Originally Published MDDI October 2003MEDICAL Packaging

October 1, 2003

10 Min Read
3-D Packaging for Medical Products

Originally Published MDDI October 2003

MEDICAL Packaging



Shape and size are key considerations for manufacturers of high-profile, sterile, disposable devices.

John P Merritt

 

Many of the medical devices used in today's market are irregularly shaped, with some degree of depth as well as height and width. The taller the product profile, the more important it is to package the product in material that closely conforms to the shape of the device. By improving the ratio of surface area to volume, less packaging material will be required, thereby reducing packaging cost (see Figure 1).

Historically, device manufacturers have looked to horizontal form-fill-seal (HFFS) machinery as the preferred means for packaging high-profile disposable medical devices. While it is still the most popular method for providing easy opening, clean peeling, and convenient access to the product, device makers should keep in mind the alternatives. For certain product niches, flow wrapping and vertical bagging are the most appropriate solutions.

Packaging Basics

Various designs and features can be produced on vertical bagging equipment (Click to enlarge).

The three most common methods of packaging finished disposable medical devices are HFFS, flow wrapping, and vertical bagging. Each technique has applications for which it is best suited.

Horizontal Form-Fill-Seal. HFFS is an intermittent-motion system featuring four basic elements. Packages are thermoformed in-line, and the product is loaded into them. The packages are then sealed and cut apart. Many variations of the HFFS concept exist, but the process can best be understood by examining the four basic elements in more depth.

Forming. Initially, the formable bottom-web component of the packages is moved into the forming station. Then, using one of a variety of forming methods, a pocket is formed in each package that mirrors or accommodates the shape of the device. The pocket can be formed using vacuum, compressed air, male plugs, or a combination of these. The cost for forming tools can vary widely, depending on the complexity of the design and the materials used.

Figure 1. Comparison of surface-to-area ratio for a tetrahedron and sphere (Click to enlarge).

Product Loading. After forming, product is manually or automatically loaded. The size of the loading area is dictated by the nature of the product and the loading method.

Sealing. A strength of the HFFS method is its ability to effect consistent, reliable seals with a wide variety of materials. This is a result of the intermittent nature of the process, which features long dwell times and a dual-web structure. The dual-web structure allows the top web to be formulated specifically for sealing, while the bottom web is formulated specifically for optimal forming.

Cutting. The cutting method chosen depends primarily on the materials being used. Rigid materials, such as polyethylene terephthalate and high-impact polystyrene, require more-sophisticated and more-costly cutting systems than are required for flexible systems. In complicated applications, for example, the cost of a matched male-female cutting system can exceed $100,000.

A typical horizontal form-fill-seal machine (Click to enlarge).

Flow Wrapping. While thermoforming shapes a package to conform to the device it holds, flow wrapping achieves its shape by wrapping a single layer of film (or other material) around the product and then sealing it. The individual packages are then cut apart. In HFFS, the product is carried through the packaging machine in the formed pockets, but flow wrappers require some means of conveying and spacing the product before the package is formed. Flow wrappers are generally run as continuous-motion systems—while HFFS machinery typically runs multiple lanes and even multiple rows per cycle, a flow wrapper generally runs one lane, with only one package per cycle. Flow wrapping comprises the same basic four elements as HFFS: forming, product loading, sealing, and cutting.

Forming and Product Loading. In flow wrapping, a roll of packaging material is fed into the machine, and the product is brought to the machine via a variety of custom-designed infeed conveyors. The product is placed on the packaging material oriented to both the print on the material and the eventual position where the cut will be made between the wrapped products. Once a product has been placed on the web, the film is wrapped around the product using a forming plow. This plow is sized to the product; however, it adjusts to accommodate a range of product sizes and is much less expensive than the cost of the forming tools used on a typical HFFS machine.

Vertical bagger (Click to enlarge).

Sealing. After the film has been formed around the product, seals are made in two stages: the longitudinal seal first, and the end seals second. The seals can be made using either rotary heat-seal dies or a flat sealing platen moved along via a slide box or an elliptical gear system.

Cutting. After sealing, and according to product placement and film repeat, the individual packages are end sealed and cut. The cutting mechanism is part of the box-motion long-dwell sealing system, which applies heat and pressure to the seal area as it “follows” the film to obtain dwell time. 

Vertical Bagging. Conceptually, vertical bagging is akin to flow wrapping. For this method, a single web of material is fed into a forming station that is vertically oriented, relying on gravity as the product-feeding mechanism. The sequence of operations is forming, loading, sealing, and cutting. Vertical bagging equipment can be run in either a continuous or intermittent mode.

Table I. Comparative strengths and weaknesses of three types of packaging (Click to enlarge).

Forming. In vertical bagging, the basic package is formed by wrapping film around a forming shoulder. Bag design varies from gusseted block bottom to square bottom, pillow bag, quatroseal, and others—some of which will require unique forming tools. In fact, the wide range of configurations available on vertical packaging machinery is one of its strengths.

The forming tools for vertical bagging are product-specific, but tooling cost is much less than one would incur with HFFS machinery.
Sealing. Sealing is accomplished using either heat-seal jaws, which utilize the variables of time, temperature, and pressure, or impulse sealing, used on polyethylene films. The film structure determines whether the back seal is a fin seal or lap seal. Top and bottom seals can feature either horizontal or vertical serrations.

Cutting. After sealing the package with the product loaded, the packaging is then cut into individual bags and released onto a discharge chute or conveyor.

Comparative Advantages and Disadvantages

Flow wrapper (Click to enlarge).

Each of the four medical device packaging methods has its strengths and weaknesses. Device manufacturers should take these into consideration when choosing an appropriate, cost-effective package for their products.

HFFS. For disposable, single-use medical devices—for which minimal contamination and aseptic transfer are primary considerations—HFFS is the preferred packaging system. Many effective forming films can be used in conjunction with top webs that have effective sealing and peeling attributes. The result is a package capable of surviving the manufacturing, transportation, and storage processes while providing fiber-free opening and easy product access. HFFS can also produce rigid trays with these same protection, easy-opening, and easy-product-access features.

Complex HFFS forming tools: top and bottom preheating, with vacuum, compressed air, and plug assist (Click to enlarge).

Despite its benefits, HFFS machinery does have its drawbacks. For starters, it is usually built specifically for a particular product. In complex applications, forming tools and punches can be quite expensive. And while multiple tool sets can be run on an HFFS machine, changeover can be time-consuming in such applications.

Another shortcoming of HFFS is that film scrap is unavoidable. The bottom film is pulled through the machine by clips and the portion of the film gripped by the clips on both sides of the machine is trimmed away. And because the machine width is fixed, overall material scrap is dictated by how well this fixed width is utilized in the package array and layout.

Flow Wrapping. Flow wrapping can provide high throughput with less-expensive tooling applications. Since the machinery is not of a fixed width, there is no resultant film scrap. Flow wrappers have no basic forming capabilities, so the range of material options can include laminations. As a result, materials with improved barrier properties and higher quality graphics can be used. This is an important feature, since the major medical packaging suppliers have all installed extensive coating and laminating systems that allow them to provide very specialized laminations at very economical prices.

Simple HFFS forming tools: bottom preheating, with vacuum forming (Click to enlarge).

Further, since no need for formability exists, the film used can be thinner in gauge and can result in increased packaging source reduction. Finally, barrier and strength components built into film structures enable medical device producers to use flow-wrap package formats for demanding new applications like those combining pharmaceuticals with traditional devices. 

The most serious limitation of flow wrapping is its sealing configuration, which reduces the ability of the system to provide a fiber-free, clean-peel opening with easy product access. The single-web nature of the concept limits the possibilities for sealing formulations, and the continuous motion requires the use of sealing systems with significant hot tack. (It should be noted, however, that with the use of elliptical-gear-driven sealing systems, within which the sealing head moves parallel with the material, the dwell time can be greatly extended.)

Vertical Bagging. The preferred method for packaging large units of product with recloseability is vertical bagging. This type of equipment is best suited for large-volume applications during which the bag will be periodically reopened and sterility is not an issue after reopening. Vertical bagging can also incorporate features for reclosing, such as zippers. As is the case for flow wrappers, vertical baggers are capable of using very sophisticated laminations offering a high degree of barrier protection, as well as sophisticated graphics.

Vertical bagger with zipper. Vertical bagging is the preferred method for packaging large units of product with recloseability, but it does not offer aseptic qualities. (Click to enlarge).

The most limiting factor for vertical bagging is the same as that of flow wrapping: It does not generally offer a good aseptic system with easy product access.

Conclusion

In any industry, progress can be defined as the end product of multiple technologies evolving in tandem, matched with an evolution in the marketplace. Today's engineer has multiple technologies upon which to draw in the packaging of high-profile, sterile, disposable medical devices. To choose a packaging system that meets the needs of the product and its applications—at the most economical cost—one must be clear in the definition of those needs and reconcile them with available technologies. 

Copyright ©2003 Medical Device & Diagnostic Industry

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