Biotribology in nature: how different microstructure morphologies change leaf wettability?

Header Image: The surface morphology with the magnification of one thousand times of the four kinds of plant leaves: (a) Photinia serrulata, (b) Ginkgo, (c) Aloe vera and (d) Hypericum monogynum. (CC BY-NC-ND 4.0)

Throughout millions of years, organisms evolved in Nature due to a need of adaptation driven by different environmental conditions imposed. Functional systems with intricate properties arose from this continuous structural development leading to, for example, super hydrophobic and self-cleaning surfaces found in lotus leafs (referred as “lotus effect”). An understanding of role of the microstructural features in these systems may help elucidating how to tailor system with an appropriate surface wettability.

In order to tackle this need, Wang and co-workers (2016) studied the wettability properties of four different types of plants (P. serrulata, Ginkgo, Aloe vera, H. monogynum) exhibiting dissimilar microstructures by means of static contact angle for deionized water.

Their results provide an insightful understanding of surface wettability. Whilst minor corrugated and raised boundary microstructures portray the highest wettability (i.e., P. serrulata), increase in cross section corrugation diminishes the liquid/surface contact area and, therefore, intensifies hydrophobicity. Also, the L/W ratio seems to play a major role in surface wettability. Ginko, although displays a corrugated microstructure on the leaf, its large L/W ratio promotes diffusion of liquid, which consequently leads to a hydrophilic surface.


Wang, L. F., & Dai, Z. D. (2016). Effects of the natural microstructures on the wettability of leaf surfaces. Biosurface and Biotribology, 2(2), 70-74.

This post was written by Pedro Luiz Lima dos Santos as part of an ongoing series of scientific communications written and curated by BioTrib’s Early Stage Researchers.

Pedro is researching the Functional Biotribology of the Surface Engineering of 3D Printed Components at the University of Leeds, UK.

Tissue Engineering for Articular Cartilage Regeneration

Light micrograph of hyaline cartilage

Articular cartilage is a living material composed of a relatively small number of cells known as chondrocytes surrounded by a multicomponent matrix. Mechanically, articular cartilage is a composite of materials with widely differing properties. Approximately 70 to 85% of the weight of the whole tissue is water. The remainder of the tissue is composed primarily of proteoglycans and collagen. Proteoglycans consist of a protein core to which glycosaminoglycans (chondroitin sulfate and keratan sulfate) are attached to form a bottlebrush-like structure.

The structure of articular cartilage is often described in terms of four zones between the articular surface and the subchondral bone: the surface or superficial tangential zone, the intermediate or middle zone, the deep or radiate zone, and the calcified zone.

Currently, the most used techniques for articular cartilage regeneration are microfracture (MF), osteochondral autologous transplantation (OAT), osteochondral allograft transplantation (OCA), particulate articular cartilage implantation (PACI), and autologous chondrocyte implantation (ACI). However, these methods have limitations including calcification, formation of transient fibrocartilaginous tissue, and the low capacity of binding to surrounding normal cartilage [1, 2]. Therefore, scaffolds with improved bulk mechanical properties could increase the efficacy of treatment and promote an earlier return to normal activity.

In recent years, tissue engineering technology has been considered the most promising method for regenerating the articular cartilage [3] [4].

In tissue engineering applications, biomaterial scaffolds play animportant role in providing a 3D environment that supports cellgrowth, matrix deposition, and tissue regeneration. An ideal tissue engineering scaffold should meet several important criteria:

  1. Be biocompatible, minimizing local tissue reactions andmaximizing cell growth and tissue integration.
  2. Be biodegradable with good absorption rate, providing support for early cell proliferation and allows for gradualdegradation after the formation of new tissue.
  3. Have adequate porosity and interconnectivity to allow cellmigration and efficient exchange of nutrients and waste.
  4. Possess suitable mechanical properties to support tissue growthunder natural mechanical loads.


To date, many biomaterial scaffolds have been extensively studied, including natural polymers extracted from living organisms and synthetic materials derived from various chemical processes used intissue repair and regeneration.

Natural biomaterials are popular as scaffolds for cartilage repair and regeneration due to their excellent biocompatibility for cell adhesion and differentiation. In particular, natural scaffolds used in tissue engineering of articular cartilage include carbohydrate-based hyaluronic acid, agarose, alginate, chitosan, and protein-based collagen or fibrin glues.

Due to its ease of fabrication and chemical modification, excellent biocompatibility, high versatility, suitable mechanical properties and controllable biodegradability, synthetic polymers are currently being investigated for their potential as a scaffold for cartilage tissue. The most common synthetic polymers for cartilage engineering scaffolds are polylactic acid (PLA, present in both L and D forms), polyglycolicacid (PGA), and its copolymer poly-lactic-co- Glycolic acid (PLGA).

Conventional natural or synthetic scaffolds still need to be improved to achieve better biocompatibility and functional properties for cartilage regeneration. Because the size of native cartilage tissue is only nanometers, and chondrocytes directly interact with nanostructured ECM, the biomimetic properties and excellent physicochemical properties of nanomaterials are essential for chondrocyte growth. [5].

Solution electrospinning (SES) is a technique that allows the production of nanofibrous scaffolds and allows for the tuning of the 3D scaffolds by changing the fiber diameter and scaffold porosity. The process consists of a pump that pushes out, through a metal needle (spinneret), the polymer solution, inserted in a syringe. The presence of a high voltage source that energizes the polymer solution causes formation of a conical jet (Taylor cone) which is then drawn into a fiber by electrostatic repulsion [5] [6]. The resulting fibers are deposited on a flat or tubular electrode (collector). The thin electrospun fibers range from a few hundred nanometers to a few micrometers and are suitable candidates to mimic the structure of the natural extracellular matrix (ECM) as they can stimulate cell ingrowth and proliferation [7].

Advances in fabrication methods have solved the scalability problem and enabled the development of porous structures that allow long-term cell invasion and growth. Despite all these advantages, electrospun scaffolds have yet to be fully evaluated in preclinical models and clinical settings, hindering widespread acceptance of this breakthrough technology in biomedicine [8]


[1] C. Vinatier and J. Guicheux, “Cartilage tissue engineering: From biomaterials and stem cells to osteoarthritis treatments,” Annals of Physical and Rehabilitation Medicine, vol. 59, pp. 139 – 144, 2016.

[2] W. Wei, Y. Maa, X. Yao, W. Zhou, X. Wang, L. Chenglin, J. Lin, Q. He, S. Leptihna and H. Ouyang, “Advanced hydrogels for the repair of cartilage defects and regeneration,” Bioactive Materials, vol. 6, p. 998–1011, 2013.

[3] S. Jiang, W. Guo, G. Tian, X. Luo, L. Peng, S. Liu, X. Sui, Q. Guo and X. Li, “Clinical Application Status of Articular Cartilage Regeneration Techniques: Tissue-Engineered Cartilage Brings New Hope,” Stem Cells International, 2020.

[4] A. Martín, H. Zlotnick, J. Carey and R. Mauck, “Merging therapies for cartilage regeneration in currently excluded ‘red knee’ populations,” Nature Partner Journal Regenerative Medicine, vol. 4, 2019.

[5] N. Maurmann, S. L and P. P, “Electrospun and Electrosprayed Scaffolds for Tissue Engineering,” Cutting-Edge Enabling Technologies for Regenerative Medicine, pp. 79 – 100, 2018.

[6] R. Soares and al., “Electrospinning and electrospray of bio-based and natural polymers for biomaterials development,” Mater Sci Eng C Mater Biol Appl, pp. 969-982, 2018.

[7] D. Alexeev and al., “Electrospun biodegradable poly(epsilon-caprolactone) membranes for annulus fibrosus repair: Long-term material stability and mechanical competence,” JOR Spine, vol. 1, 2021.

[8] E. Z. D. Yilmaz, “Electrospun Polymers in Cartilage Engineering—State of Play,” Front. Bioeng. Biotechnol., 2020.

[9] L. H. J. A. K. Zhang, “The Role of Tissue Engineering in Articular Cartilage Repair and Regeneration,” NIH Public Access, 2009.


This article was written by Elisa Bissacco as part of an ongoing series of scientific communications written and curated by BioTrib’s Early Stage Researchers.

She is studying a PhD in Tribological Characteristics of Nanofibrous Electrospun Materials at ETH Zurich.

Implant Impressions Episode 1: Anne

Are you considering joint replacement surgery and want to hear firsthand accounts of the procedure? We recently had the pleasure of interviewing a joint replacement surgery patient (Anne, 85) to learn more about their experience and gain insight into their patient perspective. This video will offer a look into the subjective experience, thoughts and feelings of a person who has gone through the joint replacement surgery process.

Self-driven Biomedical sensor: in situ wear debris from artificial hip joint

Header image adapted from Liu, 2021. Left: Working mechanism of the fabricated TENG. Right: The short-circuit current of the TENG with different debris sizes.

Mechanically assisted corrosion of metal alloys in hip implants also releases solid particles as well as metal ions into the synovial fluid. Compared to metal ions/particles in blood particles at the surrounding tissues, far fewer studies had been reported on synovial fluid during in-vitro study. Moreover, the metal ions concentrations and the wear particles sizes reported in different studies have greater variations. Also, the Wear debris can either reside as solid particles or can dissolve and further enhance the ion content. Thus it is extremely desirable to produce a technique for in-situ wear debris characterization which might be significant in predicting wear rate and understanding the wear mechanism of implant bearings.

Based on the variety of material selection, device structure, and operating mode, biomedical sensors such as the Triboelectric nanogenerator (TENG) was developed as a newly emerging energy technology for monitoring the creation of wear debris in artificial joints where the artificial joint itself can be used as a TENG by the coupling of triboelectrification and electrostatic induction (Liu et al.2021). With the TENG, different micron sizes of wear debris can be separated based on different voltage amplitude. However, the developed method is highly sensitive to test medium and did not provide any rationale in lubricant containing environment which needs further modification.

Read this interesting article using the below link:



This article was written by MM Raihan as part of an ongoing series of scientific communications written and curated by BioTrib’s Early Stage Researchers.

Raihan is researching In-situ Measurement of Nano-scale Wear Utilising Advanced Sensors at the University of Leeds, UK.

Role emotional and mental health support to help early recovery of hip replacement patients

Replacement of the human joints when diseased or damaged during trauma is an incredibly effective operation. Every year, orthopaedic surgeries effectively restore physical function and relieve pain for millions of Europeans. However, despite great surgical achievements and uniform pain alleviation after total joint replacement, there is still significant heterogeneity in functional progress after joint replacement.

Besides, physical condition, poor mental health has been identified as a key parameter impacting early recovery. The patients who are being waiting for hip replacement or already done so, need mental health support apart from just focusing on pain relief. In a study on 900 patients in UK, 72% showed deterioration in their mental health before and after the surgery. Poor functional performance have been linked to inadequate mental health, such as anxiety and depression, as well as poor coping skills and social support.

According to data from the Swedish Hip Arthroplasty Register, depression and anxiety levels were strong predictors of pain alleviation and patient satisfaction. Thus an appropriate assessment of emotional health has been suggested that may enable a modification in the way patients are managed. The emotional support can help to improve the pain tolerance of the patients. It was also observed that patients with limited pain tolerance, whether they have good or bad emotional health, are more likely to report lower postoperative gains. Thus anyone with arthritis who is awaiting or had surgery should not be left alone. Apart from the emotional support, personalised self-management support, signposting to financial support and advice have been recommended. Teams of clinicians, including physical therapists, behavioural psychologists, and other support specialists, may get involved in such activities.

More study is required to establish perioperative postoperative techniques that simultaneously promote the physical and emotional health of the patients in order to ensure maximal functional gain following technically successful surgery.



This article was written by MM Raihan as part of an ongoing series of scientific communications written and curated by BioTrib’s Early Stage Researchers.

Raihan is researching In-situ Measurement of Nano-scale Wear Utilising Advanced Sensors at the University of Leeds, UK.

Can you go surfing after a hip replacement?

High-impact sports are generally discouraged after surgery including surfing, Rugby, martial arts, and football due to significant risk of falling. In contrast, Golf, cycling, hiking, and swimming (avoid breaststroke) are all recommended as low-impact activities. There is lack of evidence available about surfing following hip resurfacing arthroplasty (HRA) or total hip arthroplasty (THA).

Vanlommel et al. thus undertook a study in a single surgeon series to evaluate the quality and viability of resuming this intense sport after HRA, with the hypothesis that return to surfing is viable after HRA. They examined 45 patients who had practised surfing prior to the beginning of pain and hip surgery. For 37 (82%) patients, complete clinical and radiological follow-up was done including several questionnaires. The results were amazing. More than 80% of patients commenced surfing within the first 6 months after surgery. During surfing, 21 patients (72%) were completely pain free. More than 80% of patients began surfing within 6 months of their surgery. 21 patients (72%) were fully pain-free when surfing.

Wait don’t go for surfing right now if you have just undergone HRA or THA surgery. This study is a short term evaluation. A prospective study based on preclinical laboratory simulation and high quality clinical study such as the High-Activity Arthroplasty Score remains necessary to let you go enjoy surfing.

To read the interesting article, follow the provided link

Vanlommel, Jan, Markus Goldhofer, and William L. Walter. “Surfing after hip resurfacing surgery.Clinical journal of sport medicine 32.2 (2022): 135-138.
This article was written by MM Raihan as part of an ongoing series of scientific communications written and curated by BioTrib’s Early Stage Researchers. Raihan is researching In-situ Measurement of Nano-scale Wear Utilising Advanced Sensors at the University of Leeds, UK.

Measurement of fluid film thickness in tribology

The measurement of film thickness is an important aspect in tribology, which is the study of friction, wear, and lubrication. The thickness of the lubricant film plays a crucial role in determining the lubrication regime of a system, and in turn, affects the friction and wear behavior of the system. There are several methods that are used to measure the thickness of a lubricant film, depending on the application and the type of lubricant.

One of the most widely used methods for measuring film thickness is the optical interferometry method. This method uses the interference of light waves to measure the thickness of a thin film. A light source is shone onto the surface of the film, and the reflected light is analyzed to determine the thickness of the film. This method is highly precise and can be used to measure film thicknesses in the nanometer range. It can be used to measure the thickness of transparent and semi-transparent films.

Another commonly used method is the laser-based method, this method uses the laser to measure the film thickness by analyzing the laser’s reflection, diffraction, or absorption.

Another method is the mechanical method; this method uses a mechanical probe to measure the film thickness. The probe is lowered into the lubricant film, and the position of the probe is measured to determine the thickness of the film.

Finally, there is the electrical method; this method uses an electrical signal to measure the film thickness by analyzing the capacitance or the impedance of the lubricant film. This method is based on the dielectric properties of the lubricant and it can be used to measure the film thickness of both liquid and solid lubricants. This method is relatively simple, easy to use, and can be used in-situ and in real-time.

In conclusion, the film thickness can be measured by different methods such as optical interferometry, laser-based, mechanical and electrical method. The choice of the method depends on the lubricant, the range of the film thickness, and the accuracy required.


[1] Dwyer-Joyce, R.S., Drinkwater, B.W. and Donohoe, C.J., 2003. The measurement of lubricant–film thickness using ultrasound. Proceedings of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences, 459(2032), pp.957-976.



This article was written by Mahdieh Mosayebias part of an ongoing series of scientific communications written and curated by BioTrib’s Early Stage Researchers.

Mahdieh is researching the Design of Self Lubricating Prothesis at ETH Zurich, Switzerland.

Newtonian and Non-Newtonian Fluids

Fluids, including liquids and gases, fall into two categories: Newtonian fluids and non-Newtonian fluids. A key difference between these two fluids is that they respond differently to the applied forces. The rheology of non-Newtonian fluids changes dramatically under processing conditions, however, that of Newtonian fluid remains constant.

Newtonian fluids: These fluids obey Newton’s law of viscosity and have a linear correlation between the rate of angular deformation and shear stress. In such fluids, viscosity remains constant regardless of shear rate. Water, air, glycerine, gasoline, alcohol can be taken as examples of these Newtonian fluids.

Non-Newtonian fluids: These fluids do not obey Newton’s law of viscosity and the viscosity declines or enhances respective to the type of fluid under applied shear. The five ways, describing how non-Newtonian fluids behave, are explained as follows (figure 1):

  • Dilatant: The viscosity of the fluid increases with an increase in shear stress. Quicksand and mud slurry are two examples of dilatant fluids.
  • Pseudoplastic: The viscosity of the fluid decreases with an increase in shear stress. Blood and ketchup are two examples of pseudoplastic fluids.
  • Bingham plastic: These fluids, like oil paint, have a linear relationship between the rate of angular deformation and shear stress. The difference between these fluids and Newtonian ones is that they have internal yield stress making them a time-dependent relation.
  • Rheopectic: The viscosity of the fluid increases with an increase in shear stress and the relation is time-dependent. Gypsum paste can be taken as an example.
  • Thixotropic: The viscosity of the fluid decreases with an increase in shear stress and the relation is time-dependent. Paint and glue are two examples of thixotropic fluids.


[1] Newtonian and Non-Newtonian Fluids | Newton’s Law of Viscosity (

This article was written by Mahdieh Mosayebias part of an ongoing series of scientific communications written and curated by BioTrib’s Early Stage Researchers.

Mahdieh is researching the Design of Self Lubricating Prothesis at ETH Zurich, Switzerland.

3D Printing in Dentistry – Digital Dental Implant Planning

Being a ‘frequent customer’ personally who has visited the dental clinic multiple times since last summer, I am officially getting a dental implant. From a patient’s point of view, during the whole process, all I have to do was visit a dental imaging clinic, stay still in front of a 360 X-ray scanner, lay down with local anaesthesia and after some carpenter works, the titanium implant is planted in my jawbone. As being personally also working in an implant-related field for my PhD, I want to reveal some details about digital implant design that the patient may not know or be informed of.

Step 1:

Scans of the patient can be taken by either a CBCT scanner (Cone Beam Computed Tomography) or an intra-oral scanner. The data was obtained and saved in an STL format and imported into the professional software for data alignment.

CBCT scanner (Cone Beam Computed Tomography) (left) Intra-oral scanner (right) [3]

Step 2:

The data was obtained and saved in an STL format and imported into the virtual implant planning software for data alignment. The specialists and technicians visualize the implant and start prosthetic planning via the CAD process. The surgical guide and prosthetic components involved are also designed with the software.

3Shape Implant Studio – an example of implant planning software

Step 3:

The manufacturing method of implants and surgical guides can either be subtractive like computer numerical control [CNC] machining; milling or additive i.e. 3D printing, for example, stereolithography (SLA), digital light projection (DLP), jet printing (PolyJet®/ProJet®), and direct laser sintering (DLMS)/selective laser sintering (SLS).

Step 4:

Now the “Best” part, the surgery! Just joking.

Digital implant design workflow [2]

The digital workflow has sped up the treatment process and improved the accuracy of implant design and dental implant placement, which have led to more successful implant surgeries.


[3] (Header Image)

This post was written by Esperanza Shi as part of an ongoing series of scientific communications written and curated by BioTrib’s Early Stage Researchers.

Esperanza is researching the Optimisation of Scanning Strategies for 3D Printed Artificial Joints at Imperial College London, UK.

3D Printed Protective Face Mask For Athletes

It’s really hard to miss out on the news about football players wearing Zorro’s masks during the games. When Son Heung-min showed up at the Qatar World Cup as South Korea face Brazil, wearing that shining, chic, black face mask, everyone on the internet was talking about it. Actually, many football players have been seen wearing similar masks to the match, including Croatian player Joško Gvardiol and Tunisia’s Ellyes Skhiri as in the cover picture. So, what are these face masks for and how are they made?

Example of 3D Printed sports face orthotic

Protective face masks have been loved by many athletes who have recently fractured a nose or an eye socket but are eager to get back to the pitch as soon as possible. The 3D surface imaging, 3D modelling, and 3D printing technology enable the design process to be accurate and customisable, 100% specific to the face of the athletes. The masks are designed to be lightweight, comfortable and unobtrusive, but provide incredible strength to protect fractured bones or prevent future injury.



Header Image Adapted from:


This post was written by Esperanza Shi as part of an ongoing series of scientific communications written and curated by BioTrib’s Early Stage Researchers.

Esperanza is researching the Optimisation of Scanning Strategies for 3D Printed Artificial Joints at Imperial College London, UK.

BioTrib Conversations: ChatGPT on biotribological research

Generative text AI tools, such as ChatGPT, have recently garnered significant attention due to its ability to provide comprehensive responses and eloquent answers across many domains of knowledge. Whilst it represents a significant technological advancement, it has been met with both positive and negative reviews. Elon Musk wrote that “ChatGPT is scary good”. It has also received widespread criticism particularly around efficacy and integrity from educators, academics and journalists plus many more.

But how should we embrace these tools? Professor Michael Bryant asks ChatGPT ‘What are the current research challenges in biotribology?’

Biotribology is the study of friction, wear, and lubrication of biological systems, including joints, implants, and prosthetics. Some of the current research challenges in biotribology include:

1. Understanding the complex interactions between biological tissues and synthetic materials: One of the major challenges in biotribology is to understand the complex interactions between biological tissues and synthetic materials used in implants and prosthetics. This requires a deep understanding of the mechanical, chemical, and biological properties of both the biological tissues and the synthetic materials.

2. Developing advanced testing methods: Biomechanical testing of biological tissues is challenging due to their complex nature. Developing advanced testing methods that can accurately measure friction, wear, and lubrication in biological systems is a critical research challenge.

3. Designing and developing better implant materials: Developing new materials and coatings for implants that can better mimic the natural properties of biological tissues is another important research challenge. This can help improve the biocompatibility, durability, and longevity of implants.

4. Improving lubrication of joint replacements: The lubrication of joint replacements is a critical factor in their performance and longevity. Developing better lubrication strategies and materials is a key research challenge in biotribology.

5. Studying the effects of aging and disease: Aging and disease can significantly impact the friction, wear, and lubrication of biological systems. Studying the effects of aging and disease on biotribology can provide valuable insights into the development of better treatments and therapies for patients.

It is a good job BioTrib is working across all of these domains to address the current research challenges highlighted by ChatGPT. What will be interesting to see is how these changes with time as the field advances. Certainly some of these challenges have been of focus to researchers for many a year.

This article was written by ChatGPT and BioTrib Lead Scientist, Professor Michael Bryant.

Alginate based bioinks for 3D bioprinting of engineered orthopedic tissues

Alginate is widely used as a biomaterial in 3D bioprinting due to its biocompatibility, biodegradability, high accessibility, shear thinning behavior, and cross-linking speed. The rheological properties of the bioink are the key factor influencing printability (ability to form and maintain the design shape), therefore investigations are conducted to enhance the weak mechanical properties of alginate gel in order to obtain hybrid hydrogels with high printability. Indeed, when using 3D bioprinting, the objective is to obtain a multilayer construction that retains its mechanical stability over time and, in order to produce relevant in vitro tissue models, the final goal is to match the native mechanical properties of the tissue.

In the review ‘Alginate based hydrogel inks for 3D bioprinting of engineered orthopedic tissues’, Murab et al. provide an overview of the different parameters such as printing method, concentration of alginate and crosslinker, and shape of the printed structures on the properties of the alginate-based printed construct. Specifically, they reviewed different strategies used in the last few years to increase the mechanical and biological performances of alginate-based hydrogels for bioprinting of bone and cartilage. For example, the advantageous properties of alginate and type I collagen have been combined to create a lattice structure with improved mechanical properties and higher expression of cartilage-specific genes in primary rat articular cartilage chondrocytes compared to the alginate control.

Another example of cartilage tissue engineering using alginate combined the latter with polycaprolactone (PCL) to create a stable PCL support scaffold with bioprinted alginate in between. The resulting construct exhibits good mechanical stability and the goat cartilage cells embedded in alginate were found to have high viability with the production of a cartilage-like matrix. Although encouraging results are presented in the literature, there is still a long way to go to use the alginate-based hydrogels for in vitro orthopedic models.



Murab, Sumit, et al. “Alginate based hydrogel inks for 3D bioprinting of engineered orthopedic tissues.” Carbohydrate Polymers (2022): 119964.


This article was written by Marie Moulin as part of an ongoing series of scientific communications written and curated by BioTrib’s Early Stage Researchers.

Marie is researching the Bioprinting of Bone and Cartilage at Uppsala University, Sweden.

Volumetric Bioprinting of Meniscus

The fabrication of functional constructs that mimic the physiological characteristics of tissues would represent a major breakthrough for the creation of complex in vitro models or for regenerative medicine. Current 3D biofabrication technologies, such as stereolithography or extrusion bioprinting, are used to attempt to achieve this goal by combining cells and biomaterials according to a specific architecture, layer by layer. This additive manufacturing method limits the ability to create clinically relevant sized constructs, as the printing time for centimeter-sized constructs is too high to preserve cell viability (cells remain in the cartridge and construct, outside of an optimal culture environment). Volumetric bioprinting is a promising technology that could produce clinically relevant sized living constructs in less than a minute.

This emerging technology uses the principle of medical tomography in reverse, projecting a 2D patterned optical light field into a volume of photopolymer, which causes cross-linking in the area where the light exposure builds up to produce a 3D construct. Paulina Nuñez Bernal et al. described in 2019 the utilisation of this technic to create a 3D meniscus-shaped construct with high resolution, high cell density, and cell viability (>85%). To do so, a gelatin-based photoresponsive hydrogel (gelMA) containing chondroprogenitor cells (ACPCs) was used. Over time, the cells in the printed constructs synthesized fibrocartilage ECM, which increased the mechanical properties of the meniscus to a compressive modulus value comparable to that of native fibrocartilage. This achievement using volumetric bioprinting could be promising for the future of knee joint repair.



Bernal, Paulina Nuñez, et al. “Volumetric bioprinting of complex living‐tissue constructs within seconds.” Advanced materials 31.42 (2019): 1904209.


This article was written by Marie Moulin as part of an ongoing series of scientific communications written and curated by BioTrib’s Early Stage Researchers.

Marie is researching the Bioprinting of Bone and Cartilage at Uppsala University, Sweden.

Wettability in biotribology applications

Wettability enhancement can improve the lubrication conditions by forming the tribofilm on the surface, reducing wear rate and friction coefficient[1];one of the way is by grafting hydrophilic acrylic acid on UHMWPE. The presence of carboxylic groups in the acrylic acid enhances the interaction with the bioactive molecules such as proteins, peptides, etc. With the grafting ratio of 5.5% , the water contact angle reduced from 83o to 35o due to the great polarity and affinity for water by the carboxyl group present in the acrylic acid. As the surface wettability improves with the graft ratio, the tensile strength decreases while the wear rate declines initially and starts to rise again. Another study done by the Lu et al.[2] on ultrasonically infiltrated with GO mixed with UHMWPE significantly changed the wettability. The surface wettability increased with the increase of ultrasound-induced time resulted in the reduction of COF and wear rate. There are various studies suggesting the improvement in the tribological properties with the enhancement of surface wettability. However, the tribological properties does depend on other various factors such as sliding speed, surface topography, materials properties, sliding temperature, applied load and pressure etc.

Figure 1 a) hydrophobic surface b) hydrophillic surface [5]
Similarly, it is not as straightforward for the bio-compatibility of materials. Wettability influences the protein adsorption, blood coagulation, bacterial adhesion, cell adhesion, platelet adhesion/activation etc [3]. Osteoblast adhesion were decreased with the increase in contact angle from 0o to 106o while fibroblast adhesion was maximum between contact angles 60o to 80o[4]. Various studies mentioned that the hydrophobic surface suitable for the cell spreading, proliferation and differentiation while the hydrophillic surface enhances the cell attachments, proliferation and differentiation [4,5,6]. Adsorption of water molecules is higher in superhydrophilic surfaces preventing protein adhesion which might lead to lower cell adhesion. Thus, moderate hydrophilicity surfaces are most effective for cell adhesion and proliferation. However, the other argument is better cell proliferation and differentiation on superhydrophobic surfaces as the cells would have more surface area available for attachment and proliferation.

Wettability properties can be measured by different methods such as contact angle measurements and Wilhelmy plate method. Understanding the wettability properties of a material can be useful in controlling the tribological behavior and the biocompatibility of a material in biotribological applications.


[1] Y. Deng, D. Xiong, and K. Wang, “Biotribological properties of UHMWPE grafted with AA under lubrication as artificial joint,” J Mater Sci Mater Med, vol. 24, no. 9, pp. 2085–2091, Sep. 2013, doi: 10.1007/s10856-013-4970-x.
[2] P. Lu, M. Wu, X. Liu, X. Ye, W. Duan, and X. Miao, “Surface modification and biotribological behavior of UHMWPE nanocomposites with GO infiltrated by ultrasonic induction,” J Biomed Mater Res B Appl Biomater, vol. 109, no. 6, pp. 808–817, Jun. 2021, doi: 10.1002/JBM.B.34746


This article was written by Dilesh Raj Shrestha as part of an ongoing series of scientific communications written and curated by BioTrib’s Early Stage Researchers.

Dilesh is researching the Development of 3D-printable, self-lubricated polymer composites with improved wear resistance for total joint replacement at Luleå University of Technology, Sweden.


Biotribological Lubrication Mechanisms

The joints experience the dynamic environment (load, speed), thus the various mode of lubrication mechanism can exist. However, number of lubricating mechanism has been proposed over the time such as weeping/squeeze film, boosted, boundary, elasthydrodynamic, micro-elastohydrodynamic, and mixed [1]–[3]. Friction and wear of any tribological systems can be influenced by the materials property, surface properties, operating conditions and the environment[4]. Since synovial joints are among the complex and sophisticated tribological systems, so it is likely that many mode of lubrication mechanisms are present.

Figure 1: Lubrication mechanism for right hip joint

If anyone walks, the interface might be lubricated with synovial fluid via the number of processes such as hydrodynamic, squeeze film/weeping, etc by supporting the load wherever it can. The synovial fluid is squeezed out under loading and consequently lubricates the articular cartilage during off loading(see figure 1). Some of the studies suggest that the synovial fluid cannot separate the articulating surface all the time [5]. When a synovial joint experience the continuous load such as standing for a longer duration, all the fluid is squeezed out of the contact and the load bearing surfaces experiences the boundary lubrication mechanism where the two articulating surface rub with each other. Thus, it can be concluded that synovial joints can encounter the fluild-film, mixed and boundary lubrication similar to the engineering bearings[1]. Murakami et al. [6] termed it as a ‘adaptive multimode lubrication’. The main three mechanism widely studied after their introduction are biphasic lubrication (a form of full film lubrication, since introduced by Mow et al. [7], electrohydrodynamic lubrication (since introduced by Dowson) and brush lubrication(a form of boundary lubrication, since introduced by Hardy et al. [8].

There is limited information on the lubrication mechanism on the artificial total joint replacement. Lubrication mechanism in artificial joints have more variables than the natural synovial joints such as material used, design, contact conditions, patient specific factors, surgical factors etc. Many designers believed that the full film lubrication is difficult to achieve so the efforts have been made towards the improvement in boundary and dry lubricated wear behaviour of implants[9], [10]. Based on the boundary lubrication theory, Charnley[11] developed the low friction arthroplasty using UHMWPE as the acetabular cup combined with the stainless steel femoral head in total hip replacement resulting low wear. In addition to this, various implant design were proposed based on fluid film, elasto-hydrodynamic, elasto-mixed etc[1].

Suitable selection of design parameters (head diameter, diametral clearance etc.) promotes the contact to undergo full hydrodynamic lubrication in hard/hard bearings implants[12]. For instance, when the head diameter is small(16 to 22.5 mm) the surface is under boundary lubrication regime, and when the head diameter is 28 mm it is under mixed lubrication regime[13]. This is because of the tendency to provide surface separation for considerable amount of gait cycle and hence evidence of lubricating film formation. Also, with the increase in the diameter results in higher sliding area which will increase the wear under boundry or mixed lubrication regime. To conclude, it is obvious that the all boundary, mixed and elasto-hydrodynamic lubrication mechanism have been supported by the past studies but most of the implants likely experienced mixed lubrication regimes more than other two.  Continuous studies are being carried out in order to mimic the natural synovial joints which undergoes full range of conditions.


This article was written by Dilesh Raj Shrestha as part of an ongoing series of scientific communications written and curated by BioTrib’s Early Stage Researchers.

Dilesh is researching the Development of 3D-printable, self-lubricated polymer composites with improved wear resistance for total joint replacement at Luleå University of Technology, Sweden.



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