Bioprinting is a technique of creating 3D cell-laden structures by accurately dispensing biomaterial to form complex synthetic tissue. The printed constructs aim to mimic the native tissue by preserving the cell functionality and viability within the printed structure. The 3D bioprinting system presented in this paper aims to facilitate the process of 3D bioprinting through its ability to control the environmental parameters within an enclosed printing chamber. This design of the bioprinter targets to eliminate the need for a laminar flow hood, by regulating the necessary environmental conditions important for cell survival, especially during long duration prints. A syringe-based extrusion (SBE) deposition method comprising multiple nozzles is integrated into the system. This allows for a wider selection of biomaterials that can be used for the formation of the extracellular matrix (ECM). Tissue constructs composed of alginate-gelatin hydrogels were mixed with fibrinogen and human endothelial cells which were then characterized and compared using two methodologies: casted and bioprinted. Furthermore, vasculature was incorporated in the bioprinted constructs using sacrificial printing. Structural and functional characterization of the constructs were performed by assessing rheological, mechanical properties, and analyzing live-dead assay measurements.

Selective laser melting (SLM) can be used to tailor both the geometry and mechanical properties of lattice structures to match bone properties. In this work, a process–structure–property (PSP) relationship for Ti6AL4V porosity graded gyroids (PGGs) structures was developed. A design of experiment approach was used to test the significance and contribution of different process parameters on microstructure, morphology, and mechanical properties. Process maps to predict the morphology errors at specific laser power and scan speed were developed. Moreover, the mechanical properties of radially PGGs with a relative density of 25% are evaluated using different SLM process parameters. The results showed that PGGs with different radial gradation designs have mechanical properties that are compatible with bone implants: apparent compressive modulus of 1.4–5.3 GPa and compressive strength 40–154 MPa.

Characterization of cell mechanical properties plays an important role in disease diagnoses and treatments. This paper uses advanced atomic force microscopy (AFM) to measure the geometrical and mechanical properties of two different human brain normal HNC-2 and cancer U87 MG cells. Based on experimental measurement, it measures the cell deformation and indentation force to characterize cell mechanical properties. A fitting algorithm is developed to generate the force-loading curves from experimental data. An inverse Hertzian method is also established to identify Young's moduli for HNC-2 and U87 MG cells. The results demonstrate that Young's modulus of cancer cells is different from that of normal cells, which can help us to differentiate normal and cancer cells from the biomechanical viewpoint.

Sterilization is a vital component of the manufacturing process for any medical device. However, some sterilization techniques may alter device properties. While it is known that electron beam sterilization can change the mechanical properties of solid polymethylmethacrylate (PMMA) constructs, its effect on porous PMMA has not been explored. Therefore, porous PMMA space maintainer constructs designed for the treatment of craniofacial bone defects were sterilized at dosages of 30 kGy and 40 kGy. Electron beam sterilization was shown to increase the compressive properties of porous PMMA space maintainer devices.

In this work, we modified the topography of commercial titanium orthopedic screws using electrochemical anodization in a 0.4 wt% hydrofluoric acid solution to produce titanium dioxide nanotube layers. The morphology of the nanotube layers were characterized using scanning electron microscopy. The mechanical properties of the nanotube layers were investigated by screwing and unscrewing an anodized screw into several different types of human bone while the torsional force applied to the screwdriver was measured using a torque screwdriver. The range of torsional force applied to the screwdriver was between 5 and 80 cN·m. Independent assessment of the mechanical properties of the same surfaces was performed on simple anodized titanium foils using a triboindenter. Results showed that the fabricated nanotube layers can resist mechanical stresses close to those found in clinical situations.

Recent advances in radio frequency (RF) sensor systems provide new opportunities to wirelessly collect data from inside the body. “Smart implants” instrumented with sensors have been used as research tools for decades, but only recently have implantable sensors become small enough and robust enough to be used in daily clinical practice. In orthopedic surgery, implants provide a vehicle onto which small RF sensors can be mounted to gather data for diagnostics. However, the sensors must function in a challenging environment which requires long term functionality under demanding physical and mechanical conditions. The purpose of this study was to parametrically test low frequency RF systems under simulated in vivo conditions to determine feasibility of sensor integration into orthopedic applications. Three low frequency RF systems were tested in several clinically relevant scenarios in vitro to characterize (1) strategies for maximizing communication range, (2) physical robustness, and (3) mechanical performance. Systems were tested in air, saline, soft tissue, bone, and in proximity to metal. Hermeticity was assessed during a 208 week period. Effects of γ-irradiation and repeated steam sterilized were measured. Strain at failure was measured by mechanical testing of various packaging configurations. All systems were capable of greater than 20 cm read range under ideal conditions. Saline, soft tissue, and bone had minimal effect on signal transmission, but read range was sensitive to the proximity of stainless steel. The electronics were tolerant of steam sterilization but not of γ-irradiation. Polymer encapsulation is robust enough for many orthopedic applications, but ceramic encapsulated sensors need to be optimized for weight-bearing applications to avoid brittle failure. Although sensor packaging remains a challenge, the technology exists to incorporate passive wireless implantable sensors into orthopedic daily practice.

Natural and synthetic hydrogels have attracted much attention for nerve regeneration. Previous studies have shown that electrical charge has significant effect on stimulation of neurite outgrowth. In this work, incorporation of a positively charged monomer into the photocrosslinkable oligo(polyethylene glycol) fumarate (OPF) hydrogel has been investigated. We have evaluated the effect of localized positive charge on neurite outgrowth in culture with an objective that positively charged hydrogels ultimately can be used for stimulating in vivo nerve regeneration. The effect of charged modification has been also studied on mechanical properties and swelling ratio of these hydrogels. Our data indicated that with increasing charge density hydrogels swelling ratio increased in water, however it remained constant in PBS. We also demonstrated that compressive modulus and tensile strength of the hydrogels improved with incorporation of electrical charge into the hydrogels. Biodegradation of modified hydrogels was investigated in a series of biomimetic solutions. OPF hydrogels appeared to be more susceptible to oxidative degradation as opposed to the hydrolytic degradation in enzymes and acidic solution, and the degradation rate was correlated to the PEG molecular weight and charge density of the hydrogels. To investigate the effect of charge modification on nerve cell attachment and differentiation, dissociated dorsal root ganglion (DRG) cells were plated onto the modified and unmodified hydrogels surfaces. DRG cells attached and extended their neurites more readily on the surface of positively charged hydrogels as opposed to the unmodified hydrogels.

It was hypothesized that the nonlinear load-displacement relationship displayed by bone could be conferred on an implant by tailoring its structure, yielding an enhanced mechanical stimulation of the tissues. Composite structures would feature piezoelectric properties that could also stimulate osteogenesis. Preliminary mechanical and electromechanical investigations of such porous structures are presented. Initial trial bowtie specimens with various aspect ratii were made from Nickel powder via a solid free form process and from stainless steel shim stocks. Poled Barium Titanate plates were sandwiched between stainless steel bowtie cells to create composite structures.Results: Under quasi-static compression, the Nickel structures displayed a nonlinear mechanical behavior at small strains and an overall strain-stress relationship similar to bone. Under cyclic compressive tests to 0.6 percent strain, all structures presented a repeatable nonlinear strain-stress behavior. The curves were fitted by a second-order polynomial whose coefficients are function of the relative density of the structure to a power n. Composite stainless steel/BaTiO3 bowtie structures confirmed that their electromechanical properties can be tailored.Discussion: Certain patients present metabolic degeneration that hamper bone healing. A ductile and tough structural material with piezoelectric properties such as the new composite structures in development presents the potential to overcome those limitations. They could have the advantages of existing devices without some of the drawbacks. Those porous implants may reduce the needs, costs, and risks linked to the additional use and implementation of an electrical stimulator and BMPs. Furthermore, the solid free form technique gives control over the mechanical properties of the structure. Thus, the mechanotransduction activity of biologic cells can be fully exploited to trigger a faster implant-tissue bonding, which could lead to reduction of surgical cost and time.

Physical therapies using mechanical loadings are widely used for improving and recovering the physical activities of human tissues. It is generally accepted that such therapies promote health and well-being by many mechanisms, including fastening muscle blood flow, parasympathetic activity, releasing relaxation hormones and inhibiting muscle tension, neuromuscular excitability and stress hormones. Nonetheless, most of current research in this area is based on statistics and thus qualitative, preventing the in-depth study of the effectiveness of these therapies. It is partially due to the lack of appropriate tools for quantitative loading and in situ tissue evaluation. To address this, we developed a medical device that resembles the mechanical motions and loadings that occur in massage therapies by applying combinations of compressive and shear loadings to the subject tissues. This device consists of a loading wheel, a force sensor, a pneumatic actuator, a control system and a data acquisition system. In this work, mechanical forces were applied to the lower limbs of rabbits with controllable magnitudes, frequencies and durations. The changes of mechanical properties of the subjects, including the compliance and the viscosity, were in situ measured as a function of the loading dose, and correlated to the results from biomolecular assay. This device can quickly identify the optimal sets of loading parameters which lead to high effectiveness, and thus provide guidance to practitioners to design their therapies. It is also expected to shed light on the fundamental study of biomechanical forces in regulation of the physiologic conditions of cells and tissues.

Moisture levels in medical device packages influence a variety of crucial device properties, e.g. mechanical properties, corrosion and leach rates, drug potency, and ultimately shelf life. This is especially true for drug releasing and biodegradable device materials. It is therefore important to establish a high degree of control and accuracy of the humidity levels at all relevant stages in the production process as well as in the final package. In the current study we demonstrate a newly developed method for accurate headspace moisture trace level analysis in medical device packages using extractive gas phase Fourier transform infrared (FTIR) spectroscopy. Volumetric aliquots were extracted, using a specially designed extraction assembly, from the headspace of medical device relevant packages. The headspace water concentration was analyzed using a validated gas phase FTIR system1. Water bands in the spectral region 1600 – 2200 cm 1 were chosen for the quantitative analysis. Sample spectra were compared, with a least square fit procedure, to water reference spectra at known concentration. Accurate quantification was demonstrated for headspace water vapor concentrations less than 100 ppm . This is considerably lower than feasible with conventional package headspace moisture analysis techniques. The results of this study demonstrate the benefits of using extractive gas phase FTIR for low level moisture analysis of small headspace volumes.

Background: Biodegradable polymeric stents represent a competitive approach to permanent and absorbable metallic stents for vascular applications. Despite major challenges resulting from the mechanical properties of polymeric biomaterials, these stent concepts gain their attraction from their intrinsic potential for controlled biodegradation and facile drug incorporation. This study demonstrates the mechanical properties of a novel balloon-expandable slotted tube stent from PLLA. Method of Approach: Polymeric balloon-expandable slotted tube stents (nominal dimensions: 6.0 × 25 mm ) were manufactured by laser machining of solution cast tubes ( I . D . = 2.8 mm , d = 270 ± 20 μ m ) from biodegradable (1) PLLA and (2) PLLA/PCL/TEC. The stents were tested in vitro for their mechanical properties: deployment, recoil, shortening, collapse, and creep behavior under a static load of 100 mm Hg . In vitro degradation was performed in Sørensen buffer solution at 37 ° C . After 0 ∕ 2 ∕ 4 ∕ 8 ∕ 12 ∕ 24 weeks the remaining collapse stability and molecular weight were assessed. Results: All stents could be deployed by balloon inflation to 8 bar at 1 bar ∕ min (PLLA) and 3 bar ∕ min (PLLA/PCL/TEC). Recoil, shortening, and collapse pressure were: 2.4 % ∕ 3.4 % ∕ 0.67 bar (PLLA), and 8.8 % ∕ 2.3 % ∕ 0.23 bar (PLLA/PCL/TEC). A static load of 100 mmHg induced pronounced creep processes in the PLLA/PCL/TEC stent. The PLLA stent remained patent and exhibited no creep propensity. During in vitro degradation an increase in collapse pressure was observed (maxima at 12 w : 1.3 bar (PLLA), 0.7 bar (PLLA/PCL/TEC)). At 24 weeks, molecular weight was decreased by 28% (PLLA), and 52% (PLLA/PCL/TEC). Conclusions: Stents fabricated from pure PLLA exhibited adequate mechanical properties. The slow permissible deployment rate, however, limits their potential application range and demands further development.