The influence of various rehydration protocols on biomechanical properties of different acellular tissue matrices.

OBJECTIVES: This study evaluated the influence of different rehydration media and time periods on biomechanical and structural properties of different acellular collagen matrices (ACMs). MATERIALS AND METHODS: Specimens of three ACMs (mucoderm®, Mucograft®, Dynamatrix®) were rehydrated in saline solution (SS) or human blood for different time periods (5-60 min). ACMs under dry condition served as controls. Biomechanical properties of the ACMs after different rehydration periods were determined by means of tensile testing. ACMs' properties were further characterized using Fourier-transform-infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). RESULTS: At dry conditions, mucoderm® presented the highest tensile strength (TS) and Dynamatrix® showed the maximum elastic modulus (EM; p each ≤0.036). Rehydration in SS and blood resulted in significant TS changes of mucoderm® (p each ≤0.05). Concering EM, mucograft® showed significantly decreased values after rehydration in SS compared to Dynamatrix® and mucoderm® after 10 min (p each ≤0.024). mucoderm® hydrated for 5 min in blood displayed nearly double TS and a significantly increased EM after 60 min (p = 0.043) compared to rehydration in SS. TS and EM values of Dynamatrix® and Mucograft® were not altered following rehydration in blood versus SS (p each ≥0.053). FTIR analysis confirmed the recovery of the graft protein backbone with increased rehydration in all samples. DSC measurements revealed that tissue hydration decreased thermal stability of the investigated ACMs. CONCLUSION: Our findings demonstrated that the rehydration protocol affects the biomechanical properties of ACMs. CLINICAL RELEVANCE: Clinicians should be aware of altered handling and mechanical properties of ACMs following different rehydration protocols.

Synchrotron X-ray microtomography for assessment of bone tissue scaffolds.

X-ray microtomography (microCT) is a popular tool for imaging scaffolds designed for tissue engineering applications. The ability of synchrotron microCT to monitor tissue response and changes in a bioactive glass scaffold ex vivo were assessed. It was possible to observe the morphology of the bone; soft tissue ingrowth and the calcium distribution within the scaffold. A second aim was to use two newly developed compression rigs, one designed for use inside a laboratory based microCT machine for continual monitoring of the pore structure and crack formation and another designed for use in the synchrotron facility. Both rigs allowed imaging of the failure mechanism while obtaining stress-strain data. Failure mechanisms of the bioactive glass scaffolds were found not to follow classical predictions for the failure of brittle foams. Compression strengths were found to be 4.5-6 MPa while maintaining an interconnected pore network suitable for tissue engineering applications.

Atomic Layer Deposition of a Silver Nanolayer on Advanced Titanium Orthopedic Implants Inhibits Bacterial Colonization and Supports Vascularized de Novo Bone Ingrowth.

Joint replacement surgery is associated with significant morbidity and mortality following infection with either methicillin-resistant Staphylococcus aureus (MRSA) or Staphylococcus epidermidis. These organisms have strong biofilm-forming capability in deep wounds and on prosthetic surfaces, with 103 -104 microbes resulting in clinically significant infections. To inhibit biofilm formation, we developed 3D titanium structures using selective laser melting and then coated them with a silver nanolayer using atomic layer deposition. On bare titanium scaffolds, S. epidermidis growth was slow but on silver-coated implants there were significant further reductions in both bacterial recovery (p < 0.0001) and biofilm formation (p < 0.001). MRSA growth was similarly slow on bare titanium scaffolds and not further affected by silver coating. Ultrastructural examination and viability assays using either human bone or endothelial cells, demonstrated strong adherence and growth on titanium-only or silver-coated implants. Histological, X-ray computed microtomographic, and ultrastructural analyses revealed that silver-coated titanium scaffolds implanted into 2.5 mm defects in rat tibia promoted robust vascularization and conspicuous bone ingrowth. We conclude that nanolayer silver of titanium implants significantly reduces pathogenic biofilm formation in vitro, facilitates vascularization and osseointegration in vivo making this a promising technique for clinical orthopedic applications.

Submicron scale-structured hydrophilic titanium surfaces promote early osteogenic gene response for cell adhesion and cell differentiation.

BACKGROUND AND PURPOSE: Titanium (Ti) surface roughness and surface hydrophilicity are key factors to regulate osteogenic cell responses during dental implant healing. In detail, specific integrin-mediated interactions with the extracellular environment trigger relevant osteogenic cell responses like differentiation and matrix synthesis via transcriptions factors. Aim of this study was to monitor surface-dependent osteogenic cell adhesion dynamics, proliferation, and specific osteogenic cell differentiation over a period of 7 days. MATERIALS AND METHODS: Ti disks were manufactured to present smooth pretreatment (PT) surfaces and rough sandblasted/acid-etched (SLA) surfaces. Further processing to isolate the uncontaminated TiO(2) surface from contact with atmosphere provided a highly hydrophilic surface without alteration of the surface topography (modSLA). Tissue culture polystyrene (TCPS) served as control. Human osteogenic cells were cultivated on the respective substrates. After 24 hours, 48 hours, 72 hours, and 7 days, cell morphology on the Ti substrates was visualized by scanning transmission electron microscopy. As a marker of cellular proliferation, cell count was assessed. For the analysis of cell adhesion and differentiation, specific gene expression levels of the integrin subunits ß1 and αv, runx-2, collagen type Iα (COL), alkaline phosphatase (AP), and osteocalcin (OC) were obtained by real-time RT-PCR for the respective time points. Data were normalized to internal controls. RESULTS: TCPS and PT surfaces preserved a rather immature, dividing osteogenic phenotype (high proliferation rates, low integrin levels, and low specific osteogenic cell differentiation). SLA and especially modSLA surfaces promoted both cell adhesion as well as the maturation of osteogenic precursors into post-mitotic osteoblasts. In detail, during the first 48 hours, modSLA resulted in lowest cell proliferation rates but exhibited highest levels of the investigated integrins, runx-2, COL, AP, and OC. CONCLUSION: Our results revealed a strong synergistic effect between submicron-scale roughness and surface hydrophilicity on early osteogenic cell adhesion and maturation.

Effects of the novel polymer gel LeGoo on human internal thoracic arteries.

PURPOSE: Established hemostatic devices can injure vessel wall integrity. LeGoo (Pluromed, Woburn, MA), a novel poloxamer gel with reverse thermosensitive properties, is a new device for temporary occlusion of blood vessels. The present study investigated the effects of LeGoo on vascular function and morphology. DESCRIPTION: The distal end of the human internal thoracic artery was used to assess vascular function of LeGoo-applied segments in organ bath experiments and by scanning electron microscopy. EVALUATION: After LeGoo application, both maximal contractile responses to noradrenaline and endothelium-dependent relaxant responses to acetylcholine were significantly reduced. Scanning electron microscopy showed areas of injured endothelium with exposure of subendothelial structures being in line with the functional changes. CONCLUSIONS: Data suggested that application of LeGoo induced significant endothelial injury and deterioration of the smooth muscle in human internal thoracic arteries.

Effect of intraluminal pillars on particle motion in bifurcated microchannels.

A central feature of intussusceptive angiogenesis is the development of an intravascular pillar that bridges the opposing sides of the microvessel lumen. In this report, we created polydimethyl siloxane (PDMS) microchannels with geometric proportions based on corrosion casts of the colon microcirculation. The structure of the PDMS microchannels was a bifurcated channel with an intraluminal pillar in the geometric center of the bifurcation. The effect of the intraluminal pillar on particle flow paths was investigated using an in vitro perfusion system. The microchannels were perfused with fluorescent particles, and the particle movements were recorded using fluorescence videomicroscopy. We found that the presence of an intravascular pillar significantly decreased particle velocity in the bifurcation system (p < 0.05). In addition, the pillar altered the trajectory of particles in the center line of the flow stream. The particle trajectory resulted in prolonged pillar contact as well as increased residence time within the bifurcation system (p < 0.001). Our results suggest that the intravascular pillar not only provides a mechanism of increasing resistance to blood flow but may also participate in spatial redistribution of cells within the flow stream.