved over the last two decades and in knee and hip replacement there has been a decrease in the failures attributed to wear and osteolysis. Despite these advancements there are still issues with patient satisfaction and early revisions due to septic and aseptic loosening in knee replacement patients. This article reviews the state of current implant material technology in hip and knee replacement surgery, discusses some of the unmet needs we have in biomaterials, and reviews some of the current biomaterials and technology that may be able to solve the most common issues in the knee and hip replacement surgery.

Modulating physical properties of porcine urethra with injection of novel biomimetic proteoglycans ex vivo.

Urinary incontinence is a significant challenge for women who are affected by it. We propose augmenting the tissue structure to restore normal biomechanics by molecularly engineering the tissue using a novel family of biomimetic proteoglycans (BPGs). This work examines the ability of BPGs to modulate the mechanical and physical properties of porcine urethras ex vivo to determine the feasibility of BPGs to be implemented as molecular treatment for stress urinary incontinence (SUI). We investigated compliance by performing a unique radial expansion testing method using urethras from six- to nine-month-old pigs. The urethras were injected with 0.5 ml BPG solution at three sites every approximately 120° (conc.: 25 mg ml-1, 50 mg ml-1 and 75 mg ml-1 in 1× phosphate-buffered saline (PBS); n = 4 per group) and compared them with PBS-injected controls. Young's modulus was calculated by treating the urethra as a thin-walled pressure vessel. A water uptake study was performed by soaking 10 mm urethra biopsy samples that were injected with 0.1 ml BPG solution (conc.: 50 mg ml-1, 100 mg ml-1 and 200 mg ml-1 in 1× PBS; n = 6 per group) in 5 ml PBS for 24 h. Although there was no significant difference in Young's modulus data, there were differences between groups as can be seen in the raw radial expansion testing data. Results showed that BPGs have the potential to increase hydration in samples, and that there was a significant difference in water uptake between BPG-injected samples and the controls (100 mg ml-1 samples versus PBS samples, p < 0.05). This work shows that BPGs have the potential to be implemented as a molecular treatment for SUI, by restoring the diminished proteoglycan content and subsequently increasing hydration and improving the compliance of urethral tissue.

In vivo molecular engineering of the urethra for treatment of stress incontinence using novel biomimetic proteoglycans.

Stress urinary incontinence (SUI), a serious condition which affects ~56% of postmenopausal women, is the involuntary leakage of urine through urethra during physical activity that causes an increase in abdominal pressure. SUI is associated with a decrease in compliance and volume of urethral tissue, likely due to a reduced proteoglycan: collagen ratio in the extracellular matrix and collagen disorganization. Here, we investigated the use of biomimetic proteoglycans (BPGs) to molecularly engineer urethral tissue of New Zealand White rabbits to examine biocompatibility in vivo. BPG concentrations of 50 mg/mL (n = 6, 1 week) and 200 mg/mL (n = 6, 1 week and n = 6, 6 weeks) dissolved in 1× phosphate-buffered saline (PBS) were injected transurethrally using a 9 French cystoscope, and were compared to PBS-injected controls (n = 3, 1 week) and non-injected controls (n = 2, 1 week). Urethral compression pressure measurements confirm BPG injections did not modify normal urethral pressure, as intended. Histological assessment demonstrated biological tolerance of BPGs in urethra and no inflammatory response was detected after 1 and 6 weeks compared to non-injected controls. Confocal imaging of fluorescently-labeled BPG injected urethral specimens demonstrated the integration of BPGs into the interstitial connective tissue and confirmed they were still present after 6 weeks. A general decrease of collagen density was exhibited near injection sites which may be due to increased hydration induced by BPGs. Injection of BPGs is a novel approach that demonstrates potential as molecular treatment for SUI and may be able to reverse some of the degenerative tissue changes of individuals affected by this condition. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: 00B: 000-000, 2019. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2409-2418, 2019.

Synthesis of macromolecular mimics of small leucine-rich proteoglycans with a poly(ethylene glycol) core and chondroitin sulphate bristles.

Small leucine-rich proteoglycans (SLRPs) are a class of molecules prevalent in almost all tissues types and are thought to be responsible for collagen organization and macro-scale biological properties. However, when they are dysfunctional or degraded, severe pathological phenotypes are observed. Here we investigate macromolecular mimics to SLRPs using poly(ethylene glycol) (PEG) as a core (replacing the protein core of natural SLRPs) and chondroitin sulphate (CS) bristle(s) in an end-on attachment (via epoxide-amine reactions), mimicking the physical structure of the natural SLRPs. Poly(ethylene glycol)-diglycidyl ether (PEG-DEG) and ethylene glycol-diglycidyl ether (EG-DGE) monomers were used to incorporate CS bristles into a macromolecule that closely mimics the SLRP biglycan structure in a grafting-to strategy. The kinetics of these reactions was studied along with the specific viscosity and cytocompatibility of resulting CS macromolecules. Structures were found to incorporate two CS chains (similar to biglycan) on average and exhibited cytocompatibility equivalent to or better than CS-only controls.

Flame time of a cigarette lighter to achieve temperature capable of inflicting a burn.

OBJECTIVE: Cigarette lighters are frequent vectors in intentional contact burns. Time and temperature needed to cause thermal injury are considered to differentiate accidental from inflicted burns. This study examines the minimum time needed to heat a cigarette lighter's top to temperatures capable of inflicting any clinically visible skin burn. This information could be useful in child abuse and other forensic cases. METHODS: A literature search was performed to establish the time and temperature at which partial/full thickness skin burns are acquired, regardless of vector. Using a thermocouple, the temperature of the top of two common lighters was measured at ten second intervals while sustaining maximal flame held both upright and sideways and during cooling once the flame was extinguished. RESULTS: In the literature, the lowest temperatures documented to cause burns in one second were 69°C-70°C for transepidermal or partial thickness burns. From an ambient temperature prior to flame ignition, it took over 50s for the lighter tops to reach 60°C when held upright. After 180s, the lighters were shut off. It then took less than 60s for the lighters to cool to less than 60°C. The BIC lighter held to the side heated to 60°C in about 15s and needed over 100s to cool to under 60°C. CONCLUSIONS: Cigarette lighter burns are often blamed on non-intentional occurrences. At least 50s of sustained flame is needed to heat typical cigarette lighter tops to temperatures capable of inflicting clinically visible skin burns. This time is longer than the time required to light a cigarette. Therefore, for a cigarette lighter to inflict a contact burn injury, there needs to be intent and preparation, making accidental cigarette lighter burns unlikely.

The Science Behind Surgical Innovations of the Forefoot.

One of the areas of foot and ankle surgery that has had particular attention over the last 5 years has been forefoot surgery. Common procedures include correction of the lessor metatarsophalangeal joints and hammertoe deformities, specifically metatarsal shortening osteotomies and proximal interphalangeal joint fusions. The goals of these surgeries are to improve patient function and allow patients to fit into shoes more comfortably in metatarsal shortening and hammertoe.

Friction and wear behavior of poly(vinyl alcohol)/poly(vinyl pyrrolidone) hydrogels for articular cartilage replacement.

Many hydrogels have been proposed as articular cartilage replacements as an alternative to partial or total joint replacements. In the current study, poly(vinyl alcohol)/poly(vinyl pyrrolidone) (PVA/PVP) hydrogels were investigated as potential cartilage replacements by investigating their in vitro wear and friction characteristics in a pin-on-disk setup. A three-factor variable-level experiment was designed to study the wear and friction characteristics of PVA/PVP hydrogels. The three different factors studied were (a) polymer content of PVA/PVP hydrogels, (b) load, and (c) effect of lubricant. Twelve tests were conducted, with each lasting 100,000 cycles against Co-Cr pins. The average coefficient of friction for synovial fluid lubrication was a low 0.035 compared with 0.1 for bovine serum lubrication. Frictional behavior of PVA/PVP hydrogels did not follow Amonton's law of friction. Wear of the hydrogels was quantified by measuring their dry masses before and after the tests. Higher polymer content significantly reduced the wear of hydrogel samples with 15% PVA/PVP samples, showing an average dry polymer loss of 4.74% compared with 6.05% for 10% PVA/PVP samples. A trend change was observed in both the friction and wear characteristics of PVA/PVP hydrogels at 125 N load, suggesting a transition in the lubricating mechanism at the pin-hydrogel interface at the critical 125 N load.

2006 Otto Aufranc Award Paper: significance of in vivo degradation for polyethylene in total hip arthroplasty.

Our research group developed an implant retrieval program to study in vivo degradation of polyethylene. We now have evidence to support our hypothesis that degradation of radiation-sterilized polyethylene occurs in the body for not only historical gamma air sterilized liners, but also for conventional gamma inert sterilized (ArCom) and annealed highly crosslinked polyethylene (Crossfire) liners as well. Our research has also led to the discovery that the most severe manifestations of in vivo oxidation typically occur in regions of the liner experiencing minimal wear, such as the rim of the component, where the body fluids (containing oxidizing species) have access to the polyethylene. Our data from historical, ArCom, and Crossfire retrievals all point to a similar scenario in which the femoral head limits the in vivo oxidation of polyethylene at the bearing surface. Consequently, provided rim impingement does not occur, and the polyethylene locking mechanisms remain relatively isolated from oxidizing fluid, in vivo oxidation does not seem to be clinically important in the first 10 years of implantation for conventional gamma sterilized polyethylene. We conclude that in vivo degradation should be included among the list of potential long-term failure modes for modular polyethylene components for total hip arthroplasty.

Functional compressive mechanics of a PVA/PVP nucleus pulposus replacement.

Emerging techniques as an alternative to the current treatments of lower back pain include nucleus replacement by an artificial material, which aims to relieve pain and restore the normal spinal motion. The compressive mechanical behavior of the PVA/PVP hydrogel nucleus implant was assessed in the present study. PVA/PVP hydrogels were made with various PVP concentrations. The hydrogels were loaded statically under unconfined and confined conditions. Hydrogels were tested dynamically up to 10 million cycles for a compression fatigue. Also, hydrogel nucleus implants with a line-to-line fit, were implanted in the human cadaveric intervertebral discs (IVD) to determine the compressional behavior of the implanted discs. Hydrogel samples exhibited typical non-linear response under both unconfined and confined compressions. Properties of the confinement ring dictated the observed response. Hydrogel moduli and polymer content were not different pre- and post-fatigues. Slight geometrical changes (mostly recoverable) were observed post-fatigue. In cadavers, hydrogels restored the compressive stiffness of the denucleated disc when compared with equivalent condition of the IVD. The results of this study demonstrate that PVA/PVP hydrogels may be viable as nucleus pulposus implants. Further studies under complex loading conditions are warranted to better assess its potential as a replacement to the degenerated nucleus pulposus.

The effect of protein-free versus protein-containing medium on the mechanical properties and uptake of ions of PVA/PVP hydrogels.

The effect of two simulated biological environments (protein-free and protein-containing) on ion uptake and physical properties of PVA/PVP hydrogels were explored in this work. It was found that over the immersion period in both media, wet mass of the hydrogels decreased and compressive moduli increased, likely due to increased polymer content with water loss as the hydrogels equilibrated with water. These changes were independent of polymer content and immersion medium. However, dry mass of the hydrogels increased dramatically when immersed in protein-free medium, changing only moderately in protein-containing medium. The increase in dry mass was attributed to ion uptake from immersion medium, as confirmed by EDXA. We postulate that differences between ion uptake in protein-free versus protein-containing medium is likely the result of serum proteins in the protein-containing medium adsorbing to the surface, inhibiting transport of ions into the hydrogel.

In vivo degradation of polyethylene liners after gamma sterilization in air.

BACKGROUND: Ultra-high molecular weight polyethylene degrades during storage in air following gamma sterilization, but the extent of in vivo degradation remains unclear. The purpose of this study was to quantify the extent to which the mechanical properties and oxidation of conventional polyethylene acetabular liners treated with gamma sterilization in air change in vivo. METHODS: Fourteen modular cementless acetabular liners were revised at an average of 10.3 years (range, 5.9 to 13.5 years) after implantation. All liners, which had been machined from GUR 415 resin, had been gamma-sterilized in air; the average shelf life was 0.3 year (range, 0.0 to 0.8 year). After removal, the components were expeditiously frozen to minimize ex vivo changes to the polyethylene prior to characterization. The average duration between freezing and testing was 0.6 year. Mechanical properties and oxidation were measured with use of the small-punch test and Fourier transform infrared spectroscopy, respectively, in the loaded and unloaded regions of the liners. RESULTS: There was substantial regional variation in the mechanical properties and oxidation of the retrieved liners. The ultimate load was observed to vary by >90% near the surface. On the average, the rim and the unloaded bearing showed evidence of severe oxidation near the surface after long-term in vivo aging, but these trends were not typically observed on the loaded bearing surface or near the backside of the liners. CONCLUSIONS: The mechanical properties of polyethylene that has been gamma-sterilized in air may decrease substantially in vivo, depending on the location in the liner. The most severe oxidation was observed at the rim, suggesting that the femoral head inhibits access of oxygen-containing body fluids to the bearing surface. This is perhaps why in vivo oxidation has not been associated with clinical performance to date.

The effect of dehydration history on PVA/PVP hydrogels for nucleus pulposus replacement.

The feasibility of the use of a copolymer gel prepared from blends of polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) for endoscopic replacement of the nucleus pulposus of a lumbar intervertebral disc was examined in this study. Hydrogels were processed with the use of three freeze/thaw cycles to induce crystallinity. As-prepared samples were dehydrated to various levels: 70.4, 46.3, 25.1, and 10.3% of their as-prepared masses and subsequently rehydrated. The dehydration history controlled the dimensions upon swelling and caused distortion of the material, with major distortion occurring when the hydrogel reached around 25% of the initial hydrated mass. The dehydration history affected the mechanical behavior of the rehydrated gels. Increased dehydration resulted in increased compressive modulus for the reswollen gels. Experiments were performed to investigate the formation of a skin layer that was found on the hydrogels during the dehydration process. The skin was found to dehydrate quickly and form a barrier to further dehydration from the core. Rubber elasticity theory was used to describe the differences in the network characteristics between the skin and the core of a drying hydrogel. The dehydration/rehydration process used in this study and an implantation of a cadaver model demonstrate the feasibility of endoscopic nucleus replacement.