Bahattin Koc

• Ph.D.
• Professor at Sabancı University

Additive manufacturing (AM), characterized by layer-by-layer material addition using computer-aided design, presents an approach to manufacturing complex parts. However, AM processes naturally bring some difficulties such as thermally induced residual stresses, particularly in laser powder bed fusion (L-PBF) processes. This research paper proposes...

In this study, a thorough examination of the chemical, thermal, and mechanical characteristics, as well as shape memory behavior at low temperatures, of blends consisting of polylactic acid (PLA) and polyurethane (TPU) is conducted. The research involves the preparation of PLA/TPU mixtures with varying concentrations of TPU using a high-speed therm...

The recent innovation in additive manufacturing (AM) of continuous fiber-reinforced composites (CFRCs) provided great potential for the design and production of high-performance complex composite structures at low cost. However, existing studies mainly focused on the manufacturing process and mechanical performances of the three-dimensional (3D) pr...

Topology optimization (TO) is a practical method to generate light-weight engineering structures for various manufacturing industries. Therefore, integrating it into commercial software used by engineers plays an important role in its widespread use. In this study, we develop a robust backend equipped with in-house peridynamics (PD) based topology...

Additive manufacturing (AM) has revolutionized the design and manufacturing of patient-specific, three-dimensional (3D), complex porous structures known as scaffolds for tissue engineering applications. The use of advanced image acquisition techniques, image processing, and computer-aided design methods has enabled the precise design and additive m...

Additive manufacturing can produce complex parts with poor surface quality, requiring post-processing machining. The combination of additive and machining processes has been identified as a potential solution for achieving sustainable and cleaner production. This approach can enable the use of eco-friendly materials such as recycled or biodegradabl...

Cryogel-based scaffolds have attracted great attention in tissue engineering due to their interconnected macroporous structures. However, three-dimensional (3D) printing of cryogels with a high degree of precision and complexity is a challenge, since the synthesis of cryogels occurs under cryogenic conditions. In this study, we demonstrated the fab...

Recent advancements in tissue engineering have demonstrated a great potential for the fabrication of three-dimensional tissue structures such as cartilage and bone. However, achieving structural integrity between different tissues and fabricating tissue interfaces are still great challenges. In this study, an in situ crosslinked hybrid, multi-mater...

Treating critical-size bone defects with autografts, allografts, or standardized implants is challenging since the healing of the defect area necessitates patient-specific grafts with mechanically and physiologically relevant structures. Three-dimensional (3D) printing using computer-aided design (CAD) is a promising approach for bone tissue engine...

Tissue interfaces include complex gradient structures transitioning of biochemical and mechanical properties in micro-scale. This characteristic allows the communication and synchronistic functioning of two adjacent but distinct tissues. It is particularly challenging to restore the function of these complex structures by transplantation of scaffol...

Topology optimization (TO) is a practical tool to generate light-weighted engineering structures for various manufacturing industries. However, manufacturing constraints and surface smoothing are still considerable challenges for TO algorithms. Existing TO frameworks utilize mechanical analysis approaches that discretize the whole domain with eleme...

This research investigates the accelerated hydrolytic degradation process of both anatomically designed bone scaffolds with a pore size gradient and a rectangular shape (biomimetically designed scaffolds or bone bricks). The effect of material composition is investigated considering poly-ε-caprolactone (PCL) as the main scaffold material, reinforce...

Additive manufacturing (AM) is an effective approach to fabricating intricate shapes obtained from topology optimization (TO). However, it may cause undesired manufacturing-induced defects/cracks due to high thermal residual stresses. This study proposes a PeriDynamics-enabled three-dimensional Topology Optimization method (PD-TO) for designing str...

Ageing population and new diseases are requiring the development of novel therapeutical strategies. 3D bioprinting an novel application domain of additive manufacturing emerged as a potential transformative strategy for tissue engineering and regenerative medicine. This paper introduces the concept of 3D bioprinting, discussing in detail key requir...

Bone defect treatment is still a challenge in clinics, and synthetic bone scaffolds with adequate mechanical and biological properties are highly needed. Adequate waste and nutrient exchange of the implanted scaffold with the surrounded tissue is a major concern. Moreover, the risk of mechanical instability in the defect area during regular activit...

Mimic the Osteochondral Interface with Mesenchymal Stem cell Differentiation Using a 3D Bioprinter

Additive manufacturing (AM) is an effective approach to fabricate intricate shapes obtained from topology optimization (TO). However, it may cause to undesired manufacturing-induced defects/cracks due to high thermal residual stresses. This study proposes a PeriDynamics-enabled three-dimensional Topology Optimization method (PD-TO) for designing st...

The optical and electronic properties of molybdenum (Mo) doped rutile TiO2 prepared by the mechanochemical method were studied both experimentally and using density functional theory (DFT). The synthesized nanoparticles were characterized by XRD, TEM, EDS-MAP, and XPS. The XRD results showed the successful incorporation of Mo in the rutile crystal...

Large bone loss injuries require high-performance scaffolds with an architecture and material composition resembling native bone. However, most bone scaffold studies focus on three-dimensional (3D) structures with simple rectangular or circular geometries and uniform pores, not able to recapitulate the geometric characteristics of the native tissue...

Emerging biomanufacturing technologies have revolutionized the field of tissue engineering by offering unprecedented possibilities. Over the past few years, new opportunities arose by combining traditional and novel fabrication techniques, shaping the hybrid designs in biofabrication. One of the potential application fields is skin tissue engineeri...

Recent studies on three-dimensional (3D) bioprinting of cell-laden gelatin methacryloyl (GelMA) hydrogels have provided promising outcomes for tissue engineering applications. However, the reliance on the use of photo-induced gelation processes for the bioprinting of GelMA and the lack of an alternative crosslinking process remain major challenges...

Although additive manufacturing technologies offer manufacturing highly complex parts, the manufactured parts generally have poor surface quality. Owing to low machinability of hard-to-cut additively manufactured parts, a synergistic approach involving advantages of additive manufacturing and machining processes is needed. This study investigates h...

The design of scaffolds with optimal biomechanical properties for load-bearing applications is an important topic of research. Most studies have addressed this problem by focusing on the material composition and not on the coupled effect between the material composition and the scaffold architecture. Polymer–bioglass scaffolds have been investigate...

In this study, a novel alloy of modified Inconel 718 which is produced by laser powder bed fusion is studied before and after in-situ Kr irradiation up to 3 dpa at 200 and 450 °C. Before irradiation, the microstructure consists of dislocation cells having a misorientation angle less than 5° and with an average size of ~500 nm. There are also second...

Most structures are preferred to be light-weighted when they are used in industrial applications such as automotive, aerospace, and naval structures. Classical continuum mechanics (CCM) formulations are commonly adopted to solve the topology optimization problems. However, CCM brings about some restrictions to the modeling, analysis, and solution o...

Processing and composition can significantly affect the mechanobiology, biodegradability, and cellular behavior of polymer-based bone scaffolds to replace damaged bone tissue. In this research, hydroxyapatite (HA), zinc-doped HA (ZnHA), and ZnHA-graphene (ZnHA-rGO) nanoparticles are composed in a polycaprolactone (PCL) matrix. After compositing PCL...

In this study, the acidity of urazole (pKa 5–6) was exploited to fabricate a hydrogel in two simple and scalable steps. Commercially available poly(hexamethylene)diisocyanate was used as a precursor to synthesize an urazole containing gel. The formation of urazole was confirmed by FT-IR and 1H-NMR spectroscopy. The hydrogel was characterized by mic...

In this study, highly ionazable protons (pKa 5-6) of urazole were exploited to obtain an anionic hydrogel in two simple and scalable steps. Commercially available multiisocyanate, poly(hexamethylene)diisocyanate, was used to prepare urazole containing gel. Urazole formation was confirmed by FT-IR and 1H-NMR spectroscopy. The hydrogel were character...

In this study, highly ionazable protons (pKa 5-6) of urazole were exploited to obtain an anionic hydrogel in two simple and scalable steps. Commercially available multiisocyanate, poly(hexamethylene)diisocyanate, was used to prepare urazole containing gel. Urazole formation was confirmed by FT-IR and 1H-NMR spectroscopy. The hydrogel were character...

Bacteria are one of the significant causes of infection in the body after scaffold implantation. Effective use of nanotechnology to overcome this problem is an exciting and practical solution. Nanoparticles can cause bacterial degradation by the electrostatic interaction with receptors and cell walls. Simultaneously, the incorporation of antibacter...

Three-dimensional (3D) bioprinting is an additive manufacturing process in which the combination of biomaterials and living cells, referred to a bioink, are deposited layer-by-layer to form biologically active 3D tissue constructs. Recent advancements in the field show that the success of this technology highly depends on the development of novel b...

Multimaterial bioprinting is a promising technology integrating multimaterial setups into bioprinting platforms for the fabrication of multicellular, heterogeneous and functional tissue constructs. By simultaneously or sequentially dispensing different categories of materials including cell-laden hydrogels or extracellular matrix components, sacrif...

The advent of bioprinting technology into the tissue engineering field has permitted the attainment of complex-shaped tissue constructs with unprecedented degree of precision and reproducibility, promising for the highly demanded tissue substitutes including vascular grafts. However, most of the bioprinted vascular tissue substitutes still lack mul...

Melanoma is a serious malignant skin tumor. Effectively eliminating melanoma and healing after-surgical wounds are always challenges in clinical studies. To address these problems, we propose manganese-doped calcium silicate nanowire-incorporated alginate hydrogels (named MCSA hydrogels) for in situ photothermal ablation of melanoma followed by the...

Large bone defects, usually associated to victims of natural disasters, wars and severe accidents, represent a major clinical problem. The search for an effective and efficient treatment is a key area of research. Our group is exploring a novel and fully automatic approach to produce synthetic grafts anatomically designed to fit on the defect site...

The Journal of Additive Manufacturing Technologies is the peer-reviewed journal that reports research work on all aspects of additive manufacturing including additive manufacturing processes, design for additive manufacturing, modelling and simulation of additive manufacturing processes, post-processing in additive manufacturing, and applications o...

There is a significant unmet clinical need to prevent amputations due to large bone loss injuries. We are addressing this problem by developing a novel, cost-effective osseointegrated prosthetic solution based on the use of modular pieces, bone bricks, made with biocompatible and biodegradable materials that fit together in a Lego-like way to form...

The field of bone tissue engineering, which is rapidly evolving, aims at the regeneration of the bone structure and its functions. In regenerative medicine, the use of 3D porous structures aims to mimic the bone structure and to promote cell attachment and tissue regeneration. Between the materials used for bone tissue engineering, bioactive glasse...

Eklemeli imalat yöntemi, geleneksel üretim yöntemlerine karşı sağladığı avantajlar ile dünyada tüm sektörlerde geleceğin imalat yöntemi olarak büyük ilgi görmektedir. Eklemeli imalat teknolojilerinin bu kadar ilgi görmesinde karmaşık geometrili parçaların hızlı bir şekilde üretimine olanak sağlaması ve yekpare üretim ile montajlı parça sayısını...

This paper deals with the development of a realtime structural health monitoring system for airframe structures to localize and estimate the magnitude of the loads causing deflections to the critical components, such as wings. To this end, a framework that is based on artificial neural networks is developed where features that are extracted from a...

Scaffold-based tissue engineering approaches have been commonly used for skin regeneration or wound healings caused by diseases or trauma. For an ideal complete healing process, scaffold structures need to meet the criteria of biocompatibility, biodegradability, and antimicrobial properties, as well as to provide geometrical necessities for the reg...

Three-dimensional bioprinting of cell-laden hydrogels in a sacrificial support-bath has recently emerged as a potential solution for fabricating complex biological structures. Physical properties of the support-bath strongly influence the bioprinting process and the outcome of the fabricated constructs. In this study, we reported the application of...

This paper investigates the use of polymer-ceramic composite scaffolds for bone regeneration. Different ratios between Poly-εcaprolactone (PCL) and Hydroxyapatite (HA) were considered. Scaffolds were produced using two different lay-down patterns (0/90° and 0/45°), and pore sizes (350 μm, 500 μm and 700 μm). Compressive and cell proliferation tests...

This study investigates the use of low cost, customizable, biodegradable, polymer-ceramic composite porous structures (bone bricks) for large bone tissue regeneration. Different ceramic materials (hydroxyapatite (HA), β-tri-calcium phosphate (TCP) and Bioglass (45S5) were mixed with poly-ε-caprolactone (PCL). Bone bricks with different material com...

The capabilities of additive manufacturing for fabrication of complex and thin-walled ceramic-based objects are restricted by the availability of ceramics inks. Formulations of current ink systems strictly depend on using high content of organic additives (5–30 wt. %). The high amounts of additives affect uniformity and dimensional accuracy of the...

In recent years, there is a growing interest in additive manufacturing (AM) technologies for aerospace industries because it offers direct digital manufacturing of highly complex fully functional critical components. Among the all AM techniques, electron beam melting (EBM), a powder bed fusion process, is one of the most promising methods because o...

Heat distribution in a thin wall cylindrical component of Ti-6Al-4V caused by continuous and 5 step circular movements of electron beam melting (EBM) as an additive manufacturing (AM) process are numerically studied. Finite volume method (FVM) was employed in order to solve governing equations of this process. Effect of speed and power of EB on tem...

Melt electrospinning writing has been emerged as a promising technique in the field of tissue engineering, with the capability of fabricating controllable and highly ordered complex three-dimensional geometries from a wide range of polymers. This three-dimensional (3D) printing method can be used to fabricate scaffolds biomimicking extracellular ma...

The mesostructure of additively manufactured nanocomposite parts can be tailored by the manipulation of process parameters to improve the properties of the final part. The effects of contributing process parameters and their interactions must be identified to be able to tune the properties of additively manufactured (3D-printed) nanocomposites base...

There is a significant unmet clinical need for modular and customized porous biodegradable constructs (scaffolds) for non-union large bone loss injuries. This paper proposes modelling and biomanufacturing of modular and customizable porous constructs for patient-specific critical bone defects. A computational geometry-based algorithm was developed...

Three-dimensional (3D) bioprinting enables the controlled fabrication of complex constructs for tissue engineering applications and has been actively explored in recent years. However, its progress has been limited by the existing difficulties in the development of bioinks with suitable biocompatibility and mechanical properties, and at the same ti...

This paper reports the synthesis of nanocomposite agarose hydrogels with improved bioactivity with the incorporation of anisotropic 2D nanosilicates (Laponite) to promote cell binding, growth and proliferation. Rheological measurements showed that the incorporation of nanosilicates slightly increased the gelation temperature (Tgel). The use of high...

Using decellularized extracellular matrix (dECM) hydrogels as bioinks has been an important step forward for bioprinting of functional tissue constructs, considering their rich microenvironment and their high degree of biomimicry. However, directly using dECM hydrogels as bioinks may not be suitable for bioprinting processes because of the loss of...

Three-dimensional (3D) melt electrospinning writing (MEW) is a promising technique for 3D printing of porous scaffolds with well-defined geometrical features. The diameter of electrospun fibers strongly affect the achievable resolution and consequently several other physical, mechanical, and structural properties of the fabricated scaffold. However...

A single additive, a grafted copolymer, is designed to ensure the stability of suspensions of highly-loaded iron oxide nanoparticles (IOPs) and facilitate 3D printing of these suspensions in the filament form. This poly (ethylene glycol) (PEG)-grafted copolymer of N-[3(dimethylamino)propyl]methacrylamide (DMAPMA) and acrylic acid (AA) harnesses bot...

In this paper, a numerical model based on a systematic study of electrified jet printing is presented. The Volume of Fluid (VOF) method which suits for modeling multiphase flows with a continuous interface is used. The surface tension force is calculated with the Continuum Surface Force (CSF) method and the electric forces are added to the momentum...

In this paper, we present the biomanufacturing of patterned electrically conductive and cell- embedded hydrogel structures, in which selectively patterned regions of hydrogels including carbon nanotubes (CNTs) and NIH 3T3 cells were demonstrated. We employed a recently developed method of multimaterial additive manufacturing of hydrogels, by using...

In this paper, a feature-based bio-CAD modeling of three-dimensional tissue scaffolds by considering spatial distribution of biologically active materials is presented for biomanufacturing and tissue engineering applications. Proposed model is based on uniform distribution of bio-active particles in different regions of scaffold, which is constrain...

In this research, a novel development of bioink from cell sheets is presented for scaffold free bioprinting applications. Poly(N-isopropylacrylamide) (PNIPAAm) coated surfaces were first prepared by using initiated Chemical Vapor Deposition (iCVD) method. Cell-sheets were then grown on these thermoresposnsive pNIPAAm coated surfaces and easily deta...

In this research, Polycaprolactone/Polypropylenesuccinate/Silver nanoparticle (PCL/PPSu/AgNP) material is proposed for preventing microbial contaminations of a wound area to improve haeling process. PEGylated AgNPs were synthesized and dispersed in PCL/PPSu copolymer structure to gain antimicrobial properties.

In this paper, a novel method of integrated modelling and bio-additive manufacturing of hybrid bioinspired structures is presented. An algorithm is developed to generate optimized and continuous path plan while changing material and internal composition spatially and hierarchically based on the assigned functionality. Biodegradable polymers and hyd...

Bioprinting is a relatively new technology where living cells with or without biomaterials are printed layer-by-layer in order to create three-dimensional (3D) living structures. In this article, novel bioprinting methodologies are developed to fabricate 3D biological structures directly from computer models using live multicellular aggregates. Mul...

Multimaterial additive manufacturing or three-dimensional (3D) printing of hydrogel structures provides the opportunity to engineer geometrically dependent functionalities. However, current fabrication methods are mostly limited to one type of material or only provide one type of functionality. In this paper, we report a novel method of multimateri...

This paper presents modeling and analysis of coiled carbon nanotube (CCNT) reinforced polymer nanocomposites. A new algorithmic representative volume element (RVE) generation method and an RVE based finite element analysis are proposed to predict the elastic properties of CCNT nanocomposites. The elastic properties of CCNT polymer nanocomposites ar...

Three-dimensional (3D) bioprinting is a rapidly advancing tissue engineering technology that holds great promise for the regeneration of several tissues, including bone. However, to generate a successful 3D bone tissue engineering construct, additional complexities should be taken into account such as nutrient and oxygen delivery, which is often in...

Tissue engineering is an emerging multidisciplinary field to regenerate damaged or diseased tissues and organs. Traditional tissue engineering strategies involve seeding cells into porous scaffolds to regenerate tissues or organs. However, there are still some challenges such as difficulty in seeding different type of cells spatially into a scaffol...

Cardiovascular diseases are the leading cause of deaths throughout the world. Vascular diseases are mostly treated with autografts and blood vessel transplantations. However, traditional grafting methods have several problems including lack of suitable harvest sites, additional surgical costs for harvesting procedure, pain, infection, lack of donor...

This research focuses on the development of a layered-based novel fabrication methodology for three-dimensional tissue scaffolds with heterogeneous structure of varying concentrations of drug molecules and/or multiple biomaterials. A pressure assisted multi-syringe single nozzle deposition (MSSND) system has been developed for the scaffold fabricat...

Thousands of people die each year due the cardiovascular health problems. The most common treatments for cardiovascular health diseases are autografts and blood vessel transplantations which has limitations due to lack of donors and the patient's conditions. Although there are several scaffold based studies about vascular tissue engineering, scaffo...

A novel tissue scaffold design technique has been proposed with controllable heterogeneous architecture design suitable for additive manufacturing processes. The proposed layer-based design uses a bi-layer pattern of radial and spiral layer consecutively to generate functionally gradient porosity, which follows the geometric shape of the scaffold....

A novel tissue scaffold design technique has been proposed with controllable heterogeneous architecture design suitable for additive manufacturing processes. The proposed layer-based design uses a bi-layer pattern of radial and spiral layers consecutively to generate functionally gradient porosity, which follows the geometry of the scaffold. The pr...

Porous scaffolds with interconnected and continuous pores have recently been considered as one of the most successful tissue engineering strategies. In the literature, it has been concluded that properly interconnected and continuous pores with their spatial distribution could contribute to perform diverse mechanical, biological and chemical functi...

This paper presents a novelfeature-based variational modeling to control the biodegradation process and thus material release kinetics of biodegradable microstructures. Pattern architecture of micro-structure is varied according to the predetermined degradation profile over the micro-structure based on tissue engineering requirements. Optimum patte...

Porous scaffolds with interconnected and continuous pores have recently been developed to stimulate tissue regeneration. Even though few researches have focused on the internal architecture of porous scaffolds but concluded that properly interconnected and continuous pores with spatial distribution might perform diverse mechanical, biological and c...

Real-time degradation studies of bioresorbable polymers can take weeks, months, and even years to conduct. For this reason, developing and validating mathematical models that describe and predict degradation can provide a means to accelerate the development of materials and devices for controlled drug release. This study aims to develop and experim...

This paper presents a new optimization methodology of material blending for heterogeneous object modeling by matching the material-governing features. The proposed method establishes point-to-point correspondence represented by a set of connecting lines between two material directrices. To blend the material features between the directrices, a heur...

A layer-based tissue scaffold is designed with heterogeneous internal architecture. The proposed layer-based design uses a bi-layer pattern of radial and spiral layer consecutively to generate functionally gradient porosity following the geometry of the scaffold. Medial region is constructed from medial axis and used as an internal geometric featur...

A novel modeling technique for porous tissue scaffolds with targeting the functionally gradient variational porosity with continuous material deposition planning has been proposed. To vary the porosity of the designed scaffold functionally, medial axis transformation is used. The medial axis of each layers of the scaffold is calculated and used as...

Development of engineered tissue scaffolds with superior control over cell-protein interactions is still very much infancy. Advancing through heterogeneous multifold scaffolds with controlled release fashion enables synchronization of regenerating tissue with the release kinetics of loaded biomolecules. This might be an engineering challenge and pr...

Reconstructing or repairing a damaged tissue with porous scaffolds to restore the mechanical, biological, and chemical functions is one of the major tissue engineering and wound healing strategies. Recent developments in three-dimensional bioprinting techniques and improvements in the biomaterial properties have made fabrication of controlled and i...

This paper presents localized and temporal control of release kinetics over 3-dimensional (3D) hybrid wound devices to improve wound-healing process. Imaging study is performed to extract wound bed geometry in 3D. Non-Uniform Rational B-Splines (NURBS) based surface lofting is applied to generate functionally graded regions. Diffusion-based release...

Spatiotemporal delivery of incorporated biological modifiers from synthesised tissue scaffolds has higher speculation to stimulate the complex tissue regeneration process via controlling the extracellular matrix. In this research, we consider the matrix material degradation profile, impregnated biological modifier and permeability of the structure...

Thousands of people die each year due the cardiovascular health problems. The most common treatments for cardiovascular health diseases are autografts and blood vessel transplantations which has limitations due to lack of donors and the patient's conditions. Although there are several scaffold based studies about vascular tissue engineering, scaffo...

Reconstructing or repairing the damaged or diseased tissues with porous scaffolds to restore the mechanical, biological and chemical functions is one of the major tissue engineering strategies. Development of Solid Free Form (SFF) techniques and improvement in biomaterial properties by synergy have provided the leverage to fabricate controlled and...

Porous membranes/scaffolds such as guided tissue regeneration (GTR) membranes, cell sheets, tissue matrices or polymeric meshes are being widely used in soft tissue engineering to regenerate damaged, diseased tissue or wound. These membranes are mostly regular porous structures with repeating internal architecture. When they are applied onto wound...