3D printed submicron patterns orchestrate the response of macrophages

A submicron forest-like silicon surface promotes bone regeneration by regulating macrophage polarization

Introduction: Silicon is a major trace element in humans and a prospective supporting biomaterial to bone regeneration. Submicron silicon pillars, as a representative surface topography of silicon-based biomaterials, can regulate macrophage and osteoblastic cell responses. However, the design of submicron silicon pillars for promoting bone regeneration still needs to be optimized. In this study, we proposed a submicron forest-like (Fore) silicon surface (Fore) based on photoetching. The smooth (Smo) silicon surface and photoetched regular (Regu) silicon pillar surface were used for comparison in the bone regeneration evaluation. Methods: Surface parameters were investigated using a field emission scanning electron microscope, atomic force microscope, and contact angle instrument. The regulatory effect of macrophage polarization and succedent osteogenesis was studied using Raw264.7, MC3T3-E1, and rBMSCs. Finally, a mouse calvarial defect model was used for evaluating the promoting effect of bone regeneration on the three surfaces. Results: The results showed that the Fore surface can increase the expression of M2-polarized markers (CD163 and CD206) and decrease the expression of inflammatory cytokines, including interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α). Fore surface can promote the osteogenesis in MC3T3-E1 cells and osteoblastic differentiation of rBMSCs. Furthermore, the volume fraction of new bone and the thickness of trabeculae on the Fore surface were significantly increased, and the expression of RANKL was downregulated. In summary, the upregulation of macrophage M2 polarization on the Fore surface contributed to enhanced osteogenesis in vitro and accelerated bone regeneration in vivo. Discussion: This study strengthens our understanding of the topographic design for developing future silicon-based biomaterials.

4D Printing for Biomedical Applications

4D (bio-)printing endows 3D printed (bio-)materials with multiple functionalities and dynamic properties. 4D printed materials have been recently used in biomedical engineering for the design and fabrication of biomedical devices, such as stents, occluders, microneedles, smart 3D-cell engineered microenvironments, drug delivery systems, wound closures, and implantable medical devices. However, the success of 4D printing relies on the rational design of 4D printed objects, the selection of smart materials, and the availability of appropriate types of external (multi-)stimuli. Here, this work first highlights the different types of smart materials, external stimuli, and design strategies used in 4D (bio-)printing. Then, it presents a critical review of the biomedical applications of 4D printing and discusses the future directions of biomedical research in this exciting area, including in vivo tissue regeneration studies, the implementation of multiple materials with reversible shape memory behaviors, the creation of fast shape-transformation responses, the ability to operate at the microscale, untethered activation and control, and the application of (machine learning-based) modeling approaches to predict the structure-property and design-shape transformation relationships of 4D (bio)printed constructs.

Enhancing silk fibroin structures and applications through angle-dependent Ar+ plasma treatment

This study tackles limitations of Silk Fibroin (SF), including availability of sites for modification. This is achieved by Direct Plasma Nanosynthesis (DPNS), an Ar+ bombardment method, to generate and modify nanostructures and nanoscale properties on the SF surface. SF samples were treated with DPNS at incidence angles of 45o and 60o, with specific ion dose and energy parameters (1 × 1018 ions/cm2 and 500 eV, respectively) maintained throughout the process. Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) primarily underscored transformations in SF's nitrogenous components. Specifically, treatment produced a boost in C-NH2, particularly pronounced in the 45o-treated samples, suggesting changes were more superficial than alterations to the secondary structure. The DPNS treatment gave rise to periodic nanocone structures on the SF surface, with a scale increase correlated to a higher angle of incidence. This resulted in a decrease in surface stiffness and significant changes in the motility of J774 macrophages interacting with the transformed SF. Furthermore, the SF samples treated at a 60o incidence showcased a confinement effect, moderating the macrophages' motility, morphology, and inflammatory response. The DPNS-induced alterations not only mitigate SF's limitations but also affect cellular behavior, expanding potential for SF in biomaterials.

Osteoimmune-modulating and BMP-2-eluting anodised 3D printed titanium for accelerated bone regeneration

3D printing of titanium (Ti) metal has potential to transform the field of personalised orthopaedics and dental implants. However, the impacts of controlled surface topographical features of 3D printed Ti implants on their interactions with the cellular microenvironment and incorporation of biological growth factors, which are critical in guiding the integration of implants with bone, are not well studied. In the present study, we explore the role of surface topological features of 3D printed Ti implants using an anodised titania nanotube (TiNT) surface layer in guiding their immune cell interaction and ability to deliver bioactive form of growth factors. TiNT layers with precisely controlled pore diameter (between 21and 130 nm) were anodically grown on 3D printed Ti surfaces to impart a nano-micro rough topology. Immune biomarker profiles at gene and protein levels show that anodised 3D Ti surfaces with smaller pores resulted in classical activation of macrophages (M1-like), while larger pores (i.e., >100 nm) promoted alternate activation of macrophages (M2-like). The in vitro bone mineralisation studies using the conditioned media from the immunomodulatory studies elucidate a clear impact of pore diameter on bone mineralisation. The tubular structure of TiNTs was utilised as a container to incorporate recombinant human bone morphogenetic protein-2 (BMP-2) in the presence of various sugar and polymeric cryoprotectants. Sucrose offered the most sustainable release of preserved BMP-2 from TiNTs. Downstream effects of released BMP-2 on macrophages as well as bone mineralisation were assessed showing bioactivity retention of the released rhBMP-2. Overall, the TiNT surface topography in combination with controlled, sustained, and local release of bioactive growth factors can potentially enhance the osseointegration outcomes of custom 3D printed Ti implants in the clinic.

Effect of Anisotropic Structural Depth on Orientation and Differentiation Behavior of Skeletal Muscle Cells

Extensive research has been conducted to examine how substrate topological factors are involved in modulating the cell behavior. Among numerous topological factors, the vital influence of the touchable depth of substrates on cell behaviors has already been extensively characterized, but the response of cells to the topological structure at untouchable depth is still elusive. Herein, the influences of substrate depth on myoblast behaviors are systematically investigated using substrates with depths ranging from touchable depth (microgrooved) to untouchable depth (microbridges). The results show that an increase in microgroove depth is accompanied by an inhibited cell spreading, an enhanced elongation, and a more obvious orientation along microgrooves. Interestingly, myoblasts located on microbridges show a more pronounced elongation with increasing culture time but a position-dependent orientation. Myoblasts on the center and parallel boundary of microbridges orient along the bridges, while myoblasts on the vertical boundary align perpendicular to the microbridges. Moreover, the differentiation results of the myoblasts indicate that the differentiated myotubes can maintain this position-dependent orientation. The simulation of the stress field in cell monolayers suggests that the position-dependent orientation is caused by the comprehensive response of myoblasts to the substrate discontinuity and substrate depth. These findings provide valuable insights into the mechanism of cell depth sensing and could inform the design of tissue engineering scaffolds for skeletal muscle and biohybrid actuation.

High-Precision 3D Printing of Microporous Cochlear Implants for Personalized Local Drug Delivery

Hearing loss is a highly prevalent multifactorial disorder affecting 20% of the global population. Current treatments using the systemic administration of drugs are therapeutically ineffective due to the anatomy of the cochlea and the existing blood-labyrinth barrier. Local drug delivery systems can ensure therapeutic drug concentrations locally while preventing adverse effects caused by high dosages of systemically administered drugs. Here, we aimed to design, fabricate, and characterize a local drug delivery system for the human cochlea. The design was relevant to the size of the human ear, included two different shapes, and incorporated two different microporous structures acting as reservoirs for drug loading and release. The four cochlear implant designs were printed using the two-photon polymerization (2PP) technique and the IP-Q photoresist. The optimized 2PP process enabled the fabrication of the cochlear implants with great reproducibility and shape fidelity. Rectangular and cylindrical implants featuring cylindrical and tapered tips, respectively, were successfully printed. Their outer dimensions were 0.6 × 0.6 × 2.4 mm3 (L × W × H). They incorporated internal porous networks that were printed with high accuracy, yielding pore sizes of 17.88 ± 0.95 μm and 58.15 ± 1.62 μm for the designed values of 20 μm and 60 μm, respectively. The average surface roughness was 1.67 ± 0.24 μm, and the water contact angle was 72.3 ± 3.0°. A high degree of polymerization (~90%) of the IP-Q was identified after printing, and the printed material was cytocompatible with murine macrophages. The cochlear implants designed and 3D printed in this study, featuring relevant sizes for the human ear and tunable internal microporosity, represent a novel approach for personalized treatment of hearing loss through local drug delivery.

Immune microenvironment: novel perspectives on bone regeneration disorder in osteoradionecrosis of the jaws

Osteoradionecrosis of the jaws (ORNJ) is a severe complication that occurs after radiotherapy of head and neck malignancies. Clinically, conservative treatments and surgeries for ORNJ exhibited certain therapeutic effects, whereas the regenerative disorder of the post-radiation jaw remains a pending problem to be solved. In recent years, the recognition of the role of the immune microenvironment has led to a shift from an osteoblasts (OBs) or bone marrow mesenchymal stromal cells (BMSCs)-centered view of bone regeneration to the concept of a complicated microecosystem that supports bone regeneration. Current advances in osteoimmunology have uncovered novel targets within the immune microenvironment to help improve various regeneration therapies, notably therapies potentiating the interaction between BMSCs and immune cells. However, these researches lack a thorough understanding of the immune microenvironment and the interaction network of immune cells in the course of bone regeneration, especially for the post-operative defect of ORNJ. This review summarized the composition of the immune microenvironment during bone regeneration, how the immune microenvironment interacts with the skeletal system, and discussed existing and potential strategies aimed at targeting cellular and molecular immune microenvironment components.

Biomaterial scaffolds regulate macrophage activity to accelerate bone regeneration

Bones are important for maintaining motor function and providing support for internal organs. Bone diseases can impose a heavy burden on individuals and society. Although bone has a certain ability to repair itself, it is often difficult to repair itself alone when faced with critical-sized defects, such as severe trauma, surgery, or tumors. There is still a heavy reliance on metal implants and autologous or allogeneic bone grafts for bone defects that are difficult to self-heal. However, these grafts still have problems that are difficult to circumvent, such as metal implants that may require secondary surgical removal, lack of bone graft donors, and immune rejection. The rapid advance in tissue engineering and a better comprehension of the physiological mechanisms of bone regeneration have led to a new focus on promoting endogenous bone self-regeneration through the use of biomaterials as the medium. Although bone regeneration involves a variety of cells and signaling factors, and these complex signaling pathways and mechanisms of interaction have not been fully understood, macrophages undoubtedly play an essential role in bone regeneration. This review summarizes the design strategies that need to be considered for biomaterials to regulate macrophage function in bone regeneration. Subsequently, this review provides an overview of therapeutic strategies for biomaterials to intervene in all stages of bone regeneration by regulating macrophages.

Two-photon polymerization for 3D biomedical scaffolds: Overview and updates

The needs for high-resolution, well-defined and complex 3D microstructures in diverse fields call for the rapid development of novel 3D microfabrication techniques. Among those, two-photon polymerization (TPP) attracted extensive attention owing to its unique and useful characteristics. As an approach to implementing additive manufacturing, TPP has truly 3D writing ability to fabricate artificially designed constructs with arbitrary geometry. The spatial resolution of the manufactured structures via TPP can exceed the diffraction limit. The 3D structures fabricated by TPP could properly mimic the microenvironment of natural extracellular matrix, providing powerful tools for the study of cell behavior. TPP can meet the requirements of manufacturing technique for 3D scaffolds (engineering cell culture matrices) used in cytobiology, tissue engineering and regenerative medicine. In this review, we demonstrated the development in 3D microfabrication techniques and we presented an overview of the applications of TPP as an advanced manufacturing technique in complex 3D biomedical scaffolds fabrication. Given this multidisciplinary field, we discussed the perspectives of physics, materials science, chemistry, biomedicine and mechanical engineering. Additionally, we dived into the principles of tow-photon absorption (TPA) and TPP, requirements of 3D biomedical scaffolders, developed-to-date materials and chemical approaches used by TPP and manufacturing strategies based on mechanical engineering. In the end, we draw out the limitations of TPP on 3D manufacturing for now along with some prospects of its future outlook towards the fabrication of 3D biomedical scaffolds.

Osteoimmunomodulatory potential of 3D printed submicron patterns assessed in a direct co-culture model

Modulation of the immune response following the implantation of biomaterials can have beneficial effects on bone regeneration. This involves complex interactions between the inflammatory and osteogenic cells. Therefore, the study of cell-cell interactions using direct co-culture models integrated with biomaterials is of great interest. This research aimed to study the viability, morphology, and osteogenic activity of preosteoblasts (OBs) co-cultured with pro-inflammatory macrophages (M1s) on the 3D printed (non)patterned surfaces. OBs and M1s remained alive and proliferated actively for 14 days in the mixture of Dulbecco's Modified Eagle's Medium (DMEM) and alpha Minimum Essential Medium (α-MEM) (1:1), regardless of the cell ratio in the co-cultures. The spatial organization of the two types of cells changed with the time of culture from an initially uniform cell distribution to the formation of a thick layer of OBs covered by clusters of M1s. On day 7, the expression of PGE2 and TNF-α were upregulated in the co-culture relative to the mono-culture of OBs and M1s. The inflammation decreased differentiation and matrix mineralization of OBs after 28 days of culture. Interestingly, the incorporation of 3D printed submicron pillars into the direct co-culture model enhanced the differentiation of preosteoblasts, as shown by relatively higher RUNX2 expression, thereby revealing the osteoimmunomodulatory potential of such surface patterns.

Two-Photon Polymerization of 2.5D and 3D Microstructures Fostering a Ramified Resting Phenotype in Primary Microglia

Microglia are the resident macrophages of the central nervous system and contribute to maintaining brain’s homeostasis. Current 2D “petri-dish” in vitro cell culturing platforms employed for microglia, are unrepresentative of the softness or topography of native brain tissue. This often contributes to changes in microglial morphology, exhibiting an amoeboid phenotype that considerably differs from the homeostatic ramified phenotype in healthy brain tissue. To overcome this problem, multi-scale engineered polymeric microenvironments are developed and tested for the first time with primary microglia derived from adult rhesus macaques. In particular, biomimetic 2.5D micro- and nano-pillar arrays (diameters = 0.29–1.06 µm), featuring low effective shear moduli (0.25–14.63 MPa), and 3D micro-cages (volume = 24 × 24 × 24 to 49 × 49 × 49 μm³) with and without micro- and nano-pillar decorations (pillar diameters = 0.24–1 µm) were fabricated using two-photon polymerization (2PP). Compared to microglia cultured on flat substrates, cells growing on the pillar arrays exhibit an increased expression of the ramified phenotype and a higher number of primary branches per ramified cell. The interaction between the cells and the micro-pillar-decorated cages enables a more homogenous 3D cell colonization compared to the undecorated ones. The results pave the way for the development of improved primary microglia in vitro models to study these cells in both healthy and diseased conditions.

Physico-Chemical Characteristics and Posterolateral Fusion Performance of Biphasic Calcium Phosphate with Submicron Needle-Shaped Surface Topography Combined with a Novel Polymer Binder

A biphasic calcium phosphate with submicron needle-shaped surface topography combined with a novel polyethylene glycol/polylactic acid triblock copolymer binder (BCP-EP) was investigated in this study. This study aims to evaluate the composition, degradation mechanism and bioactivity of BCP-EP in vitro, and its in vivo performance as an autograft bone graft (ABG) extender in a rabbit Posterolateral Fusion (PLF) model. The characterization of BCP-EP and its in vitro degradation products showed that the binder hydrolyses rapidly into lactic acid, lactide oligomers and unaltered PEG (polyethylene glycol) without altering the BCP granules and their characteristic submicron needle-shaped surface topography. The bioactivity of BCP-EP after immersion in SBF revealed a progressive surface mineralization. In vivo, BCP-EP was assessed in a rabbit PLF model by radiography, manual palpation, histology and histomorphometry up to 12 weeks post-implantation. Twenty skeletally mature New Zealand (NZ) White Rabbits underwent single-level intertransverse process PLF surgery at L4/5 using (1) autologous bone graft (ABG) alone or (2) by mixing in a 1:1 ratio with BCP-EP (BCP-EP/ABG). After 3 days of implantation, histology showed the BCP granules were in direct contact with tissues and cells. After 12 weeks, material resorption and mature bone formation were observed, which resulted in solid fusion between the two transverse processes, following all assessment methods. BCP-EP/ABG showed comparable fusion rates with ABG at 12 weeks, and no graft migration or adverse reaction were noted at the implantation site nor in distant organs.