Can you print an organ with the collagen from the pharmacy?
Sodium dodecyl sulfate polyacrylamide gel electrophoresis results of hydrolyzed collagen (left) and native collagen (right) molecules demonstrating the vast difference in molecular weight between the two. Bousopha et al.
We are often asked why we don’t simply buy collagen from the pharmacy instead of bothering with extracting collagen from animal byproducts ourselves. In other words, how is our collagen different from the one readily available as a remedy for skin, hair and joints? The short answer is that what the pharmacy sells is not really collagen. If you pay close attention to the label, you will notice that it says hydrolyzed collagen, collagen peptides, or collagen hydrolysate, as it refers to the product of the process of breaking down the collagen molecule into constituent peptides and oligopeptides.
Collagen is important for our health because it is the most abundant protein in mammals, accounting for approximately one-third of the total protein in the human body. It is the main component of various connective tissues in the body, making it effectively the substance that holds the body together. A whole family of collagen molecules has been identified but the vast majority in the human body is type I, II, or III. The distinguishing characteristic of collagens is a repeating Gly-X-Y structure, wherein Gly is glycine while X and Y are any other amino acid, but most frequently proline and 4-hydroxyproline, respectively.
Notably, the native collagen molecule cannot be absorbed by the body in whole form, rather, the protein must be broken down during the digestive process before absorption into the bloodstream. Nevertheless, the heat treatment typically accompanying the preparation of collagen-containing foods for consumption, i.e. cooking muscle-containing meat, fish, egg whites or a bone broth, turns collagen into various constituent molecules, which after additional breakdown in various parts of the digestive system, like the stomach and the duodenum, are absorbed in the bloodstream. On the other hand, hydrolyzed collagen refers to collagen broken down, through a process called hydrolysis, into peptides, which are arguably even more readily absorbed. Thus, the hydrolyzed collagen provides some of the building blocks our bodies need to make collagen.
However, calling the peptides obtained from collagen hydrolyzed collagen is like calling a brick a broken down house. Sure, it might be historically descriptive and accurate, and sure, you could build a house using the resulting brick but you may also use it for a wall surrounding the future house. Notably, in both cases, you still need to spend energy and other resources to build the complete structure so it would be quite misleading to call a pile of bricks a house.
Scientific interest in collagen peptides
But is it misleading to call the peptides (derived from collagen) hydrolyzed collagen or simply collagen as most people, even some chemists, refer to it? And if it is, what is wrong with that? It certainly is misleading when coupled with claims of health benefits which are often not based on established science. Commonly, people, especially those focused on advertising, reason that since the skin, the hair, and the nails contain collagen, to maintain them, surely it is obvious that we would need to consume collagen. However, here is the deal: a panel of experts assembled by the European Food Safety Authority on Dietetic Products, Nutrition and Allergies has concluded that based on the scientific evidence present at the time, no cause and effect relationship had been established between the consumption of collagen hydrolysate and maintenance of joints, for instance. Furthermore, it is interesting to look at the limitations of the studies which the experts considered to reach this conclusion. These limitations included the trials being conducted in patients or without a control group, lack of significant differences in the results or even clear lack of positive effect and finally, a study being in vitro. All of these limitations gave the panel reasons to reject the studies as irrelevant to the claimed health benefit of the hydrolyzed collagen on joints.
In another scientific opinion from 2006, the panel once again concluded that no cause and effect had been established between the use of a specific collagen hydrolysate product and health effects related to improvement in skin elasticity and skin function. Here, it is noteworthy that in the absence of evidence for an effect on skin function in humans, the panel explicitly rejected looking into animal and in vitro studies.
About fifteen years later, the matter seems to be far from settled. Today, there is even more research into the health benefits of collagen peptides, including a number of clinical trials reporting beneficial effects on joints, skin, nails, and bone. For instance, a meta-analysis from 2018 concluded that the supplement alleviated osteoarthritis symptoms while another one from 2021 reported reduced skin aging. However, both of these studies have since been followed by peer criticism. In a letter to the editor, Paul T. von Hippel insists that the meta-analytic results from the 2018 study do not support strong conclusions linking reduction of symptoms of osteoarthritis to collagen supplements intake. Furthermore, a 2017 meta-analysis concluded that there was small or clinically unimportant effect of collagen hydrolysates on the treatment of osteoarthritis. In another letter to the editor, Peres et al. pointed out numerous concerns regarding the meta-analysis from 2021 including combining the effects of different measures, different brands of collagen peptides, dosages, association with antioxidants, duration of intervention, age-groups of participants, measurements from different body sites, and small sample size trials. In addition, they noted that due to unclear data selection process, the analysis of publication bias was impracticable. As a result, they recommended that the conclusion from the meta-analysis be changed to “because of the low quality and heterogeneity of the available studies, further large-sample double-blind randomized controlled trials, especially using histological outcomes, are necessary to establish HC [hydrolyzed collagen] effectiveness on skin aging.”
Finally, it is important to keep in mind that collagen peptides are sold as a food supplement which is a class of products not regulated in the same way drugs are. Still, there are specific health claims that the European Commission prohibits when marketing collagen products. In particular, the following claims are not authorized for collagen products since they have not been substantiated: 1) Collagen can/could contribute to the maintenance of the healthy function of joints; 2) Helps the skin to preserve its firmness and elasticity. Has beneficial effect in the maintenance of skin firmness and elasticity. Similarly, the unauthorized claims related to collagen hydrolysate products are: 1) Contributes to the functioning of cartilage building cells; 2) Supports the (natural) regeneration of joint cartilage; 3) Stimulates the build-up of joint cartilage; 4) Contributes to improved joint functioning and joint mobility; 5) Contributes to joint comfort; 6) Provides the building blocks (peptides) for the biosynthesis of cartilage; 7) Provides strength, flexibility and support to skin connective tissues, ligaments, tendons, bones and other parts of the body; 8) beneficial physiological effect on the maintenance of joint health in physically active people. The health claims which the commission actually authorizes are only in the context of Vitamin C which helps collagen formation for the normal function of blood vessels, bones, cartilage, gums, skin, and teeth.
In contrast, the collagen type I molecule we obtain from bovine tendons has a number of characteristics which make it not only suitable for tissue engineering and bioprinting but indeed an excellent choice. These properties which also distinguish it from collagen hydrolysates include the availability of cell attachment domains, appropriate enzymatic stability, as well as suitable viscosity, rheological (flow) and thermal gelation properties of its solutions.
Scientific interest in bioprinting collagen
Collagen provides several cell attachment sites where the triple helical structure is selectively recognized by specific receptors, called integrins, on the cell’s membrane while additional binding sites, such as the RGD (Arg-Gly-Asp) ligand, may also become available to cell attachment after unfolding of the collagen triple helix.
The proper stability of collagen against the enzymes produced by the embedded cells, which are part of a tissue model, depends on its ability to self-assemble into hierarchically organized fibrillar structures. The latter manifests itself as the ability of a neutral collagen solution to turn into a gel at the physiological temperature. In extrusion-based bioprinting, to be able to create high fidelity structures, it is crucial that this process of thermal gelation occurs within seconds. This is challenging in the case of collagen which requires long time, on the order of minutes, to be able to assemble into well-defined hierarchical fibrils.
Finally, the viscosity of collagen solutions and their rheological behavior make it suitable for various approaches to tissue engineering, including extrusion-based bioprinting. In particular, by varying the collagen concentration between 0.5 and 5%, both low viscosity solutions and high viscosity hydrogels can be obtained. These can then be optimized for a particular cell line best suited for the desired tissue model. Apart from viscosity, however, in extrusion-based bioprinting, it is important that the ink decreases its viscosity during extrusion (shear thinning), to minimize the negative effect of the shear stresses during extrusion, which is a typical behavior of collagen solutions and hydrogels.
In conclusion, collagen is a great choice for tissue engineering but we don’t recommend using the “collagen“ sold at the pharmacy. Indeed, while expecting the accumulation of high quality scientific evidence, we remain skeptical that the hydrolyzed collagen is appropriate remedy for any medical condition.