Biomaterials in Fibrous Medical Products

Engineered to interact with biological systems, biomaterials—many with multifunctional properties—play a vital role in providing diagnostic and therapeutic capabilities in contact with biological tissues and organs. Fiber-based medical applications include advanced drug delivery, stents and other implantable devices, scaffolds for tissue regeneration and wound care. The drivers behind medical advancement mean that modified biomaterial formulations, as well as processing methods, are a growing area for the development and manufacture of new medical product formats, for a wide range of clinical needs.

Some biomaterials are well-established as to their compatibility with existing fiber spinning and textile processing methods, while others are incorporated within mixed polymer formations as components for fibers or coatings. Certain inorganic compounds can be directly converted into fibers and fabrics, or can be incorporated with fibers as dispersed nanoparticles. Commonly, natural biopolymers and synthetic polymers are used as materials for making fibers and filaments—either alone, or as additives in commixed polymer formulations—fabrics and porous coatings.

Natural biopolymers can be divided into:

• Polysaccharides: such as alginates; cellulose, including carboxymethyl cellulose (CMC); regenerated cellulose; chitosan; pectin, hyaluronan and dextrin.
• Polypeptides: such as collagen, gelatin, fibrin and various forms of silk.

Offering excellent biocompatibility, natural polymers are suitable for a range of applications, including wound care and tissue engineering.

Synthetic polymers include: aliphatic polyesters and copolyesters (including PLA, PGA, PLGA, PCL, PHAs and PHBs); polyanhydrides; polyolefins (including PE, HDPE and UHMWPE, and PP); PVOH; polyamides, polycarbonates and polyurethanes.

The versatility of biopolymers has already been noted and, of these synthetic polymers, the controlled degradation properties of PLGA make it suitable for drug delivery applications, while the strength of PP means it is widely used in sutures and similar devices. The development of bio-based synthetics, such as BioPP, are also gaining momentum. Typically derived from sugarcane, molasses or vegetable oils, they can offer the same performance levels as PP, and research and developments with bioPP make it available for the production of fibers, films and nanoparticles. But further work is needed to increase bio-based content and optimize production at commercial scale. There are limitations across the breadth of biopolymers, and each material formulation needs to be consider a range of factors: physical properties, regulatory requirements, cost factors and compatibility with the appropriate fiber or textile manufacturing platform, together with the specific needs for the application.

Developmental Challenges

Developing biomaterials for clinical use can raise significant issues, particularly in processing and manufacturing into fibers and fabrics at different scales, which usually requires specialist techniques, modifications to processes and expertise. These elements can add significantly to development costs and extend a product’s time to market. Critical concerns regarding meeting regulatory requirements demand careful planning, documented and expert manufacturing practice and validation at all stages. Limited infrastructure, where organizations lack the facilities to conduct end-to-end biomaterial development, can be a significant challenge.

Biocompatibility can be investigated in laboratory settings, but the safety and performance for extended periods of time must also be addressed. Careful consideration of materials’ selection is paramount. Materials such as alginate and collagen are sensitive to processing conditions such as temperature, pH and ionic strength, and over-processing can denature proteins or alter the molecular structure, affecting material functionality and performance. Controlling moisture levels of highly hydrophilic biomaterials during processing is also challenging, but critical to maintaining their structural integrity and performance in the final application. Many biopolymers used in medical applications lack inherent mechanical strength, requiring reinforcement through blending or cross-linking to achieve the necessary balance between flexibility and durability.

Electrospinning and Wound Care/Tissue Engineering

The main process focus in advanced fibers and fabrics for biomaterials and medical products has, to-date, involved electrospun membranes, particularly for wound dressing, wound care and tissue engineering and regeneration.

As Sara Baptista-Silva has noted, “The electrospinning method is considered the most effective method for producing suitable nanofibers for wound dressing because this technique is also adequate to deliver bioactive compounds in the long-term to local tissues…” ¹

Given concerns over multidrug-resistant bacteria arising because of continuous use of antibiotics, they note the development of materials with nanostructure fibers, which can accommodate compounds with antimicrobial properties. Crucially, when considering drug-releasing medical textiles, “…considering the difference in intrinsic functionality and physiochemical properties of various materials, selecting the right material or polymer plays a crucial role in designing and developing releasing drug textiles.”²

When considering regenerative medicine and tissue engineering, the authors highlight two distinct aspects relating to electrospun nonwovens, firstly: “an ultrafine fibrous network with a high surface-to-volume ratio resembles the natural extracellular matrix. (Dias et al., 2020). Nonwoven fabrics with the capability to deliver bioactive components, such as antibiotics, growth factors, and chemotherapeutic agents, have proven to accelerate or inhibit certain activities during tissue regeneration and remodelling. Release of encapsulated bone morphogenetic proteins growth factor from electrospun composite scaffolds made of silk fibroin/PEO or poly(d,l-lactide-co-glycolide)/hydroxyapatite (PLGA/HAp) accelerated osteogenesis and nerve regeneration processes. (Nie et al., 2008).”³

However, it is also noted that “cell infiltration through the nanofiber is still the major limitation of this method due to their small pore size.”⁴

Electrospun nonwovens offer significant benefits in these areas of medical care—particularly given the above-mentioned resemblance to the extracellular matrix—and the ability to precisely control a range of parameters, including porosity and fiber diameter. That said, there are both medical and commercial drawbacks to the electrospun process: limitations on the range of biomaterials that are compatible and the ability to produce fibers on a large scale.

Opportunities Beyond Electrospinning

Beyond electrospinning to produce nanofibrous webs from polymer solutions, other highly versatile fiber spinning and fabric forming methods are often overlooked, yet have the capacity to produce better-performing products.

This includes wet, dry, dry-wet and gel spinning of biomaterials into continuous filaments, or staple fibers. For thermoplastic polymers, meltspinning can have a range of medical applications, in drug delivery, for example, with the controlled release of therapeutic agents. Dependant on the application, meltspinning can be cost-effective, given its suitability for high-volume production.

Whichever production process is found to be most appropriate given the range of parameters to be considered, a large variety of fabric forming techniques can then follow, depending on the final products’ required structure-property relationships, and high reproducibility and speed of production are possible. Drylaid, wetlaid and spunlaid nonwovens, followed by appropriate web bonding, can enable three-dimensional, porous fabrics to be made very cost-effectively from biomaterials that can be challenging to make using other processes.

In addition to fiber and fabric manufacturing, textile substrates and the materials from which they are made can also be modified. And functionalization is a key area of innovation. By modifying biomaterials at the molecular level, as well as at the fiber and fabric levels, it is possible to enhance physical properties and therefore performance, tailoring materials to meet precise clinical needs.

Concluding Thoughts

When looking at biocompatibility, and at the earliest stages of biomaterial design development, it is crucial—both medically and commercially—to engage with nonwoven specialists who have both the expertise and the facilities to manage the need for end-to-end prototyping and to offer advice into commercial production decisions, for example around scalability. As this overview demonstrates, this requires a capacity to manage polymer formulations, fibers, filaments, films and coatings, with performance validation and benchmarking.

“The main obstacle to using bio textiles for tissue engineering and regenerative medicine is combining state-of-the-art textile machinery, new biomaterials and biological advances to create structurally advanced tissues, organs, and electronic textiles.”5
Developments in biomaterials’ processing provide an exciting frontier for innovation. In addition to biomaterials formulation, alternative methods of processing biomaterials into finished textile formats provide a basis to improve diagnostic and therapeutic devices that meet regulatory demands and redefine patient care standards. 

Baptista-Silva, S. (2022) Chapter 23: Research, development, and future trends for medical textile products. In Md. Ibrahim H. Mondal (Ed.), Medical Textiles from Natural Resources. (p.3) Woodhead Publishing.
Ibid. p.18
Ibid. p.24
Ibid. p.24
Ibid. p.29-30