Cells resident to precision templated 40-µm pore scaffolds generate small extracellular vesicles that affect CD4+ T cell phenotypes through regulatory TLR4 signaling.

Precision porous templated scaffolds (PTS) are a hydrogel construct of uniformly sized interconnected spherical pores that induce a pro-healing response (reducing the foreign body reaction, FBR) exclusively when the pores are 30-40µm in diameter. Our previous work demonstrated the necessity of Tregs in the maintenance of PTS pore size specific differences in CD4+ T cell phenotype. Work here characterizes the role of Tregs in the responses to implanted 40µm and 100µm PTS using WT and FoxP3+ cell (Treg) depleted mice. Proteomic analyses indicate that integrin signaling, monocytes/macrophages, cytoskeletal remodeling, inflammatory cues, and vesicule endocytosis may participate in Treg activation and the CD4+ T cell equilibrium modulated by PTS resident cell-derived small extracellular vesicles (sEVs). The role of MyD88-dependent and MyD88-independent TLR4 activation in PTS cell-derived sEV-to-T cell signaling is quantified by treating WT, TLR4ko, and MyD88ko splenic T cells with PTS cell-derived sEVs. STAT3 and mTOR are identified as mechanisms for further study for pore-size dependent PTS cell-derived sEV-to-T cell signaling. STATEMENT OF SIGNIFICANCE: Unique cell populations colonizing only within 40µm pore size PTS generate sEVs that resolve inflammation by modifying CD4+ T cell phenotypes through TLR4 signaling.

Lignin-Based Porous Biomaterials for Medical and Pharmaceutical Applications.

Over the past decade, lignin-based porous biomaterials have been found to have strong potential applications in the areas of drug delivery, tissue engineering, wound dressing, pharmaceutical excipients, biosensors, and medical devices. Lignin-based porous biomaterials have the addition of lignin obtained from lignocellulosic biomass. Lignin as an aromatic compound is likely to modify the materials' mechanical properties, thermal properties, antioxidant, antibacterial property, biodegradability, and biocompatibility. The size, shape, and distribution of pores can determine the materials' porous structure, porosity, surface areas, permeability, porosity, water solubility, and adsorption ability. These features could be suitable for medical applications, especially controlled drug delivery systems, wound dressing, and tissue engineering. In this review, we provide an overview of the current status and future potential of lignin-based porous materials for medical and pharmaceutical uses, focusing on material types, key properties, approaches and techniques of modification and fabrication, and promising medical applications.

Morphological and mechanical characterisation of three-dimensional gyroid structures fabricated by electron beam melting for the use as a porous biomaterial.

Additive manufactured porous biomaterials based on triply periodic minimal surfaces (TPMS) are a highly discussed topic in the literature. With their unique properties in terms of open porosity, large surface area and surface curvature, they are considered to have bone mimicking properties and remarkable osteogenic potential. In this study, scaffolds of gyroid unit cells of different sizes consisting of a Ti6Al4V alloy were manufactured additively by electron beam melting (EBM). The scaffolds were analysed by micro-computed tomography (micro-CT) to determine their morphological characteristics and, subsequently, subjected to mechanical tests to investigate their quasi-static compressive properties and fatigue resistance. All scaffolds showed an average open porosity of 71-81%, with an average pore size of 0.64-1.41 mm, depending on the investigated design. The design with the smallest unit cell shows the highest quasi-elastic gradient (QEG) as well as the highest compressive offset stress and compression strength. Furthermore, the fatigue resistance of all unit cell size (UCS) variations showed promising results. In detail, the smallest unit cells achieved fatigue strength at 106 cycles at 45% of their compressive offset stress, which is comparatively good for additively manufactured porous biomaterials. In summary, it is demonstrated that the mechanical properties can be significantly modified by varying the unit cell size, thus enabling the scaffolds to be specifically tailored to avoid stress shielding and ensure implant safety. Together with the morphological properties of the gyroid unit cells, the fabricated scaffolds represent a promising approach for use as a bone substitute material.

Comparison and characterization of enriched mesenchymal stem cells obtained by the repeated filtration of autologous bone marrow through porous biomaterials.

BACKGROUND: When bone marrow is repeatedly filtered through porous material, the mesenchymal stem cells (MSCs) in the bone marrow can adhere to the outer and inner walls of the carrier material to become enriched locally, and this is a promising method for MSC enrichment. In this process, the enrichment efficiency of MSCs involved in the regulation of the cell ecology of postfiltration composites containing other bone marrow components is affected by many factors. This study compared the enrichment efficiency and characterized the phenotypes of enriched MSCs obtained by the filtration of autologous bone marrow through different porous bone substitutes. METHODS: Human bone marrow was filtered through representative porous materials, and different factors affecting MSC enrichment efficiency were evaluated. The soluble proteins and MSC phenotypes in the bone marrow before and after filtration were also compared. RESULTS: The enrichment efficiency of the MSCs found in gelatin sponges was 96.1% ± 3.4%, which was higher than that of MSCs found in allogeneic bone (72.5% ± 7.6%) and porous ß-TCP particles (61.4% ± 5.4%). A filtration frequency of 5-6 and a bone marrow/material volume ratio of 2 achieved the best enrichment efficiency for MSCs. A high-throughput antibody microarray indicated that the soluble proteins were mostly filtered out and remained in the flow through fluid, whereas a small number of proteins were abundantly (> 50%) enriched in the biomaterial. In terms of the phenotypic characteristics of the MSCs, including the cell aspect ratio, osteogenetic fate, specific antigens, gene expression profile, cell cycle stage, and apoptosis rate, no significant changes were found before or after filtration. CONCLUSION: When autologous bone marrow is rapidly filtered through porous bone substitutes, the optimal enrichment efficiency of MSCs can be attained by the rational selection of the type of carrier material, the bone marrow/carrier material volume ratio, and the filtration frequency. The enrichment of bone marrow MSCs occurs during filtration, during which the soluble proteins in the bone marrow are also absorbed to a certain extent. This filtration enrichment technique does not affect the phenotype of the MSCs and thus may provide a safe alternative method for MSC enrichment.

Injectable, porous, biohybrid hydrogels incorporating decellularized tissue components for soft tissue applications.

Biodegradable injectable hydrogels have been extensively studied and evaluated in various medical applications such as for bulking agents, drug delivery reservoirs, temporary barriers, adhesives, and cell delivery matrices. Where injectable hydrogels are intended to facilitate a healing response, it may be desirable to encourage rapid cellular infiltration into the hydrogel volume from the tissue surrounding the injection site. In this study, we developed a platform technique to rapidly form pores in a thermally responsive injectable hydrogel, poly(NIPAAm-co-VP-co-MAPLA) by using mannitol particles as porogens. In a rat hindlimb muscle injection model, hydrogels incorporating porosity had significantly accelerated cellular infiltration. To influence the inflammatory response to the injected hydrogel, enzymatically digested urinary bladder matrix (UBM) was mixed with the solubilized hydrogel. The presence of UBM was associated with greater polarization of the recruited macrophage population to the M2 phenotype, indicating a more constructive foreign body response. The hybrid hydrogel positively affected the wound healing outcomes of defects in rabbit adipose tissue with negligible inflammation and fibrosis, whereas scar formation and chronic inflammation were observed with autotransplantation and in saline injected groups. These results demonstrate the value of combining the effects of promoting cell infiltration and mediating the foreign body response for improved biomaterials options soft tissue defect filling applications. STATEMENT OF SIGNIFICANCE: Our objective was to develop a fabrication process to create porous injectable hydrogels incorporating decellularized tissue digest material. This new hydrogel material was expected to exhibit faster cellular infiltration and a greater extent of pro-M2 macrophage polarization compared to control groups not incorporating each of the functional components. Poly(NIPAAm-co-VP-co-MAPLA) was chosen as the representative thermoresponsive hydrogel, and mannitol particles and digested urinary bladder matrix (UBM) were selected as the porogen and the bioactive decellularized material components respectively. In rat hindlimb intramuscular injection models, this new hydrogel material induced more rapid cellular infiltration and a greater extent of M2 macrophage polarization compared to control groups not incorporating all of the functional components. The hybrid hydrogel positively affected the wound healing outcomes of defects in rabbit adipose tissue with negligible inflammation and fibrosis, whereas scar formation and chronic inflammation were observed with autotransplantation and in saline injected groups. The methodology of this report provides a straightforward and convenient mechanism to promote cell infiltration and mediate foreign body response in injectable hydrogels for soft tissue applications. We believe that the readership of Acta Biomaterialia will find the work of interest both for its specific results and general translatability of the findings.

Isolated and modulated effects of topology and material type on the mechanical properties of additively manufactured porous biomaterials.

In this study, we tried to quantify the isolated and modulated effects of topological design and material type on the mechanical properties of AM porous biomaterials. Towards this aim, we assembled a large dataset comprising the mechanical properties of AM porous biomaterials with different topological designs (i.e. different unit cell types and relative densities) and material types. Porous structures were additively manufactured from Co-Cr using a selective laser melting (SLM) machine and tested under quasi-static compression. The normalized mechanical properties obtained from those structures were compared with mechanical properties available from our previous studies for porous structures made from Ti-6Al-4V and pure titanium as well as with analytical solutions. The normalized values of elastic modulus and yield stress were found to be relatively close to each other as well as in agreement with analytical solutions regardless of material type. However, the material type was found to systematically affect the mechanical properties of AM porous biomaterials in general and the post-elastic/post-yield range (plateau stress and energy absorption capacity) in particular. To put this in perspective, topological design could cause up to 10-fold difference in the mechanical properties of AM porous biomaterials while up to 2-fold difference was observed as a consequence of changing the material type.

Fatigue performance of additively manufactured meta-biomaterials: The effects of topology and material type.

Additive manufacturing (AM) techniques enable fabrication of bone-mimicking meta-biomaterials with unprecedented combinations of topological, mechanical, and mass transport properties. The mechanical performance of AM meta-biomaterials is a direct function of their topological design. It is, however, not clear to what extent the material type is important in determining the fatigue behavior of such biomaterials. We therefore aimed to determine the isolated and modulated effects of topological design and material type on the fatigue response of metallic meta-biomaterials fabricated with selective laser melting. Towards that end, we designed and additively manufactured Co-Cr meta-biomaterials with three types of repeating unit cells and three to four porosities per type of repeating unit cell. The AM meta-biomaterials were then mechanically tested to obtain their normalized S-N curves. The obtained S-N curves of Co-Cr meta-biomaterials were compared to those of meta-biomaterials with same topological designs but made from other materials, i.e. Ti-6Al-4V, tantalum, and pure titanium, available from our previous studies. We found the material type to be far more important than the topological design in determining the normalized fatigue strength of our AM metallic meta-biomaterials. This is the opposite of what we have found for the quasi-static mechanical properties of the same meta-biomaterials. The effects of material type, manufacturing imperfections, and topological design were different in the high and low cycle fatigue regions. That is likely because the cyclic response of meta-biomaterials depends not only on the static and fatigue strengths of the bulk material but also on other factors that may include strut roughness, distribution of the micro-pores created inside the struts during the AM process, and plasticity. STATEMENT OF SIGNIFICANCE: Meta-biomaterials are a special class of metamaterials with unusual or unprecedented combinations of mechanical, physical (e.g. mass transport), and biological properties. Topologically complex and additively manufactured meta-biomaterials have been shown to improve bone regeneration and osseointegration. The mechanical properties of such biomaterials are directly related to their topological design and material type. However, previous studies of such biomaterials have largely neglected the effects of material type, instead focusing on topological design. We show here that neglecting the effects of material type is unjustified. We studied the isolated and combined effects of topological design and material type on the normalized S-N curves of metallic bone-mimicking biomaterials and found them to be more strongly dependent on the material type than topological design.

Porous architected biomaterial for a tibial-knee implant with minimum bone resorption and bone-implant interface micromotion.

This investigation presents the numerical development of a fully porous tibial knee implant that is suggested to alleviate the clinical problems associated with current prostheses that are fully solid. A scheme combining multiscale mechanics and topology optimization is proposed to handle the homogenized analysis and property tailoring of the porous architecture with the aim of reducing the stiffness mismatch between the implant and surrounding bone. The outcome of applying this scheme is a graded lattice microarchitecture that can potentially offer the implant an improved degree of load bearing capacity while reducing concurrently bone resorption and interface micromotion. Asymptotic Homogenization theory is used to characterize the mechanics of its building block, a tetrahedron based unit cell, and the Soderberg fatigue criterion to represent the implant fatigue resistance under multiaxial physiological loadings. The numerical results suggest that the overall amount of bone resorption around the graded porous tibial stem is 26% lower than that around a conventional, commercially available, fully dense titanium implant of identical shape and size. In addition, an improved interface micromotion is observed along the tibial stem, with values at the tip of the stem as low as 17µm during gait cycle and 22µm for deep bend compared to a fully dense implant. This decrease in micromotion compared to that of an identical solid implant made of titanium can reasonably be expected to alleviate post-operative end of stem pain suffered by some patients undergoing surgery at the present time.

Mechanical characterization of structurally porous biomaterials built via additive manufacturing: experiments, predictive models, and design maps for load-bearing bone replacement implants.

Porous biomaterials can be additively manufactured with micro-architecture tailored to satisfy the stringent mechano-biological requirements imposed by bone replacement implants. In a previous investigation, we introduced structurally porous biomaterials, featuring strength five times stronger than commercially available porous materials, and confirmed their bone ingrowth capability in an in vivo canine model. While encouraging, the manufactured biomaterials showed geometric mismatches between their internal porous architecture and that of its as-designed counterpart, as well as discrepancies between predicted and tested mechanical properties, issues not fully elucidated. In this work, we propose a systematic approach integrating computed tomography, mechanical testing, and statistical analysis of geometric imperfections to generate statistical based numerical models of high-strength additively manufactured porous biomaterials. The method is used to develop morphology and mechanical maps that illustrate the role played by pore size, porosity, strut thickness, and topology on the relations governing their elastic modulus and compressive yield strength. Overall, there are mismatches between the mechanical properties of ideal-geometry models and as-manufactured porous biomaterials with average errors of 49% and 41% respectively for compressive elastic modulus and yield strength. The proposed methodology gives more accurate predictions for the compressive stiffness and the compressive strength properties with a reduction of the average error to 11% and 7.6%. The implications of the results and the methodology here introduced are discussed in the relevant biomechanical and clinical context, with insight that highlights promises and limitations of additively manufactured porous biomaterials for load-bearing bone replacement implants. STATEMENT OF SIGNIFICANCE: In this work, we perform mechanical characterization of load-bearing porous biomaterials for bone replacement over their entire design space. Results capture the shift in geometry and mechanical properties between as-designed and as-manufactured biomaterials induced by additive manufacturing. Characterization of this shift is crucial to ensure appropriate manufacturing of bone replacement implants that enable biological fixation through bone ingrowth as well as mechanical property harmonization with the native bone tissue. In addition, we propose a method to include manufacturing imperfections in the numerical models that can reduce the discrepancy between predicted and tested properties. The results give insight into the use of structurally porous biomaterials for the design and additive fabrication of load-bearing implants for bone replacement.

A porous medium-chain-length poly(3-hydroxyalkanoates)/hydroxyapatite composite as scaffold for bone tissue engineering.

Polyhydroxyalkanoates (PHA) are hydrophobic biopolymers with huge potential for biomedical applications due to their biocompatibility, excellent mechanical properties and biodegradability. A porous composite scaffold made of medium-chain-length poly(3-hydroxyalkanoates) (mcl-PHA) and hydroxyapatite (HA) was fabricated using particulate leaching technique and NaCl as a porogen. Different percentages of HA loading was investigated that would support the growth of osteoblast cells. Ultrasonic irradiation was applied to facilitate the dispersion of HA particles into the mcl-PHA matrix. The different P(3HO-co-3HHX)/HA composites were investigated using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDXA). The scaffolds were found to be highly porous with interconnecting pore structures and the HA particles were homogeneously dispersed in the polymer matrix. The scaffolds biocompatibility and osteoconductivity were also assessed following the proliferation and differentiation of osteoblast cells on the scaffolds. From the results, it is clear that scaffolds made from P(3HO-co-3HHX)/HA composites are viable candidate materials for bone tissue engineering applications.

Fully porous 3D printed titanium femoral stem to reduce stress-shielding following total hip arthroplasty.

Current hip replacement femoral implants are made of fully solid materials which all have stiffness considerably higher than that of bone. This mechanical mismatch can cause significant bone resorption secondary to stress shielding, which can lead to serious complications such as peri-prosthetic fracture during or after revision surgery. In this work, a high strength fully porous material with tunable mechanical properties is introduced for use in hip replacement design. The implant macro geometry is based off of a short stem taper-wedge implant compatible with minimally invasive hip replacement surgery. The implant micro-architecture is fine-tuned to locally mimic bone tissue properties which results in minimum bone resorption secondary to stress shielding. We present a systematic approach for the design of a 3D printed fully porous hip implant that encompasses the whole activity spectrum of implant development, from concept generation, multiscale mechanics of porous materials, material architecture tailoring, to additive manufacturing, and performance assessment via in vitro experiments in composite femurs. We show that the fully porous implant with an optimized material micro-structure can reduce the amount of bone loss secondary to stress shielding by 75% compared to a fully solid implant. This result also agrees with those of the in vitro quasi-physiological experimental model and the corresponding finite element model for both the optimized fully porous and fully solid implant. These studies demonstrate the merit and the potential of tuning material architecture to achieve a substantial reduction of bone resorption secondary to stress shielding. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1774-1783, 2017.