DFM for Pharmaceutical Unit Dose Package

Human Factors Engineering

When potential new hires ask what traits are required to become a Natech Engineer, one of the first things that comes to mind is research-based problem solving.  Continuous improvement requires continuous learning, so we look for people with an unquenchable appetite for knowledge.  By definition, every project is unique, which means the outcomes are uncertain, so some knowledge must be acquired on each project.

For example, on a recent project a medical client recruited Natech to engineer an applicator package that would release a liquid drug from a glass ampoule.  The requirements included the constraint that the user must be able to press the device to crack the ampoule with one hand to adequately release the solution.

Product Development Drug Delivery

The philosophy of product developers can be categorized into two major camps.  In one camp, iteration is the goal, so one concept after another may be tried and tested.  In the predictive modeling camp, data is collected and analyzed in advance with the hopes to arrive at the optimal solution earlier.

Our engineers were faced with a major decision.  Should they just start building and see what happens or should they consume the time and resources to gather and analyze data?  Practically speaking, each project requires a unique blend of intuition and data.  Natech engineers use the Structured Problem Solving Framework to find the right balance.

 Structured Problem Solving Framework

Problem Framing

First, the problem should be defined in a concrete manner.  The Natech engineers boiled the problem down to two critical questions:

How much pressure would users be able to generate to crack the ampoule?

Would end users be able to adequately crack the ampoule?

The first question could be seen as setting the specification, while the second question focused on meeting the specification.  Rather than losing precious time by addressing each question in series, the team decided they could work on both in parallel.

 

Problem Structuring

To create the roadmap to the solution the problem should be broken down into a logical set of smaller pieces.  To determine the pressure a user could generate, our engineers identified two critical questions:

How would users pinch the component?

What factors should be considered to identify a reasonable expectation for pinch strength?

Whether users would be able to crack the ampoule required an understanding of:

The material selection

The wall thickness of the material

 

Research and Analysis

Rather than rely on intuition, the engineers performed secondary research of peer-reviewed journals and discovered that Mathiowetz et al. identified three pinch types, with the Key Pinch offering the greatest strength:

Thumb-Forefinger Tip Pinch – the thumb tip meets the index fingertip.

Lateral Key Pinch – the thumb pad meets the lateral aspect of the middle phalanx of the index finger.

Palmar Pinch – the thumb pad meets the pads of the index and middle fingers.

D’Souza et al. found that influencing factors included disability, age, gender, and hand preference.  Considering variations in age and gender for the key pinch with the assumptions of no disability and use of the preferred hand, the minimum mean for key pinch in pounds was 12.6 with a standard deviation of 2.3 and a low of 8.

To further accommodate the pinch action, the engineers designed a reduced wall thickness in the breakage area.  HDPE and LDPE were selected for their chemical resistance properties as well as their durometer ranges and other physical properties.  These were modeled in a DOE mold flow analysis to analyze deflection, gating, and fill progression to optimize moldability.

Grip Ergonomics Mold Flow

Once the injection mold was designed and built, the team set up a DOE to determine the optimal blend of material.  Sample runs were performed of custom material blends of 0/100, 25/75, 50/50, 75/25, and 100/0.  Quantitative crush tests were performed on each blend to identify the blends that met the specifications for break force.  After user tests, the client made the final material selection of the blend that tested as most preferred by users.

Spending time and resources on early research resulted in overall savings for the project.  Had the team relied solely on intuition, several additional rounds of iterations would have been required.  Secondary research is a valid complement to experience.  When properly managed, individual learning feeds organizational knowledge.  Over time, this translates into a faster, more economical development process for clients.